Synthesis of building blocks for an iterative approach towards oligomers of the Streptococcus pneumoniae type 1 zwitterionic capsular polysaccharide repeating unit

Article abstract of DOI:10.1139/cjc-2016-0006

Zwitterionic capsular polysaccharide extracts, 8 kDa in mass, from Streptococcus pneumoniae type 1 (Spt1) have shown unique T-cell activating properties. Oligomers of the trisaccharide repeating unit of the Spt1 capsular polysaccharide [3)-4-NH₂-α-d-QuipNAc-(14)-α-d-GalpA-(13)-α-d-GalpA-(1-]_n of defined length are needed to further investigate this response. An approach towards iteratively extendable trisaccharide building blocks of the zwitterionic capsular polysaccharides of Spt1 is described. Key elements include the comparison of pre-glycosylation oxidation and post-glycosylation oxidation approaches using thioglycoside donors to the target trisaccharide, the optimisation of the post-glycosylation oxidation approach, and the conversion of the trisaccharide to building blocks tailored for iterative glycosylation. The construction and evaluation of stereotunable 2-N-3-O-oxazolidinone donors for the common bacterial 2-acetamido-4-amino-2,4,6-trideoxy-α-d-galactopyranoside motif is also described, as is a key intermediate for their efficient synthesis.

Full text of DOI:10.1139/cjc-2016-0006

940
ARTICLE
Synthesis of building blocks for an iterative approach towards
oligomers of the Streptococcus pneumoniae type 1 zwitterionic
capsular polysaccharide repeating unit
Aisling Ní Cheallaigh and Stefan Oscarson
Abstract: Zwitterionic capsular polysaccharide extracts, ϳ8 kDa in mass, from Streptococcus pneumoniae type 1 (Spt1) have shown
unique T-cell activating properties. Oligomers of the trisaccharide repeating unit of the Spt1 capsular polysaccharide [¡3)-4-NH2-
␣-D-QuipNAc-(1¡4)-␣-D-GalpA-(1¡3)-␣-D-GalpA-(1-]n of defined length are needed to further investigate this response. An approach
towards iteratively extendable trisaccharide building blocks of the zwitterionic capsular polysaccharides of Spt1 is de-
scribed. Key elements include the comparison of pre-glycosylation oxidation and post-glycosylation oxidation approaches using
thioglycoside donors to the target trisaccharide, the optimisation of the post-glycosylation oxidation approach, and the conver-
sion of the trisaccharide to building blocks tailored for iterative glycosylation. The construction and evaluation of stereotunable
2-N-3-O-oxazolidinone donors for the common bacterial 2-acetamido-4-amino-2,4,6-trideoxy-␣-D-galactopyranoside motif is also
described, as is a key intermediate for their efficient synthesis.
Key words: Streptococcus pneumoniae type 1, glycosylation, uronic acids, zwitterionic.
Résumé : On a découvert que des extraits de polysaccarides capsulaires amphotères, de poids moléculaire avoisinant les 8 kDa,
issus de l’espèce Streptococcus pneumoniae de type 1 (Spt1) présentaient des propriétés exceptionnelles d’activation des lymphocytes
T. Afin d’étudier cette réponse de façon plus poussée, on doit pouvoir fabriquer des oligomères d’une longueur déterminée par
répétition d’une unité trisaccaridique pour former des polysaccarides capsulaires de Spt1 de formule [¡3)-4-NH2-␣-D-QuipNAc-
(1¡4)-␣-D-GalpA-(1¡3)-␣-D-GalpA-(1-]n. Dans le présent article, nous décrivons une approche itérative visant a` construire des
synthons par allongement de la chaîne de trisaccarides afin d’accéder a` des polysaccarides capsulaires amphotères de Spt1. Parmi
les principaux éléments de la synthèse, notons la comparaison entre les méthodes d’oxydation avant et après la glycosylation,
dans lesquelles interviennent des donneurs a` base de thioglycosides pour former le trisaccharide cible; l’optimisation de la
méthode d’oxydation post-glycosylation et la transformation du trisaccharide en synthons adaptés aux étapes successives de
glycosylation. En outre, nous décrivons et évaluons la synthèse de donneurs a` base de 2-N-3-O-oxazolidinone stéréoréglables
permettant la formation du groupement 2-acétamido-4-amino-2,4,6-tridésoxy-␣-D-galactopyranoside, communément présent
chez la bactérie, car celui-ci constitue un intermédiaire clé dans le cadre d’une synthèse a` haut rendement de ces composés.
[Traduit par la Rédaction]
Mots-clés : Streptococcus pneumoniae de type 1, glycosylation, acides uroniques, amphotère.
charged polysaccharides interact with the immune cells, struc-
tures of a well-defined nature are necessary.
Introduction
Bacterial capsular polysaccharides (CPS) are the outermost layer
The CPS of Streptococcus pneumoniae type 1 (Spt1) and Bacteroides
of bacterial cells and interact with the human immune system.1
fragilis were used to identify this response and the nitric oxide-
CPS are processed by antigen presenting cells but not presented
mediated degradation of the polymers in the MHC II pathway.5
by MHC class II proteins and so are not presented to T-cells.2 This
Spt1 is a virulent bacterium and a causative agent in meningitis,
inhibits the interleukin release necessary to produce antibody
pneumonia, septicaemia, and otitis media.6 It is currently in-
maturation that gives the desired long-term protective immuno-
cluded in multivalent glycoconjugate vaccines (Prevnar (Pfizer)
globulin G. The CPS is commonly used in vaccine formulations, in
and Synflorix (GSK)), which are implemented in mass vaccination
which case, it is often conjugated to a carrier protein (glycoconju-
gate).3 The presence of this protein allows for MHC II presentation
and stimulation of CD4+ T-cell proliferation, giving long-term im-
munogenic protection. A notable exception is the unique class of
polysaccharides that bear a zwitterionic repeating motif, zwitte-
rionic polysaccharides. This is the only known class of carbohy-
drates capable of initiating T-cell proliferation in the absence of
any protein.4 To fully elucidate the pathway by which these
schemes for the prevention of bacterial meningitis.7 There is evi-
dence to suggest that repeat exposure to a recurring carrier pro-
tein can lead to a suppressed immune response against the
epitope. With most humans being exposed multiple times to spe-
cific carrier proteins, this may have an effect on future vaccine
efficiency.8 Therefore, the possibility of removing the need for
protein conjugation in the case of zwitterionic polysaccharide
serotypes could be advantageous.
Received 5 January 2016. Accepted 9 March 2016.
A. Ní Cheallaigh and S. Oscarson. Centre for Synthesis and Chemical Biology, School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland.
Corresponding author: Stefan Oscarson (email: stefan.oscarson@ucd.ie).
This article is part of a Special Issue dedicated to Professor David Bundle in recognition of his seminal contributions and lifetime achievements in the fields of carbohydrate
chemistry and glycobiology.
Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from RightsLink.
Can. J. Chem. 94: 940–960 (2016) dx.doi.org/10.1139/cjc-2016-0006
Published at www.nrcresearchpress.com/cjc on 12 April 2016.

Ní Cheallaigh and Oscarson
941
Fig. 1. Chemical structure of the zwitterionic capsular
polysaccharide repeating unit of Streptococcus pneumoniae type 1.
displaced by iodine before reduction. These methodologies was
adopted by Sharon,19 Lonngren,20 Pozsgay,21 Schmidt,22 Grindley,23
van der Marel,24 and their respective co-workers. Synthetic efforts
have also been made from D-glucal by Bundle25 and D-mannose by
van Boom26 and Kulkarni27 and also, a de novo strategy from
Cbz-protected L-threonine has been derived.28
A versatile thioglycoside intermediate 6 to ATT donors, allow-
ing flexible 2,3-protection, was designed and synthesized from
D-glucosamine (Scheme 1).
Phthalimido protection and acetylation of D-glucosamine hy-
drochloride followed by thioglycoside formation was carried out
under standard conditions.29 The Garegg–Samuelsson reaction30
was employed for iodination followed by in situ acetylation to
give 2. The iodine was reduced with tributyltin hydride and
AIBN (¡3, 99%) and following deacetylation, a regioselective 3-O-
benzoylation was carried out at –30 °C to give 4 in a 91% yield.22,23
The 4-position was subjected to an SN2 displacement of a triflate with
sodium azide to give 5 in 86% yield.31 Treatment with ethylene
diamine in ethanol deprotected the 2-N and 3-O positions giving
the target intermediate 6 (82%).32 This route was repeated on a
large scale to give multigram quantities of the intermediate 6 in
nine steps with an overall yield of 32%.
The Spt1 CPS contains a nonbranched, trisaccharide repeating
unit [¡3)-4-NH2-␣-D-QuipNAc-(1¡4)-␣-D-GalpA-(1¡3)-␣-D-GalpA-(1-]n
(Fig. 1).9 The first total synthesis of this trisaccharide and also a
hexasaccharide dimer as their methyl glycosides was achieved by
Bundle and co-workers employing galactose donors and a late-
stage oxidation to galacturonic acid esters.10 This was followed by
the preparation by Christina et al. of all three possible frame shifts
of the trisaccharide repeating unit using conformationally locked
galacturonic acid donors.11 More recently, Bundle and co-workers
reported a subsequent synthesis adopting their previous ap-
proach but with an alternative frame shift12 and Seeberger and
co-workers produced a trisaccharide repeating unit disulfide syn-
thesised from galacturonic acid donors.13
However, none of these synthetic targets when biologically
tested have so far been able to activate the desired immune re-
sponse. Molecular modelling studies have shown that a 6-mer (six
repeats of the trisaccharide unit) is required to form secondary
helical structure, which is thought to be necessary to activate the
response.14 The previously reported syntheses lacked the ability
for iterative glycosylations, which would allow access to these
larger structures.
The pre-glycosylation oxidation approach
To investigate the extent of potential problems using galac-
turonic acid as donors and acceptors in the synthesis of the trisac-
charide, a pre-glycosylation oxidation approach was performed
involving use of ATT donor 7, a derivative of 6 bearing a nonpar-
ticipating imine group in the 2N-position, and galacturonic acid
ester building blocks 10 and 16 (Schemes 2 and 3). Initial attempts
to build up a thioglycoside trisaccharide repeating unit using tri-
chloracetimidate donors and a galacturonic ester thioglycoside
acceptor met with severe problems mainly due to aglycon transfer
side reactions. Thus, an alternative approach using a trimethylsi-
lyl ethyl (TMSE) glycoside acceptor and thioglycoside donors was
developed.33 The selection of the imine-protecting group in 7 was
initially based on reports from Nguyen et al. showing excellent
yields and ␣-selectivity in nickel-catalysed formation of 1,2-cis 2-
aminoglycosides using this type of imine trichloroacetimidate do-
nors.34 In our case, the approach failed, and recently, Nguyen
et al. have also reported on problems with the use of these donors
in orthogonal glycosylations to thioglycoside acceptors.35 How-
ever, as shown below, the imine thioglycoside 7 was found to be
an excellent donor although not very stereoselective.
Donor 7 was readily synthesised from 6 by treatment with
p-trifluoromethyl benzaldehyde with trimethylorthoformate as a
dehydrating solvent followed by acetylation (93%). TEMPO/BAIB
oxidation36 of compound 837 followed by esterification afforded
galacturonic acid ester 913 (Scheme 2, 67%). Subsequent protection
with an orthogonal chloroacetate group gave 10 (92%). Benzyla-
tion of TMSE glycoside 1138 followed by mild acidic hydrolysis
yielded 13 (87%), which was oxidized with the TEMPO/BAIB re-
agent and the crude carboxylic acid was then esterified to give
methyl ester 14 (56%). An exchange of the isopropylidene acetal
for a benzylidene acetal was then performed to prepare for sub-
sequent reductive opening of the benzylidene acetal to afford the
4-O-benzyl-protected acceptor 16. Formation of the 3,4-O-benzylidene
acetal using benzaldehyde dimethylacetal on the corresponding
ethyl thioglycoside compound gave an endo:exo ratio of ϳ10:1
(which is what is normally found); however and surprisingly, the
TMSE glycoside gave an endo:exo ratio of only 2.2:1.
We here report the investigation of both a pre-glycosylation
oxidation and post-glycosylation oxidation approach to the Spt1
trisaccharide repeating unit and the synthesis of a trisaccharide
building block suitable for iterative glycosylation to access spacer-
equipped oligomers of the repeating unit.
Results and discussion
The trisaccharide motif is a challenging target containing exclu-
sively 1,2-cis linkages15 as well as the unusual 2-acetamido-4-amino-
2,4,6-trideoxy-␣-D-galactopyranoside (AAT) motif.16 Furthermore,
galacturonic acids are generally regarded as both poor glycosyl do-
nors and poor glycosyl acceptors due to the electron-withdrawing
effect of the carboxylic acid ester at C5.17,18 Also, the targeted itera-
tive approach adds additional complexity to the protecting group
pattern and often requires orthogonal glycosylations. In light of this,
both a pre-glycosylation oxidation approach and a post-glycosylation
oxidation approach were investigated to identify the optimum route
for production of the trisaccharide unit. Also, the synthesis and gly-
cosylation properties of a number of AAT donors with variant pro-
tecting group pattern were investigated.
Synthesis of AAT intermediate
Multiple groups have been working towards the synthesis of
AAT moieties and there are many published routes towards the
target. Using glucosamine as a precursor, introduction of the ami-
no group to the 4-position with inversion of stereochemistry and
deoxygenation of the 6-position needs to be achieved. Axial amino
group introduction is generally accomplished via SN2 displace-
ment of an equatorial leaving group (mesylate, tosylate, triflate)
with a nucleophile such as azide or phthalimide. Deoxygenation
has been carried out by introduction of a leaving group such as
mesylate, tosylate, or bromine, which is either reduced directly or
In most cases, the regioselectivity in the reductive opening of
eq,ax-dioxolane acetals has been found to be dependent on the
configuration of the acetal and not on the reagent or solvent used
(in contrast with dioxane 4,6-acetals), endo giving the axial benzyl
ether and exo the equatorial. However, Tanaka et al. showed that
opening of mannose exo-2,3-O-benzylidene acetals could show sol-
vent (and reagent) dependence, CH2Cl2 affording the axial 2-O-
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Can. J. Chem. Vol. 94, 2016
Scheme 1. Synthesis of common intermediate 6. Reagents: (i) (a) NaOMe, Et3N, phthalic anhydride, MeOH; (b) Ac2O, pyridine; (c) EtSH, BF3·Et2O,
CH2Cl2; (ii) (a) NaOMe, MeOH; (b) Ph3P, I2, imidazole, toluene, reflux; (c) Ac2O, 92% over three steps; (iii) AIBN, Bu3SnH, toluene, reflux, 99%;
(iv) (a) NaOMe, MeOH; (b) BzCl, pyridine, –30 °C, 91%; (v) (a) Tf2O, pyridine, CH2Cl2, –20 °C; (b) NaN3, DMF, 86%; (vi) ethylenediamine, EtOH, 70 °C, 82%.
Scheme 2. Synthesis of ATT donor 7 and of galacturonic acid donor 10 and acceptor 16. Reagents: (i) (a) trifluoromethylbenzaldehyde,
trimethylorthoformate, DMF; (b) Ac2O, pyridine; (ii) (a) TEMPO, BAIB, CH2Cl2–H2O; (b) MeI, K2CO3, DMF, 67%; (iii) ClAcCl, pyridine, CH2Cl2, 92%;
(iv) (a) BnBr, NaH, DMF; (b) 4/1 AcOH–H2O, 88%; (v) (a) TEMPO, BAIB, CH2Cl2–H2O; (b) MeI, K2CO3, DMF, 56%; (vi) (a) 4/1 AcOH–H2O, 80 °C;
(b) PhCH(OMe)2, CSA, DMF, 76%; (vii) endo: BH3·NMe3, AlCl3, THF, H2O, 68%; (viii) exo: 1 M BH3 in THF, 1 M Bu2BOTf in toluene, 81%, 3/2 4OBn–3OBn.
Scheme 3. Synthesis of the trisaccharide repeating unit as its TMSE glycoside. Reagents: (i) Me2S2–Tf2O, 3/2 Et2O–CH2Cl2, 0 °C, 74%;
(ii) thiourea, NaHCO3, TBAI, THF, 60 °C, 84%; (iii) Me2S2–Tf2O, 3/2 Et2O–CH2Cl2, 0 °C, 96%, 3␣:2␤; (iv) (a) CSA, MeOH; (b) Ac2O, MeOH, 64%.
benzyl and toluene the equatorial 3-O-benzyl product.39 In light of
this, endo 15 was subjected to trimethylaminoborane and alumi-
num chloride to give the wanted and expected 4-OBn product 16
in a 68% yield. However, when exo 15 was subjected to the
“Tanaka” conditions for 4-OBn selectivity, it resulted in an unse-
lective opening with a 3:2 ratio of 16 and 17, respectively, in an
80% yield (48% being the desired 4-O-benzylated product).
The glycosylation of acceptor 16 with donor 10 employing the
dimethyl disulphide/triflic anhydride promoter system40 worked
smoothly to give the ␣-linked disaccharide 18 in a 78% yield with
no 1,2-trans product observed and showing none of the anticipated
problems with galacturonic acid donors and acceptors (Scheme 3).
Removal of the chloroacetate group and subsequent glycosylation
with donor 7 gave a separable mixture of 1,2-cis 20 and 1,2-trans 21
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Ní Cheallaigh and Oscarson
943
Scheme 4. Synthesis of oxazolidinone donors 24 and 25. Reagents:
(i) triphosgene, sat. aq. NaHCO3, MeCN, 78%; (ii) Boc2O,
4-dimethylaminopyridine, THF, 60 °C, 91%; (iii) AcCl, DIPEA, CH2Cl2, 99%.
in Boc-protected 31 could selectively be removed by sodium me-
thoxide treatment to give 32 in a 92% yield.
The synthesis of the galactose derivatives 35 and 39 started
from the earlier used galactose precursors 8 and 13 (Scheme 6).
Naphthylmethylidene acetal, introduced to 8, was subjected to
reductive ring opening conditions of NaCNBH3 and HCl to give the
6-O-methylnaphthyl-protected 34 (76%), which was acetylated to
give 35. 13 was alkylated using NapBr to afford 36. The exchange
of the isopropylidene group for a benzylidene acetal again resulted
in an unusually low 1:1 endo:exo ratio, similar to that observed for 15.
The endo product was subjected to reductive ring opening conditions
of BH3·NMe3 and AlCl3, while the exo was subjected to 1 M BH3 in THF
with 1 M Bu2BOTf in toluene. As observed before, the endo opened to
the desired 4-OBn, whilst the exo opening was unselective with a
4-OBn:3-OBn ratio of 1:1.2 being observed.
Acceptor 39 and donor 35 were coupled using the Me2S2/Tf2O
promoter system in diethyl ether and dichloromethane (Scheme 7).
This gave ␣-linked disaccharide 41 in an excellent yield of 92%
with no 1,2-trans product observed. The acetate group was re-
moved by treatment with sodium methoxide and the resulting
acceptor 42 was glycosylated with Boc-donor 24 to give 43 in a 51%
yield. An inverse glycosylation procedure45 was then applied to
the reaction that increased the yield to 65%; however, prolonged
reaction times resulted in partial loss of 6-O-Nap and (or) 6=-O-Nap
protecting groups by acidic cleavage.
products in a 96% yield with a 3:2 ratio. The imine group was then
removed by mild acidic cleavage with camphorsulfonic acid in
methanol and the resulting amine was acetylated with acetic an-
hydride in methanol to give the target trisaccharide 22 in a 35%
overall yield from the building blocks 7, 10, and 16.
The post-glycosylation oxidation approach
Glycosylation attempts were also made using the acetylated
donor 25. Using the inverse glycosylation approach, trisaccharide
44 was formed in a 74% yield with little loss of the 6-O-Nap groups.
Trisaccharide 44 was treated with sodium methoxide and the
2,3-N,O-oxazolidinone was removed in a 92% yield. The removal of
the Nap ether was achieved by oxidative cleavage with 2,3-dichloro-
5,6-dicyanobenzoquinone (DDQ) in dichloromethane and methanol.
This reaction provided a complex mixture, as partial benzyl group
removal was also observed. Triol 46 was isolated in a 65% yield but
the removal issues in combination with the complex mixture
obtained during glycosylation highlighted that Nap ethers are not
the optimum protecting group for the 6- and 6=-positions.
Selective oxidation of the primary 6 and 6= hydroxyl groups was
achieved using TEMPO and BAIB and the acids were esterified with
cesium fluoride and benzyl bromide to give the benzyl ester 47 with
a 57% yield over the two steps. From building blocks 24, 35, and 39,
trisaccharide 47 was achieved in a 20% yield over six steps.
In the post-glycosylation oxidation approach, stereotunable
AAT moiety donors 24 and 25 were investigated together with
galactose building blocks 35 and 39, with a temporary 6-O-Nap
protecting group to allow later oxidations.
Glucosamine 2-N-acetyl-2,3-N,O-oxazolidinone donors are known
to possess an innate stereoselective tunability in glycosylations;
0.1 equiv. of silver triflate and 1 equiv. of N-iodosuccinimide (NIS)
as promoter system results in the 1,2-trans product, whilst
0.4 equiv. of silver triflate and 1 equiv. of NIS yields the 1,2-cis
product through an efficient anomerisation of the initially
formed trans-product via an endo-cyclic opening mechanism.41
Since the AAT motif is found both 1,2-cis and 1,2-trans linked in a
number of different bacterial structures,42 a single donor that
could be used to create both types of linkages is of interest.
Treatment of intermediate 6 with triphosgene and saturated
aqueous sodium bicarbonate in acetonitrile produced the 2,3-N,O-
oxazolidinone 23, treatment of which with a strong base and
either Boc anhydride or acetyl chloride gave the corresponding
product 24 or 25, respectively (Scheme 4).
Optimised postglycosylation oxidation approach
An optimised route for the post-glycosylation oxidation ap-
proach was then carried out using the N-acetyl oxazolidinone AAT
donor 25 together with galactose building blocks 49 and 56 in
which the 6-O-NAP ether had been changed to a benzoyl ester
(Scheme 8). Using low temperatures of –30 °C and a stoichiometric
quantity of benzoyl chloride, the intermediate 46 was obtained
from 8 in a 73% yield.46 The chloroacetyl group was introduced to
the 4-position to give donor 49 in an 82% yield. The acetal and
mixed acetal were removed from 12 by acid hydrolysis to give the
triol, to which a 4,6-O-benzylidene acetal was introduced.47 The
reductive ring opening of 51 gave low selectivity for the 4-OBn
over the 6-OBn with a 2:1 ratio observed. It has been empirically
found that the selectivity of reductive ring openings is reduced
with the number of free hydroxyl groups on the substrate.48 To
increase the selectivity, the 3-position of 51 was acetylated and the
resulting product 54 was subjected to the reductive ring opening
reagents. This gave 55 in a 70% yield with no 6-O-benzyl product
observed. The acetate group was subsequently removed with Zem-
plén conditions in a 97% yield. A benzoyl group was introduced
selectively to the 6-position as described for compound 48 to give
acceptor 56 in a 70% yield.
The 2-N-acetyl-2,3-N,O-oxazolidinone-protected donor 25 was
initially tested in glycosylations with known galactose acceptors
26 and 29 (Scheme 5).43 Using silver triflate (0.1 equiv.) and NIS in
dichloromethane with a short reaction time of 10 min gave a 65%
yield of disaccharide as a 6:1 ␣/␤ mixture (27/28). Using silver
triflate (0.4 equiv.) and NIS in dichloromethane with a longer
reaction time of 40 min gave exclusively the 1,2-cis product 27 in a
59% yield, in accordance with what has been found earlier for
glucosamine compounds. Although the acetylated 2,3-oxazolidinones
have been shown to be efficient and stereotunable donors, a draw-
back of their use are problems found in the removal of the cyclic
carbamate to give the target acetamide, which is often not selec-
tive and thus low yielding. Benzylated 2,3-oxazolinones have been
introduced to address this problem44 and here, a Boc-protected
version 24 was investigated.
Donor 24 was coupled to acceptor 29 using 0.1 equiv. of silver
triflate; this led to the formation of the ␤ product with a small
trace of ␣ as observed by thin-layer chromatography (TLC). After
complete consumption of the donor, a further 0.3 equiv. of silver
triflate was added to the reaction. The previously observed ␤ prod-
uct anomerised over half an hour to give exclusively the 1,2-cis
product 31 in a 52% yield, showing that the Boc derivative also
allowed efficient anomerisation. As expected, the 2,3-N,O-oxazolidinone
Glycosylation of acceptor 56 with donor 49 was achieved in a
94% yield with only the desired 1,2-cis product 57 observed using
Me2S2/Tf2O as the promoter (Scheme 9). The chloroacetate group
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Can. J. Chem. Vol. 94, 2016
Scheme 5. Glycosylations with donors 24 and 25. Reagents: (i) AgOTf (0.1 equiv.), NIS, CH2Cl2, 0 °C, 10 min, 65%, 1␣:6␤; (ii) AgOTf (0.4 equiv.),
NIS, CH2Cl2, 0 °C, 40 min, 59%; (iii) AgOTf (0.1 equiv.), NIS, CH2Cl2, 0 °C, 10 min; (iv) AgOTf (0.3 equiv.), 0 °C, 30 min, 52%; (v) NaOMe, MeOH, 92%.
Scheme 6. Synthesis of galactose donor 35 and acceptor 39. Reagents: (i) NapCH(OMe)2, CSA, DMF, 83%; (ii) NaCNBH3, HCl, THF, 77%;
(iii) Ac2O, pyridine, 99%; (iv) 2-NapBr, NaH, DMF, 92%; (v) (a) AcOH/H2O, 80 °C, 99%; (b) PhCH(OMe)2, CSA, DMF, 77%; (v) 37 endo: BH3NMe3, AlCl3,
THF, 76%; (vi) 38 exo: BH3 in THF, Bu2BOTf in toluene, 88%, 1.2/1 4OBn–3OBn.
was then removed and the resulting 3=-O-acceptor 58 glycosylated
with 25 using the inverse addition procedure. The desired 1,2-cis-
linked trisaccharide (60%) and the 1,2-trans product (12%) were
isolated and the 1,2-trans product was anomerised by treatment
with silver triflate in dichloromethane, giving a total of 71% yield
of the ␣-trisaccharide 59 from the glycosylation.
Compound 59 was treated with barium hydroxide for complete
removal of the 2-N-acetyl–2,3-N,O-oxazolidinone functionality and
the primary benzoyl esters.49 After heating for 16 h, acetic anhy-
dride was added, leading to acetamide formation giving the de-
sired 60 in an 80% yield. The triol was selectively oxidized at the
primary positions using the previously employed biphasic TEMPO
and BAIB method to give the corresponding uronic acid. The
crude was esterified with methyl iodide and potassium carbonate
to give the methyl ester 61 in a 70% yield.
With the new protecting group pattern employed, the trisac-
charide 61 was obtained from building blocks 25, 49, and 56 in
five steps with a yield of 35%.
Although the overall yield from the building blocks to the target
trisaccharide is the same, 35%, in the pre- and post-glycosylation
approach, the much simpler preparation of the building blocks in
the post-glycosylation approach makes this the preferred route to
the target trisaccharide, which now was converted to a donor and
subsequently to a spacer-equipped acceptor (Scheme 10).
Building blocks for the iterative approach
A chloroacetyl group was introduced to 61 using standard con-
ditions to give 62 in an 84% yield. The TMSE glycoside was then
hydrolyzed with trifluoroacetic acid and water to give the hemi-
acetal product 63 (80%) from which the trichloroacetimidate (TCA)
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Ní Cheallaigh and Oscarson
945
Scheme 7. Synthesis of the trisaccharide repeating unit. Reagents: (i) Me2S2–Tf2O (1.2 equiv.); 3/2 Et2O–CH2Cl2, 0 °C, 92%; (ii) NaOMe, MeOH, 99%;
(iii) (a) 24, NIS, AgOTf (0.4 equiv.), CH2Cl2, 51%; (b) 24, NIS, AgOTf (0.4 equiv.), CH2Cl2, inverse addition, 65%; (c) 25, NIS, AgOTf (0.4 equiv.), CH2Cl2,
inverse addition, 74%; (iv) 43, NaOMe, MeOH, 92%; (v) DDQ, MeOH, CH2Cl2, 62%; (vi) (a) TEMPO, BAIB, CH2Cl2, H2O; (b) BnBr, CsF, DMF, 57%.
Scheme 8. Synthesis of donors 49 and 56 for optimized route. Reagents: (i) BzCl, pyridine, –30 °C, 73%; (ii) ClAcCl, pyridine, CH2Cl2, 0 °C, 82%;
(iii) 4/1 AcOH–H2O, 80 °C; (iv) PhCH(OMe)2, CSA, DMF 70% over two steps; (v) 1 M BH3 in THF, 1 M Bu2BOTf in toluene, 2/1 52–53, 68%; 55, 70%;
(vi) NaOMe, MeOH, 99%; (vii) BzCl, pyridine, CH2Cl2, 70%.
Scheme 9. Optimized synthesis of the trisaccharide repeating unit. Reagents: (i) Me2S2–Tf2O, 3/2 Et2O–CH2Cl2, 95%; (ii) thiourea, NaHCO3, TBAI, THF, 96%;
(iii) NIS, AgOTf, CH2Cl2, 71%; (iv) (a) Ba(OH)2·8H2O, EtOH–H2O; (b) Ac2O, 80%; (v) (a) TEMPO, BAIB, 2/1 CH2Cl2–H2O; (b) MeI, K2CO3, DMF, 70%.
donor 64 was formed. Prolonged reaction times resulted in only the
␣ TCA being produced in a 98% yield.
Choosing a suitable linker for the Spt1 repeating unit was
complicated by the high functionality in the structure (amino,
acetamido, carboxylic acid, and alcohol groups). After much con-
sideration, an allyl linker was decided upon. Compound 64 was
glycosylated with an excess of allyl alcohol acceptor to give 65 in
an 82% yield (Scheme 10). Despite the use of a combination of
Published by NRC Research Press

946
Can. J. Chem. Vol. 94, 2016
Scheme 10. Synthesis of the trisaccharide trichloroacetimidate donor 64 and trisaccharide OAll acceptor 66. Reagents: (i) ClAcCl, pyridine,
CH2Cl2, 0 °C, 84%; (ii) 9/1 TFA–H2O, 80%; (iii) Cl3CCN, K2CO3, CH2Cl2, 84%; (iv) allyl alcohol, TMSOTf, CH2Cl2, Et2O, 0 °C, 82%; (v) thiourea,
NaHCO3, TBAI, THF, 60 °C, 86%.
ethereal solvent, high temperatures, and TMSOTf as a promotor,
the trisaccharide isolated was exclusively ␤ at the new anomeric
linkage. The chloroacetate group was removed using standard
conditions to provide trisaccharide 66 in an 86% yield ready for
use as the reducing end acceptor.
mediate 6, from which many building blocks can be derived util-
ising the native chemoselectivity of the amide, hydroxyl, and thio
functionalities. Two stereotunable AAT donors 24 and 25 are
also described that can be used to give either the 1,2-cis or the
1,2-trans product by varying the reaction conditions. The N-Boc-
N,O-oxazolidinone derivative also provides an alternative to the
previously seen N-acetyl and N-benzyl oxazolidinone donors while
retaining the tunability of the reaction. No issues were observed
when glycosylating the O-4s of the galacturonic acid. This position
is notorious for being less reactive as a nucleophile.50 The use of
galacturonic acid donors provided only slightly lower yields than
the comparable galactose donors. In this case, we have found that
the classification of galacturonic acids as poor glysosyl donors and
acceptors is lacking in its justification, making the pre- and post-
glycosylation approaches similar in efficiency of providing the
trisaccharide building blocks.
With the repeating unit acceptor and donor available, forma-
tion of a dimer was attempted. Glycosylation of donor 64 and
acceptor 66 with TMSOTf as the promoter and diethyl ether as a
participating solvent resulted in a hexasaccharide in a high 83%
yield, but again the ␤-linked product was formed exclusively
(Scheme 11). Interestingly, all of the ␣-linkages in the Spt1 CPS
structure could possibly be obtained through anomerisation
of the corresponding ␤-linkages, for the ATT motif using
oxazolidinone donors as discussed above and for the galacturonic
acid moieties through TiCl4-assisted anomerisation again via an
endocyclic cleavage mechanism facilitated by complexation of
the titanium to the carboxylic acid part as shown and developed
by Murphy and co-workers.49 In this project, we have had success
with the anomerisation of ␤-galacturonic acid glycosidic linkages
on the mono- and disaccharide level utilising the TiCl4 methodol-
ogy, and so an anomerisation was also attempted on the hexasa-
ccharide. This successfully anomerised the aglycon ␤-linkage but
unfortunately not the internal ␤-linkage (Scheme 11). This can
clearly be observed from the HSQC experiments shown in Fig. 2
that illustrate the movement of the C1 signal from 103 ppm in 67
to 97 pmm in 68 but no movement of the C1ٞ signal in the spectra.
Throughout this work, it has been noted that the glycosylation
outcome with galacturonic acid TCA donors has been exclusively
1,2-trans, despite the use of alpha directing solvents and higher
temperatures. However, when exploiting thioglycosides as the
galacturonic acid donor, the outcome has been consistently 1,2-
cis.32 With this in mind, it is envisioned that by converting TCA
donor 64 to a thioglycoside donor, the glycosylation with trisac-
charide 66 should form a 1,2-cis hexasaccharide.
Experimental
General materials and methods
All chemicals were purchased from commercial suppliers and
used without purification. Anhydrous dichloromethane, tetrahy-
drofuran (THF), diethyl ether, and toluene were obtained from
PureSolv-ENTM solvent purification system. All other anhydrous
solvents were purchased from Sigma-Aldrich in AcroSeal bot-
®
tles. Reactions were monitored by TLC using Merck aluminum foil
coated TLC plates carrying silica gel 60 F254 with a 0.2 mm thick-
ness. Ultraviolet light, sulphuric acid (8% H2SO4 in ethanol) and
(or) ninhydrin (3 g of ninhydrin and 3 mL of acetic acid in 100 mL
of ethanol) were used to detect compounds. Purification of com-
pounds was carried out using column chromatography (Grace
Davidsil chromatographic silica LC60A 40–60 ␮m particle size) or
flash chromatography using a Biotage system (SNAP KP-Sil) or
Grace Reveleris system (Silica 40 ␮m particle size). All compounds
were analysed by nuclear magnetic resonance (NMR) spectroscopy
1
with H NMR spectra recorded at 400 or 500 MHz and 13C NMR
Conclusions
recorded at 106 or 125 MHz on Varian spectrometers at 20 °C.
Additional experiments were frequently performed for novel
compounds to aid complete characterisation including 1H–1H
homonuclear correlation spectroscopy (COSY), total correlation
We have described the synthesis of the zwitterionic trisaccha-
irde repeating unit of the CPS of Spt1 via both a pre-glycosylation
oxidation and a post-glycosylation oxidation approach. In most
cases, excellent yields and selectivity were observed during glyco-
sylation, in particular with the implementation of the Me2S2/Tf2O
methodology. The post-glycosylation oxidation approach was op-
timised and scaled up for the synthesis of the iterative glycosyla-
tion building blocks. Iterative building block donor and acceptor
were constructed from the trisaccharide 62 in high yields. A
multigram-scale synthesis was also carried out of a key AAT inter-
1
spectroscopy (TOCSY), H–13C heteronuclear single quantum co-
herence spectroscopy (HSQC), and heteronuclear multiple bond
correlation spectroscopy (HMBC). Spectra were recorded in deu-
terated solvents and were standardised against the deuterated
solvent peak and the internal tetramethylsilane (TMS) standard
(CDCl3 ␦ = 7.26 ppm, CH3OD ␦ = 3.31 ppm, TMS ␦ = 0.00 ppm).
Published by NRC Research Press

Ní Cheallaigh and Oscarson
947
Scheme 11. Glycosylation of 64 and 66 to hexasaccharide 67 and subsequent anomerisation to 68. Reagents: (i) CH2Cl2, Et2O, TMSOTf, 0 °C,
83%; (ii) TiCl4, CH2Cl2, 0 °C, 65%.
Fig. 2. HSQC showing the anomeric region of 67 (left) and 68 (right).
Coupling constants (J values) are expressed in Hz and were calcu-
lated using MestraNova processing software. Low-resolution mass
spectrometry (LRMS) was often used for monitoring reactions (mi-
cromass Quattro microTM LC-MS/MS instrument). High-resolution
mass spectrometry (HRMS) was carried out using Waters micro-
mass LCT LC-TOF instrument with ESI detection in positive or
negative mode. Optical rotation was recorded at 20 °C in a 1 cm3
cell at a g/100 mL concentration in the indicated solvent using a
Perkin-Elmer polarimeter.
hexane – ethyl acetate, 2/1 v/v). The product was isolated (8.21 g) as
a white foam with a 92% recovered yield (starting material 5.40 g).
[␣]D = +38.9 (c = 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 7.86–7.73
(m, 4H, ArH), 5.82 (dd, 1H, H-3, J = 10.2, 9.1 Hz), 5.53–5.51 (d, 1H, H-1,
J = 10.6 Hz), 4.98 (t, 1H, H-4, J = 9.4 Hz), 4.38 (t, 1H, H-2, J = 10.4 Hz),
3.70 (m, 1H, H-5), 3.33–3.20 (m, 2H, H-6a, H-6b), 2.83–2.63 (m, 2H,
SCH2CH3), 2.06 (s, 3H, COCH3), 1.85 (s, 3H, COCH3), 1.26 (t, 3H,
SCH2CH3, J = 7.4 Hz). 13C NMR (500 MHz, CDCl3) ␦: 170.1–167.4 (2 ×
NCO, 2 × C=O) 123.7 (2 × ArCH), 80.9 (C1), 77.5 (C5), 72.9 (C4), 71.2
(C3), 54.1 (C2), 24.6 (SCH2CH3), 20.9, 20.5 (COCH3), 15.2 (SCH2CH3),
3.5 (C6) HRMS C20H22NO7SINa [M + Na+] calculated: 570.0059;
found: 570.0048.
Ethyl 3,4-di-O-acetyl-2,6-dideoxy-6-iodo-2-N-phthalimido-1-thio-
␤-D-glucopyranoside (2)
A solution of triphenylphosphine (12.6 g, 48.1 mmol) and imida-
zole (6.54 g, 96.2 mmol) in dry toluene (252 mL, 0.112 M) was
prepared and heated to 60 °C under a flow of nitrogen. To this,
deacetylated 1 (10.0 g, 28.3 mmol) was added portion wise to pro-
mote dissolution. Iodine pellets (17.2 g, 67.9 mmol) were then
added to the reaction, which was stirred vigorously at 90 °C for
2 h. The reaction was cooled to 0 °C and acetic anhydride (80.0 mL)
was added and stirred until acetylation was complete. The iodine
was quenched by washing with 10% Na2S2O3 and the organic
phase was dried over Na2SO4 and reduced by rotary evaporation.
The compound 2 was isolated from a mixture of product and
acetylated starting material by column chromatography (cyclo-
Ethyl 3,4-di-O-acetyl-2,6-dideoxy-2-N-phthalimido-1-thio-
␤-D-glucopyranoside (3)
Compound 2 (8.00 g, 14.6 mmol) and triphenyltin hydride
(20.5 g, 58.5 mmol) were added in a round-bottom flask, covered in
tin foil, and dried under reduced pressure overnight. Toluene
(96.0 mL), degassed by freeze–thaw methods, was then added. The
solution was heated to reflux and AIBN (178 mg, 0.73 mmol) was
added under a strict flow of nitrogen. After 30 min, the reaction
was complete as indicated by LRMS. The solvent was removed and
the product was purified by column chromatography (cyclohex-
ane – ethyl acetate, 4/1 v/v) to yield 3 (6.60 g, 99%) as a white foam.
Published by NRC Research Press

948
Can. J. Chem. Vol. 94, 2016
[␣]D = +57.2 (c = 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 7.86–7.75
(m, 4H, ArH), 5.79 (dd, 1H, H-3, J = 10.2, 9.3 Hz), 5.46–5.44 (d, 1H, H-1,
J = 10.6 Hz), 4.92 (t, 1H, H-4, J = 9.5 Hz), 4.38 (t, 1H, H-2, J = 10.4 Hz),
3.80–3.74 (m, 1H, H-5), 2.75–2.60 (m, 2H, SCH2CH3), 2.05 (s, 3H,
COCH3), 1.86 (s, 3H, COCH3), 1.31–1.29 (d, 3H, H-6a, H-6b, H-6c, J =
6.2 Hz) 1.20 (t, 1H, SCH2CH3, J = 7.4 Hz). 13C NMR (126 MHz, CDCl3)
␦: 170.3–167.4 (2 × C=O, 2 × NCO), 134.5, 134.3, 123.8, 123.7 (ArC,
ArCH), 80.7 (C1), 74.5 (C5), 74.1 (C4), 71.7 (C3), 54.1 (C2), 24.1
(SCH2CH3), 20.9 (COCH3), 20.6 (COCH3), 17.9 (C6), 14.9 (SCH2CH3).
HRMS C20H23NO6SNa [M + Na+] calculated: 444.1093; found:
444.1080.
removed by rotary evaporation and the crude was coevaporated to
dryness with acetonitrile. The residue was purified by column
chromatography (ethyl acetate – methanol – water, 7/2/1 v/v) to
yield compound 6 (2.23 g, 82%) as a white solid. On a large scale,
the crude was dry loaded onto silica gel due to solubility issues
when loading the column. 1H NMR (500 MHz, CDCl3) ␦: 4.13 (d, 1 H,
H-1, J = 9.8 Hz), 3.72–3.62 (m, 2H, H-4, H-5), 3.58 (dd, 1 H, H-3, J = 10.8,
3.7 Hz), 2.87 (t, 1H, H-2, J = 9.8 Hz), 2.75–2.66 (m, 2H, SCH2CH3), 2.18
(s, 3H NH2, OH), 1.34 (d, 3H, CH3, J = 6.1 Hz) 1.29 (t, 3H, SCH2CH3, J =
7.3 Hz). 13C NMR (126 MHz, CDCl3) ␦: 87.6 (C1), 75.8 (C3), 73.8 (C4/5),
65.3 (C4/5), 53.2 (C2), 24.1 (SCH2CH3), 18.1 (C6), 15.3 (SCH2CH3).
1H NMR data recorded were in accordance with those found in the
literature.31
Ethyl 3-O-benzoyl-2,6-dideoxy-2-N-phthalimido-1-thio-
␤-D-glucopyranoside (4)
Compound 3 (6.60 mg, 15.7 mmol) was deacetylated by addition
of NaOMe in MeOH (200 mL, 0.10 M). After 2 h, the solution was
acidified to pH 7 using IR-120 H+ resin. The resin was filtered off
and the solvent was removed. The crude was dissolved in pyridine
(97.0 mL, 0.16 M) and cooled to –30 °C. A diluted solution of ben-
zoyl chloride (1.05 equiv.) in pyridine (20.5 mL, 0.81 M) was then
added dropwise over 10 min. The reaction was stirred for 1 h and
quenched with water. The solution was diluted with EtOAc
(200 mL) and washed with 2 M HCl (50 mL × 2), saturated NaHCO3
(50 mL), and brine (50 mL) and then concentrated under vacuum.
The crude was purified by column chromatography (cyclohexane –
ethyl acetate, 4/1 v/v) to yield 4 (6.29 mg, 91%) as a white foam. [␣]D =
+118.8 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 7.88–7.33 (m, 8H,
ArH), 5.85 (dd, 1H, H-3, J = 10.2, 8.9 Hz), 5.52–5.50 (d, 1H, H-1, J =
10.5 Hz), 4.52 (t, 1H, H-2, J = 10.4 Hz), 3.76–3.71 (m, 1H, H-5), 3.56 (t,
1H, H-4, J = 9.3 Hz), 2.94 (s, 1H, OH), 2.77–2.63 (m, 2H, SCH2CH3),
1.46–1.45 (d, 3H, CH3, J = 6.1 Hz) 1.22 (t, 3H, SCH2CH3, J = 7.3 Hz).
13C NMR (500 MHz, CDCl3) ␦: 168.0–167.4 (NCO, C=O) 134.3, 134.2,
133.6 (ArC), 129.9, 128.8, 128.6, 123.7, 123.6 (ArCH), 80.7 (C1), 76.7
(C5), 75.8 (C3), 75.7 (C4), 54.0 (C2), 24.4 (SCH2CH3), 18.1 (C6), 15.0
(SCH2CH3). HRMS C23H23NO6SNa [M + Na+] calculated: 464.1144;
found: 464.1149.
Ethyl 3-O-acetyl-4-azido-2-N-(4-trifluoromethylbenzylidene)-
2,4,6-trideoxy-1-thio-␤-D-galactopyranoside (7)
Compound 6 (35.1 mg, 0.15 mmol) was suspended in trime-
thylorthoformate (0.30 mL), and to this, 4-(trifluoromethyl)
benzaldehyde (21.0 ␮L, 0.15 mmol) was added. After 2 h, the trimeth-
ylorthoformate was removed under reduced pressure and the
crude product was dissolved in pyridine (2.00 mL), cooled to 0 °C,
and acetic anhydride (1.00 mL) added. The reaction was stirred at
room temperature until there was no starting material observed.
The solvent was removed and the product was coevaporated with
toluene and then purified by column chromatography (cyclohex-
ane – ethyl acetate, 5/1 v/v) to give 7 as a 93% yield as a white foam.
[␣]D = –92.4 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 8.34 (s, 1H,
NH), 7.86–7.84 (d, 2H, ArH), 7.68–7.66 (d, 2H, ArHA), 5.27–5.25 (dd,
1H, H-3 J = 9.7, 3.6 Hz), 4.77–4.75 (d, 1H, H-1, J = 9.7 Hz), 3.91 (dd, 1H,
H-4, J = 3.5, 0.9 Hz), 3.88 (m, 1H, H-5), 3.62 (t, 1H, H-2, J = 9.7 Hz), 2.68
(m, 2H, SCH2CH3), 1.98 (s, 3H, CH3), 1.40–1.39 (d, 3H, H-6a-c, J =
6.3 Hz), 1.23 (t, 3H, SCH2CH3, J = 7.4 Hz). 13C NMR (126 MHz, CDCl3)
␦: 170.0 (C=O), 163.4 (C=N), 138.7 (ArC), 133.3–132.5 (q, CCF3, 2JCF3
=
3
32.5 Hz), 128.8 (ArCX), 125.8–125.7 (q, ArCA, JCF3 = 3.8 Hz), 127.2–
120.7 (q, CF3, 1JCF3 = 274 Hz), 84.2 (C1), 75.1 (C3), 73.4 (C5), 69.6 (C2),
62.7 (C4), 24.6 (SCH2CH3), 20.6 (CH3) 18.0 (C6), 15.0 (SCH2CH3).
HRMS C18H21F3N4O3SNa [M + Na+] calculated: 453.1184; found:
453.1203.
Ethyl 4-azido-3-O-benzoyl-2,4,6-trideoxy-2-N-phthalimido-1-thio-
␤-D-glucopyranoside (5)
Compound 4 (6.00 g, 13.6 mmol) was dissolved in dry CH2Cl2
(97.0 mL, 0.14 M) under a flow of nitrogen and, to this, pyridine
(1.43 mL, 17.7 mmol) was added. The solution was cooled to –20 °C
and a solution of triflic anhydride (2.70 mL, 16.3 mmol) in CH2Cl2
(30.0 mL) was added over 30 min. The solution was stirred for a
further 30 min at –20 °C and then diluted with CH2Cl2 and washed
with water (2 × 100 mL), saturated NaHCO3 (2 × 100 mL), and brine
(1 × 100 mL). The organic layer was dried over Na2SO4, filtered
through a silica plug, and concentrated to give the triflate inter-
mediate. This was then redissolved in dimethylformamide (DMF)
(85 mL, 0.16 M) under a flow of nitrogen and NaN3 (2.21 g,
40.8 mmol) was added. After stirring at room temperature for 1 h,
the solvent was removed and the product 5 (5.40 g, 86%) was
isolated by column chromatography (cyclohexane – ethyl acetate,
4/1 v/v) as a white foam. [␣]D = –30.4 (c = 1.0, CHCl3). 1H NMR
(500 MHz, CDCl3) ␦: 7.95–7.93 (m, 2H, BzH), 7.80(m, 2H NPhthH)
7.68 (m, 2H, NPhthH), 7.53–7.50 (m, 1H, BzH) 7.39–7.36 (m, 2H,
BzH), 6.08 (dd, 1 H, H-3, J = 10.8, 3.7 Hz), 5.44 (d, 1H, H-1, J = 10.5 Hz),
4.83 (t, 1H, H-2, J = 10.6 Hz), 4.12 (dd, 1H, H-4, J = 3.7, 0.8 Hz), 4.03 (qd,
1H, H-5), 2.83–2.59 (m, 2H, SCH2CH3), 1.43 (s, 3H, CH3), 1.22 (t, 3H,
SCH2CH3). 13C NMR (126 MHz, CDCl3) ␦: 168.1, 167.4 (2 × NCO), 165.4
(C=O), 134.2–123.4 (ArC, ArCH), 80.6 (C1), 73.5 (C5), 71.8 (C3), 63.8
(C4), 50.0 (C2), 23.7 (SCH2CH3), 17.8 (C6), 14.8 (SCH2CH3) HRMS
C23H22N4O5SNa [M + Na+] calculated: 489.1209; found: 489.1205.
Methyl (ethyl 2,3-di-O-benzyl-1-thio-␤-D-galactopyranoside)
uronate (9)
Diol 8 (1.00 g, 2.47 mmol) was dissolved in a biphasic mixture of
CH2Cl2 and water (12 mL, 2/1 v/v) and cooled to 0 °C. BAIB (2.00 g,
6.18 mmol) was added followed by TEMPO (77.0 mg, 0.49 mmol)
and the reaction was vigorously stirred for 20 min. The reaction
was quenched by addition of Na2S2O3 (5 mL, 10% w/v aqueous
solution). The solution was diluted with CH2Cl2 and the organic
layer was separated. The aqueous phase was acidified to pH 1 with
1 M HCl and extracted with ethyl acetate (3 × 50 mL). The organic
layers were dried over Na2SO4, combined, and the solvent re-
moved under reduced pressure. The crude was dried under vac-
uum and then dissolved in DMF (12.0 mL). To this, K2CO3 (1.02 g,
7.41 mmol) and MeI (0.46 mL, 7.41 mmol) were added and the
reaction was stirred overnight. The reaction was diluted with eth-
yl acetate (100 mL) and the organic phase was washed with water
(3 × 100 mL) and dried over Na2SO4. The solvent was removed and
the product was isolated by column chromatography (cyclohexane –
ethyl acetate, 4/1 v/v) to give 9 (715 mg, 67%) as a white
foam. 1H NMR (400 MHz, CDCl3) ␦: 7.40–7.26 (m, 10H, ArH),
4.90–4.69 (dd × 2, 4H, CH2Ph), 4.44–4.41 (d, 1H, H-1, J = 9.8 Hz),
4.39 (s, 1H), 4.06 (s, 1H), 3.82 (s, 3H, COOCH3), 3.70 (t, 1H, H-2, J =
9.4 Hz), 3.62–3.59 (dd, 1H, H-3, J = 9.2, 3.4 Hz), 2.84–2.72 (m, 2H,
SCH2CH3), 1.32 (t, 3H, SCH2CH3, J = 7.3 Hz). Data recorded were
in accordance with those found in the literature.13
Ethyl 2-amino-4-azido-2,4,6-trideoxy-1-thio-␤-D-glucopyranoside (6)
A solution of compound 5 (5.40 g, 11.7 mmol) and ethylene
diamine (2.63 mL, 39.3 mmol) in ethanol (120 mL, 0.10 M) was
prepared and heated to 70 °C for 1.5 h. The solvent was then
Published by NRC Research Press

Ní Cheallaigh and Oscarson
949
Methyl (ethyl 4-O-chloroacetyl-2,3-di-O-benzyl-1-thio-
␤-D-galactopyranoside) uronate (10)
(c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3) ␦: 7.37–7.24 (m, 5H,
ArH), 4.83–4.75 (dd, 2H, CH2Ph), 4.43–4.42 (dd, 1H, H-4), 4.35–
4.33 (m, 2H, H-1, H-5), 4.20 (dd, 1H, H-3, J = 6.4, 6.0 Hz), 4.09–4.02
(m, 1H, OCH2CH2Si(CH3)3), 3.81 (s, 3H, OCH3), 3.57–3.50 (m, 1H,
OCH2CH2Si(CH3)3), 3.44 (dd, 1H, H-2, J = 7.6, 6.8 Hz), 1.32 (s, 3H CH3),
1.31 (s, 3H, CH3), 1.03 (m, 2H, OCH2CH2Si(CH3)3), 0.00 (s, 9H,
Si(CH3)3). 13C NMR (101 MHz, CDCl3) ␦: 168.0 (C=O), 138.3 (ArC),
128.4, 127.7 (ArCH), 110.6 (qC), 102.5 (C1), 78.8 (C2), 78.8 (C3), 74.1
(C4), 73.7 (CH2Ph), 72.2 (C5), 67.6 (OCH2CH2Si(CH3)3), 52.6 (OCH3),
27.7 (CH3), 26.5 (CH3), 18.5 (OCH2CH2Si(CH3)3), –1.3 (Si(CH3)3). HRMS
C22H34O7SiNa [M + Na+] calculated: 461.1972; found: 461.1977.
Compound 9 (163 mg, 0.37 mmol) was dissolved in anhydrous
CH2Cl2 (2.50 mL). Dry pyridine (0.17 mL) was added to the solution
and the temperature was reduced to 0 °C. Chloroacetyl chloride
(0.06 mL, 0.75 mmol) was added and the reaction was stirred for
1 h. The solvent was removed under reduced pressure and the
residue was coevaporated with toluene. Purification by column
chromatography (toluene – ethyl acetate, 6/1 v/v) gave 10 (176 mg,
92%) as a pale yellow oil. [␣]D = +14.9 (c 1.0, CHCl3). 1H NMR
(500 MHz, CDCl3) ␦: 7.38–7.30 (m, 10H, ArH), 5.90–5.89 (dd, 1H, H-4,
J = 3.3, 1.1 Hz), 4.84–4.54 (m × 2, 4H, 2 × CH2Ph), 4.51 – 4.49 (d, 1H,
H-1, J = 11.2 Hz), 4.19 (d, 1H, H-5, J = 9.7 Hz), 3.77 (s, 3H, COOCH3),
3.71–3.69 (dd, 1H, H-3, J = 9.1, 3.4 Hz), 3.62–3.58 (t, 1H, H-2, J =
9.4 Hz), 2.84–2.73 (m, 2H, SCH2CH3), 1.33 (t, 3H, SCH2CH3, J =
7.4 Hz). 13C NMR (126 MHz, CDCl3) ␦: 167.0, 166.8 (C=O × 2), 137.9,
137.3 (ArC), 128.6–128.1 (ArCH), 85.6 (C1), 80.3 (C3), 77.2 (C2), 76.1
(CH2Ph), 75.6 (C5), 72.5 (CH2Ph), 69.9 (C4), 53.0 (COOCH3), 40.9
(CH2Cl), 25.3 (SCH2CH3), 15.1 (SCH2CH3). HRMS C25H29O7SClNa [M +
Na+] calculated: 531.1220; found: 531.1234.
Methyl (2-(trimethylsilyl)ethyl 2-O-benzyl-endo-3,4-O-benzylidene-
␤-D-galactopyranoside) uronate (15 endo) and methyl
(2-(trimethylsilyl)ethyl 2-O-benzyl-exo-3,4-O-benzylidene-
␤-D-galactopyranoside) uronate (15 exo)
A solution of acetic acid and water (25.0 mL, 4/1 v/v) was added to
compound 14 (890 mg, 2.02 mmol) and the reaction was heated to
80 °C for 1 h. Upon completion, the reaction was cooled to room
temperature and poured onto excess ice-cold saturated NaHCO3.
The product was extracted with CH2Cl2 (50.0 mL) and washed with
saturated NaHCO3 (2 × 100 mL) and water (2 × 100 mL). The organic
layer was dried over Na2SO4 and the product was purified by fil-
tration through a silica plug. The solvent was removed to give
the diol (735 mg, 91%) as a clear oil. HRMS C19H30O7SiNa [M +
Na+] calculated: 421.1659; found: 421.1674. Camphorsulfonic acid
(21.0 mg, 0.09 mmol) was added to a stirred solution of the crude
diol (735 mg, 1.84 mmol) and benzaldehyde dimethyl acetal
(0.55 mL, 3.68 mmol) in DMF (13.0 mL) at 0 °C. The reaction was
stirred at 60 °C for 24 h and quenched by addition of Et3N at 0 °C.
The solvent was removed and the diastereomers were isolated by
column chromatography (cyclohexane – ethyl acetate, 4/1 v/v) to
give 15 endo and 15 exo as clear oils with a ratio of 2.2/1 (693 mg,
76%). Analysis for (15 endo): [␣]D = –1.8 (c 1.0, CHCl3). 1H NMR
(400 MHz, CDCl3) ␦: 7.41–7.22 (m, 10H, ArH), 5.90 (s, 1H, CHPh),
4.75–4.66 (dd, 2H, CH2Ph), 4.55–4.53 (dd, 1H H-3, J = 6.3, 2.5 Hz),
4.46–4.45 (m, 1H, H-5), 4.44–4.42 (d, 1H, H-1, J = 7.5 Hz), 4.37 (t, 1H,
H-2, J = 6.2 Hz), 4.10–4.03 (m, 1H, OCH2CH2Si(CH3)3), 3.81 (s, 3H,
COOCH3), 3.59–3.49 (m, 2H, OCH2CH2Si(CH3)3), 1.04–1.00 (m, 2H,
H-4, OCH2CH2Si(CH3)3), 0.00 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR
(101 MHz, CDCl3) ␦: 167.7 (C=O), 138.2, 137.0 (ArC), 129.4–127.0
(ArCH), 104.9 (CHPh), 102.6 (C1), 79.3 (C4), 78.5 (C2), 756.0 (C3), 73.7
(CH2Ph), 72.2 (C5), 67.6 (OCH2CH2Si(CH3)3), 52.7 (COOCH3), 18.5
(OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3). HRMS C26H34O7SiNa
[M + Na+] calculated: 509.1972; found: 509.1987. Analysis for (15
exo): [␣]D = +8.3 (c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3) ␦:
7.40–7.24 (m, 10H, ArH), 5.93 (s, 1H, CHPh), 4.89–4.80 (dd, 2H,
CH2Ph), 4.55 (t, 1H, H-2, J = 6.0 Hz), 4.52–4.50 (dd, 1H, H-4, J =
5.72, 2.09 Hz), 4.45–4.43 (d, 1H, H-1, J = 7.8), 4.34 (d, 1H, H-5, J =
2.1 Hz), 4.12–4.06 (m, 1H, OCH2CH2Si(CH3)3), 3.63–3.56 (m, 2H, H-3,
OCH2CH2Si(CH3)3), 1.05 (t, 2H, OCH2CH2Si(CH3)3, J = 8.5 Hz), 0.03 (s,
9H, OCH2CH2Si(CH3)3). 13C NMR (101 MHz, CDCl3) ␦: 167.9 (COOMe),
138.1 (ArC), 129.4–126.5 (ArCH), 103.8 (CHPh), 102.3 (C1), 79.7 (C2),
76.5 (C3), 74.3 (C4), 73.8 (CH2Ph), 72.7 (C5), 67.7 (OCH2CH2Si(CH3)3),
18.5 (OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3). HRMS C26H34O7SiNa
[M + Na+] calculated: 509.1972; found: 509.1964.
2-(Trimethylsilyl)ethyl 2-O-benzyl-3,4-O-isopropylidene-
␤-D-galactopyranoside (13)
Compound 11 (3.91 g, 9.98 mmol) was dissolved in DMF (100 mL)
and cooled to 0 °C before addition of sodium hydride (60% disper-
sion, 798 mg, 20.0 mmol). The reaction was stirred at 0 °C for
30 min following which benzyl bromide (2.44 mL, 20.0 mmol) was
added. The reaction was stirred at room temperature for 1 h and
then cooled to 0 °C and quenched by slow addition of MeOH. The
solvent was removed and a solution of acetic acid – water (4/1,
50.0 mL) was added to the crude (9.98 mmol) at room temperature.
The solution was stirred for 30 min and then quenched by pouring
onto ice-cold saturated NaHCO3 (200 mL). The product was ex-
tracted with CH2Cl2 (150 mL) and washed with saturated NaHCO3
(2 × 100 mL) and water (2 × 100 mL). The organic layer was dried
over Na2SO4 and the product was purified by column chromatog-
raphy (cyclohexane – ethyl acetate, 5/1 v/v). The solvent was re-
moved to give 13 (3.6 g, 88%) as a clear oil. [␣]D = +30.8 (c 1.0, CHCl3).
1H NMR (400 MHz, CDCl3) ␦: 7.3–7.22 (m, 5H, ArH), 4.85–4.77 (dd,
2H, CH2Ph), 4.33–4.31 (d, 1H, H-1, J = 8 Hz), 4.16 (m, 1H, H-4), 4.11 (dd,
1H, H-3, J = 5.6, 1.9 Hz), 3.99 (m, 2H, H-6a, OCH2CH2Si(CH3)3), 3.80
(m, 2H, H-5, H-6b), 3.58 (m, 1H, OCH2CH2Si(CH3)3), 3.36 (dd, 1H, H-2,
J = 8.0, 7.0 Hz), 2.15 (s, 1H, H6-OH), 1.03 (m, 2H, OCH2CH2Si(CH3)3),
0.01 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR (126 MHz, CDCl3) ␦: 138.5
(ArC), 128.3, 127.7 (ArCH), 110.3 (qC), 102.6 (C1), 79.7 (C2), 79.4
(C3), 74.2 (C4), 73.7 (CH2Ph), 73.2 (C5), 67.5 (OCH2CH2Si(CH3)3),
62.7 (C6), 27.9, 26.5 (C(CH3)2), 18.6 (OCH2CH2Si(CH3)3), –1.3
(OCH2CH2Si(CH3)3). HRMS C21H34O6SiNa [M + Na+] calculated:
433.2022; found: 433.2042.
Methyl (2-(trimethylsilyl)ethyl 2-O-benzyl-3,4-O-isopropylidene-
␤-D-galactopyranoside) uronate (14)
Bis(acetoxyiodo)benzene (3.26 g, 10.1 mmol) was added to a bi-
phasic solution of CH2Cl2 and water (20.0 mL, 2/1 v/v) containing 13
(1.66 g, 4.05 mmol). The solution was cooled to 0 °C and TEMPO
(120 mg, 0.81 mmol) was added. The reaction was stirred vigor-
ously for 1 h and then quenched by addition of 10% sodium
thiosulfate solution (20 mL). The mixture was diluted with CH2Cl2
and the organic phase was washed with saturated NaHCO3 (2 ×
50 mL) and water (2 × 50 mL). After drying over sodium sulphate
and filtration, the solvent was removed from the organic layer.
The crude material and K2CO3 (1.12 g, 8.10 mmol) were dried under
reduced pressure overnight before dissolving in DMF (40 mL). The
solution was cooled to 0 °C and MeI (0.50 mL, 8.10 mmol) was
added dropwise. The solution was stirred at room temperature
overnight. The solvents were removed and the product was
isolated by column chromatography (cyclohexane – ethyl ace-
tate, 3/1 v/v) to give 14 (992 mg, 56%) as a clear oil. [␣]D = +8.4
Methyl (2-(trimethylsilyl)ethyl 2,4-di-O-benzyl-␤-D-galactopyranoside)
uronate (16)
Method 1
Compound 15 endo (200 mg, 0.41 mmol) was dissolved in anhy-
drous THF (10.0 mL) and borane timethyl amine was added
(124 mg, 1.74 mmol) to the solution. The reaction was cooled to
0 °C and aluminum chloride (348 mg, 2.62 mmol) was added. The
reaction was stirred for 30 min before water (16 ␮L, 0.82 mmol)
was added. The product was taken up in CH2Cl2 and washed with
1 M hydrochloric acid solution (2 × 100 mL), saturated NaHCO3 (2 ×
Published by NRC Research Press

950
Can. J. Chem. Vol. 94, 2016
100 mL), and water (2 × 100 mL). The organic layer was then dried
over Na2SO4 and the product was isolated by column chromatog-
raphy (cyclohexane – ethyl acetate, 4/1 v/v) to give 16 (136 mg, 68%)
as a clear oil.
bicarbonate (39.0 mg, 0.46 mmol) were added. The suspension was
heated to 60 °C for 16 h. The reaction was then diluted with CH2Cl2
and filtered through a Celite plug. The solvent was removed and
the crude was purified by column chromatography (toluene – ethyl
acetate, 3/1 v/v) to give 19 (112 mg, 84%) as a clear oil. [␣]D = +32.8
(c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 7.36–7.06 (m, 20 H, ArH),
5.26–5.25 (d, 1H, H-1=, J = 3.3 Hz), 5.03–4.37 (m × 4, 8H, CH2Ph),
4.37–4.36 (d, 1H, H-1, J = 7.5 Hz), 4.24 (m, 1H, H-5=), 4.12–4.07 (m, 2H,
OCH2CH2Si(CH3)3), 4.05 (m, 1H, H-4=), 4.03 (m, 1H, H-5), 3.98–3.95
(dd, 1H, H-3, J = 9.9, 3.3 Hz), 3.89–3.86 (dd, 1H, H-2=, J = 9.9, 3.3 Hz),
3.85–3.84 (m, 2H, H-2, H-3=), 3.66 (s, 3H, COOCH3), 3.62 (s, 3H,
COOCH3), 3.58 – 3.52 (m, 1H, OCH2CH2Si(CH3)3), 1.0 (m, 2H,
OCH2CH2Si(CH3)3), 0.00 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR
(126 MHz, CDCl3) ␦: 169.2, 168.7 (2 × C=O), 138.6, 138.6, 137.9, 137.8
(4 × ArC), 128.8–127.3 (ArCH), 103.5 (C1), 95.1 (C1=), 77.5, 77.2 (C2,
C2=), 76.5 (C3), 75.3, 75.0, 74.8 (3 × CH2Ph), 74.7 (C3=), 74.4 (C5), 74.0
(C4), 72.5 (CH2Ph), 69.9 (C4=), 68.4 (C5=), 67.9 (OCH2CH2Si(CH3)3),
52.5 (COOCH3), 52.3 (COOCH3), 18.7 (OCH2CH2Si(CH3)3), –1.31
(OCH2CH2Si(CH3)3). HRMS C47H58O13SiNa [M + Na+] calculated:
881.3544; found: 881.3558.
Method 2
Compound 15 exo (50 mg, 0.10 mmol) was dissolved in 1 M, BH3
in THF (1.00 mL) at 0 °C; to this, 1 M Bu2BOTf in toluene (0.10 mL)
was added and the solution was stirred for 2 h. The reaction was
quenched with Et3N followed by slow addition of MeOH until H2
evolution ceased. The solvents were removed and the two prod-
ucts were separated by column chromatography using a gradient
elution (dichloromethane–methanol, 1/0 to 5/1 v/v) to give an 81%
yield (40 mg) with a 3/2 ratio of 4OBn (24 mg) to 3OBn (16 mg) as
clear oils.
[␣]D = +1.2 (c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3) ␦: 7.35–7.24
(m, 10H, ArH), 4.99–4.60 (dd × 2, 4H, CH2Ph), 4.36–4.34 (d, 1H, H-1,
J = 7.4 Hz), 4.18–4.17 (m, 1H), 4.12–4.05 (m, 2H), 3.70–3.65 (m, 4H),
3.60–3.51 (m, 2H), 1.33–1.31 (d, 1H, OH) 1.10–0.99 (m, 2H,
OCH2CH2Si(CH3)3), 0.01 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR (101 MHz,
CDCl3) ␦: 168.8 (C=O), 138.6, 138.2 (ArC), 128.6–127.8 (ArCH), 103.1 (C1),
78.9, 76.9, 75.0, 74.8, 74.1, 73.9 (C2, C3, C4, C5, 2 × CH2Ph), 67.8
(OCH2CH2Si(CH3)3), 52.4 (COOCH3), 18.6 (OCH2CH2Si(CH3)3), –1.3
(OCH2CH2Si(CH3)3). HRMS C26H36O7SiNa [M + Na+] calculated: 511.2128;
found: 511.2131.
2-(Trimethylsilyl)ethyl (3-O-acetyl-4-azido-2-N-
(4-trifluoromethylbenzylidene)-2,4,6-trideoxy-D-galactopyranosyl-
␣(1¡4)-methyl (2,3-di-O-benzyl-D-galactopyranosyl) uronate-
␣(1¡3)-methyl (2,4-di-O-benzyl-␤-D-galactopyranoside)
uronate) (20) and 2-(trimethylsilyl)ethyl (3-O-acetyl-4-azido-2-N-
(4-trifluoromethylbenzylidene)-2,4,6-trideoxy-D-galactopyranosyl-
␤(1¡4)-methyl (2,3-di-O-benzyl-D-galactopyranosyl) uronate-␣(1¡3)-
methyl (2,4-di-O-benzyl-␤-D-galactopyranoside) uronate) (21)
Donor 7 (38.0 mg, 0.08 mmol), disaccharide acceptor 19
(64.0 mg, 0.07 mmol), and 4 Å molecular sieves were dried under
reduced pressure. To this, a solution of Et2O and CH2Cl2 (3/2,
1.00 mL) was added and stirred at room temperature under ni-
trogen for 30 min and then cooled to 0 °C. Meanwhile, a 1 M
solution of promoter was prepared by adding dimethyldisulfide
(0.10 mL, 1.10 mmol) and triflic anhydride (0.17 mL, 1.00 mmol) to
anhydrous CH2Cl2 (0.75 mL) at 0 °C. The solution was stirred for
30 min before adding the promoter (126 ␮L, 0.13 mmol) to the
glycosylation reaction. The glycosylation was allowed come to
room temperature and after 30 min was quenched by the addition
of excess triethylamine. The reaction was diluted with CH2Cl2 and
washed with 1 M hydrochloric acid (2 × 50 mL), saturated NaHCO3
(2 × 50 mL), and water (2 × 50 mL) and the organic layer was then
dried over Na2SO4 and the solvent was removed. The trisaccharide
was obtained in a 96% yield as a 3␣/2␤ mixture, which was sepa-
rable by column chromatography to give the ␣-trisaccharide prod-
uct 20 (49.0 mg, 57%) and the ␤-trisaccharide 21 (34.0 mg, 39%)
both as clear oils.
2-(Trimethylsilyl)ethyl (methyl (4-O-chloroacetyl-2,3-di-O-benzyl-
D-galactopyranosyl) uronate-␣(1¡3)-methyl (2,4-di-O-benzyl-
␤-D-galactopyranoside) uronate) (18)
Donor 10 (150 mg, 0.22 mmol), acceptor 16 (90.0 mg, 0.18 mmol),
and 4 Å molecular sieves were dried under reduced pressure. To
this, a solution of Et2O and CH2Cl2 (3/2, 2.52 mL) was added and
stirred at room temperature under nitrogen for 30 min and then
cooled to 0 °C. Meanwhile, a 1 M solution of promoter was pre-
pared by adding dimethyl disulfide (0.10 mL, 1.10 mmol) and triflic
anhydride (0.17 mL, 1.00 mmol) to anhydrous dichloromethane
(0.75 mL) at 0 °C. The solution of promoter was stirred for 30 min
before adding the promoter (0.33 mL, 0.33 mmol) to the glycosyl-
ation reaction. The glycosylation was allowed to come to room
temperature and after 30 min was quenched by the addition of
excess Et3N. The reaction was diluted with CH2Cl2 and washed
with 1 M hydrochloric acid (2 × 50 mL), saturated NaHCO3 solution
(2 × 50 mL), and water (2 × 50 mL) and the organic layer was
then dried over Na2SO4 and the solvent was removed. The
␣-disaccharide product 18 (128 mg, 74%) was isolated by column
chromatography (toluene – ethyl acetate, 6/1 v/v) as a clear oil with
1
no ␤-disaccharide observed. [␣]D = +64.5 (c 1.0, CHCl3). H NMR
(400 MHz, CDCl3) ␦: 7.33–7.04 (m, 20H, ArH), 5.48 (dd, 1H, H-4=, J =
3.2, 1.8 Hz), 5.22 (d, 1H, H-1=, J = 3.3), 5.01–4.96 (dd, 2H, CH2Ph), 4.95
(d, 1H, H-5=, J = 1.6 Hz), 4.79–4.37 (m, 6H, CH2Ph), 4.36 (d, 1H, H-1, J =
6..9), 4.21 (m, 1H, H-5), 4.1 (m, 1H, OCH2CH2Si(CH3)3)1, 4.05 (m, 1H,
H-4), 3.95–3.91 (dd, 1H, H-3, J = 10.1, 3.3 Hz), 3.82 (m, 3H, H-2, H-2=,
H-3=), 3.61 (s, 3H, CH3), 3.55 (m, 4H, CH3, OCH2CH2Si(CH3)3), 1.00
(m, 2H, OCH2CH2Si(CH3)3), –0.01 (s, 9H, OCH2CH2Si(CH3)3).
13C NMR (101 MHz, CDCl3) ␦: 168.6, 168.0, 166.5 (3 × C=O), 138.5,
138.4, 137.7, 137.6 (4 × ArC), 128.6–127.4 (ArCH), 103.5 (C1), 95.3 (C1=),
77.5, 76.7 (C2, C2=), 75.8 (C3), 75.3, 75.0, 74.8 (3 × CH2Ph), 74.4 (C3=),
74.3 (C5), 74.0 (C4), 72.5 (CH2Ph), 70.9 (C4=), 68.8 (C5=), 67.9
(OCH2CH2Si(CH3)3), 52.5, 52.4 (2 × COOCH3), 40.7 (CH2Cl), 18.6
(OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3). HRMS C49H59O14SiClNa
[M + Na+] calculated: 957.3260; found: 957.3242.
Analysis 20: [␣]D = +69.2 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3)
␦: 8.32 (s, 1H, NH), 7.91–7.02 (m, 24H, ArH), 5.40–5.37 (dd, 1H H-3== ),
5.33 (d, 1H, H-1=, J = 3.3 Hz), 5.08 (d, 1H, CH2Ph), 4.88–4.84 (m, 2H,
CH2Ph, H-1== , J = 3.3 Hz), 4.82–4.70 (m, 4H CH2Ph), 4.59 (s, 1H, H-4=),
4.47–4.43 (m, 4H, CH2Ph, H-2== , H-1, J = 7.8 Hz), 4.25 (s, 1H, H-5), 4.13
(m, 2H, H-3=, H-2/H-2=), 4.03 (m, 2H, H-4, OCH2CH2Si(CH3)3), 3.89–
3.85 (m, 3H, H-3, H-4== , H-5== ), 3.78–3.75 (m, 2H, H-2/H-2== , H-5=), 3.64
(s, 3H, COOCH3), 3.56–3.49 (m, 1H, OCH2CH2Si(CH3)3), 3.03 (s, 3H,
COOCH3), 1.94 (s, 3H, COOCH3), 1.04–1.03 (d, 3H, H-6a-c), 1.01–0.94
(m, 2H, OCH2CH2Si(CH3)3), –0.02 (s, 9H, OCH2CH2Si(CH3)3).
13C NMR (101 MHz, CDCl3) ␦: 170.1, 168.7, 168.3 (3 × C=O), 163.5
(N=C), 138.7, 138.5, 137.8 (ArC), 137.8–133.7 (q, CCF3, 2JCF3 = 32.5 Hz),
129.5–127.4 (ArCH), 103.5 (C1), 101.1 (C1== ), 94.8 (C1=), 75.1, 75.0, 74.3,
73.0 (4 × CH2Ph) 77.6, 77.4, 76.5, 76.4, 74.7, 74.5, 74.0, 71.3, 70.3,
68.6, 65.4, 63.9 (C2, C2=, C2== , C3, C3=, C3== , C4, C4=, C4== , C5, C5=,
C5== ), 67.9 (OCH2CH2Si(CH3)3), 52.5 (COOCH3), 51.7 (COOCH3), 20.6
(COCH3), 18.6 (C6), 17.4 (OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3).
HRMS C63H73N4O16SiF3Na [M + Na+] calculated: 1249.4641; found:
1249.4618.
2-(Trimethylsilyl)ethyl (methyl 2,3-di-O-benzyl-D-galactopyranosyl
uronate-␣(1¡3)-methyl 2,4-di-O-benzyl-␤-D-galactopyranoside
uronate) (19)
Disaccharide 18 (144 mg, 0.15 mmol) was dissolved in THF
(1.70 mL), and to this solution, thiourea (37.0 mg, 0.51 mmol),
tetrabutylammonium iodide (11.0 mg, 0.03 mmol), and sodium
Published by NRC Research Press

Ní Cheallaigh and Oscarson
951
Analysis 21: [␣]D = +36.6 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3)
␦: 8.41 (s, 1H, NH), 7.82–6.75 (m, 24H, ArH), 5.23–5.20 (dd, 1H, H-3== ,
J = 10.2, 3.7 Hz), 5.11 (d, 1H, H-1=, J = 3.3 Hz), 4.99–4.98 (d, 1H, H-1== ,
J = 7.6 Hz), 4.96–4.83 (dd, 2H, CH2Ph), 4.80 (m, 1H, H-4=), 4.68–4.55
(dd, 3H, CH2Ph), 4.32 (d, 1H, H-1, J = 7.2 Hz), 4.24 (m, 2H, H-2== ),
4.22–4.15 (m, 2H, CH2Ph), 4.11 (s, 1H, H-5=), 4.03 (m, 1H,
OCH2CH2Si(CH3)3), 3.96 (m, 1H, H-3== ), 3.82–3.77 (m, 5H, CH2Ph,
H-4, H-3, H-4== , H-2=), 3.68–3.66 (m, H-5=, H-5== ), 3.61 (s, 3H, COOCH3),
3.57 (s, 3H, COOCH3), 3.54–3.50 (m, 2H, H-2, OCH2CH2Si(CH3)3),
1.99 (s, 3H, COCH3), 1.34–1.33 (d, 3H, H-6a-cٞ, J = 6.3 Hz), 1.04–0.96
(m, 2H, OCH2CH2Si(CH3)3), –0.02 (s, 9H, OCH2CH2Si(CH3)3).
13C NMR (101 MHz, CDCl3) ␦: 170.3 168.6, 168.6 (3 × C=O), 163.3
(C=N), 139.2, 139.2, 138.7, 138.6, 138.5, 137.7 (6 × ArC), 137.8–133.7 (q,
3.89–3.86 (m, 2H, H-2, H-5), 2.78–2.70 (m, 1H, SCH2CH3), 1.40–1.39
(d, 3H, CH3, J = 6.4 Hz), 1.32–1.29 (t, 3H, SCH2CH3, J = 7.4 Hz).
13C NMR (126 MHz, CDCl3) ␦: 158.0 (C=O), 83.5 (C1), 82.2 (C3), 75.1
(C2), 61.0 (C4), 55.0 (C5), 24.7 (SCH2CH3), 17.9 (C6), 15.4 (SCH2CH3).
HRMS C9H14N4O3SNa [M + Na+] calculated: 281.0684; found:
281.0691.
Ethyl 4-azido-2-N-tert-butyloxycarbonyl-2,3-N,O-oxazolidinone-
2,4,6-trideoxy-1-thio-␤-D-glucopyranoside (24)
To a stirred solution of 23 (3.50 mg, 0.14 mmol) in THF (1.00 mL),
Boc2O (147 mg, 0.68 mg) and 4-dimethylaminopyridine (2.00 mg,
0.01 mmol) were added. The solution was heated to 60 °C and
monitored by TLC (cyclohexane – ethyl acetate, 2/1 v/v). After 1 h,
the solvent was removed and the product 24 (44.0 mg, 91%) was
isolated as a white foam by column chromatography (cyclohexane –
ethyl acetate, 2/1 v/v). [␣]D = –66.8 (c 1.0, CHCl3). 1H NMR
(500 MHz, CDCl3) ␦: 4.60 (d, 2H, H-1, J = 8.4 Hz), 4.28–4.20 (m, 2H,
H-2, H-3), 4.06 (m, 1H, H-4), 3.90–3.86 (m, 1H, H-5), 2.67 (m, 2H,
SCH2CH3), 1.57 (s, 9H, 3 × CH3), 1.40 (d, 3H, CH3, J = 6.3 Hz), 1.25 (t,
3H, SCH2CH3, J = 7.4 Hz). 13C NMR (126 MHz, CDCl3) ␦: 153.1, 150.7
(2 × C=O), 85.7 (qC), 85.3 (C1), 79.7 (C3), 75.0 (C5) 61.1 (C4), 56.5 (C2),
27.9 (C(CH3)3), 25.0 (SCH2CH3), 17.6 (C6), 14.6 (SCH2CH3). HRMS
C14H22N4O5SNa [M + Na+] calculated: 381.1209; found 381.1214.
2
CCF3, JCF3 = 32.5 Hz), 128.8–125.6 (ArCH), 103.5 (C1), 100.9 (C1== ),
95.4 (C1=), 75.0, 74.9, 74.8 (3 × CH2Ph), 70.8 (CH2Ph), 78.0, 77.3, 76.7,
76.5, 74.6, 74.5, 74.0, 73. 5, 72.9, 70.2, 69.1, 62.2 (C2, C2=, C2== , C3,
C3=, C3== , C4, C4=, C4== , C5, C5=, C5== ), 67.9 (OCH2CH2Si(CH3)3), 52.4,
52.2 (2 × COOCH3), 20.6 (COCH3), 18.6 (OCH2CH2Si(CH3)3), 17.7
(C6== ), –1.3 (OCH2CH2Si(CH3)3). HRMS C63H73N4O16SiF3Na [M + Na+]
calculated: 1249.4641; found: 1249.4642.
2-(Trimethylsilyl)ethyl (2-N-acetamido-3-O-acetyl-4-azido-
2,4,6-trideoxy-D-galactopyranosyl-␣(1¡4)-methyl
(2,3-di-O-benzyl-D-galactopyranosyl) uronate-␣(1¡3)-methyl
(2,4-di-O-benzyl-␤-D-galactopyranoside) uronate) (22)
Methanol (2.00 mL) was added to trisaccharide 20 (49.0 mg,
0.04 mmol) and a couple of drops of CH2Cl2 were added to help
solubility. A catalytic quantity of camphor sulfonic acid was then
added and the reaction was stirred for 6 h. The reaction was
quenched by addition of Et3N and the solvent was removed. The
crude was dried under reduced pressure and then taken up in
methanol (2.00 mL) and acetic anhydride was added (0.40 mL) and
the reaction was stirred overnight. The solvent was then removed
and the crude was coevaporated with toluene before being puri-
fied by column chromatography (dichloromethane–methanol, 9/1
Ethyl 2-N-acetyl-4-azido-2,3-N,O-oxazolidinone-2,4,6-trideoxy-
1-thio-␤-D-glucopyranoside (25)
Compound 23 (172 mg, 0.67 mmol) was dissolved in anhydrous
dichloromethane and cooled to 0 °C. N,N-diisopropylethylamine
(0.59 mL, 3.37 mmol) and acetyl chloride (0.24 mL, 3.37 mmol)
were added and the reaction was stirred for 1 h. TLC (cyclohexane –
ethyl acetate, 1/1 v/v) indicated that the reaction was complete
and the reaction was diluted with CH2Cl2, washed with saturated
NaHCO3, water, and 1 M HCl and dried over Na2SO4. Column
chromatography (cyclohexane – ethyl acetate, 1/1 v/v) gave the
product 25 in a quantitative yield as a white foam. [␣]D = –64.5 (c =
1
v/v) to give 22 (28.0 mg, 64%) as a clear oil. H NMR (400 MHz,
CDCl3) ␦: 7.59–7.00 (m, 20H, ArH), 5.54–5.52 (d, 1H), 5.26–5.26 (d,
1H, H-1=, J = 3.1 Hz) 5.04–4.97 (m, 2H), 4.87–4.84 (d, 1H), 4.76–4.65
(m, 3H), 4.60–4.48 (m, 3H), 4.42–4.39 (d, 1H), 4.32–4.27 (dd, 2H),
4.20–4.16 (m, 2H), 4.07–3.98 (m, 3H), 3.93–3.90 (dd, 1H), 3.85–3.82
(dd, 1H), 3.80–3.71 (dd, 1H), 3.75–3.71 (m, 1H), 3.62 (s, 3H, COOCH3),
3.56–3.47 (m, 1H, OCH2CH2Si(CH3)3), 3.30 (s, 3H, COOCH3),
2.08 (s, 3H, COCH3), 1.97 (s, 3H, COCH3), 1.74–1.70 (m, 2H,
OCH2CH2Si(CH3)3), 0.96–0.95 (d, 3H, H-6a-c== , J = 6.3 Hz), –0.04 (s,
9H, OCH2CH2Si(CH3)3). 13C NMR (101 MHz, CDCl3) ␦: 171.0, 170.9,
168.9, 168.6 (4 × C=O), 138.5, 138.2, 138.2, 137.4 (ArC), 128.8–127.8
(ArCH), 103.4, (C1), 99.4 (C1== ), 94.6 (C1=), 77.3, 77.29, 76.6, 75.3,
75.2, 75.0, 74.5, 74.4, 74.2, 73.9, 73.2, 71.0, 70.2, 67.9, 65.6, 64.4
(C2, C2=, C3, C3=, C3== , C4, C4=, C4== , C5, C5=, C5== , CH2Ph × 4,
OCH2CH2Si(CH3)3), 52.8, 52.5 (COOCH3), 52.0 (C2== ), 23.4 (COCH3),
20.8 (COCH3), 18.6 (OCH2CH2Si(CH3)3), 17.2 (C6== ), –1.4
(OCH2CH2Si(CH3)3).
1
1.0, CHCl3). H NMR (500 MHz, CDCl3) ␦: 4.63–4.61 (d, 1H, H-1, J =
8.1 Hz), 4.33–4.30 (m, 2H, H-3, H-2), 4.08 (m, 1H, H-4), 3.90–3.86 (m,
1H, H-5), 2.65–2.59 (m, 2H, SCH2CH3), 2.51 (s, 3H, COCH3), 1.40–1.39
(d, 3H, H-6a-c, J = 6.3 Hz), 1.23 (t, 3H SCH2CH3, J = 7.4 Hz). 13C NMR
(126 MHz, CDCl3) ␦: 172.9 (C=O), 153.6 (C=O), 85.4 (C1), 79.8 (C3),
74.9 (C5), 61.1 (C4), 56.3 (C2), 25.1 (SCH2CH3), 25.0 (COCH3), 17.5 (C6),
14.2 (SCH2CH3). HRMS C11H16N4O4SNa [M + Na+] calculated:
323.0790; found: 323.0778.
Methyl (2-N-acetyl-4-azido-2,3-N,O-carbonyl-2,4,6-trideoxy-
D-galactopyranosyl-␣(1¡4)-6-O-benzoyl-2,3-di-O-benzyl-
␣-D-galactopyranoside (27)
Donor 25 (20.0 mg, 0.07 mmol) and acceptor 26 (27.0 mg,
0.06 mmol) were dissolved in CH2Cl2 (1.00 mL) and cooled to 0 °C.
NIS (25.0 mg, 0.11 mmol) was added followed by AgOTf (5.60 mg,
0.02 mmol). The reaction was stirred for 30 min and then
quenched with Et3N. The crude was loaded directly onto a column
for purification (toluene – ethyl acetate, 6/1 v/v). This gave exclu-
sively the ␣-disaccharide 27 in a 59% yield (23.0 mg) as a white
foam. 1H NMR (500 MHz, CDCl3) ␦: 8.02–7.29 (m, 15H, ArH), 5.67–
5.66 (d, 1H, H-1=, J = 2.5 Hz), 4.84–4.77 (m, 4H, H-1), 4.73–4.64 (m,
3H), 4.57–4.48 (m, 1H), 4.45–4.41 (dd, 1H), 4.22–4.17 (m, 2H), 4.10–
4.10 (d, 1H), 4.07–3.98 (m, 3H), 3.92–3.85 (m, 2H), 3.80–3.77 (m, 2H),
3.37 (s, 3H, OCH3), 2.54 (s, 3H, COCH3), 0.98–0.96 (d, 3H, H-6a-c=, J =
6.4 Hz). 13C NMR (126 MHz, CDCl3) ␦: 172.6, 165.0, 153.0 (C=O),
138.4–133.3 (ArC), 129.8–128.0 (ArCH), 98.2 (C1), 97.4 (C1=), 77.6,
76.7, 76.3, 75.2, 73.8, 73.3, 73.1, 68.3, 67.5, 62.9, 62.3, 56.3, 55.5
(OCH3), 24.0 (COCH3), 17.0 (C6=). HRMS C37H40N4O11Na [M + Na+]
calculated: 739.2591; found: 739.2615.
Ethyl 4-azido-2,3-N,O-oxazolidinone-2,4,6-trideoxy-1-thio-
␤-D-glucopyranoside (23)
Compound 6 (1.02 g, 4.40 mmol) was dissolved in mixture of
acetonitrile (40.0 mL) and saturated NaHCO3 (20.0 mL) and stirred
for 30 min. The reaction was cooled to 0 °C and triphosgene
(781 mg, 2.64 mmol) was added. The reaction was stirred for
30 min and monitored by TLC (methanol – ethyl acetate – water,
7/2/1 v/v). A solution of ethylenediamine (10.0 mL) in ethyl acetate
(60.0 mL) was added to the reaction and stirred for a further
30 min. The organic layer was then separated, washed with water,
dried over Na2SO4, filtered, and reduced to dryness. The crude was
purified by column chromatography (cyclohexane – ethyl acetate,
1/1 v/v) to give 23 (885 mg, 78%) as a white foam. [␣]D = –116.7 (c = 1.0,
CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 5.20 (s, 1H, NH), 4.51 (d, 1H, H-1,
J = 9.7 Hz), 4.31–4.28 (dd, 1H, H-3, J = 11.2, 3.9 Hz), 4.00 (m, 1H, H-4),
Published by NRC Research Press

952
Can. J. Chem. Vol. 94, 2016
Methyl (2-N-acetyl-4-azido-2,3-N,O-carbonyl-2,4,6-trideoxy-
D-galactopyranosyl-␤(1¡4)-6-O-benzoyl-2,3-di-O-benzyl-
␣-D-galactopyranoside (28)
Ethyl 2,3-di-O-benzyl-4,6-O-naphtylmethylidene-1-thio-
␤-D-galactopyranoside (33)
A solution of 8 (3.20 g, 14.3 mmol) in DMF (90.0 mL) was added
with dimethyl naphthaldehyde (8.70 g, 42.9 mmol) and camphor
sulfonic acid (660 mg, 2.86 mmol). The mixture was heated up to
60 °C and stirred overnight. The reaction was then cooled down to
0 °C and added with Et3N until pH 7 was reached. The solvent was
removed under reduced pressure and the crude was taken up with
CH2Cl2 and washed with water. The crude was purified by flash
column chromatography (ethyl acetate – cyclohexane, 9/1 v/v) to
give 33 (4.30 g, 83% yield) as a white foam. [␣]D = +26.7 (c 0.88,
CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 8.03–7.19 (m, 17H, ArH), 5.63 (s,
1H, CHNap), 4.90 (d, 1H, H-1, J = 10.2), 4.84 (d, 1H, CH2Ph), 4.81–4.72
(m, 2H, CH2Ph), 4.46 (d, 1H, CH2Ph), 4.36 (dd, 1H, H-6a), 4.23–4.21
(m, 1H, H-4), 4.01 (dd, 1H, H-6b), 3.92 (t, 1H, H-2, J = 6.4 Hz), 3.62 (dd,
1H, H-3, J = 4.6, 1.2 Hz), 3.41–3.37 (m, 1H, H-5), 2.93–2.72 (m, 2H,
SCH2CH3), 1.34 (t, 3H, SCH2CH3, J = 7.4 Hz). 13C NMR (126 MHz,
CDCl3) ␦: 138.7–133.2 (ArC), 128.6–124.4 (ArCH), 101.8 (NapCH), 84.7
(C1), 81.4 (C3), 77.1 (C2), 75.9 (CH2Ph), 74.3 (C4), 72.0 (CH2Ph), 70.1
(C5), 69.7 (C6), 24.1 (SCH2CH3), 15.3 (SCH2CH3). HRMS C33H34O5SNa
[M + Na+] calculated: 565.2025; found: 565.2031.
Donor 25 (20.0 mg, 0.07 mmol) and acceptor 26 (27.0 mg,
0.06 mmol) were dissolved in CH2Cl2 (1.00 mL) and cooled to 0 °C.
NIS (25.0 mg, 0.11 mmol) was added followed by AgOTf (1.40 mg,
5.50 ␮mol). The reaction was stirred for 10 min and then quenched
with Et3N. The crude was loaded directly onto a column for puri-
fication (toluene – ethyl acetate, 6/1 v/v). This gave a 1␣:6␤ ratio of
disaccharide in a 65% yield (25 mg) as a white foam. Analysis for
1
major product: H NMR (500 MHz, CDCl3) ␦: 8.02–7.27 (m, 15H,
ArH), 4.88–4.81 (dd, 2H, CH2Ph), 4.67–4.57 (m, 5H, CH2Ph, H-1, H-1=,
H-6a), 4.41–4.37 (dd, 1H, H-6b), 4.25–4.20 (m, 2H), 4.05–4.02 (m,
2H), 3.90–3.86 (m, 3H), 3.69–3.64 (m, 1H), 3.32 (s, 3H, OCH3), 2.30 (s,
3H, COCH3), 1.29–1.28 (m, 3H, H-6a-c=). 13C NMR (126 MHz, CDCl3) ␦:
171.3 (C=O), 153.8 (C=O), 138.9–133.2 (ArC), 129.7–127.8 (ArCH), 103.8
(C1=), 99.0 (C1), 78.1, 77.8, 74.0, 71.8, 67.8, 60.4, 56.6 (C2, C2=, C3, C3=,
C4, C4=, C5, C5=), 77.0 (CH2Ph), 76.7 (CH2Ph), 64.7 (C6), 55.5 (OCH3),
25.0 (COCH3), 17.3 (C6=). HRMS C37H40N4O11Na [M + Na+] calculated:
739.2591; found: 739.2605.
Methyl (2-N-tert-butyloxycarbonyl-4-azido-2,3-N,O-carbonyl-
2,4,6-trideoxy-D-galactopyranosyl-␣(1¡4)-6-O-acetyl-
2,3-di-O-benzyl-␤-D-galactopyranoside (31)
Ethyl-2,3-di-O-benzyl-6-O-2-naphtylmethyl-1-thio-
␤-D-galactopyranoside (34)
A solution of 33 (200 mg, 0.37 mmol) in anhydrous THF contain-
ing activated crushed 3 Å molecular sieves (200 mg) was added
with NaCNBH3 (136 mg, 2.16 mmol). The solution was then added
with HCl·Et2O until pH 1–2 was reached and was stirred for 1 h.
The reaction was then cooled down to 0 °C and added with Et3N
until pH 7 was reached. The sieves were filtered off and the solvent
was removed under reduced pressure. The crude was purified
by flash column chromatography (cyclohexane – )ethyl acetate,
Donor 24 (40.0 mg, 0.11 mmol) and acceptor 29 (19.0 mg,
0.05 mmol) were dissolved in CH2Cl2 (1.00 mL) and cooled to 0 °C.
NIS (25.0 mg, 0.11 mmol) was added followed by AgOTf (4.60 mg,
0.01 mmol). The reaction was stirred for 30 min, the formation of
the ␤-disaccharide 30 was observed by TLC, another 0.3 equiv. of
AgOTf was added, and the anomerisation to the ␣-disaccharide
was observed. The reaction was then quenched by addition of
Et3N. The crude was loaded directly onto a column for purification
(toluene – ethyl acetate, 6/1 v/v). This gave exclusively the
␣-disaccharide 31 in a 52% yield (17.0 mg). 1H NMR (500 MHz,
CDCl3) ␦: 7.40–7.29 (m, 10H, ArH), 5.48–5.47 (d, 1H, H-1=, J = 2.6 Hz),
4.92–4.90 (d, 1H, CH2Ph), 4.78–4.74 (m, 2H, CH2Ph), 4.70–4.67 (d,
1H, CH2Ph), 4.66–4.63 (dd, 1H), 4.32–4.28 (m, 1H, H-6a), 4.26–4.23
(m, 2H, H-1, J = 7.5 Hz), 4.16–4.13 (dd, 1H), 4.03–3.99 (m, 2H), 3.78 (s,
1H), 3.57 (m, 1H), 3.53 (s, 3H, OCH3), 3.48 (t, 1H), 3.41–3.38 (dd, 1H),
2.06 (s, 3H, COCH3), 1.53 (s, 9H, C(CH3)3), 0.96–0.94 (d, 3H, H-6a-c=,
J = 6.4 Hz). 13C NMR (126 MHz, CDCl3) ␦: 170.6 (C=O), 151.2, 151.0
(C=O), 138.4, 138.1 (ArC), 128.6–127.8 (ArCH), 105.1 (C1), 97.0 (C1=),
84.9 (qC), 74.8 (CH2Ph), 73.6 (CH2Ph), 79.8, 78.3, 74.1, 72.7, 71.9, 67.4,
62.2 (C2, C3, C3=, C4, C4=, C5, C5=), 61.9 (C6), 57.1, 56.3 (C2=), 28.1
(C(CH3)3), 21.0 (COCH3), 17.0 (C6=). HRMS C37H40N4O11Na [M + Na+]
calculated: 735.2853; found: 735.2841.
4/1 v/v) to give 34 (156 mg, 77% yield) as a colourless syrup. [␣]D
=
1
–4.2 (c 1.1, CHCl3). H NMR (500 MHz, CDCl3) ␦: 7.91–7.16 (m, 15H,
ArH), 4.87–4.76 (dd, 2H, CH2Ph, J = 58.0, 10.3 Hz), 4.73 (s, 2H,
CH2Ph), 4.70–4.67 (m, 2H, CH2Ph), 4.42 (d, 1H, H-1, J = 9.7), 4.10–4.08
(s, 1H, H-4), 3.81 (dd, 1H, H-6a, J = 10.0, 5.9 Hz), 3.77 (dd, 1H, H-6b, J =
9.9, 5.9 Hz), 3.67 (t, 1H, H-2, J = 9.3 Hz), 3.58 (t, 1H, H-5, J = 5.8 Hz),
3.54 (dd, 1H, H-3, J = 9.0, 3.2 Hz), 2.82–2.66 (m, 2H, SCH2CH3), 1.30
(t, 3H, SCH2CH3, J = 7.4 Hz). 13C NMR (126 MHz, CDCl3) ␦: 138.4–
133.2 (ArC), 128.7–125.9 (ArCH), 85.3 (C1), 82.6 (C3), 78.1 (C2), 77.2
(C6), 76.0 (CH2Ph), 74.0 (CH2Ph), 72.3 (CH2Nap), 69.6 (C5), 67.1 (C4),
24.9 (SCH2CH3), 15.3 (SCH2CH3). HRMS C33H36O5SNa [M + Na+] cal-
culated: 567.2182; found: 567.2205.
Ethyl-4-O-acetyl-2,3-di-O-benzyl-6-O-2-naphtylmethyl-1-thio-
␤-D-galactopyranoside (35)
Compound 34 (150 mg, 0.28 mmol) was dissolved in pyridine
(1.90 mL, 0.14 M), cooled to 0 °C, and acetic anhydride (56.0 ␮L,
0.55 mmol) was added. The solution was stirred for 4 h and the
solvent was then removed under reduced pressure and the prod-
uct was isolated by column chromatography (cyclohexane – ethyl
acetate, 4/1 v/v) to give 35 (159 mg, 99%) as a white foam. [␣]D = +2.1
(c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 7.84–7.26 (m, 17 H, ArH),
5.66 (m, 1H, H-4), 4.81–4.47 (dd × 3, d, 7H, CH2Ph × 2, CH2Nap, H-1),
3.75 (t, 1H, H-2, J = 6.4 Hz), 3.62–3.55 (m, 4H, H-3, H-5, H-6a, H-6b),
2.75 (m, 2H, SCH2CH3), 2.04 (s, 3H, COCH3), 1.31 (t, 3H, SCH2CH3, J =
7.4 Hz). 13C NMR (126 MHz, CDCl3) ␦: 170.5 (C=O), 138.3, 137.9, 135.2,
133.4, 133.2 (ArC), 128.5, 128.5, 128.4, 128.4, 128.3, 128.1, 127.9, 127.8,
127.0, 126.3, 126.1, 126.1 (ArCH), 85.6 (C1), 81.2 (C3), 78.0 (C5), 76.0
(C2, CH2Ar), 74.0, 72.0 (CH2Ar), 68.4 (C6), 67.1(C4), 25.2 (SCH2CH3),
21.1 (COCH3), 15.2 (SCH2CH3). HRMS C35H38O6SNa [M + Na+] calcu-
lated: 609.2287; found: 609.2294.
Methyl (2-N-tert-butyloxycarbonyl-4-azido-2,4,6-trideoxy-
D-galactopyranosyl-␣(1¡4)-2,3-di-O-benzyl-␤-D-galactopyranoside (32)
Disaccharide 31 (8.00 mg, 0.01 mmol) was dissolved in MeOH
(1.00 mL) and a couple of drops of CH2Cl2 were added to increase
solubility. The solution was cooled to 0 °C and added to a freshly
prepared solution of NaOMe in MeOH until a pH 11 was achieved.
After 30 min, the reaction was quenched by addition of IR-120 H+
resin until pH 7 was reached. The resin was filtered off and the
solvent was removed. The product was isolated after column chro-
matography (toluene – ethyl acetate, 6/1 v/v) to give 32 (6.60 mg,
92%). 1H NMR (500 MHz, CDCl3) ␦: 7.39–7.28 (m, 10H, ArH), 5.35 (s,
1H, NH), 4.90–4.88 (d, 2H, CH2Ph), 4.78–4.68 (m, 4H, H-1, H-1=,
CH2Ph), 4.34–4.29 (m, 2H), 4.07–4.06 (d, 1H), 3.97–3.91 (m, 2H),
3.85–3.82 (dd, 1H, H-6a), 3.72–3.66 (m, 1H, H-6b), 3.60–3.54 (m, 2H),
3.57 (s, 3H, OCH3), 3.45–3.40 (m, 2H), 1.47 (s, 9H, C(CH3)3), 1.43 (d,
1H, OH), 1.01 – 1.00 (d, 3H, H-6a-c=, J = 6.3 Hz). 13C NMR (126 MHz,
CDCl3) ␦: 138.4, 138.0 (ArC), 128.4–127.4 (ArCH), 105.2 (C1), 98.3 (C1=),
79.7, 74.9, 78.9, 74.9, 74.6, 72.8, 72.7, 71.1, 66.7, 65.7 (C2, C3, C3=, C4,
C4=, C5, C5=), 61.0 (C6), 57.2 (OCH3), 51.9 (C2=), 28.3 (C(CH3)3), 17.3
(C6=).
2-(Trimethylsilyl)ethyl 2-O-benzyl-3,4-O-isopropylidene-
6-O-naphthylmethyl-␤-D-galactopyranoside (36)
Compound 13 (1.93 g, 4.70 mmol) was dissolved in DMF
(50.0 mL) and cooled to 0 °C under a nitrogen atmosphere. To this
Published by NRC Research Press

Ní Cheallaigh and Oscarson
953
solution, sodium hydride (60% dispersion, 377 mg, 9.41 mmol) was
addedandthereactionwasstirredfor30minbefore2-(bromometh-
yl)naphthalene (2.08 g, 9.41 mmol) was added. The reaction was
stirred at room temperature for 30 min and returned to 0 °C
before quenching by addition of MeOH. The solvent was re-
moved and the product was isolated by column chromatogra-
phy (cyclohexane – ethyl acetate, 4/1 v/v) to give 36 (2.38 g, 92%) as
a clear oil. [␣]D = +15.2 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦:
7.81–7.23 (m, 13H, ArH), 4.84–4.69 (m, 4H, CH2Ph, CH2Nap), 4.32–
4.30 (d, 2H, H-1, J = 8.2 Hz), 4.14 (m, 2H, H-3, H-4), 4.06–4.00 (m, 1H,
OCH2CH2Si(CH3)3), 3.93 (m, 1H, H-5) 3.82 (m, 2H, H-6a, H-6b) 3.58
(m, 1H, OCH2CH2Si(CH3)3), 3.36 (dd, 1H, H-2, J = 8.0, 6.3 Hz), 1.33 (s,
3H, CH3), 1.31 (s, 3H, CH3), 1.03 (t, 2H, OCH2CH2Si(CH3)3, J = 8.6 Hz),
0.00 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR (126 MHz, CDCl3) ␦: 138.6–
133.1 (ArC), 128.3–125.8 (ArCH), 110.0 (qC), 102.6 (C1), 79.9 (C2), 79.3
(C4), 74.0, 73.9, 73.7 (C3, CH2Ph, CH2Nap), 72.4 (C5), 69.8 (C6), 67.4
(OCH2CH2Si(CH3)3), 27.9 (CH3), 26.6 (CH3), 18.6 (OCH2CH2Si(CH3)3),
–1.3 (OCH2CH2Si(CH3)3). HRMS C32H42O6SiNa [M + Na+] calculated:
573.2648; found: 573.2649.
OCH2CH2Si(CH3)3) 0.04 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR
(101 MHz, CDCl3) ␦: 138.5–133.1 (ArC), 129.3–125.8 (ArCH), 104.7
(CHPh), 102.6 (C1), 80.5 (C2), 78.9 (C3), 76.3 (C4), 73.9, 73.6 (2 ×
CH2Ar), 72.2 (C5), 69.5 (C6), 67.4 (OCH2CH2Si(CH3)3), 18.5
(OCH2CH2Si(CH3)3), –1.3(OCH2CH2Si(CH3)3). HRMS C38H41O6SiNa
[M + Na+] calculated: 621.2672; found: 621.2672.
2-(Trimethylsilyl)ethyl 2,4-di-O-benzyl-6-O-naphthylmethyl-
␤-D-galactopyranoside (39)
Method 1
Compound 37 endo (940 mg, 1.57 mmol) was dissolved in anhy-
drous THF (32.0 mL) and Me3NBH3 was added (458 mg, 6.28 mmol)
to the solution. The reaction was cooled to 0 °C and aluminum
chloride (1.26 g, 9.43 mmol) was added. The reaction was stirred
for 30 min before water (56.0 ␮L, 3.14 mmol) was added. The
reaction was monitored by TLC and quenched by the addition of
excess water. The product was taken up in CH2Cl2 and washed
with 1 M hydrochloric acid solution (2 × 100 mL), saturated
NaHCO3 (2 × 100 mL), and water (2 × 100 mL). The organic layer was
then dried over Na2SO4 and the product was isolated by column
chromatography (cyclohexane – ethyl acetate, 4/1 v/v) to give 39
(824 mg, 88%) as a clear oil.
2-(Trimethylsilyl)ethyl 2-O-benzyl-endo-3,4-O-benzylidene-
6-O-naphthylmethyl-␤-D-galactopyranoside (37 endo) and
2-(trimethylsilyl)ethyl 2-O-benzyl-exo-3,4-O-benzylidene-
6-O-naphthylmethyl-␤-D-galactopyranoside (38 exo)
Method 2
A solution of acetic acid and water (4/1, 200 mL) was added to
compound 36 (2.38 g, 4.32 mmol) and the reaction was heated to
80 °C for 2 h. Upon completion, the reaction was cooled to room
temperature and poured on to excess ice-cold saturated NaHCO3.
The product was extracted with CH2Cl2 and washed with satu-
rated NaHCO3 (2 × 100 mL) and water (2 × 100 mL). The organic
layer was dried over Na2SO4 and the product was purified by fil-
tration through a silica plug. The solvent was removed to give the
Compound 38 exo (60 mg, 0.10 mmol) was dissolved in 1 M BH3
in THF (1.00 mL) at 0 °C. To this, 1 M Bu2BOTf in toluene (0.10 mL)
was added. The reaction was stirred for 2 h until the reaction
had completed as indicated by TLC (cyclohexane – ethyl ace-
tate, 4/1 v/v). The reaction was quenched with Et3N followed by
slow addition of MeOH until H2 evolution ceased. The solvents
were removed and the two products were separated by column
chromatography using a gradient elution (dichloromethane–
methanol, 1/0–5/1 v/v) to give a 76% yield (45.0 mg) with a 1.2:1 ratio
of 39 (24.0 mg) to 40 (20.0 mg).
1
diol (2.20 g, 99%) as a clear oil. [␣]D = +4.6 (c 1.0, CHCl3). H NMR
(500 MHz, CDCl3) ␦: 7.81–7.26 (m, 12 H, ArH), 4.96–4.65 (m, 2H,
CH2Nap), 4.72 (s, 2H, CH2Ph), 4.37–4.35 (d, 1H, H-1, J = 7.7 Hz), 4.05
(m, 1H, OCH2CH2Si(CH3)3), 3.99 (m, 1H, H-5), 3.83–3.74 (m, 2H,
H-6a, H-6b), 3.63–3.54 (m, 3H, H-3, H-4, OCH2CH2Si(CH3)3),
3.47,(dd, 1H, H-2, J = 7.9, 6.5 Hz), 2.53, 2.47 (s, 2H, 3-OH, 4-OH),
[␣]D = –8.0 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 7.83–7.25
(m, 17H, ArH), 5.01–4.61 (dd × 3, 6H, CH2Ph × 2, CH2Nap), 4.39–4.37
(d, 1H, H-1, J = 7.6 Hz), 4.06–4.00 (m, 1H, OCH2CH2Si(CH3)3), 3.90–
3.89 (d, 1H, H-5), 3.70–3.66 (m, 3H, H-4, H-6a, H-6b), 3.60–3.54 (m,
2H, H-2, OCH2CH2Si(CH3)3), 2.67 (s, 1H, H-3), 2.28 (s, 1H, 3-OH), 1.04
(m, 2H, OCH2CH2Si(CH3)3), 0.02 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR
(126 MHz, CDCl3) ␦: 138.8–133.1 (ArC), 128.6–125.9 (ArCH), 103.4 (C1),
79.9 (C2), 75.7 (C5), 75.1, 74.7, 73.7 (CH2Ph × 2, CH2Nap), 74.2 (C4),
68.9 (C6), 67.4 (OCH2CH2Si(CH3)3), 54.3 (C3), 18.6 (OCH2CH2Si(CH3)3), –1.3
(OCH2CH2Si(CH3)3). HRMS C36H44O6SiNa [M + Na+] calculated: 623.2805;
found: 623.2814.
1.02 (t, 2H, OCH2CH2Si(CH3)3,
J = 8.6 Hz), –0.00 (s, 9H,
OCH2CH2Si(CH3)3). 13C NMR (126 MHz, CDCl3) ␦: 138.7–135.5
(ArC), 133.2–125.8 (ArCH), 103.3 (C1), 79.4 (C2), 74.7 (CH2Nap),
74.0 (CH2Ph), 73.4, 73.4 (C3, C4), 69.5 (C6), 69.1 (C5), 67.5
(OCH2CH2Si(CH3)3), 18.7 (OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3).
HRMS C29H38O6SiNa [M + Na+] calculated: 533.2335; found: 533.2325.
Camphor sulfonic acid (50.0 mg, 0.22 mmol) was added to a
stirred solution of the diol (2.20 g, 4.32 mmol) and benzaldehyde
dimethyl acetal (1.84 mL, 13.0 mmol) in DMF (30.0 mL) at 0 °C. The
reaction was stirred at room temperature for 16 h and quenched
by addition of triethylamine at 0 °C. The solvent was removed and
the diastereomers were isolated by column chromatography
(cyclohexane – ethyl acetate, 6/1 v/v) to give 37 endo and 38 exo as clear
oils with a ratio of 1:1 (1.99 g, 77%). Analysis for 37 endo: [␣]D = +9.2
(c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3) ␦: 7.84–7.29 (m, 17H, ArH),
5.95 (s, 1H, CHPh), 4.96–4.86, 4.82–4.70 (2 × dd, 4H, 2 × CH2Ar), 4.53
(m, 1H, H-3), 4.44 (d, 1H, H-1, J = 7.8 Hz), 4.23 (dd, 1H, H-4, J = 6.2,
2.2 Hz), 4.11–4.09 (m, 1H, OCH2CH2Si(CH3)3), 3.94–3.88 (m, 3H, H-5,
H-6a, H-6b), 3.70–3.63 (m, 1H OCH2CH2Si(CH3)3), 3.56 (t, 1H, H-2,
2-(Trimethylsilyl)ethyl (4-O-acetyl-2,3-di-O-benzyl-6-O-napthylmethyl-
D-galactopyranosyl-␣(1¡3)-2,4-di-O-benzyl-6-O-naphthylmethyl-
␤-D-galactopyranoside) (41)
Donor 35 (542 mg, 0.93 mmol), acceptor 39 (645 mg, 1.08 mmol),
and 4 Å molecular sieves were dried under reduced pressure. To
this a solution of Et2O and CH2Cl2 (3/2, 12.0 mL) was added and
stirred at room temperature under nitrogen for 30 min and then
cooled to 0 °C before adding to the Me2S2/Tf2O promoter (1.35 mL,
1.35 mmol) to the glycosylation reaction. The glycosylation was
allowed come to room temperature and after 30 min was
quenched by the addition of excess Et3N. The reaction was diluted
with CH2Cl2 and washed with 1 M hydrochloric acid (2 × 50 mL),
saturated NaHCO3 (2 × 50 mL), and water (2 × 50 mL) and the
organic layer was then dried over Na2SO4 and the solvent was
removed. The ␣-disaccharide product 41 (966 mg, 92%) was iso-
lated by column chromatography (toluene – ethyl acetate, 6/1 v/v)
as a clear oil with no ␤-disaccharide observed. [␣]D = +35.4 (c 1.0,
CHCl3). 1H NMR (400 MHz, CDCl3) ␦: 7.84–7.07 (m, 34H, ArH), 5.36–
5.35 (d, 1H, H-4=, J = 3.40 Hz), 5.20–5.19 (d, 1H, H-1=, J = 3.4 Hz),
5.01–4.37 (6 × dd, 12H, CH2Ar), 4.46 (m, 1H, H-5), 4.28–4.26 (d, 1H,
H-1, J = 7.8 Hz), 3.99–3.90 (m, 3H, OCH2CH2Si(CH3)3, H-3=, H-5),
J
= 8.6 Hz), 1.10 (m, 2H, OCH2CH2Si(CH3)3), 0.06 (s, 9H,
OCH2CH2Si(CH3)3). 13C NMR (101 MHz, CDCl3) ␦: 138.7–133.1 (ArC),
129.3–125.8 (ArCH), 103.5 (PhCH), 102.4 (C1), 80.3 (C3), 77.4 (C2), 74.2
(C4), 73.9, 73.8 (CH2Ph, CH2Nap), 72.7 (C5), 69.7 (C6), 67.4
(OCH2CH2Si(CH3)3), 18.6 (OCH2CH2Si(CH3)3), –1.2 (OCH2CH2Si(CH3)3).
Analysis for 38 exo: [␣]D = +13.6 (c 1.0, CHCl3). 1H NMR (400 MHz,
CDCl3) ␦: 7.85–7.24 (m, 17H, ArH), 5.91 (s, 1H, CHPh), 4.84–4.73 (m,
4H, CH2Ar × 2), 4.44–4.42 (d, 1H, H-1, J = 8.0 Hz) 4.35 (t, 1H, H-3, J =
6.3 Hz), 4.28–4.26 (dd, 1H, H-4, J = 6.2, 2.2 Hz), 4.06 (m, 2H, H-5,
OCH2CH2Si(CH3)3), 3.98–3.87 (m, 2H, H-6a, H-6b), 3.66–3.59 (m, 1H,
OCH2CH2Si(CH3)3) 3.52–3.48 (dd, 1H, H-2, J = 7.9, 6.5 Hz), 1.07 (m, 2H
Published by NRC Research Press

954
Can. J. Chem. Vol. 94, 2016
3.88–3.84 (dd, 1H, H-2=, J = 10.0, 3.4 Hz), 3.79–3.78 (m, 2H, H-2,
H-4), 3.57–3.56 (m, 2H, H-3, H-6a), 3.51–3.44 (m, 1H, H-6b,
OCH2CH2Si(CH3)3), 3.41–3.37 (dd, 1H, H-6a=, J = 10.0, 6.5 Hz), 3.28–
3.25 (dd, 1H, H-6b=, J = 10.1 5.7 Hz), 1.01 (m, 2H, OCH2CH2Si(CH3)3),
0.95 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR (101 MHz, CDCl3) ␦: 170.5
(C=O), 139.0, 138.9, 138.4, 138.3, 138.0, 135.8, 135.7, 133.4, 133.38,
133.1, 133.0 (ArC), 129.2–125.4 (ArCH), 103.9 (C1), 95.8 (C1=), 78.5,
77.9, 76.6, 75.7, 73.4, 72.7, 67.4, 68.5 (C2, C2=, C3, C3=, C4, C4=,
C5, C5=), 75.21, 74.6, 74.57, 73.7, 73.1, 71.8 (6 × CH2Ar), 68.9,
68.8 (C6, C6=), 67.5 (OCH2CH2Si(CH3)3), 21.1 (COCH3), 18.7
(OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3). HRMS C69H76O12SiNa [M +
Na+] calculated: 1147.5004; found: 1147.4982.
62.4 (H4== ), 56.3 (C2== ), 28.2 (C(CH3)3), 18.6 (OCH2CH2Si(CH3)3), 17.0
(C6== ), –1.3 (OCH2CH2Si(CH3)3). HRMS C79H90N4O16SiNa [M + Na+]
calculated: 1401.6019; found: 1401.6027.
2-(Trimethylsilyl)ethyl (2-N-acetyl-4-azido-2,3-N,O-carbonyl-
2,4,6-trideoxy-D-galactopyranosyl-␣(1¡4)-2,3-di-O-benzyl-
6-O-napthylmethyl-D-galactopyranosyl-␣(1¡3)-2,4-di-O-benzyl-
6-O-naphthylmethyl-␤-D-galactopyranoside) (44)
Donor 25 (42.0 mg, 0.07 mmol) was dissolved in CH2Cl2 (1.50 mL)
and added dropwise to a stirred solution of acceptor 42 (53.0 mg,
0.05 mmol), NIS (33.0 mg, 0.15 mmol), and AgOTf (7.00 mg,
0.03 mmol) in CH2Cl2 at 0 °C. The addition was carried out over 2 h
and the reaction was subsequently quenched with Et3N. The reac-
tion was then diluted in CH2Cl2 and washed with Na2S2O3 (2 ×
5 mL, 10% aqueous solution). The organic layer was dried over
Na2SO4, filtered, and the solvent was removed. The crude was
purified by column chromatography using a gradient elution
(toluene – ethyl acetate, 16/1–8/1 v/v) to give trisaccharide 44 (48.0 mg,
76%). [␣]D = +72.0 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 7.83–
7.15 (m, 34H, ArH), 5.64–5.63 (d, 1H, H-1== , J = 2.6 Hz), 5.25 (d, 1H,
H-1=, J = 2.7 Hz), 5.04–4.41 (6 × dd, 16H, CH2Ar), 4.71–4.69 (dd, 1H,
H-3== , J = 12.0, 2.8 Hz), 4.35–4.31 (m, 2H, H-5== , H-4=), 4.28–4.27 (d,
1H, H-1, J = 7.6 Hz), 4.21–4.18 (dd, 1H, H-2== , J = 12.1, 2.6 Hz), 4.04
(m, 1H, H-3=), 3.97–3.92 (m, 2H, OCH2CH2Si(CH3)3, H-3), 3.91–
3.90 (m, 2H, H-2=, H-5=), 3.82–3.81 (t, 1H, H-4== , J = 8.3 Hz), 3.79–
3.78 (m, 2H, H-2, H-5), 3.62–3.60 (m, 2H, H-6=a/b), 3.54–3.46 (m,
2H, H-4, OCH2CH2Si(CH3)3), 3.43–3.27 (m, 2H, H-6a/b), 2.50 (s,
3H, CH3), 1.03–0.90 (m, 3H, OCH2CH2Si(CH3)3, H-6== a-c), 0.00 (s,
8H, OCH2CH2Si(CH3)3). 13C NMR (126 MHz, CDCl3) ␦: 172.1
(COOCH3), 153.2 (C=O), 139.1, 138.9, 138.4, 138.0, 136.0, 135.6,
133.4, 133.4, 133.1, 133.0 (10 × ArC), 128.6–125.8 (ArCH), 103.9 (C1),
96.3 (C1== ), 95.0 (C1=), 78.4 (C2), 77.9 (C5), 77.0 (C2=), 75.7 (C5=),
75.0 (CH2Ar), 74.6 (CH2Ar), 74.3 (C3=), 73.8 (CH2Ar), 73.7 (CH2Ar),
73.3 (C3== ), 73.3 (C4), 73.1 (CH2Ar), 72.9 (C3), 72.6 (CH2Ar), 68.8
(C4=, C6=), 67.9 (C6), 67.5 (OCH2CH2Si(CH3)3), 67.1 (C5== ), 62.4
(C4== ), 56.2 (C2== ), 24.0 (CH3), 18.6 (OCH2CH2Si(CH3)3), 17.0 (C6== ),
–1.3 (OCH2CH2Si(CH3)3). HRMS C76H84N4O15SiNa [M + Na+] calcu-
lated: 1343.5600; found: 1343.5660.
2-(Trimethylsilyl)ethyl (2,3-di-O-benzyl-6-O-napthylmethyl-
D-galactopyranosyl-␣(1¡3)-2,4-di-O-benzyl-6-O-naphthylmethyl-
␤-D-galactopyranoside) (42)
Disaccharide 41 (920 mg, 0.82 mmol) was dissolved in a solution
of MeOH–CH2Cl2 (9/1 v/v, 20.0 mL), cooled to 0 °C, and a catalytic
quantity of NaOMe (4.50 mg, 0.08 mmol) was added. The reaction
was stirred for 3 h and Amberlite IR-150 H+ resin was added until
pH 7 was achieved. The resin was filtered off and the solvent was
removed. The product was purified by column chromatography
(toluene – ethyl acetate, 6/1 v/v) to give 42 (877 mg, 99%) as a clear
oil. [␣]D = +16.7 (c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3) ␦: 7.80–7.10
(m, 34H, ArH), 5.21–5.20 (d, 1H, H-1=, J = 3.4 Hz), 5.04–4.37 (6 × dd,
12H, CH2Ar), 4.28 (m, 2H, H-1, H-5) 4.02–3.86 (m, 4H, H-2=, H-3=,
H-5=, OCH2CH2Si(CH3)3), 3.81–3.77 (m, 3H, H-4=, H-2, H-4), 3.58–
3.57 (m, 2H, H-6a, H-6b), 3.53–3.45 (m, 4H, H-6a=, H6-b=,
OCH2CH2Si(CH3)3, H-3), 0.98 (m, 2H, OCH2CH2Si(CH3)3), 0.00 (s, 9H,
OCH2CH2Si(CH3)3). 13C NMR (101 MHz, CDCl3) ␦: 139.1, 139.0, 138.4,
135.7, 135. 7, 133.4, 133.1, 133.06 (ArC), 129.2–125.7 (ArCH), 103.9
(C1), 95.4 (C1=), 78.6, 77.9, 77.6, 75.9, 73.3, 72.7, 68.6, 67.9 (C2, C2=,
C3, C3=, C4, C4=, C5, C5=), 75.2, 74.6, 74.6, 73.6, 73.4, 72.1 (6 ×
CH2Ar), 70.3, 68.9 (C6, C6=), 67.5 (OCH2CH2Si(CH3)3), 18.7
(OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3). HRMS C67H74O11SiNa
[M + Na+] calculated: 1105.4898; found: 1105.4854.
2-(Trimethylsilyl)ethyl (4-azido-2-N-Boc-2,3-N,O-carbonyl-
2,4,6-trideoxy-D-galactopyranosyl-␣(1¡4)-2,3-di-O-benzyl-
6-O-napthylmethyl-D-galactopyranosyl-␣(1¡3)-2,4-di-O-benzyl-
6-O-naphthylmethyl-␤-D-galactopyranoside) (43)
2-(Trimethylsilyl)ethyl (4-azido-2-N-Boc-2,4,6-trideoxy-
Donor 24 (144 mg, 0.40 mmol), disaccharide acceptor 42
(299 mg, 0.28 mmol), and 4 Å molecular sieves were dried under
reduced pressure. CH2Cl2 (4.20 mL) was then added and the reac-
tion was cooled to 0 °C. N-iodosuccinimde (180 mg, 0.80 mmol) was
added to the reaction followed by silver triflate (41.3 mg,
0.16 mmol). The reaction was quenched after 1 h by addition of 10%
sodium thiosulfate solution (5.00 mL). The reaction was diluted
with CH2Cl2 and the organic layer was washed with saturated
NaHCO3 (3 × 25 mL) and water (2 × 25 mL) before being dried over
Na2SO4. The solvent was filtered off and then removed. The unre-
acted acceptor (110 mg) was recovered and the product was iso-
lated by column chromatography (toluene – ethyl acetate, 16/1 v/v)
to give 43 (193 mg, 51%) as a clear oil. [␣]D = +79.7 (c 1.0, CHCl3).
1H NMR (500 MHz, CDCl3) ␦: 7.83–7.14 (m, 34H, ArH), 5.53–5.52 (d,
1H, H-1== , J = 2.8 Hz), 5.25–5.24(d, 1H, H-1=, J = 3.0 Hz), 5.02–4.54 (m,
11 H, 5 × CH2Ar, H-3== ) 4.42–4.29 (m, CH2Ar, H-5=, H-4=), 4.26–4.24 (d,
1H, H-1, J = 7.0 Hz), 4.20–4.17 (dd, 1H, H-2== , J = 12.0, 2.6 Hz), 4.11(m,
1H, H-3=), 3.97–3.90 (m, 4H, H-5== , H-2=, H-3, OCH2CH2Si(CH3)3),
3.79–3.72 (m, 3H, H-4== , H-5, H-2), 3.61–3.57 (m, 2H, H-6a,b=), 3.52–
3.36 (m, 3H, H-4, H-6a,b, OCH2CH2Si(CH3)3), 1.55 (s, 9H, C(CH3)3),
1.02–0.90 (m, 5H, H6a,b,c== , OCH2CH2Si(CH3)3), –0.00 (s, 9H,
OCH2CH2Si(CH3)3). 13C NMR (126 MHz, CDCl3) ␦: 151.6, 151.0 (2 ×
C=O), 139.03, 139.0, 138.4, 138.0, 136.0, 135.6, 133.39, 133.37, 133.2,
133.0 (10 × ArC), 129.2–125.4 (ArCH), 103.9 (C1), 96.2 (C1== ), 95.2 (C1=),
84.8 (C(CH3)3), 75.0, 74.6, 73.9, 73.7, 73.2, 72.4 (6 × CH2Ar), 78.5, 78.1,
76.9, 76.0, 74.0, 73.3, 68.8, 73.0, 67.1 (C2, C2=, C3, C3=, C3== , C4, C4=,
C5, C5=, C5== ), 72.7 (C6=), 68.6, 67.5 (C6), 67.4 (OCH2CH2Si(CH3)3),
D-galactopyranosyl-␣(1¡4)-2,3-di-O-benzyl-6-O-napthylmethyl-
D-galactopyranosyl-␣(1¡3)–2,4-di-O-benzyl-6-O-naphthylmethyl-
␤-D-galactopyranoside) (45)
Trisaccharide 43 (30.0 mg, 0.02 mmol) was dissolved in meth-
anol–dichloromethane (10/1, 3.00 mL) and a catalytic quantity of
NaOMe was added. The reaction was stirred for 1 h and Amberlite
IR-150 H+ resin was added until pH 7 was achieved. The resin was
filtered off and the solvent was removed. The product was purified
by column chromatography (toluene – ethyl acetate, 6/1 v/v) to
give 45 (27.0 g, 92%) as a clear oil. [␣]D = +19.5 (c 1.0, CHCl3). 1H NMR
(500 MHz, CDCl3) ␦: 7.83–7.16 (m, 34H, ArH), 5.22–5.21 (d, 1H, H-1=,
J = 3.3 Hz), 5.03 – 4.49 (m, 13H, 6 × CH2Ar, H-1== ), 4.40–4.37 (m, 3H,
CH2Ar, H-4=), 4.29–4.28 (d, 1H, H-1, J = 7.0 Hz), 4.20 (m, 1H, H-5=),
4.01–3.70 (m, 8H, H-2, H-2=, H-3, H-3=, H-3== , H5, H5== ,
OCH2CH2Si(CH3)3), 3.61 (m, 3H, H-4== , H-6a,b=), 3.53–3.47 (m, 2 H,
H-4, OCH2CH2Si(CH3)3), 3.34–3.24 (m, 2H, H-6a,b), 1.44 (s, 9H,
C(CH3)3), 0.95 (m, OCH2CH2Si(CH3)3, H-6a-c== ), 0.00 (s, 9H,
OCH2CH2Si(CH3)3). 13C NMR (126 MHz, CDCl3) ␦: 158.0 (C=O), 139.0,
138.9, 138.5, 138.0, 135.6, 135.1, 133.4, 133.3, 133.1 (ArC), 128.5–125.8
(ArCH), 103.9 (C1), 98.0 (C1== ), 95.6 (C1=), 80.7 (C(CH3)3), 75.1, 74.7,
74.3, 73.7, 73.2, 72.7 (CH2Ar), 78.4, 78.2, 77.0, 76.0, 74.5, 73.3,
73.0, 68.7, 67.0, 65.6 (C2, C2=, C3, C3=, C4, C4=, C4== , C5, C5=, C5== ),
72.0 (C3== ), 68.8 (C6=), 68.0 (C6), 67.5 (OCH2CH2Si(CH3)3), 52.1
(C2== ), 28.5 (C(CH3)3), 18.6 (OCH2CH2Si(CH3)3), 17.5 (C6== ), –1.3
(OCH2CH2Si(CH3)3). HRMS C78H92N4O15SiNa [M + Na+] calculat-
ed: 1375.6226; found: 1375.6210.
Published by NRC Research Press

Ní Cheallaigh and Oscarson
955
2-(Trimethylsilyl)ethyl (4-azido-2-N-Boc-2,4,6-trideoxy-
D-galactopyranosyl-␣(1¡4)-2,3-di-O-benzyl-D-galactopyranosyl-
␣(1¡3)-2,4-di-O-benzyl-␤-D-galactopyranoside) (46)
tion was poured onto ice water and extracted with ethyl acetate.
The organic layer was washed with aqueous 1 M HCl (3 × 200 mL),
saturated NaHCO3 (2 × 200 mL), and water (1 × 200 mL). It was then
dried over Na2SO4, filtered, and the solvent was removed. The
crude was then purified by column chromatography (cyclohex-
ane – ethyl acetate, 4/1 v/v) to give 48 (4.317 g, 73%) as a clear oil.
1H NMR (400 MHz, CDCl3) ␦: 8.02–7.27 (m, 15H, ArH), 4.88–4.73 (m,
2H, CH2Ph), 4.75–4.68 (m, 2H, CH2Ph), 4.61–4.51 (m, 2H, H-6a,
H-6b), 4.45–4.43 (d, 1H, H-1, J = 9.6 Hz), 4.02 (s, 1H, H-4), 3.75–3.72 (t,
1H, H-5), 3.69–3.64 (t, 1H, H-2), 3.58–3.55 (dd, 1H, H-3), 2.81–2.64 (m,
2H, SCH2CH3), 2.48 (s, 1H, OH), 1.27 (t, 3H SCH2CH3). 13C NMR
(101 MHz, CDCl3) ␦: 166.3 (C=O), 138.0, 137.6, 133.1 (ArC), 129.7,
128.6, 128.4, 128.1, 127.9 (ArCH), 85.1 (C1), 82.2 (C3), 77.8 (C2), 75.8
(CH2Ph), 75.6 (C5), 72.5 (CH2Ph), 66.8 (C4), 63.6 (C6), 24.9 (SCH2CH3),
15.1 (SCH2CH3). Data recorded were in accordance with those that
Trisaccharide 45 (51.0 mg, 0.04 mmol) was dissolved in dichlo-
romethane–methanol (1 mL, 10/1 v/v) and to this, DDQ (33.0 mg,
0.11 mmol) was added. The reaction was stirred for 7 h at room
temperature and monitored by TLC (toluene – ethyl acetate, 1/1
v/v). The reaction was diluted with CH2Cl2 and washed with
NaHCO3 (2 × 10 mL) and Na2S2O3 (2 × 10 mL, 10% aqueous solution).
The organic phase was dried over Na2SO4, filtered, and the solvent
was removed. The product was isolated by column chromatogra-
phy (toluene – ethyl acetate, 1/1 v/v) to give 46 as a clear oil
1
(25.0 mg, 62%). H NMR (500 MHz, CDCl3) ␦: 7.42–7.16 (m, 20H,
ArH), 5.12–5.11 (d, 1H, H-1== , J = 3.5 Hz), 5.00–4.70 (m, 6H, CH2Ph,
H-1=), 4.47–4.32 (m, 4 H, CH2Ph, H-1, H-3== ), 4.00–3.73 (m, 11H,
H-2, H-2=, H-2== , H-3, H-3=, H-4, H-4=, H-4== , H-5== , H-6b=,
OCH2CH2Si(CH3)3), 3.59–3.45(m, 3H, H-6a=, OCH2CH2Si(CH3)3,
H-5=), 3.37 (m, 1H, H-5), 3.26–3.06 (m, 2H, H-6ab), 1.44 (s, 9H,
were found in the literature42
.
Ethyl 4-O-chloroacetyl-2,3-di-O-benzyl-6-O-2-naphtylmethyl-
1-thio-␤-D-galactopyranoside (49)
C(CH3)3), 1.08 (d, 3H, H-6a-c== ,
J = 6.3 Hz), 1.00 (m, 2H,
OCH2CH2Si(CH3)3), 0.00 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR
(126 MHz, CDCl3) ␦: 138.7–137.9 (ArC), 129.2–125.4 (ArCH), 104.0 (C1),
98.3 (C1== ), 95.6 (C1=), 74.7, 74.5, 74.47, 72.7 (CH2Ph), 78.6, 78.2, 76.9,
76.1, 75.5, 74.4, 72.7, 71.8, 70.4, 67.7, 66.9 (C2, C2=, C3, C3=, C3== ,
C4, C4=, C4== , C5, C5=, C5== ), 65.7 (C6=), 62.1 (C6), 54.9 (C2== ), 28.5
(C(CH3)3), 18.8 (OCH2CH2Si(CH3)3), 17.5 (C6== ), –1.3 (OCH2CH2Si(CH3)3)
HRMS C56H72N4O15SiNa [M + Na+] calculated: 1095.4974; found:
1095.4969.
Chloroacetyl chloride (1.35 mL, 17.0 mmol) was added dropwise
to a stirred solution of 48 (4.32 g, 8.49 mmol) and pyridine
(4.00 mL) in CH2Cl2 (60.0 mL). The solution was stirred for 1.5 h and
monitored by TLC (cyclohexane – ethyl acetate, 4/1 v/v). The reac-
tion was diluted with dichloromethane and poured onto ice wa-
ter. The organic layer was then washed with saturated NaHCO3
and brine and then dried over Na2SO3. The solvent was re-
moved and the product was isolated by column chromatogra-
phy (cyclohexane – ethyl acetate, 4/1 v/v) to give 49 (4.17 g, 82%) as
a white foam. [␣]D = –1.1 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦:
8.04–7.26 (m, 15H, ArH), 5.69–5.68 (d, 1H, H-4, J = 3.2 Hz), 4.84–4.74
(m, 3H, CH2Ph), 4.56–4.52 (m, 3H, CH2Ph, H-1, H-6a), 4.34–4.31 (m,
1H, H-6b), 4.24–4.17 (m, 2H, CH2Cl), 3.95 (td, 1H, H-5, J = 6.8, 0.7 Hz),
3.70–3.67 (dd, 1H, H-3, J = 9.2, 3.3 Hz), 3.61 (t, 1H, H-2, J = 9.7 Hz),
2.82–2.69 (m, 2H, SCH2CH3), 1.31 (t, 3H, SCH2CH3, J = 7.4 Hz).
13C NMR (126 MHz, CDCl3) ␦: 167.2, 166.2 (C=O), 138.0, 137.4, 133.5
(ArC), 129.9–128.0 (ArCH), 85.6 (C1), 80.8 (C3), 77.7 (C2), 76.1 (CH2Ph),
74.2 (CH2Ph), 72.6 (C5), 69.1 (C4), 62.2 (C6), 41.0 (CH2Cl), 25.2
(SCH2CH3), 15.3 (SCH2CH3) HRMS C31H33O7SClNa [M + Na+] calcu-
lated: 607.1533; found: 607.1212.
2-(Trimethylsilyl)ethyl (4-azido-2-N-Boc-2,4,6-trideoxy-
D-galactopyranosyl-␣(1¡4)-benzyl (2,3-di-O-benzyl-
D-galactopyranosyl) uronate-␣(1¡3)-benzyl (2,4-di-O-benzyl-
␤-D-galactopyranoside) uronate) (47)
Bisacetoxyiodo benzene (18.0 mg, 0.06 mmol) was added to a
biphasic solution of CH2Cl2 and water (0.50 mL, 2/1 v/v) containing
46 (24.0 mg, 0.02 mmol). The solution was cooled to 0 °C and
TEMPO (1 mg, 4.40 ␮mol) was added. The reaction was stirred
vigorously for 4 hand then quenched by addition of 10% sodium
thiosulfate solution (20.0 mL). The mixture was diluted with
CH2Cl2 and the organic phase was washed with saturated sodium
bicarbonate solution (2 × 50.0 mL) and water (2 × 50.0 mL). After
drying over sodium sulphate and filtration, the solvent was re-
moved from the organic layer. The crude material was dried under
reduced pressure before dissolving in DMF (1.0 mL). The solution
was cooled to 0 °C and benzyl bromide (7.00 ␮L, 0.06 mmol) and
cesium fluoride (8.80 mg, 0.06 mmol) were added. The reaction
was stirred for 48 h following which the solvents were removed
and the crude was purified by column chromatography (toluene –
ethyl acetate, 6/1 v/v) to give 47 (16.0 mg, 57%) as a yellow oil. 1H NMR
(500 MHz, CDCl3) ␦: 8.07–7.05 (m, 30H, ArH), 5.26–5.25 (d, 1H, H-1== ),
5.17–4.98 (m, 4H, CH2Ph), 4.84 – 4.68 (m, 6H), 4.59–4.56 (d, 1H,
CH2Ph), 4.42–4.40 (d, 1H), 4.33–4.31 (d, 2H), 4.26 (s, 1H), 4.23 (s, 1H),
4.10–4.04 (m, 2H), 4.02 (s, 1H), 3.93 (s, 1H), 3.85–3.82 (dd, 1H), 3.80–
3.79 (m, 2H), 3.77–3.70 (m, 3H), 3.60–3.50 (m, 2H), 1.48 (s, 9H,
C(CH3)3), 1.03–0.95 (m, 5H, H-6a-c== , OCH2CH2Si(CH3)3), –0.01
(OCH2CH2Si(CH3)3). 13C NMR (126 MHz, CDCl3) ␦: 129.9–127.3 (ArC,
ArCH), 103.3 (C1), 99.2 (C1== ), 94.5 (C1=), 75.0, 74.6, 74.0, 72.8 (4 ×
CH2Ph), 77.3, 76.7, 76.5, 75.9, 74.3, 74.2, 73.7, 72.1, 70.1, 66.7, 65.7
(C2, C2=, C3, C3=, C3== , C4, C4=, C4== , C5, C5=, C5== ), 67.2, 66.9
(COOCH2Ph), 67.7 (OCH2CH2Si(CH3)3), 51.5 (C2== ), 28.3 (C(CH3)3),
18.3 (OCH2CH2Si(CH3)3), 17.1 (C6== ), –1.2 (OCH2CH2Si(CH3)3). HRMS
C70H84N4O17SiNa [M + Na+] calculated: 1303.5498; found: 1303.5540.
2-(Trimethylsilyl)ethyl 2-O-benzyl-4,6-O-benzylidene-
␤-D-galactopyranoside (50, 51)
Compound 12 (5.20 g, 12.7 mmol) was dissolved in a solution of
acetic acid and water (90.0 mL, 4/1 v/v) and heated to 80 °C for 4 h.
The reaction was monitored by TLC and upon complete hydrolysis
of the acetal, the reaction was diluted with ethyl acetate and
washed with water and NaHCO3. The organic layer was dried over
Na2SO4, filtered and the solvent was removed to give the crude
triol. Triol 50 (4.69 g, 12.7 mmol) was dissolved in DMF (90.0 mL)
and PhCH(OMe)2 (3.80 mL, 25.4 mmol) was added. The solution
was cooled to 0 °C and CSA (60.0 mg, 0.25 mmol) was added. The
reaction was stirred at room temperature for 3 days and then
quenched by addition of triethylamine. The solution was poured
onto ice water (500 mL) and extracted with ethyl acetate (3 ×
200 mL). The organic phase was dried over Na2SO3, the solvent was
removed, and the crude was purified by column chromatography
(cyclohexane – ethyl acetate, 4/1 v/v) to yield 51 (3.98 g, 70%) as a
clear oil. 1H NMR (400 MHz, CDCl3) ␦: 7.53–7.28 (m, 10H, ArH), 5.56
(s, 1H, CHPh), 5.01–4.72 (dd, 2H, CH2Ph), 4.42–4.40 (d, 1H, H-1),
4.36–4.32 (d, 1H, H-6a), 4.22–4.21 (d, 1H, H-4), 4.11–4.04 (m, 2H,
H-6b, OCH2CH2Si(CH3)3), 3.76–3.71 (m, 1H, H-3), 3.64–3.55 (m, 2H,
H2, OCH2CH2Si(CH3)3), 3.44 (s, 1H, H-5), 2.49–2.47 (d, 1H, OH), 1.08–
1.03 (m, 2H, OCH2CH2Si(CH3)3), 0.04 (t, 9H, OCH2CH2Si(CH3)3).
13C NMR (101 MHz, CDCl3) ␦: 138.9, 137.8 (2 × ArC), 129.3–126.7
(ArCH), 103.3 (C1), 101.6 (CHPh), 79.5 (C2), 75.7 (C4), 75.0 (CH2Ph),
72.7 (C3), 69.4 (C6), 67.6 (OCH2CH2Si(CH3)3), 66.6 (C5), 18.6
(OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3). Data recorded were in
Ethyl 6-O-benzoyl-2,3-di-O-benzyl-1-thio-␤-D-galactopyranoside (48)
Compound 8 (4.71 g, 11.6 mmol) was dissolved in pyridine
(82.0 mL) and cooled to –20 °C. A dilute solution of benzoyl chlo-
ride (1.42 mL, 12.2 mmol in 10 mL pyridine) was added dropwise
over 30 min. The reaction was stirred for 1 h and monitored by TLC
(cyclohexane – ethyl acetate, 2/2 v/v). Upon completion, the reac-
accordance with those that were found in the literature43
.
Published by NRC Research Press

956
Can. J. Chem. Vol. 94, 2016
2-(Trimethylsilyl)ethyl 2,4-di-O-benzyl-␤-D-galactopyranoside (52)
3.0 Hz), 3.79–3.74 (m, 2H, H-6a, H-2), 3.60–3.50 (m, 3H, H-5, H-6b,
OCH2CH2Si(CH3)3), 2.34 (s, 1H, OH), 1.95 (s, 3H, COCH3), 1.04–1.00
(m, 2H, OCH2CH2Si(CH3)3), 0.00 (t, 9H, OCH2CH2Si(CH3)3, J =
8.7 Hz). 13C NMR (126 MHz, CDCl3) ␦: 170.6 (C=O), 138.8, 137.8 (2 ×
ArC), 129.2–127.7 (ArCH), 103.6 (C1), 77.1 (C2), 75.4 (C3), 74.9 (CH2Ph),
74.9 (CH2Ph), 74.5 (C5), 74.0 (C4), 67.8 (OCH2CH2Si(CH3)3), 62.0 (C6),
21.1 (COCH3), 18.7 (OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3).
HRMS C27H38O7SiNa [M + Na+] calculated: 525.2285; found:
525.2277.
Method 1
Benzylidene protected 51 was dissolved in a solution of 1 M BH3
in THF (5.30 mL) at 0 °C and to this, 1 M Bu2OTf in toluene (0.75 mL)
was added. The solution was quenched with Et3N after 30 min and
MeOH was added dropwise. Once liberation of H2 had ceased, the
solvent was removed with coevaporation of MeOH. Column chro-
matography gave a mixture of the 4-OBn and 6-OBn product in a
2:1 ratio, 68% yield.
2-(Trimethylsilyl)ethyl 6-O-benzoyl-2,4-di-O-benzyl-
␤-D-galactopyranoside (56)
Method 2
Compound 55 (2.04 g, 4.06 mmol) was dissolved in MeOH
(30.0 mL) cooled to 0 °C and NaOMe was added until pH 9 was
reached. Upon completion of the reaction, Amberlite IR-150H+
resin was added until pH 7 was achieved and the solution was
filtered from the resin. The solvent was removed and the crude
was purified by column chromatography (cyclohexane – ethyl ac-
etate, 2/1 v/v) to give 52 (1.80 g, 97%) as a clear oil.
Diol 52 (1.59 g, 3.45 mmol) was dissolved in pyridine (30.0 mL)
and cooled to 0 °C. A dilute solution of benzoyl chloride (0.43 mL,
3.62 mmol) in pyridine (5.00 mL) was added dropwise over 15 min.
The reaction was stirred for 4 h and then poured onto excess ice
water and extracted with ethyl acetate. The organic layer was
washed with 1 M HCl (3 × 100 mL), saturated NaHCO3 (2 × 100 mL),
and brine (1 × 100 mL) and then dried over Na2SO3. The solvent was
removed and the crude was purified by column chromatography
(cyclohexane – ethyl acetate, 4/1 v/v) to isolate the product 56
(1.51 g, 70%), remaining starting material, and 3-O-benzoylated
and dibenzoylated products. The 3-O-benzoylated and dibenzo-
ylated products were recovered, combined, and treated with
NaOMe to recover the starting material. [␣]D = –15.6 (c 1.0, CHCl3).
1H NMR (400 MHz, CDCl3) ␦: 8.13–7.17 (m, 15H, ArH), 5.03- 4.69
(dd × 2, 4H, 2 × CH2Ph), 4.56–4.52 (dd, 1H, H-6a, J = 11.5, 6.9 Hz),
4.41–4.39 (d, 1H, H-1, J = 7.2 Hz), 4.40–4.35 (m, 1H, H-6b), 4.05–3.98
(m, 1H, OCH2CH2Si(CH3)3), 3.89 (d, 1H, H-5, J = 2.6 Hz), 3.77 (t, 1H,
H-3, J = 6.7 Hz), 3.73–3.69 (m, 1H, H-4), 3.68–3.63 (m, 1H, H-2),
3.61–3.55 (m, 1H, OCH2CH2Si(CH3)3), 2.36 (s, 1H, OH), 1.06–1.02 (m,
2H, OCH2CH2Si(CH3)3), 0.01(m, 1H, OCH2CH2Si(CH3)3). 13C NMR
(101 MHz, CDCl3) ␦: 166.2 (C=O), 138.6, 138.3, 133.9, 133.3, 130.3,
129.8, 128.7, 128.6, 128.5, 128.5, 128.4, 128.3, 128.0, 127.9 (ArC,
ArCH), 103.4 (C1), 79.5 (C2), 75.1 (CH2Ph), 74.9 (C5), 74.8 (CH2Ph),
74.4 (C4), 72.3 (C3), 67.4 (OCH2CH2Si(CH3)3), 63.2 (C6), 18.6
(OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3). HRMS C32H40O7SiNa
[M + Na+] calculated: 587.2441; found: 587.2424.
[␣]D = –3.1 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 7.39–7.30
(m, 10H, ArH), 5.02–5.00 (d, 1H, CH2Ph), 4.85–4.83 (d, 1H, CH2Ph),
4.71–4.65 (m, 2H, CH2Ph), 4.39–4.37 (d, 1H, H-1, J = 7.8 Hz), 4.04–
3.98 (m, 1H, OCH2CH2Si(CH3)3), 3.83–3.78 (m, 2H, H-6a, H-5), 3.69–
3.65 (m, 1H, H-3), 3.63–3.55 (m, 3H, H-2, H-6b, OCH2CH2Si(CH3)3),
3.48–3.46 (m, 1H, H-4), 2.37 (d, 1H, C3-OH, J = 4.0 Hz), 1.66–1.64 (dd,
1H, C6-OH, J = 8.7, 4.0 Hz), 1.03 (m, 2H, OCH2CH2Si(CH3)3), 0.02 (s,
9H, OCH2CH2Si(CH3)3). 13C NMR (126 MHz, CDCl3) ␦: 138.7, 138.3
(ArC), 128.7–128.0 (ArCH), 103.5 (C1), 79.7 (C2), 74.9, 74.9, 74.8, 74.76
(C4, C5, CH2Ph, CH2Ph), 74.4 (C3), 67.6 (OCH2CH2Si(CH3)3), 62.2
(C6), 18.7 (OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3). HRMS
C25H36O6SiNa [M + Na+] calculated: 483.2179; found: 483.2172.
2-(Trimethylsilyl)ethyl 3-O-acetyl-2-O-benzyl-4,6-O-benzylidene-
␤-D-galactopyranoside (54)
Compound 51 (3.48 g, 7.59 mmol) was dissolved in pyridine
(55.0 mL), cooled to 0 °C, and acetic anhydride (10.0 mL) was added.
The reaction was stirred at room temperature for 2 h. The solvent
was removed under reduced pressure and the product was iso-
lated by column chromatography (cyclohexane – ethyl acetate, 4/1
v/v) to yield 54 (3.11 g, 82%) as a clear oil. [␣]D = +71.8 (c 1.0, CHCl3).
1H NMR (500 MHz, CDCl3) ␦: 7.47–7.20 (m, 10H, ArH), 5.44 (s, 1H,
CHPh), 4.89–4.85 (m, 2H, CH2Ph, H-3), 4.62–4.59 (d, 1H, CH2Ph),
4.44–4.42 (d, 1H, H-1, J = 7.7 Hz), 4.30 – 4.26 (m, 2H, H-4, H-6a)
4.05–3.98 (m, 2H, H-6b, OCH2CH2Si(CH3)3), 3.79–3.76 (dd, 1H, H-2,
J = 10.2, 7.4 Hz), 3.57–3.52 (m, 1H, OCH2CH2Si(CH3)3), 3.42 (s, 1H,
H-5), 2.00 (s, 3H, COCH3), 1.02–0.98 (m, 2H, OCH2CH2Si(CH3)3),
–0.02 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR (126 MHz, CDCl3) ␦: 171.0
(C=O), 138.9, 137.9 (ArC), 129.1–126.5 (ArCH), 103.3 (C1), 101.2 (CHPh),
76.6 (C2), 75.0 (CH2Ph), 74.0 (C4), 73.7 (C3), 69.2 (C6), 67.7
(OCH2CH2Si(CH3)3), 66.2 (C5), 21.2 (COCH3), 18.6 (OCH2CH2Si(CH3)3), –1.3
(OCH2CH2Si(CH3)3). HRMS C27H36O7SiNa [M + Na+] calculated: 523.2128;
found: 523.2134.
2-(Trimethylsilyl)ethyl (4-chloroacetyl-6-O-benzoyl-2,3-di-O-benzyl-
D-galactopyranosyl-␣(1¡3)-6-O-benzoyl-2,4-di-O-benzyl-
␤-D-galactopyranoside) (57)
Donor 49 (1.50 g, 2.56 mmol) and acceptor 55 (1.44 g, 2.54 mmol)
were dissolved in Et2O–CH2Cl2 (3/2, 18.5 mL, 0.16 M), 4 Å molecular
sieves were added, and the solution was stirred for 1 h before
cooling to 0 °C. Once the solution had reached 0 °C, Me2S2/Tf2O
promoter (4.00 mL, 1 M solution in CH2Cl2) was added and the
reaction was stirred for 10 min. The reaction was quenched with
Et3N and diluted with CH2Cl2. The molecular sieves were removed
by filtration and the organic phase was washed with 2 M aqueous
HCl, saturated NaHCO3, and water. The organic phase was dried
over Na2SO4, filtered, and the solvent was removed. The disaccha-
ride was isolated by column chromatography using a gradient
elution (toluene – ethyl acetate, 16/1–8/1 v/v) to give 57 (2.62 g, 94%)
as a clear oil. [␣]D = +49.1 (c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3) ␦:
8.07–7.17 (m, 30H, ArH) 5.17 (s, 2H, H-1=, H-4=), 5.07–4.47 (4 × dd, 8H,
CH2Ph), 4.56 (s, 1H, H-5), 4.42–4.34 (m 2H, H-6a, H-6b), 4.21–4.00 (m,
2H, H-6a, H-6b), 4.17 (m, 1H, H-1), 4.10 (d, 2H, CH2Cl), 3.98–3.50 (m,
2H, OCH2CH2Si(CH3)3), 3.89–3.78 (m, 5H, H-2, H-2=, H-3=, H-4, H-5=),
3.56 (t, 1H, H-3), 1.01 (m, 2H, OCH2CH2Si(CH3)3), 0.02 (s, 9H,
OCH2CH2Si(CH3)3). 13C NMR (101 MHz, CDCl3) ␦: 166.9, 166.1, 165.9
(3 × C=O), 138.8, 138.4, 138.0, 137.8, 133.3, 133.2 (6 × ArC), 130.0–
127.6 (ArCH), 103.9 (C1), 94.9 (C1=), 78.3, 77.0, 76.4, 75.0, 72.1,
71.6, 70.4, 63.0 (C2, C2=, C3, C3=, C4, C4=, C5, C5=), 75.4, 74.8,
74.5, 72.2 (4 × CH2Ph), 67.5 (OCH2CH2Si(CH3)3), 66.8, 63.3 (C6,
C6=), 40.9 (CH2Cl), 18.6 (OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3).
HRMS C61H67O14SiClNa [M + Na+] calculated: 1109.3886; found:
1109.3921.
2-(Trimethylsilyl)ethyl 3-O-acetyl–2,4-di-O-benzyl-
␤-D-galactopyranoside (55)
Benzylidene protected 54 (2.85 g, 5.69 mmol) was dissolved in a
cold solution of 1 M BH3 in THF (20.0 mL). The reaction was cooled
to 0 °C and a 1 M Bu2BOTf in toluene (5.70 mL) was added and the
reaction was stirred for 1 h. The reaction was quenched by addi-
tion of triethylamine and MeOH was added dropwise until the
evolution of H2 ceased. The solvent was removed under reduced
pressure and coevaporated three times with MeOH. Column chro-
matography was carried out using a gradient elution (cyclohexane –
ethyl acetate, 10/1–3/1 v/v) to give 55 (2.04 g, 70%) as an
opaque oil. [␣]D = +67.2 (c 1.0, CHCl3). 1H NMR (500 MHz, CDCl3) ␦:
7.34–7.27 (m, 10H, ArH), 4.90–4.87 (m, 2H, CH2Ph, H-3), 4.67–4.64
(q, 2H, CH2Ph), 4.50–4.47 (d, 1H, CH2Ph), 4.43–4.42 (d, 1H, H-1, J =
7.7 Hz), 4.03–3.97 (m, 1H, OCH2CH2Si(CH3)3), 3.86 (d, 1H, H-4, J =
Published by NRC Research Press

Ní Cheallaigh and Oscarson
957
2-(Trimethylsilyl)ethyl (6-O-benzoyl-2,3-di-O-benzyl-
D-galactopyranosyl-␣(1¡3)-6-O-benzoyl-2,4-di-O-benzyl-
␤-D-galactopyranoside) (58)
1 and extracted with ethyl acetate (3 × 50 mL). The organic layers
were combined, dried over Na2SO4, and the solvent was removed
under reduced pressure. The crude product was purified by col-
umn chromatography (100% ethyl acetate to ethyl acetate – methanol,
95/5 v/v) to give 60 (415 mg, 80%) as an opaque oil. [␣]D = +78.4
(c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3) ␦: 7.44–7.09 (m, 20 H, ArH),
5.11–5.11 (d, 1H, H-1=, J = 3.1 Hz), 5.01 (m, 2H, CH2Ph), 4.87–4.84 (d,
1H, CH2Ph), 4.76–4.69 (m, 4H, CH2Ph, H-1== ), 4.50–4.47 (d, 1H,
CH2Ph), 4.37–4.34 (m, 2H, CH2Ph, H-1), 4.27–4.19 (m, 2H), 4.03–3.96
(m, 2H), 3.91–3.84 (m, 4H), 3.79–3.73 (m, 4H), 3.70–3.67 (dd, 1H,
J = 10.0, 2.5 Hz), 3.65 (d, 1H, J = 1.6 Hz), 3.61- 3.52 (m, 3H), 3.38 (t,
1H, J = 6.21 Hz), 3.17–3.08 (m, 2H, H-6ab/H-6ab=), 1.97 (s, 3H,
COCH3), 1.10–1.09 (d, 3H, H-6abc== , J = 6.3 Hz), 1.03–0.98 (m, 2H,
OCH2CH2Si(CH3)3), 0.00 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR
(101 MHz, CDCl3) ␦: 173.7 (NCO), 138.7, 138.7, 138.4, 137.8 (ArC),
128.7–127.7 (ArCH), 103.9 (C1), 99.0 (C1== ), 95.9 (C1=), 75.5, 74.7, 74.5,
72.7 (4 × CH2Ph), 78.7, 78.4, 76.7 (2) 75.8, 74.45 72.7, 72.5, 69.3, 66.8,
65.8 (C2, C2=, C3, C3=, C3== , C4, C4=, C4== , C5, C5=, C5== ), 67.7
(OCH2CH2Si(CH3)3), 62.0, 61.1 (C6, C6=), 51.3 (C2== ), 22.9 (COCH3),
18.8 (OCH2CH2Si(CH3)3), 17.5 (C6== ), –1.3 (OCH2CH2Si(CH3)3). HRMS
C53H70N4O14SiNa [M + Na+] calculated: 1037.4556; found: 1037.4602.
Disaccharide 57 (1.80 g, 1.66 mmol) was dissolved in THF
(18.0 mL) and to this, NaHCO3 (460 mg, 5.47 mg), thiourea (378 mg,
4.97 mmol), and TBAI (122 mg, 0.33 mmol) were added. The reac-
tion was heated to 60 °C for 4 h. The reaction was diluted with
CH2Cl2, washed with water, and dried over Na2SO4. Column chro-
matography (cyclohexane – ethyl acetate, 5/1 v/v) of the crude gave
the pure product 58 (1.56 g, 93%) as a white foam. [␣]D = +34.0 (c 1.0,
CHCl3). 1H NMR (500 MHz, CDCl3) ␦: 8.07–7.17 (m, 30H, ArH), 5.19
(d, 1H, H-1=, J = 3.5 Hz), 5.07–4.48 (4 × dd, 8H, CH2Ph), 4.44–4.27 (m,
5H, H-5, H-6a, H-6b, H-6a=, H-6b=), 4.09 (m, 1H, H-1), 3.96 (dd, 1H,
H-2=, J = 9.7, 3.3 Hz), 3.90–3.41 (m, 2H, OCH2CH2Si(CH3)3), 3.86
(s,1H, H-5=), 3.82–3.79 (m, 3H, H-2, H-3=, H-4), 3.63 (s, 1H, H-4=), 3.53
(t, 1H, H-3, J = 6.5 Hz), 2.39 (s, 1H, OH), 1.01–0.93 (m, 2H,
OCH2CH2Si(CH3)3), –0.00 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR
(126 MHz, CDCl3) ␦: 166.1, 166.1 (C=O), 139.0, 138.5, 138.1, 138.0,
133.3, 133.0 (ArC), 130.5–127.6 (ArCH), 103.9 (C1), 94.7 (C1=), 78.2,
78.0, 76.7, 75.5, 72.1, 71.7, 68.0, 67.9 (C2, C2=, C3, C3=, C4, C4=, C5,
C5=), 75.1, 74.7, 74.5, 72.4 (4 × CH2Ph), 67.5 (OCH2CH2Si(CH3)3), 64.5,
63.4 (C6, C6=), 18.5 (OCH2CH2Si(CH3)3), –1.3 (OCH2CH2Si(CH3)3),
HRMS C59H66O13SiNa [M + Na+] calculated: 1033.4170; found:
1033.4202.
2-(Trimethylsilyl)ethyl (2-N-acetamido-4-azido-2,4,6-trideoxy-
D-galactopyranosyl-␣(1¡4)-methyl (2,3-di-O-benzyl-
D-galactopyranosyl) uronate-␣(1¡3)-methyl (2,4-di-O-benzyl-
␤-D-galactopyranoside) uronate) (61)
2-(Trimethylsilyl)ethyl (2-N-acetyl-4-azido-2,3-N,O-carbonyl-
2,4,6-trideoxy-D-galactopyranosyl-␣(1¡4)-6-O-benzoyl-
2,3-di-O-benzyl-D-galactopyranosyl-␣(1¡3)-6-O-benzoyl-
2,4-di-O-benzyl-␤-D-galactopyranoside) (59)
Trisaccharide 60 (415 mg, 0.41 mmol) was dissolved in CH2Cl2
and water (3.00 mL, 2/1 v/v) and cooled to 0 °C. To this, BAIB
(789 mg, 2.45 mmol) was added followed by TEMPO (63.0 mg,
0.41 mmol) and the reaction was vigorously stirred for 2 h. Once
only the desired product was observed by LRMS, the reaction was
diluted with CH2Cl2 and quenched by addition of Na2S2O3
(1.00 mL, 10% aqueous solution). The organic layer was separated
and the aqueous phase was acidified to pH 1 and extracted with
ethyl acetate (3 × 3 mL). The organic layers were combined and
dried over Na2SO4, filtered, and the solvent was removed under
reduced pressure. The crude was redispersed in DMF (4.00 mL),
cooled to 0 °C, and added with K2CO3 (225 mg, 1.64 mmol) and MeI
(76.0 ␮L, 1.23 mmol). The reaction was allowed to come to room
temperature where it was stirred for 16 h. The reaction was di-
luted with ethyl acetate (20 mL) and washed with water (3 × 20 mL)
and brine (20 mL). The organic layers were dried over NaSO4 and
the solvent was removed. The product 61 was isolated (304 mg,
70%) as a white foam following purification by column chroma-
tography using a gradient elution (ethyl acetate – methanol, 1/0–
Donor 25 (554 mg, 1.84 mmol) as a solution in CH2Cl2 (12.0 mL)
was added dropwise to a stirred solution of acceptor 58 (1.56 mL,
1.54 mmol), NIS (689 mg, 3.08 mmol), AgOTf (197 mg, 0.77 mmol),
and 4 Å molecular sieves in CH2Cl2 (12.0 mL) at 0 °C for 1 h. The
reaction was quenched with Et3N and diluted with CH2Cl2. The
organic phase was washed with 10% aqueous Na2S2O3 and water
and then dried over Na2SO4. The solvent was removed and the
crude was purified by column chromatography (toluene – ethyl
acetate, 12/1 v/v) to isolate the desired ␣-trisaccharide (1.15 g, 60%),
the ␤-trisaccharide (230 mg, 12%), and unreacted acceptor (217 mg,
14%) to give the reaction a recovered yield of 84%. Following ano-
merisation of the ␤-trisaccharide (207 mg, 90%), a total of 1.309 g
(71%) of trisaccharide 59 was obtained. [␣]D = +73.8 (c 1.0, CHCl3).
1H NMR (500 MHz, CDCl3) ␦: 8.06–7.18 (m, 30 H, ArH), 5.54–5.53 (d,
1H, H-1== , J = 2.6 Hz), 5.20–5.19 (d, 1H, H-1=, J = 3.3 Hz), 5.10–4.47 (m,
9H, 4 × CH2Ph, H-3== ), 4.43–4.40 (dd, 1H, H-6a/H6-a=) 4.34–4.29 (m,
2H, H-2== , H-6b/H-6b=), 4.25–4.21 (dd, 1H, H-6a/H-6a=), 4.17–4.14
(m, 2H, H-5, H-5== ), 4.08–4.06 (d, 1H, H-1, J = 7.2 Hz), 3.95–3.89 (m,
1H, OCH2CH2Si(CH3)3), 3.87–3.73 (m, 7H, H-2, H-3, H-3=, H-4, H-4== ,
H-5=, H-6b/H-6b=), 3.69 (m, 1H, H-2), 3.47–3.42 (m, 2H, H-4=,
OCH2CH2Si(CH3)3), 2.55 (s, 3H, COCH3), 1.01–0.93 (m, 5H, H-6a,b,c== ,
OCH2CH2Si(CH3)3), 0.01 (s, 9H, OCH2CH2Si(CH3)3). 13C NMR
(126 MHz, CDCl3) ␦: 172.5, 166.1, 165.7, 152.9 (C=O), 138.9, 138.4,
138.3, 137.8, 133.3, 133.1 (ArC), 130.3–125.4 (ArCH), 103.8 (C1), 97.4
(C1== ), 94.1 (C1=), 75.1, 74.5, 74.0, 73.0 (4 × CH2Ph), 78.1, 77.0, 76.6,
76.6, 74.9, 73.3, 72.1, 71.7, 68.9, 67.4, 62.3 (C2, C2=, C3, C3=, C3== , C4,
C4=, C4== , C5, C5=, C5== ), 67.5 (OCH2CH2Si(CH3)3), 63.4, 63.3 (C6, C6=),
56.3 (C2== ), 24.0 (COCH3), 18.6 (OCH2CH2Si(CH3)3), 17.0 (C6== ), –1.4
(OCH2CH2Si(CH3)3). HRMS C69H76N4O17SiNa [M + Na+] calculated:
1271.4872; found: 1271.4935.
1
5/1 v/v). [␣]D = +89.8 (c 1.0, CHCl3). H NMR (400 MHz, CDCl3) ␦:
7.44–7.05 (m, 20H, ArH), 6.10–6.08 (d, 1H, NH), 5.29 (s, 1H, H-1=),
5.05–5.02 (d, 1H, CH2Ph), 4.91–4.89 (d, 1H, CH2Ph), 4.80–4.70 (m,
4H, CH2Ph), 4.68 (s, 1H), 4.49–4.48 (d, 1H, H-1== , J = 3.8 Hz), 4.44–4.41
(d, 1H, CH2Ph), 4.37–4.33 (m, 2H, H-1, CH2Ph), 4.23–4.16 (m, 3H),
4.11–4.01 (m, 4H), 3.89 (s, 2H), 3.82–3.75 (m, 3H), 3.66 (s, 3H,
COOCH3), 3.57–3.50 (m, 2H), 3.43 (s, 3H, COOCH3), 2.09 (s, 3H,
COCH3), 1.08–0.94 (m, 5H, H-6a-c== , OCH2CH2Si(CH3)3), –0.01 (s,
9H, OCH2CH2Si(CH3)3). 13C NMR (101 MHz, CDCl3) ␦: 173.7 (NCO),
169.8, 168.5 (C=O), 138.4, 138.2, 138.0, 137.4 (ArC), 128.6–127.4
(ArCH), 103.4 (C1), 98.6 (C1== ), 94.8 (C1=), 77.2, 76.8, 76.6, 75.4, 75.0,
75.0, 74.6, 74.6, 74.2, 73.9, 73.0, 72.1, 69.9, 66.7, 66.0, (C2, C2=, C3,
2-(Trimethylsilyl)ethyl (2-N-acetyl-4-azido-2,4,6-trideoxy-
D-galactopyranosyl-␣(1¡4)-2,3-di-O-benzyl-D-galactopyranosyl-
␣(1¡3)-2,4-di-O-benzyl-␤-D-galactopyranoside) (60)
Ba(OH)2.8H2O (2.46 g, 7.80 mmol) was added to a suspension of
trisaccharide 59 (650 mg, 0.52 mmol) in ethanol (20 mL) and water
(10 mL). The solution was heated at 70 °C for 16 h and then cooled
to room temperature. Ac2O (344 ␮L, 3.64 mmol) was added and the
reaction was stirred for 3 h. The aqueous phase was acidified to pH
C3=, C3== , C4, C4=, C4== , C5, C5=, C5== , CH2Ph
× 4) 67.9
(OCH2CH2Si(CH3)3), 52.4 (COOCH3), 52.0 (COOCH3), 50.8 (C2== ), 22.9
(COCH3), 18.6 (OCH2CH2Si(CH3)3), 17.3 (C6== ), –1.4 (OCH2CH2Si(CH3)3).
HRMS C55H70N4O16SiNa [M + Na+] calculated: 1093.4454; found:
1093.4501.
Published by NRC Research Press

958
Can. J. Chem. Vol. 94, 2016
2-(Trimethylsilyl)ethyl (2-N-acetamido-4-azido-3-O-chloroacetyl-
2,4,6-trideoxy-D-galactopyranosyl-␣(1¡4)-methyl (2,3-di-O-benzyl-
D-galactopyranosyl) uronate-␣(1¡3)-methyl (2,4-di-O-benzyl-
␤-D-galactopyranoside) uronate) (62)
2-N-acetamido-4-azido-3-O-chloroacetyl-2,4,6-trideoxy-
D-galactopyranoside-␣(1¡4)-methyl (2,3-di-O-benzyl-
D-galactopyranosyl) uronate-␣(1¡3)-methyl (2,4-di-O-
benzyl-D-galactopyranosyl trichloroacetimidate) uronate (64)
Hemiacetal 63 (165 mg, 0.16 mmol) was dissolved in DCE
(1.20 mL) and cooled to 0 °C. To this solution, trichloroacetonitrile
(31.0 ␮L, 0.31 mmol) and K2CO3 (43.0 mg, 0.31 mmol) were added
and the solution was stirred for 24 h. The reaction mixture was
loaded directly onto a silica gel column for chromatography (ethyl
acetate – cyclohexane, 4/1 v/v) where the product 64 (143 mg, 84%)
was isolated and the unreacted hemiacetal was recovered. The
major isomer was found to be alpha trichloroacetimidate, the
spectra of which is given herein: 1H NMR (400 MHz, CDCl3) ␦: 8.58
(s, 1H, NH), 7.43–7.10 (m, 18H, ArH), 6.99–6.97 (m, 2H, ArH), 6.80 (d,
1H, H-1, J = 3.2 Hz), 5.50–5.48 (d, 1H, NH), 5.34–5.34 (d, 1H, H-1=, J =
3.2 Hz), 5.12–5.05 (m, 2H, Hx, CH2Ph), 4.83–4.75 (m, 3H, CH2Ph),
4.71–4.58 (m, 5H, CH2Ph, Hx, Hx), 4.55–4.53 (m, 2H, H-3== , H-1== ),
4.46–4.43 (d, 1H, CH2Ph), 4.43–4.39 (m, 2H), 4.30 – 4.27 (d, 1H,
CH2Ph), 4.24–4.20 (m, 2H), 4.15–4.09 (d, 2H, CH2Cl), 4.09–4.08 (d,
1H, J = 1.4 Hz), 4.00 (s, 1H), 3.96–3.93 (dd, 1H, J = 10.4, 3.2 Hz),
3.88–3.85 (dd, 1H, J = 10.4, 2.6 Hz), 3.67 (s, 3H, COOCH3), 3.64 (s, 1H),
3.36 (S, 3H, COOCH3), 2.04 (s, 3H, COCH3), 1.98 (s, 3H, COCH3),
0.99–0.97 (d, 3H, H-6a-c== , J = 6.3 Hz). 13C NMR (101 MHz, CDCl3) ␦:
170.7, 168.7, 168.1, 167.2 (C=O), 160.6 (C=N), 138.1, 137.9, 137.2, 137.1
(ArC), 128.7–127.5 (ArCH), 99.3 (C1== ), 94.1 (C1=), 93.9 (C1), 90.9 (CCl3),
75.3, 74.2, 73.1, 73.0 (CH2Ph), 77.1, 75.3, 75.0, 74.3, 74.2, 73.2, 72.9,
72.3, 69.9, 65.6, 64.2 (C2, C2=, C3, C3=, C3== , C4, C4=, C4== , C5, C5=,
C5== ), 52.6, 51.9 (COOCH3), 47.2 (C2== ), 40.4 (CH2Cl), 26.9, 23.3
(COCH3), 17.0 (C6== ).
Trisaccharide 61 (300 mg, 0.28 mmol) was dissolved in anhy-
drous CH2Cl2 (2.00 mL) and cooled to 0 °C. To the solution, pyri-
dine (0.20 mL) was added followed by a dropwise addition of
chloroacetyl chloride (44.0 ␮L, 0.56 mmol). The reaction was
stirred at 0 °C for 40 min and monitored by TLC (cyclohexane – ethyl
acetate, 1/1 v/v). The reaction was then quenched with Et3N and the
material was loaded directly onto a column. Chromatography pu-
rification was carried out using a gradient elution (cyclohex-
ane – ethyl acetate, 2/1–1/3 v/v) to give 62 (270 mg, 84%) as a white
foam. [␣]D = +49.1 (c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3) ␦: 7.44–
7.01 (m, 20H, ArH), 5.53–5.50 (d, 1H, NH), 5.30–5.29 (d, 1H, H-1=, J =
2.6 Hz), 5.09–5.05 (dd, 2H, CH2Ph, H-3== ), 4.90–4.88 (d, 1H, CH2Ph),
4.78–4.72 (m, 4H, CH2Ph), 4.69–4.64 (m, 1H), 4.55 (m, 2H, H-1=,
H-2== ), 4.46–4.44 (d, 1H CH2Ph) 4.35–4.30 (dd, 2H, CH2Ph, H-1), 4.24–
4.17 (m, 2H), 4.14–4.01 (m, 5H, Hx, Hx, CH2Cl, OCH2CH2Si(CH3)3),
3.95–3.92 (dd, 1H, J = 10.4, 3.1 Hz), 3.88–3.85 (dd, 1H, J = 10.4, 3.6 Hz),
3.83–3.80 (dd, 1H, J = 10.1, 3.5 Hz), 3.79–3.74 (m, 1H), 3.65 (s, 3H,
COOCH3), 3.57–3.50 (m, 1H, OCH2CH2Si(CH3)3), 3.38 (s, 3H,
COOCH3), 1.99 (s, 3H, COCH3), 1.07–0.93 (m, 2H, OCH2CH2Si(CH3)3),
1.00–0.98 (d, 3H, H-6a-c== , J = 6.2 Hz), –0.01 (s, 9H, OCH2CH2Si(CH3)3).
13C NMR (101 MHz, CDCl3) ␦: 170.8, 169.0, 168.6, 167.5 (C=O), 138.5,
138.3, 138.1, 137.4 (ArC), 129.2–127.5 (ArCH), 103.4 (C1), 99.3 (C1== ),
94.6 (C1=), 75.2, 75.1, 74.2, 73.3 (CH2Ph), 77.4, 77.3, 76.6, 75.2, 74.6,
74.4, 73.9, 70.1, 65.7, 64.3 (C2, C2=, C3, C3=, C4, C4=, C4== , C5, C5=,
C5== ), 73.2 (C3== ), 67.9 (OCH2CH2Si(CH3)3), 52.5, 52.0 (COOCH3), 47.2
(C2== ), 40.6 (CH2Cl), 23.5 (COCH3), 18.7 (OCH2CH2Si(CH3)3), 17.1
(C6== ), –1.3 (OCH2CH2Si(CH3)3). HRMS showed a fragmented struc-
ture of the molecule where the chloroacetate group was not pres-
ent. HRMS C55H70N4O16SiNa [M + Na+] calculated: 1093.4448;
found: 1093.2372.
Allyl (2-N-acetamido-4-azido-3-O-chloroacetyl-2,4,6-trideoxy-
D-galactopyranoside-␣(1¡4)-methyl (2,3-di-O-benzyl-
D-galactopyranosyl) uronate-␣(1¡3)-methyl (2,4-di-O-benzyl-
␤-D-galactopyranoside) uronate) (65)
Donor 64 (50.0 mg, 41.9 ␮mol) and allyl alcohol (2.00 ␮L,
83.9 ␮mol) were dissolved in CH2Cl2 (200 ␮L) and Et2O (300 ␮L) and
stirred with 4 Å molecular sieves for 3 h. The solution was cooled
to 0 °C and a TMSOTf (20.0 ␮L, 10% v/v solution of TMSOTf in Et2O,
ϳ8.00 ␮mol) was added. The reaction was quenched with Et3N
after 15 min. The reaction mixture was loaded directly onto a silica
gel column for chromatography (ethyl acetate – toluene, 3/1 v/v).
The isolated product 65 (37.0 mg, 82%) was exclusively the
␤-anomer. [␣]D = +79.0 (c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3) ␦:
7.45–7.00 (m, 20H, ArH), 5.95–5.85 (m, 1H, CHCH2), 5.52–5.50 (d,
1H, NH) 5.31–5.26 (m, 2H, H-1=, CHCH2), 5.19–5.16 (dd, 1H, CHCH2,
J = 10.4, 1.4 Hz), 5.08–5.01 (m, 2H, H-3== , CH2Ph), 4.89–4.87 (d, 1H,
CH2Ph), 4.79–4.69 (m, 4H, CH2Ph), 4.62 (s, 1H), 4.59–4.54 (m, 2H,
H-1== , Hx), 4.50–4.44 (m, 2H, CH2Ph, OCH2), 4.40–4.38 (d, 1H, H-1,
J = 7.7 Hz), 4.31–4.29 (d, 1H, CH2Ph), 4.25 (s, 1H), 4.22–4.17 (q, 1H, J =
6.6 Hz), 4.14–4.08 (m, 3H, OCH2, CH2Cl), 4.02–4.01 (m, 2H), 3.95–
3.92 (dd, 1H, J = 10.4, 3.1 Hz), 3.89–3.86 (dd, 1H, J = 10.4, 2.6 Hz),
3.82–3.81 (m, 2H), 3.66 (s, 4H, Hx, COOCH3), 3.38 (s, 3H, COOCH3),
2.36 (s, 3H, COCH3), 1.99 (s, 3H, COCH3), 1.01–0.99 (d, 3H, H6a-c== , J =
6.3 Hz). 13C NMR (101 MHz, CDCl3) ␦: 170.8, 168.9, 168.5, 167.5 (C=O),
138.5, 138.1, 138.1, 137.4 (ArC), 133.9 (CHCH2), 129.2–125.4 (ArCH),
117.7 (CHCH2), 102.7 (C1), 99.3 (C1== ), 94.6 (C1), 75.3, 75.1, 74.2, 73.3
(CH2Ph), 77.4, 77.2, 76.6, 75.1, 74.5, 74.4, 74.0, 73.2, 70.2, 65.7,
64.3 (C2, C2=, C3, C3=, C3== , C4, C4=, C4== , C5, C5=, C5== ), 70.5 (OCH2),
52.6, 52.0 (COOCH3), 47.3 (C2== ), 40.6 (CH2Cl), 23.4, 21.6 (COCH3),
17.1 (C6== ). HRMS showed a fragmented structure of the molecule
where the chloroacetate group was not present. HRMS C53H62N4O16Na
[M + Na+] calculated: 1033.4059; found: 1033.2223.
2-N-acetamido-4-azido-3-O-chloroacetyl-2,4,6-trideoxy-
D-galactopyranoside-␣(1¡4)-methyl (2,3-di-O-benzyl-
D-galactopyranosyl) uronate-␣(1¡3)-methyl
(2,4-di-O-benzyl-D-galactopyranosyl) uronate (63)
Trisaccharide 62 (300 mg, 0.26 mmol) was dissolved in CH2Cl2
(1.20 mL) and cooled to 0 °C. Trifluoroacetic acid (2.40 mL) was
added and the reaction was stirred at 0 °C for 3 h. Upon complete
consumption of the starting material, the reaction was diluted in
CH2Cl2 and quenched by pouring onto excess saturated NaHCO3.
The organic phase was washed with saturated NaHCO3 (3 × 20 mL)
and brine (2 × 20 mL) before drying over Na2SO4. The solvent was
removed under reduced pressure and the product was isolated by
column chromatography (100% ethyl acetate) to give 63 (219 mg,
80%) with a 2.5:1 ␣ to ␤ ratio. NMR data for major anomer: 1H NMR
(500 MHz, CDCl3) ␦: 7.46–7.05 (m, 20H, ArH), 5.62–5.60 (m, 1H, NH),
5.43–5.42 (d, 1H, H-1, J = 3.4 Hz), 5.34 (d, 1H, H-1=, J = 3.2 Hz),
5.12–5.09 (dd, 1H, H-3== , J = 10.7, 3.5 Hz), 5.06–5.04 (d, 1H, CH2Ph),
4.80–4.75 (m, 4H, CH2Ph), 4.63–4.57 (m, 4H), 4.51–4.38 (m, 3H,
CH2Ph), 4.33 (s, 1H), 4.25–4.20 (m, 2H), 4.15 (s, 1H), 4.11 (m, 2H,
CH2Cl), 4.02–3.99 (dd, 1H, J = 10.1, 3.5 Hz), 3.98–3.95 (dd, 1H, J = 10.4,
3.2 Hz), 3.92–3.90 (dd, 1H, J = 10.3, 2.9 Hz), 3.69–3.68 (m, 1H), 3.67 (s,
3H, COOCH3), 3.46 (s, 3H, COOCH3), 2.01 (s, 3H, COCH3), 1.02–1.01
(d, 3H, H-6a=cٞ, J = 6.3 Hz). 13C NMR (126 MHz, CDCl3) ␦: 170.9 (NCO),
169.2, 168.8, 167.5 (C=O), 138.6, 138.1, 137.4, 137.3 (ArC), 128.9–127.5
(ArCH), 99.3 (C1== ), 95.3 (C1=), 91.3 (C1), 75.2, 74.1, 73.1, 73.0 (4 ×
CH2Ph), 77.2, 75.8, 75.2, 75.1, 74.6, 74.0, 73.1, 70.8, 70.2, 65.7, 64.2
(C2, C2=, C3, C3=, C3== , C4, C4=, C4== , C5, C5=, C5== ), 52.5 (COOCH3),
52.1 (COOCH3), 47.3 (C2== ), 40.6 (CH2Cl), 23.4 (COCH3), 17.2 (C6== ).
LRMS C52H59ClN4O17Na [M + Na+] calculated: 1069.34; found
1069.46. HRMS showed a fragmented structure of the molecule
where the chloroacetate group was not present. HRMS
C50H58N4O16Na [M + Na+] calculated: 993.3746; found: 993.3765.
Allyl (2-N-acetamido-4-azido-2,4,6-trideoxy-D-galactopyranoside-
␣(1¡4)-methyl (2,3-di-O-benzyl-D-galactopyranosyl) uronate-
␣(1¡3)-methyl (2,4-di-O-benzyl-␤-D-galactopyranoside) uronate) (66)
Trisaccharide 65 (35.0 mg, 32.2 ␮mol) was dissolved in THF
(0.40 mL). NaHCO3 (9.00 mg, 106 ␮mol), thiourea (7.00 mg,
Published by NRC Research Press

Ní Cheallaigh and Oscarson
959
96.0 ␮mol), and TBAI (2.00 mg, 6.40 ␮mol) were added and the
reaction was heated at 60 °C for 16 h. The reaction was placed
directly onto a silica gel column for chromatography (ethyl
acetate – cyclohexane, 4/1 v/v to 100% ethyl acetate) to give 66
(28.0 mg, 86%). [␣]D = +84.4 (c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3)
␦: 7.44–7.03 (m, 20H, ArH), 6.09 – 6.07 (d, 1H, NH), 5.95–5.85 (m, 1H,
CHCH2), 5.31–5.26 (m, 2H, H-1=, CHCH2), 5.18–5.15 (dd, 1H, CHCH2),
5.05–4.87 (dd, 2H, CH2Ph), 4.80–4.70 (m, 4H, 2 × CH2Ph), 4.66 (s,
1H), 4.49–4.46 (m, 2H, H-1=, OCH2), 4.44–4.41 (d, 1H, CH2Ph), 4.39–
4.37 (m, 1H, H-1), 4.35–4.32 (d, 1H, CH2Ph), 4.23 (s, 1H), 4.21–4.17 (m,
2H), 4.13–4.08 (m, 1H, OCH2), 4.03 (s, 1H), 4.00 (d, 1H), 3.89 (s, 2H),
3.81–3.80 (m, 2H), 3.65 (s, 3H, COOCH3), 3.57–3.56 (m, 1H), 3.42 (s,
3H, COOCH3), 2.09 (s, 3H, COCH3), 1.04–1.02 (d, 3H, H-6a-c== , J =
6.3 Hz). 13C NMR (101 MHz, CDCl3) ␦: 173.8 (NC=O), 169.9, 168.5
(C=O), 138.5, 138.1, 138.1, 137.5 (ArC), 133.9 (CHCH2), 128.7–127.5
(ArCH), 117.7 (CHCH2), 102.8 (C1), 98.7 (C1== ), 94.9 (C1=), 77.2, 76.7,
75.4, 74.6 (2), 74.0, 72.2, 70.1, 66.7, 66.1, 60.5 (C2, C2=, C3, C3=, C3== ,
C4, C4=, C4== , C5, C5=, C5== ), 70.6 (OCH2), 75.3, 75.1, 74.3, 73.1
(CH2Ph), 52.6, 52.1 (COOCH3), 50.9 (C2== ), 23.0 (COCH3), 17.4 (C6== ).
HRMS C53H62N4O16Na [M + Na+] calculated: 1033.4059; found:
1033.4097.
tion. 67: 13C NMR (101 MHz, CDCl3) ␦: 105.0, 102.61, 100.0, 99.1, 94.7,
94.2 (anomeric carbons before anomerisation). 68: 13C NMR
(101 MHz, CDCl3) ␦: 105.0, 100.1, 99.1, 96.2, 95.5, 94.2 (anomeric
carbons after anomerisation).
Supplementary material
Supplementary material is available with the article through
the journal Web site at http://nrcresearchpress.com/doi/suppl/
10.1139/cjc-2016-0006.
Acknowledgements
We are thankful for financial support from the Irish Research
Council (IRCSET EMBARK Ph.D. Scholarship to A.N.C.) and Science
Foundation Ireland (grants 08/IN.1/B2067 and 13/IA/1959).
References
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Allyl (2-N-acetamido-4-azido-3-O-chloroacetyl-2,4,6-trideoxy-
D-galactopyranoside-␣(1¡4)-methyl (2,3-di-O-benzyl-D-galactopyranosyl)
uronate-␣(1¡3)-methyl (2,4-di-O-benzyl-D-galactopyranosyl) uronate-
␤(1¡3)-2-N-acetamido-4-azido-2,4,6-trideoxy-D-galactopyranoside-
␣(1¡4)-methyl (2,3-di-O-benzyl-D-galactopyranosyl) uronate-
␣(1¡3)-methyl (2,4-di-O-benzyl-␤-D-galactopyranoside) uronate) (67)
Donor 64 (26.0 mg, 21.8 ␮mol) and acceptor 66 (21.0 mg,
20.0 ␮mol) were dissolved in CH2Cl2 (120 ␮L) and Et2O (180 ␮L). The
reaction was stirred with 4 Å molecular sieves at room tempera-
ture for 2 h before cooling to 0 °C and adding TMSOTf (1 ␮L,
4 ␮mol, added 10 ␮L of a 10% v/v solution TMSOTf/Et2O). The reac-
tion was stirred for 3 h until at which point it was quenched with
Et3N. The solution was added directly onto a column for chro-
matography and a gradient elution (toluene – ethyl acetate, 1/1–
0/1 v/v) was preformed to isolate the hexasaccharide 67 (25.0 mg,
83% considering recovery) and recover the unreacted acceptor
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(6.00 mg). H NMR (400 MHz, CDCl3) ␦: 7.46–6.97 (m, 40H, ArH),
5.91–5.84 (m, 1H, CHCH2), 5.50–5.47 (d, 1H, NH), 5.43–5.40 (d, 1H,
NH), 5.28–5.25 (m, 3H, H-1== , H-1ٞ== , CHCH2), 5.18–5.15 (dd, 1H,
CHCH2), 5.11–5.04 (m, 3 H, CH2Ph, H-3ٞ== ), 4.89–4.27 (m, 24H, 7 ×
CH2Ph, OCH2, H1=, H1== , H1== == , H1ٞ== , H2== , H2ٞ== , 3 × Hx), 4.23 (s, 2H),
4.17–4.05 (m, 5H, CH2Cl, OCH2, Hx, Hx), 3.99 (s, 2H), 3.91–3.75 (m,
10H), 3.70–3.61 (m, 2H), 3.66 (s, 3H, COOCH3), 3.62 (s, 3H, COOCH3),
3.49 (s, 3H, COOCH3), 3.32 (s, 3H, COOCH3), 2.00 (s, 3H, COCH3),
1.64 (s, 3H, COCH3), 1.06 – 1.04 (d, 3H, H-6a-c== , J = 6.4 Hz), 0.91–0.90
(d, 3H, H-6a-cٞ== , J = 6.3 Hz). 13C NMR (101 MHz, CDCl3) ␦: 170.7, 170.5
(2 × NCO), 169.1, 169.0, 168.6, 168.0, 167.5 (5 × C=O), 138.7, 138.4,
138.4, 138.1, 138.06, 138.0, 137.6, 137.4 (8 × ArC), 133.9 (CHCH2),
129.2–127.2 (ArCH), 117.7 (CHCH2), 105.1 (C1ٞ), 102.7 (C1), 100.2, 99.2
(C1== , C1ٞ== ), 94.8, 94.4 (C1=, C1ٞ=), 77.4, 77.3, 77.0, 76.7, 76.1, 75.5,
75.45, 75.4, 75.3, 75.1, 74.7, 74.6, 74.3, 74.2, 74.09, 74.03, 74.02, 73.8,
73.2, 73.1, 73.0, 70.6, 70.3, 70.1, 66.0, 65.7, 65.7, 64.3 (C2, C2=, C2ٞ,
C2== == , C3, C3=, C3== , C3ٞ, C3== == , C3ٞ== , C4, C4=, C4== , C4ٞ, C4== == , C4ٞ== ,
C5, C5=, C5== , C5ٞ, C5== == , C5ٞ== , 8 × CH2Ph, OCH2), 52.6, 52.5, 52.1,
51.9 (4 × COOCH3), 48.2, 47.3 (C2== , C2ٞ== ), 40.6 (CH2Cl), 23.5, 23.4 (2 ×
COCH3), 17.5, 17.0 (C6== , C6ٞ== ).
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