Efficient stereoselective synthesis of oligosaccharides of Streptococcus pneumoniae serotypes 6A and 6B containing multiple 1,2-cis glycosidic linkages

Article abstract of DOI:10.1016/j.tet.2007.07.036

The synthesis of the repeating units of pneumococcal polysaccharide serotypes 6A and 6B and derivatives thereof is described. Application of S-benzoxazolyl and S-thiazolinyl glycosides allowed rapid oligosaccharide assembly and provided complete stereosel

Full text of DOI:10.1016/j.tet.2007.07.036

Tetrahedron 63 (2007) 10083–10091
Efficient stereoselective synthesis of oligosaccharides
of Streptococcus pneumoniae serotypes 6A and 6B
containing multiple 1,2-cis glycosidic linkages
Archana R. Parameswar, Papapida Pornsuriyasak, Nicole A. Lubanowski
*
and Alexei V. Demchenko
Department of Chemistry and Biochemistry, University of Missouri—St. Louis, One University Boulevard, St. Louis, MO 63121, USA
Received 31 May 2007; revised 5 July 2007; accepted 10 July 2007
Available online 19 July 2007
Abstract—The synthesis of the repeating units of pneumococcal polysaccharide serotypes 6A and 6B and derivatives thereof is described.
Application of S-benzoxazolyl and S-thiazolinyl glycosides allowed rapid oligosaccharide assembly and provided complete stereoselectivity
in challenging 1,2-cis glucosylations and galactosylations. The oligosaccharide assembly was accomplished in an efficient manner by selec-
tive activation of thioimidoyl leaving groups over thioglycosides.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
invasive pneumococcal disease worldwide.10 This fact stim-
ulated extensive structural studies leading to establishing the
structures of capsular polysaccharides of both 6A and 6B
(Fig. 1).11–13 Serotype-specific antibodies are formed in
response to vaccination with the pneumococcal polysaccha-
ride or saccharide–protein conjugate, so it was believed that
due to similarity in the carbohydrate core structures of
SPn6A and SPn6B, the elicited antibodies would be cross-
reactive against both types.12,14–16 As a result, only hydrolyt-
ically more stable and, hence, easier accessible natural
isolate of SPn6B was selected and included in all currently
licensed multi-component vaccines. A common approach
to vaccine development is based on the isolated natural poly-
saccharides either neat or conjugated to a protein carrier.
A number of linear chemical syntheses of SPn6B, their
mimetics, and conjugates have also emerged.17–22
Involvement of complex glycostructures in a variety of dam-
aging and healing processes has already been acknowledged
by development of carbohydrate-based vaccines1–3 and ther-
apeutics.4,5 The bacteria Streptococcus pneumoniae (SPn)
have become one of the most frequent causes of pneumonia,
bacteremia, and meningitis in the elderly, immunocompro-
mised, and, especially, in young children. As a matter of
fact, SPn has one of the largest public health and economic
impacts amongst all bacterial infectious diseases. The inci-
dence of pneumococcal infection varies geographically,
but elevated rates have been observed in both developed
and developing countries. In accordance with the joint
United Nations Children’s Fund (UNICEF)/World Health
Organization (WHO) survey, over 2 million children die an-
nually worldwide due to pneumonia, accounting for almost
20% of deaths under age five.6 More than half of these deaths
are attributed to SPn. This situation is further complicated by
the rapid increase in anti-microbial drug resistance during
the last decade. Since the SPn bacterial cell is surrounded
by a polysaccharide capsule, preventive vaccination based
on polysaccharide or saccharide–protein conjugates is a suit-
able tool against the bacterial invasion.7
Recent cross-reactivity studies challenged the hypothesis of
the cross-reactivity by determining that SPn6B-based vac-
cines produce 6B-specific antibodies that cross-react with
SPn6A at a much lower rate.9,22–24 In this context, similar
observations had also been made for the capsular polysac-
charide types 19F and 19A.25 Hence, the importance of
including the SPn6A carbohydrate conjugates in the future
generations of multi-serotype anti-SPn vaccines has been
acknowledged.26 However, the achievement of this is chal-
lenging for a number of reasons, major of which is low
hydrolytic stability of SPn6A isolates that results in their
low availability in sufficiently pure form.27 A possible solu-
tion for this would be the chemical synthesis of the related
sugar derivatives and their application as oligosaccharide–
protein conjugate vaccine components. Although natural28
Amongst over 90 elucidated SPn serotypes,8 6A and 6B are
equally important causes of bacterial infections.9 In addition,
this serogroup has been ranked within the top three causes of
Keywords: Carbohydrates; Streptococcus pneumoniae; Synthetic vaccines;
Glycosylation; Oligosaccharides; Thioimidates.
* Corresponding author. E-mail: demchenkoa@umsl.edu
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.07.036

10084
A. R. Parameswar et al. / Tetrahedron 63 (2007) 10083–10091
O-
O-
P
OH OH
3
OH
OH
4
P
O
O
OH
O
O
OH
O
O
HO
HO
HO
HO
OH
O
OH
O
O
O
HO
HO
O
O
HO
OH
HO
OH
O
O
O
O
HO
HO
O
O
OH
2
OH
1
Streptococcus Pneumoniae
Streptococcus Pneumoniae
Serotype 6A
Serotype 6B
Figure 1. Compound numbers 1 and 2 correspond to the phosphateless pseudo-tetrasaccharide units only.
and synthetic saccharides17–19 of the SPn6A series have been
investigated, no systematic studies have yet emerged.
Herein, we report the application of new thioimidoyl meth-
odology developed in our laboratory to efficient stereoselec-
tive synthesis of pseudo-disaccharides, pseudo-trisaccharides,
and pseudo-tetrasaccharides (1–6, Figs. 1 and 2) structurally
related to SPn6A and SPn6B.
linked (1,2-cis) to the C-3 of a D-glucose unit; the latter is
linked via 1,2-cis-glycosidic bond to the C-3 of L-rhamnose,
which is connected via a-glycosidic linkage (1,2-trans) to
the C-3 of D-ribitol (SPn6A) or C-4 of D-ribitol (SPn6B). Ef-
ficient chemical synthesis of the repeating units of SPn6A,
SPn6B and structurally related glycoconjugates thereof
will help to quickly obtain substantial quantities of pure
samples for immunological studies and subsequent fully
synthetic vaccine development.
OH
OH OH
HO
OH
HO
OH
From the chemical point of view, a number of synthetic chal-
lenges could be anticipated. It should be noted that even
nowadays chemical synthesis of complex carbohydrates of
this caliber, especially those containing ‘difficult’ 1,2-cis
glycosidic linkages, is still regarded as laborious and ineffi-
cient.29 Our goal was to investigate whether the application
of glycosyl thioimidates, excellent building blocks for
1,2-cis glycosylation,30,31 would allow high 1,2-cis stereo-
selectivity and yields when applied to the synthesis of pneu-
mococcal oligosaccharides. Therefore, the use of the
anomeric thioimidoyl moieties, S-benzoxazolyl (SBox) or
S-thiazolinyl (STaz), was projected for the introduction of
1,2-cis glycosidic linkages of oligosaccharides 1, 2, 5, and
6. A non-participating group at C-2, O-benzyl, is required
to facilitate the introduction of 1,2-cis-linked galactose
and glucose units. Since the thioimidoyl moiety can be selec-
tively activated over conventional thioglycosides,32 S-ethyl
moiety was chosen for the introduction of the rhamnose unit.
O
OH
O
O
O
HO
HO
HO
HO
OH
OH
4
3
OH
OH OH
O
HO
OH
HO
O
OH
OH
O
O
O
HO
HO
HO
O
OH
HO
OH
HO
HO
HO
HO
O
OH
5
O
OH
6
Figure 2.
2. Retrosynthetic analysis
Having analyzed the target oligosaccharide structures and
possible challenges associated with their synthesis, we nar-
rowed down possible candidates for the key building blocks
to the following compounds: D-galactose (7), D-glucose
(8a,b), L-rhamnose (9–11) and D/L- or D-ribitol (12 or 13, re-
spectively, Scheme 1).33 A variety of rhamnose derivatives
SPn6A and SPn6B repeating units consist of structurally
similar complex pseudo-tetrasaccharides 1 and 2, respec-
tively (Fig. 1), which in the natural polysaccharide are con-
nected via a phosphate (5/2000) linkage. Both 1 and 2 bear
a terminal D-galactosyl residue, which is a-glycosidically
α
α
α
-D-Gal
α
1
3
3
-D-Glc
α
1
3
-L-Rha
α
1
3 or 4 Ribitol
SEt
OR3
AcO OAc
Ph
O
O
O
O
O
R1O
STaz
SBox
RO
BnO
OBn
AcO
BnO
R2O
OR1
OBn
OR4 OBn
8a: R=Ac
8b: R=H
7
12: R3=H, R4=Bn
13: R3=Bn, R4=H
9: R1=R2=Bz
10: R1=Bz, R2=H
11: R1=Bn, R2=H
N
O
N
S
SBox =
S
STaz =
S
Scheme 1. Retrosynthetic analysis of oligosaccharides of SPn6A and SPn6B.

A. R. Parameswar et al. / Tetrahedron 63 (2007) 10083–10091
10085
BnO
O
OBn
were to be investigated in an attempt to optimize the stereo-
selectivity and yield of rhamnosylation.
BnO
OBn
O
NIS/TMSOTf
1. NaOMe, MeOH
2. H2, Pd/C
87%
9 + 12
3
4Å MS, 1,2-DCE
80%
BzO
3. Synthesis of building blocks
BzO
20
OBz
Synthesis of the 3-OH ribitol building block 12 was carried
out from known precursor 14 as shown in Scheme 2.34 Thus,
allylation of 14 was accomplished in 99% yield and the
resulting compound 15 was subjected to acetal cleavage
followed by benzylation to afford fully protected intermedi-
ate 17 in over 90% yield for two steps. Deallylation of 17
using PdCl2 in MeOH lead to glycosyl acceptor 12 in 95%
yield. It is noteworthy that the synthesis of compound 12
has been previously accomplished using less expeditious
pathways.18 Unfortunately, the direct use of 3-OH ribitol
14 as glycosyl acceptor was found to be impractical. Partial
loss of acetal protecting groups that has occurred during
glycosylation resulted in the formation of an inseparable
mixture.
OBn
BnO
OBn
1. NaOMe, MeOH
2. H2, Pd/C
90%
NIS/TMSOTf
OBn
O
9 + 13
4
4Å MS, 1,2-DCE
O
85%
BzO
BzO
OBz
21
Scheme 3. Synthesis of pseudo-disaccharides of SPn6A (3) and SPn6B (4).
S-ethyl moiety of glycosyl acceptor 10 in the presence of
silver(I) triflate (Scheme 4). This reaction proceeded with
complete 1,2-cis stereoselectivity as no traces of the diaste-
reomer were detected by analyzing crude reaction mixture.
Subsequently, the S-ethyl moiety of 22 was activated with
NIS and TMSOTf for glycosylation of glycosyl acceptors
12 and 13. As a result, saccharides 23 and 24 were isolated
in 71 and 76% yield, respectively. These rhamnosylations
also proceeded with complete a-stereoselectivity. The pro-
tected pseudo-trisaccharides 23 and 24 were subjected to
standard deprotection conditions, deacylation followed by
hydrogenation, to afford compounds 5 and 6 in 80 and
88% yield, respectively.
Synthesis of 4-OH ribitol building block 13, a component of
SPn6B, was achieved by the reduction of known compound
1835 to obtain 1936 in 90% yield (Scheme 2). The intermedi-
ate 19 was then regioselectively benzylated under phase
transfer conditions to afford 4-OH glycosyl acceptors 13
as a major regioisomer in 52% yield. Other building blocks,
D-galactose (7),30 D-glucose (8a,b),32 and L-rhamnose (9–
11),37–39 have been obtained as described previously.
4. Oligosaccharide synthesis
For the synthesis of pseudo disaccharides 3 and 4, fully
protected rhamnose building block 9 was used as a glycosyl
donor. Coupling of 9 with ribitol acceptors 12 and 13 in the
presence of NIS/TMSOTf afforded glycosides 20 and 21
with complete a-selectivity in 80 and 85% yield, respec-
tively (Scheme 3). Complete 1,2-trans stereoselectivity
achieved herein is credited to the use of a neighboring
participating substituent in 9. The compounds obtained
were then subjected to a two-step sequential deprotection:
deacylation (NaOMe in MeOH) and hydrogenation using
palladium on charcoal to obtain pseudo-disaccharides 3
and 4 in 87 and 90% yield, respectively, over two steps.
Finally, we were aimed for the synthesis of pseudo-tetrasac-
charides 1 and 2, the ultimate targets of this work. For this
purpose, we first investigated sequential activation of the
SBox moiety of 7 over the STaz moiety of glucosyl acceptor
8b. Unfortunately, this reaction resulted in the formation of
an unseparable mixture of anomers (a–b¼7/1). This misfor-
tune stimulated us to adopt a new strategy, according to
which glucosyl donor bearing the STaz leaving group (8a)
was first selectively activated over the S-ethyl moiety of the
rhamnose acceptor (11) in the presence of AgOTf. Although
this reaction was performed in 1,2-dichloroethane, a solvent
that does not normally favor a-glycosylation, the disaccha-
ride 25 was obtained as a single a-anomer (1,2-cis) in 81%
yield (Scheme 5). Subsequently, 30-acetyl group in 25 was
removed by Zemplen method and the resulting disaccharide
acceptor 26 was coupled with glycosyl donor 7. Selective
For the synthesis of pseudo-trisaccharides 5 and 6, disaccha-
ride intermediate 22 was obtained in 72% yield by selective
activation of the STaz moiety of glycosyl donor 8a over the
OAll
OR
PdCl2, MeOH
10% TFA-DCM
O
RO
O
OR
12
98%
95%
O
O
RO
OR
16: R = H
17: R = Bn
14: R = H
15: R = All
BnBr, NaH
DMF, 95%
AllBr, NaH
DMF, 99%
BnO
OBn
O
OH
NaBH4, EtOH
90%
BnBr, Bu4NBr
5% aq. NaOH
DCM, 52%
BnO
13
OH
BnO
OBn
OH
19
OBn
18
Scheme 2. Synthesis of ribitol acceptors 12 and 13.

10086
A. R. Parameswar et al. / Tetrahedron 63 (2007) 10083–10091
BnO
OBn
BnO
OBn
O
12, NIS/TMSOTf
4Å MS, 1,2-DCE
71%
SEt
O
1. H2, Pd/C
BzO
5
2. NaOMe, MeOH
80%
O
OBz
BnO
O
AcO
O
O
BzO
BnO
23
O
Ph
AgOTf, 3Å MS
1,2-DCE, 72%
O
8a + 10
OBz
OBn
AcO
O
O
BnO
OBn
O
Ph
22
OBn
O
1. H2, Pd/C
13, NIS/TMSOTf
O
BzO
BnO
6
4Å MS, 1,2-DCE
2. NaOMe, MeOH
88%
O
76%
OBz
24
AcO
O
O
O
Ph
Scheme 4. Synthesis of pseudo-trisaccharides of SPn6A (5) and SPn6B (6).
activation of the SBox moiety over the S-ethyl moiety was
accomplished in the presence of AgOTf, and, in this case,
trisaccharide 27 was obtained with complete a-selectivity
in 76% yield. No trace of the b-anomer could be detected
by analysis of the crude reaction mixture. To complete the
assembly, the trisaccharide 27 was coupled with ribitol ac-
ceptors 12 and 13 in the presence of NIS and TMSOTf. As
a result, pseudo-tetrasaccharide derivatives 28 and 29 were
obtained in 70 and 80% yield, respectively. Finally, the
deprotection of 28 and 29 was carried out using conventional
deacylation–hydrogenation sequence to afford pseudo-
tetrasaccharides 1 and 2 in 75 and 78% yield, respectively.
5. Conclusions and future directions
We developed an efficient convergent approach to the syn-
thesis of pneumococcal oligosaccharides of SPn6A and
SPn6B. Rapid oligosaccharide assembly was accomplished
by selective activation of the STaz and SBox leaving group
of glycosyl donors over the S-ethyl anomeric moiety of
glycosyl acceptors. Application of the STaz and SBox
methodologies has also allowed completely stereoselective
introduction of two challenging 1,2-cis glycosidic moieties.
It is to be expected that the protocol reported herein will be
suitable for the synthesis of recently discovered structurally
SEt
8
O
AgOTf, 3Å MS
1,2-DCE, 81%
BnO
BnO
O
OBn
11
RO
O
O
O
Ph
25: R = Ac
26: R = H
7
NaOMe
MeOH
90%
AgOTf, 3Å MS
1,2-DCE, 76%
SEt
AcO OAc
O
O
BnO
BnO
AcO
O
OBn
12
BnO
O
13
NIS/TMSOTf
4Å MS, 1,2-DCE
70%
O
NIS/TMSOTf
O
O
Ph
4Å MS, 1,2-DCE
80%
27
OBn
BnO
BnO
OBn
OBn
BnO
OBn
OBn
O
O
AcO OAc
AcO OAc
O
O
O
BnO
BnO
O
BnO
BnO
AcO
O
AcO
O
OBn
OBn
BnO
O
BnO
O
O
O
O
O
O
Ph
O
Ph
29
28
1. NaOMe, MeOH
2. H2, Pd/C
78%
1. NaOMe, MeOH
2. H2, Pd/C
75%
2
1
Scheme 5. Synthesis of pseudo-tetrasaccharides of SPn6A (1) and SPn6B (2).

A. R. Parameswar et al. / Tetrahedron 63 (2007) 10083–10091
10087
similar serotypes SPn6C and SPn6D.40 Further studies re-
lated to the synthesis of spacer-containing oligosaccharides
for subsequent conjugation and immunological studies are
underway in our laboratory.
poured in crushed ice (w50 mL), stirred for 15 min, and
extracted with ethyl acetate/ether (1/1, v/v, 3ꢁ80 mL). The
combined organic extract was dried over anhydrous
MgSO4 and concentrated in vacuo. The residue was purified
by column chromatography on silica gel (ethyl acetate–
hexane gradient elution) to afford compound 17 as a syrup
(2.27 g, 98% yield). Analytical data for 17 were essentially
the same as reported previously.18
6. Experimental part
6.1. 3-O-Allyl-1,2:4,5-di-O-isopropylidene-D/L-ribitol
(15)
6.4. 1,2,4,5-Tetra-O-benzyl-D/L-ribitol (12)
Allyl bromide (0.75 mL, 8.62 mmol) was added to a stirring
solution of 1,2:4,5-di-O-isopropylidene-D/L-ribitol (14,
1.0 g, 4.3 mmol) in dry DMF (10 mL) at 0 ꢀC. Sodium hy-
dride (60% suspension in mineral oil, 12.9 mmol) was added
slowly until evolution of hydrogen gas has seized. The reac-
tion mixture was stirred for 20 min at rt until complete dis-
appearance of starting material as indicated by TLC. The
reaction mixture was poured in crushed ice (w100 mL),
stirred for 15 min, and extracted with ethyl acetate/ether
(1/1, v/v, 3ꢁ100 mL). The combined organic phase was
dried over anhydrous MgSO4 and concentrated in vacuo.
The residue was purified by column chromatography on
silica gel (ethyl acetate–hexane gradient elution) to afford
compound 15 as a syrup (1.16 g, 99% yield). Analytical
data: Rf¼0.50 (ethyl acetate–hexanes, 1/5, v/v); [a]2D6 ꢂ0.7
To a stirring solution of 17 (1.5 g, 2.7 mmol) in MeOH
(15 mL), PdCl2 (0.6 g) was added and the reaction mixture
was stirred at rt for 12 h. The solid was then filtered-off
through Celite, washed with methanol (3ꢁ10 mL), and
concentrated in vacuo. The residue was purified by column
chromatography on silica gel (ethyl acetate–hexane gradient
elution) to afford compound 12 as a syrup (1.29 g, 93%
yield). Analytical data: Rf¼0.42 (ethyl acetate–hexanes,
1
3/7, v/v); [a]2D3 +4.3 (c 1.0, CHCl3); H NMR: d 3.54–3.60
(m, 2H, H-2,4), 3.63–3.68 (m, 4H, H-1, 5), 3.98 (dd, 1H,
J3,4¼10.9 Hz, H-3), 4.38–4.62 (m, 8H, 4ꢁCH2Ph), 7.16–
7.25 (m, 20H, aromatic) ppm; 13C NMR d 70.7 (ꢁ2), 72.1,
72.5 (ꢁ2), 73.9 (ꢁ2), 78.6 (ꢁ2), 128.1 (ꢁ3), 128.1 (ꢁ3),
128.2 (ꢁ4), 128.4 (ꢁ4), 128.8 (ꢁ4), 128.9 (ꢁ4), 136.6,
138.9 ppm; HR-FABMS [M+H]+ calcd for C33H37O5
513.2641, found 513.2642. It should be noted that partial
analytical data for 12 were reported previously.18
1
(c 1.0, CHCl3); H NMR: d 1.27, 1.35 (2 s, 12H, 4ꢁCH3),
3.57 (dd, 1H, J3,4¼4.8 Hz, H-3), 3.59–3.99 (m, 4H, H-1,
5), 4.01–4.05 (m, 2H, H-2, 4), 4.17 (m, 2H, OCH2), 5.06–
5.21 (m, 2H, CH2]), 5.80–5.91 (m, 1H, ]CH–) ppm;
13C NMR: d 25.7 (ꢁ2), 25.8 (ꢁ2), 66.2 (ꢁ2), 74.2, 76.6
(ꢁ2), 78.8, 110.0 (ꢁ2), 117.3, 135.3 ppm, HR-EIMS
[MꢂCH3]+ calcd for C13H21O5 257.1384, found 257.1389.
6.5. 2,3,5-Tri-O-benzyl-D-ribitol (19)
To a stirring suspension of NaBH4 (350 mg, 9.2 mmol) in
absolute ethanol (17 mL) at 0 ꢀC, was added a solution of
2,3,5-tri-O-benzyl-D-ribose (18, 2.28 g, 5.4 mmol) in abso-
lute ethanol (19 mL) and the reaction mixture was stirred
for 15 min at rt. Upon completion, 96% aq acetic acid was
added until pH 5 (w1.0 mL). The resulting mixture was
diluted with DCM (100 mL), washed with 1 M HCl
(30 mL), and water (2ꢁ30 mL). The organic phase was sep-
arated, dried over MgSO4, and concentrated in vacuo. The
residue was purified by column chromatography on silica
gel (ethyl acetate–hexane gradient elution) to afford com-
pound 19 as a syrup (2.07 g, 90% yield). Analytical data:
Rf¼0.53 (ethyl acetate–hexanes, 2/3, v/v); [a]2D2 +19.9 (c
6.2. 3-O-Allyl-D/L-ribitol (16)
To a stirred solution of 15 (1.16 g, 4.6 mmol) in CH2Cl2
(10 mL), 90% aq trifluoroacetic acid (1 mL) was added
dropwise and the reaction was kept for 30 min at rt until
complete disappearance of the starting material (monitored
by TLC). The reaction mixture was neutralized with triethyl-
amine (w1 mL) and concentrated in vacuo. The residue was
purified by column chromatography on silica gel (methanol–
dichloromethane gradient elution) to afford compound 16 as
a syrup (0.81 g, 98% yield). Analytical data: Rf¼0.46 (meth-
anol–dichloromethane, 1/5, v/v); [a]2D8 ꢂ1.5 (c 1.0, metha-
nol); 1H NMR (CD3OD): d 3.47 (dd, 1H, J2,3¼5.7 Hz,
H-3), 3.57–3.63 (m, 2H, H-5), 3.70–3.75 (m, 2H, H-1),
3.79–3.84 (m, 2H, H-2, 4), 4.13–4.16 (m, 2H, OCH2),
5.09–5.27 (m, 2H, CH2]), 5.84–5.98 (m, 1H, ]CH–)
ppm; 13C NMR (CD3OD): d 65.1 (ꢁ2), 72.6 (ꢁ2), 73.9,
82.1, 117.9, 136.7 ppm; HR-FABMS [M+Na]+ calcd for
C8H16O5Na 215.0895, found 215.0895.
1
1.0, CHCl3); H NMR: d 3.55–3.58 (m, 2H, H-5), 3.69–
3.76 (m, 2H, H-2, 3), 3.78–3.82 (m, 2H, H-1), 3.92–4.02
(m, 1H, H-4), 4.38–4.71 (m, 6H, 3ꢁCH2Ph), 7.13–7.21 (m,
15H, aromatic) ppm; 13C NMR: d 61.6, 71.2, 71.6, 72.6,
74.0, 74.6, 79.9, 80.0, 128.4 (ꢁ3), 128.5 (ꢁ2), 128.6 (ꢁ2),
128.7 (ꢁ2), 129.0 (ꢁ2), 129.1 (ꢁ4), 138.5, 138.6 (ꢁ2)
ppm; HR-FABMS [M+H]+ calcd for C26H31O5 423.2172,
found 423.2176. It should be noted that the synthesis and
partial analytical data of compound 19 was previously
described.36,41
6.3. 3-O-Allyl-1,2,4,5-tetra-O-benzyl-D/L-ribitol (17)
6.6. 1,2,3,5-Tetra-O-benzyl-D-ribitol (13)
Benzyl bromide (2.5 mL, 21.1 mmol) was added to a stirring
solution of 16 (0.81 g, 4.21 mmol) in dry DMF (15 mL) at
0 ꢀC. Sodium hydride (60% suspension in mineral oil,
1.26 g, 31.6 mmol) was added slowly until evolution of
hydrogen gas has seized. The reaction mixture was stirred
for 30 min at rt until complete disappearance of starting
material as indicated by TLC. The reaction mixture was
To a solution of compound 19 (724 mg, 1.71 mmol) in
CH2Cl2 (15 mL), BnBr (0.3 mL, 1.22 mmol) was added
followed by Bu4NBr (110 mg, 0.34 mmol) and 5% aq
NaOH (4.5 mL). The reaction mixture was stirred for 16 h
under reflux (50 ꢀC), then cooled to rt, diluted with
CH2Cl2 (50 mL), and washed with saturated aq NaHCO3

10088
A. R. Parameswar et al. / Tetrahedron 63 (2007) 10083–10091
(15 mL) and water (3ꢁ15 mL). The organic phase was sep-
arated, dried over MgSO4, and concentrated in vacuo. The
residue was purified by column chromatography on silica
gel (ethyl acetate–hexanes gradient elution) to afford 13 as
white crystals (458 mg, 52% yield). Also the regioisomer
(2,3,4,5-tetra-O-benzyl-D-ribitol) was isolated in 32% yield.
Analytical data for 13: Rf¼0.46 (ethyl acetate–toluene, 3/7,
v/v); [a]2D2 +18.1 (c 1.0, CHCl3); mp 40 ꢀC; 1H NMR:
d 3.59–3.61 (m, 2H, H-5), 3.68–3.73 (m, 1H, H-3), 3.76–
3.84 (m, 2H, H-1), 3.92–3.96 (m, 1H, H-2), 3.98–4.04 (m,
1H, H-4), 4.50–4.75 (m, 8H, 4ꢁCH2Ph), 7.18–7.33 (m,
20H, aromatic) ppm; 13C NMR: d 70.3, 71.6, 71.8, 73.1,
74.0 (ꢁ2), 74.3, 79.5, 79.7, 128.1, 128.2 (ꢁ2), 128.3 (ꢁ3),
128.4 (ꢁ2), 128.5 (ꢁ2), 128.6 (ꢁ2), 128.9 (ꢁ4), 129.0
(ꢁ4), 138.7, 138.8, 138.9, 139.0 ppm; HR-FABMS
[M+H]+ calcd for C33H37O5 513.2641, found 513.2642.
67.9, 69.2, 70.3 (ꢁ2), 71.5, 72.4, 72.7 (ꢁ3), 73.9 (ꢁ3),
78.5, 98.4, 128.1 (ꢁ3), 128.2 (ꢁ2), 128.4 (ꢁ2), 128.5
(ꢁ6), 128.9 (ꢁ6), 129.0 (ꢁ3), 129.1 (ꢁ2), 129.2 (ꢁ2),
130.1 (ꢁ3), 130.4 (ꢁ4), 130.6 (ꢁ2), 133.9 (ꢁ3), 139.9
(ꢁ4), 166.1, 166.2, 166.4 ppm; HR-FABMS [M+Na]+ calcd
for C60H58O12Na 993.3826, found 993.3840.
6.7.2. 4-O-(2,3,4-Tri-O-benzoyl-a-L-rhamnopyranosyl)-
1,2,3,5-tetra-O-benzyl-D-ribitol (21). This compound
was obtained by Method B from 9 and 13 in 85% yield.
Analytical data for 21: Rf¼0.51 (ethyl acetate–hexanes,
1
3/7, v/v); [a]2D2 +39.6 (c 1, CHCl3); H NMR: d 1.15 (d,
3H, H-60), 3.71–3.90 (m, 6H, H-1, 2, 3, 5), 4.26–4.36 (m,
1H, H-50), 4.42–4.81 (m, 9H, H-4, 4ꢁCH2Ph), 5.48 (s, 1H,
0
H-10), 5.64 (dd, 1H, J2 ,3 ¼9.9 Hz, H-3 ), 5.78–5.87 (m,
2H, H-20, 40), 7.19–8.12 (m, 35H, aromatic) ppm; 13C
NMR: d 18.0, 67.7, 70.6, 70.7, 71.4, 71.6, 72.5, 73.3, 73.9
(ꢁ2), 76.4, 78.7, 79.5, 97.4, 128.1 (ꢁ2), 128.2 (ꢁ2), 128.3
(ꢁ3), 128.4 (ꢁ3), 128.5 (ꢁ3), 128.6 (ꢁ3), 128.7 (ꢁ2),
128.9 (ꢁ6), 129.1 (ꢁ2), 129.9 (ꢁ2), 130.0, 130.2 (ꢁ4),
130.5 (ꢁ2), 133.6, 133.8, 133.9, 138.7 (ꢁ2), 138.9 (ꢁ2),
165.8, 165.9, 166.3 ppm; HR-FABMS [M+Na]+ calcd for
C60H58O12Na 993.3826, found 993.3840.
0
0
6.7. Typical glycosylation procedures: preparation of
di- and oligosaccharides
Method A: AgOTf-promoted activation of the STaz and SBox
glycosyl donors. A mixture the glycosyl donor (0.11 mmol),
glycosyl acceptor (0.10 mmol), and freshly activated molec-
˚
ular sieves (3 A, 200 mg) in ClCH2CH2Cl (2 mL) was
stirred under argon for 1.5 h. Freshly conditioned AgOTf
(0.22 mmol) was added and the reaction mixture was stirred
for 15 min at rt, then diluted with CH2Cl2, the solid was fil-
tered-off, and the residue was washed with CH2Cl2. The
combined filtrate (30 mL) was washed with 20% aq
NaHCO3 (15 mL) and water (3ꢁ10 mL), the organic phase
was separated, dried over MgSO4, and concentrated
in vacuo. The residue was purified by column chromato-
graphy on silica gel (ethyl acetate–hexane gradient elution)
or Sephadex LH-20 (methanol–dichloromethane, 1/1, v/v
elution) to afford a di- or a trisaccharide derivative.
6.7.3. O-(a-L-Rhamnopyranosyl)-(1/3)-D/L-ribitol (3).
To a solution of 20 (100 mg, 0.103 mmol) in dry methanol
(1.0 mL) was added 1 M NaOMe till pH¼10 (w0.1 mL).
The reaction mixture was stirred for 15 h at rt, then neu-
tralized with Dowex (H+), filtered, and concentrated
in vacuo. The crude residue was dissolved in ethyl acetate/
ethanol (1/1, v/v, 2.0 mL) and 10% Pd–C (20 mg) was
added. The reaction mixture was stirred under an atmo-
sphere of H2 for 15 h. The catalyst was then filtered-off,
washed with methanol, and the filtrate was concentrated
under reduced pressure. The residue was purified by
column chromatography on Sephadex G-15 (water elution)
to afford compound 3 as a syrup (26.8 mg, 87% yield).
Analytical data: Rf¼0.52 (methanol–dichloromethane, 1/1,
Method B: NIS/TMSOTf-promoted activation of S-ethyl gly-
cosyl donors. A mixture the glycosyl donor (0.13 mmol),
glycosyl acceptor (0.10 mmol), and freshly activated molec-
1
v/v); [a]2D6 ꢂ45.4 (c 0.8, H2O); H NMR (D2O): d 1.20
0
ular sieves (4 A, 200 mg) in ClCH2CH2Cl (2 mL) was
(d, 3H, H-60), 3.37 (dd, 1H, J3 ,4 ¼9.7 Hz, H-4 ), 3.52–
3.58 (m, 2H, H-1b, 5b), 3.66–3.74 (m, 5H, H-1a, 5a, 3,
30, 50), 3.82–3.88 (m, 2H, H-2, 4), 3.90 (dd, 1H,
˚
0
0
stirred for 1 h under argon. NIS (0.25 mmol) and TMSOTf
(0.025 mmol) were added at 0 ꢀC and the reaction mixture
was stirred for 10 min. Upon completion, the solid was
filtered-off and the residue was washed with CH2Cl2. The
combined filtrate (30 mL) was washed with 20% aq
Na2S2O3 (15 mL) and water (3ꢁ10 mL). The organic phase
was separated, dried over MgSO4, and concentrated
in vacuo. The residue was purified by column chromato-
graphy on silica gel (ethyl acetate–hexane gradient elution)
or Sephadex LH-20 (methanol–dichloromethane, 1/1, v/v
elution) to afford a di- or an oligosaccharide derivative.
0
0
0
0
0
0
J2 ,3 ¼1.7 Hz, H-2 ), 4.88 (d, 1H, J1 ,2 ¼1.7 Hz, H-1 ) ppm;
13C NMR (D2O): d 16.9 (C-60), 62.7 (C-1), 63.0 (C-5),
69.7 (C-50), 70.5 (C-30), 70.7 (C-20), 71.1 (C-4), 72.0
(C-2), 72.2 (C-40), 80.2 (C-3), 100.9 (C-10) ppm; HR-
FABMS [M+Na]+ calcd for C11H22O9Na 321.1161, found
321.1171.
6.7.4. O-(a-L-Rhamnopyranosyl)-(1/4)-D-ribitol (4).
Compound 4 was obtained from 21 in 90% yield as de-
scribed for the synthesis of compound 3. Analytical data:
Rf¼0.43 (methanol–dichloromethane, 1/1, v/v); [a]D25
6.7.1. 3-O-(2,3,4-Tri-O-benzoyl-a-L-rhamnopyranosyl)-
1,2,4,5-tetra-O-benzyl-D/L-ribitol (20). This compound
was obtained by Method B from ethyl 2,3,4-tri-O-benzoyl-
1-thio-L-rhamnopyranoside 9 and 12 in 80% yield. Analyti-
cal data for 20: Rf¼0.49 (ethyl acetate–hexanes, 3/7, v/v);
1
ꢂ34.3 (c 1, H2O); H NMR (D2O): d 1.23 (d, 3H, H-60),
3.51 (dd, 1H, J3 ,4 ¼9.6 Hz, H-40), 3.69 (dd, 1H,
J1a,1b¼4.9 Hz, H-1b), 3.77–3.86 (m, 4H, H-2, 3, 30, 50),
3.90 (dd, 1H, H-1a), 3.93 (d, 1H, J5a,5b¼3.1 Hz, H-5b),
0
0
1
[a]2D2 +56.3 (c 1, CHCl3); H NMR: d 1.14 (d, 3H, H-60),
3.95–3.99 (m, 2H, H-4, 5a), 4.07 (dd,0 1H, J2 ,3 ¼1.7 Hz,
0
0
H-20), 5.07 (d, 1H, J1 ,2 ¼1.5 Hz, H-1 ) ppm; 13C NMR
(D2O): d 16.9 (C-60), 59.7 (C-5), 62.9 (C-1), 69.5 (C-2),
70.6 (C-30), 70.7 (C-20), 71.9 (C-3), 72.3 (C-40, 50), 78.9
(C-4), 100.5 (C-10) ppm; HR-FABMS [M+Na]+ calcd for
C11H22O9Na 321.1161, found 321.1171.
0
0
3.70–3.77 (m, 2H, H-1), 3.79–3.82 (m, 2H, H-5), 3.89–
3.91 (m, 1H, H-2), 3.99–4.01 (m, 1H, H-4), 4.31–4.34 (m,
2H, H-3, 50), 4.45–4.75 (m, 8H, 4ꢁCH2Ph), 5.30 (s, 1H,
H-10), 5.54–5.67 (m, 2H, H-20, 40), 5.73–5.87 (m, 1H, H-
30), 7.21–8.09 (m, 35H, aromatic) ppm; 13C NMR: d 17.9,

A. R. Parameswar et al. / Tetrahedron 63 (2007) 10083–10091
10089
6.7.5. Ethyl O-(3-O-acetyl-2-O-benzyl-4,6-O-benzyl-
idene-a-D-glucopyranosyl)-(1/3)-2,4-di-O-benzoyl-1-
thio-a-L-rhamnopyranoside (22). The title compound was
obtained by Method A from 2-thiazolinyl 3-O-acetyl-2-O-
benzyl-4,6-O-benzylidene-1-thio-b-D-glucopyranoside (8a)
and ethyl 2,4-di-O-benzoyl-1-thio-a-L-rhamnopyranoside
(10) in 72% yield. Analytical data: Rf¼0.48 (ethyl acetate–
hexanes, 3/7, v/v); [a]2D2 +81.9 (c 1, CHCl3); mp 74–76 ꢀC;
1H NMR: d 1.28 (t, 3H, CH2CH3), 1.32 (d, 3H, H-6), 1.78
(s, 3H, COCH3), 2.59–2.72 (m, 2H, CH2CH3), 3.24 (dd,
138.4, 138.8 (ꢁ2), 139.0 (ꢁ3), 166.3, 166.8, 169.8 ppm;
HR-FABMS [M+Na]+ calcd for C75H76O17Na 1271.4981,
found 1271.4978.
6.7.8. O-(a-D-Glucopyranosyl)-(1/3)-O-(a-L-rhamno-
pyranosyl)-(1/3)-D/L-ribitol (5). The title compound
was obtained from 23 in 80% yield as described for the syn-
thesis of compound 3. Analytical data: Rf¼0.52 (methanol–
dichloromethane–water, 9/9/2, v/v); [a]2D6 +37.1 (c 0.7,
1
H2O); H NMR (D2O): d 1.36 (d, 3H, H-60), 3.5300(dd, 1H,
0
0
0
00
0
0
0
00 00
1H, J4 ,5 ¼9.6 Hz, H-4 ), 3.28–3.37 (m, 2H, H-2 , 6b ), 3.65
J4 ,5 ¼9.2 Hz, H-4 ), 3.60–3.65 (m, 2H, H-4 , 2 ), 3.68–
3.74 (m, 2H, H-1b, 5b), 3.82–3.93 (m, 8H, H-1a, 3, 5a, 30,
50, 300, 6a00, 6b00), 3.98–4.05 (m, 3H, H-2, 4, 500), 4.25 (dd,
0
0
0
0
0
(dd, 1H, J4 ,5 ¼4.8 Hz, H-5 ), 3.84 (dd, 1H, J5 ,6a ¼4.8 Hz,
H-60), 4.22–4.37 (m, 4H, H-3, 5, CH2Ph), 4.93 (d, 1H,
0
0
0
0
0
0
0
0
0
0
J1 ,2 ¼3.6 Hz, H-1 ), 5.15–5.19 (m, 2H, H-3 , CHPh), 5.43
(d, 1H, J1,2¼1.4 Hz, H-1), 5.52–5.60 (m, 2H, H-2, 4),
7.00–8.05 (m, 20H, aromatic) ppm; 13C NMR: d 14.7,
15.6, 18.2, 21.4, 26.4, 30.3, 63.5, 68.1, 69.1, 70.9, 71.6,
73.0, 73.4, 73.9, 79.8, 82.9, 96.1, 101.7, 126.8 (ꢁ2), 128.2,
128.3 (ꢁ2), 128.4 (ꢁ2), 128.8 (ꢁ2), 129.3 (ꢁ4), 130.0
(ꢁ2), 130.3 (ꢁ2), 133.7, 133.9, 137.7, 138.3, 130.6 (ꢁ2),
166.1, 166.9, 169.8 ppm; HR-FABMS [M+H]+ calcd for
C44H47O12S 799.2788, found 799.2796.
1H, J2 ,3 ¼2.7 Hz, H-2 ), 5.07 (d, 1H, J1 ,2 ¼1.8 Hz, H-1 ),
5.15 (d, 1H, J1 ,2 ¼3.8 Hz, H-1 ) ppm; 13C NMR (D2O):
00
00 00
d 17.0 (C-60), 60.6 (C-50), 62.7 (C-1), 63.0 (C-5), 67.4 (C-
20), 69.7 (C-400), 69.8 (C-600), 70.5 (C-40), 71.1 (C-200), 71.8
(C-500), 72.1 (C-2, 4), 73.3 (C-300), 75.8 (C-30), 80.2 (C-3),
95.9 (C-100), 100.5 (C-10) ppm; HR-FABMS [M+Na]+ calcd
for C17H32O14Na 483.1690, found 483.1684.
6.7.9. O-(a-D-Glucopyranosyl)-(1/3)-O-(a-L-rhamno-
pyranosyl)-(1/4)-D-ribitol (6). The title compound was
obtained from 24 in 88% yield as described for the synthesis
of compound 3. Analytical data: Rf¼0.55 (methanol–
dichloromethane–water, 9/9/2, v/v); [a]2D5 +13.2 (c 1.0,
6.7.6. O-(3-O-Acetyl-2-O-benzyl-4,6-O-benzylidene-a-D-
glucopyranosyl)-(1/3)-O-(2,4-di-O-benzoyl-a-L-rham-
nopyranosyl)-(1/3)-1,2,4,5-tetra-O-benzyl-D/L-ribitol
(23). The title compound was obtained by Method B from 22
and 12 in 71% yield. Analytical data: Rf¼0.33 (ethyl acetate–
hexanes, 3/7, v/v); [a]2D2 +48.7 (c 1, CHCl3); 1H NMR: d 1.15
1
H2O); H NMR (D2O): d 1.35 (d, 3H, H-60), 3.51 (dd, 1H,
00
00
00 00
J4 ,5 ¼9.5 Hz, H-4 ), 3.60–3.64 (m, 2H, H-4, 2 ), 3.68
(dd, 1H, J1a,1b¼6.7 Hz, H-1b), 3.78–3.94 (m, 9H, H-1a, 2,
(d, 3H, H-60), 1.88 (s, 3H, COCH3), 3.32 (dd, 1H, J1a,1b
¼
3, 5b, 30, 50, 300, 6a00, 6b00), 3.96–4.05 (m, 3H, H-4, 5a, 500),
9.6 Hz, H-1a), 3.39–3.45 (m, 2H, H-20, 5a), 3.68–3.79 (m,
4H, H-1b, 2, 4, 5b), 3.85–3.90 (m, 2H, H-30, H-40), 3.96–
4.02 (m, 1H, H-3), 4.20–4.34 (m, 4H, H-50, 500, 6a00, 6b00),
4.28 (dd, 1H, J2 ,3 ¼2.4 Hz, H-2 ), 5.12 (d, 1H, J1 ,2 ¼1.6 Hz,
0
0
0
0
0
H-10), 5.14 (d, 1H, J1 ,2 ¼3.8 Hz, H-1 ) ppm; 13C NMR
00
00 00
(D2O): d 17.1 (C-60), 59.8 (C-5), 60.6 (C-60), 62.9 (C-1),
67.4 (C-20), 69.7 (C-300, 50), 70.6 (C-400), 71.8 (C-200), 71.9
(C-40), 72.0 (C-3), 72.3 (C-500), 73.3 (C-2), 75.9
(C-30), 79.0 (C-4), 95.9 (C-100), 100.2 (C-10) ppm; HR-
FABMS [M+Na]+ calcd for C17H32O14Na 483.1690, found
483.1684.
0
0
4.46–4.68 (m, 8H, 4ꢁCH2Ph), 5.05 (d, 1H, J1 ,2 ¼3.5 Hz,
H-10), 5.17–5.26 (m, 3H, H-100, 300, CHPh), 5.55–5.58 (m,
2H, H-200, 400), 7.00–8.07 (m, 40H, aromatic) ppm; 13C
NMR: d 18.3, 21.5, 63.4, 68.1, 69.2, 69.5, 69.6, 70.8, 71.0,
72.7, 72.8 (ꢁ2), 72.9, 73.1, 73.8, 73.9, 77.3, 77.7, 78.2,
78.6, 79.9, 95.6, 98.4, 101.8, 127.0, 128.1, 128.2 (ꢁ4),
128.3 (ꢁ3), 128.5 (ꢁ5), 128.8 (ꢁ3), 128.9 (ꢁ4), 129.0
(ꢁ6), 129.1 (ꢁ3), 129.4, 130.2 (ꢁ2), 130.4 (ꢁ2), 130.7
(ꢁ2), 133.7, 133.9, 166.2, 166.9, 169.8 ppm; HR-FABMS
[M+Na]+ calcd for C75H76O17Na 1271.4981, found
1271.4978.
6.7.10. Ethyl O-(3-O-acetyl-2-O-benzyl-4,6-O-benzyl-
idene-a-D-glucopyranosyl)-(1/3)-2,4-di-O-benzyl-1-
thio-a-L-rhamnopyranoside (25). The title compound was
obtained by Method A from 8a and ethyl 2,4-di-O-benzyl-
1-thio-a-L-rhamnopyranoside (11) in 80% yield. Analytical
data for 25 were essentially the same as reported
previously.32
6.7.7. O-(3-O-Acetyl-2-O-benzyl-4,6-O-benzylidene-a-D-
glucopyranosyl)-(1/3)-O-(2,4-di-O-benzoyl-a-L-rham-
nopyranosyl)-(1/4)-1,2,3,5-tetra-O-benzyl-D-ribitol
(24). The title compound was obtained by Method B from 22
and 13 in 76% yield. Analytical data: Rf¼0.41 (ethyl acetate–
hexanes, 3/7, v/v); [a]2D2 +45.7 (c 1, CHCl3); 1H NMR: d 1.07
00 00
6.7.11. Ethyl O-(2-O-benzyl-4,6-O-benzylidene-a-D-glu-
copyranosyl)-(1/3)-2,4-di-O-benzyl-1-thio-a-L-rham-
nopyranoside (26). A solution of NaOMe in MeOH (1.0 M,
0.2 mL, 1.0 mmol) was added to a stirred suspension of 25
(160 mg, 0.35 mmol) in methanol (2.0 mL) and the reaction
mixture was stirred for 15 h at rt. The reaction mixture was
then neutralized with Dowex (H+), filtered, and concentrated
in vacuo to yield crude 26 as a white foam 99%. Analytical
data: Rf¼0.38 (ethyl acetate–hexanes, 3/7, v/v); [a]2D7 7.5 (c
1.0, CHCl3); 1H NMR: d 1.20 (t, 3H, CH2CH3), 1.29 (d, 3H,
H-6), 2.54 (q, 2H, CH2CH3), 3.44–3.52 (m, 2H, H-20, 50),
3.62–3.70 (m, 3H, H-3, 40, 6a0), 3.98–4.05 (m, 4H, H-2, 4,
(d, 3H, H-60), 1.72 (s, 3H, COCH3), 3.20 (dd, 1H, J3 ,4
¼
9.6 Hz, H-400), 3.26–3.34 (m, 2H, H-3, 200), 3.55–3.67 (m,
4H, H-5, 500, 6b00), 3.70–3.79 (m, 4H, H-1, 2, 6a00), 4.12–
4.17 (m, 1H, H-50), 4.25–4.29 (m, 1H, H-4), 4.30–4.36 (m,
0
0
0
0
0
1H, J1 ,2 ¼1.3 Hz, H-1 ), 5.47 (dd, 1H, J3 ,4 ¼10.9 Hz, H-
40), 5.62 (d, 1H, J2 ,3 ¼2.3 Hz, H-2 ), 6.80–8.02 (m, 40H, ar-
omatic) ppm; 13C NMR: d 18.4, 21.5, 63.3, 68.1, 69.2, 70.7
(ꢁ2), 70.9, 72.2, 72.6, 73.1, 73.3, 74.0, 74.1 (ꢁ2), 74.2,
76.4, 77.2, 79.1, 79.7, 79.9, 94.9, 97.4, 101.7, 126.9 (ꢁ3),
128.1, 128.2 (ꢁ2), 128.3 (ꢁ5), 128.4 (ꢁ3), 128.5 (ꢁ2),
128.6 (ꢁ4), 128.8 (ꢁ2), 129.0 (ꢁ8), 129.1 (ꢁ2), 129.3,
130.1, 130.2, 130.3 (ꢁ2), 130.7 (ꢁ2), 133.7, 133.9, 137.7,
0
0
0
5, 6b0), 4.06–4.21 (m, 2H, H-30, OH), 4.55–4.96 (m, 6H,
0
0
0
3ꢁCH2Ph), 5.12 (d, 1H, J1 ,2 ¼3.5 Hz, H-1 ), 5.26 (d, 1H,
J1,2¼1.8 Hz, H-1), 5.47 (s, 1H, CHPh), 7.20–7.37 (m,
20H, aromatic) ppm; 13C NMR: d 15.2, 18.0, 25.6, 30.0,

10090
A. R. Parameswar et al. / Tetrahedron 63 (2007) 10083–10091
62.9, 68.8, 69.1, 70.8, 72.7, 73.0, 79.3, 80.4, 81.6, 82.0, 95.2,
102.2, 126.7 (ꢁ2), 127.9 (ꢁ2), 128.0 (ꢁ2), 128.2, 128.3
(ꢁ2), 128.4 (ꢁ4), 128.5 (ꢁ2), 128.6 (ꢁ2), 128.7 (ꢁ2),
129.3, 137.4, 137.9, 138.2, 138.3 ppm; HR-FABMS
[M+Na]+ calcd for C42H48O9SNa 751.2917, found
751.2929.
6.7.14. O-(3,4,6-Tri-O-acetyl-2-O-benzyl-a-D-galactopyr-
anosyl)-(1/3)-O-(2-O-benzyl-4,6-O-benzylidene-a-D-
glucopyranosyl)-(1/3)-O-(2,4-di-O-benzyl-a-L-rham-
nopyranosyl)-(1/4)-1,2,3,5-tetra-O-benzyl-D-ribitol
(29). The title compound was obtained by Method B from 13
and 27 in 76% yield. Analytical data: Rf¼0.49 (ethyl ace-
tate–hexanes, 3/7, v/v); [a]2D7 +54.9 (c 1.0, CHCl3); 1H
NMR: d 1.25 (d, 3H, H-60), 1.84, 1.97, 1.99 (3 s, 3H,
3ꢁCOCH3), 3.55–3.60 (m, 2H, H-5), 3.63–3.77 (m, 10H,
H-1, 2, 3, 20, 40, 2000, 4000, 6a00, 6b000), 3.79–3.90 (m, 4H, H-4,
30, 50, 6b00), 3.96–3.99 (m, 2H, H-200, 500), 4.08–4.11 (m,
6.7.12. Ethyl O-(2-O-benzyl-3,4,6-tri-O-acetyl-a-D-galac-
topyranosyl)-(1/3)-O-(2-O-benzyl-4,6-O-benzylidene-
a-D-glucopyranosyl)-(1/3)-2,4-di-O-benzyl-1-thio-a-L-
rhamnopyranoside (27). The title compound was obtained
by Method A from benzoxazolyl 3,4,6-tri-O-acetyl-2-O-
benzyl-1-thio-b-D-galactopyranoside (7) and 26 in 76%
yield. Analytical data: Rf¼0.49 (ethyl acetate–hexanes, 3/7,
v/v); [a]2D6 +48.8 (c 1.0, CHCl3); 1H NMR: d 1.25 (t,
3H, CH2CH3), 1.32 (d, 3H, H-6), 1.84, 1.97, 2.00 (3 s, 9H,
1H, H-300), 4.20 (dd, 1H, J5 ,6a ¼2.7 Hz, J6a ,6b ¼9.2 Hz,
H-6a000), 4.23 (dd, 2H, CH2Ph), 4.29–4.32 (m, 1H, H-5000),
4.38–4.70 (m, 12H, 6ꢁCH2Ph), 5.08 (dd, 2H, CH2Ph),
000
000
000
000
5.26 (d, 1H, J1 ,2 ¼3.5 Hz, H-1000), 5.31 (d, 1H,
000 000
00
000
00 00
J1 ,2 ¼3.4 Hz, H-1 ), 5.33 (s, 2H, H-3 , CHPh), 5.56 (d,
0
0
0
3ꢁCOCH3), 2.56–2.66 (q, 2H, CH2CH3), 3.55 (dd, 1H,
1H, J1 ,2 ¼3.5 Hz, H-1 ), 7.14–7.43 (m, 45H, aromatic)
ppm; 13C NMR: d 14.6, 18.6 (ꢁ2), 21.1 (ꢁ2), 21.3 (ꢁ3),
23.2, 30.2 (ꢁ2), 32.4, 62.2, 62.6, 66.6, 69.2, 69.5, 70.4,
71.4, 72.6, 72.8, 72.9, 73.2, 73.8, 73.9, 74.2, 74.9, 76.1,
78.8, 79.8, 83.3, 96.8, 97.4, 102.5, 127.1 (ꢁ2), 127.6 (ꢁ3),
127.9 (ꢁ4), 128.0, 128.1 (ꢁ2), 128.2 (ꢁ2), 128.3 (ꢁ3),
128.4 (ꢁ2), 128.5, 128.6 (ꢁ2), 128.7 (ꢁ3), 128.77 (ꢁ2),
128.80 (ꢁ6), 128.83 (ꢁ3), 128.9 (ꢁ2), 129.0 (ꢁ2), 129.1
(ꢁ2), 129.7, 137.7, 138.3, 138.6 (ꢁ3), 138.7, 138.8, 138.9,
142.4, 142.7, 142.9, 170.4, 170.6, 170.9 ppm; HR-FABMS
[M+Na]+ calcd for C92H100O22Na 1579.6604, found
1579.6609.
00
00
00
00
00
J5 ,6a ¼6.3 Hz, J6a ,6b ¼11.1 Hz, H-6b ), 3.63–3.74 (m,
5H, H-2, 4, 20, 40, 200), 3.76–3.87 (m, 1H, H-6a00), 4.04–
4.10 (m, 4H, H-3, 5, 50, 6b0), 4.18 (dd, 1H, J5 ,6a ¼5.4 Hz,
0
0
0
0
0
J6a ,6b ¼10.3 Hz, H-6a ), 4.25 (d, 1H, CH2Ph), 4.39 (dd,
0
00
0
0
1H, J3 ,4 ¼9.4 Hz, H-3 ), 4.47–4.52 (m, 2H, H-5 , 1/2
CH2Ph), 4.61–4.74 (m, 4H, 2ꢁCH2Ph), 4.96 (d, 1H, 1/2
00
00 00
CH2Ph), 5.21 (d, 1H, J4 ,5 ¼2.3 Hz, H-4 ), 5.25 (d, 1H,
0
00
0
0
J1 ,2 ¼3.4 Hz, H-1 ), 5.30–5.3800(m, 3H, H-1, 3 , CHPh),
00 00
5.57 (d, 1H, J1 ,2 ¼3.6 Hz, H-1 ), 6.95–7.43 (m, 25H, aro-
matic) ppm; 13C NMR: d 15.3, 18.2, 20.8, 20.9 (ꢁ2), 21.0
(ꢁ2), 25.7, 31.2, 61.7, 62.7, 66.2 (ꢁ2), 68.8 (ꢁ2), 69.2,
71.2, 72.5 (ꢁ2), 72.9 (ꢁ2), 75.7, 75.9, 80.3, 81.6, 82.9,
94.2, 96.6, 102.3, 126.7 (ꢁ2), 126.8 (ꢁ3), 127.3, 127.7
(ꢁ3), 127.9, 128.0 (ꢁ4), 128.3 (ꢁ3), 128.7 (ꢁ5), 128.8
(ꢁ3), 129.5, 137.4, 137.8, 138.0, 138.2, 170.2, 170.3,
170.6 ppm; HR-FABMS [M+H]+ calcd for C61H70O17SNa
1129.4231, found 1129.4238.
6.7.15. O-(a-D-Galactopyranosyl)-(1/3)-O-(a-D-gluco-
pyranosyl)-(1/3)-O-(a-L-rhamnopyranosyl)-(1/3)-
D/L-ribitol (1). The title compound was obtained from 28 in
75% yield as described for the synthesis of compound 3. An-
alytical data: Rf¼0.33 (methanol–dichloromethane–water,
9/9/2, v/v); [a]D26 +78.2 (c 0.8, H2O); 1H NMR (D2O):
0
d 1.25 (d, 3H, H-60), 3.53 (dd, 1H, J4 ,5 ¼9.7 Hz, H-4 ),
0
0
6.7.13. O-(3,4,6-Tri-O-acetyl-2-O-benzyl-a-D-galactopyr-
anosyl)-(1/3)-O-(2-O-benzyl-4,6-O-benzylidene-a-D-
glucopyranosyl)-(1/3)-O-(2,4-di-O-benzyl-a-L-rham-
nopyranosyl)-(1/3)-1,2,4,5-tetra-O-benzyl-D/L-ribitol
(28). The title compound was obtained by Method B from 12
and 27 in 70% yield. Analytical data: Rf¼0.47 (ethyl ace-
tate–hexanes, 2/3, v/v); [a]2D5 +55.4 (c 1.0, CHCl3); 1H
NMR: d 1.27 (d, 3H, H-60), 1.82, 1.96, 1.98 (3 s, 3H,
3ꢁCOCH3), 3.52–3.57 (m, 2H, H-40, 5b), 3.60–3.65 (m,
5H, H-1a, 4, 400, 6a00, 6a000), 3.69–3.76 (m, 6H, H-2, 20, 2000,
4000, 6b00, 6b000), 3.79–3.86 (m, 3H, H-5a, 30, 50), 3.95 (dd,
1H, H-200), 3.99 (m, 1H, H-500), 4.05–4.13 (m, 4H, H-1b, 3,
300, 5000), 4.26 (d, 1H, 1/2 CH2Ph), 4.32–4.68 (m, 14H,
3.58–3.65 (m, 4H, H-200, 400, 5a, 6a00), 3.70 (dd, 2H,
000
000
000
000
J6a ,6b ¼11.2 Hz, H-6a , 6b ), 3.72–3.82 (m, 8H, H-1a,
1b, 2, 3, 5b, 30, 50, 2000), 3.84–3.90 (m, 3H, H-4, 300, 3000),
3.92–3.96 (m, 3H, H-4000, 500, 6b00), 4.15 (dd, 1H,
0
000
0
0
000 000
J2 ,3 ¼2.3 Hz, H-2 ), 4.19 (dd, 1H, J4 ,5 ¼6.3 Hz, H-5 ),
0
0
0
00 00
4.97 (d, 1H, J1 ,2 ¼1.7 Hz, H-1 ), 5.05 (d, 1H, J1 ,2 ¼6.0 Hz,
H-100), 5.33 (d, 1H, J1 ,2 ¼3.9 Hz, H-1 ) ppm; 13C NMR
000
000 000
(D2O): d 16.9, 60.3, 61.1, 62.5, 62.9, 67.1, 68.8, 69.3,
69.6, 69.7, 70.0, 70.3, 70.4, 70.9, 71.0, 71.7, 71.9, 75.5,
79.8, 80.1, 95.6, 99.5, 100.3 ppm; HR-FABMS [M+Na]+
calcd for C23H42O19Na 645.2218, found 645.2210.
7ꢁCH2Ph), 4.99 (d, 1H, 1/2 CH2Ph), 5.16 (d, 10H0 ,
6.7.16. O-(a-D-Galactopyranosyl)-(1/3)-O-(a-D-gluco-
pyranosyl)-(1/3)-O-(a-L-rhamnopyranosyl)-(1/4)-D-
ribitol (2). The title compound was obtained from 29 in 78%
yield as described for the synthesis of compound 3. Selected
analytical data: Rf¼0.33 (methanol–dichloromethane–
water, 9/9/2, v/v); [a]2D7 +70.7 (c 1.0, H2O); 1H NMR
000
000 000
00 00
J1 ,2 ¼2.1 Hz, H-1 ), 5.18 (d, 1H, J1 ,2 ¼3.4 Hz, H-1 ),
000
000 000
5.33 (dd, 1H, J3 ,4 ¼3.3 Hz, H-3 ), 5.38 (s, 1H, CHPh),
0
0
0
5.56 (d, 1H, J1 ,2 ¼3.4 Hz, H-1 ), 6.95–7.40 (m, 45H, aro-
matic) ppm; 13C NMR: d 18.5, 20.9, 21.2 (ꢁ2), 30.1, 62.0,
62.6, 66.4, 69.1, 69.3 (ꢁ2), 70.3, 70.5, 71.3, 72.6, 72.8,
73.0 (ꢁ2), 73.1 (ꢁ2), 73.7, 73.8, 74.6, 76.0, 78.3 (ꢁ3),
78.9, 79.9, 83.2, 93.1, 96.7, 98.8, 102.5, 126.9 (ꢁ2), 127.5
(ꢁ2), 127.8 (ꢁ2), 127.9 (ꢁ6), 128.0 (ꢁ2), 128.1 (ꢁ2),
128.3 (ꢁ2), 128.4 (ꢁ2), 128.5 (ꢁ3), 128.6 (ꢁ2), 128.7
(ꢁ5), 128.7 (ꢁ3), 128.8 (ꢁ2), 128.9 (ꢁ2), 129.7, 137.6
(ꢁ2), 138.2 (ꢁ2), 138.4 (ꢁ2), 138.5 (ꢁ2), 138.6 (ꢁ2),
138.7 (ꢁ2), 138.8 (ꢁ2), 138.9 (ꢁ2), 170.3, 170.5,
170.8 ppm; HR-FABMS [M+Na]+ calcd for C92H100O22Na
1579.6604, found 1579.6609.
(D2O): d 1.26 (d, 3H, H-60), 3.53 (dd, 1H, J4 ,5 ¼9.7 Hz,
H-40), 3.58–3.64 (m, 4H, H-1b, 5b, 200, 6a00), 3.66–3.75 (m,
8H, H-1a, 2, 50, 400, 6b00, 2000, 6a000, 6b000), 3.78–3.81 (m, 2H,
H-3, 3000), 3.83–3.89 (m, 4H, H-4, 5a, 30, 300), 3.94–3.96
(m, 2H, H-20, 5000), 5.02 (br s, 1H, H-10), 5.06 (d, 1H,
0
0
00
000
00 00
000 000
J1 ,2 ¼3.7 Hz, H-1 ), 5.34 (d, 1H, J1 ,2 ¼3.8 Hz, H-1 )
ppm; 13C NMR data for 2 were essentially the same as re-
ported previously;42 HR-FABMS [M+Na]+ calcd for
C23H42O19Na 645.2218, found 645.2210.

A. R. Parameswar et al. / Tetrahedron 63 (2007) 10083–10091
10091
18. Slaghek, T. M.; van Oijen, A. H.; Maas, A. A. M.; Kamerling,
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Acknowledgements
The authors thank ACS PRF (42397-G1) and NSF (CA-
REER CHE-0547566) for financial support of this research;
NSF for grants to purchase the NMR spectrometer (CHE-
9974801) and the mass spectrometer (CHE-9708640) used
in this work; Dr. R. S. Luo for assistance with 500 MHz
2D NMR experiments; and Dr. R. E. K. Winter and Mr. J.
Kramer for HRMS determinations.
20. Thijssen, M. J. L.; van Rijswijk, M. N.; Kamerling, J. P.;
Vliegenthart, J. F. G. Carbohydr. Res. 1998, 306, 93–109.
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Supplementary data
General experimental techniques and spectra for all new
compounds. This material is available free of charge via
the Internet. Supplementary data associated with this article
can be found in the online version, at doi:10.1016/
j.tet.2007.07.036.
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