Access to antigens related to anthrose using pivotal cyclic sulfite/sulfate intermediates

Article abstract of DOI:10.1021/jo200340q

Anthrose is the upstream terminal unit of the tetrasaccharide side chain from a major glycoprotein of Bacillus anthracis exosporium and is part of important antigenic determinants. A novel entry to anthrose-containing antigens and precursors is described. The synthetic route, starting from d(+)-fucose, makes use of intermediates featuring a cyclic sulfite or sulfate function which serves successively as a protecting and a leaving group.

Full text of DOI:10.1021/jo200340q

ARTICLE
pubs.acs.org/joc
Access to Antigens Related to Anthrose Using Pivotal Cyclic
Sulfite/Sulfate Intermediates
Ophꢀelie Milhomme, Cꢀedric John, Florence Djedaïni-Pilard, and Cyrille Grandjean*
Laboratoire des Glucides, UMR CNRS 6219, Institut de Chimie de Picardie, Universitꢀe de Picardie Jules Verne, 33 rue Saint Leu,
80039 Amiens Cedex, France
S Supporting Information
b
ABSTRACT:
Anthrose is the upstream terminal unit of the tetrasaccharide side chain from a major glycoprotein of Bacillus anthracis exosporium
and is part of important antigenic determinants. A novel entry to anthrose-containing antigens and precursors is described. The
synthetic route, starting from D(+)-fucose, makes use of intermediates featuring a cyclic sulfite or sulfate function which serves
successively as a protecting and a leaving group.
’ INTRODUCTION
Bacillus anthracis, the etiological agent of anthrax, is a spore-
forming Gram positive bacterium. Because of the ease of
production, storage, and dissemination of the spores as well as
the high lethality that result from spore exposure, this pathogen
has recently emerged as a potential biological weapon.1 This has
stimulated the development of effective detection methods and
vaccines against this pathogen. The structure of a tetrasaccharide 1,
present as multiple copies on a glycoprotein (BclA) of B.
anthracis exosporium,2 has recently been disclosed. The terminal
unit of this linear tetrasaccharide features a rare sugar, called
anthrose, which, to date, has only been detected on B. anthracis
Figure 1. Structure of the anthrose-terminated tetrasaccharide 1 of
B. anthracis surface glycoprotein, BclA.
and related Bacillus species (Figure 1).3
This unique feature has encouraged several laboratories, in-
cluding ours, to prepare this tetrasaccharide and analogues by
chemical synthesis4ꢀ16 or purification from bacterial strains.17 The
tetrasaccharide as well as related fragments and analogues have
been key in establishing that the anthrose unit is part of immuno-
dominant antigenic determinants and that analogues featuring an
intact or a slightly modified anthrose moiety could be used for
detection or sufficed to induce the production of antibodies in
detection kits or as immunogens for vaccination.5,8,13,16ꢀ21
We are interested in developing a glycoconjugate vaccine that
might offer an improved alternative to, or complement, the lower
than optimal vaccines currently marketed. The latter exploit
the immunogenicity of only one virulence factor.22 The
development of such alternative glycoconjugate vaccines would
necessitate the determination of whether tetrasaccharide 1 is fully
required or truncated analogues comprising the anthrose moiety
suffice to induce a memory immune response in addition to
optimize synthetic access to anthrose-related immunogens. That
implies the preparation of anthrose-related intermediates suita-
ble for further glycosylation to rhamnosyl derivatives or coupling
to protein carriers.
Received: March 4, 2011
Published: June 16, 2011
r
2011 American Chemical Society
5985
dx.doi.org/10.1021/jo200340q J. Org. Chem. 2011, 76, 5985–5998
|

The Journal of Organic Chemistry
ARTICLE
Scheme 1. Overall Route to Anthrose-Derivatives Based on a
Dual Role Played by a Cyclic Sulfite
corresponding bis-cyclic sulfite 2 as a mixture of the four possible
diastereomers. This mixture, either purified or crude, was next
glycosylated with an excess of N-Cbz-ethanolamine, in the
presence of a catalytic amount of ytterbium(III) trifluorometha-
nesulfonate according to the literature29,30 so as to introduce the
spacer-arm precursor required for future conjugation. The
desired β-glycoside 3b could not be separated from the un-
reacted alcohol acceptor, used in excess, by chromatographic
purification. Moreover, the ratio of anomers varied with each
experiment and up to 60% of the R-anomer 3a was sometimes
detected in the reaction mixture. Partial isomerization has already
been observed in the past for sugar donors bearing electron-
withdrawing substituents.29 When a polar solvent such as
dioxane and prolonged reaction times were used, we observed
that the formation of the undesired isomer was favored. How-
ever, a set of standardized experimental conditions which limited
isomerization to the unwanted isomer could not be established.
To avoid obtaining such uncontrollable mixture, the cyclic sulfite
3b (obtained as a 40/60 endo/exo mixture) was unambiguously
synthesized by an alternative route via tri-O-acetyl-D-fucopyra-
nose 431 using Schmidt’s trichloroacetimidate glycosylation32
followed by Zemplꢁen deacetylation and then reaction with
thionyl chloride (Scheme 2).
O-Methylation of the pure alcohol 3b, or the crude glycosyla-
tion mixture, carried out using methyl iodide and silver(I) oxide,
proceeded in almost quantitative yield. The cyclic sulfite survived
these methylation conditions, and formation of any 2,3-oxirane
byproduct did not occur. Attempts to accelerate the O-methyla-
tion rate by adding catalytic amount of dimethyl sulfide led to
methylation of the carbamate nitrogen atom, an issue which was
suggested by ESI monitoring of the reaction. On the other hand,
the O-methylated derivative 5b was easily separated from its
corresponding R-anomer 5a, or any N-Cbz-(2-methoxyethyl)-
carbamic acid contaminant when the O-methylation was con-
ducted on the crude glycosylation mixture.
The anthrose moiety in tetrasaccharide 1 is a β-linked
6-deoxy-sugar, having a gluco configuration and displaying a
3-hydroxy-3-methylbutanamido side chain at C-4 and a methoxy
at C-2. The most efficient syntheses of anthrose or derivatives
thereof reported so far make use of either commercially available
D(+)-galactose or D(+)-fucose as starting material and all rely on
an SN2-type reaction between a sulfonate and an azide to install
the amide side chain with the correct configuration at
C-4.5,8,12,13,16,23 Whatever the starting sugar or the strategy
envisaged, conventional and extensive protecting group
(typically isopropylidene, stannylidene, or benzylidene) manip-
ulations have been required in order to differentiate each
hydroxyl group of the starting sugar ring.5,8,12,13,16,23
We thought to examine a strategy whereby a bis-functional
group such as a cyclic sulfite (or sulfate) could serve first as a 3,4-
diol protecting group in a D-fucose derivative, thereby allowing
selective methylation or orthogonal protection of the remaining
free 2-OH group and subsequently serve as a leaving group to
enable the stereo- and regioselective introduction of an azido
group and thus the anthrose side chain (Scheme 1). Upon
adopting this strategy, our goal was ultimately to shorten and
to improve the synthesis of anthrose-related antigens.
’ RESULTS AND DISCUSSION
The crucial nucleophilic substitution step was examined using
5b, whose anomeric configuration was that of the anthrosyl
residue featuring in BclA glycoprotein (see Figure 1). Treatment
of the cyclic sulfite 5b with sodium azide led, as expected, to ring-
opening to give a 4:1 mixture of regioisomers in 66% isolated
yield (Scheme 3). These were easily separable but the unwanted
gulo isomer 6b predominated. The stereochemistry of each
regioisomer was evident from their proton NMR data: in
particular, coupling constants (J2,3 = 9.0 Hz, J3,4 = 9.5 Hz,
J4,5 = 9.5 Hz) are in full agreement with four H-2, H-3, H-4,
and H-5 protons in a trans-diaxial relationship on a pyranose ring
in the 4C1 conformation for compound 6a. For comparison, J2,3
and J3,4 coupling constants of compound 6b were found equal to
3.8 and 3.7 Hz, respectively, and are compatible with a gulo
configuration for this derivative.
Cyclic sulfites and sulfates have long been known as versatile
electrophiles, and particularly as epoxide surrogates, in both
noncarbohydrate and carbohydrate chemistry.24,25 However,
the substitution of cyclic sulfites (or sulfates) other than those
involving the anomeric center or a primary hydroxyl group of a
sugar has scarcely been studied despite its broad synthetic
potential: To our knowledge, no attempt of substitution on a
pyranoside 3,4-cyclic sulfate has been reported so far. On the
other hand, Guiller et al. reported the preparation of some methyl
4-azido-R-D-arabinopyranosides from their corresponding 3,4-
cyclic sulfites in high yields and complete regioselectivity.26
However, when the same authors iterated the reaction on a
(R-L-arabinopyranosyl)uracil derivative, the 30-azido compound
was the sole isolated product, in 50% yield, from a complex
mixture in which they tentatively identified the presence of the
40-azido regioisomer.27 From these extremely limited results, we
envisioned that the anomeric substituent plays an important role
in controlling the nucleophilic attack either at the C-3 or C-4 site
and that existing 1,3-diaxial interactions will strongly disfavor
attack at the former site.28
The reaction was carried out on cyclic sulfite 5b as a whole,
which comprises a 60/40 mixture of both exo and endo isomers.
The identity of each isomer was established on the basis of
1
literature data33 while the integration of the H NMR signals
corresponding to the H-3 exo, H-4 exo, H-3 endo, and H-4 endo
protons, observed at 4.72, 4.68, 4.53, and 4.24 ppm, respectively,
was used to determine the isomeric ratio. To check whether the
ring-opening regioselectivity was sensitive to the stereochemical
nature of the leaving group, part of 5b was repurified by silica gel
chromatography so that the reaction was iterated on either
enriched endo-5b (endo/exo > 85:15) or exo-5b (exo/endo >
90:10) cyclic sulfites respectively. Whatever the mixture used,
Cyclic Sulfate/Sulfite Ring-Opening from β-Anomers. We
nevertheless decided to test our strategy on a β-intermediate:
Indeed, we reasoned that the anthrose-derived antigen targets
would be more readily accessed if we could secure the required β-
anomeric configuration at an early stage of the synthesis. Thus,
D-(+)-fucose was reacted with thionyl diimidazole to afford the
5986
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
Scheme 2. Preparation of the Key 2-O-Methylated β-Glycosylated Cyclic Sulfite Intermediate
Scheme 3. Nucleophilic Substitution and Final Elaboration of the Anthrose-Related Antigen
identical ratios of products were obtained. However, a modest
change in regioselectivity was observed upon using the alter-
native cyclic sulfate 7 which reacted smoothly to give the azides
6a/6b 3:7 ratio and in a slightly improved yield.
(18 steps from D(+)-galactose in 4.6% yield),13 the overall yield
(11%) suffers from the poor regioselectively of the ring-opening
step by azide. To further control this step, the strategy was thus
revisited from R-glycoside precursors.
The synthesis of a first target anthrose analogue 10 was
achieved from pure 6a upon reduction of the azido group,
acylation of the formed amine function with the β-hydroxy-
isovaleric acid succinimidyl ester 8, and subsequent removal of
the benzyloxycarbonyl protective group by hydrogenation.
Although the synthesis of an anthrose-related immunogen was
realized in only seven or eight steps from D(+)-fucose, a route
which is considerably shorter than any previously disclosed one
Cyclic Sulfate/Sulfite Ring-Opening from r-Anomers.
With adoption of this alternative strategy, the anomeric sub-
stituent should ideally first serve to orient the 3,4-cyclic sulfite/
sulfate ring-opening and further be activated in a glycosylation
process. We sought to use glycosyl fluorides, but we anticipated
that fluorine might be a too small substituent to exert an effective
control of the ring-opening regioselectivity. We also did not
investigate the use of R-thioglycosides because they are not as
5987
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
Scheme 4. Preliminary Cyclic Sulfite/Sulfate Formation and Reactivity Study
easily accessible as their corresponding β-anomers, although the
latter appeared as valuable intermediates for the preparation of
numerous anthrose-derived oligosaccharides.8,10ꢀ13 We finally
chose to test alkyl R-fucopyranosides, readily prepared under
Fisher-type glycosylation conditions while enabling glycosyla-
tion either by direct activation or after being exchanged to a
trichloroacetimidate or a halogen leaving group.34 4-Pentenyl
D-fucopyranoside 1135 was prepared following Gin’s condi-
tions36 in an R/β mixture (81:19) in 81% yield (Scheme 4).
This derivative was successively reacted with tributyltin oxide
and thionyl chloride33 to give the 3,4-cyclic sulfite 12 in 85%
yield. Unfortunately, this intermediate did not react with sodium
azide under reported conditions26 (105 °C) (recovery of the
starting material) and decomposed at more elevated temperature
(135 °C). If some products of substitution were formed, we have
been unable to detect them in the crude reaction mixture. It is
likely that, in accordance with our initial hypothesis, attack at C-3
is prevented on account of the presence of the axial anomeric
pentenyl group but that steric hindrance by the methyl group at
C-5, not present in the arabinose series described in the
literature,26 suffices to block attack at C-4. We failed in preparing
the more reactive 3,4-cyclic sulfate 13 via a stannylidene as for the
preparation of compound 12. Attempts to oxidize sulfite 12 into
sulfate under Sharpless conditions proceeded with concomitant
oxidation of the alkene function. This sulfate was therefore
obtained directly from triol 11 upon treatment with sulfuryl
chloride in 42% yield together with recovered starting material
(50%): because hydroxyls at sites C-2 and C-3 of the pyranose
were vicinal to an axial substituent, they probably possess close
reactivity, accounting for the modest, less than 50% percent
conversion. It is likely that the 3,4-cyclic sulfate can only be
formed when the initial reaction takes place at the 3-OH
(considering that the 4-OH is marginally reactive). Indeed, if
the reaction first takes place at the concurrent 2-OH, it is likely
that the resulting 2-chlorosulfonate cannot cyclize with the 3-OH
which is in a trans-diequatorial relationship to give the 2,3-cyclic
sulfate product and is too deactivated to react with a further
equivalent of sulfuryl chloride, ending in a 3,4-cyclic sulfate.
Finally, the 2-chlorosulfonate is apparently hydrolyzed back to
the starting material during workup.37 The preparation of an alkyl
fucopyranoside 3,4-cyclic sulfite which could be oxidized into its
corresponding sulfate without any further protective steps should
circumvent thislimiting step. Meanwhile, thekey ring-openingwas
attempted on compound 13. The 4-azido derivative 14, having the
gluco configuration, was isolated upon reaction with sodium azide
at 50 °C as a unique product in 88% yield, a yield identical or even
superior to that reported for the substitution of a trifluorometha-
nesulfonate leaving group.5,8,9,12,13,16
Encouraged by this result, the reaction sequence was iterated
from methyl R-D-fucopyranoside 15, whose anomeric substituent is
stable toward oxidative experimental conditions. Methylation or
acetylation of sulfite 16, obtained from 15 in 86% yield as
described above, gave intermediates 17 or 18 in 86% and 90%
yields, respectively (Scheme 5).
These sulfites were oxidized under Sharpless conditions38 to
afford cyclic sulfates 19 and 20. Key nucleophilic ring-opening
using sodium azide at 50 °C in DMF followed by aqueous acid
hydrolysis of the resulting acyclic sulfates afforded the 4-azido
fucopyranosides 21 and 22 in 81% and 74% yields for this three-
step sequence. Remarkably no trace of the gulo 3-azido regioi-
somers was detected in the reaction mixture. Treatment of
compound 21 with benzyl bromide gave the corresponding
3-O-benzylated derivative 23 in 96% yields. The anomeric
methyl group was then removed under acetolysis conditions23
to give compound 24 in a 79:21 (R/β) anomeric mixture in 87%
yield. Notably, this reaction was chemospecific and not accom-
panied by the removal of the benzyl protective group.39 Deace-
tylation of 24 using sodium methoxide followed by treatment
with trichloroacetonitrile gave the known trichloroacetimidate
donor 258 in 82% yield for the two steps. In parallel, compound
22 was either benzylated using benzyl trichloroacetimidate in the
presence of a catalytic amount of triflic acid40 or benzoylated to
give 26 and 27 in 70% and quantitative yield, respectively.
Acetolysis, followed by selective removal of the anomeric acet-
ates and treatment with trichloroacetonitrile in the presence of
DBU afforded trichloracetimidates, 32 and known 33,16 in 43%
and 38% yields for the three steps, respectively.
The three anthrose-related donors 25, 32, and 33 have been
synthesized in nine steps in 32%, 13%, and 22% yield, respec-
tively. For comparison, donors 25 and 33 were previously
obtained following conventional protection/deprotection steps
both in either 12 or 13 steps from D(+)-galactose and 388 or
11%16 overall yield, respectively.
Synthesis of a Disaccharide Related to Anthrax Tetrasac-
charide. To fully demonstrate the efficiency of a synthetic
approach based on the use of a cyclic sulfate, the synthesis of
an anthrose-containing antigen disaccharide has been achieved
using novel trichloroacetimidate 32 and a rhamnopyranoside
acceptor (Scheme 6).
To this aim, N-Z-aminoethyl L-rhamnopyranoside 34, ob-
tained in a 5:1 (R/β) anomeric mixture upon pTsOH-catalyzed
condensation of N-Cbz-aminoethanol onto L-rhamnose, was
5988
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
Scheme 5. Syntheses of Anthrose-Related Donors from Cyclic Sulfates
Scheme 6. Synthesis of Rhamnose-Derived Acceptor 37
deprotection using DDQ afforded acceptor 37 in 44% yield
(two steps). Donor 32 was then reacted with acceptor 37 at
ꢀ40 °C for 1 h in the presence of TMSOTf to afford disaccharide
38, having the β-configuration, in 68% yield (Scheme 7).
Zemplꢀen deacetylation of compound 38 gave alcohol 39 which
was further methylated by treatment with excess methyl iodide to
give 40 (47% yield for the two steps). Hydride reduction of the
azido group of intermediate 40, followed by acylation using
3-hydroxy-3-methylbutanoic acid, preactivated with HOBt/
HATU, rather than the succinimidyl ester 8 which proved
insufficiently reactive, gave intermediate 41 in 55% yield. Dis-
accharide 42 was finally obtained after removal of the protecting
groups by catalytic hydrogenation in 91% yield.
’ CONCLUSION
The synthetic potential of sugar-derived cyclic sulfite/sulfate,
not involving primary or anomeric hydroxyls, has largely been
overlooked. The approach reported herein relied on the unpre-
cedented, sequential use of 3,4-cyclic sulfite/sulfates on pyra-
noses as protecting and leaving groups and was successfully
applied to the preparation of several anthrose-related antigens
and precursors. We have been able to demonstrate that the key
nucleophilic ring-opening could be performed in the presence of
various functionalities (alcohol, ether, and ester) but was sensi-
tive to steric hindrance. In particular, an attack at the C-3 site is
strongly favored by a β-configuration of the anomeric substituent
whenever a cyclic sulfite or sulfate was used. While cyclic sulfites
do not react, the reaction proceeds in very high yield and
converted to the 3-O-p-MeO-benzyl intermediate 35 by regio-
selective stannylene-mediated alkylation41 in 28% yield for the
two steps. Benzylation of the two remaining hydroxyls as well as
the carbamate group gave intermediate 36, whose selective
5989
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
Scheme 7. Synthesis of an Anthrose-Derived Disaccharide
exclusively at the C-4 site when it was conducted on cyclic
sulfates derived from R-glycopyranosides.
0 °C. The reaction mixture was stirred under argon for 30 min and
was then cooled to ꢀ20 °C. D(+)-fucose (500 mg, 3 mmol) was then
added in one portion. The reaction mixture was stirred at this
temperature under argon for 2 h. The reaction mixture was then
concentrated, and the residue was diluted in CH2Cl2 (50 mL) and
washed by aqueous 1 M HCl (2 ꢁ 25 mL) and water (25 mL). The
organic layer was dried over anhydrous MgSO4, filtered, and con-
centrated in vacuo to give crude compound 2 which was used in the
next step without purification.
A solution of crude 2 (554 mg), Yb(OTf)3 (135 mg, 0.21 mmol), and
4 Å molecular sieves in anhydrous toluene (7.5 mL) was stirred under Ar
for 30 min. 2-[(N-Benzyloxycarbonyl)amino]ethanol (1.27 g, 6.4
mmol) was then added, and the mixture was heated at 100 °C for 4 h.
The reaction mixture was then diluted in EtOAc (80 mL) and washed
successively with aqueous 1 M HCl (2 ꢁ 25 mL), saturated aqueous
NaHCO3, and brine (25 mL). The organic phase was dried over
anhydrous MgSO4 and concentrated under vacuum. The crude reaction
mixture was purified by flash chromatography on silica gel using
cyclohexane/ethyl acetate (1:1) to give 3b in a mixture with a two-fold
excess of 2-[(N-benzyloxycarbonyl)amino]ethanol, and, depending on
the experiments, its R-anomer 3a.
In a typical example, a 6:4 mixture of compounds 3a/3b with 2-[(N-
benzyloxycarbonyl)amino]ethanol (1.56 g) was dissolved in dry
CH2Cl2 (50 mL), and silver(I) oxide (2.6 g, 32.4 mmol) was added.
The reaction mixture was stirred at rt for 1 h. Iodomethane (4.03 mL,
64.8 mmol) was then added dropwise, and the reaction mixture was
stirred at rt for 5 d. Silver(I) oxide was filtered trough a Celite pad, and
the filtrate was concentrated. The residue was purified by flash chroma-
tography using cyclohexane/ethyl acetate (7:3) as eluent to give 5a (329
mg) and 5b (220 mg) as pale yellow oils. (5a): 20/80 endo/exo mixture;
Rf 0.35 (cyclohexane/ethyl acetate 1:1); 1H NMR (300 MHz, CDCl3) δ
7.35ꢀ7.30 (m, 5 H endo and 5 H exo), 5.55 (br s, H endo and H exo),
5.27 (m, 2 H endo and 2 H exo), 4.91 (dd, J = 5.4 and 8.2 Hz, 1 H exo),
4.91 (d, J = 3.8 Hz, 1 H endo), 4.86 (d, J = 3.5 Hz, 1 H exo), 4.77 (dd,
J = 5.4 and 2.3 Hz, 1 H exo), 4.67 (dd, J = 5.5 and 8.2 Hz, 1 H endo),
4.35ꢀ4.22 (m, 2 H endo and 2 H exo), 4.21ꢀ4.07 (m, 1 H endo), 4.02
(dd, J = 3.8 and 8.8 Hz, 1 H endo), 3.84ꢀ3.72 (m, 1 H endo and 1 H
’ EXPERIMENTAL SECTION
General. All reactions were monitored by TLC on Kieselgel 60
F254. Detection was achieved by charring with vanillin. Silica gel
(240ꢀ400 mesh) was used for chromatography. Optical rotation was
measured with a digital polarimeter, using a sodium lamp (λ = 589 nm)
at 20 °C. All NMR experiments were performed at 300.13 and 500.13
MHz on spectrometers equipped with a Z-gradient unit for pulsed-field
gradient spectroscopy. Assignments were performed by stepwise identi-
fication using COSY, successive RELAY, HSQC, and HMBC experi-
ments using standard pulse programs. Chemical shifts are given relative
to external TMS with calibration involving the residual solvent signals.
When D2O was used, TMS was used as internal standard reference in a
previous 13C NMR experiment performed in the same experimental
conditions. Low-resolution ESI mass spectra were obtained on a hybrid
quadrupole/time-of-flight (Q-TOF) instrument, equipped with a pneu-
matically assisted electrospray (Z-spray) ion source. High-resolution
mass spectra were recorded in positive mode on a TOF tandem hydrid
mass spectrometer with EBETOF geometry. The compounds were
individually dissolved in MeOH at a concentration of 10 μg cmꢀ3 and
then infused into the electrospray ion source at a flow rate of
10 mm3 minꢀ1 at 60 °C. The mass spectrometer was operated at
4 kV while scanning the magnet at a typical range of 4000ꢀ100 Da.
The mass spectra were collected as continuum profile data. Accu-
rate mass measurement was achieved using polyethylene glycol
as internal reference with a resolving power set to a minimum of
10 000 (10% valley).
Preparation of 2-[(N-Benzyloxycarbonyl)amino]ethyl 3,4-
Cyclic Sulfite-6-deoxy-2-O-methyl-R-D-galacto-pyranoside
(5a) and 2-(N-Benzyloxycarbonyl)aminoethyl 3,4-Cyclic
Sulfite-6-deoxy-2-O-methyl-β-D-galactopyranoside (5b) via
1,2:3,4-Bis-cyclic Sulfite-6-deoxy-β-D-galactopyranose (2).
To a solution of imidazole (1.25 g, 19 mmol) in anhydrous THF
(7.5 mL) was added thionyl chloride (0.8 mL, 12.2 mmol) dropwise at
5990
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
exo), 3.58ꢀ3.33 (m, 2 H endo and 2 H exo), 3.47 (s, 3 H exo), 3.51 (s,
3 H endo), 3.16 (dd, J = 3.5 and 8.2 Hz, 1 H exo), 1.37 (d, J = 6.6 Hz, 3 H
endo) 1.36 (d, J = 6.6 Hz, 3 H exo); 13C NMR (75 MHz, CDCl3) δ
156.4 (C endo and C exo), 136.6, 128.5, 128.2, 128.1 (6 C endo and
6 C exo), 97.1 (C endo), 96.6 (C exo), 83.9 (C endo), 81.2 (C exo), 80.1
(C endo), 78.9 (C exo), 78.1 (C endo and C exo), 67.9 (C endo and C
exo), 66.6 (C endo and C exo), 62.8 (C endo), 61.9 (C exo), 59.3
(C endo), 58.8 (C exo), 40.7 (C endo and C exo), 16.3 (C endo and C
exo). HR-ESI-MS m/z Calcd for C17H23NO8S 402.1223 [M + H]+.
Found 402.1217.
and 5.7 Hz, 1 H endo), 4.24 (dd, J = 5.7 and 1.5 Hz, 1 H endo), 4.16 (d,
J = 7.6 Hz, 1 H endo and 1 H exo), 3.95ꢀ3.82 (m, 2 H exo and 1 H
endo), 3.77 (q, J = 6.6 Hz, 1 H endo), 3.64ꢀ3.51 (m, 1 H endo and 1 H
exo), 3.50ꢀ3.23 (m, 3 H endo and 3 H exo), 1.41 and 1.38 (2 d, J = 6.6
Hz, 3 H endo and 3 H exo); 13C NMR (75 MHz, CDCl3) δ 157.0
(C endo and C exo), 136.4ꢀ128.0 (6 C endo and 6 C exo), 102.7 and
101.8 (C endo and C exo), 83.9 (C endo), 83.8 (C exo), 82.7 (C endo),
76.1 (C exo), 72.8 (C endo and C exo), 69.4 (C endo and C exo), 67.9
(C exo), 67.3 (C endo), 66.8 (C endo and C exo), 40.9 (C endo and
C exo), 16.7 (C endo and C exo); HR-ESI-MS m/z Calcd for C16H21-
NO8S 410.0886 [M + Na]+, Found 410.0894.
See below for the description of 5b.
2-[(N-Benzyloxycarbonyl)amino]ethyl 3,4-Cyclic Sulfite-
6-deoxy-2-O-methyl-β-D-galactopyranoside (5b). To a solu-
tion of 3b (944 mg, 2.6 mmol) in dry CH2Cl2 (50 mL) was added
silver(I) oxide (2.8 g, 7.8 mmol). The reaction mixture was stirred at rt
for 1 h. Iodomethane (1.5 mL, 26 mmol) was then added dropwise, and
the reaction mixture was stirred at rt for 5 days. Silver(I) oxide was
filtered through a Celite pad, and the filtrate was concentrated. The
residue was purified by flash chromatography using cyclohexane/ethyl
acetate (7:3) as eluent to give 5b as a 40/60 endo/exo mixture as a pale
yellow oil (962 mg, 92%). Rf 0.26 (cyclohexane/ethyl acetate 5:5); 1H
NMR (300 MHz, CDCl3) δ 7.38ꢀ7.29 (m, 5 H endo and 5 H exo), 5.48
(br s, 1 H endo), 5.41 (br s, 1 H exo), 5.12 (s, 2 H endo and 2 H exo),
4.80 (dd, J = 5.5 and 1.8 Hz, 1 H exo), 4.76 (dd, J = 6.7 and 5.7 Hz, 1 H
exo), 4.53 (dd, J = 7.6 and 5.7 Hz, 1 H endo), 4.36 (dd, J = 5.9 and 1.7 Hz,
1 H endo), 4.25 (d, J = 7.9 Hz, 1 H exo), 4.24 (d, J = 7.9 Hz, 1 H endo),
4.02 (dq, J = 1.8 and 6.6 Hz, 1 H exo), 3.94ꢀ3.80 (m, 2 H endo and 2 H
exo), 3.77ꢀ3.72 (m, 1 H endo and 1 H exo), 3.60 (s, 3 H endo), 3.56 (s,
3 H exo), 3.46ꢀ3.43 (m, 2 H endo and 2 H exo), 1.46 (d, J = 6.6 Hz, 3 H
endo and 3 H exo,); 13C NMR (75 MHz, CDCl3) δ 156.5 and 156.4 (C
endo and C exo), 136.6 (C endo and C exo), 128.5, 128.1, and 128.0 (5
C endo and 5 C exo), 103.0 (C endo), 102.1 (C exo), 83.9 (C endo),
83.5 (C exo), 82.8 (C endo), 81.6 (C exo and C endo), 76.8 (C exo),
69.3 (C exo and C endo), 67.4 (C endo), 67.2 (C exo), 66.7 (C exo),
66.6 (C endo), 60.3 (C exo and C endo), 41.1 (C exo and C endo), 16.7
(C exo and C endo); IR (selected data) (ν) 3357 (NH), 1709 (CO),
1517 (NH), 1210 (SO); HR-ESIMS m/z Calcd for C17H24NO8S [M +
H]+: 402.1223. Found 402.1233.
Preparation of 2-[(N-Benzyloxycarbonyl)amino]ethyl
4-Azido-4,6-dideoxy-2-O-methyl-β-D-glucopyranoside (6a)
and 2-[(N-Benzyloxycarbonyl)amino]ethyl 3-Azido-3,6-di-
deoxy-2-O-methyl-β-D-gulopyranoside (6b) from Sulfite
5b. A mixture of 5b (733 mg, 1.8 mmol) and NaN3 (900 mg,
3.6 mmol) in dry DMF (10 mL) was stirred for 2 d at 105 °C. The
solvent was then removed under vacuum. The residue was dissolved
in EtOAc (200 mL) and washed with water (2 ꢁ 100 mL) and brine
(100 mL). The organic layer was dried over anhydrous Na2SO4,
filtered, and concentrated in vacuo. The residue was purified by flash
chromatography using cyclohexane/ethyl acetate (1:1) as eluent to
give 6a (76 mg, 13%) as a white solid and 6b (361 mg, 53%) as a
yellow oil, in a 20/80 ratio.
2-[(N-Benzyloxycarbonyl)amino]ethyl 3,4-Cyclic Sulfite-
6-deoxy-β-D-galactopyranoside (3b). To a solution of 431
(2.0 g, 6.8 mmol) and trichloroacetonitrile (15 mL, 150 mmol) in
CH2Cl2 (20 mL) was added DBU (0.252 mL, 1.6 mmol) dropwise at
0 °C. The mixture was then strirred at rt for 2 h and then filtered trough
a Celite pad. The filtrate was concentrated in vacuo, and the residue
was purified by flash chromatography on silica gel using 2% Et3N in
cyclohexane/ethyl acetate (7:3) as eluent to give 2,3,4-tri-O-acetyl-6-
deoxy-β-D-galactopyranosyl trichloroacetimidate42 (2.5 g, 84%) as a pale
yellow oil as a mixture of R/β (9/1) anomers. (R-anomer) Rf 0.72
(cyclohexane/ethyl acetate 1:1); ESI-MS m/z 457 [M + Na]+; 1H
NMR (300 MHz, CDCl3) δ 8.64 (s, 1 H), 6.59 (d, J = 3.5 Hz, 1 H),
5.51ꢀ5.35 (m, 3 H), 4.43ꢀ4.37 (br q, J = 6.6 Hz, 1 H), 2.22, 2.05, and
2.04 (3 s, 3 ꢁ 3 H), 1.15 (d, J6,5 = 6.6 Hz, 3 H); 13C NMR (75 MHz,
CDCl3) δ 170.4ꢀ170.0 (3 ꢁ C), 161.1, 93.9, 77.2, 70.5, 67.9, 66.9, 67.5,
20.7ꢀ20.6 (3 ꢁ C), 15.9. A solution of the trichloroacetimidate (2.2 g,
5.1 mmol), 2-[(N-benzyloxycarbonyl)amino]ethanol (1.9 g, 10.2
mmol) and 4 Å molecular sieves (500 mg) in dry CH2Cl2 (30 mL)
was stirred for 15 min at rt. The mixture was cooled to 0 °C, and a
solution of TMSOTf in CH2Cl2 (0.1 N, 60 μL) was added dropwise.
After being stirred for 2 h, the reaction mixture was quenched with Et3N,
diluted in CH2Cl2, and then washed with saturated aqueous NaHCO3.
The organic layer was dried over Na2SO4, filtered, and concentrated in
vacuo. The residue was purified by flash chromatography using cyclo-
hexane/ethyl acetate (7:3) as eluent to give the 2-[(N-benzyloxycarbo-
nyl)amino]ethyl 2,3,4-tri-O-acetyl-6-deoxy-β-D-galactopyranoside
(1.2 g, 55%) as a pale yellow oil. Rf 0.65 (cyclohexane/ethyl acetate 1:1);
[R]D +8 (c 2.0, CHCl3); 1H NMR (300 MHz, CDCl3) δ 7.29ꢀ7.21 (m,
5 H), 5.43ꢀ5.35 (m, 1 H), 5.15ꢀ5.02 (m, 2 H), 5.00 (s, 2 H), 4.93 (dd,
J = 3.7 and 10.5 Hz, 1 H), 4.35 (d, J = 7.9 Hz, 1 H), 3.82ꢀ3.75 (m, 1 H),
3.71 (m, 1 H), 3.60ꢀ3.58 (m, 1 H), 3.39ꢀ3.17 (m, 2 H), 2.06, 1.93, and
1.88 (3 s, 3 ꢁ 3 H), 1.11 (d, J = 6.7 Hz, 3 H); 13C NMR (75 MHz,
CDCl3) δ 170.5, 170.0, and 169.6 (3 ꢁ C), 156.3, 136.6ꢀ128.0 (6 C),
101.1, 71.1, 70.1, 69.1, 69.0, 68.9, 66.5, 40.7, 20.5 (3 ꢁ C), 15.9. HR-ESI-
MS m/z Calcd for C22H29NO10 490.1689 [M + Na]+, Found 490.1680.
2-[(N-Benzyloxycarbonyl)amino]ethyl 2,3,4-tri-O-acetyl-6-deoxy-β-D-
galactopyranoside (1.2 g, 2.8 mmol) was treated by a 0.2 M methanolic
NaOMe solution (42 mL, 8.4 mmol) for 1 h at rt. The reaction mixture
was then neutralized by resin Amberlite 120 H+. The resin was filtered
off, and the filtrate was concentrated in vacuo. The crude residue was
dissolved in THF (10 mL) at 0 °C. Et3N (1 mL) was added to the
reaction mixture, followed by dropwise addition of thionyl chloride
(530 μL, 3.6 mmol). The reaction mixture was warmed to rt and stirred
for 2 h. The mixture was then diluted with CHCl3 and washed with water
and brine. The organic layer was dried over anhydrous NaSO4 and
filtered. The solvent was evaporated under reduced pressure, and the
residue was purified by flash chromatography on silica gel using
cyclohexane/ethyl acetate (4:6) as eluent to give 3b (944 mg, 87% over
two steps) as an 40/60 endo/exo mixture as pale yellow oil. Rf 0.65
(cyclohexane/ethyl acetate 1:1); 1H NMR (300 MHz, CDCl3) δ
7.37ꢀ7.30 (m, 5 H endo and 5 H exo), 5.98 and 5.91 (2 br s, 1 H
endo and 1 H exo), 5.06 (s, 2 H endo and 2 H exo), 4.72 (dd, J = 7.6 and
5.3 Hz, 1 H exo), 4.68 (dd, J = 5.3 and 1.5 Hz, 1 H exo), 4.53 (dd, J = 7.6
2-[(N-Benzyloxycarbonyl)amino]ethyl 4-Azido-4,6-dideoxy-
2-O-methyl-β-D-glucopyranoside (6a) and 2-[(N-Benzyloxy-
carbonyl)amino]ethyl 3-Azido-3,6-dideoxy-2-O-methyl-β-D-
gulopyranoside (6b). To 5b (962 mg, 2.4 mmol) was added a
cold solution of CCl4 (7 mL) and CH3CN (7 mL). The mixture
was cooled to 0 °C, and cold water was added (10 mL). RuCl3 H2O
3
(276 mg, 1.2 mmol) and NaIO4 (1.0 g, 4.8 mmol) were added in
one portion, and the reaction mixture was stirred vigorously at 0 °C.
After the mixture was stirred 2 h at this temperature, diethyl ether
(200 mL) was added and the layers were separated. The aqueous layer
was extracted with diethyl ether (100 mL), and the combined organic
layers were washed with brine (100 mL), dried over MgSO4, filtered, and
concentrated under vacuum to give 7. This material is used in the next
5991
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
step without any further purification. A mixture of crude 7 and NaN3
(1.2 g, 4.8 mmol) in dry DMF (10 mL) was stirred for 2 h at 60 °C. The
solvent was then removed in vacuo. The residue was suspended in dry
THF (20 mL), and concd H2SO4 (117 μL) and water (42 μL) were
added and the mixture was stirred at rt for 1 h. The reaction mixture was
then quenched by sodium bicarbonate in excess and stirred for 20 min.
The mixture was then concentrated under vacuum, and the residue was
purified by flash chromatography using cyclohexane/ethyl acetate (6:4)
to give a mixture of 6a (240 mg, 26%) as a white solid and 6b (561 mg,
61%) as a pale yellow oil, in a 30/70 ratio. (6a): Rf (cyclohexane/ethyl
2-Aminoethyl 4,6-Dideoxy-4-(3-hydroxy-3-methylbutan-
amido)-2-O-methyl-β-D-glucopyranoside (10). Compound 9
(20 mg, 0.04 mmol) in a 3:2 mixture of EtOH/AcOH (4 mL) was
deprotected under 10 bar H2 using catalytic Pd(OH)2 at 50 °C. After 30
min, the reaction mixture was concentrated in vacuo. The residue was
dissolved in H2O (10 mL) and was washed with CH2Cl2 (7 mL). The
organic layer was extracted by water (5 ꢁ 5 mL). The aqueous phases
were combined and concentrated under vacuum. The crude was then
purified on cation exchange resin (AG MP-50 Resin, analytical grade
100ꢀ200 mesh) to give 10 (12 mg, 91%) as a yellow solid after
lyophilization. [R]D +19 (c 0.1, H2O) [lit.13 [R]D +17 (c 0.17,
1
acetate 5:5) 0.36; [R]D +12 (c 1.2, CHCl3). H NMR (300 MHz,
1
CDCl3) δ 7.40ꢀ7.35 (m, 5 H), 5.36 (br s, 1 H), 5.14 (s, 2 H), 4.25 (d, J =
7.9 Hz, 1 H), 3.95ꢀ3.82 (m, 1 H), 3.82ꢀ3.72 (m, 1 H), 3.61 (s, 3 H),
3.55 (br dd, J = 9.0 and 9.5 Hz, 1 H), 3.50ꢀ3.42 (m, 2 H), 3.30ꢀ3.19 (m,
1 H), 3.11 (br t, J = 9.5 Hz, 1 H), 3.01 (dd, J = 7.9 and 9.0 Hz, 1 H), 2.96
(br s, 1 H), 1.36 (d, J = 6.0 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ
156.4, 136.5, 128.5, 128.2, 103.2, 83.3, 75.2, 70.7, 69.4, 67.1, 66.8, 60.4,
41.2, 18.3; IR (selected data) ν 3307 (NH), 2932, 2924, 2912 (OH),
2121 (N3), 1684 (CO), 1274 (OH); HR-ESIMS: m/z Calcd for
C17H24N4O6 [M + H]+: 381.1774. Found 381.1766. (6b): Rf
H2O)]; H NMR (300 MHz, CDCl3) δ 4.52 (d, J = 8.0 Hz, 1 H),
4.02ꢀ3.98 (m, 1 H), 3.88ꢀ3.84 (m, 1 H), 3.64ꢀ3.56 (m, 1 H), 3.15 (br
t, J = 8.0 Hz, 1 H), 3.08 (br t, J = 8.3 Hz, 2 H), 2.47 (s, 2 H), 1.27 (s, 3 H),
1.24 (s, 3 H), 1.17 (d, J = 5.9 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ
174.1, 109.9, 101.8, 83.1, 73.6, 72.9, 70.9, 70.2, 66.6, 60.1, 56.5, 48.9,
39.5, 28.2, 28.1, 16.9; HR-ESIMS: m/z Calcd for C14H28N2O6 [M +
H]+: 321.2026. Found 321.2023.
4-Penten-1-yl D-Fucopyranoside (11). D-(+)-Fucose (2 g, 12.2
mmol, 1.0 equiv) was added to a stirred mixture of 4-pentenol (11.3 mL,
110 mmol, 9.0 equiv) and acetyl chloride (0.8 mL, 12.2 mmol, 1.0 equiv)
cooled at ꢀ10 °C. The reaction mixture was stirred for 18 h at rt before
NaHCO3 was added and was then concentrated under reduced pressure.
The crude residue was purified by flash column chromatography using
ethyl acetate as eluent to afford 11 (2.27 g, 81%) as an R/β (81:19)
mixture. R-anomer: Rf 0.17 (ethyl acetate); 1H NMR (400 MHz,
CDCl3) δ 5.89ꢀ5.74 (m, 1 H), 5.08ꢀ4.92 (m, 2 H), 4.83 (d, J = 3.3
Hz, 1 H), 3.83ꢀ3.42 (m, 6 H), 2.18ꢀ2.06 (m, 2 H), 1.80ꢀ1.66 (m,
2 H), 1.26 (d, J = 6.6 Hz, 3 H); 13C NMR (75 MHz, CD3OD) δ 138.0,
115.0, 98.7, 72.1, 71.3, 69.0, 67.6, 66.0, 30.3, 28.7, 16.2; HR-ESI-MS m/z
Calcd for C11H20O5 255.1208 [M + Na]+; Found 255.1206.
4-Penten-1-yl 3,4-Cyclic Sulfite-r-D-fucopyranoside (12).
A mixture of 4-pentenyl D-fucopyranoside (1.6 g, 6.9 mmol) and dibutyl
oxide (1.88 g, 7.6 mmol) was refluxed in dry MeOH (40 mL) under
stirring for 5 h. The cleared reaction mixture was then concentrated
under reduced pressure for 2 h and then diluted with CH2Cl2 (20 mL).
Thionyl chloride (505 μL, 6.9 mmol) was next added dropwise to the
reaction vessel cooled at 0 °C. The reaction mixture was stirred for 20
min at rt before NaHCO3 was added and was then concentrated under
reduced pressure. The crude residue was purified by flash chromatog-
raphy using cyclohexane/ethyl acetate (8:2) as eluent to give compound
12 (1.63 g, 85%). Rf 0.49 (cyclohexane/ethyl acetate 7:3); major isomer:
1H NMR (400 MHz, CDCl3) δ 5.89ꢀ5.76 (m, 1 H, H-10), 5.10ꢀ5.00
(m, 2 H, H-11), 4.91ꢀ4.85 (m, 2 H), 4.82 (d, J = 3.9 Hz,1 H), 4.40ꢀ4.29
(m, 1 H), 3.82ꢀ3.73 (m, 2 H), 3.63 (br s, 1 H), 3.56ꢀ3.47 (m, 2 H),
2.20ꢀ2.10 (m, 2 H), 1.81ꢀ1.69 (m, 2 H), 1.42 (d, J = 6.6 Hz, 3 H); 13C
NMR (75 MHz, CDCl3) δ 137.8, 115.2, 97.6, 81.8, 78.3, 69.7, 68.1, 62.1,
30.3, 28.5, 16.3; HR-ESI-MS m/z Calcd for C11H18O6S 301.0722 [M +
Na]+; Found 301.0718.
4-Penten-1-yl 3,4-Cyclic Sulfate-r-D-fucopyranoside (13).
Sulfuryl chloride (1 M in CH2Cl2, 5.2 mL, 5.2 mmol) was added
dropwise at ꢀ10 °C to a mixture of 4-pentenyl D-fucopyranoside (600
mg, 2.6 mmol) and Et3N (1.44 mL, 10.8 mmol) in dry CH2Cl2 (20 mL)
under Ar. The reaction mixture was stirred at rt overnight, diluted with
CH2Cl2, and successively washed with H2O, saturated aqueous NaH-
CO3, and brine. The organic layer was dried (Na2SO4), filtered, and
concentrated under reduce pressure. The crude residue was purified by
flash chromatography using cyclohexane/ethyl acetate (8:2) and then
ethyl acetate as eluent to give compound 13 (319 mg, 42%) and then 12
(300 mg). Rf 0.68 (cyclohexane/ethyl acetate 5:5); [R]D +135.2 (c 1.0,
CHCl3); 1H NMR (400 MHz, CDCl3) δ 5.88ꢀ5.72 (m, 1 H),
5.07ꢀ5.80 (m, 5 H), 4.22ꢀ4.12 (m, 2 H), 3.77ꢀ3.70 (m, 1 H),
3.8ꢀ3.73 (m, 1 H), 2.96 (br s, 1 H), 3.56ꢀ3.47 (m, 2 H), 2.18ꢀ2.10
(m, 2 H), 1.78ꢀ1.69 (m, 2 H), 1.38 (d, J = 6.6 Hz, 3 H); 13C NMR
1
(cyclohexane:EtOAc 5:5) 0.26; [R]D + 4 (c 2.7, CHCl3). H NMR
(300 MHz, CDCl3) δ 7.39ꢀ7.29 (m, 5 H), 5.48 (br s, 1 H), 5.14 (s, 2
H), 4.63 (d, J = 7.8 Hz, 1 H), 4.17 (dd, J = 3.8 and 3.7 Hz, 1 H),
3.94ꢀ3.87 (m, 2 H), 3.76ꢀ3.80 (m, 1 H), 3.53 (s, 3 H), 3.59ꢀ3.51 (m,
1 H), 3.49ꢀ3.41 (m, 2 H), 3.46 (dd, J = 7.8 and 3.8 Hz, 1 H), 1.24 (d, J =
6.6 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ 156.4, 136.6, 128.0, 128.1,
101.3, 77.5, 71.0, 69.6, 68.9, 66.7, 62.3, 41.2, 15.7; HR-ESIMS: m/z
Calcd for C17H24N4O6 [M + H]+: 381.1774. Found 381.1782.
β-Hydroxyisovaleric Acid Succinimidyl Ester (8). To a solu-
tion of β-hydroxyisovaleric acid (1.0 g, 9.8 mmol) in CH2Cl2 (10 mL)
were added N-hydroxysuccinimide (1.1 g, 9.8 mmol) and EDC (1.9 g,
9.8 mmol). The reaction mixture was stirred at rt for 2 h and was then
concentrated in vacuo. The residue was then purified by flash chroma-
tography using cyclohexane/ethyl acetate (5:5) as eluent to provide 8
(1.6 g, 77%) as a white solid. Rf 0.24 (cyclohexane/ethyl acetate 1:1); 1H
NMR (300 MHz, CDCl3) δ 3.21 (s, 1 H), 2.63 (br s, 4 H), 2.57 (s, 2 H),
1.18 (s, 6 H); 13C NMR (75 MHz, CDCl3) δ 169.9 (2 ꢁ C), 166.4, 69.2,
44.5, 28.9 (2 C), 25.4 (2 C).
2-[(N-Benzyloxycarbonyl)amino]ethyl 4,6-Dideoxy-4-(3-
hydroxy-3-methylbutanamido)-2-O-methyl-β-D-glucopyra-
noside (9). To a solution of 6a (240 mg, 0.6 mmol) in a mixture of dry
CH2Cl2 (9 mL) and EtOH (42 mL) were added sodium borohydride
(45 mg, 1.2 mmol) and a catalytic amount of NiCl2 6H2O. The reaction
3
mixture was stirred at rt for 1 h and was concentrated in vacuo. The
residue was dissolved in CH2Cl2 (200 mL). The organic layer was
washed with water (2 ꢁ 100 mL) and brine (100 mL), dried over
Na2SO4, filtered, and concentrated in vacuo to provide 2-[(N-benzylox-
ycarbonyl)amino]ethanol 4-amino-4,6-dideoxy-2-O-methyl-β-D-gluco-
pyranoside which was used in the next step without purification. The
crude was dissolved in dry CH3CN (10 mL), and 8 (30 mg, 0.5 mmol)
and DIEA (297 μL, 1.2 mmol) were added. The reaction mixture was
stirred under argon at rt for 4 h and was then concentrated under
reduced pressure. The residue was purified by flash chromatography
using ethyl acetate/MeOH (95:5) as eluent to provide 9 (272 mg,
quantitative over two steps) as a white solid. Rf 0.14 (cyclohexane/ethyl
acetate 1:9); [R]D +17 (c 1.0, CHCl3) [lit.13 [R]D +16 (c 0.13, CHCl3)];
1H NMR (300 MHz, CDCl3) δ 7.38ꢀ7.30 (m, 5 H), 6.63 (d, J = 8.5 Hz,
1 H), 5.55ꢀ5.47 (m, 1 H), 5.12 (s, 2 H), 4.29 (d, J = 7.9 Hz, 1 H),
3.92ꢀ3.63 (m, 3 H), 3.59 (s, 3 H), 3.56ꢀ3.41 (m, 4 H), 3.03 (dd, J = 7.9
and 8.8 Hz, 1 H), 2.41 (s, 2 H), 1.32 (s, 3 H), 1.31 (s, 3 H), 1.27 (s, 3 H,
J = 6.1 Hz, 1 H); 13C NMR (75 MHz, CDCl3) δ 173.3, 156.5,
136.5ꢀ128.1 (6 C), 103.2, 83.8, 74.1, 70.8, 70.0, 69.3, 66.7, 60.8, 57.0,
48.6, 41.2, 29.8, 29.2, 18.0; HR-ESI-MS m/z Calcd for C22H35N2O8
455.2393 [M + H]+; Found 455.2405 [M + H]+.
5992
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
(75 MHz, CDCl3) δ 137.8, 115.2, 97.8, 84.8, 82.8, 68.4, 67.7, 62.3, 30.1,
28.3, 15.9; HR-ESI-MS m/z Calcd for C11H18O7S 317.0671 [M + Na]+;
Found 317.0683.
(d, J = 3.6 Hz, 1 H), 4.51 (dd, J = 3.6 and 8.6 Hz, 1 H), 4.17 (dq, J = 2.4
and 6.6 Hz, 1 H), 3.24 (s, 3 H), 1.98 (s, 3 H), 1.28 (d, J = 6.6 Hz, 3 H);
13C NMR (75 MHz, CDCl3) δ 169.7, 96.3, 78.3, 77.9, 71.0, 61.2, 55.2,
20.2, 15.8; HR-ESIMS: m/z Calcd for C9H14NaO7S [M + Na+]:
289.0358. Found 289.0344.
Methyl 2-O-Acetyl-3,4-O-cyclic Sulfate-R-D-fucopyrano-
side (20). To compound 18 (1.85 g, 6.9 mmol) was added a cold
solution of CCl4 (15 mL) and CH3CN (15 mL). The mixture was
4-Penten-1-yl 4-Azido-4,6-dideoxy-r-D-glucopyranoside
(14). A mixture of 13 (250 mg, 0.85 mmol) and NaN3 (110 mg, 1.7
mmol) in dry DMF (2 mL) was stirred for 1.5 h at 50 °C. The solvent
was then removed in vacuo. The residue was suspended in dry THF
(4 mL), concd H2SO4 (45 μL, 0.85 mmol) and water (16 μL, 0.85
mmol) were added, and the mixture was stirred at rt for 20 min. The
reaction mixture was then quenched by sodium bicarbonate in excess
and stirred for 20 min. The mixture was then concentrated under
vacuum, and the residue was purified by flash chromatography using
cyclohexane/ethyl acetate (7.5:2.5 then 6:4) as eluent to give 14
(160 mg, 88%) as a white oil. Rf 0.28 (cyclohexane/ethyl acetate 7:3);
[R]D +176.4 (c 1, CHCl3). 1H NMR (300 MHz, CDCl3) δ 5.89ꢀ5.76
(m, 1 H), 5.0.9ꢀ4.99 (m, 2 H), 4.82 (d, J = 3.8 Hz, 1 H), 3.82ꢀ3.68 (m,
2 H), 3.66ꢀ3.55 (m, 2 H), 3.51ꢀ344 (m, 1 H), 3.05 (t, J = 9.7 Hz, 1 H),
2.81 (br s, 1 H), 2.20ꢀ2.09 (m, 2 H), 1.79ꢀ1.68 (m, 2 H), 1.31 (d, J =
6.2 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ 137.9, 115.2, 98.0, 73.5,
72.7, 67.7 (2 C-4), 66.3, 30.3, 28.6, 18.2; HR-ESIMS: m/z Calcd for
C11H19N3O4 [M + Na]+: 280.1273. Found 280.1286.
Methyl 3,4-Cyclic Sulfite-r-D-fucopyranoside (16). To a
solution of methyl D-fucopyranoside 15 (2.5 g, 14.2 mmol) in dry
MeOH (75 mL) was added dibutyltin oxide (3.5 g, 14.2 mmol). The
mixture was heated to reflux under inert atmosphere for 6 h and was then
evaporated to dryness. The residue was dried under vacuum for 2 h and
was then dissolved in dry CH2Cl2 (100 mL). Thionyl chloride (1.1 mL,
14.2 mmol) diluted in CH2Cl2 (10 mL) was added dropwise at 0 °C.
The reaction mixture was stirred for 1 h under inert atmosphere at rt and
was evaporated in vacuo. The crude residue was purified by flash
chromatography using cyclohexane/ethyl acetate (5:5) as eluent to give
compound 16 (2.7 g, 86%). Rf 0.48 (cyclohexane/ethyl acetate 1:1); 1H
NMR (300 MHz, CDCl3) (major isomer) δ 4.82 (dd, J = 7.7 and 7.6 Hz,
1 H), 4.79 (dd, J = 7.6 and 2.2 Hz, 1 H), 4.63 (d, J = 3.7 Hz, 1 H), 3.24
(dq, 1 H, J = 2.2 and 6.5 Hz, 1 H), 3.52ꢀ3.48 (m, 1 H), 3.37 (s, 3 H),
3.30 (d, J = 7.3 Hz, 1 H), 1.35 (d, J = 6.5 Hz, 3 H); 13C NMR (75 MHz,
CDCl3) δ 99.0, 82.0, 78.3, 69.9, 61.7, 55.8, 16.3; HR-ESIMS: m/z Calcd
for C7H12O6S [M + Na]+: 247.0252. Found 247.0250.
Methyl 3,4-Cyclic Sulfite-2-O-methyl-R-D-fucopyranoside
(17). Alcohol 16 (943 mg, 4.21 mmol) was dissolved in dry CH2Cl2
(10 mL), and silver(I) oxide (2.44 g, 10.5 mmol) was added. The
reaction mixture was stirred at rt for 1 h. Iodomethane (2.62 mL,
42.1 mmol) was then added dropwise, and the reaction mixture was
stirred at rt for 5 d. Silver(I) oxide was filtered through a Celite pad, and
the filtrate was concentrated. The residue was purifiedbyflash chromatog-
raphy using cyclohexane/ethyl acetate (7:3) as eluent to give 17 (824
mg, 82%). Rf 0.52 (cyclohexane/ethyl acetate 1:1); 1H NMR (300 MHz,
CDCl3) (major isomer) δ 4.85ꢀ4.65 (m, 3 H), 4.22ꢀ4.15 (m, 1 H),
3.40 (s, 3 H), 3.31 (s, 3 H), 3.08 (dd, J = 3.1 and 8.1 Hz, 1 H), 1.30 (d, J =
6.7 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ 97.1, 81.3, 78.6, 78.0, 61.3,
58.7, 55.6, 16.2; HR-ESIMS: m/z Calcd for C8H14O6S [M + Na]+:
261.0419. Found 261.0409.
Methyl 2-O-Acetyl-3,4-cyclic Sulfite-R-D-fucopyranoside
(18). To a solution of compound 16 (2.4 g, 10.7 mmol) in CH2Cl2
(50 mL) at 0 °C were successively added Ac2O (3.0 mL, 32.1 mmol),
Et3N (1.52 mL, 10.7 mmol), and DMAP (144 mg, 1.07 mmol). The
reaction mixture was warmed up to rt and was stirred for 2 h. The
mixture was then diluted in CH2Cl2 and was washed by saturated aq
KHSO4, saturated aq NaHCO3, and water. The organic phase was then
dried over Na2SO4, filtered, and concentrated in vacuo. The residue was
then purified by flash chromatography using cyclohexane/ethyl acetate
(8:2) as eluent to give acetate 18 (2.56 g, 90%) as a white solid. Rf 0.72
(cyclohexane/ethyl acetate 4:6); 1H NMR (300 MHz, CDCl3) δ 4.88
(dd, J = 8.6 and 5.1 Hz, 1 H), 4.76 (dd, J = 5.2 and 2.4 Hz, 1 H), 4.67
cooled to 0 °C, and cold water was added (20 mL). RuCl3 H2O (10 mg,
3
0.7 mmol) and NaIO4 (2.8 g, 13.8 mmol) were added in one portion,
and the reaction mixture was stirred vigorously at 0 °C. After the mixture
was stirred for 2 h at this temperature, diethyl ether was added and the
layers were separated. The aqueous layer was extracted with diethyl
ether, and the combined organic layers were washed with brine, dried
over MgSO4, filtered, and concentrated under vacuum to give crude
sulfate 20. An aliquot of this material was purified for characterization by
flash chromatography using cyclohexane/ethyl acetate (8:2) as eluent. Rf
0.57 (cyclohexane/ethyl acetate 6:4); [R]D = +129.6 (c 1, CHCl3); 1H
NMR (300 MHz, CDCl3) δ 5.25 (dd, J = 3.5 and 8.4 Hz, 1 H), 5.08 (dd,
J = 8.4 and 5.0 Hz, 1 H), 5.06 (dd, J = 5.0 and 2.0 Hz, 1 H), 5.00 (d, J = 3.5
Hz, 1 H), 4.20 (dq, J = 2.0 and 6.8 Hz, 1 H), 3.41 (s, 3 H), 2.17 (s, 3 H),
1.43 (d, J = 6.8 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ 169.8, 96.6,
82.3, 81.0, 69.3, 61.9, 56.0, 20.7, 15.8; HR-ESIMS: m/z Calcd for
C9H14O8S [M + Na]+: 305.0296. Found 305.0307.
Methyl 4-Azido-4,6-dideoxy-2-O-methyl-R-D-glucopyra-
noside (21). To cyclic sulfite 17 (800 mg, 3.36 mmol) was added a
cold solution of CCl4 (10 mL) and CH3CN (10 mL). The mixture was
cooled to 0 °C, and cold water was added (15 mL). RuCl3 H2O (10.7
3
mg, 0.05 mmol) and NaIO4 (1.44 g, 6.72 mmol) were added in one
portion, and the reaction mixture was stirred vigorously at 0 °C. After the
mixture was stirred for 2 h at this temperature, diethyl ether was added
and the layers were separated. The aqueous layer was extracted with
diethyl ether, and the combined organic layers were washed with brine,
dried over MgSO4, filtered, and concentrated under vacuum to give
sulfate 19. This material is used in the next step without any further
purification. A mixture of crude 19 and NaN3 (437 mg, 6.72 mmol) in
dry DMF (8 mL) was stirred for 2 h at 50 °C. The solvent was then
removed in vacuo. The residue was suspended in dry THF (5 mL),
concd H2SO4 (176 μL, 3.36 mmol) and water (62 μL, 3.36 mmol) were
added, and the mixture was stirred at rt for 1 h. The reaction mixture was
then quenched by NaHCO3 in excess and stirred for 20 min. The
mixture was then concentrated under vacuum, and the residue was
purified by flash chromatography using cyclohexane/ethyl acetate (6:4)
as eluent to give azide 21 (592 mg, 81% over two steps) as a white solid.
Rf 0.38 (cyclohexane/ethyl acetate 1:1); [R]D +164.5 (c 1, CHCl3). 1H
NMR (300 MHz, CDCl3) δ 4.82 (d, J = 3.5 Hz, 1 H), 3.81 (dt, J = 9.5
and 3.3 Hz, 1 H, H-3), 3.69 (d, J = 3.3 Hz, 1 H), 3.50ꢀ3.42 (m, 1 H),
3.41 (s, 3 H), 3.30 (s, 3 H), 3.12 (dd, J = 3.5 and 9.5 Hz, 1 H), 2.97 (t, J =
9.5 Hz, 1 H), 1.20 (d, J = 6.4 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ
96.7, 81.4, 71.5, 67.8, 65.7, 58.2, 55.1, 18.2; HR-ESIMS: m/z Calcd for
C8H15N3O4 [M + Na]+: 240.0963. Found 240.0960.
Methyl 2-O-Acetyl-4-azido-4,6-dideoxy-R-D-glucopyra-
noside (22). To crude compound 20 in dry DMF (20 mL) was added
NaN3 (897 mg, 13.8 mmol). The reaction mixture was stirred for
2 h at 50 °C. The solvent was then removed in vacuo. The residue was
suspended in dry THF (15 mL), H2SO4 (350 μL) and water (120 μL)
were added, and the mixture was stirred at rt for 1 h. The reaction
mixture was then quenched by NaHCO3 in excess and stirred for 20 min.
The mixture was then concentrated in vacuo, and the residue was
purified by flash chromatography using cyclohexane/ethyl acetate (6:4)
as eluent to give azide 22 (1.25 g, 74% over two steps) as a white solid. Rf
0.68 (cyclohexane/ethyl acetate 4:6); [R]D = +152.6 (c 0.5, CHCl3); 1H
NMR (300 MHz, CDCl3) δ 4.82 (d, J = 3.5 Hz, 1 H), 4.70 (dd, J = 3.5
and 9.9 Hz, 1 H), 3.96 (br t, J = 10.0 Hz, 1 H), 3.58 (dq, J = 6.2 and
5993
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
9.9 Hz, 1H), 3.38 (s, 3 H), 3.37 (br s, 1 H), 3.11 (t, J = 9.9 Hz, 1 H), 2.14
(s, 3 H), 1.30 (d, J = 6.2 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ 171.1,
96.8, 76.7, 70.3, 68.4, 65.8, 55.2, 20.9, 18.1; HR-ESIMS: m/z Calcd for
C9H15N3O5 [M + Na]+: 268.0909. Found 268.0915.
161.3 (CR and Cβ), 138.0 (CR and Cβ),128.6 (2 CR), 128.4 (2 Cβ),
128.2 (2 CR), 128.0 (2 Cβ), 127.9 (CR and Cβ), 97.9 (Cβ), 93.5 (CR),
83.3 (Cβ), 82.7 (Cβ), 81.8 (CR), 79.0 (CR), 77.6 (CR and Cβ), 75.4
(Cβ), 75.6 (CR), 71.5 (Cβ), 69.0 (CR), 67.2 (CR and Cβ), 60.9 (Cβ),
58.8 (CR), 18.6 (CR), 18.5 (Cβ).
Methyl 4-Azido-3-O-benzyl-4,6-dideoxy-2-O-methyl-R-D-
glucopyranoside (23). To a solution of alcohol 21 (460 mg, 2.13
mmol) in dry THF (5 mL) was added NaH (110 mg 6% in oil, 2.77
mmol) under Ar at 0 °C. After a period of 10 min, BnBr (306 μL, 4.26
mmol) was added and the reaction mixture stirred overnight at rt. The
reaction mixture was then quenched by aqueous saturated NH4Cl in
excess and stirred for 2 min. The mixture was then concentrated under
vacuum, and the residue was purified by flash chromatography using
cyclohexane/ethyl acetate (1:0 to 8:2) as eluent to give compound 23
(633 mg, 96%) as an oil. Rf 0.38 (cyclohexane/ethyl acetate 9:1);
[R]D +180.6 (c 1, CHCl3). 1H NMR (300 MHz, CDCl3) δ 7.46ꢀ7.27
(m, 5 H), 4.92 (d, J = 10.7 Hz, 1 H), 4.80 (d, J = 10.7 Hz, 1 H), 4.80
(d, J = 3.5 Hz, 1 H), 3.79 (t, J = 9.6 Hz, 1 H), 3.65ꢀ3.52 (m, 1 H), 3.52
(s, 3 H), 3.42 (s, 3 H), 3.35 (dd, J = 3.5 and 9.6 Hz, 1 H), 3.11 (t, J =
9.6 Hz, 1 H), 1.32 (d, J = 6.2 Hz, 3 H); 13C NMR (75 MHz, CDCl3)
δ 138.2, 128.4 (2 C), 128.3 (2 C), 127.8, 97.3, 82.4, 79.8, 75.4, 67.9, 65.9,
58.9, 55.2, 18.4; HR-ESIMS: m/z Calcd for C15H21N3O4 [M + Na]+:
330.1418. Found 330.1430.
1-Acetyl-4-azido-3-O-benzyl-4,6-dideoxy-2-O-methyl-D-
glucopyranose (24). A solution of methyl glycoside 23 (600 mg, 1.95
mmol) in Ac2O/AcOH/H2SO4 (2.7:0.472:0.011 mL) was stirred at rt
for 1.5 h. The reaction mixture was then quenched by NaHCO3 in
excess, diluted in H2O, and extracted with ethyl acetate. The organic
layer was washed with brine, dried (Na2SO4), filtered, and concentrated
in vacuo. The crude residue was purified by flash chromatography using
cyclohexane/ethyl acetate (9:1) as eluent to give compound 24 (570 mg,
87%) in a 79:21 R/β mixture as an oil. Rf 0.59 (cyclohexane/ethyl
acetate 8:2); 1H NMR (300 MHz, CDCl3) δ 7.46ꢀ7.27 (m, 5 H), 6.35
(d, J = 3.6 Hz, 1 HR), 5.53 (d, J = 8.2 Hz, 1 Hβ), 4.95 (d, J = 10.8 Hz, 1
HR), 4.91 (d, J = 10.8 Hz, 1 Hβ), 4.84 (d, J = 10.8 Hz, 1 Hβ), 4.82 (d, J =
10.8 Hz, 1 HR), 3.76 (t, J = 9.5 Hz, 1 HR), 3.74ꢀ3.65 (m, 1 HR), 3.57 (s,
3 H, CH3β), 3.51 (t, J = 9.4 Hz, 1 Hβ), 3.46 (s, 3 HR), 3.42 (dd, J = 3.6
and 9.5 Hz, 1 HR), 3.32ꢀ3.41 (m, 1 Hβ), 3.29 (dd, J = 8.2 and 9.4 Hz, 1
Hβ), 3.18 (t, J = 9.5 Hz, 1 HR), 3.16 (t, J = 9.4 Hz, 1 Hβ), 1.34 (d, J = 6.2
Hz, 3 Hβ), 1.34 (d, J = 6.2 Hz, 3 HR); 13C NMR (75 MHz, CDCl3) δ
169.2 (CR), 169.1 (Cβ), 138.2 (CR), 138.0 (Cβ), 128.4 (2 CR), 128.3
(2 Cβ), 128.2 (2 CR), 128.2 (2 Cβ), 128.0 (Cβ), 127.9 (CR), 93.8
(Cβ), 89.1 (CR), 83.1 (Cβ), 82.7 (Cβ), 81.4 (CR), 79.5 (CR), 75.5
(Cβ), 75.4 (CR), 71.3 (Cβ), 68.5 (CR), 67.2 (CR), 60.6 (Cβ), 58.8
(CR), 20.9 (CR and Cβ), 18.5 (CR), 18.3 (Cβ); HR-ESIMS: m/z Calcd
for C16H21N3O5 [M + Na]+: 358.1389. Found 358.1379.
4-Azido-3-O-benzyl-4,6-dideoxy-2-O-methyl-D-glucopyr-
anosyl Trichloroacetimidate (25).8. To a solution of 24 (570 mg,
1.70 mmol) in MeOH (5 mL) was added sodium methoxide (110 mg,
2.04 mmol) at rt. The reaction mixture was stirred for 20 min and then
concentrated under reduced pressure. The crude residue was dissolved
in CH2Cl2 (5.2 mL). To this solution were added trichloroacetonitrile
(3.61 mL, 37.4 mmol) and DBU (54 μL, 0.39 mmol) dropwise at 0 °C.
The mixture was then strirred at rt for 2 h and then concentrated in
vacuo. The residue was purified by flash chromatography on silica gel
using 2% Et3N in cyclohexane/ethyl acetate (9:1) as eluent to give 25
(558 mg, 82%) as a pale yellow oil as a mixture of R/β (63/37) anomers.
Rf 0.79 (cyclohexane/ethyl acetate 7:3); ESI-MS: m/z 459 [M + Na]+;
1H NMR (300 MHz, CDCl3) δ 8.75 (s, 1 Hβ), 8.68 (s, 1 HR),
7.47ꢀ7.28 (m, 10 H), 6.52 (d, J = 3.3 Hz, 1 HR), 5.70 (d, J1β,2β = 8.2
Hz, 1 Hβ), 4.99 (d, J = 10.7 Hz, 1 HR), 4.97 (d, J = 10.8 Hz, 1 Hβ), 4.89
(d, J = 10.8 Hz, 1 Hβ), 4.87 (d, J = 10.7 Hz, 1 HR), 3.89 (t, J = 9.5 Hz, 1
H-3R), 3.74ꢀ3.65 (m, 1 HR), 3.68 (s, 3 Hβ), 3.61ꢀ3.39 (m, 4 H, 1 HR,
3 Hβ), 3.25 (t, J = 9.3 Hz, 1 Hβ), 3.24 (t, J = 9.5 Hz, 1 HR), 1.41 (d, J =
6.4 Hz, 3 Hβ), 1.37 (d, J = 6.4 Hz, 3 HR); 13C NMR (75 MHz, CDCl3) δ
Methyl 2-O-Acetyl-4-azido-3-O-benzyl-4,6-dideoxy-R-D-
glucopyranoside (26). To a solution of alcohol 22 (500 mg, 2.04
mmol) and benzyl trichloroacetimidate (570 μL, 3.06 mmol) in a
mixture of dry cyclohexane/CH2Cl2 (2:1) (21 mL) was added trifluor-
omethanesulfonic acid (100 μL) under Ar at rt. The reaction mixture
was stirred for 2.5 h at rt. The reaction mixture was then filtered through
a Celite pad and the filtrate washed with 5% aq NaHCO3 and brine. The
organic layer was dried (Na2SO4), filtered, and concentrated under
reduced pressure, and the resulting crude residue was purified by flash
chromatography using cyclohexane/ethyl acetate (9:1) as eluent to give
compound 26 (478 mg, 70%) as an oil. Rf 0.64 (cyclohexane/ethyl
acetate 7:3); [R]D +148.3 (c 1, CHCl3); 1H NMR (300 MHz, CDCl3) δ
7.40ꢀ7.21 (m, 5 H), 4.91ꢀ4.85 (m, 3 H), 4.77 (d, J = 11.2 Hz, 1 H),
3.91 (t, J = 9.4 Hz, 1 H-3), 3.65ꢀ3.52 (m, 1 H), 3.38 (s, 3 H), 3.35 (dd,
J = 3.5 and 9.4 Hz, 1 H), 3.21 (t, J = 9.4 Hz, 1 H), 2.06 (s, 3 H), 1.32
(d, J = 6.3 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ 170.1, 138.0, 128.4
(2 C), 127.8 (4 C), 97.0, 78.3, 75.4, 73.7, 68.0, 65.9, 55.2, 20.7, 16.0;
HR-ESIMS: m/z Calcd for C16H21N3O5 [M + Na]+: 358.1374. Found
358.1379.
Methyl 2-O-Acetyl-4-azido-3-O-benzoyl-4,6-dideoxy-R-D-
glucopyranoside (27). To a solution of compound 22 (612 mg, 2.55
mmol) in pyridine (25 mL) at 0 °C was added benzoyl chloride
(0.35 mL, 5.10 mmol). The reaction mixture was stirred at rt for 12 h
and was then quenched by addition of MeOH. The solvent was
evaporated in vacuo, and the residue was dissolved in EtOAc and
washed with brine. The organic phase was dried (Na2SO4), filtered,
and concentrated in vacuo. The crude residue was purified by flash
chromatography using cyclohexane/ethyl acetate (6:4) as eluent to give
ester 27 (890 mg, quantitative) as a white solid. Rf 0.82 (cyclohexane/
ethyl acetate 4:6); [R]D = +154 (c 0.4, CHCl3); 1H NMR (300 MHz,
CDCl3) δ 8.11ꢀ7.26 (m, 5 H), 5.66 (t, J = 10.0 Hz, 1 H), 5.00 (dd, J =
3.5 and 10.0 Hz, 1 H), 4.84 (d, J = 3.4 Hz, 1 H), 3.73 (dq, J = 10.0 and 6.2
Hz, 1 H), 3.34 (s, 3 H, OCH3), 3.31 (t, J = 10.0 Hz, 1 H), 1.88 (s, 3 H),
1.32 (d, J = 6.2 Hz, 3 H); 13C NMR (75 MHz, CDCl3) δ 170.3, 165.4,
133.4, 129.8, 128.5 (6 C), 96.9, 71.2, 71.0, 66.3, 65.9, 55.2, 20.6, 18.1;
HR-ESIMS: m/z Calcd for C16H19N3O6 [M + Na]+: 372,1172. Found
372.0956.
4-Azido-3-O-benzyl-1,2-di-O-acetyl-4,6-dideoxy-D-gluco-
pyranoside (28). A solution of methyl glycoside 26 (360 mg, 1.07
mmol) in Ac2O/AcOH/H2SO4 (1.41:0.246:0.016 mL) was stirred at rt
for 1.5 h. ant then was neutralized upon addition of NaHCO3 at 0 °C.
The reaction mixture was diluted with ethyl acetate and washed with
water and brine. The organic layer was dried (Na2SO4), filtered, and
purified by by flash chromatography using cyclohexane/ethyl acetate
(9:1) as eluent to give ester 28 (316 mg, 78%) as a white solid. Rf 0.80
(cyclohexane/ethyl acetate 7:3); R anomer 1H NMR (300 MHz,
CDCl3) δ 7.38ꢀ7.25 (m, 5 H), 6.26 (d, J = 3.7 Hz, 1 H), 5.04 (dd,
J = 3.7 and 9.8 Hz, 1 H-2), 4.89 (d, J = 11.2 Hz, 1 H), 4.77 (d, J = 11.2 Hz,
1 H), 3.88 (t, J = 9.8 Hz, 1 H), 3.74 (dq, J = 9.8 and 6.2 Hz, 1 H), 3.24
(t, J = 9.8 Hz, 1 H), 2.15 (s, 3 H), 1.99 (s, 3 H), 1.35 (d, J = 6.2 Hz, 3 H);
13C NMR (75 MHz, CDCl3) δ 169.7, 169.0, 137.7, 128.5 (2 C), 128.2,
127.9 (2 C), 89.6, 78.0, 75.3, 72.0, 68.9, 67.4, 20.9, 20.6, 18.4; HR-ESIMS:
m/z Calcd for C17H21N3O6 [M + Na]+: 386.1337. Found 386.1328.
2-O-Acetyl-4-azido-3-O-benzyl-4,6-dideoxy-D-glucopyra-
nose (30). To a solution of compound 28 (242 mg, 0.67 mmol) in dry
THF (3 mL) was added benzylamine (80 μL, 0.73 mmol). The reaction
mixture was stirred at rt under inert atmosphere overnight and then
quenched with 1 N aq HCl. The solvent was evaporated under reduced
pressure, and the crude residue was purified by flash chromatography
5994
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
using cyclohexane/ethyl acetate (7:3) as eluent to provide compound 30
(180 mg, 84%) as a white solid. Rf 0.45 (cyclohexane/ethyl acetate 7:3);
1H NMR (300 MHz, CDCl3) δ 7.40ꢀ7.30 (m, 5 H), 5.38 (d, J = 3.6 Hz,
1 H), 4.87 (d, J = 11.2 Hz, 1 H), 4.86 (dd, J = 3.6 and 9.8 Hz, 1 H), 4.77
(d, J = 11.2 Hz, 1 H), 3.96 (t, 1 H, J = 9.8 Hz, 1 H), 3.94ꢀ3.85 (m, 1 H),
3.21 (t, 1 H, J = 9.8 Hz, 1 H), 2.08 (s, 3 H), 1.34 (d, J = 6.2 Hz, 3 H); 13C
NMR (75 MHz, CDCl3) δ 170.7, 137.7, 128.5 (2 C), 128.2, 127.9 (2 C),
90.3, 77.8, 75.4, 73.9, 68.0, 66.1, 20.9, 20.9, 18.4; HR-ESIMS: m/z Calcd
for C15H19N3O5 [M + Na]+: 344.1219. Found 344.1222.
was then strirred at rt for 2 h and then concentrated in vacuo. The
residue was purified by flash chromatography on silica gel using 2% Et3N
in cyclohexane/ethyl acetate (8:2) as eluent to give 33 (906 mg, 70%) as
a pale yellow oil as a mixture of R/β (15/1) anomers. Rf 0.55
1
(cyclohexane/ethyl acetate 7:3); ESI-MS m/z 501.0 [M + Na]+; H
NMR (300 MHz, CDCl3) δ (R isomer) 8.68 (s, 1 HR), 8.04ꢀ7.37 (m, 5
H) 6.50 (d, J = 3.7 Hz, 1 H), 5.79 (t, J = 10.1 Hz, 1 H), 5.24 (dd, J = 3.7
and 10.1 Hz,1 H), 4.01 (dq, J = 6.0 and 10.1 Hz, 1 H), 3.46 (t, J = 10.1
Hz, 1 H), 1.88 (s, 3 H), 1.40 (d, J = 6.2 Hz, 3 H); 13C NMR (75 MHz,
CDCl3) δ 170.0, 165.4, 160.9, 133.6 (2 C), 129.6 (2 C), 128.6 (2 C),
93.3, 71.9, 70.2, 69.1, 65.8, 20.4, 18.3.
2-O-Acetyl-4-azido-3-O-benzoyl-4,6-dideoxy-D-glucopyr-
anose (31).16 A solution of compound 27 (880 mg, 2.5 mmol) in
Ac2O/AcOH/H2SO4 (14 mL, 14:4:0.1) was stirred at rt for 12 h.
NaOAc trihydrate (300 mg) was then added and the solvent was
evaporated in vacuo. The residue was dissolved in ethyl acetate and
was washed with saturated aq NaHCO3 and brine. The organic phase
was then dried over Na2SO4, filtered, and concentrated in vacuo. The
crude residue 29 was used in the next step without any further
purification. Rf 0.41 (cyclohexane/ethyl acetate 4:6); ESIMS m/z
399.8 [M + Na]+. To a solution of crude residue 29 in dry THF
(5 mL) was added benzylamine (300 μL, 2.8 mmol). The reaction
mixture was stirred at rt under inert atmosphere for 12 h and then
quenched with 38% HCl. The solvent was evaporated under reduced
pressure, and the crude residue was purified by flash chromatography
using cyclohexane/ethyl acetate (8:2) as eluent to provide compound 31
(461 mg, 54% over two steps) as a mixture of anomers (R/β 60/40), as a
white solid. Rf 0.49 and 0.35 (cyclohexane/ethyl acetate 7:3); ESIMS m/
z 358.1 [M + Na]+; 1H NMR (300 MHz, CDCl3) δ 8.10ꢀ7.44 (m, 5 H),
5.74 (t, J = 10.0 Hz, 1 HR), 5.46ꢀ5.39 (m, 1 HR and 1 Hβ), 5.04 (dd, J =
3.6 and 10.0 Hz, 1 HR), 4.97 (dd, J = 8.2 Hz, J = 10.0 Hz, 1 Hβ), 4.76 (t,
J = 8.2 Hz, 1 Hβ), 4.08 (dq, J = 10.0 and 6.2 Hz, 1 HR), 3.75 (d, J =
8.2 Hz, 1 Hβ), 3.75 (dq, J = 10.0 and 6.2 Hz, 1 Hβ), 3.40 (t, J = 10.0 Hz,
1 HR), 3.34 (t, J = 10.0 Hz, 1 Hβ), 1.98 (s, 3 Hβ), 1.97 (s, 3 HR), 1.44
(d, J = 6.2 Hz, 3 Hβ), 1.37 (d, J = 6.2 Hz, 3 HR); 13C NMR (75 MHz,
CDCl3) δ 171.2 and 170.4 (CR and Cβ), 165.8 (CR and Cβ), 133.7,
133.5, 129.9, 128.6 (6 CR and 6 Cβ), 95.3 (Cβ), 90.5 (CR); 73.9 (Cβ),
73.4 (Cβ), 71.7 (CR), 71.3 (Cβ), 70.8 (CR), 66.5 (Cβ), 66.2 (2 CR),
20.8 (CR and Cβ), 18.5 (Cβ), 18.4 (CR).
2-O-Acetyl-4-azido-3-O-benzyl-4,6-dideoxy-D-glucopyra-
nosyl Trichloroacetimidate (32). To a solution of 30 (160 mg, 0.50
mmol) in CH2Cl2 (2 mL) were added trichloroacetonitrile (1.10 mL, 11
mmol) and DBU (17 μL, 0.12 mmol) dropwise at 0 °C. The mixture was
then strirred at rt for 2 h and then concentrated in vacuo. The residue
was purified by flash chromatography on silica gel using 2% Et3N in
cyclohexane/ethyl acetate (8:2) as eluent to give 32 (180 mg, 78%) as a
pale yellow oil as a mixture of R/β (70/30) anomers. Rf 0.60
(cyclohexane/ethyl acetate 7:3); 1H NMR (300 MHz, CDCl3) δ 8.72
(s, 1 Hβ), 8.66 (s, 1 HR), 7.40ꢀ7.23 (m, 10 H), 6.48 (d, J = 3.6 Hz, 1
HR), 5.75 (d, J = 8.3 Hz, 1 Hβ), 5.32 (dd, J = 8.3 and 9.5 Hz, 1 Hβ), 5.07
(dd, J = 3.6 and 9.8 Hz, 1 HR), 4.92 (d, J = 11.2 Hz, 1 HR), 4.77 (d, J =
11.6 Hz, 1 Hβ), 4.81 (d, J = 10.7 Hz, 1 HR), 4.77 (d, J = 10.8 Hz, 1 Hβ),
4.01 (t, J = 9.5 Hz, 1 H-3R), 3.91ꢀ3.80 (m, 1 HR), 3.68 (s, 3 Hβ),
3.56ꢀ3.47 (m, 1 Hβ), 3.35 (t, J = 9.5 Hz, 1 Hβ), 3.32 (t, J = 9.5 Hz, 1
HR), 1.99 and 1.98 (2 s, 3 HR and 3 Hβ), 1.45 (d, J = 6.2 Hz, 3 Hβ), 1.37
(d, J = 6.2 Hz, 3 HR); 13C NMR (75 MHz, CDCl3) δ 169.9 (CR), 169.0
(Cβ), 161.2 (Cβ), 160.8 (CR), 137.6 (CR), 137.5 (Cβ), 128.5ꢀ128.0
(5 CR and 5 Cβ), 95.8 (Cβ), 93.6 (CR), 81.1 (Cβ), 77.6 (CR and Cβ),
77.5 (CR), 75.3 (CR), 74.9 (Cβ), 73.1 (CR), 72.0 (Cβ), 71.9 (Cβ), 69.2
(CR), 67.3 (CR and Cβ), 20.8 (Cβ), 20.6 (CR), 18.5 (CR and Cβ);
HR-ESIMS: m/z Calcd for C17H19Cl3N4O5 [M + Na]+: 487.0316.
Found 487.0319.
2-[(N-Benzyloxycarbonyl)amino]ethyl L-Rhamnopyrano-
side (34). To a mixture of L-rhamnose (10.0 g, 61 mmol) and 2-[(N-
benzyloxycarbonyl)amino]ethanol (17.0 g, 102 mmol) in toluene
(100 mL) was added a catalytic amount of p-toluenesulfonic acid (200
mg, 1.2 mmol), and the mixture was heated to reflux overnight. The
reaction mixture was cooled, neutralized with Et3N, and then concen-
trated in vacuo. The residue was purified by flash chromatography on
silica gel using CH2Cl2ꢀMeOH (98:2) as eluent to give a 5/1 mixture of
N-(benzyloxycarbonyl)aminoethyl L-rhamnopyranoside 34 (12.8 g,
64%) as a 5/1 R/β anomeric mixture, as a pale yellow oil. Rf 0.22 (R)
and 0.29 (β) (CH2Cl2:MeOH 9:1); 1H NMR (300 MHz, MeOD) δ (R
isomer) 7.38ꢀ7.31 (m, 5 H), 5.10 (br s, 2 H), 4.71 (d, J = 1.8 Hz, 1 H),
3.85 (dd, J = 1.8 and 3.6 Hz, 1 H), 3.79ꢀ3.72 (m, 1 H), 3.70 (dd, J = 3.6
and 9.5 Hz, 1 H-3), 3.65ꢀ3.58 (m, 1 H), 3.54ꢀ3.47 (m, 1 H), 3.41 (t,
1H, J = 9.5 Hz, 1 H), 3.37ꢀ3.32 (m, 2 H), 1.28 (d, J = 6.2 Hz, 3 H); 13C
NMR (75 MHz, MeOD) δ (R isomer) 157.6, 136.9, 128.1, 127.6, 127.4,
100.3, 72.6, 71.1, 70.8, 68.5, 66.1, 66.0, 40.3, 16.7; HR-MS (ESI) m/z
Calcd for C16H23NO7 [M + Na]+: 364.1383. Found 364.1378.
2-[(N-Benzyloxycarbonyl)amino]ethyl 3-O-(3-Methoxy)-
benzyl-R-L-rhamnopyranoside (35). A suspension of com-
pound 34 (852 mg, 2.5 mmol) and dibutyltin oxide (622 mg,
2.5 mmol) were heated at relux in dry MeOH (26 mL) for 5 h, evapo-
rated under reduced pressure, and further dried in vacuo for 2 h. To the
crude residue diluted in dry DMF (7 mL) was added p-methoxybenzyl
bromide (420 μL, 3 mmol). After 5 h, the reaction mixture was
concentrated under reduced pressure, and the crude residue was
purified by flash chromatography on silica gel using cyclohexane/ethyl
acetate 4:6 to 3:7 as eluent to give compound 35 (600 mg, 54%). Rf 0.2
1
(cyclohexane/ethyl acetate 4:6); [R]D = ꢀ21.3 (c 0.5, MeOH); H
NMR (300 MHz, CDCl3) δ 7.37ꢀ7.31 (m, 5 H), 7.28 (d, J = 8.8 Hz,
2 H), 6.87 (d, J = 8.8 Hz, 2 H), 5.34 (br s, 1 H), 5.12 (br s, 2 H), 4.78
(br s, 1 H), 4.59ꢀ4.54 (d, 1 H, J = 11.2 Hz, 1 H), 4.50ꢀ4.49 (d, J =
11.2 Hz, 1 H), 3.95 (br s, 1 H), 3.78 (s, 3 H), 3.79ꢀ3.53 (m, 4 H),
3.53ꢀ3.30 (m, 3 H), 1.28 (d, J = 6.2 Hz, 3 H); 13C NMR (75 MHz,
CDCl3) δ 159.5, 156.5, 144.0 (2 C), 136.5, 129.9, 129.7 (2 C), 128.6
(2 C), 128.2 (2 C), 99.6, 79.4, 71.5 (2 C), 68.3, 67.9, 66.8, 66.7, 55.3,
40.8, 17.7; HR-MS (ESI) m/z Calcd for C24H31NO8 [M + Na]+:
484.1947. Found 484.1942.
2-[(N,N0-Benzyl-benzyloxycarbonyl)amino]ethyl 2,4-Di-
O-benzyl-3-O-(3-methoxy)benzyl-R-L-rhamnopyranoside (36).
To a solution of 35 (580 mg, 1.3 mmol) in DMF (20 mL) at 0 °C was
added NaH (60% dispersion in mineral oil, 301 mg, 7.6 mmol) followed
by dropwise addition of benzyl bromide (540 μL, 4.5 mmol). The
reaction mixture was stirred at rt for 2 h, and the excess of NaH was
neutralized by dropwise addition of MeOH (5 mL) at 0 °C. The mixture
was concentrated in vacuo, and the residue was purified by flash
chromatography using (cyclohexane/ethyl acetate 9:1) as eluent to give
compound 36 (610 mg, 64%) as a pale yellow oil and mixture of
conformers. Rf 0.33 (cyclohexane/ethyl acetate 8:2); [R]D = ꢀ15.6
(c 1.1, CHCl3); 1H NMR (300 MHz, CDCl3) δ 7.48ꢀ6.88 (m, 24 H),
5.26ꢀ5.23 (m, 2 H), 5.03 (d, J = 11.0 Hz, 41 H), 4.85ꢀ4.79 and
4.73ꢀ4.69 (m, 4 H), 4.65ꢀ4.47 (m, 4 H), 3.89ꢀ3.80 (m, 2 H), 3.78 (s, 3
H), 3.76ꢀ3.74 (m, 1 H), 3.72ꢀ3.64 (m, 2 H), 3.62ꢀ3.54 (m, 1 H),
2-O-Acetyl-4-azido-3-O-benzoyl-4,6-dideoxy-D-glucopyr-
anosyl Trichloroacetimidate (33).16 To a solution of 31 (923 mg,
2.7 mmol) in CH2Cl2 (5 mL) were added trichloroacetonitrile (5.4 mL,
54 mmol) and DBU (100 μL, 0.7 mmol) dropwise at 0 °C. The mixture
5995
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
3.52ꢀ3.35 (m, 2 H), 1.38ꢀ1.34 (m, 3 H); 13C NMR (75 MHz, CDCl3)
δ 156.3 and 156.0 (1 C), 159.0, 138.6, 138.3, 137.7, 136.5, 130.4, 129.4,
129.1, 128.4, 128.2, 127.8, 127.7, 127.5, 127.3, 127.2, 127.1, 113.7, 98.0
and 97.7 (1 C), 80.3, 79.2, 75.2, 74.9, 72.7, 71.5, 68.1, 67.2, 65.7 and 65.2
(1 C), 55.0, 51.6, and 51.4 (1 C), 46.7 and 45.7 (1 C), 17.9; HR-MS
(ESI) m/z Calcd for C45H49NO8 [M + Na]+: 754.3356. Found
754.3331.
4.75ꢀ4.39 (m, 6 H), 4.04ꢀ3.95 (m, 1 H), 3.80 (dd, J = 1.9 and 3.0 Hz, 1
H), 3.77ꢀ3.30 (m, 8 H), 3.13 (t, J = 9.6 Hz, 1 H), 3.25ꢀ3.10 (m, 1 H),
2.69 (br s, 1 H), 1.35ꢀ1.25 (m, 6 H); 13C NMR (75 MHz, CDCl3) δ
156.5 and 156.3 (1 C), 138.6, 138.1, 138.0, 137.8, 136.6, 128.7, 128.6,
128.5, 128.4, 128.3, 128.1, 128.0, 127.8, 127.6, 127.5, 127.3, 104.0, 98.7
and 98.5 (1 C), 82.3, 80.6, 80.1, 77.7, 75.7, 75.5, 74.9, 73.4, 70.8, 68.3,
67.4, 67.2, 65.8 and 65.6 (1 C), 51.6, 46.7 and 45.7 (1 C), 18.7 and 18.2
(1 C); HR-MS (ESI) m/z Calcd for C50H56N4O10 [M + Na]+:
895.3894. Found 895.3871.
2-[(N,N0-Benzyl-benzyloxycarbonyl)amino]ethyl 2,4-Di-
O-benzyl-R-L-rhamnopyranoside (37). To a solution of deriva-
tive 36 (610 mg, 0.83 mmol) in a mixture of CH2Cl2 (14 mL) and H2O
(1 mL) was added DDQ (216 mg, 1.91 mmol) at 0 °C. After the mixture
was stirred 30 min at this temperature, the reaction mixture was warmed
to rt and stirred overnight. The mixture was then diluted with CH2Cl2
and quenched with Na2CO3. The layers were separated, and the organic
phase was washed with satd aq Na2CO3, dried over Na2SO4, filtered, and
concentrated in vacuo. The residue was then purified by flash chroma-
tography on silica gel using (cyclohexane/ethyl acetate 8:2) as eluent to
provide alcohol 37 (350 mg, 69%) as a colorless oil (mixture of
conformers). Rf 0.52 (cyclohexane/ethyl acetate 7:3); [R]D = ꢀ4.8 (c
2-[(N,N0-Benzyl-benzyloxycarbonyl)amino]ethyl O-(4-Azido-
3-O-benzyl-4,6-dideoxy-2-O-methyl-R-D-glucopyranosyl)-
(1f3)-2,4-di-O-benzyl-R-L-rhamnopyranoside (40). To
a
solution of alcohol 39 (185 mg, 0.21 mmol) in DMF was added NaH
(60% dispersion in mineral oil, 12 mg, 0.31 mmol) at 0 °C, followed by
dropwise addition of MeI (44 μL, 0.72 mmol). The reaction mixture was
stirred at rt overnight, and the excess of NaH was neutralized by
dropwise addition of methanol (20 mL) at 0 °C. The mixture was then
evaporated to dryness, and the residue was purified by flash chroma-
tography on silica gel using cyclohexane/ethyl acetate (9:1) as eluent
to give compound 40 (118 mg, 62%) as a colorless oil (mixture of
conformers). Rf 0.56 (cyclohexane/ethyl acetate 8:2); [R]D = +2.7
(c 1.1, CHCl3); 1H NMR (300 MHz, CDCl3) δ 7.35ꢀ7.05 (m, 25 H),
5.08ꢀ5.06 (m, 2 H), 4.92 (d, J = 10.6 Hz, 1 H), 4.83 (d, J = 10.6 Hz,
1 H), 4.73 (d, J = 10.6 Hz, 2 H), 4.67ꢀ4.34 (m, 6 H), 3.98ꢀ3.90 (m,
1 H), 3.71 (dd, J = 1.8 and 3.1 Hz, 1 H), 3.58 (s, 3 H), 3.77ꢀ3.30 (m,
3 H), 3.49ꢀ3.20 (m, 4 H), 3.07 (t, J = 8.4 Hz, 1 H), 3.04ꢀ2.99 (m, 2 H),
1.22ꢀ1.14 (m, 6 H); 13C NMR (75 MHz, CDCl3) δ 156.5 and 156.2
(1 C), 137.8, 136.7, 128.7, 128.5, 128.4, 128.3, 128.0, 127.9, 127.6, 103.7,
98.8 and 98.7 (1 C), 84.9, 82.8, 80.8, 78.8, 78.6, 75.5, 75.0, 72.9, 70.3,
68.1, 67.8, 67.4, 66.0 and 65.8 (1 C), 60.9, 51.7 and 51.6 (1 C), 46.7 and
45.7 (1 C), 18.6, 18.0; HR-MS (ESI) m/z Calcd for C51H58N4O10 [M +
Na]+: 909.4051. Found 909.4058.
1
1.0, CHCl3); H NMR (300 MHz, CDCl3) δ 7.38ꢀ7.18 (m, 20 H),
5.21ꢀ5.19 (m, 2 H), 4.91 (d, J = 10.9 Hz, 1 H), 4.83 (br s, 0.5 H),
4.75ꢀ4.49 (m, 5.5 H), 3.92ꢀ3.89 (m, 1 H), 3.85ꢀ3.73 (m, 1 H),
3.73ꢀ3.51 (m, 2 H), 3.65 (dd, J = 1.5 and 3.7 Hz, 1 H), 3.51ꢀ3.34 (m, 2
H), 3.32 (t, 1 H, J = 9.2 Hz, 1 H), 2.24 (br s, 1 H), 1.37ꢀ1.23 (m, 3 H);
13C NMR (75 MHz, CDCl3) δ 156.6 and 156.4 (1 C), 138.6, 137.8,
136.7, 131.0, 128.5, 128.1, 128.0, 127.9, 127.8, 127.3, 97.2 and 96.8 (1
C), 82.3, 78.6, 75.2, 73.2 and 73.1 (1 C), 71.7, 67.4 (2 C), 66.0 and 65.5
(1 C), 51.8 and 51.7 (1 C), 46.8 and 46.0 (1 C), 18.1; HR-MS (ESI) m/z
Calcd for C37H41NO7 [M + Na]+: 634.2781. Found 634.2780.
2-[(N,N-Benzyl-benzyloxycarbonyl)amino]ethyl O-(2-O-Acetyl-
4-azido-3-O-benzyl-4,6-dideoxy-R-D-glucopyranosyl)-
(1f3)-2,4-di-O-benzyl-R-L-rhamnopyranoside (38). To
a
solution of trichloroacetimide 32 (230 mg, 0.49 mmol), alcohol 37
(253 mg, 0.41 mmol), and 4 Å molecular sieves (200 mg) in dry CH2Cl2
(10 mL) under inert atmosphere at ꢀ40 °C was added TMSOTf
(52 μL, 0.29 mmol). After the mixture was stirred 30 min at this
temperature, the reaction mixture was neutralized by Et3N and filtered.
The filtrate was washed with water, dried over Na2SO4, filtered, and
concentrated in vacuo. The residue was purified by flash chromatogra-
phy using cyclohexane/ethyl acetate (8:2) as eluent to give disaccharide
38 (257 mg, 68%) as a white powder (mixture of conformers). Rf 0.54
(cyclohexane/ethyl acetate 7:3); [R]D = ꢀ2.4 (c 0.9, CHCl3); 1H NMR
(300 MHz, CDCl3) δ 7.44ꢀ7.15 (m, 25 H), 5.24ꢀ5.21 (m, 2 H), 5.18
(dd, J = 7.9 and 9.5 Hz, 1 H), 4.90ꢀ4.83 (m, 3 H), 4.80ꢀ4.50 (m, 7 H),
4.10ꢀ4.01 (m, 1 H), 3.86ꢀ3.82 (m, 1 H), 3.82ꢀ3.17 (m, 7 H),
3.15ꢀ3.04 (m, 2 H), 1.86 (s, 3 H), 1.32ꢀ1.27 (m, 6 H); 13C NMR
(75 MHz, CDCl3) δ 169.2, 156.5, and 156.1 (1 C), 138.7, 138.3, 137.8,
137.7, 137.4, 136.6, 128.6, 128.5, 128.2, 128.1, 128.0, 127.8, 127.5, 127.2,
101.3, 98.8 and 98.7 (1 C), 81.4, 80.3, 79.5 and 79.4 (1 C), 78.0, 74.9
(2 C), 73.4 (2 C), 70.7, 68.1, 67.7, 67.3, 65.8 and 65.6 (1 C), 51.6 and
51.5 (1 C), 46.6 and 45.6 (1 C), 20.9, 18.4, 17.9; HR-MS (ESI) m/z
Calcd for C52H58N4O11 [M + Na]+: 937.4000. Found 937.3981.
2-[(N,N0-Benzyl-benzyloxycarbonyl)amino]ethyl O-(4-Azido-
3-O-benzyl-4,6-dideoxy-R-D-glucopyranosyl)-(1f3)-2,4-
di-O-benzyl-R-L-rhamnopyranoside (39). Compound 38 (257 g,
0.28 mmol) was treated by NaOMe (0.2 M solution in MeOH) (2.8 mL,
0.56 mmol) for 12 h at rt. The reaction mixture was then neutralized
by resin Amberlite IR120 H+. The resin was filtered off, and the
filtrate was concentrated in vacuo. The residue was purified by flash
chromatography on silica gel using cyclohexane/ethyl acetate (8:2) as
eluent to give alcohol 39 (187 mg, 75%) as a white powder (mixture of
conformers). Rf 0.48 (cyclohexane/ethyl acetate 7:3); [R]D = +4 (c 0.1,
CHCl3); 1H NMR (300 MHz, CDCl3) δ 7.48ꢀ7.20 (m, 25 H),
5.19ꢀ5.16 (m, 2 H), 4.93 (d, J = 10.9 Hz, 1 H), 4.90ꢀ4.83 (m, 3 H),
2-[(N,N0-Benzyl-benzyloxycarbonyl)amino]ethyl O-[3-O-
Benzyl-4-(3-hydroxy-3-methylbutanamido)-4,6-dideoxy-
2-O-methyl-R-D-glucopyranosyl]-(1f3)-2,4-di-O-benzyl-R-L-
rhamnopyranoside (41). To a solution of azide 40 (118 mg,
0.13 mmol) in a mixture of CH2Cl2 (2.5 mL) and EtOH (10 mL) were
added sodium borohydride (8 mg, 0.21 mmol) and a catalytic amount of
NiCl2 6H2O. The reaction mixture was stirred at rt for 1 h and then was
3
concentrated in vacuo. The residue was dissolved in CH2Cl2. The
organic layer was washed with water and brine, dried over Na2SO4,
filtered, and concentrated in vacuo to provide an amine intermediate
which was used in the next step without purification. Rf 0.29
(cyclohexane/ethyl acetate 7:3); MS (ESI) m/z 883.4 [M + Na]+. To
a solution of crude amine (112 mg, 0.13 mmol) in dry DMF (10 mL)
was added dropwise 3-hydroxy-3-methylbutanoic acid (20 μL, 0.16
mmol), followed by HOBt (22 mg, 0.16 mmol), by HATU (63 mg, 0.16
mmol), and then by DIPEA (27 μL, 0.16 mmol). The reaction mixture
was stirred under argon at rt for 18 h, diluted with CH2Cl2, and washed
with satd aq NaHCO3 and water. The organic phase was dried over
Na2SO4, filtered, and concentrated in vacuo. The residue was purified by
flash chromatography on silica gel using cyclohexane/ethyl acetate (6:4)
as eluent to provide intermediate 41 (57 mg, 55% over two steps) as a
colorless oil (mixture of conformers). Rf 0.42 (cyclohexane/ethyl acetate
1
5:5); [R]D = +32.2 (c 0.8, CHCl3); H NMR (300 MHz, CDCl3) δ
7.34ꢀ7.04 (m, 25 H), 5.71 (br s, 1 H), 5.08ꢀ5.06 (m, 2 H), 4.93 (d, J =
10.3 Hz, 1 H), 4.79 (m, J = 11.6 Hz, 1 H), 4.77 (d, J = 10.6 Hz, 2 H)
4.67ꢀ4.36 (m, 7 H), 3.98ꢀ3.91 (m, 1 H), 3.79ꢀ3.49 (m, 6 H), 3.58 (s, 3
H), 3.49ꢀ3.10 (m, 6 H), 2.18ꢀ2.04 (m, 2 H), 1.28ꢀ1.18 (m, 3 H), 1.14
(s, 3 H), 1.12 (s, 3 H), 1.07ꢀ1.02 (br d, J = 4.0 Hz 3 H); 13C NMR (75
MHz, CDCl3) δ 172.6, 156.5, 138.8, 138.6, 138.5, 137.7, 136.6, 129.6,
128.6, 128.5, 128.4, 128.3, 127.9, 127.8, 127.6, 103.9, 98.9, and 98.7
(1 C), 85.0, 80.6, 80.3, 79.2 and 79.1 (1 C), 78.5, 74.9, 73.9, 73.6, 70.9,
69.5, 68.2, 67.3, 65.9, and 65.8 (1 C), 60.7, 51.7 and 51.6 (1 C), 47.8,
5996
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
46.6, and 45.7 (1 C), 29.5 and 29.4 (1 C), 18.2, 18.0; HR-MS (ESI) m/z
Calcd for C56H68N2O12 [M + Na]+: 983.4670. Found 983.4656.
2-Aminoethyl O-[4,6-Dideoxy-4-(3-hydroxy-3-methyl-
butanamido)-2-O-methyl-R-D-glucopyranosyl]-(1f3)-R-L-
rhamnopyranoside (42). Compound 41 (57 mg, 0.06 mmol) in
EtOH/AcOH (6 mL/2 mL) was treated with a catalytic amount of a
Pd(OH)2 under 10 bar of hydrogen at 50 °C for 30 min. The reaction
mixture was then concentrated in vacuo. The residue was dissolved in
H2O (10 mL) and was washed with CH2Cl2 (2 ꢁ 5 mL). The organic
layer was extracted with water (5 ꢁ 10 mL). The aqueous phases were
combined and concentrated under vacuum. The crude was then purified
by RP-HPLC [on an C18 5 μm (250 ꢁ 22 mm) column, with detection
at 215 nm, at a 22 mL/min flow rate and a gradient of 0% B during 5 min,
0 to 100% solvent B over 25 min, 100% B, 5 min (eluent A: 0.05% TFA in
H2O; eluent B: 0.05% TFA in CH3CN:H2O 60:40)] to give compound
42 (11 mg, 91%) as a white solid after lyophilization. [R]D = +6 (c 0.3,
CHCl3); 1H NMR (600 MHz, D2O) δ 4.85 (d, J = 1.7 Hz, 1 H), 4.77 (d,
J = 8.0 Hz, 1 H), 4.20 (dd, J = 1.8 and 3.1 Hz, 1 H), 4.01ꢀ3.97 (m, 1 H),
3.95 (dd, J = 3.1 and 9.2 Hz, 1 H), 3.75ꢀ3.69 (m, 2 H), 3.66ꢀ3.62 (m, 2
H) 3.65 (s, 3 H), 3.59ꢀ3.53 (m, 2 H), 3.32ꢀ3.24 (m, 1 H), 3.23ꢀ3.21
(m, 1 H), 3.15 (dd, J = 8.0 and 9.2 Hz, 1 H), 2.41 (d, J = 13.4 Hz, 1 H),
2.39 (d, J = 13.4 Hz, 1 H), 1.33 (s, 3 H), 1.33 (d, J = 6.2 Hz, 1 H), 1.32 (s,
3 H), 1.16 (d, J = 5.5 Hz, 1 H); 13C NMR (75 MHz, CDCl3) δ 174.1,
103.6, 99.7, 83.3, 79.3, 72.7, 71.2, 70.8, 70.2, 69.7, 69.0, 63.3, 60.0, 56.6,
48.9, 39.0, 28.3, 28.1, 17.1, 16.6; HR-ESIMS: m/z Calcd for
C20H38N2O10 [M + H]+: 467.2605. Found 467.2590.
(8) Mehta, A. S.; Saile, E.; Zhong, W.; Buskas, T.; Carlson, R.;
Kannenberg, E.; Reed, Y.; Quinn, C. P.; Boons, G.-J. Chem., Eur. J. 2006,
12, 9136–9149.
(9) Werz, D. B.; Adibekian, A.; Seeberger, P. H. Eur. J. Org. Chem.
2007, 1976–1982.
(10) Saksena, R.; Adamo, R.; Kovꢁaꢂc, P. Bioorg. Med. Chem. 2007,
15, 4283–4310.
(11) Saksena, R.; Adamo, R.; Kovꢁaꢂc, P. Bioorg. Med. Chem. Lett.
2006, 16, 615–617.
(12) Crich, D.; Vinogradova, O. J. Org. Chem. 2007, 72, 6513–6520.
(13) Dhenin, S. G. Y.; Moreau, V.; Morel, N.; Nevers, M.-C.;
Volland, H.; Crꢀeminon, C.; Djedaïni-Pilard, F. Carbohydr. Res. 2008,
343, 2101–2110.
(14) Guo, H.; O’Doherty, G. A. Angew. Chem. 2007, 46, 5206–5208.
(15) Guo, H.; O’Doherty, G. A. J. Org. Chem. 2008, 73, 5211–5220.
(16) Dhenin, S. G. Y.; Moreau, V.; Nevers, M.-C.; Crꢀeminon, C.;
Djedaïni-Pilard, F. Org. Biomol. Chem. 2009, 7, 5184–5199.
(17) Kubler-Kielb, J.; Vinogradov, E.; Hu, H.; Leppla, S. H.;
Robbins, J. B.; Schneerson, R. Proc. Natl. Acad. Sci. U.S.A. 2008,
105, 8709–8712.
(18) Tamborrini, M.; Werz, D. B.; Frey, J.; Pluschke, G.; Seeberger,
P. H. Angew. Chem., Int. Ed. 2006, 45, 6581–6582.
(19) Wang, D.; Caroll, G. T.; Turro, N. J.; Koberstein, J. T.; Kovꢁaꢂc,
P.; Saksena, R.; Adamo, R.; Herzenberg, L. A.; Herzenberg, L. A.;
Steinman, L. Proteomics 2007, 7, 180–184.
(20) Parthasarathy, N.; Saksena, R.; Kovꢁaꢂc, P.; DeShazer, D.;
Peacock, S. J.; Wuthiekanun, V.; Heine, H. S.; Friedlander, A. M.; Cote,
C. K.; Welkos, S. L.; Adamovucz, J. J.; Bavari, S.; Waag, D. M. Carbohydr.
Res. 2008, 343, 2783–2788.
’ ASSOCIATED CONTENT
(21) Tamborrini, M.; Oberli, M. A.; Werz, D. B.; Sch€urch, N.; Frey,
J.; Seeberger, P. H.; Pluschke, G. J. Appl. Microbiol. 2009, 106, 1618–
1628.
(22) Cybulski, R. J., Jr.; Snaz, P.; O’Brien, A. D. Mol. Aspects Med.
2009, 30, 490–502.
(23) Hou, S.; Kovꢁaꢂc, P. Eur. J. Org. Chem. 2008, 1947–1952.
(24) (a) Lohray, B. B. Synthesis 1992, 1035–1052. (b) Moon, H. R.;
Kim, H. O.; Chun, M. W.; Jeong, L. S. J. Org. Chem. 1999, 64, 4733–
4741.
(25) (a) Byun, H.-S.; He, L.; Bittman, R. Tetrahedron 2000, 56,
7071–7091. (b) Fuentes, J.; Angulo, M.; Pradera, M. A. J. Org. Chem.
2002, 67, 2577–2587.
S
Supporting Information. Spectral data for all new com-
b
pounds. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Phone: +33 (0)322828812. Fax: +33 (0)322827562. E-mail:
cyrille.grandjean@u-picardie.fr.
(26) Guiller, A.; Gagnieu, C. H.; Pacheco, H. Tetrahedron Lett. 1985,
26, 6343–6344.
’ ACKNOWLEDGMENT
(27) Gagnieu, C. H.; Guiller, A.; Pacheco, H. Carbohydr. Res. 1988,
180, 223–231.
We are grateful to the Direction Gꢀenꢀerale de l’Armement for
financial support to O.M., to Dr. A. Siriwardena for helpful
discussion and proofreading the manuscript, and to Drs. A.
Wadouachi and M. Benazza for sharing their experience.
(28) For a representative example of anomeric controlled nucleo-
philic substitution, see: Grandjean, C.; Lukacs, G. J. Carbohydr. Chem.,
1996, 15, 831ꢀ855.
(29) Sanders, W. J.; Kiessling, L. L. Tetrahedron Lett. 1994, 35,
7335–7338.
’ REFERENCES
(30) Sanders, W. J.; Manning, D. D.; Koeller, K. M.; Kiessling, L. L.
Tetrahedron 1997, 53, 16391–16422.
(31) Kajihara, Y.; Endo, T.; Ogasawara, H.; Kodama, H.; Hashimoto,
H. Carbohydr. Res. 1995, 269, 273–294.
(32) Schmidt, R. R.; Kinzy, W. Adv. Carbohydr. Chem. Biochem.
1994, 50, 21–123.
(1) Borio, L.; Frank, D.; Mani, V.; Chiriboga, C.; Pollanen, M.;
Ripple, M.; Ali, S.; DiAngelo, C.; Lee, J.; Arden, J.; Titus, J.; Fowler, D.;
O’Toole, T.; Masur, H.; Bartlett, J.; Inglesby, T. JAMA, J. Am. Med. Assoc.
2001, 286, 2554–2559.
(2) Daubenspeck, J. M.; Zeng, H.; Chen, P.; Dong, S.; Steichen,
C. T.; Krishna, N. R.; Pritchard, D. G.; Turnbough, C. L., Jr. J. Biol. Chem.
2004, 279, 30945–30953.
(33) Guiller, A.; Gagnieu, C. H.; Pacheco, H. Tetrahedron Lett. 1985,
26, 6067–6070.
(34) For some representative examples, see: (a) Fraser-Reid, B.;
Udodong, U. E.; Wu, Z.; Ottosson, H.; Meritt, R. J.; Rao, S. C.; Roberts,
C.; Madsen, R. Synlett 1992, 927–942. (b) Hotha, S.; Kashyap, S. J. Am.
Chem. Soc. 2006, 128, 9620–9621. (c) Kuroiwa, Y.; Sekine, M.; Tomono,
S.; Takahashi, D.; Toshima, K. Tetrahedron Lett. 2010, 51, 6294–6297.
(d) Wang, Y.; Zhang, X.; Wang, P. Org. Biomol. Chem. 2010, 8, 4322–
4328.
(35) Given the a priori facile access to alkyl cyclic sulfite R-D-
fucopyranosides, the substitution was not tested on intermediate 5b as
a model compound.
(3) Dong, S.; McPherson, S. A.; Tan, L.; Chesnokova, O. N.;
Turnbough, C. L., Jr.; Pritchard, D. G. J. Bacteriol. 2008, 190, 2350–2359.
(4) Saksena, R.; Adamo, R.; Kovꢁaꢂc, P. Carbohydr. Res. 2005, 340,
1591–1600.
(5) Werz, D. B.; Seeberger, P. H. Angew. Chem., Int. Ed. 2005, 44,
6315–6318.
(6) Adamo, R.; Saksena, R.; Kovꢁaꢂc, P. Carbohydr. Res. 2005, 340,
2579–2582.
(7) Saksena, R.; Adamo, R.; Kovꢁaꢂc, P. Bioorg. Med. Chem. Lett. 2006,
16, 615–617.
5997
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998

The Journal of Organic Chemistry
ARTICLE
(36) Kim, Y.-J.; Wang, P.; Navarro-Villalobos, M.; Rohde, B. D.;
DerryBerry, J. M.; Gin, D. Y. J. Am. Chem. Soc. 2006, 128, 11906–11915.
(37) For comparison, that the 3,4-cyclic sulfite could be prepared
from thionyl chloride in an almost quantitative yield under the same
conditions underscores the deactivating effect of a postulated 2-chlor-
osulfonate intermediate.
(38) (a) Sharpless, K. B.; Carlsen, H. J.; Katsuki, T.; Martin, V. S.
J. Org. Chem. 1981, 46, 3936–3938. (b) Kim, B. M.; Sharpless, K. B.
Tetrahedron Lett. 1989, 30, 655–659.
(39) Elchert, B.; Li, J.; Wang, J.; Hui, Y.; Rai, R.; Ptak, R.; Ward, P.;
Takemoto, J. Y.; Bensaci, M.; Chang, C.ꢀW. T. J. Org. Chem. 2004,
69, 1513–1523.
(40) Iversen, T.; Bundle, D. R. J. Chem. Soc., Chem. Commun. 1981,
1240–1241.
(41) Banaszek, A.; Zaitsev, V. Tetrahedron: Asymmetry 2004, 15,
299–306.
(42) Liu, M.; Yu, B.; Wu, X.; Hui, Y.; Fung, K.-P. Carbohydr. Res.
2000, 329, 745–754.
5998
dx.doi.org/10.1021/jo200340q |J. Org. Chem. 2011, 76, 5985–5998