Synthesis and scalable conversion of L-iduronamides to heparin-related Di- and tetrasaccharides

Article abstract of DOI:10.1021/jo300722y

A diastereomerically pure cyanohydrin, preparable on kilogram scale, is efficiently converted in one step into a novel L-iduronamide. A new regioselective acylation of this iduronamide and a new mild amide hydrolysis method mediated by amyl nitrite enable

Full text of DOI:10.1021/jo300722y

Article
pubs.acs.org/joc
Synthesis and Scalable Conversion of L‑Iduronamides to Heparin-
Related Di- and Tetrasaccharides
Steen U. Hansen,†,§ Gavin J. Miller,†,§ Marek Barath,†,# Karl R. Broberg,† Egle Avizienyte,‡
́
Madeleine Helliwell,† James Raftery,† Gordon C. Jayson,‡ and John M. Gardiner*,†
†School of Chemistry and Manchester Interdisciplinary Biocentre, The University of Manchester, 131 Princess Street, Manchester M1
7DN, U. K.
‡School of Cancer and Enabling Sciences, The University of Manchester, Wilmslow Road, Manchester M20 4BX, U. K.
S
* Supporting Information
ABSTRACT: A diastereomerically pure cyanohydrin, prepar-
able on kilogram scale, is efficiently converted in one step into
a novel L-iduronamide. A new regioselective acylation of this
iduronamide and a new mild amide hydrolysis method
mediated by amyl nitrite enables short, scalable syntheses of
an L-iduronate diacetate C-4 acceptor, and also L-iduronate C-
4 acceptor thioglycosides. Efficient conversions of these to a
range of heparin-related gluco-ido disaccharide building blocks
(various C-4 protection options) including efficient multigram
access to key heparin-building block ido-thioglycoside donors
are described. A 1-OAc disaccharide is converted into a heparin-related tetrasaccharide, via divergence to both acceptor and
donor disaccharides. X-ray and NMR data of the 1,2-diacetyl iduronate methyl ester and the analogous iduronamide show that
1
4
while both adopt C4 conformations in solution, the iduronate ester adopts the C1 conformation in solid state. An X-ray
4
structure is also reported for the novel, C1-conformationally locked bicyclic 1,6-anhydro iduronate lactone along with an X-ray
structures of a novel distorted 4C1 iduronate 4,6-lactone. Deuterium labeling also provides mechanistic insight into the formation
of lactone products during the novel amyl nitrite-mediated hydrolysis of iduronamide into the parent iduronic acid functionality.
of tris-(phenylthio)methyllithium (a carboxylate surrogate)6 to
a C-5 aldehyde has also provided stereoselective introduction of
the L-stereochemistry.7 Oxidation of L-iditose components in
oligosaccharides has also been employed.8
INTRODUCTION
■
Heparin/heparan sulfate (H/HS) are linear highly sulfated
glycosaminoglycan (GAG) 1,4-linked polysaccharides consist-
ing of repeating disaccharide units of D-glucosamine and either
L-iduronic acid or D-glucuronic acid. They play critical roles
through binding to a wide range of proteins,1 offering
considerable potential for development of therapeutic agents.2,3
The complex heterogeneity of natural HS oligosaccharides
means that defining the roles of specific HS sequences is best
addressed through the synthesis of structurally defined
oligosaccharide sequences, also underpinning provision of
designed sequences for potential therapeutic applications.
Biological evidence implicates L-iduronic containing domains
and the number/location of sulfates as key to effects on a
number of fibroblast growth factors (FGFs).4 Synthesis of
heparin-related oligosaccharides requires access to component
L-ido-monosaccharides with suitable C-4 and C-1 functionaliza-
tion to enable introduction of the necessary α1,4-glycosidic
linkages. L-Iduronic acid is a rare sugar and not readily available
in commercial quantities, so there have been considerable
efforts directed at syntheses delivering suitably functionalized
iduronic acid derivatives.5 As L-iduronic acid is the C-5 epimer
of D-glucuronic acid, a majority of stereoselective routes have
involved inversion of the C-5 stereochemistry of D-sugar
precursors, in some cases with subsequent oxidation of
intermediate L-idose derivatives.5d−j Low temperature addition
We previously reported a large scale (kg)9 stereoselective
route to cyanohydrin 1, introducing the key C-5 stereocenter
relevant to L-iduronic acid via a highly diastereoselective
cyanohydrin reaction.10 We reported the conversion of 1 into
1,2-O-isopropylidine iduronate acceptors and demonstrated
synthesis of various heparin-related (GlcN-Ido) disaccharides
with this 1,2-O-protection in place. Such a strategy has been
employed in several heparan sulfate-related saccharide
syntheses.
RESULTS AND DISCUSSION
■
Our interests have been in developing new routes to iduronate
building blocks that are short but also viable for economic,
larger scale synthesis, as there remains a need for scalable routes
to diverse iduronates.
We now report alternative elaborations of cyanohydrin 1 in
3−5 steps to provide new routes to several other key iduronate
building blocks bearing free C-4 hydroxyl acceptor function-
alities. These routes provide significantly improved access to
Received: May 4, 2012
© XXXX American Chemical Society
A
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these valuable building blocks, underpinned by important new
methods for the regioselective acylation of novel iduronamide
intermediates and for carboxamide to ester conversion.
The use of a variety of alternate strategies to obtain
important L-ido acceptors, including thioglycosides, via this
new approach is reported. These scalable entries to such L-
iduronic glycosyl donors were required for scaled syntheses of
HS-related disaccharide building blocks, specifically to access
larger, structurally defined HS mimetics on sufficient scales for
in vivo evaluations.
Thus, with cyanohydrin 1 available on very large scale, we
evaluated a range of methods for direct elaboration of 1 into
idopyranosides. Three key methodology developments under-
pinned this new approach.
A number of methods are available for conversion of nitriles
to carboxylic derivatives, including strong base or acid-catalyzed
hydrolysis, basic peroxide catalysis, enzymatic hydrolysis, Pt-
catalyzed hydration and acid catalyzed alcoholysis.11 As the
cyanohydrin 1 epimerises under mildy basic conditions and
scalability was a key issue, none of the above approaches were
feasible. In the case of acid-catalyzed methanolysis (Pinner
reaction), a mixture of methyl furanosides and pyranosides
were anticipated that would limit further elaboration into
suitably protected donors at the reducing end.
Hydrolysis using strongly acidic conditions was initially
discarded as incompatible with saccharides. However, it was
found that acid-catalyzed reaction of 1 using 30% aq HCl did,
in this case, effect nitrile hydration (no hydrolysis to the acid
was observed) and concurrent acetal hydrolysis leading directly
to isolation of the amide pyranoside 2 in 72% yield (Scheme 1).
we are aware 1,2-di-O-regioselective acetylation has not
previously been observed in such pyranose systems.
This thus provides an efficient and scalable two step route
from cyanohydrin 1 to novel carboxamido iduronic analogue 3,
suitably functionalized as a potential acceptor for glycosylation
itself but, critically, as a suitable precursor to iduronate esters as
key reagents toward HS-related oligosaccharide synthesis.
The next challenge was thus converting the primary amide
functionality of 3 into the ester functionality of iduronate
targets for oligosaccharide syntheses. There are a wide range of
synthetic tools available to interchange between different
carboxylic acid derivatives. Indirect transformation via the
carboxylic acid, using classical acid or base catalysis, is
complicated by the lability of the acetate groups under both
acidic and basic conditions. The direct transformation of
primary amides to esters has been described using the dimethyl
acetal of DMF,14 Meerwein’s reagent15 or acid-catalyzed
alcoholysis16 or by two step procedures involving conversion
of amide NH2 to pyrrole or di-Boc leaving groups followed by
base-catalyzed hydrolysis/alcoholysis,17 but again these reaction
conditions were not compatible with the protecting groups in
our case. Nitrosyl type reagents, such as NOCl, NOBF4, N2O4,
N2O5 and BuONO (combined with HCl gas) have been
used.18 Indeed dinitrogen tetroxide is reported to convert a
primary amide to the carboxylic acid on an acetylated D-
glucuronic derivative.19 However, the highly toxic and corrosive
nature of gaseous N2O4 made us dismiss the use of this reagent
as unsuitable to deploy on large scale. Investigating nontoxic,
readily available alternative reagents with similar properties, we
explored the use of isopentyl nitrite (amyl nitrite). Satisfyingly,
this less reactive nitrite did convert amide 3 to the acid 4 in
69% yield, when heated to 80−100 °C in neat acetic acid
(Scheme 2). This third key development is, as far as we know, a
new milder method for the selective conversion of a primary
amide to a carboxylic acid.
a
Scheme 1. Nitrile Hydration and Regioselective Acylation
Scheme 2. Isopentyl Nitrite Catalyzed Hydrolysis of Primary
a
Amides and Esterification
a
Reagents: (a) HCl, 30% aq; (b) Ac2O, DMAP, CH2Cl2.
It was unexpected that 2 would be stable under such
concentrated acidic conditions; however, it was observed that
extending the reaction time or heating did drastically reduce the
yield of the reaction. This necessitated the development of an
endothermic workup using saturated bicarbonate solution to
quench the acid. The polar product 2 could be extracted with
THF from the resulting brine solution, thus avoiding
evaporation of large volumes of aqueous brine. It was also
found that the product 2 could be purified by precipitation
making the reaction feasible on larger scale.
Peracylation of L-iduronic acid derivatives is known to be less
selective than observed with D-sugars, with respect to the
isolated pyranoside:furanoside ratio, unless low temperature
and extended reaction times are used.7b,12 So it was a key
discovery that iduronamide 2 underwent regioselective 1,2-di-
O-acetylation (or 1,2-di-O-benzoylation) by employing acyla-
tion conditions using only 1−2 mol % of DMAP and no other
base. Thus, the 6-carboxyamide L-iduronic system 2 could be
converted into diacetate 3 in 66% yield. Critically the product
could be isolated by crystallization in a yield of 43%, making the
reaction viable on large scale. The remaining mixture
containing triacetylated pyranose and furanose products could
be recycled by acid-catalyzed deprotection to give 2.13 As far as
a
Reagents: (a) Isopentyl nitrite, AcOH; (b) MeI, KHCO3, DMF, 60%
(2 steps from 3); (c) DMF·DMA, DCM, 84%.
Elaboration to the iduronate ester 5 was effected through
subsequent methylation using either the dimethyl acetal of
DMF or a preferred alkylation with methyl iodide20 (Scheme
2). The acid 4 was not crystalline, so to avoid column
chromatography purification on scale, the crude product could
be directly converted into 5 using a small excess of the
alkylating agent. To quench traces of the highly toxic methyl
iodide an excess of potassium acetate was added. The ester 5
could be purified by crystallization making the overall process
from cyanohydrin 1 to 1,2-di-O-acetyl iduronate 5 truly
scalable, avoiding all chromatograhy.
This provides a new methodology for the conversion of
amides to esters, efficiently illustrated by this synthesis of
iduronate acceptor 5 (previously reported as a mixture of
anomers21) in 60% yield over 2 steps. This mild amide-to-ester
chemistry offers considerable synthetic value underpinning the
B
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viable exploitation of iduronamide intermediate 2 for the
synthesis of a number of iduronic acid derivatives on scale.
Interestingly, while the hydrolysis of 3 with isopentyl nitrite
gave a good yield of the acid 4 (69%), two side-products,
lactone 6 and triacetate acid 7 (Scheme 3), were reproducibly
to intermediate C (related analogues of which we have
prepared independently), with a subsequent 4-exo-trig process
leading to the isolated 4,6-lactone 6. Steric considerations are
central to the viability of this proposed pathway, and a ring flip
1
from the favored (deduced from NMR data) C4 chair form to
0
the S2 skew boat form brings the C-2 acetate close enough in
Scheme 3. Mechanism of Isopentyl Nitrite-Promoted Amide
Hydrolysis
space to the depicted acylium intermediate, enabling pathway 2
to proceed via intermediate C. An alternative reaction pathway
to deliver the second observed byproduct 7 is external
nucleophilic attack from the acetic acid solvent on the acylium
ion B giving anhydride intermediate D (path 3). This is then
set up for intramolecular acyl transfer via a 6-membered ring to
furnish 7.
a
To provide some further insight into these proposed
mechanisms, distinguishing between the intramolecular path-
way 2 and the intermolecular pathways, experiments were
performed using deuterated acetic acid-d4 as the solvent under
the same reaction conditions. Indeed, we observed the same
lactone 6 was formed, supporting the intramolecular acyl
transfer mechanism, giving rise to this novel lactone. However,
a mixture of deuterated and nondeuterated product 7 was
observed.22 If the reaction proceeded via pathway 3 only, we
were expecting to see fully deuterated acyl incorporation at C-4.
This outcome is consistent with some reaction via pathway 3,
but the observation of mixed label incorporation suggests
alternative pathway(s), which acylate 4 with unlabeled acetate.
This must derive from the starting material acetyl groups (in
the reaction with only acetic acid-d4 solvent) and could arise
from direct acylation from an intermeidate acylium (akin to
path 3), or other processes leading to acetic acid-d4 forming a
mixed anhydride from acetate byproduct. Noting that total
material recovery of 4, 6 and 7 is around 80%, there is mass
balance to account for this via other pathways, but without
isolation of further byproduct the exact source for this
unlabeled acylation pathway is not conclusive.
a
Reagents: (a) Isopentylnitrite, CH3COOH; (b) isopentylnitrite,
CD3COOD.
obtained, each in ca. 3−5% yield. The mechanism of this
hydrolysis is anticipated to proceed via the nitroso intermediate
A, which loses water and N2 to give the highly reactive acylium
intermediate B. If water then acts as the external nucleophile,
the predominant product carboxylic acid 4 will be formed (path
1). However, this reactive onium ion could be intercepted by a
competing internal or alternative external nucleophile. While
such reaction using C-4 is clasically disfavored (4-exo-dig), the
C-2 acetate oxygen could act as an internal nucleophile leading
With this new, scalable access to differentiated iduronates 3
and 5, suitable as acceptors for glycosylations, our attention
turned to their elaboration into suitable monosaccharide donors.
Thioglycosides are well established as effective glycosyl donors
and have advantages in relation to compability with most
a
Scheme 4. Elaboration of Iduronamide and Iduronates
a
Reagents: (a) ClCH2COCl, pyridine; (b) isopentyl nitrite, AcOH; (c) DMF·DMA, CH2Cl2; (d) Bz2O, DMAP, THF; (e) Ac2O, DMAP, pyridine,
CH2Cl2; (f) MeI, KHCO3, DMF; (g) TMSOTf, DCM.
C
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a
protecting group manipulations and stability, compared with
many other glycosyl donors. There are several reported
syntheses of L-iduronate thioglycosides. Thioglycoside 20 (see
Scheme 5) or its t-butyl ester analogue have been previously
prepared from an iditol thioglycoside precursor via a late-stage
oxidation of C-6.23−25 These approaches employ C-5 inversion
through the C-5, C-6 epoxide derived from a 1,2-isopropylidine
glucofuranoside. A different strategy for iduronate thioglyco-
sides routes through a D-xlyose-derived dithioacetal, affording a
iduronate thioethyl glycoside with a free C-4 hydroxyl in 14
steps overall from D-xylose.26
Scheme 5. Synthesis of Iduronate Thioglycosides
Consequently, elaboration of the novel iduronamide 3 into
iduronate thioglycosides was a key aim. To approach this from
intermediate 3, which has the differentation of the C-4 hydroxyl
embedded within it, protection of C-4 with chloroacetate was
employed to provide 8 (Scheme 4). In this case, esterolysis was
completed using DMF·DMA to yield ester 10 via the
carboxylate 9. While this reagent was able to effect the
necessary conversion, yields were less reliable than the use of
methyl iodide (for carboxylate methylation), but the reagent
was preferred in this case as we observed that using methyl
iodide alkylation on chloroacetate modified derivatives such as
9 efficiently produced iodoacetate products.27
Amidotriol 2 also underwent regiocontrolled 1,2-di-O-
benzoylation using the same conditions effective for diacylation,
affording 1,2-di-O-benzoate 11 (Scheme 4). This approach also
illustrates an alternative sequence of amide to ester conversion,
followed by C-4 hydroxyl protection, affording 14 (with the
parallel chemistry converting diacetate 5 into the C-4-
chloroacetate 10). Additionally, amido triol 2 was peracylated
by standard conditions using pyridine as base, yielding the
triacetyl iduronamide 15 in good yield (81%). This then
provided a further substrate to illustrate application of the
isopentyl nitrite-based amide hydrolysis, in this case with
methyl iodide methylation yielding the known triacetyl
iduronate17 via the acid 7. This provides a scalable alternative
method to provide 16, a valuable iduronate intermediate that
has been used as a key starting point for several syntheses of HS
oligosaccharides. When the acid 7 was subjected to standard
conditions for forming thioglycosides, none of the expected
product was observed. Instead an intramolecular reaction of the
carboxylate formed the 1,6-lactone 17, isolated in a reasonable
yield of 53% using TMSOTf catalysis.
With fully protected L-iduronate derivatives 10, 14 and 16
available on large scale, our attention turned to the
aforementioned thioglycoside donors. The C-4-chloroacetyl
protected iduronates 10 and 14 were converted into thiophenyl
glycoside donors 18 and 19, respectively, under standard
conditions using borontrifluoride etherate and thiophenol
(Scheme 5). One of the main drawbacks of thioglycoside
synthesis, which has prevented its use on large scale, is the
toxicity and obnoxious odors encountered when handling thiol
reagents. This inspired us to another key development in
making such thioiduronate donors accessible on larger scale.
We observed a valuable modification for the workup of this
reaction, whereby the initial inclusion of I2 (oxidizing any
remaining thiophenol to its disulfide) in the aqueous NaHCO3
workup solution, followed by addition of Na2S2O3 to remove
any remaining I2, provided a reliable method for removing the
excess malodorous thiophenol. The iodine can be directly
added to the extraction during workup, as its consumption can
be visually monitored within seconds of shaking the extraction
funnel. This provides a simple method for the efficient and
a
Reagents: (a) (1) PhSH, BF3.OEt2, DCM, (2) I2, NaHCO3; (b)
BnNH2, Et2O (69% for 20, 68% for 21); (c) thiourea, ethanol (80%
for 20); (d) (1) NaOMe, MeOH, (2) Bu2SnO, MeOH, (3) BzCl, 1,4-
dioxane (55%, 3 steps).
practially facile removal of all traces of thiols during the
workup, without affecting the thioglycoside. This is a valuable
practical discovery, and the methodology has been utilized
successfully for other similar processes within our laboratory,
for example, in the large scale synthesis of glucoazide
thioglycoside 24 (Scheme 6).
a
Scheme 6. Synthesis of 4,6-O-Benzylidine Thioglucosides
a
Reagents: (a) (1) K2CO3, MeOH, imidazole-1-sulfonyl azide,
CuIISO4, (2) Ac2O, pyridine; (b) (1) CCl3COCl, NEt3, MeOH, (2)
Ac2O, pyridine; (c) PhSH, BF3·Et2O, DCM; (d) PhSH, TMSOTf,
DCM; (e) K2CO3, MeOH, then imidazole-1-sulfonyl azide, CuIISO4,
MeOH; (f) NaOMe, MeOH; (g) PhCH(OMe)2, TsOH, MeCN; (h)
KOH, THF/MeOH/H2O; (i) PMB(OMe)2, CSA, THF; (j) BnBr,
NaH, DMF.
The C-4-chloroacetate protecting group could be selectively
removed with either benzylamine or thiourea, providing C-4
acceptor thioglycosides 20 and 21, in good yields. Alternatively,
21 was also accessed by conversion of triacetate 16 into
thioglycoside 22 followed by deacetylation, and finally
regioselective C-2-benzoylation using dibutyltin oxide and
benzoyl chloride as described previously.28 This provides two
routes for the conversion of novel iduronamide 2 into the
known thioglycoside 20, in 6 steps via C-4-chloroacetate
protection or in 5 steps via the iduronamide triacetate 15 (in
this case using tin acetal chemistry, which is less suited for large
scale).
To summarize the overall approach, novel L-iduronamide 2
can, efficiently and on large scale, be converted into
D
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Table 1. NMR Data for Ring Protons in Diacetylated L-Iduronic Acid Derivatives (1H, 400 MHz, CDCl3)
cpd
H1
J1,2
H2
J2,3
8.2
H3
J3,4
H4
J4,5
H5
17
6
5.90
6.27
6.07
6.07
2.1
2.6
1.6
1.6
5.02
5.14
5.12
5.15
3.95
4.30
3.89
3.85
8.2
2.2
3.2
3.2
5.05
4.84
4.18
3.99
4.6
6.7
1.6
2.0
4.59
5.33
4.57
4.71
10.0
3.2
3
a
5
3.2, 1.2
a
J2,4 W-coupling observed. Proton shifts in ppm; coupling constants in Hz.
Figure 1. X-ray structures of iduronate 5, iduronamide 3, and lactones 17 and 6.33
thioglycoside iduronates of type 18 in 6 steps from cyanohydrin
1 (15% overall yield) and 10 steps (12% overall yield) from
commercial diacetone-D-glucose. This compares with alter-
native syntheses to compounds of type 18 in 14 steps from
commerial D-xylose (routing via an alternative cyanohydrin
intermediate)26 or in 9 steps starting from diacetone-D-glucose
(via a late stage oxidation of C-6).25
the novel diacetate derivatives 3 and 5 and locked lactones 6
and 17 in both solid phase (X-ray) and solution phase (NMR).
NMR data for the ring protons of the diacetates 3 and 5 and
lactones 6 and 17 (Table 1) show that the diacetates 3 and 5
have small and similar J values <4 Hz, which corresponds to a
1C4 conformational preference, with ring protons in equatorial
positions (except H-5). Additionally, a rare J2,4 W-coupling of
1.2 Hz was seen for 5, which would only be observed in the 1C4
conformation. For lactone 17 the J2,3 and J3,4 values of 8.2 Hz
L-Iduronic acid is a pyranose sugar that, in contrast to most
other pyranoses, in solution is in equilibrium between the main
1
2
4
4
conformations C4, S0 and C1. This conformational flexibility
is believed significant in the context of the binding of
heparinoid oligosaccharides to proteins, although there is
evidence of a relatively small overall impact on oligosaccharide
shape.29 The energy barrier between the different conforma-
tions is low and dependent on subtle variations in substitution
patterns in the monosaccharide,30 while the conformational
array of oligosaccharides is likely perturbed by the other
components of the oligosaccharide, including other sulfation
sites.31 Locked derivatives of L-iduronic acid have been used for
studying different conformations and, in certain cases, shown to
enhance binding to proteins.32 The versatility of outcomes from
the different inter/intramolecular reactions (Scheme 3) led to
an intriguing conformational diversity across the monocyclic
iduronate and iduronamide and the bicyclic lactones 6 and 17.
We thus pursued a more detailed study of the conformations of
were in good agreement with the locked C1 conformation, as
H-2, H-3 and H-4 would be expected to have an axial
orientation. The J3,4 value of 2.2 Hz for 6 and the relatively
large J2,3 value of 10.0 Hz are closely consistent with predicted
values for the 4,6-lactone structure 6.
To compare the solution structures, particularly of the
monocyclic conformationally flexible iduronic derivatives, with
those in the solid state and to confirm the structure of 6, we
obtained single crystal X-ray structures of diacetates 3 and 5
and lactones 6 and 17 (Figure 1).
Interestingly, we found that while amide 3 adopted the
1
expected C4 conformation, as observed in solution, ester 5 in
4
the solid state assumed a C1 conformation. For amide 3 the
crystal packing showed evident hydrogen bonding involving
unsymmetrical dimers with one amide as an H-bond acceptor
and donor, interacting with the C-2 acyl (sp3) oxygen and
E
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a
Scheme 7. Synthesis of C-6, C-4-Differentiated Thioglycoside and Trichloroacetimidate Glucoazides
a
Reagents: (a) Et3SiH, BF3·Et2O, DCM; (b) Bu2BOTf, BH3·THF; (c) 60% aq AcOH; (d) BzCl, Et3N, DCM; (e) NaH, PMBCl, THF; (f)
Cl3CCOCl, Et3N, DCM; (g) Ac2O, pyridine, DMAP, DCM; (h) BzCl, pyridine, DMAP, DCM; (i) NBS, Me2CO; (j) Cl3CCN, NaH, DCM; (k)
Cl3CCN, DBU, DCM.
amide NH of the other iduronate unit. These dimers pack as a
C2-symmetric pair in the unit cell (see the Supporting
Information). This could account for the difference in solid
state structures found between 3 and 5 and may have relevance
to the role of solvation and H-bonding in effecting conforma-
tional changes in L-iduronic acid derivatives. The conforma-
no further purification after workup (following removal of the
imidazole byproduct with an acidic aqueous wash). This offers a
significant practical improvement for synthesis of this
commonly employed valuable intermediate precursor to 2-
aminoglucoside containing targets. Intermediate 27 was then
elaborated into benzylidine derivative 28.39
Alternatively, azido transfer could be deferred by converting
24 into known 2-amino derivative 2540 using standard
deacylation conditions, followed by benzylidene formation
and base-catalyzed hydrolysis of the trichloroacetamide moiety
(100 g). Aminoglucoside 25 was thus amenable to the above-
mentioned azido transfer chemistry, followed by benzylation to
afford an alternative entry to benzylidine 28.
Additionally, 4-O-p-methoxybenzylidine (PMB) donor 29
was obtained through a route involving introduction of the
azide at C-2 as the first step (completing three different points
for utilizing this diazo transfer step), a reaction that also proved
efficiently scalable (Scheme 6). Thus, direct azidation of
glucosamine 23 was effected using imidazole-1-sulfonyl azide,
followed by acylation giving 2641 in 94% yield over two steps.36
Further elaborations into the equivalent PMP-benzylidene
donor 29 involved deacetylation with NaOMe, PMP
benzylidene formation and benzylation.42 Importantly most of
these steps yielded crystalline products allowing ready
purification on large scales.
Benzylidine acetals 28 and 29 then served as precursors to
azido thioglycoside donors 34−38 bearing different C-4 and C-
6 protecting groups patterns (Scheme 7). Selective opening of
benzylidene 28 using triethylsilane/BF3·OEt2 gave the C-6-
benzyl derivative 30. Similar selective opening of PMP
benzylidene 29 using nBu2BOTf/BH3·THF gave the C-4-
PMB derivative 31. Benzylidene 28 could also be hydrolyzed to
yield 32, followed by selective benzoylation giving novel
derivative 33. The C-4 hydroxyl of 30 and 33 were then
protected to give either the PMB benzyl ether 34 or the novel
trichloroacetate esters 35 and 36. The C-6 hydroxyl of 31 was
protected as either the acetate ester 37 or novel benzoate ester
38. Finally, thioglycosides 34−38 were converted to their
trichloroacetimidate donors 44−48 in a two step process using
standard conditions. Generally the yields were high for the NBS
promoted hydrolysis of 34−38 (to 39−4343) except for C-4-
trichloroacetyl (TCA) derivatives 40 and 41. The trichlor-
4
tionally locked lactone 17 adopted a C1 conformation in the
solid state, validating the solution state data. Additionally, the
X-ray structure of 6 confimed the identity of an interesting 4,6-
bridged lactone species, in which C3−C4−C5 are essentially
coplanar, and provides a new example of conformational
constraint within the iduronate family.34
With scalable access to the acetate and thioglycoside
iduronates 5, 20 and 21, and the novel iduronamide 3
established, demonstrating their utility in the synthesis of HS
related disaccharide building blocks was investigated.
Concomitant with this we also required a scalable synthesis
of the appropriate 2-azido glucoside donors, specifically with
variable C-6 hydroxyl protection, to provide a diversity of
disaccharide variants for oligosaccharide syntheses. To deliver
this we evaluated an alternative to the traditional triflic azide
method for conversion of 2-amino glucosides into 2-azido
derivatives,35 in large part due to scalability issues. We thus
explored the use of the diazo-transfer reagent imidazole-1-
sulfonyl azide, which had been shown to covert glucosamine to
its 2-azido derivative.36 The major improvement developed
here involved a one pot O-/N-acyl deprotection and diazo
transfer and additionally the demonstration of three alternative
entry points for installing the crucial azido moiety at C-2 during
the synthesis of glucosamines 26 and 28 (Scheme 6). First, a
synthesis of 3,4,6-tetraacetyl-2-trichloroacetate thioglycoside
2437 was carried out in good yield (Scheme 6), importantly
affording the desired material as a single β-anomeric product,
thus avoiding any chromatographic isomer separation issues.
This large scale synthesis (>140 g of 24 was prepared in a single
batch) was also assisted by application of the iodine workup
described above for the iduronate thioglycoside syntheses (18
and 19).
To access the required 2-azido thioglycoside 27,38 thioglyco-
side 24 was treated with K2CO3 in MeOH at 60 °C followed by
addition of imidazole-1-sulfonyl azide and CuIISO4 at room
temperature to furnish 27 in excellent yield (92%) in one step.
This reaction could be performed on scale (100 g) and needed
F
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a
Scheme 8. Exploring L-Ido Acceptor Reactivity with Different Types of Donors
a
Reagents: (a) NIS, AgOTf, DCM; (b) I2, CH3CN; (c) TMSOTf, DCM.
a
Scheme 9. Synthesis of Various C-4, C-6 Differentiated Glc-Ido Thioglycosides
a
Reagents: (a) α/β-20,TMSOTf, DCM; (b) α-21 or β-21,TMSOTf, DCM; (c) CAN, CH3CN/H2O; (d) CCl3COCl, pyridine, DCM.
oacetimidate donors 44−48 were also formed in high yields
using CCl3CN and either DBU or NaH as the base.
azide. Several attempts failed and only produced elimination
products that have been observed previously in similar α-
iodomannosides.44 Though these reactions do thus demon-
strate that iduronamide 3 can be employed as an acceptor to
provide novel amido mimetics of HS-related disaccharide
building blocks (50 and 51), the modest yields consolidate the
proposal10 that these idoamides are less reactive as acceptors
than the corresponding iduronate esters.
The acceptor 5 has the advantage of being compatible with
many types of donors as the C-1 acetate is not reactive under
most glycosylation conditions. As such, 5 was employed for the
synthesis of the differentially C-6-protected disaccharides 52
and 53, obtained using either thioglycoside donors (37 and 34)
or the corresponding trichloroacetimidate 47. The yields
obtained were not that high, indicating that the acceptor C-4
hydroxyl was not strongly reactive as a nucleophile, and
unreacted acceptor could be recovered from the product
mixture. The C-6 acyl-protected donors gave high α selectivity,
while the C-6 benzyl donor was less selective (ca. α/β 6:1). The
disaccharides 52 and 53 serve as precursors for either selective
removal of the C-4 terminal protecting group to generate a
disaccharide acceptor or selective C-1 manipulation into a more
active donor function (see Scheme 10).
With scalable access to various 2-azidoglucoside donors
established, application to disaccharide synthesis was under-
taken. Utilizing our entry to the novel iduronamides reported
here, we sought to assess their utility as acceptors in
glycosylation reactions. While we have previously observed
that amide-containing 1,2-O-acetonide-protected ido acceptors
function less efficiently than their analogous esters,10 the use of
the amide reported here, without that conformational locking
group, would provide a useful comparitor to indicate if the
reactivity difference is more general, but conversely may also
provide access to new amide-containing iduronate disaccharide
analogues. Reaction of iduronamide diacetate acceptor 3 with
donor 37 led to the novel disaccharide 50 but only in poor
yield (18%) (Scheme 8).
In parallel, reactivity of iduronamide acceptor 3 with triacyl
glucal 49 under iodine-mediation did afford better yields of the
2-iodo α-linked disaccharide 51 (it was noted that the iodine
promotion only worked when it was added directly as a solid to
the solution of reactants also containing powdered molecular
sieves). It was anticipated that disaccharide 51 could be
converted to an azido gluco derivative by SN2 substitution with
G
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a
Scheme 10. Iterative Elongation to Tetrasaccharide
a
Reagents: (a) BnNH2, Et2O; (b) CCl3CN, DBU, DCM; (c) DDQ, DCM/H2O; (d) TMSOTf, DCM.
Alongside synthesis of 1,2-O-diacetate iduronate-containing
disaccharides (Scheme 8), the iduronate thioglycosides 20 and
21 were also employed as acceptors for the construction of a
range of differentially protected Glc-Ido thioglycoside dis-
accharides (Scheme 9). Thus, glucoazide trichloracetimidates
44−48, bearing variable C-4 and C-6 protection, were reacted
with 20 and 21 to provide an array of Glc-Ido thioglycoside
disaccharides 55−59 in yields highly dependent on the donor.
The C-6 acyl donors 47 and 48 generally gave good yields and
selective formation of α-glycosides, while the C-6 O-benzyl
donors 44−46 gave modest to high yields and αβ-mixtures.
The yields using donors 44−46 also depended on a slow
reverse addition of excess donor at low temperatures. Because
of the modest yield obtained with donor 45, an alternative
method to access disaccharide 56 was investigated. A two-step
deprotection of PMB derivative β-55 with high purity CAN to
give 60, followed by reprotection with trichloroacetyl chloride,
provided β-56 in high yield (87% two steps).
Because of the modest yield obtained with donor 45, an
alternative method to access the disaccharide 56 was
investigated. A two-step deprotection of PMB derivative β-55,
with high purity CAN to give 60, followed by reprotection with
trichloroacetyl chloride provided β-56 in high yield (87% two
steps). Overall, this thus provides a matrix of Glc-Ido
disaccharide thioglycosides, bearing differentiated C-6 protec-
tion (acyl groups, or benzyl protection), ultimately allowing
correlating deprotections/reactions of Glc-C-6 with L-ido C-2
or orthogonal to it, but also with different C-4 protection
options, to provide a range of different orthogonal options for
C-4 deprotections of these disaccharides or of derived longer
saccharides following their use as thioglycoside donors.
Moreover, as this is underpinned by our improved scalable
syntheses of both the L-ido and D-glucosamine monosaccharide
precursors, access to these disaccharides can now be routinely
and readily achieved on multigram scales.
trichloroacetimidate derivative 62 (Scheme 10). The selective
C-1 deacetylation did not go to completion, and extending the
reaction time led to product degradation. Thus it was decided
that the optimal process involved partial deprotection to 61
(54%) and recovery of starting material 52 (39%), which was
then utilized for C-4 deprotection with DDQ to acceptor
disaccharide 63. Donor 62 and acceptor 63 were then reacted
to afford the novel HS-component tetrasaccharide 64 in good
yield. This illustrates a convenient use of disaccharide 52 to
function as a sole disaccharide building building block for the
provision of acceptor and donor modules to access higher
oligosaccharide sequences, which could be further extended to
longer sequences. Such protecting group combinations have
previously been successfully elaborated into oligosaccharde
components bearing sulfates on the gluco N and C-6, and L-ido
C-2 positions.5d
CONCLUSIONS
■
This synthesis provides a scalable access to a diversity of
disaccharides suitable as both donor and acceptor species to
elaborate further to heparin-related oligosaccharides. The
chemistry is underpinned by the novel and scalable synthesis
of L-iduronamides and accesses iduronate building blocks
through the application of a novel and mild amide to ester
conversion to provide L-iduronate methyl esters. Additionally, a
new mild method for removal of thiols with iodine from
reaction mixtures has made thioglycosides available on large
scale. This facilitates routine access to multigram scale
syntheses of these disaccharides, bearing a range of different
C-6 and C-4 protection group combinations, which afford
valuable applications in the selection of chemistry for further
oligosaccharide synthesis and options for programmability of
different site-specific modifications of ultimate HS-related
oligosaccharides. An illustrative application to a tetrasaccharide
is also provided. In addition, structural studies have provided
interesting examples of iduronate conformational promiscuity
as a function of the nature of the C-6 group, with carboxylate
and carboxamides adopting different solid-state conformations,
as well as conformationally locked lactone derivatives.
Mechanistic studies using deuterium labeling have also
provided insight into the mechanism for the novel isopentyl
nitrite-mediated mild hydrolysis of primary amides to
carboxylic acids.
With the capacity to generate scalable access to a diversity of
thioglycoside disaccharides in hand, we also wished to
demonstrate that the use of the C-4 O-PMB protection in
1,2-di-O-acetate protected disaccharide 52 would facilitate
access to further saccharide homologation without involving
thioglycoside donors. Thus, 52 was converted into a donor
disaccharide in two steps, via selective C-1 deacylation and
conversion of the resulting C-1 hydroxyl into its C-1 O-
H
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yielding 4 (3.14 g, 8.5 mmol, 69%) as an oil: Rf 0.06 (EtOAc/hexane
EXPERIMENTAL SECTION
■
20
1
2:1 + 1% HCOOH); [α]D = +44.5 (c = 0.82, CH2Cl2); H NMR
(400 MHz, CDCl3) δ 7.37−7.32 (m, 5H, Ph), 6.08 (d, J = 1.6 Hz, 1H,
H-1), 5.16−5.14 (m, 1H, H-2), 4.74 (d, J = 2.0 Hz, 1H, H-5), 4.71 (d,
J = 11.6 Hz, 1H, CH2Ph), 4.67 (d, J = 12.0 Hz, 1H, CH2Ph), 4.07−
4.05 (m, 1H, H-4), 3.88 (t, J = 3.6 Hz, 1H, H-3), 2.14 (s, 3H,
COCH3), 2.10 (s, 3H, COCH3); 13C NMR (100 MHz, CDCl3) δ
172.0, 169.3, 168.6, 136.5, 128.6, 128.3, 127.9, 90.0, 74.8, 74.7, 72.8,
67.4, 66.7, 20.8, 20.7; HRMS (TOF-ES+) m/z calcd for C17H19O9 [M
+ H]+ 367.1029, found 367.1032.
3-O-Benzyl-L-idopyranuronamide (2). To L-ido cyanohydrin 1
(75.7 g, 0.248 mol) was added THF (120 mL) and 36% HCl (600
mL) at 0 °C. The mixture was stirred for 4 h at rt. The solution was
neutralized by slow addition to aqueous NaHCO3 (600 g in 500 mL
water). The resulting aqueous brine phase was then extracted 5 times
with THF (800 mL, 500 mL, 3 × 300 mL). The organic phase was
dried with MgSO4, filtered and evaporated to yield an oil. Stirring this
crude oil with CHCl3 (400 mL) overnight and filtering off the
resulting solid gave L-idopyranose amide 2 (50.9 g, 0.18 mol, 72%) as a
powder (mixture of anomers). An alternative method for purification
on smaller scale involved column chromatography of the crude
material, using CHCl3/MeOH 10:1: Rf 0.11 (CHCl3/MeOH 10:1);
1H NMR (400 MHz; DMSO-d6) for major anomer of mixture δ 7.40−
7.29 (m, 5H), 6.90 (brs, 1H, NH), 6.79 (d, J = 7.9 Hz, 1H, OH), 5.12
(d, J = 6.7 Hz, 1H, OH), 4.86 (d, J = 8.8 Hz, 1H, OH), 4.85 (dd, J =
8.0, 0.8 Hz, 1H, H-1), 4.63 (s, 2H, CH2Ph), 4.10 (d, J = 1.4 Hz, 1H,
H-5), 3.89 (dt, J = 8.6, 1.5 Hz, 1H, H-2), 3.71 (t, J = 3.1 Hz, 1H, H-3),
3.62−3.59 (m, 1H, H-4); 13C NMR (100 MHz; DMSO-d6) δ 171.2,
138.1, 128.3, 127.6, 127.5, 93.0, 76.5, 75.0, 70.9, 68.1, 66.3; HRMS
(TOF-ES+) m/z calcd for C13H18NO6 [M + H]+ 284.1129, found
284.1133; Elemental analysis calcd (%) for C13H17NO6, C 55.12, H
6.05, N 4.94, found C 55.25, H 6.17, N 4.78.
Methyl 1,2-Di-O-acetyl-3-O-benzyl-β-L-idopyranuronate
(5).21 Method A. To the acid 4 (1.73 g, 4.70 mmol) was added dry
DCM (25 mL), and then dimethylformamide dimethylacetal
(DMF·DMA) was added dropwise over 40 min (0.7 mL, 4.93
mmol) at 0 °C . The mixture was left for 5 h at room temperature
under a N2 atmosphere. The reaction was quenched by addition of
AcOH, solvents removed in vacuo, and the residue purified by flash
column chromatography (EtOAc/hexane, 1:1), yielding 5 (1.50 g, 3.9
mmol, 84%) as a white foam. The product could be crystallized by
dissolving in EtOAc and adding hexane (1:3 v/v) giving white needles.
Method B. The amide 3 was converted to the acid 4, and then the
crude product used directly to prepare the ester 5. To the diacetylated
L-ido amide 3 (53.0 g, 0.144 mol) was added acetic acid (1 L) and
isoamyl nitrite (77 mL, 0.577 mol), and the mixture was heated for 6 h
to 90 °C under N2. The solvents were removed, and the residue
azeotroped with toluene (3 × 500 mL) yielding crude 4. To this reside
was added anhydrous DMF (400 mL), potassium hydrogencarbonate
(14.5 g, 0.144 mol) and methyliodide (9.0 mL, 0.144 mol) under N2.
The mixture was vigorously stirred for 16 h. Potassium acetate (10 g,
0.102 mol) was added to quench excess methyliodide, and the mixture
stirred for another 8 h. The solution was then extracted with DCM (1
L) and washed with water (4 × 500 mL) to remove DMF from the
organic phase. After extraction, the organic phase was dried (MgSO4),
filtered, evaporated, and the residue purified by flash column
chromatography (EtOAc/hexane, 1:2 to 1:1). This yielded 5 (33.0
g, 86.0, mmol 60%) as a syrup. The product could be crystallized by
dissolving in diethylether and cooling to 0 °C followed by filtration
yielding pure 5 as a white powder: Rf 0.18 (EtOAc/hexane 1:1); mp
1,2-Di-O-acetyl-3-O-benzyl-β-L-idopyranuronamide (3). To
the powdered L-ido amide 2 (103.2 g, 0.36 mol) was added
dichloromethane (900 mL), and the solution cooled to 0 °C in an
icebath. Acetic anhydride (81 mL, 0.86 mol) and DMAP (0.45 g, 3.7
mmol) were then added. The cooling was removed, and the mixture
stirred for 5 h at room temperature. The reaction was quenched with
EtOH (10 mL), and solvents removed in vacuo. The crude product
was extracted with EtOAc (1.2 L), washed with water (800 mL) and
saturated aqueous NaHCO3 (800 mL). The organic phase was dried
(MgSO4), filtered and evaporated. The product was crystallized by
dissolving in EtOAc (800 mL) and adding hexane (500 mL). The
precipitated solid was filtered after 1 day yielding 3 (57.0 g, 43%) as a
white powder. The filtrate containing a mixture of triacetylated
furanoside and pyranoside byproduct and more diacetylated pyrano-
side could be purified by flash column chromatography using EtOAc as
eluent. This gave 12% of the triacetylated pyranoside (12), 15%
triacetylated furanoside and another batch of 3 to give the total yield of
3 (87.5 g, 0.24 mol, 66%). The residual mixture of triacylated
pyranoside and furanoside, with some unseparated diacetate, could be
recycled as described below: Rf 0.21 (EtOAc); mp 148−152 °C;
20
1
77−78 °C; [α]D = +39.2 (c = 0.93, CH2Cl2); H NMR (400 MHz,
CDCl3) δ 7.36−7.30 (m, 5H, Ph), 6.07 (d, J = 1.6 Hz, 1H, H-1), 5.15
(ddd, J = 3.2 Hz, 1.6 Hz, 1.2 Hz, 1H, H-2), 4.71 (d, J = 2.0 Hz, 1H, H-
5), 4.70 (d, J = 11.6 Hz, 1H, CH2Ph), 4.65 (d, J = 11.6 Hz, 1H,
CH2Ph), 4.01−3.98 (m, 1H, H4), 3.85 (t, J = 3.2 Hz, 1H, H-3), 3.80
(s, 3H, C(O)OCH3), 2.92 (d, J = 12.4 Hz, 1H, OH), 2.13 (s, 3H,
COCH3), 2.09 (s, 3H, COCH3); 13C NMR (100 MHz, CDCl3) δ
169.1, 168.4, 168.2, 136.6, 128.6, 128.2, 127.8, 90.1, 75.3, 74.7, 72.6,
67.5, 66.8, 52.4, 20.8, 20.7; HRMS (TOF-ES+) m/z calcd for
C18H26O9N [M + NH4]+ 400.1608, found 400.1611; Elemental
analysis calcd (%) for C18H22O9, C 56.54, H 5.80, found C 56.65, H
5.75.
20
1
[α]D = +69.2 (c = 0.83, CH2Cl2); H NMR (400 MHz; CDCl3) δ
7.37−7.29 (m, 5H), 6.47 (brs, 1H, NH), 5.70 (brs, 1H, NH), 6.07 (d, J
= 1.6 Hz, 1H, H-1), 5.12 (m, 5.13−5.11, 1H, H-2), 4.67 (s, 2H,
CH2Ph), 4.56 (s, 1H, H-5), 4.18 (brd, J = 10.3 Hz, 1H, H-4), 3.89 (t, J
= 3.2 Hz, 1H, H-3), 2.08 (d, J = 11.2 Hz, 1H), 2.17 (s, 3H, CH3), 2.13
(s, 3H, CH3). 13C NMR (100 MHz; CDCl3) δ 170.9, 169.5, 168.6,
136.8, 128.6, 128.3, 127.9, 90.4, 76.1, 74.8, 72.7, 67.2, 66.3, 21.0, 20.9;
HRMS (TOF-ES+) m/z calcd for C17H21NO8Na [M + Na]+ 390.1159,
found 390.1156; Elemental analysis calcd (%) for C17H21NO8, C
55.58, H 5.76, N 3.81, found C 55.19, H 5.79, N 3.68.
Method B Employing CD3CO2D. To the amide 3 (136 mg, 0.37
mmol) was added deuterated acetic acid-d4 (1 mL) and then isoamyl
nitrite (0.2 mL, 1.5 mmol). The mixture was heated for 6 h to 90 °C
under a N2 atmosphere. The solution was evaporated and then
coevaporated with toluene (2 × 10 mL). The crude product was
purified by flash column chromatography (EtOAc/hexane gradient 1:3
then 1:1 containing 1% formic acid). This yielded 4 (94 mg, 69%),
along with 6 (5 mg, 4%), 7 as a 1:1 mixture of 4-O-CH3CO- and 4-O-
CD3CO- (4 mg, 3%).
Recycling Acetylated L-Iduronamide Products to Reform 2.
To a mixture of di- and triacetylated L-iduronamide pyranose and
furanose (132.4 g, ∼0.32 mol) was added THF (650 mL) and HCl 4
M (650 mL), and the mixture was stirred for 24 h. The reaction
mixture was poured slowly (foaming) onto solid NaHCO3 with
stirring, and the brine-like aqueous phase extracted with THF (3 ×
500 mL). The combined organic phases were dried (MgSO4), filtered,
and solvent evaporated. This gave the crude 3-O-benzyl-L-iduronamide
triol (85 g, 93%).
1,2-Di-O-acetyl-3-O-benzyl-β-L-idopyranuronic acid (4). To
the amide 3 (4.55 g, 12.4 mmol) was added acetic acid (100 mL) and
then isoamyl nitrite (4.3 mL, 37.2 mmol). The flask was fitted with a
condenser, and the mixture was heated for 4 h to 100 °C under N2.
The solution was evaporated and then coevaporated with toluene (2 ×
100 mL). The crude product was purified by flash column
chromatography (EtOAc/hexane, 2:1 containing 1% formic acid),
1,2-Di-O-acetyl-3-O-benzyl-β-L-idopyranurono-4,6-lactone
(6). This compound was isolated from the amide hydrolysis/
esterification (3 to 5, method B) reaction as a byproduct using flash
column chromatography (EtOAc/hexane, 1:3). This yielded 6 (2.8 g,
20
8.0 mmol, 5%): Rf 0.28 (EtOAc/hexane 1:3); mp 88−90 °C; [α]D
=
+99.8 (c = 0.49, CH2Cl2); 1H NMR (400 MHz; CDCl3) δ 7.42−7.33
(m, 5H, Ph), 6.27 (d, J = 2.6 Hz, 1H, H-1), 5.33 (d, J = 6.7 Hz, 1H, H-
5), 5.14 (dd, J = 10.0, 2.6 Hz, 1H, H-2), 4.84 (dd, J = 6.7, 2.2 Hz, 1H,
H-4), 4.82 (d, J = 12.0 Hz, 1H, CH2Ph), 4.66 (d, J = 12.0 Hz, 1H,
CH2Ph), 4.30 (dd, J = 10.0, 2.2 Hz, 1H, H-3), 2.12 (s, 3H, COCH3),
2.09 (s, 3H, COCH3); 13C NMR (100 MHz; CDCl3) δ 169.8, 168.8,
I
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The Journal of Organic Chemistry
Article
168.7, 136.8, 128.6, 128.3, 127.8, 89.4, 76.8, 76.2, 75.3, 72.5, 69.1, 20.7,
20.5; MS-MALDI m/z = 373 [M + Na]+; HRMS (FTMS-NSI+) m/z
calcd for C17H18O8Na [M+Na]+ 373.0899, found 373.0902; Elemental
analysis calcd (%) for C17H18O8, C 58.28, H 5.18, found C 58.61, H
5.13.
CH2Cl2 (100 mL), THF (100 mL) and then benzoic anhydride (18.8
g, 83.1 mmol) and DMAP (230 mg, 1.90 mmol). The mixture was
stirred for 3 h, and more benzoic anhydride (4.4 g, 19.4 mmol) was
added. After 5 h the solvents were removed, and the residue extracted
with EtOAc (500 mL), washed with 1% HCl (300 mL) and saturated
aqueous NaHCO3 (300 mL). The organic phase was dried (MgSO4)
filtered, evaporated, and flash column chromatography (EtOAc/
Hexane, 3:2) yielded 11 (8.68 g, 17.6 mmol, 47%) as a white powder.
The product could be recrystallized by dissolving in EtOAc and adding
hexane: Rf 0.31 (EtOAc/hexane 2:1); mp 79−80 °C; [α]D20 = +56.3 (c
1,2-Di-O-acetyl-3-O-benzyl-4-O-chloroacetyl-β-L-idopyra-
nuronamide (8). To the diacetylated L-ido amide 3 (4.57 g, 12.45
mmol) was added dry dichloromethane (80 mL), pyridine (1.6 mL,
19.7 mmol), and chloroacetyl chloride (1.4 mL, 17.6 mmol) dropwise
over 15 min, and the mixture was stirred for a further 90 min under
N2. The reaction mixture was then extracted with dichloromethane
(300 mL), washed with 1% HCl (200 mL) and saturated aqueous
NaHCO3 (200 mL). The organic phase was dried (MgSO4), filtered
and evaporated. The crude product was purified by flash column
chromatography (EtOAc/Hexane 1:1), yielding 8 (5.25 g, 11.8 mmol,
95%) as a white solid. The product was recrystallized by dissolving in
EtOAc and adding hexane (1:2 v/v) to give white needles: Rf 0.37
1
= 0.55, CH2Cl2); H NMR (400 MHz; CDCl3) δ 8.12−8.09 (m, 2H,
ArH), 7.97−7.94 (m, 2H, ArH), 7.65−7.55 (m, 2H, ArH), 7.52−7.47
(m, 2H, ArH), 7.42−7.31 (m, 7H, ArH), 6.60 (d, J = 2.9 Hz, 1H, NH),
6.43 (d, J = 1.6 Hz, 1H, H-1), 6.18 (d, J = 2.9 Hz, 1H, NH), 5.53 (dd, J
= 3.6, 1.6 Hz, 1H, H-2), 4.80 (s, 2H, CH2Ph), 4.73 (d, J = 2.1 Hz, 1H,
H-5), 4.34 (dd, J = 3.6, 2.1 Hz, 1H, H-4), 4.16 (t, J = 3.6 Hz, 1H, H-3),
3.11 (s, 1H, OH); 13C NMR (100 MHz; CDCl3) δ 171.1, 165.4, 164.3,
136.9, 133.8, 133.7, 130.0, 129.9, 129.2, 128.7, 128.6, 128.6, 128.3,
128.0, 91.1, 75.9, 75.4, 73.0, 68.0, 66.8; HRMS (TOF-ES+) m/z calcd
for C27H25NO8Na [M + Na]+ 514.1478, found 514.1482.
20
(EtOAc/hexane 2:1); mp 124−126 °C; [α]D = +45.3 (c = 0.87,
1
CH2Cl2); H NMR (400 MHz; CDCl3) δ 7.39−7.34 (m, 5H, Ph),
6.54 (brs, 1H, NH), 6.09 (d, J = 1.8 Hz, 1H, H-1), 6.06 (brs, 1H, NH),
5.38−5.34 (m, 1H, H-4), 5.07 (dd, J = 2.9, 1.8 Hz, 1H, H-2), 4.80 (d, J
= 11.6 Hz, 1H, CH2Ph), 4.73 (d, J = 11.6 Hz, 1H, CH2Ph), 4.71 (d, J =
2.0 Hz, 1H, H-5), 4.08 (d, J = 14.8 Hz, 1H, CH2Cl), 4.01 (d, J = 14.8
Hz, 1H, CH2Cl), 4.00 (t, J = 2.8 Hz, 1H, H3), 2.15 (s, 6H, 2 x
COCH3); 13C NMR (100 MHz; CDCl3) δ 169.7, 168.9, 168.5, 166.3,
136.4, 128.7, 128.4, 128.0, 90.1, 74.0, 73.1, 72.6, 67.8, 66.2, 40.5, 20.91,
20.83; HRMS (TOF-ES+) m/z calcd for C19H22ClNO9Na [M + Na]+
466.0881, found 466.0886; Elemental analysis calcd (%) for
C19H22ClNO9, C 51.42, H 5.00, N 3.16, found C 51.30, H 4.98, N
3.08.
1,2-Di-O-benzoyl-3-O-benzyl-β-L-idopyranuronic acid (12).
To the dibenzoylated L-ido amide 11 (15.0 g, 30.5 mmol) was
added acetic acid (200 mL) and isoamyl nitrite (20 mL, 150 mmol).
The mixture was heated to 90 °C for 5 h under N2. The solvents were
removed and coevaporated with toluene (2 × 200 mL) and flash
column chromatography (EtOAc/Hexane 1:1 containing 1%
HCOOH) yielded 12 (8.86 g, 18.0 mmol, 59%) as an oil: Rf 0.27
20
(EtOAc/hexane 2:1 + 1% HCOOH); [α]D = +43.0 (c = 0.67,
1
CH2Cl2); H NMR (400 MHz; CDCl3) δ 8.08−8.05 (m, 2H, ArH),
7.95−7.92 (m, 2H, ArH), 7.63−7.59 (m, 1H, ArH), 7.56−7.52 (m,
1H, ArH), 7.50−7.46 (m, 2H, ArH), 7.40−7.34 (m, 7H, ArH), 6.45 (d,
J = 1.8 Hz, 1H, H1), 5.52 (ddd, J = 3.8, 1.7, 0.9 Hz, 1H, H-2), 4.85−
4.77 (m, 3H, CH2Ph, H-5), 4.19−4.17 (m, 1H, H-4), 4.15 (t, J = 3.8
Hz, 1H, H-3); 13C NMR (100 MHz; CDCl3) δ 172.5, 165.5, 164.4,
136.9, 134.0, 130.3, 130.1, 129.1, 129.0, 128.8, 128.7, 128.6, 128.2,
128.0, 91.1, 75.3, 74.8, 73.4, 68.1, 68.0; HRMS (TOF-ES+) m/z calcd
for C27H24O9Na [M + Na]+ 515.1318, found 515.1322).
1,2-Di-O-acetyl-3-O-benzyl-4-O-chloroacetyl-β-L-idopyra-
nuronic acid (9). To the amide 8 (551 mg, 1.24 mmol) was added
acetic acid (6 mL) and isoamyl nitrite (0.67 mL, 4.96 mmol). The
mixture was heated for 5 h to 90 °C under N2, solvents were removed,
coevaporated with toluene (2 × 20 mL), and the residue was purified
by flash column chromatography (EtOAc/hexane, 1:1 containing 1%
formic acid). This yielded 9 (372 mg, 0.84 mmol, 67%) as an oil: Rf
20
0.10 (EtOAc/hexane 1:1 + 1% HCOOH); [α]D = +28.9 (c = 0.88,
Methyl 1,2-Di-O-benzoyl-3-O-benzyl-β-L-idopyranuronate
(13). To the dibenzoylated L-ido acid 12 (8.70 g, 17.7 mmol) was
added dry dichloromethane (150 mL), and the mixture cooled to 0 °C
in an ice-bath. N,N-Dimethylformamide dimethyl acetal (2.2 mL, 17.7
mmol) was added dropwise over 15 min. Cooling was removed, and
the reaction stirred for 7 h under N2. Solvents were then evaporated,
and purification of the residue by flash column chromatography
(EtOAc/Hexane, 1:2) yielded pure 13 (5.25 g, 10.3 mmol, 59%) as an
1
CH2Cl2); H NMR (400 MHz; CDCl3) δ 7.54 (brs, 1H, CO2H),
7.41−7.36 (m, 5H, Ph), 6.12 (d, J = 1.7 Hz, 1H, H-1), 5.25−5.23 (m,
1H, H-4), 5.10 (m, 1H, H-2), 4.88 (d, J = 2.1 Hz, 1H, H-5), 4.78 (m,
2H, CH2Ph), 4.10, (d, J = 14.8 Hz, 1H, CH2Cl), 4.02 (d, J = 14.8 Hz,
1H, CH2Cl), 4.02 (t, J = 2.8 Hz, 1H, H-3), 2.14 (s, 6H, 2 x COCH3);
13C NMR (100 MHz; CDCl3) δ 170.1, 169.9, 168.7, 166.5, 136.3,
129.1, 128.7, 128.5, 128.3, 128.0, 89.9, 73.3, 72.7, 72.6, 68.3, 65.8, 40.4,
20.8, 20.8; HRMS (TOF-ES−) m/z calcd for C19H20ClO10 [M-H+]
443.0750, found 443.0767.
20
oil: Rf 0.24 (EtOAc/hexane 1:2); [α]D = +37.5 (c = 0.84, CH2Cl2);
1H NMR (400 MHz; CDCl3) δ 8.09−8.06 (m, 2H, ArH), 7.98−7.95
Methyl 1,2-Di-O-acetyl-3-O-benzyl-4-O-chloroacetyl-β-L-ido-
pyranuronate (10). To the acid 9 (2.03 g, 4.57 mmol) was added dry
DCM (30 mL) and then N,N-dimethylformamide dimethyl acetal
(0.65 mL, 4.57 mmol) dropwise over 5 min. The mixture was stirred
for 1 h at room temperature under N2. The reaction was quenched
with AcOH (0.5 mL), solvents evaporated, and the residue purified by
flash column chromatography (EtOAc/hexane, 1:2) yielding 10 (1.19
g, 2.59 mmol, 57%) as a white solid. The product could be crystallized
(m, 2H, ArH), 7.66−7.55 (m, 2H, ArH), 7.51−7.47 (m, 2H, ArH),
7.42−7.33 (m, 7H, ArH), 6.49 (d, J = 2.0 Hz, 1H, H-1), 5.53 (ddd, J =
4.2, 1.9, 0.9 Hz, 1H, H-2), 4.89−4.81 (m, 3H, CH2Ph, H-5), 4.21−
4.15 (m, 2H, H-3, H-4), 3.74 (s, 3H, CO2CH3); 13C NMR (100 MHz;
CDCl3) δ 169.1, 165.3, 164.1, 136.9, 133.8, 130.1, 129.9, 129.1, 128.7,
128.7, 128.6, 128.5, 128.3, 128.0, 91.0, 75.3, 74.8, 73.3, 68.4, 68.3, 52.6;
HRMS (TOF-ES+) m/z calcd for C28H26O9Na [M + Na]+ 529.1469,
found 529.1467; Elemental analysis calcd (%) for C28H26O9, C 66.40,
H 5.17, found C 66.30, H 5.17.
by dissolving in EtOAc and adding hexane (1:3 v/v) giving white
20
needles: Rf 0.18 (EtOAc/hexane 1:2); mp 143−145 °C; [α]D
=
Methyl 1,2-Di-O-benzoyl-3-O-benzyl-4-O-chloroacetyl-β-L-
idopyranuronate (14). To the dibenzoylated L-ido ester 13 (3.0 g,
5.93 mmol) was added dry dichloromethane (50 mL), pyridine (1.0
mL, 12.3 mmol) and chloroacetyl chloride (0.9 mL, 11.3 mmol). The
mixture was stirred for 90 min under N2, extracted with dichloro-
methane (200 mL), the organics washed with 1% HCl (200 mL) and
saturated NaHCO3 (200 mL). The organic phase was dried (MgSO4),
filtered, and solvents removed in vacuo. Purification of the crude
residue by flash column chromatography (EtOAc/Hexane 1:3) yielded
14 (3.18 g, 5.45 mmol, 92%) as a white foam: Rf 0.43 (EtOAc/hexane
1
+16.3 (c = 0.60, CH2Cl2); H NMR (400 MHz; CDCl3) δ 7.34−7.25
(m, 5H, Ph), 6.02 (d, J = 1.8 Hz, 1H, H-1), 5.15−5.14 (m, 1H, H-4),
5.00−4.98 (m, 1H, H-2), 4.75 (d, J = 2.0 Hz, 1H, H-5), 4.69 (d, J =
12.0 Hz, 2H, CH2Ph), 3.97, (d, J = 14.8 Hz, 1H, CH2Cl), 3.91 (d, J =
14.8 Hz, 1H, CH2Cl), 3.91 (t, J = 2.8 Hz, 1H, H-3), 3.72 (s, 3H,
C(O)OCH3), 2.06 (s, 6H, 2 x COCH3); 13C NMR (100 MHz;
CDCl3) δ 169.9, 168.5, 167.0, 166.4, 136.4, 128.7, 128.5, 128.0, 89.9,
73.2, 73.0, 72.8, 68.6, 65.8, 52.8, 40.4, 20.92, 20.84; HRMS (TOF-ES+)
m/z calcd for C20H23ClO10Na [M + Na]+ 481.0877, found 481.0882;
Elemental analysis calcd (%) for C20H23ClO10, C 52.35, H 5.05, found
C 52.34, H 4.99.
20
1:2); [α]D = +32.5 (c = 0.57, CH2Cl2); 1H NMR (400 MHz;
CDCl3) δ 8.09−8.02 (m, 2H, ArH), 7.87−7.85 (m, 2H, ArH), 7.57−
7.51 (m, 1H, ArH), 7.47−7.36 (m, 3H, ArH), 7.36−7.22 (m, 7H,
ArH), 6.37 (d, J = 1.6 Hz, 1H, H-1), 5.37−5.35 (m, 1H, H-2), 5.27−
1,2-Di-O-benzoyl-3-O-benzyl-β-L-idopyranuronamide (11).
To the powdered L-ido amide 2 (10.7 g, 37.8 mmol) was added
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5.24 (m, 1H, H-4), 4.90 (d, J = 2.1 Hz, 1H, H-5), 4.77 (s, 2H,
CH2Ph), 4.12 (t, J = 3.2 Hz, 1H, H-3), 3.84 (d, J = 14.9 Hz, 1H,
CH2Cl), 3.73−3.67 (m, 4H, CH2Cl, CO2CH3); 13C NMR (100 MHz;
CDCl3) δ 167.2, 166.5, 165.5, 164.2, 136.5, 133.8, 133.7, 130.1, 130.0,
129.2, 128.7, 128.6, 128.4, 128.4, 128.0, 90.7, 73.4, 73.1, 73.0, 68.8,
66.8, 52.8, 40.3; HRMS (TOF-ES+) m/z calcd for C30H31ClO10N [M
+ NH4]+ 600.1631, found 600.1633; Elemental analysis calcd (%) for
C30H27ClO10, C 61.81, H 4.67, found C 61.64, H 4.63.
by dissolving in EtOAc and adding hexane (1:3 v/v): Rf 0.34 (EtOAc/
hexane 1:3); mp 107−108 °C; [α]D20 = +87.9 (c = 0.66, CH2Cl2); 1H
NMR (400 MHz; CDCl3) δ 7.39−7.26 (m, 5H, ArH), 5.90 (d, J = 2.1
Hz, 1H, H-1), 5.05 (dd, J = 8.2, 4.6 Hz, 1H, H-4), 5.01 (dd, J = 8.2, 2.1
Hz, 1H, H-2), 4.73−4.66 (m, 2H, CH2Ph), 4.59 (d, J = 4.6 Hz, 1H, H-
5), 3.95 (t, J = 8.2 Hz, 1H, H-3), 2.09 (s, 3H, COCH3), 2.08 (s, 3H,
COCH3); 13C NMR (100 MHz; CDCl3) δ 170.0, 169.9, 168.5, 137.4,
128.6, 128.1, 127.7, 100.3, 75.1, 73.2, 69.9, 69.1, 20.7; MS-MALDI m/z
= 351 [M + H]+; HRMS (FTMS-NSI+) m/z calcd for C17H19O8 [M +
H]+ 351.1074, found 351.1075; Elemental analysis calcd (%) for
C17H18O8, C 58.28, H 5.18, found C 58.54, H 5.30.
1,2,4-Tri-O-acetyl-3-O-benzyl-β-L-idopyranuronamide (15).
To the amide triol 2 (19.5 g, 0.069 mol) was added dichloromethane
(300 mL), and the mixture cooled to 0 °C in an ice-bath. Acetic
anhydride (23 mL, 0.241 mol) and 4-(dimethylamino)pyridine (168
mg, 1.38 mmol) were added. The insoluble starting material was
gradually consumed while being vigorously stirred for 4 h, slowly
warming to room temperature. Pyridine (22 mL, 0.276 mol) was
added and stirred for another 16 h. The solvents were removed, and
the residue azeoptroped twice with toluene (2 × 200 mL). The crude
product was purified by column chromatography using EtOAc/hexane
(2:1) as eluent, yielding triacetylated L-ido amide 15 (22.7 g, 55.5
mmol 81%) as a white solid. The product was recrystallized by
dissolving in EtOAc (600 mL) and adding hexane (600 mL) yielding
white needles of pure 15 (19.4 g, 47.4 mmol, 69%): Rf 0.25 (EtOAc/
hexane 2:1); mp 201−202 °C; [α]D20 = +58.9 (c = 0.53, CH2Cl2); 1H
NMR (300 MHz, CDCl3) δ 7.37−7.31 (m, 5H, Ph), 6.52 (brs, 1H,
CONH2), 6.06 (d, J = 1.5 Hz, 1H, H1), 5.88 (brs, 1H, CONH2), 5.26
(s, 1H, H-4), 5.02 (s, 1H, H-2), 4.78 (d, J = 11.7 Hz, 1H, CH2Ph),
4.69 (d, J = 12.3 Hz, 1H, CH2Ph), 4.66 (s, 1H, H-5), 3.97 (t, J = 2.7
Hz, 1H, H-3), 2.13 (s, 3H, COCH3), 2.12 (s, 3H, COCH3), 2.03 (s,
3H, COCH3); 13C NMR (100 MHz, CDCl3) δ 169.6, 169.5, 169.1,
168.4, 136.6, 128.5, 128.2, 127.9, 90.0, 74.2, 72.9, 72.6, 66.5, 66.3, 20.8,
20.7, 20.6; HRMS (TOF-ES+) m/z calcd for C19H23NO9Na [M +
Na]+ 432.1265, found 432.1266; Elemental analysis calcd (%) for
C19H23NO9, C 55.74, H 5.66, N 3.42, found C 55.78, H 5.81, N 3.32.
1,2,4-Tri-O-acetyl-3-O-benzyl-β-L-idopyranuronic acid (7).
To the triacetylated L-ido amide 15 (19.3 g, 47.2 mmol) was added
acetic acid (200 mL) and isoamyl nitrite (25 mL, 189 mmol). The
mixture was heated to 90 °C for 5 h under N2, solvents removed in
vacuo and coevaporated with toluene (2 × 200 mL). Purification of
the residue by flash column chromatography (EtOAc/Hexane 2:1
containing 1% HCOOH) yielded 7 (13.1 g, 32 mmol, 68%) as a solid.
The solid was recrystallized by dissolving in EtOAc (200 mL) and
Methyl (Phenyl 2-O-acetyl-3-O-benzyl-4-O-chloroacetyl-1-
thio-β-L-idopyranoside)uronate (18). To the L-ido ester 10 (3.72
g, 8.12 mmol) was added dry dichloromethane (70 mL),
borontrifluoride diethyl etherate (5.1 mL, 40.6 mmol) and thiophenol
(0.91 mL, 8.93 mmol). The mixture was stirred for 21 h under N2 and
was then quenched by adding to a mixture of saturated NaHCO3 (200
mL) and dichloromethane (150 mL) with stirring. To this mixture was
added iodine until a dark red color persisted, indicating all remaining
thiophenol had been oxidized to diphenyldisulfide, thus removing all
odor from the product mixture. The excess of iodine was reduced to
iodide by adding enough sodium thiosulfate solution (10% aq) until
the dark red color disappeared. The organic phase was separated, dried
(MgSO4), filtered and evaporated. Purification by flash column
chromatography (EtOAc/Hexane 1:4) yielded 16 (2.43 g, 4.77
mmol, 59%, α/β 3:1) as an oil. Starting material 10 (0.52 g, 14%)
was recovered: Rf 0.42 (EtOAc/hexane 1:2); See the Supporting
1
Information for copies of H and 13C NMR spectra; HRMS (TOF-
ES+) m/z calcd for C24H25ClO8SNa [M + Na]+ 531.0856, found
531.0870.
Methyl (Phenyl 2-O-benzoyl-3-O-benzyl-4-O-chloroacetyl-1-
thio-L-idopyranoside) uronate (19). To the L-ido ester 14 (3.1 g,
5.32 mmol) was added dry dichloromethane (50 mL), thiophenol
(0.84 mL, 7.23 mmol) and borontrifluoride diethyl etherate (2.4 mL,
16.7 mmol), and the mixture was stirred 15 h under N2 and was then
quenched by adding to a mixture of saturated NaHCO3 (200 mL) and
dichloromethane (150 mL) with stirring. To this mixture was added
iodine until a dark red color persisted, indicating all remaining
thiophenol had been oxidized to diphenyldisulfide, thus removing all
odors from the product mixture. The excess of iodine was reduced to
iodide by adding sodium thiosulfate solution (10% aq) dropwise until
the dark red color disappeared. The organic phase was separated, dried
(MgSO4), filtered and evaporated, and purification by flash column
chromatography (EtOAc/Hexane 1:4) yielded 19 (1.36 g, 45%, 2.39
mmol, α/β 3:1) as an oil, along with recovery of starting material (0.95
g, 31%). 19α: Rf 0.18 (EtOAc/hexane 1:5); [α]D20 = −64.1 (c = 0.57,
adding hexane (400 mL) to yield a white solid (9.75 g): Rf 0.07
20
(EtOAc/hexane 2:1 + 1% HCOOH); mp 150−151 °C; [α]D
=
1
+38.3 (c = 0.72, CH2Cl2); H NMR (400 MHz, CDCl3) δ 7.38−7.32
(m, 5H, Ph), 6.09 (d, J = 1.6 Hz, 1H, H-1), 5.17−5.15 (m, 1H, H-4),
5.04−5.02 (m, 1H, H-2), 4.82 (d, J = 2.0 Hz, 1H, H-5), 4.76 (d, J =
11.6 Hz, 1H, CH2Ph), 4.72 (d, J = 11.6 Hz, 1H, CH2Ph), 3.97 (t, J =
2.8 Hz, 1H, H-3), 2.11 (s, 3H, COCH3), 2.09 (s, 3H, COCH3), 2.04
(s, 3H, COCH3); 13C NMR (100 MHz, CDCl3) δ 170.4, 169.9, 169.8,
168.6, 136.4, 128.6, 128.3, 127.9, 89.8, 73.0, 72.8, 72.6, 66.8, 65.9, 20.7,
20.7, 20.6; HRMS (FTMS-NSI+) m/z calcd for C19H22O10Na [M +
Na]+ 433.1105, found 433.1099.
1
CH2Cl2); H NMR (400 MHz; CDCl3) δ 8.00−7.95 (m, 2H, ArH),
7.53−7.42 (m, 3H, ArH), 7.42−7.16 (m, 10H, ArH), 5.71 (s, 1H, H-
1), 5.44 (d, J = 2.0 Hz, 1H, H-5), 5.37 (dd, J = 2.6, 1.2 Hz, 1H, H-2),
5.29−5.27 (m, 1H, H-4), 4.86 (d, J = 11.7 Hz, 1H, CH2Ph), 4.72 (d, J
= 11.8 Hz, 1H, CH2Ph), 3.95−3.92 (m, 1H, H-3), 3.83 (d, J = 14.9 Hz,
1H, CH2Cl), 3.77−3.69 (m, 4H, CH2Cl, CO2CH3); 13C NMR (100
MHz; CDCl3) δ 168.4, 166.4, 165.1, 136.7, 135.3, 133.8, 131.3, 129.9,
129.1, 129.1, 128.6, 128.5, 128.2, 127.8, 127.7, 86.5, 73.0, 71.3, 69.4,
68.6, 66.7, 52.8, 40.3; HRMS (TOF-ES+) m/z calcd for
C29H27ClO8SNa [M + Na]+ 593.1007, found 593.1005; Elemental
analysis calcd (%) for C29H27ClO8S, C 61.00, H 4.77, found C 60.70,
H 4.82.
Methyl 1,2,4-Tri-O-acetyl-3-O-benzyl-β-L-idopyranuronate
(16). To the L-ido acid 7 (112 mg, 0.27 mmol) was added dry
DMF (1 mL), KHCO3 (28 mg, 0.27 mmol) and then iodomethane
(25 μL, 0.40 mmol). The mixture was stirred for 24 h under N2,
solvents removed in vacuo, and the residue extracted with DCM (25
mL), and H2O (25 mL), the organic phase was dried (MgSO4),
filtered and evaporated. Purification by flash column chromatography
using (EtOAc/hexane (1:1) yielded 16 (113 mg, 0.27 mmol, 99%) as a
white solid. The product could be recrystallized using ether. Data for
this compound matched those previously reported.5g
2,4-Di-O-acetyl-3-O-benzyl-β-L-idopyranurono-1,6-lactone
(17). To the acid 7 (13.3 g, 32.5 mmol) was added dry DCM (100
mL) and then trimethylsilyl trifluoromethanesulfonate (TMSOTf)
(1.2 mL, 9.74 mmol). The mixture was stirred for 30 h at room
temperature under N2, after which time the reaction was quenched
with pyridine, solvents removed, and the residue purified by flash
column chromatography (EtOAc/hexane, 1:2), yielding 17 (6.01 g,
17.0 mmol, 53%) as a white solid. The product could be recrystallized
Methyl (Phenyl 2-O-acetyl-3-O-benzyl-1-thio-L-idopyrano-
side) uronate (20). Method A. To the L-ido thioglycoside 18 (0.65
g, 1.28 mmol) was added diethylether (6 mL), and this solution cooled
to 0 °C with an ice-bath. Benzylamine (0.4 mL, 3.83 mmol) was then
added, and the mixture stirred for 1 h at 0 °C. The reaction was
extracted with EtOAc (100 mL) and 1 M HCl (100 mL). The organic
phase was separated, dried (MgSO4), filtered, and solvents removed.
Purification of the residue by flash column chromatography (EtOAc/
Hexane 1:1) yielded 20 (382 mg, 0.88 mmol, 69%, α/β 2:1) as an oil.
Method B. To the L-ido thioglycoside 18 (92 mg, 0.18 mmol) was
added ethanol (5 mL), thiourea (20 mg, 0.27 mmol), sodium
hydrogencarbonate (30 mg, 0.36 mmol), and the mixture was heated
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to 70 °C with stirring for 3 h. The reaction was extracted with
dichloromethane (50 mL), and the organics washed with water (50
mL). The organic phase was separated, dried (MgSO4) filtered and
evaporated. Purification by flash column chromatography (EtOAc/
Hexane 1:2) yielded 20 (69 mg, 0.16 mmol, 80%, α/β 2:1) as an oil.
(m, 1H, H-2), 4.74 (s, 2H, CH2Ph), 4.62 (d, J = 1.5 Hz, 1H, H-5),
3.93 (t, J = 0.7 Hz, 1H, H-3), 3.80 (s, 3H, OCH3), 2.13 (s, 3H,
COCH3), 2.06 (s, 3H, COCH3); 13C NMR (100 MHz; CDCl3) δ
170.3, 170.1, 168.1, 137.1, 134.2, 132.3, 129.3, 128.9, 128.6, 128.5,
128.2, 128.2, 125.6, 85.0, 74.6, 73.2, 72.5, 69.3, 67.1, 52.9, 21.1, 21.0.
Phenyl 3,4,6-Tri-O-acetyl-2-deoxy-l-thio-2-trichloroacetami-
do-β-D-glucopyranoside (24). 1. D-Glucosamine·HCl (86.4 g, 401
mmol) was suspended in MeOH (1.0 L) at room temperature. Et3N
(112.0 mL, 802 mmol, 2.0 equiv) was added, and the suspension
cooled to 0 °C. Trichloroacetyl chloride (45.0 mL, 401 mmol, 1.0
equiv) was then added dropwise. The suspension was warmed to room
temperature and stirred for 5 days. The reaction was filtered through a
plug of Celite, washing with MeOH, and the solvent removed in
vacuo. The crude residue was dissolved in pyridine (800 mL) and
cooled to 0 °C. Ac2O (300 mL) was added dropwise, and the solution
allowed to warm to room temperature and stirred for 16 h. The
reaction was filtered through a Celite plug, and solvent removed in
vacuo, including coevaporation with toluene (3 × 350 mL). The crude
material was taken in EtOAc (450 mL) and washed with 1 M HCl (5
× 100 mL), saturated aqueous NaHCO3 (3 × 200 mL), saturated
aqueous NaCl (1 × 200 mL), dried (MgSO4), and solvent removed in
vacuo to reveal 175.0 g of a brown solid. This was recrystallized from
EtOH (1.2 L) to give 71.0 g of product (alpha anomer only). The
liquors were reduced in volume in vacuo to produce a second crop of
material, 38.0 g (1:1, α/β mixture). Finally the liquors were evaporated
to dryness and purified on a short silica plug (eluting with diethyl
ether/DCM, 5/95) to give another 30.3 g of product (4:6, α/β
mixture) and an overall yield of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-
trichloroacetamido-β-D-glucopyranose (139.0 g, 282 mmol, 70%).
Data for this compound matched those previously reported.45,46
2. To 1,3,4,6-tetra-O-acetyl-2-deoxy-2-trichloroacetamido-β-D-glu-
copyranose (184.4 g, 374 mmol) dissolved in dry DCM (900 mL) at
room temperature under nitrogen was added PhSH (50.0 mL, 486
mmol, 1.3 equiv) and (dropwise) TMSOTf (68.0 mL, 374 mmol, 1.0
equiv). The resulting dark red solution was stirred at room
temperature for 18 h and then poured onto a vigorously stirred
solution of aqueous NaHCO3 (70.0 g in 60 mL H2O) and stirred for
30 min. I2 (32.2 g, 131 mmol, 0.35 equiv) was then added, and the
solution stirred vigorously for another 30 min. Na2S2O3 (41.4 g, 262
mmol, 0.70 equiv) was added, and stirring continued for a final 30 min.
The layers were separated, and the aqueous extracted with DCM (1 ×
200 mL). The organics were combined, dried (MgSO4), and solvent
removed in vacuo afforded crude 24 (220.0 g) as a dark brown solid,
which was then recrystallized from hexane/EtOAc (350 mL, 1:1),
filtered and washed with cold hexane:EtOAc (150 mL, 2:1) to yield 24
(135.0 g, 67%) as a tan solid. The liquors were stripped and passed
through a silica plug (eluting with hexane:EtOAc, 5:1 then 2:1), and
solvent removed in vacuo to give a brown solid, recrystallization of
which (hexane:EtOAc, 60 mL:120 mL) gave a second batch of 24
(11.6 g, 5%) as a faint tan solid. Overall yield of 24 (146.4 g, 269
mmol, 72%). Data collected for 24 matched those previously
reported.37
20
20α: Rf 0.10 (EtOAc/hexane 1:2); [α]D = −110.7 (c = 0.61,
1
CH2Cl2); H NMR (400 MHz; CDCl3) δ 7.46−7.40 (m, 2H, ArH),
7.36−7.15 (m, 8H, ArH), 5.49 (s, 1H, H-1), 5.26 (d, J = 1.7 Hz, 1H,
H-5), 5.20 (dd, J = 2.7, 1.3 Hz, 1H, H-2), 4.76 (d, J = 11.9 Hz, 1H,
CH2Ph), 4.56 (d, J = 11.9 Hz, 1H, CH2Ph), 4.03−4.00 (m, 1H, H-4),
3.75 (s, 3H, C(O)OCH3), 3.70−3.67 (td, J = 2.7, 1.2 Hz, 1H, H-3),
2.65 (brs, 1H, OH), 2.00 (s, 3H, COCH3); 13C NMR (100 MHz;
CDCl3) δ 169.5, 169.0, 136.8, 135.6, 131.1, 129.1, 128.5, 128.1, 127.8,
127.6, 86.6, 73.1, 72.3, 69.0, 68.6, 68.2, 52.4, 20.9; MS-MALDI m/z =
450 [M + NH4]+; HRMS (FTMS-NSI+) m/z calcd for C22H28NO7S
[M + NH4]+ 450.1581, found 450.1587.
Methyl (Phenyl 2-O-benzoyl-3-O-benzyl-1-thio-L-idopyrano-
side) uronate (21).28 To the L-ido thioglycoside 19 (2.71 g, 4.76
mmol) was added diethylether (25 mL) and benzylamine (1.1 mL,
14.3 mmol). After stirring for 3 h the reaction was extracted with
EtOAc (100 mL) and HCl aq (1M, 100 mL). The organic phase was
separated, dried (MgSO4), filtered and evaporated. The crude material
was purified by flash column chromatography (EtOAc/Hexane 1:3).
̃
This yielded 21 (1.59 g, 3.21 mmol, 68%, αβ 3:1) as an oil. Repeated
flash column chromatography allowed separation of the anomers.
20
β-21: Rf 0.35 (EtOAc/hexane 1:2); [α]D = +55.2 (c = 0.37,
1
CH2Cl2); H NMR (400 MHz; CDCl3) δ 8.21 (d, J = 8.1 Hz, 2H,
ArH), 7.74−7.65 (m, 3H, ArH), 7.58 (t, J = 7.5 Hz, 2H, ArH), 7.51−
7.37 (m, 8H, ArH), 5.54 (d, J = 0.9 Hz, 1H, H-1), 5.44 (s, 1H, H-5),
4.92 (d, J = 11.8 Hz, 1H, CH2Ph), 4.84 (d, J = 11.8 Hz, 1H, CH2Ph),
4.75 (s, 1H, H-4), 4.17−4.15 (m, 2H, H-2, H-3), 3.95 (s, 3H,
C(O)OCH3), 2.69 (brs, 1H, OH); 13C NMR (100 MHz; CDCl3) δ
169.2, 165.8, 137.4, 134.2, 132.0, 130.4, 129.5, 129.1, 129.0, 128.7,
128.3, 128.2, 85.8, 76.8, 74.9, 73.2, 70.8, 67.9, 52.9.
20
α-21: Rf 0.32 (EtOAc/hexane 1:2); [α]D = −86.7 (c = 1.09,
1
CH2Cl2); H NMR (400 MHz; CDCl3) δ 8.03−8.00 (m, 2H, ArH),
7.62−7.56 (m, 3H, ArH), 7.48−7.30 (m, 10H, ArH), 5.79 (s, 1H, H-
1), 5.55 (dd, J = 2.7, 1.3 Hz, 1H, H-2), 5.46 (d, J = 1.6 Hz, 1H, H-5),
4.95 (d, J = 11.8 Hz, 1H, CH2Ph), 4.74 (d, J = 11.8 Hz, 1H, CH2Ph),
4.21 (s, 1H, H4), 3.99 (td, J = 3.0, 1.3 Hz, 1H, H-3), 3.86 (s, 3H,
C(O)OCH3), 2.92 (s, 1H, OH); 13C NMR (100 MHz; CDCl3) δ
169.7, 137.0, 133.9, 131.4, 129.8, 129.2, 128.8, 128.7, 128.6, 128.2,
127.8, 127.7, 86.9, 73.5, 72.5, 69.7, 69.1, 68.3, 52; HRMS (TOF-ES+)
m/z calcd for C27H26O7Na [M+Na]+ 517.1297, found 517.1294.
Methyl (Phenyl 2,4-Di-O-acetyl-3-O-benzyl-1-thio-L-idopyr-
anoside) uronate (22).28 To the L-ido ester 16 (18.0 g, 42.5 mmol)
was added dry dichloromethane (300 mL), thiophenol (6.7 mL, 63.7
mmol) and borontrifluoride diethyl etherate (28 mL, 212 mmol), and
the mixture was stirred for 16 h under N2. The reaction was quenched
by adding to a mixture of saturated aqueous NaHCO3 (800 mL) and
dichloromethane (500 mL) with stirring. To this mixture was added
iodine until a dark red color persisted, indicating all remaining
thiophenol had been oxidized to diphenyldisulfide, thus removing all
odor from the product mixture. The excess of iodine was reduced to
iodide by adding sodium thiosulfate solution (10% aq) dropwise until
the dark red color disappeared. The organic phase was separated, dried
(MgSO4), filtered, and solvents removed. Purification by flash column
chromatography (EtOAc/Hexane 1:2) yielded 22 (12.2 g, 44.4 mmol,
Phenyl 4,6-O-Benzylidene-1-thio-β-D-glucosaminopyrano-
side (25). 1. To 24 (101.2 g, 0.186 mol) was added dry MeOH (1
L) and Sodium (0.3 g, 0.013 mol). The mixture was stirred overnight
under N2. Then the reaction was quenched by adding Amberlite
strongly acidic resin (3 g) and stirring another 30 min. After filtration
and evaporation of solvent phenyl 1-thio-2-trichloroacetamide-β-D-
glucosaminopyranoside (77.7 g, 0.186 mol, 100%) was obtained in
high enough purity to be used in the next step. Data collected matched
those previously reported.47
̃
61%, αβ 2:1) as an oil, along with recovered starting material (1.38 g,
8%): HRMS (FTMS-NSI+) m/z calcd for C24H27O8S [M + H]+
1
475.1421, found 475.1407. α-22: Rf 0.09 (EtOAc/hexane 1:3); H
NMR (400 MHz; CDCl3) δ 7.55−7.25 (m, 10H, Ph), 5.68−5.67 (m,
1H, H-4), 5.42 (d, J = 2.0 Hz, 1H, H-1), 5.24−5.23 (m, 1H, H-2),
5.18−5.17 (m, 1H, H-5), 4.82 (d, J = 10.0 Hz, 2H, CH2Ph), 3.90−3.89
(m, 1H, H-3), 3.81 (s, 3H, OCH3), 2.07 (s, 3H, COCH3), 2.06 (s, 3H,
COCH3); 13C NMR (100 MHz; CDCl3) δ 169.8, 169.6, 168.7, 136.9,
135.7, 130.9, 129.1, 128.6, 128.1, 127.7, 127.4, 86.1, 72.7, 71.3, 68.6,
67.9, 67.0, 52.6, 20.9, 20.7.
2. To phenyl 1-thio-2-trichloroacetamide-β-D-glucosaminopyrano-
side (140.7 g, 0.337 mol) was added dry THF (800 mL),
benzaldehyde dimethyl acetal (67 mL, 0.404 mol) and camphorsul-
fonic acid (4.2 g, 0.017 mol). To the reaction flask was fitted a Dean−
Stark collector and condenser. The mixture was heated to mild reflux
allowing slow removal of the THF/MeOH azeotrope (100 mL over 2
h). After 2 h the reaction was quenched by addition of NEt3 (5 mL),
and the solvent evaporated. The crude was extracted with EtOAc (1
L)/aq NaHCO3(sat) (1 L), organic phase dried (MgSO4), filtered and
β-22: Rf 0.11 (EtOAc/hexane 1:3); 1H NMR (400 MHz; CDCl3) δ
7.59−7.15 (m, 10H, Ph), 5.20−5.18 (m, 2H, H-1, H-4), 5.12−5.11
L
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evaporated. The white solid obtained was recrystallized by dissolving
in THF/EtOAc and excess hexane added. This was repeated twice
with filtrates to yield phenyl 4,6-O-benzylidene-1-thio-2-trichloroace-
tamide-β-D-glucosaminopyranoside (143.7 g, 0.284 mol, 84% over 2
steps). Data collected matched those previously reported.47 See the
hydrochloride36 (40.4 g, 193 mmol, 1.05 equiv) was then added in
four portions over 40 min followed by CuIISO4 (459 mg, 1.8 mmol,
0.01 equiv). The suspension was stirred for 2 h at room temperature.
The reaction was filtered, and MeOH removed in vacuo. H2O (200
mL) was added, and the pH adjusted to 3 with 1 M HCl. The aqueous
phase was extracted with EtOAc (3 × 300 mL), and the combined
organics washed with saturated aqueous NaHCO3, saturated aqueous
NaCl, dried (MgSO4), and solvent removed in vacuo to reveal the
required azido-triol β-27 (50.3 g, 169 mmol, 92%) as a pale yellow
solid. Data collected for β-27 matched reported data.41
α-27: To 26 (16.8 g, 0.040 mol) was added dry MeOH (200 mL)
and sodium (0.1 g, 4.3 mmol). The mixture was stirred 90 min under
N2. Then the reaction was quenched by adding Amberlite strongly
acidic resin (1 g) and stirring another 30 min. After filtration and
evaporation of solvent α-27 (11.6 g, 39.0 mmol, 100%) was obtained
in high enough purity to be used in the next step. Data collected for α-
27 matched those reported.38
1
Supporting Information for copies of H and 13C NMR spectra.
3. To phenyl 4,6-O-benzylidene-1-thio-2-trichloroacetamido-β-D-
glucosaminopyranoside (10.2 g, 20.2 mmol) was added THF (65 mL),
MeOH (15 mL) and water (15 mL). Then KOH (3.4 g, 60.7 mmol)
in 15 mL water was added with vigorous stirring. After 2 h, brine (200
mL) and THF (150 mL) were added. A gel was formed that could be
removed by filtration. The aqueous brine layer was then again
extracted with THF (3 × 100 mL). The combined organic layers were
dried (MgSO4), filtered and evaporated. To the crude mixture was
added THF (200 mL), the material filtered again and evaporated to
yield 25 (7.2 g, 20.0 mmol, 99%) as a white solid. The product could
be recrystallized from hot MeOH (300 mL), which upon cooling gave
a white cotton-like solid.
Phenyl 2-Azido-4,6-O-benzylidene-3-O-benzyl-2-deoxy-1-
thio-β-D-glucopyranoside (β-28). Method A. Triol 27 (110.0 g,
370 mmol) was dissolved in MeCN (1100 mL) at ambient temprature
and benzaldehyde dimethylacetal (66.6 mL, 444 mmol, 1.2 equiv) and
p-TsOH (3.2 g, 19 mmol, 0.05 equiv) added, and the reaction stirred
for 72 h. To the reaction mixture was added Et3N (5 mL), and the
solvents removed in vacuo. The residue was recrystallized from
propan-2-ol (1.1 L), affording pure benzylidine acetal (94.8 g, 66%).
The reduced mother liquors were purified through a short silica plug
(eluting with hexane/EtOAc, 9/3, 3/1) to provide, when combined
with the recrystallized material, the required benzylidine acetal (104.8
g, 272 mmol, 78%). To this 3-OH intermediate (48 g, 125 mmol)
dissolved in THF (500 mL) at ambient temperature was added NaH
(5.5 g, 138 mmol, 1.1 equiv) over 30 min, and the reaction stirred for 1
h. Benzyl bromide (16.4 mL, 138 mmol, 1.1 equiv) was then added,
and the mixture heated at 50 °C for 3 h, over which period a
precipitate formed. The reaction was cooled and quenched by addition
of water (5 mL), the solvents removed in vacuo, and the residue taken
up into ethyl acetate (300 mL) and water (200 mL), the organics
separated, washed with brine (100 mL), dried (MgSO4), and solvents
removed in vacuo to yield a tan solid. Recrystallization from ethyl
acetate:hexane, and washing the resulting product with neat hexane,
yielded β-28 as a tan solid (51.7 g, 109 mmol, 87%).
Method B. To 25 (7.4 g, 20.6 mmol) was added THF (20 mL),
MeOH (80 mL), K2CO3 (4.27 g, 30.9 mmol), imidazole-1-sulfonyl
azide hydrochloride (5.18 g, 24.7 mmol) and CuSO4·5H2O (52 mg,
0.21 mmol). The mixture was stirred for 5 h and extracted with DCM
(200 mL) and H2O (2 × 200 mL). The organic layer was dried
(MgSO4), filtered and evaporated. After evaporation of solvent the
crude was purified by flash column chromatography using EtOAc/
Hexane 1:4 as the eluent. This yielded phenyl 2-azido-4,6-O-
benzylidene-2-deoxy-1-thio-β-D-glucopyranoside (7.45 g, 0.019
mmol, 94%) as a white solid.
(Large scale): 1. To 25 (43.5 g, 0.121 mol) was added MeOH (700
mL), K2CO3 (25 g, 0.18 mol), imidazole-1-sulfonyl azide hydro-
chloride (30.3 g, 0.145 mol) and CuSO4·5H2O (150 mg, 0.60 mmol).
The mixture was stirred for 16 h, and more reagents added (K2CO3 (5
g, 0.036 mol), imidazole-1-sulfonyl azide hydrochloride (6.0 g, 0.024
mol) and CuSO4·5H2O (30 mg, 0.12 mmol)). After another 2 h the
solvent was evaporated, and the crude extracted with EtOAc (1.5 L)
and H2O (1 L). The organic layer was dried (MgSO4), filtered and
evaporated. The crude was purified by filtering through a short layer (3
cm) of silica gel in a 1 L funnel using first DCM and then DCM/
EtOAc 20:1). The product was further purified by crystallization. It
was dissolved in the minimum amount of EtOAc (230 mL) and adding
hexane (800 mL). This yielded phenyl 2-azido-4,6-O-benzylidene-2-
deoxy-1-thio-β-D-glucopyranoside (33.1 g, 0.86 mmol, 70%) as a white
solid.
3. (Large scale): To phenyl 4,6-O-benzylidene-1-thio-2-trichlor-
oacetamido-β-D-glucosaminopyranoside (108.3 g, 0.214 mol) was
added THF (600 mL), MeOH (150 mL) and water (150 mL). Then
was added KOH (36 g, 0.642 mol) in 150 mL of water over 15 min.
After 3 h the remixture was extracted with brine (1 L) and THF (1 L,
2 × 500 mL). The combined organic layers were dried with MgSO4,
filtered and evaporated. To the crude mixture was added THF (2 L),
filtered again and evaporated to give a crude yield of 25 (90.8 g) as a
white solid. The product could be recrystallized from hot MeOH (1.5
L), which upon cooling gave a white cotton like solid (33.4 g). The
filtrate was evaporated and purified by filtering through a short layer (5
cm) of silica gel in a 1 L funnel using first EtOAc and then EtOAc/
MeOH 10:1 also containing NEt3 1%. This yielded another batch of
25 (29.6 g) and gave a combined yield (63.0 g, 0.175 mol, 82%). Data
for 25 matched those reported.40
Phenyl 2-Azido-3,4,6-tri-O-acetyl-2-deoxy-1-thio-α-D-gluco-
pyranoside (26). D-Glucosamine hydrochloride (24.1 g, 0.112 mol),
imidazole-1-sulfonyl azide hydrochloride [WARNING: this material is
potentially explosive and should be handled with due caution]36 (28.1
g, 0.134 mol), copper sulfate pentahydrate (250 mg, 0.96 mmol) and
potassium carbonate (38.0 g, 0.275 mol) were combined and then
dissolved in MeOH (500 mL). This mixture was stirred 4 h at room
temperature. The solution was filtered, solvent evaporated and then
azeotroped with toluene (3 × 300 mL). The crude solid was dissolved
in pyridine (100 mL) whereupon significant amounts of insoluble salts
were observed. Acetic anhydride (84 mL, 0.90 mol) was added to the
solution cooled in an icebath, and the reaction mixture stirred
overnight at room temperature. The mixture was concentrated in
vacuo and azeotroped with toluene (2 × 300 mL). The residue was
then diluted with EtOAc (35 mL), washed with water (15 mL), the
organic layer dried (MgSO4), and solvents removed in vacuo.
Purification of this residue by flash column chromatography
(EtOAc/hexane gradient 1:3 and then 1:2) afforded 1,3,4,6-tetra-O-
̃
acetyl-2-azido-2-deoxy-αD-glucopyranoside (39.1 g, 0.105 mol, 94%)
as a yellow solid. It could be recrystallized from hot EtOH. Data
collected matched those previously reported.41 To a solution of
̃
1,3,4,6-tetra-O-acetyl-2-azido-2-deoxy-αD-glucose (37.3 g, 0.100
mmol) in dry DCM (300 mL), under anhydrous conditions, was
added thiophenol (15.0 mL, 0.147 mol) and TMSOTf (5.4 mL, 0.030
mol). The reaction mixture was stirred under N2 at room temperature
for 6 days. Then the reaction was quenched with NEt3 (5 mL), and
solvent evaporated. Flash column chromatography (EtOAc/hexane
1:3) gave 26 (27.1 g, 64.0 mmol, 64%) along with starting material
(8.0 g, 21% recovery). The product was recrystallized from hot
ethanol. Data collected for 26 matched those previously reported.48
Phenyl 2-Azido-2-deoxy-1-thio-D-glucopyranoside (27). β-
27: Triacetate 24 (100.0 g, 184 mmol) was suspended in MeOH (900
mL) at room temperature. K2CO3 (127.0 g, 920 mmol, 5.0 equiv) in
H2O (100 mL) was added, and the mixture heated at 60 °C for 18 h.
The reaction was cooled, filtered and washed with MeOH (300 mL).
To this solution was then added further K2CO3 (26.7 g, 193 mmol,
1.05 equiv). The diazo transfer reagent imidazole-1-sulfonyl azide
2. To phenyl 2-azido-4,6-O-benzylidene-2-deoxy-1-thio-β-D-gluco-
pyranoside (36.0 g, 0.094 mol) was added dry THF (350 mL), benzyl
bromide (12.2 mL, 0.103 mol), and then NaH (60% in mineral oil)
(4.1 g, 0.103 mol) was added in portions over 60 min (NOTE:
Exothermic reaction and hydrogen liberated) while being kept under
M
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Article
N2. The mixture was then heated to 50 °C for 12 h. The reaction (at
room temperature) was quenched by careful addition of MeOH (25
mL) followed by water (5 mL). The solvent (containing precipitated
NaBr) was evaporated and extracted with DCM (500 mL)/H2O (500
mL) and brine (300 mL). The organic layer was dried (MgSO4),
filtered and evaporated. The crude was purified by eluting through a
short layer (5 cm) of silica gel in a 1 L funnel using DCM. This yielded
β-28 (42.4 g, 0.089 mol, 95%). Data collected for the intermediate
benzylidine acetal and β-28 matched those previously reported.17
Phenyl 2-Azido-3-O-benzyl-2-deoxy-4,6-O-p-methoxyben-
zylidene-1-thio-α-D-glucopyranoside (α-29). 1. To α-27 (15.2
g, 0.051 mol) was added dry CH3CN (160 mL), anisaldehyde
dimethyl acetal (11.2 mL, 0.061 mol) and camphorsulfonic acid (777
mg, 2.55 mmol). After stirring 16 h the reaction was quenched by
addition of NEt3 (1 mL), and the solvent evaporated. The crude was
extracted with DCM (300 mL)/aq NaHCO3(sat) (300 mL), organic
phase dried (MgSO4), filtered and evaporated. The product was
purified by flash column chromatography (EtOAc/hexane 1:3
containing 10% DCM) yielding Phenyl 2-azido-2-deoxy-4,6-O-p-
methoxybenzylidene-1-thio-α-D-glucopyranoside (20.2 g, 48.7 mmol,
90%) as a white solid. It could be recrystallized by dissolving in
minimum amount EtOAc and adding 4 times the volume hexane.42
2. To phenyl 2-azido-2-deoxy-4,6-O-p-methoxybenzylidene-1-thio-
α-D-glucopyranoside (20.3 g, 0.049 mol) was added dry DMF (150
mL), benzyl bromide (6.5 mL, 0.054 mol) and then NaH (60% in
mineral oil) (2.36 g, 0.059 mol) was added in 3 portions over 30 min
(NOTE: Exothermic reaction and gas liberated) while being kept
under N2. The mixture was stirred for 5 h. The reaction (at room
temperature) was quenched by careful addition of EtOH (1 mL)
followed by water (150 mL). At this stage heavy precipitation was
observed, and the solid was filtered off and washed with water (3 ×
100 mL) and hexane (3 × 100 mL). After drying in the air the residue
was recrystallized from hot EtOH (1 L) to yield α-29 (20.7 g, 0.041
mol, 84%) as a white solid. Data collected matched those previously
reported.42
Phenyl 2-Azido-2-deoxy-3,6-O-dibenzyl-1-thio-β-D-gluco-
pyranoside (β-30). To β-28 (18.0 g, 0.038 mol) was added dry
DCM (200 mL), while keeping under N2 and cooled to 0 °C using an
icebath. Then first triethylsilane (18.2 mL, 0.114 mol) was added
followed by BF3·OEt2 (14.5 mL, 0.114 mol) over 5 min. The mixture
was stirred at 0 °C for 4 h and then quenched by pouring into sat.
NaHCO3 (400 mL) and DCM (200 mL) (NOTE: Gas liberated).
The phases were separated, the organic layer dried (MgSO4), filtered
and evaporated. The crude was purified by flash column chromatog-
raphy (EtOAc/hexane gradient 1:4, 1:3, 1:0) to yield β-30 (14.1 g,
0.030 mol, 84%). Starting material was also recovered (2.2 g, 12%),
and two more polar products identified as phenyl 2-azido-3-O-benzyl-
4-O-benzyl-2-deoxy-1-thio-β-D-glucopyranoside (0.40 g, 2%) and
phenyl 2-azido-3-O-benzyl-2-deoxy-1-thio-β-D-glucopyranoside (0.99
g, 7%). Data collected matched those previously reported.38
to yield the crude material as a yellow oil. This was purified on a silica
plug (eluting with EtOAc/hexane, 3/1, 1/1) to yield β-32 (29.8 g, 77.0
mmol, 83%) as a white solid. Data recorded for this compound
matched those in the literature.24
Phenyl 2-Azido-6-O-benzoyl-3-O-benzyl-2-deoxy-1-thio-β-D-
glucopyranoside (β-33). Glucoside diol β-32 (3.30 g, 8.5 mmol)
was dissolved in dry DCM (30 mL) at room temperature under N2.
Et3N (1.3 mL, 9.4 mmol, 1.1 equiv) was added, and the solution
cooled to 0 °C. BzCl (987 μL, 8.5 mmol, 1.0 equiv) was added, and
the reaction warmed to room temperature over 30 min. The reaction
was poured onto 1 M HCl (50 mL), and the layers separated. The
organics were washed with saturated aqueous NaHCO3 (20 mL),
saturated aqueous NaCl (20 mL), dried (MgSO4), and solvent
removed in vacuo to provide a white solid. This was slurried in Et2O
and filtered to give β-33 (3.81 g, 7.8 mmol, 91%) as a fluffy white
20
1
solid: [α]D = −50.0 (c = 0.07, DCM); mp 152−155 °C; H NMR
(400 MHz, CDCl3) δ 8.10−8.07 (m, 2H, ArH), 7.67−7.59 (m, 3H,
ArH), 7.52−7.48 (m, 2H, ArH), 7.41−7.26 (m, 6H, ArH), 7.21−7.17
(m, 2H, ArH), 4.94 (d, J = 10.9 Hz, 1H, CH2Ph), 4.84 (d, J = 10.9 Hz,
1H, CH2Ph), 4.75 (dd, J = 12.2, 3.9 Hz, 1H, H-6), 4.60 (dd, J = 12.2,
2.1 Hz, 1H, H-6′), 4.49 (d, J = 9.6 Hz, 1H, H-1), 3.59 (ddd, J = 9.7,
3.9, 2.1 Hz, 1H, H-5), 3.52 (ddd, J = 9.6, 8.9, 3.4 Hz, 1H, H-4), 3.42
(dd, J = 9.6, 8.9 Hz, 1H, H-3), 3.31 (t, J = 9.6, 8.9 Hz, 1H, H-2), 2.82
(d, J = 3.4, 1H, OH); 13C NMR (100 MHz; CDCl3) δ 168.8, 139.4,
135.7, 135.3, 132.4, 131.6, 131.2, 130.7, 130.5, 130.3, 130.3, 130.11,
130.1, 87.6, 86.0, 79.7, 77.5, 71.5, 66.2, 65.0; ES MS m/z 514 [M +
Na]+; HRMS (TOF-ES+) m/z calcd for C26H25N3O5SNa [M + Na]+
514.1408, found 514.1400.
Phenyl 2-Azido-2-deoxy-3,6-di-O-benzyl-4-O-p-methoxy-
benzyl-1-thio-β-D-glucopyranoside (β-34). To β-30 (25.2 g,
0.053 mol) was added dry THF (300 mL), p-methoxybenzyl chloride
(11.5 mL, 0.085 mol), and then NaH (60% in mineral oil) (3.1 g,
0.078 mol) was added in portions over 60 min (NOTE: Exothermic
reaction and gas liberated) while being kept under N2. The mixture
was then heated to 60 °C for 36 h. The reaction (at room
temperature) was quenched by careful addition of MeOH (25 mL)
followed by water (5 mL). The solvent (containing precipitated NaCl)
was evaporated and extracted with DCM (500 mL)/H2O (500 mL)
and brine (300 mL). The organic layer was dried (MgSO4), filtered
and evaporated. The product was purified by flash column
chromatography (EtOAc/hexane gradient 1:6, 1:4) yielding β-34
(29.3 g, 0.049 mol, 93%). Data collected matched those previously
reported.38
Phenyl 2-Azido-2-deoxy-3,6-di-O-benzyl-4-O-trichloroace-
tyl-1-thio-β-D-glucopyranoside (β-35). Glucoside β-30 (17.2 g,
36.0 mmol) was dissolved in dry DCM (150 mL) at room temperature
under N2. Et3N (5.30 mL, 38.0 mmol, 1.05 equiv) was added, and the
solution cooled to 0 °C. Trichloroacetyl chloride (4.23 mL, 38.0
mmol, 1.05 equiv) was added, and the pale yellow solution stirred at
room temperature for 2 h. The reaction was then poured onto 1 M
HCl (100 mL), and the layers separated. The organics were washed
with saturated aqueous NaHCO3 (50 mL), saturated aqueous NaCl
(50 mL), dried (MgSO4), and solvent removed in vacuo to give the
crude as a yellow gum. This was purified by passage through a short
plug of silica gel, eluting with hexane/EtOAc, 15/1 to give β-35 (20.8
g, 33.4 mmol, 92%) as a yellow solid: 1H NMR (400 MHz; CDCl3) δ
1H NMR (400 MHz; CDCl3) δ 7.52−7.47 (m, 2H, ArH), 7.31−7.13
(m, 13H, ArH), 5.07 (t, J = 9.6 Hz, 1H, H-4), 4.71 (d, J = 10.4 Hz, 1H,
CH2Ph), 4.64 (d, J = 10.4 Hz, 1H, CH2Ph), 4.46 (s, 2H, CH2Ph), 4.39
(d, J = 10.1 Hz, 1H, H-1), 3.63 (ddd, J = 10.4, 4.9, 2.7 Hz, 1H, H-5),
3.58−3.50 (m, 3H, H-3, H-6, H-6′), 3.35 (dd, J = 10.0, 9.4 Hz, 1H, H-
2). 13C NMR (100 MHz; CDCl3) δ 160.6, 137.6, 136.9, 133.8, 130.5,
129.2, 128.7, 128.6, 128.5, 128.2, 128.0, 127.8, 89.6, 86.2, 82.1, 77.0,
75.8, 75.0, 73.7, 68.5, 64.8; MS ES+ m/z 644 [M + Na]+; HRMS
(TOF-ES+) m/z calcd for C28H26N3O5NaSCl3 [M + Na]+ 644.0551,
found 644.0545.
Phenyl 2-Azido-6-O-benzoyl-3-O-benzyl-2-deoxy-1-thio-4-
trichloroacetyl-β-D-glucopyranoside (β-36). To β-33 (24.8 g,
50.5 mmol) dissolved in dry DCM (250 mL) at room temperature
under N2 was added Et3N (7.40 mL, 53.0 mmol, 1.05 equiv) and
Phenyl 2-Azido-3-O-benzyl-2-deoxy-4-O-p-methoxybenzyl-
1-thio-α-D-glucopyranoside (α-31). Derivative α-29 (16.7 g, 0.033
mol) was dissolved in 1 M BH3·THF in THF (100 mL, 0.10 mmol)
cooled to 0 °C. Then 1 M Bu2BOTf in DCM (34 mL, 0.034 mol) was
added over 40 min, and the reaction mixture stirred a further 1 h
before being quenched with triethylamine (5 mL), followed by slow
addition of methanol (NOTE: Hydrogen being liberated). The
solvents were evaporated and then azeotroped with methanol (2 × 100
mL) to remove borate esters. The residue was purified by flash column
chromatography (EtOAc/hexane 1:3) to yield α-31 (12.48 g, 0.025
mol, 74%) as a clear gum. Data collected matched those previously
reported.42
Phenyl 2-Azido-3-O-benzyl-2-deoxy-1-thio-β-D-glucopyra-
noside (β-32).24 Benzylidine glucoside β-28 (43.3 g, 91.0 mmol)
was suspended in 60% aq AcOH (400 mL). The suspension was then
heated to 100 °C whereupon the substrate went into solution. The
reaction temperature was maintained at 100 °C for 3 h, cooled and
then cautiously poured onto a solution of aqueous NaHCO3 (400 g in
1 L H2O). The solution was then extracted with EtOAc (3 × 200 mL),
the organics combined, dried (MgSO4), and solvent removed in vacuo
N
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trichloroacetyl chloride (5.90 mL, 53.0 mmol, 1.05 equiv), and the pale
yellow solution stirred at room temperature for 5 h. The reaction was
then poured onto 1 M HCl (100 mL), and the layers separated. The
organics were washed with saturated aqueous NaHCO3 (50 mL),
saturated aqueous NaCl (50 mL), dried (MgSO4), and solvent
removed in vacuo to give the crude as a brittle yellow solid. This was
slurried in Et2O and filtered to give phenyl-2-azido-6-O-benzoyl-3-O-
benzyl-2-deoxy-1-thio-4-trichloroacetyl-β-D-glucopyranoside (24.3 g)
as a white solid. The remaining liquors were purified by silica gel flash
chromatography (eluting with hexane/EtOAc, 8/1) to give a further
5.2 g of product as a white solid, providing β-36 (29.5 g, 46.3 mmol,
mmol, 85%) as a white solid: MS ES [M + Na]+ m/z 528. See the
1
Supporting Information for copies of H and 13C NMR spectra.
2-Azido-3,6-di-O-benzyl-2-deoxy-4-trichloroacetyl-α̃β-D-glu-
copyranose (40). To β-35 (11.66 g, 18.7 mmol) was added acetone
(300 mL), and the mixture cooled to 0 °C in an icebath. N-
bromosuccinimide (3.5 g, 19.4 mmol) was then added. After 40 min
another portion of N-bromosuccinimide (1.26 g, 7.0 mmol) was
added. After 2 h the solvent was evaporated, and the mixture extracted
with DCM (200 mL) and water (200 mL). The organic layer was
dried (MgSO4), filtered and evaporated. The crude mixture was
purified by flash column chromatography using EtOAc/hexane (1:4)
as the eluent to yield 40 (8.89 g, 16.7 mmol, 89%) as a white solid.
The product could be recrystallized by dissolving in minimum amount
of EtOAc and adding 4 times the volume of hexane giving a white
cotton like solid: Rf 0.24 (EtOAc/hexane 1:3); mp 131−132 °C; MS
ES [M + Na]+ m/z 552.0; HRMS (FTMS-NSI+) m/z calcd for
C22H22N3O6Cl3Na [M + Na]+ 552.0467, found 554.0462. See the
20
1
92%): [α]D = −37.6 (c = 0.06, DCM); mp 117−119 °C; H NMR
(400 MHz, CDCl3) δ 8.00−7.97 (m, 2H, ArH), 7.57−7.53 (m, 1H,
ArH), 7.48−7.39 (m, 4H, ArH), 7.29−7.16 (m, 6H, ArH), 7.06−7.01
(m, 2H, ArH), 5.15 (t, J = 9.7 Hz, 1H, H-4), 4.77−4.66 (m, 3H,
CH2Ph, H-6′), 4.42 (d, J = 10.1 Hz, 1H, H-1), 4.25 (dd, J = 12.5, 4.3,
1H, H-6), 3.84 (ddd, J = 9.7, 4.3, 2.1 Hz, 1H), 3.63 (t, J = 9.3 Hz, 1H,
H-3), 3.36 (dd, J = 10.1, 9.7 Hz, 1H, H-2); 13C NMR (100 MHz;
CDCl3) δ 165.9, 160.7, 136.6, 134.5, 133.5, 129.9, 129.6, 129.4, 129.1,
129.0, 128.7, 128.6, 128.37, 128.2, 89.4, 85.9, 81.9, 76.1, 75.5, 74.2,
64.6, 61.9; ES MS m/z 658/660 [M + Na]+; HRMS (TOF-ES+) m/z
calcd for C28H24N3O6SCl3Na [M + Na+] 658.0344, found 658.0328.
Phenyl 6-O-Acetyl-2-azido-3-O-benzyl-2-deoxy-1-thio-4-p-
methoxybenzyl-α-D-glucopyranoside (α-37).42 To a stirred
solution of α-31 (6.7 g, 13.12 mmol) in dry DCM (75 mL) and
pyridine (2.1 mL) at 0 °C was added dropwise acetic anhydride (1.9
mL, 19.8 mmol) followed by catalytic amount of N,N-dimethylami-
nopyridine. The cooling was removed and stirred for another 2 h.
Then solvents were evaporated, and the residue was diluted with DCM
(250 mL) and washed with NaHCO3 and brine. The product was
purified by flash column chromatography (EtOAc/hexane 1:4)
yielding α-37 (10.7 g, 99%): MS ES+ [M + Na]+ m/z 571.1. See
1
Supporting Information for copies of H and 13C NMR spectra.
2-Azido-6-O-benzoyl-3-O-benzyl-2-deoxy-4-trichloroacetyl-
α̃β-D-glucopyranose (41). To β-36 (15.0 g, 24.0 mmol) dissolved in
Me2CO (160 mL) at room temperature was added NBS (6.4 g, 36.0
mmol, 1.5 equiv), and the pale yellow solution stirred for 2 h at room
temperature. TLC analysis (hexane/EtOAc, 3:1) showed the reaction
to be incomplete, and further NBS (1.0 equiv) was added, and stirring
continued for another 2 h. Saturated aqueous NaHCO3 (4 mL) was
added, and the solvents removed in vacuo. The crude residue was
taken up in EtOAc (100 mL) and washed with saturated aqueous
NaHCO3 (50 mL), dried (MgSO4), solvents removed in vacuo, and
the residue purified by silica gel flash chromatography (eluting with
hexane/EtOAc, 5:1 → 3:1) to give the intermediate 1-OH glucoazide,
41 (7.6 g, 14.0 mmol, 59%) as a yellow gum which was used
immediately: MS ES+ m/z 566 [M + Na]+; HRMS (FTMS-NSI+) m/z
calcd for C22H24N4O7SCl3 [M + NH4]+ 561.0705, found 561.0706.
1
the Supporting Information for copies of H and 13C NMR spectra.
1
See the Supporting Information for copy of H NMR spectrum.
Phenyl 2-Azido-6-O-benzoyl-3-O-benzyl-2-deoxy-1-thio-4-
O-p-methoxybenzyl-α-D-glucopyranoside (α-38). To a stirred
solution of α-31 (8.5 g, 0.017 mol) in dry DCM (100 mL) and
pyridine (1.5 mL, 0.018 mol) was added dropwise benzoyl chloride
(2.2 mL, 0.018 mol) followed by catalytic amount of N,N-
dimethylamino pyridine (42 mg, 0.34 mmol). The mixture was stirred
for 4 h, more DCM (200 mL) added, extracted with water (300 mL)
and sat. NaHCO3 (200 mL). The organic phase was dried (MgSO4),
filtered and evaporated. The white solid obtained could be
recrystallized by dissolving in minimum amount EtOAc (50 mL)
and hexane added (250 mL) yielding α-38 (9.6 g, 94%) as large white
6-O-Acetyl-2-azido-3-O-benzyl-2-deoxy-4-p-methoxyben-
zyl-α̃
β-D-glucopyranose (42).43b To α-37 (7.0 g, 12.7 mmol) was
added acetone (85 mL), and the mixture was cooled to 0 °C in an ice
bath. Then was added N-bromosuccinimide (2.38 g, 13.4 mmol), and
the mixture was stirred for 30 min. The reaction was quenched by
addition of saturated NaHCO3 solution (5 mL), the acetone
evaporated, and DCM (200 mL) and water (200 mL) added. The
organic phase was separated, dried (MgSO4), filtered and evaporated.
The crude was purified using flash column chromatography (EtOAc/
hexane 1:3). This yielded the product 42 (4.87 g, 10.7 mmol, 84%) as
a white solid. The product could be recrystallized by dissolving in
minimum amount of EtOAc and adding 5 times the volume of hexane:
MS ES [M + Na]+ m/z 480. See the Supporting Information for copies
20
1
needles: mp = 115−116 °C; [α]D = +163.0° (c = 1.00, CHCl3); H
NMR (CDCl3, 400 MHz) δ 7.97−7.94 (m, 2H, aromatic), 7.59−7.55
(m, 1H, ArH), 7.49−7.32 (m, 9H, ArH), 7.23−7.18 (m, 5H, ArH),
6.84−6.80 (m, 2H, ArH), 5.61 (d, 1H, H-1, J = 5.2 Hz), 4.98 (d, 1H,
benzylic CHa, J = 10.4 Hz), 4.93 (d, 1H, benzylic CHb, J = 10.4 Hz),
4.84 (d, 1H, H-6a, J = 10.4 Hz), 4.59−4.54 (m, 2H, H-5, H-6b), 4.52−
4.47 (m, 2H), 3.98 (dd, 1H, H-2, J = 5.2, 10.0 Hz), 3.89 (dd, 1H, H-3,
1
of H and 13C NMR spectra.
2-Azido-6-O-benzoyl-3-O-benzyl-2-deoxy-4-O-p-methoxy-
benzyl-α̃β-D-glucopyranose (43). To a solution of α-38 (1.5 g, 2.45
mmol) in acetone (20 mL) at 0 °C was added NBS (437 mg, 2.46
mmol), and the solution was left stirring at 0 °C for 40 min and then
quenched with saturated NaHCO3 solution followed by evaporation of
solvents. The crude was redissolved into DCM (100 mL) and was
washed with saturated aqueous NaHCO3 and brine. The organics were
dried (MgSO4), filtered and evaporated in vacuo to yield a yellow gum,
which was purified by column chromatography (hexane:EtOAc, 3:1)
to give the intermediate 43 as a white powder (1.10 g, 2.12 mmol,
87%): HRMS (TOF-ES+) m/z calcd for C28H29N3O7Na [M + Na+]
542.1898, found 542.1909. See the Supporting Information for copies
J = 8.4, 10.0 Hz), 3.74 (s, 3H), 3.68 (dd, 1H, H4, J = 8.4, 9.6 Hz); 13
C
NMR (CDCl3, 100 MHz) δ 166.1, 159.5, 137.6, 133.0, 132.5, 129.8,
129.7, 129.2, 128.6, 128.1, 128.0, 127.9, 114.0, 87.1, 81.7, 77.6, 75.8,
74.8, 72.5, 70.3, 64.1, 63.2, 55.2; HRMS (TOF-ES+) m/z calcd for
C34H33N3O6SNa [M + Na+] 634.1988, found 634.1980; Elemental
analysis calcd (%) for C34H33N3O6S, C 66.76, H 5.44, N 6.87, found C
66.37, H 5.79, N 6.86.
2-Azido-3,6-di-O-benzyl-2-deoxy-4-O-p-methoxybenzyl-α̃β-
D-glucopyranose (39).43a To β-34 (20.1 g, 0.034 mol) was added
acetone (600 mL), and the mixture was cooled to 0 °C in an icebath.
Then was added N-bromosuccinimide (6.0 g, 0.034 mol), and the
mixture was stirred for 30 min. The reaction was quenched by addition
of saturated NaHCO3 solution (15 mL), the acetone evaporated and
DCM (300 mL), and water (300 mL) added. The organic phase was
separated, dried (MgSO4), filtered and evaporated. The crude was
purified using flash column chromatography (EtOAc/hexane 1:3),
followed by recrystallization by dissolving in EtOAc (50 mL) and
adding hexane (300 mL). This yielded the product 39 (14.5 g, 0.029
1
of H and 13C NMR spectra.
2-Azido-3,6-di-O-benzyl-2-deoxy-4-O-p-methoxybenzyl-1-
O-trichloroacetimidate-α̃
β-D-glucopyranoside (44).43a The de-
rivative 39 (8.46 g, 16.7 mmol) was dissolved in dry DCM (100 mL)
and to this was added trichloroacetonitrile (8.5 mL, 85 mmol) and
DBU (0.12 mL, 0.84 mmol) while being kept under N2. The mixture
was stirred 90 min, solvents were then evaporated, and the product
immediately purified by flash column chromatography (EtOAc/hexane
1:3 + 1% triethylamine) to yield 44 (10.8 g, 16.6 mmol, 99%) as sticky
oil. This compound was used immediately for glycosylation.
O
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2-Azido-3,6-di-O-benzyl-2-deoxy-4-O-trichloroacetyl-1-O-
catalytic amount of AgOTf after another 5 min. The mixture was
stirred 3 h at room temperature (the solution slowly becomes dark red
from the iodine formed), and then another catalytic amount of AgOTf
added. After a total of 4 h the reaction was quenched by pouring into a
mixture of saturated NaHCO3 (20 mL), sodium thiosulfate 10% aq (3
mL) and DCM (20 mL). The two phase mixture was shaken until the
iodine color disappeared, filtered to separate the powdered molecular
sieves and then extracted with DCM (2 × 10 mL). The combined
organic phase was dried (MgSO4), filtered and evaporated, and
purification by flash column chromatography (EtOAc/hexane, 1:1,
then a second column using DCM/EtOAc 4:1) yielded 50 (60 mg,
trichloroacetimidate-α̃β-D-glucopyranoside (45). To 40 (8.52 g,
16.0 mmol) was added dry DCM (100 mL), CCl3CN (8 mL, 80
mmol) and sodium hydride 60% (64 mg, 1.6 mmol). The solution was
stirred for 45 min, the solvent was evaporated and purified by flash
column chromatography using EtOAc/hexane (1:6 + 1% NEt3) as the
eluent. This yielded 45 (8.10 g, 12.0 mmol, 75%) as a white solid: MS
ES+ m/z 566 [M + Na]+; HRMS (FTMS-NSI+) m/z calcd for
C24H22N4O6Cl6Na [M + Na]+ 694.9563, found 694.9559. See the
1
Supporting Information for copy of H NMR spectrum.
2-Azido-6-O-benzoyl-3-O-benzyl-2-deoxy-4-O-trichloroace-
tyl-1-O-trichloroacetimidate-α̃β-D-glucopyranoside (46). The
20
0.07 mmol, 18%) as a white foam: Rf 0.27 (EtOAc/hexane 1:1); [α]D
1
intermediate 41 (5.4 g, 9.9 mmol) was dissolved in dry DCM (50
mL) under N2. Trichloroacetonitrile (5.0 mL, 50.0 mmol, 5.0 equiv)
and NaH (40 mg, 0.1 mmol, 0.1 equiv) were added, and the reaction
stirred for 1.5 h. Solvent was removed in vacuo, and the crude brown
solid slurried in hexane/EtOAc, 5/1 and filtered. This gave the β-
anomer of 46 (2.29 g). The remaining liquors were purified by silica
gel flash chromatography (hexane/EtOAc, 5:1 +1% Et3N) to give the
α-anomer (3.17 g), affording a total yield for 46 (5.46 g, 7.9 mmol,
= +68.0 (c = 0.57, CH2Cl2); H NMR (400 MHz, CDCl3) δ 7.37−
7.31 (m, 10H, Ph), 7.18 (d, J = 8.8 Hz, 2H, PMP), 6.84 (d, J = 8.8 Hz,
2H, PMP), 6.54 (d, J = 3.6 Hz, 1H, CONH2), 6.03 (d, J = 1.6 Hz, 1H,
H-1), 5.65 (d, J = 3.6 Hz, 1H, CONH2), 5.05−5.04 (m, 1H, H-2),
4.88−4.65 (m, 4H, CH2Ph), 4.79 (d, J = 3.6 Hz, 1H, H′-1), 4.73 (d, J
= 10.8 Hz, 1H, CH2PMP), 4.57 (d, J = 2.0 Hz, 1H, H-5), 4.49 (d, J =
10.8 Hz, 1H, CH2PMP), 4.28 (dd, J = 12.4 Hz, J = 2.0 Hz, 1H, H′-6a),
4.20 (dd, J = 12.4 Hz, J = 3.6 Hz, 1H, H′-6b), 4.14 (m, 1H, H-4), 4.01
(t, J = 2.4 Hz, 1H, H-3), 3.94 (dt, J = 10.0 Hz, J = 2.8 Hz 1H, H′-5),
3.85 (dd, J = 10.0 Hz, J = 8.8 Hz, 1H, H′-3), 3.79 (s, 3H, PhOCH3),
3.51 (dd, J = 10.0 Hz, J = 9.2 Hz, 1H, H′-4), 3.33 (dd, J = 10.4 Hz, J =
3.6 Hz, 1H, H′-2), 2.20 (s, 3H, COCH3), 2.13 (s, 3H, COCH3), 2.03
(s, 3H, COCH3); 13C NMR (100 MHz, CDCl3) δ 170.7, 170.5, 169.7,
168.6, 159.4, 137.6, 136.4, 129.7, 129.5, 128.6, 128.5, 128.3, 127.9,
127.9, 127.9, 113.8, 96.0, 90.2, 80.0, 77.2, 75.4, 74.5, 72.7, 71.3, 70.0,
69.6, 66.2, 63.4, 62.5, 55.2, 20.9, 20.8, 20.7; HRMS (TOF-ES+) m/z
calcd for C40H50N4O14N [M + NH4]+ 824.3354, found 824.3356.
3,4,6-Tri-O-acetyl-2-deoxy-2-iodo-α-D-mannopyranosyl-(1−
4)-1,2-di-O-acetyl-3-O-benzyl-β-L-idopyranuronamide (51). To
3,4,6-tri-O-acetyl-D-glucal 49 (370 mg, 1.25 mmol) and the iduronic
amide acceptor 3 (367 mg, 1.00 mmol) was added dry CH3CN (8
mL) and powdered molecular sieves 4 Å (500 mg). The solution was
kept under an inert N2 atmosphere, and iodine (480 mg, 1.89 mmol)
added as a solid. The mixture was stirred for 1 h, and the reaction was
quenched by pouring into a mixture of saturated aqueous NaHCO3
(50 mL) containing sodium thiosulfate and DCM (50 mL). The two-
phase mixture was filtered to separate the powdered molecular sieves
and then extracted with DCM (2 × 25 mL). The combined organic
phase was dried (MgSO4), filtered, evaporated, and purification by
flash column chromatography using EtOAc/hexane 2:1 as the eluent
yielded 51 (363 mg, 0.47 mmol, 48%) as a white foam: Rf 0.20
1
80%). For β-46: H NMR (400 MHz, CDCl3) δ 8.80 (s, 1H, NH),
8.07 (d, J = 8.4 Hz, 2H, ArH), 7.60 (t, J = 7.4 Hz, 1H, ArH), 7.48 (t, J
= 7.4 Hz, 2H, ArH), 7.40−7.33 (m, 5H, ArH), 5.77 (d, J = 8.4 Hz, 1H,
H1), 5.42 (dd, J = 9.6 Hz, 1H, H4), 4.91 (d, J = 10.6 Hz, 1H, CH2Ph),
4.81 (d, J = 10.6 Hz, 1H, CH2Ph), 4.66 (dd, J = 12.6, 2.3 Hz, 1H, H6′),
4.42 (dd, J = 12.6, 4.5 Hz, 1H, H6), 4.08 (ddd, J = 9.6, 4.5, 2.3 Hz, 1H,
H5), 3.89 (dd, J = 8.4, 9.6 Hz, 1H, H2), 3.78 (dd, J = 9.6 Hz, 1H, H3);
1
For α-46: H NMR (400 MHz, CDCl3) δ 8.83 (s, 1H, NH), 8.06−
8.02 (m, 2H, ArH), 7.62−7.58 (m, 1H, ArH), 7.49−7.45 (m, 2H,
ArH), 7.40−7.32 (m, 6H, ArH), 6.53 (d, J = 3.6 Hz, 1H, H1), 5.47 (dd,
J = 10.1, 9.4 Hz, 1H), 4.91−4.84 (m, 2H, CH2Ph), 4.66−4.62 (m,
1H), 4.43−4.36 (m, 2H), 4.19 (t, J = 9.7 Hz, 1H), 3.89 (dd, J = 10.0,
3.6 Hz, 1H, H2).
6-O-Acetyl-2-azido-3-O-benzyl-2-deoxy-4-p-methoxyben-
zyl-α̃
β-D-glucopyranose (47). The derivative 4243b (182 mg, 0.398
mmol) was dissolved in dry DCM (3 mL), and to this was added
trichloroacetonitrile (0.2 mL, 1.99 mmol) and DBU (0.05 mL, 0.04
mmol) while being kept under N2. The mixture was stirred 3 h, and
solvents were then evaporated, and the product immediately purified
by flash column chromatography (EtOAc/hexane 1:3 + 1% triethyl-
amine) to yield 47 (213 mg, 0.35 mmol, 89%) as a sticky oil. This
compound was used immediately for glycosylation.
2-Azido-6-O-benzoyl-3-O-benzyl-2-deoxy-4-O-p-methoxy-
benzyl-1-O-trichloroacetimidate-α̃β-D-glucopyranoside (48).
20
1
(EtOAc/hexane 2:1); [α]D = 40.3 (c = 0.76, CH2Cl2); H NMR
(400 MHz, CDCl3) δ 7.37−7.29 (m, 5H, Ph), 6.61 (d, J = 3.2 Hz, 1H,
CONH2), 6.03 (d, J = 1.6 Hz, 1H, H-1), 5.78 (d, J = 3.2 Hz, 1H,
CONH2), 5.34 (t, J = 10.0 Hz, 1H, H′-4), 5.19 (s, 1H, H′-1), 5.09−
5.08 (m, 1H, H-2), 4.69 (d, J = 11.6 Hz, 1H, CH2Ph), 4.65 (d, J = 11.6
Hz, 1H, CH2Ph), 4.58 (d, J = 2.0 Hz, 1H, H-5), 4.47 (t, J = 4.4 Hz,
1H, H′-3) 4.45−4.42 (m, 1H, H′-2). 4.20−4.19 (m, 1H, H-4), 4.19−
4.11 (m, 2H, H′-5), 3.95 (t, J = 2.8 Hz, 1H, H-3), 2.15 (s, 3H,
COCH3), 2.12 (s, 3H, COCH3), 2.10 (s, 3H, COCH3), 2.05 (s, 3H,
COCH3), 2.03 (s, 3H, COCH3); 13C NMR (100 MHz, CDCl3) δ
170.7, 169.8, 169.8, 169.4, 168.5, 136.2, 128.6, 128.4, 127.7, 98.3, 89.8,
74.9, 73.0, 70.8, 69.7, 68.9, 68.3, 66.6, 65.9, 61.8, 28.6, 20.8, 20.7, 20.7,
20.7, 20.6; HRMS (TOF-ES+) m/z calcd for C29H36INO15Na [M +
Na]+ 788.1022, found 788.1011.
The derivative 43 (3.26 g, 6.28 mmol) was dissolved in DCM (20
mL), and to this was added trichloroacetonitrile (3.78 mL, 37.68
mmol) and DBU (4 drops). The mixture was stirred at rt for 2 h,
solvents were then evaporated, and the product immediately purified
by column chromatography (3:1 hexane:ethyl acetate +1% triethyl-
amine) to yield 48 (3.27 g, 4.93 mmol, 79%) as a mixture of anomers:
1H NMR α-anomer (CDCl3, 400 MHz) δ 8.72 (s, 1H, NH), 7.98−
7.95 (m, 2H, ArH), 7.92−7.54 (m, 1H, ArH), 7.45−7.36 (m, 7H,
ArH), 7.21−7.19 (m, 2H, ArH), 6.80−6.78 (m, 2H, ArH), 6.42 (d, 1H,
H1, J = 3.6 Hz), 5.00−4.94 (dd, 2H, J = 10.4, 14.0 Hz), 4.82 (d, 1H, J
= 10.4 Hz), 4.57 (d, 1H, J = 10.4 Hz), 4.54−4.45 (m, 2H, C6, CH2),
4.18−4.14 (m, 1H, H5), 4.14−4.07 (m, 2H), 3.81−3.76 (dd, 1H, H3),
1
3.72 (s, 3H); H NMR β anomer (CDCl3, 400 MHz) δ 8.70 (s, 1H,
NH), 8.00−7.97 (m, 2H, ArH), 7.85−7.54 (m, 1H, ArH), 7.43−7.35
(m, 7H, ArH), 7.18−7.16 (m, 2H, ArH), 6.79−6.77 (m, 2H, ArH),
5.64 (d, 1H, H1, J = 8.4 Hz), 4.97−4.87 (dd, 2H, J = 10.8, 2.6 Hz),
4.79 (d, 1H, J = 10.8 Hz), 4.55 (d, 1H, J = 10.8 Hz), 4.56−4.44 (m,
2H, C6, CH2), 3.75−3.70 (m, 3H, H2, H3, H4), 3.72 (s, 3H), 3.62−
3.57 (m, 1H, H5).
6-O-Acetyl-2-azido-3-O-benzyl-2-deoxy-4-O-p-methoxyben-
zyl-α-D-glucopyranosyl-(1−4)-1,2-di-O-acetyl-3-O-benzyl-β-L-
idopyranuronamide (50). To the thioglycoside azido donor α-37
(262 mg, 0.49 mmol) and the iduronic amide acceptor 3 (149 mg,
0.41 mmol) was added dry DCM (3 mL). The solution was cooled to
0 °C, and activated powdered molecular sieves 4 Å (150 mg) added.
After 10 min, NIS (328 mg, 1.48 mmol) was added followed by a
6-O-Acetyl-2-azido-3-O-benzyl-2-deoxy-4-O-p-methoxyben-
zyl-α-D-glucopyranosyl-(1−4)-methyl 1,2-di-O-acetyl-3-O-ben-
zyl-β-L-idopyranuronate (52). Method A. To trichloroacetimidate
azido donor 47 (2.22 g, 3.69 mmol) and iduronic ester acceptor 5
(1.21 g, 3.17 mmol) was added dry toluene, and this was then
evaporated (twice). The residue was dried under high vacuum for 1 h,
and while being kept under argon, dry DCM (20 mL) was added. The
solution was cooled to −25 °C using a 65:35 mixture of iPrOH/H2O/
dry ice bath, and then TMSOTf (7 μL, 0.039 mmol) was added
dropwise. The mixture was kept at this temperature for 1 h and then
quenched with two drops of NEt3. The solvent was evaporated, and
the residue purified by flash column chromatography (first EtOAc/
hexane 1:2, followed by a second column using DCM/EtOAc 20:1,
P
dx.doi.org/10.1021/jo300722y | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
which separates CCl3CONH2), yielding 52 (1.74 g, 2.11 mmol, 67%)
as a white foam, along with recovery of acceptor 5 (0.28 g, 23%).
Method B. To thioglycoside azido donor α-37 (388 mg, 0.72
mmol) and iduronic ester acceptor 5 (211 mg, 0.55 mmol) was added
dry DCM (3 mL). The solution was cooled to 0 °C, and activated
powdered molecular sieves 4 Å (250 mg) were added. After 10 min,
NIS (373 mg, 1.66 mmol) was added, followed by a catalytic amount
of AgOTf after another 5 min. The mixture was stirred for 15 min (the
solution became dark red from the iodine formed) and quenched by
pouring into a mixture of saturated NaHCO3 (40 mL) containing
sodium thiosulfate and DCM (40 mL). The two phase mixture was
filtered to separate the powdered molecular sieves and then extracted
with DCM (2 × 20 mL). The combined organic phase was dried
(MgSO4), filtered, evaporated, and purification by flash column
chromatography (EtOAc/hexane 1:2) yielded 52 (269 mg, 0.33 mmol,
59%) as a white foam, along with recovery of acceptor 5 (78 mg,
PMP), 5.58 (s, 1H, H1), 5.23 (d, J = 2.9 Hz, 1H, H5), 5.13−5.11 (m,
1H, H2), 4.82 (d, J = 3.6 Hz, H1′), 4.81 (d, J = 11.7 Hz, 1H, CH2Ar),
4.80−4.74 (m, 2H, CH2Ar), 4.70 (d, J = 10.8 Hz, 1H, CH2Ar), 4.65 (d,
J = 11.7 Hz, 1H, CH2Ar), 4.46 (d, J = 10.8 Hz, 1H, CH2Ar), 4.26 (dd,
J = 12.2, 2.1 Hz, 1H, H6″), 4.13 (dd, J = 12.2, 3.7 Hz, 1H, H6′), 4.07 (t,
J = 2.9 Hz, 1H, H4), 3.94 (t, J = 2.9 Hz, 1H, H3), 3.85−3.77 (m, 2H,
H3′, H5′), 3.75 (s, 3H, PhOCH3), 3.74 (s, 3H, COOCH3), 3.47 (t, J =
9.2 Hz, 1H, H4′), 3.29 (dd, J = 10.3, 3.6 Hz, 1H, H2′), 2.07 (s, 3H,
COCH3), 1.97 (s, 3H, COCH3); 13C NMR (100 MHz; CDCl3) δ
170.6, 170.2, 169.3, 159.3, 137.5, 137.0, 135.2, 131.3, 129.8, 129.4,
129.1, 128.6, 128.1, 128.0, 127.9, 127.5, 113.8, 97.4, 86.2, 80.2, 75.5,
74.5, 73.2, 72.8, 71.7, 70.0, 68.8, 68.6, 63.5, 62.4, 55.3, 52.4, 21.0, 20.8;
HRMS (TOF-ES+) m/z calcd for C45H49N3O13SNa [M + Na+]
894.2883, found 894.2894; Elemental analysis calcd (%) for
C45H49N3O13S, C 61.99, H 5.66, N 4.82, found C 61.60, H 5.68, N
4.85.
Methyl (Phenyl 4-O-(2-azido-3,6-di-O-benzyl-2-deoxy-4-O-
p-methoxybenzyl-α-D-glucopyranosyl)-2-O-benzoyl-3-O-ben-
zyl-1-thio-L-idopyranoside)-uronate (α-55 and β-55). α-55: To
iduronic ester acceptor α-21 (5.90 g, 11.9 mmol) was added dry
toluene, and the solvent evaporated twice. The residue was dried
under the high vacuum for 2 h, and while being kept under nitrogen,
dry DCM (70 mL) was added. The solution was cooled to −30 °C
using a 65:35 mixture of iPrOH/H2O in a dry ice bath, and TMSOTf
(22 μL, 0.016 mmol) was added to the acceptor solution. To the
trichloroacetimidate azido donor 44 (9.35 g, 14.4 mmol) was added
dry toluene, and the solvent evaporated twice. The residue was
dissolved in dry DCM (10 mL) and added dropwise via a gastight
syringe over 1 h to the acceptor solution, while the reaction mixture
temperature was maintained at −30 °C. After another 15 min the
reaction was quenched with two drops of NEt3. The solvent was
evaporated, and flash column chromatography [EtOAc/hexane, 1:4
and then a second column using DCM/EtOAc, 20:1 (to remove
CCl3CONH2)] yielded α-55 (9.21 g, 9.4 mmol, 78%) as a white foam,
along with recovered acceptor 21 (1.10 g, 19%): Rf 0.34 (EtOAc/
hexane 1:3); [α]D20 = −52.0 (c = 0.57, CH2Cl2); 1H NMR (400 MHz;
CDCl3) δ 8.16−8.14 (m, 2H, Ph), 7.63−7.52 (m, 4H, Ph), 7.46−7.42
(m, 2H, Ph), 7.41−7.22 (m, 15H, Ph), 7.17−7.13 (m, 2H, Ph), 7.13−
7.07 (m, 2H, Ph), 6.91−6.85 (m, 2H, Ph), 5.82 (s, 1H, H1), 5.49−5.47
(brs, 1H, H2), 5.42 (d, J = 2.0 Hz, 1H, H5), 5.04 (d, J = 11.7 Hz, 1H,
CH2Ar), 4.82 (d, J = 11.7 Hz, 1H, CH2Ar), 4.81 (d, J = 2.8 Hz, 1H,
H1′), 4.66 (d, J = 12.0 Hz, 1H, CH2Ar), 4.60 (d, J = 10.4 Hz, 1H,
CH2Ar), 4.52 (d, J = 12.0 Hz, 1H, CH2Ar), 4.44 (d, J = 10.4 Hz, 1H,
CH2Ar), 4.27 (td, J = 2.9, 1.0 Hz, 1H, H3), 4.15−4.12 (m, 2H, H4,
CH2Ar), 3.96−3.88 (m, 2H, H5′, CH2Ar), 3.88−3.86 (m, 1H, H6′),
3.86 (s, 3H, PhOCH3), 3.80 (s, 3H, COOCH3), 3.76−3.67 (m, 2H,
H6″, H4′), 3.51 (t, J = 9.6 Hz, 1H, H3′), 3.30 (dd, J = 10.3, 3.5 Hz, 1H,
H2′); 13C NMR (100 MHz; CDCl3) δ 169.2, 165.5, 159.2, 137.9,
137.8, 137.1, 135.5, 133.3, 131.5, 130.6, 130.1, 129.5, 129.4, 129.1,
128.9, 128.5, 128.4, 128.3, 128.1, 128.1, 127.8, 127.7, 127.6, 127.6,
113.6, 100.6, 87.0, 80.2, 74.5, 74.4, 73.6, 72.8, 72.5, 71.8, 69.2, 68.4,
67.8, 63.8, 55.4, 52.4; MS-MALDI m/z = 999 [M + NH4]+; HRMS
(FTMS-NSI+) m/z calcd for C55H55O12N3SNH4 [M + NH4]+
999.3845, found 999.3854; [isotope pattern in the Supporting
Information].
20
37%): Rf 0.15 (EtOAc/hexane 1:2); [α]D = +37.1 (c = 0.56,
1
CH2Cl2); H NMR (400 MHz, CDCl3) δ 7.38−7.32 (m, 10H, Ph),
7.16 (d, J = 8.8 Hz, 2H, PMP), 6.84 (d, J = 8.8 Hz, 2H, PMP), 6.06 (d,
J = 2.0 Hz, 1H, H-1), 5.06−5.05 (m, 1H, H-2), 4.84−4.75 (m, 4H,
CH2Ph), 4.75 (d, J = 3.6 Hz, 1H, H′-1), 4.69 (d, J = 10.8 Hz, 1H,
CH2PMP), 4.68 (d, J = 2.0 Hz, 1H, H-5), 4.49 (d, J = 10.8 Hz, 1H,
CH2PMP), 4.28 (dd, J = 12.4 Hz, J = 2.0 Hz, 1H, H′-6a), 4.16 (dd, J =
12.4 Hz, J = 3.6 Hz, 1H, H′-6b), 4.08 (t, J = 3.2 Hz, 1H, H-3), 3.99 (t,
J = 2.4 Hz, 1H, H-4), 3.86−3.80 (m, 2H, H′-3, H′-5), 3.80 (s, 3H,
PhOCH3), 3.77 (s, 3H, COOCH3), 3.50 (dd, J = 10.4 Hz, J = 9.2 Hz,
1H, H′-4), 3.36 (dd, J = 10.4 Hz, J = 3.2 Hz, 1H, H′-2), 2.16 (s, 3H,
COCH3), 2.12 (s, 3H, COCH3), 2.02 (s, 3H, COCH3); 13C NMR
(100 MHz, CDCl3) δ 170.5, 170.5, 168.7, 167.9, 159.3, 137.4, 136.6,
129.6, 129.3, 128.6, 128.5, 128.3, 128.0, 127.9, 113.8, 97.6, 90.2, 83.2,
80.2, 75.4, 74.4, 73.0, 73.0, 72.5, 70.0, 66.3, 63.5, 62.2, 55.2, 52.5, 20.8,
20.7, 20.7; HRMS (TOF-ES+) m/z calcd for C41H47N3O15Na [M +
Na+] 844.2905, found 844.2898; Elemental analysis calcd (%) for
C41H47N3O15, C 59.92, H 5.76, N 5.11, found C 60.13, H 5.73, N 5.08.
2-Azido-3,6-di-O-benzyl-2-deoxy-4-O-p-methoxybenzyl-α-
D-glucopyranosyl-(1−4)-methyl-1,2-di-O-acetyl-3-O-benzyl-β-
L-idopyranuronate (53). To thioglycoside azido donor β-34 (3.70 g,
6.20 mmol) and iduronic ester acceptor 5 (1.97 g, 5.16 mmol) was
added dry DCM (30 mL). The solution was cooled to 0 °C, and
activated powdered molecular sieves 4 Å (1.5 g) were added. After 10
min, NIS (2.32 g, 10.3 mmol) was added followed by a catalytic
amount of AgOTf (13 mg, 0.062 mmol) after another 5 min. The
mixture was stirred for 30 min (the solution becomes dark red from
the iodine formed), and more AgOTf (13 mg, 0.062 mmol) added.
After stirring for 2 h at 0 °C the reaction was quenched by pouring
into a mixture of saturated NaHCO3 (40 mL) containing sodium
thiosulfate and DCM (40 mL). The two phase mixture was filtered,
extracted with DCM (2 × 20 mL), and the combined organic phases
dried (MgSO4), filtered and evaporated. The residue was purified by
flash column chromatography (EtOAc/hexane, 1:2) yielding 53 (2.38
g, 2.74 mmol, 53%, α/β 6:1) as a white foam, along with recovery of
20
acceptor 5 (0.77 g (39%): Rf 0.23 (EtOAc/hexane 1:2); [α]D
=
+19.7 (c = 1.06, CH2Cl2); See the Supporting Information for copies
of 1H and 13C NMR spectra; HRMS (TOF-ES+) m/z calcd for
+
C46H55O14N4 [M + NH4 ] 887.3715, found 887.3726.
β-55: To iduronic ester acceptor β-21 (6.90 g, 13.9 mmol) was
twice added dry toluene, and the solvent evaporated. The residue was
dried under high vacuum for 2 h, and while being kept under nitrogen,
dry DCM (100 mL) was added. The solution was cooled to −30 °C
using a 65:35 mixture of iPrOH/H2O and a dry ice bath, and TMSOTf
(25 μL, 0.016 mmol) was then added. To the trichloroacetimidate
azido donor 44 (10.50 g, 16.2 mmol) was added twice dry toluene, and
the solvent evaporated. The residue was dissolved in dry DCM (20
mL) and added dropwise via a gastight syringe over 90 min to the
acceptor solution, while the reaction mixture was maintained at −30
°C. After another 15 min the reaction was quenched with two drops of
NEt3, solvents were removed in vacuo, and flash column
chromatography (EtOAc/hexane, 1:4 as the eluent and then a second
column using DCM/EtOAc, 20:1) yielded β-55 (10.50 g, 10.7 mmol,
77%) as a white foam, along with recovered acceptor 21 (0.99 g, 14%):
Methyl (Phenyl 4-O-(6-O-Acetyl-2-azido-3-O-benzyl-2-
deoxy-4-O-p-methoxybenzyl-α-D-glucopyranosyl)-2-O-acetyl-
3-O-benzyl-1-thio-α-L-idopyranoside)-uronate (54). To the
trichloroacetimidate azido donor 47 (1.03 g, 1.71 mmol) and the
iduronic ester acceptor α-20 (363 mg, 0.84 mmol) was added dry
toluene and evaporated twice. The residue was dried under high
vacuum for 1 h, and while being kept under nitrogen, dry DCM (5
mL) was added. The solution was cooled to 0 °C using an ice-bath,
TMSOTf (3 μL, 0.016 mmol) was added, and the mixture was kept at
this temperature for 30 min and then quenched with two drops of
NEt3. The solvent was evaporated, and flash column chromatography
(EtOAc/hexane 1:3) yielded 54 (519 mg, 0.60 mmol, 71%) as a white
foam: Rf 0.16 (EtOAc/hexane 1:3); [α]D20 = −5.3 (c = 0.70, CH2Cl2);
1H NMR (400 MHz; CDCl3) δ 7.49−7.43 (m, 2H, Ph), 7.37−7.23
(m, 13H, Ph), 7.15−7.09 (m, 2H, 2H, PMP), 6.83−6.77 (m, 2H,
Q
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The Journal of Organic Chemistry
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20
1
Rf 0.31 (EtOAc/hexane 1:3); [α]D = +28.9 (c = 0.60, CH2Cl2); H
NMR (400 MHz; CDCl3) δ 8.26−8.24 (m, 2H. Ph), 7.63−7.58 (m,
2H, Ph), 7.44−7.28 (m, 19H, Ph), 7.14−7.06 (m, 4H, Ph), 6.92−6.84
(m, 2H, Ph), 5.34 (d, J = 1.9 Hz, 1H, H1), 5.31 (t, J = 1.7 Hz, 1H, H2),
4.92 (d, J = 11.6 Hz, 1H, CH2Ar), 4.82 (d, J = 11.6 Hz, 1H, CH2Ar),
4.72 (d, J = 3.5 Hz, 1H, H1′), 4.66 (d, J = 12.0 Hz, 1H, CH2Ar), 4.61−
4.59 (m, 2H, CH2Ar, H5),4.51 (d, J = 12.0 Hz, 1H, CH2Ar), 4.43 (d, J
= 10.5 Hz, 1H, CH2Ar), 4.36 (t, J = 2.6 Hz, 1H, H3), 4.06 (s, 1H, H4),
4.04 (d, J = 10.7 Hz, 1H, CH2Ar), 3.97−3.93 (m, 2H, H5′, H6′), 3.88−
3.82 (m, 4H, H6″, PhOCH3), 3.79 (s, 3H, COOCH3), 3.75 (d, J = 10.7
Hz, 1H, CH2Ar), 3.67 (t, J = 9.5 Hz, 1H, H4′), 3.46 (t, J = 9.5 Hz, 1H,
H3′), 3.27 (dd, J = 9.5, 3.5 Hz, 1H, H2); 13C NMR (100 MHz; CDCl3)
δ 168.5, 166.1, 159.2, 137.9, 137.9, 137.0, 134.9, 133.3, 131.2, 130.6,
130.2, 129.5, 129.4, 129.0, 128.9, 128.6, 128.2, 128.3, 128.3, 128.2,
128.1, 127.7, 127.6, 127.5, 113.6, 100.1, 85.9, 80.2, 75.7, 75.6, 74.5,
74.4, 73.6, 73.2, 73.0, 71.7, 70.0, 63.8, 55.4, 52.4; HRMS (FTMS-
NSI+) m/z calcd for C55H55O12N3SNH4 [M + NH4]+ 999.3850, found
999.3848; Elemental analysis calcd (%) for C55H55N3O12S, C 67.26, H
5.64, N 4.28, found C 67.38, H 5.77, N 4.14.
168.6, 166.2, 160.2, 137.3, 136.8, 136.8, 134.7, 133.5, 131.2, 130.1,
129.9, 129.1, 128.8, 128.6, 128.5, 128.4, 128.42, 128.33, 128.18, 127.8,
127.7, 99.5, 89.8, 86.0, 77.9, 76.2, 75.8, 74.9, 74.8, 73.8, 73.0, 72.2,
70.2, 69.2, 67.3, 63.6, 52.4.
Method B. The disaccharide β-60 (640 mg, 0.74 mmol) was
dissolved in dry DCM (10 mL), cooled to 0 °C in an icebath, and then
dry pyridine (0.18 mL, 2.22 mmol) and trichloroacetyl chloride (0.13
mL, 1.11 mmol) was added. The solution was stirred for 90 min. The
solution was then extracted with DCM (50 mL) and water (50 mL),
dried (MgSO4), filtered and evaporated. The crude was purified using
flash column chromatography (EtOAc/hexane 1:4). This yielded the
product β-56 (718 mg, 0.71 mmol, 96%) as a white foam.
Methyl [Phenyl 4-O-(2-azido-3-O-benzyl-6-O-benzoyl-4-O-p-
methoxybenzyl-α-D-glucopyranosyl)-2-O-benzoyl-3-O-benzyl-
1-thio-α-L-ido-pyranoside] uronate (α̃57). Acceptor α-21 (1.88 g,
3.8 mmol) was dissolved in DCM (20 mL) in anhydrous conditions
under N2, this solution was cooled to −20 °C, and TMSOTf (∼6 μL)
was added. A dropwise addition of the donor trichloroacetimidate 48
(3.27 g, 4.9 mmol predissolved in DCM (10 mL)) was then added to a
reaction mixture over 30 min. The solution was stirred for 30 min at
which point only starting materials were observed (TLC), and pH ∼ 7.
A further portion of TMSOTf (20 μL) was added, and the mixture
stirred for a further 40 min when the reaction was deemed complete
(TLC). The reaction was quenched with triethylamine (1 mL),
solvents were removed in vacuo, and purification by flash
chromatography (hexane:EtOAc, 5:1 → 3:1 gradient, followed by
Methyl [Phenyl 4-O-(2-azido-3,6-O-dibenzyl-2-deoxy-4-O-
trichloroacetyl-α-D-glucopyranosyl)-2-O-benzoyl-3-O-benzyl-
1-thio-L-ido-pyranoside] uronate (α-56 and β-56). Method A. To
a 1:2 α/β mixture of ido acceptor 21 (4.92 g, 9.94 mmol) was added
dry toluene, and the mixture was evaporated twice. The residue was
dried on the high vacuum for 2 h, and while being kept under nitrogen,
dry DCM (70 mL) was added. The solution was cooled to −30 °C
i
using a 65:35 mixture of PrOH/H2O and dry ice bath. To the
40:1 → 30:1 DCM:EtOAc, to remove the trichloroacetamide) yielded
20
trichloroacetimidate azido donor 45 (8.05 g, 11.9 mmol) was added
dry toluene, and the mixture was evaporated twice. Then TMSOTf
(72 μL, 0.39 mmol) was added to the acceptor solution, the donor was
dissolved in dry DCM (10 mL) and added dropwise via a gastight
syringe over 1 h while the reaction mixture was maintained at −30 °C.
After another 15 min the reaction was quenched with two drops of
NEt3. The solvent was evaporated, and product purified by flash
column chromatography (EtOAc/hexane 1:4 as the eluent and then a
second column using DCM) yielding α/β-56 (4.11 g, 4.08 mmol,
41%) as a white foam. Also 2.04 g (41%) of acceptor 21 was
recovered. For analysis, the α/β anomers could be separated by flash
column chromatography (EtOAc/hexane, 1:5).
α
̃
57 as a white foam (2.43 g, 2.44 mmol, 64%): [α]D = +57° (c =
1
0.30, CHCl3); H NMR (400 MHz, CDCl3) δ 8.23−8.20 (m, 2H,
ArH), 7.96−7.94 (m, 2H, ArH), 7.59−7.52 (m, 4H, ArH), 7.42−7.28
(m, 17H, ArH), 7.16−7.10 (m, 4H, ArH), 6.81−6.78 (m, 2H, ArH),
5.29 (d, 1H, IdoA H5, J = 2.0 Hz), 5.25 (br s, 1H, IdoA H1), 4.87 (d,
1H, IdoA Benzyl CHa, J = 11.2 Hz), 4.76 (d, 1H, IdoA Benzyl CHb, J =
11.6 Hz), 4.68 (d, 1H, GlcN H1, J = 3.6 Hz), 4.67−4.63 (m, 1H, GlcN
H6a), 4.64 (d, 1H, PMB CHa, J = 10.4 Hz), 4.55 (d, 1H, IdoA H4, J =
1.2 Hz), 4.52−4.48 (dd, 1H, GlcN H6b, J = 2.4 Hz, 12.0 Hz), 4.47 (d,
1H, PMB CHb, J = 10.8 Hz), 4.32 (dd, 1H, IdoA H2, J = 2.4 Hz),
4.14−4.11 (m, 1H, GlcN H5), 4.05 (br s, 1H, IdoA H3), 3.97 (d, 1H,
GlcN Benzyl CHa, J = 10.4 Hz), 3.79 (s, 3H, IdoA methyl ester CH3),
3.75 (d, 1H, GlcN Benzyl CHb, J = 10.8 Hz), 3.73 (s, 3H, PMB OMe),
3.57 (dd, 1H, GlcN H4, J = 8.8 Hz), 3.48 (dd, 1H, GlcN H3, J = 10.0
Hz), 3.20 (dd, 1H, GlcN H2, J = 3.6 Hz, 10.0 Hz); 13C NMR (100
MHz, CDCl3) δ 168.6, 166.1, 159.3, 137.6, 137.0, 133.3, 133.1, 131.3,
130.2, 129.76, 129.71, 129.62, 129.07, 128.94, 128.60, 128.46, 128.43,
128.40, 128.32, 128.19, 128.12, 127.99, 127.95, 127.7, 113.8, 99.6,
86.0, 80.3, 77.3, 76.9, 75.5, 74.7, 74.5, 73.0, 70.1, 63.8, 62.6, 55.2, 52.5;
Low res MS (ES+) 1018.6 [M + Na]; HRMS (TOF-ES+) m/z calcd.
for C55H52O13N3SNa [M + Na]+ 1018.3197, found 1018.3182.
Methyl [Phenyl 4-O-(2-azido-3-O-benzyl-6-O-benzoyl-4-O-
trichloroacetyl-α-D-glucopyranosyl)-2-O-benzoyl-3-O-benzyl-
1-thio-α-L-ido-pyranoside] uronate (α-58). Iduronate acceptor α-
21 (3.3 g, 6.6 mmol) was dissolved in dry DCM (40 mL) under N2.
The reaction solution was cooled to −30 °C, and TMSOTf (72 μL,
0.39 mmol, 0.06 equiv) added. The solution color changed to pale
yellow (pH = 3). To this solution was added dropwise 46 (5.46 g, 7.9
mmol, 1.2 equiv) dissolved in dry DCM (50 mL). Stirring was
continued for 2 h at −30 °C, and the reaction then allowed to warm to
room temperature, Et3N (100 μL) was added, and the solvents
removed in vacuo to give a brown gum. This material was purified by
flash chromatography (hexane/EtOAc, 5:1 → 2:1) to give α-58 (4.03
g, 3.95 mmol, 60%) as a pale yellow foam along with recovery of
unreacted α-21 (1.21 g): [α]D (c = 0.11, DCM) +0.20; 1H NMR (400
MHz, CDCl3) δ 8.01−7.98 (m, 2H, Ar−H), 7.82−7.79 (m, 2H, Ar−
H), 7.36−7.01 (m, 19H, Ar−H), 6.81−6.77 (m, 2H, Ar−H), 5.64 (d, J
= 2.5, 1H, H1′), 5.22 (d, J = 1.9, 1H, H5′), 5.20−5.19 (m, 1H, H2′),
5.02 (t, J = 9.7, 1H, H4), 4.82 (d, J = 11.8, 1H), 4.58 (d, J = 12.0, 1H),
4.62 (d, J = 12.8, 1.0, 1H, H6A), 4.45 (d, J = 3.7, 1H, H1), 4.08−4.06
(m, 1H, H3′), 4.04−3.97 (m, 2H, H5+H6B), 3.80 (s, 1H, H4′), 3.67−
3.63 (m, 4H), 3.40 (d, J = 10.1, 1H), 3.31 (t, J = 9.6, 1H, H2), 3.15
(dd, J = 10.0, 3.6, 1H); 13C NMR (100 MHz, CDCl3) δ 169.4, 165.9,
20
α-56: Rf 0.13 (EtOAc/hexane 1:4); [α]D = −28.6 (c = 0.47,
CH2Cl2); 1H NMR (400 MHz; CDCl3) δ 8.23 (d, J = 8.2 Hz, 2H, Ph),
7.59−7.52 (m, 4H, Ph), 7.50−7.42 (m, 5H, Ph), 7.39−7.28 (m, 12H,
Ph), 7.06 (d, J = 7.9 Hz, 2H, Ph), 5.89 (s, 1H, H1), 5.47 (d, J = 2.0 Hz,
1H, H5), 5.46−5.42 (m, 1H, H2), 5.30 (dd, J = 10.2, 9.4 Hz, 1H, H4′),
5.06 (d, J = 11.7 Hz, 1H, CH2Ar), 4.83 (d, J = 11.7 Hz, 1H, CH2Ar),
4.69 (d, J = 3.7 Hz, 1H, H1′), 4.54 (d, J = 11.9 Hz, 1H, CH2Ar), 4.47
(d, J = 11.9 Hz, 1H, CH2Ar), 4.31 (td, J = 2.7, 1.0 Hz, 1H, H3), 4.05−
4.02 (m, 2H, H5′, H4), 3.99 (d, J = 10.2 Hz, 1H, CH2Ar), 3.78 (s, 3H,
COOCH3), 3.72 (d, J = 10.2 Hz, 1H, CH2Ar), 3.65 (dd, J = 11.0, 2.6
Hz, 1H, H6′), 3.58−3.50 (m, 2H, H3′, H6″), 3.40 (dd, J = 10.1, 3.6 Hz,
1H, H2′); 13C NMR (100 MHz; CDCl3) δ 169.4, 165.5, 160.2, 137.3,
137.0, 136.8, 135.4, 133.5, 131.2, 130.0, 129.8, 129.2, 128.8, 128.5,
128.4, 128.3, 128.3, 128.3, 128.1, 127.9, 127.8, 127.6, 100.2, 89.7, 87.0,
77.9, 77.6, 77.4, 74.9, 74.7, 73.8, 72.8, 71.4, 69.5, 69.2, 68.3, 67.1, 63.5,
52.5; MS-MALDI m/z = 1025 [M + NH4]+; HRMS (FTMS-NSI+) m/
z calcd for C49H50O12N4SCl3 [M + NH4]+ 1023.2207, found
1023.2216; [isotope pattern in the Supporting Information];
Elemental analysis calcd (%) for C49H46Cl3N3O12S, C 58.42, H 4.60,
N 4.17, found C 58.22, H 4.92, N 4.07.
20
β-56: Rf 0.07 (EtOAc/hexane 1:4); [α]D = +56.1 (c = 0.59,
CH2Cl2); H NMR (400 MHz; CDCl3) δ 8.24−8.18 (m, 2H, Ph),
1
7.50−7.14 (m, 21H, Ph), 7.00−6.89 (m, 2H, Ph), 5.23 (d, J = 1.8 Hz,
1H, H1), 5.19−5.13 (m, 2H, H2, H4′), 4.81 (d, J = 11.7 Hz, 1H,
CH2Ar), 4.70 (d, J = 11.7 Hz, 1H, CH2Ar), 4.52 (d, J = 1.7 Hz, 1H,
H5), 4.48 (d, J = 3.6 Hz, 1H, H1′), 4.43 (d, J = 11.9 Hz, 1H, CH2Ar),
4.35 (d, J = 11.9 Hz, 1H, CH2Ar), 4.26 (t, J = 2.5 Hz, 1H, H3), 3.90 (d,
J = 10.4 Hz, 1H, CH2Ar), 3.89−3.83 (m, 2H, H4, H5′), 3.66 (s, 3H,
COOCH3), 3.56 (d, J = 10.4 Hz, 1H, CH2Ar), 3.54−3.50 (m, 1H,
H6′), 3.46 (d, J = 9.6 Hz, 1H, H3′), 3.40 (dd, J = 11.0, 2.6 Hz, 1H, H6″),
3.28 (dd, J = 10.1, 3.6 Hz, 1H, H2); 13C NMR (100 MHz; CDCl3) δ
R
dx.doi.org/10.1021/jo300722y | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
165.5, 160.5, 137.0, 136.5, 135.3, 133.6, 133.3, 131.4, 130.0, 129.8,
129.5, 129.2, 128.9, 128.6, 128.5, 128.5, 128.3, 128.3, 128.1, 127.9,
127.8, 100.5, 89.5, 87.2, 78.4, 77.9, 74.8, 74.5, 72.8, 71.4, 69.5, 68.4,
68.2, 63.7, 61.2, 52.7; MS m/z 1044.10 (M + Na)+; HRMS (TOF-
ES+) m/z calcd for C49H48Cl3N4O13S [M + NH4] + 1037.1999, found
1037.2000.
mg, 39%): Rf 0.28 (EtOAc/hexane 1:1); 1H NMR (400 MHz, CDCl3)
δ 7.38−7.32 (m, 10H, Ph), 7.17 (d, J = 8.8 Hz, 2H, PMP), 6.85 (d, J =
8.8 Hz, 2H, PMP), 5.34−5.32 (m, 1H, H-2a), 5.15−5.13 (m, 1H, H-
2b), 4.90−4.49 (m, 9H, CH2Ph, CH2PMP, H′-1, H-1, H-5), 4.32−3.81
(m, 6H, H-3, H-4, H′-3, H′-5, H′-6a, H′-6b), 3.80 (s, 3H, PhOCH3),
3.78 (s, 3H, COOCH3), 3.54−3.48 (m, 1H, H′-4), 3.36−3.30 (m, 1H,
H′-2), 2.17 (s, 3H, COCH3), 2.11 (s, 3H, COCH3), 2.02 (s, 3H,
COCH3); HRMS (TOF-ES+) m/z calcd for for C39H45N3O14Na [M +
Na]+ 802.2799, found 802.2783; Elemental analysis calcd (%) for
C39H45N3O14, C 60.07, H 5.82, N 5.39, found C 60.24, H 5.83, N 5.29.
6-O-Acetyl-2-azido-3-O-benzyl-2-deoxy-4-O-p-methoxyben-
zyl-α-D-glucopyranosyl-(1−4)-methyl-2-O-acetyl-3-O-benzyl-1-
Methyl (Phenyl 4-O-(6-O-acetyl-2-azido-3-O-benzyl-2-
deoxy-4-O-p-methoxybenzyl-α-D-glucopyranosyl)-2-O-benzo-
̃
yl-3-O-benzyl-1-thio-β-L-idopyranoside)-uronate (β59). To idur-
onic ester acceptor. α/β-21 (2.85 g, 5.76 mmol) and trichloroaceti-
midate donor 47 (4.7 g, 7.77 mmol) was added dry toluene, and this
solvent evaporated twice. The residue was dried on under high vacuum
for 2 h, and while being kept under nitrogen, dry DCM (65 mL) was
added. The solution was cooled to −30 °C using a 65:35 mixture of
iPrOH/H2O in dry ice, TMSOTf (15 μL, 0.08 mmol) was added, and
after 30 min the reaction was quenched with two drops of NEt3. The
solvent was evaporated and flash column chromatography (EtOAc/
O-trichloroacetimidate-α̃β-L-idopyranuronate (62). To the in-
termediate 1-OH disaccharide 61 (781 mg, 1.00 mmol) was added dry
DCM (10 mL), CCl3CN (0.7 mL, 7.0 mmol) and DBU (0.01 mL,
0.07 mmol). The solution was stirred for 90 min, and the mixture was
evaporated and purified by flash column chromatography (EtOAc/
hexane 1:2 containing 1% NEt3 as the eluent) yielding (796 mg, 0.86
mmol, 86%) of disaccharide donor 62 as an oil, which was used
directly for the synthesis of tetrasaccharide 64.
̃
hexane 2:9) yielded β59 (4.0 g, 4.28 mmol, 75%) as a white foam: Rf
0.14 (EtOAc/hexane 1:3); 1H NMR (400 MHz; CDCl3) δ 8.12 (d, J =
8.0 Hz, 2H, Ph), 7.48 (d, J = 7.7 Hz, 2H, Ph), 7.31−7.15 (m, 14H,
Ph), 7.08 (d, J = 8.3 Hz, 2H, Ph), 7.01 (d, J = 7.3 Hz, 2H, Ph), 6.79 (d,
J = 8.2 Hz, 2H, Ph), 5.20 (s, 1H, H1), 5.16 (s, 1H, H2), 4.78 (d, J =
11.6 Hz, 1H, CH2Ar), 4.68 (d, J = 11.6 Hz, 1H, CH2Ar), 4.56 (d, J =
3.3 Hz, 1H, H1′), 4.51 (d, J = 10.5 Hz, 1H, CH2Ar), 4.45 (s, 1H, H5),
4.34−4.19 (m, 4H, CH2Ar, H3, H6′, H6″), 3.93−3.86 (m, 3H, CH2Ar,
H4, H3′), 3.71 (s, 3H, COOCH3), 3.70 (s, 3H, PhOCH3), 3.66 (d, J =
10.6 Hz, 1H, CH2Ar), 3.34 (t, J = 8.1 Hz, 2H, H3′, H4″), 3.08 (dd, J =
9.5, 3.0 Hz, 1H, H2), 1.91 (s, 3H, C(O)CH3); 13C NMR (100 MHz;
CDCl3) δ 171.0, 168.9, 166.5, 159.8, 138.2, 137.4, 135.1, 131.7, 130.6,
130.4, 130.1, 130.0, 129.4, 129.3, 129.0, 128.7, 128.7, 128.6, 128.2,
128.1, 128.0, 114.2, 100.1, 86.4, 80.6, 76.0, 75.9, 74.9, 74.9, 73.2, 73.3,
70.5, 70.4, 64.2, 62.7, 55.7, 52.9, 21.3; HRMS (TOF-ES+) m/z calcd
for C50H51N3O13SNa [M + Na+] 956.3035, found 956.3025.
6-O-Acetyl-2-azido-3-O-benzyl-2-deoxy-α-D-glucopyrano-
syl-(1−4)-methyl-1,2-di-O-acetyl-3-O-benzyl-β-L-idopyranuro-
nate (63). To disaccharide 52 (370 mg, 0.45 mmol) was added DCM
and H2O (5 mL/0.1 mL) followed by DDQ (150 mg, 0.68 mmol).
The solution was stirred for 1 h, and another portion of DDQ (20 mg)
was added. After a total of 90 min the mixture was evaporated and
purified by flash column chromatography (EtOAc/hexane 2:3)
yielding 63 (268 mg, 0.38 mmol, 85%) as a white foam: Rf 0.14
20
1
(EtOAc/hexane 2:3); [α]D = +32.1 (c = 0.68, CH2Cl2); H NMR
(400 MHz, CDCl3) δ 7.38−7.32 (m, 10H, Ph), 6.06 (d, J = 2.0 Hz,
1H, H-1), 5.07−5.06 (m, 1H, H-2), 4.87−4.75 (m, 6H, CH2Ph, H′-1,
H-5), 4.56 (dd, J = 12.8 Hz, J = 3.2 Hz, 1H, H′-6a), 4.13 (dd, J = 12.8
Hz, J = 2.0 Hz, 1H, H′-6b), 4.07 (t, J = 3.2 Hz, 1H, H-3), 4.00 (t, J =
2.4 Hz, 1H, H-4), 3.78 (s, 3H, COOCH3), 3.75−3.68 (m, 2H, H′-3,
H′-5), 3.42 (dt, J = 10.0 Hz, J = 3.6 Hz, 1H, H′-4), 3.30 (dd, J = 10.0
Hz, J = 3.6 Hz, 1H, H′-2), 2.96 (d, J = 3.6 Hz, 1H, OH), 2.17 (s, 3H,
COCH3), 2.12 (s, 3H, COCH3), 2.10 (s, 3H, COCH3); 13C NMR
(100 MHz, CDCl3) δ 172.0, 170.5, 168.7, 168.0, 137.6, 136.6, 128.6,
128.3, 128.1, 128.1, 127.9, 97.8, 90.2, 79.1, 75.2, 74.4, 73.1, 72.9, 72.5,
71.0, 70.3, 66.1, 62.9, 62.5, 52.4, 20.8, 20.8, 20.8; HRMS (TOF-ES+)
m/z calcd for C33H39N3O14Na [M + Na+] 724.2330, found 724.2321;
Elemental analysis calcd (%) for C33H39N3O14, C 56.49, H 5.60, N
5.99, found C 56.64, H 5.61, N 5.86.
Methyl [Phenyl 4-O-(2-azido-3,6-O-dibenzyl-α-D-glucopyra-
̃
nosyl)-2-O-benzoyl-3-O-benzyl-1-thio-βL-ido-pyranoside] uro-
nate (β-60). To β-55 (370 mg, 0.377 mmol) was added CH3CN (8
mL) and water (0.8 mL) followed by ammonium cerium(IV) nitrate
(>99.99%) (439 mg, 0.801 mmol). The orange solution was stirred for
90 min, more CAN was added (80 mg, 0.146 mmol), and the mixture
stirred for another 1 h. The solution was then extracted with DCM (2
× 100 mL) and water (100 mL), dried (MgSO4), filtered and
evaporated. The crude product was purified using flash column
chromatography (EtOAc/hexane, 1:3) to yield the product β-60 (325
6-O-Acetyl-2-azido-3-O-benzyl-2-deoxy-4-O-p-methoxyben-
zyl-α-D-glucopyranosyl-(1−4)-methyl-2-O-acetyl-3-O-benzyl-
α-L-idopyranosyluronate-(1−4)-6-O-acetyl-2-azido-3-O-ben-
zyl-2-deoxy-4-O-p-methoxybenzyl-α-D-glucopyranosyl-(1−4)-
methyl-2-O-acetyl-3-O-benzyl-β-L-idopyranosyluronate (64).
To donor 62 (458 mg, 0.49 mmol) and disaccharide acceptor 63
(268 mg, 0.38 mmol) was added dry toluene, which was evaporated
(two cycles). Then, while the flask was kept under N2, dry DCM (5
mL) was added, and the mixture cooled to −30 °C using a 70:30
mixture of iPrOH/H2O and dry ice. TMSOTf (5 μL, 0.027 mmol) was
added dropwise, and the mixture was kept at this temperature for 2 h
and then quenched with two drops of NEt3. The solvent was
evaporated, and flash column chromatography (EtOAc/hexane 2:3)
yielded 64 (340 mg, 0.23 mmol, 61%) as a white foam, along with
recovery of acceptor 63 (64 mg, 24%): Rf 0.17 (EtOAc/hexane 2:3);
20
mg, 92%) as a white foam: Rf 0.18 (EtOAc/hexane 1:3); [α]D
=
1
+41.8 (c = 0.46, CH2Cl2); H NMR (400 MHz; CDCl3) δ 8.32−8.26
(m, 2H, Ph), 7.65−7.58 (m, 2H, Ph), 7.55−7.26 (m, 19H, Ph), 7.21−
7.12 (m, 2H, Ph), 5.34 (d, J = 1.9 Hz, 1H, H1), 5.32−5.26 (brs, 1H,
H2), 4.91 (d, J = 11.6 Hz, 1H, CH2Ar), 4.80 (d, J = 11.6 Hz, 1H,
CH2Ar), 4.67−4.54 (m, 4H, CH2Ar, H5, H1′), 4.35 (t, J = 2.6 Hz, 1H,
H3), 4.13 (d, J = 10.8 Hz, 1H, CH2Ar), 4.04 (brs, 1H, H4), 3.93−3.84
(m, 2H, CH2Ar, H5), 3.82 (dd, J = 10.3, 3.3 Hz, 1H, H6′), 3.76 (s, 3H,
COOCH3), 3.70−3.62 (m, 2H, H4′, H6″), 3.39 (t, J = 10.2 Hz, 1H,
H3′), 3.18 (dd, J = 10.2, 3.5 Hz, 1H, H2′), 2.54 (s, 1H, OH); 13C NMR
(100 MHz; CDCl3) δ 168.5, 166.2, 138.1, 137.7, 137.0, 134.8, 133.4,
131.2, 130.3, 129.7, 129.1, 128.8, 128.6, 128.4, 128.3, 128.35, 128.2,
127.9, 127.8, 127.7, 127.6, 99.4, 86.0, 80.0, 75.7, 75.1, 74.7, 73.7, 72.9,
72.8, 72.6, 70.4, 70.1, 69.5, 63.2, 52.3; MS ES m/z = 884.9 [M + Na]+;
HRMS (FTMS-NSI+) calcd for C47H47O11N3SNa [M + Na]+
884.2824, found 884.2808.
20
1
[α]D = +37.6 (c = 0.76, CH2Cl2); H NMR (400 MHz, CDCl3) δ
7.38−7.30 (m, 20H, Ph), 7.18 (d, J = 8.4 Hz, 2H, PMP), 6.85 (d, J =
8.8 Hz, 2H, PMP), 6.05 (d, J = 2.0 Hz, 1H, H-1), 5.28 (d, J = 4.8 Hz,
1H, H″-1), 5.05−5.04 (m, 1H, H-2), 5.02 (d, J = 3.6 Hz, 1H, H‴-1),
4.90−4.89 (m, 1H, H″-2), 4.88−4.48 (m, 13H, CH2Ph, CH2PMP, H′-
1, H-5, H″-5), 4.39 (dd, J = 12.4 Hz, J = 1.6 Hz, 1H, H′-6a), 4.24−4.20
(m, 3H, H′-6b, H‴-6a, H‴-6b), 4.05 (t, J = 3.2 Hz, 1H, H-3), 4.02
(dd, J = 6.0 Hz, J = 4.8 Hz, 1H, H″-4), 3.98 (t, J = 2.0 Hz, 1H, H-4),
3.93 (t, J = 6.0 Hz, 1H, H″-3), 3.88−3.68 (m, 5H, H′-3, H′-4, H′-5,
H‴-3, H‴-5), 3.80 (s, 3H, PhOCH3), 3.73 (s, 3H, COOCH3), 3.58 (s,
3H, COOCH3), 3.51 (dd, J = 9.6 Hz, J = 8.8 Hz, 1H, H‴-4), 3.37 (dd,
J = 10.4 Hz, J = 3.2 Hz, 1H, H′-2), 3.24 (dd, J = 10.4 Hz, J = 3.2 Hz,
1H, H‴-2), 2.14 (s, 3H, COCH3), 2.12 (s, 3H, COCH3), 2.12 (s, 3H,
6-O-Acetyl-2-azido-3-O-benzyl-2-deoxy-4-O-p-methoxyben-
zyl-α-D-glucopyranosyl-(1−4)-methyl-2-O-acetyl-3-O-benzyl-L-
idopyranuronate (61). To the disaccharide 52 (1.63 g, 1.98 mmol)
was added diethyl ether (30 mL), the mixture was cooled to 0 °C, and
benzylamine (1.0 mL, 8.9 mmol) added. The solution was stirred for 3
h at 0 °C and then extracted with EtOAc (2 × 50 mL) and 1 M HCl
(50 mL). The organic phase was washed with saturated aqueous
NaHCO3 (50 mL), dried (MgSO4), filtered and evaporated.
Purification by flash column chromatography (EtOAc/hexane 1:1)
yielded the intermediate free 1-OH disaccharide (838 mg, 1.01 mmol,
54%) as a white foam, along with recovered starting materal 52 (638
S
dx.doi.org/10.1021/jo300722y | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
COCH3), 2.07 (s, 3H, COCH3), 1.97 (s, 3H, COCH3); MS-MALDI
m/z = 1480 [M + NH4]+; HRMS (FTMS-NSI+) m/z calcd for
C72H86O27N7 [M + NH4]+ 1480.5566, found 1480.5587 [isotope
pattern in the Supporting Information].
2003, 44, 7767−7770. (f) Ojeda, R.; de Paz, J. L.; Martín-Lomas, M.;
Lassaletta, J. M. Synlett 1999, 1316−1318. (g) Jacquinet, J.-C.; Petitou,
M.; Duchaussoy, P.; Lederman, I.; Choay, J.; Torri, G. P.; Sinay, P.
̈
Carbohydr. Res. 1984, 130, 221−241. (h) Yu, H. N.; Furukawa, J.-i.;
Ikeda, T.; Wong, C.-H. Orglett 2004, 6, 723−726. (i) Blanc-Muesser,
M.; Defaye, J.; Horton, D.; Tsai, J.-H. Methods Carbohydr. Chem. 1980,
8, 177−183. (j) Davis, N. J.; Flitsch, S. L. Tetrahedron Lett. 1993, 34,
1181−1184.
ASSOCIATED CONTENT
■
S
* Supporting Information
General experimental methods, copies of H and 13C NMR,
1
(6) Seebach, D. Angew. Chem., Int. Ed. Engl. 1967, 6, 442−443.
(7) (a) Lohman, G. J. S.; Hunt, D. K.; Hogermeier, J. A.; Seeberger,
P. H. J. Org. Chem. 2003, 68, 7559−7561. (b) Gavard, O.; Hersant, Y.
COSY and HMQC spectra for new compounds, and mass
spectra for oligosaccharide 64. CIF data files for the X-ray
analyses of 3, 5, 6 and 17. Unit cell ORTEP for amide 3. This
material is available free of charge via the Internet at http://
pubs.acs.org.
I.; Alais, J.; Duverger, V.; Dilhas, A.; Bascou, A.; Bonnaffe,
Org. Chem. 2003, 3603−3620. (c) Lubineau, A.; Gavard, O.; Alais, J.;
Bonnaffe, D. Tetrahedron Lett. 2000, 41, 307−311.
́
D. Eur. J.
́
(8) (a) Polat, T.; Wong, C.-H. J. Am. Chem. Soc. 2007, 129, 12795−
12800. (b) Hu, Y.-P.; Lin, S. Y.; Huang, C.-Y.; Zulueta, M. M. L.; Liu,
J.-Y.; Chang, W.; Hung, S.-C. Nat. Chem. 2011, 3, 557−563. (c) Wang,
Z.; Xu, Y.; Yang, B.; Tiruchinapally, G.; Sun, B.; Liu, R.; Dulaney, S.;
Liu, J.; Huang, X. Chem.Eur. J. 2010, 16, 8365−8375.
(d) Tiruchinapally, G.; Yin, Z.; El-Dakdouki, M.; Wang, Z.; Huang,
X. Chem.Eur. J. 2011, 17, 10106−10112.
AUTHOR INFORMATION
Corresponding Author
*Tel: (+44) 161 206 4530. E-mail: gardiner@manchester.ac.uk.
■
Present Address
#Institute of Chemistry, Centre of Glycomics, Dubravska Cesta
9, 845 38 Bratislava, Slovakia.
(9) Synthesis of 1−1.2 kg of cyanohydrin 1 conducted in parallel (0.5
kg × 2) using standard laboratory equipment.
Author Contributions
§These authors contributed significantly to the synthetic
experimental work and contributed to the research planning
and manuscript preparation. Experimental design and planning
and primary contributions to the iduronate development
chemistry by SUH; work on glucosides (and scale work)
additionally contributed by GJM along with major contribution
to the manuscript, experimental and supporting data analysis
and interpretation of iduronates and glucosides. MB and KB
contributions to iduronate development and saccharide syn-
thesis methods. X-ray data analyses were obtained by MH and
JR. EA and GCJ were involved in overall oligosaccharide target
selection.
́
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(13) Large scale procedure for synthesis (of 3)/recycling (to 2) is
provided in the Experimental Section.
Notes
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The CRUK [C2075/A9106], MRC [G0601746 and G902173],
and Holt Foundation are thanked for project grant funding.
EPSRC for NMR instrumentation (GR/L52246) and the
EPSRC National Mass Spectrometry Service, Swansea, are also
thanked for mass spectroscopic analyses.
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