A highly α-stereoselective synthesis of oligosaccharide fragments of the VI antigen from salmonella typhi and their antigenic activities

Article abstract of DOI:10.1002/chem.201102615

In this paper, a convenient approach to the synthesis of the repeating α-(1→4)-linked N-acetyl galactosaminuronic acid units from the capsular polysaccharide of Salmonella typhi is reported. The exclusively α-stereoselective glycosylation reactions were a

Full text of DOI:10.1002/chem.201102615

DOI: 10.1002/chem.201102615
A Highly a-Stereoselective Synthesis of Oligosaccharide Fragments of the
Vi Antigen from Salmonella typhi and Their Antigenic Activities
Lin Yang,[a] Jingjing Zhu,[a, b] Xiu-Jing Zheng,[a] Guihua Tai,[b] and Xin-Shan Ye*[a]
Abstract: In this paper, a convenient
approach to the synthesis of the repeat-
ing a-(1!4)-linked N-acetyl galactosa-
minuronic acid units from the capsular
polysaccharide of Salmonella typhi is
reported. The exclusively a-stereose-
lective glycosylation reactions were
achieved by using oxazolidinone-pro-
tected glycosides as building blocks
based on a pre-activation protocol. Di-,
tri-, and tetrasaccharides were pre-
pared by this short and efficient ap-
proach in high yields. The enzyme-
linked immunosorbent assay experi-
ments show that our synthetic tri- and
tetrasaccharide had much higher anti-
genic activities than previously report-
ed ones in the inhibition of antibody
binding by the native polysaccharide.
The results demonstrate that the anti-
genic activities of saccharides can be
strengthened greatly by increasing the
number of acetyl groups present.
Keywords: antigens · glycosylation ·
oxazolidinones · salmonella typhi ·
stereoselectivity · Vi antigens
Introduction
Typhoid fever is caused by Salmonella typhi and remains an
important health threat in many parts of the world, with an
estimated 16 million cases and 600000 deaths occurring an-
nually.[1] Although the incidence is negligible in many devel-
oped countries, those who travel to epidemic areas, live in
the rural parts of the country, and military personnel are fre-
quently subject to the illness. The emergence of multi-drug
resistant Salmonella typhi strains has increased the impact
of this disease.[2]
The Vi antigen is a capsular polysaccharide found mainly
in Salmonella typhi and Salmonella paratyphi C, two sero-
types of Salmonella that are responsible for severe infections
in humans.[3] It is a linear homopolymer of a-(1!4)-linked
N-acetyl galactosaminuronic acid, variably O-acetylated at
the C3 position (Figure 1).[4] This antigen increases the re-
sistance to post-phagocytic oxidative burst.[5] The antigen
disrupts the binding of the C3 complement factor to the sur-
face of Salmonella typhi and helps bacteria to reduce the
killing by the serum, the killing via the alternative pathway
of the complement, and opsonization as can be measured by
phagocytosis by the human polymorphonuclear leukocytes
(PMNs). It was also found that strains of Salmonella typhi
containing the Vi antigen are less susceptible to killing by
Figure 1. The repeating unit of the Salmonella typhi Vi antigen.
H2O2 than strains without this antigen.[6] As an immunogen-
ic capsular polysaccharide, the purified Vi polysaccharide
(Vi PS) of Salmonella typhi has become an effective vaccine
to combat typhoid disease.[7]
The industrial production of the typhoid Vi capsular poly-
saccharide vaccine comprises extrication and purification
from cultures of the Salmonella typhi strain.[7c] The process
is controlled by strict checks at various stages and the prod-
uct is a mixture of polysaccharides with inhomogeneous
sizes and structures. This can cause a quality control prob-
lem. Sinaꢀ and co-workers have chemically synthesized the
corresponding di-, tri-, tetra-, and hexa-saccharides and
shown that the tetra- and hexa-saccharides were able to in-
hibit antibody binding by native polysaccharides.[8] However,
the whole synthetic route was long and complicated. Herein,
we report a convenient and highly a-selective approach to
the synthesis of the repeating a-(1!4)-linked N-acetyl gal-
actosaminuronic acid units. The antigenic activities of these
synthetic oligosaccharide fragments are also investigated.
[a] L. Yang, J. Zhu, Dr. X.-J. Zheng, Prof. X.-S. Ye
State Key Laboratory of Natural a0nd Biomimetic Drugs
School of Pharmaceutical Sciences, Peking University
Xue Yuan Road 38, Beijing 100191 (China)
E-mail: xinshan@bjmu.edu.cn
Results and Discussion
[b] J. Zhu, Prof. G. Tai
Synthesis: Since oxazolidinone-protected glucosamine as an
a-selective glycosyl donor was first described by the Kerns
group,[9] subsequent investigations have been focused on its
N-acetyl analogues, confirming that the ring-fused oxazolidi-
School of Life Sciences, Northeast Normal University
Changchun 130024 (China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201102615.
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FULL PAPER
none moiety is an effective nonparticipating group for the
stereoselective synthesis of a-linked 2-amino-2-deoxy-d-hex-
opyranosides.[10] This protecting group has also been intro-
duced onto glycosyl acceptors to enhance the reactivity of
the 4-hydroxy group during glycosylations[11] because the
tied-back nature of the oxazolidinone can reduce the hin-
drance around the nucleophilic oxygen.[12] Moreover, the N-
acetyloxazolidinone functionality also decreases the tenden-
cy for amide glycosylation[13] and removes the possibility of
problematic hydrogen-bonding networks.[14] Recently, our
group has also achieved advances in the stereochemistry of
glycosylations by virtue of oxazolidinone protecting-group
strategies,[15] and the application of this protecting group to
the chemical synthesis of oligosaccharide fragments has
been realized.[16] N-Acetyloxazolidinone is not only able to
serve as a stereoselective directing group and an orthogonal
protecting group, but can also be easily removed by chemo-
selective deprotection.[11,17] Consequently, we decided to in-
troduce it into the galactosamine moiety to construct the oli-
gosaccharides of the Vi antigen.
Both the oxazolidinone-containing glycosyl donor and the
acceptor can be readily prepared from commercially avail-
able d-galactosamine hydrochloride in high yield on a large
scale (Scheme 1). Compound 1 was prepared according to a
previously published approach,[16] and then underwent silyla-
tion with tert-butyldimethylsilyl chloride to afford the thio-
glycoside 2 as the donor in quantitative yield. In the synthe-
sis of the acceptor the amino functionality of d-galactosa-
mine was protected with the benzyloxycarbonyl group to
give compound 3. This was followed by glycosylation with
methanol to produce methyl glycoside 4. The two hydroxyl
groups in 4 were protected with benzylidene to afford com-
pound 5 smoothly. 2,3-Oxazolidinone-protected compound 6
was formed after treatment of 5 with sodium hydride fol-
lowed by acetylation. The reductive cleavage of the benzyli-
dene acetal in 6 by using Et3SiH/TfOH[18] provided acceptor
7 with a free hydroxyl group at the 4 position.
As an alternative mode of glycosylation, the “pre-activa-
tion” protocol[19] has triggered considerable interest, mean-
ing that a glycosyl donor is completely activated and con-
sumed (by TLC detection) prior to the addition of a glycosyl
acceptor. This protocol has been successfully applied to oli-
gosaccharide assembly. Under the pre-activation conditions,
the coupling reaction of donor 2 with acceptor 7 was per-
formed first. After trying different promoter systems, the
best result was obtained by using a combination of diphenyl
sulfoxide (Ph2SO) and triflic anhydride (Tf2O),[20] along with
the hindered base TTBP.[21] By using this procedure, disac-
charide 8 was produced exclusively as the a-anomer in 72%
isolated yield (Scheme 2). After desilylation of 8, the new
acceptor 9 was produced smoothly. Repeating the glycosyla-
tion step with the same donor 2 and the synthetic method
based on the pre-activation protocol, trisaccharide 10 was
obtained as the a-only product in 61% yield. The silyl
group in 10 was then removed to give trisaccharide acceptor
11. In the same way, the coupling reaction of donor 2 with
acceptor 11 successfully provided tetrasaccharide 12 as the
a-only product in 53% isolated yield. It is noteworthy that a
small amount of the acceptors remained unreacted during
the glycosylation reactions and these materials were recy-
cled. The coupling yield of each a product was quantitative
based on the recovery of the glycosyl acceptor. As the reac-
tivity of the 4-OH group de-
creased, that is, as the acceptor
became larger, the amount of
unreacted acceptor increased,
leading to the lower yields of
the a-only products.
As we have developed an ef-
fective method to increase the
length of the repeating a-(1!
4)-linked
N-acetylgalactosa-
mine units, our attention was
then focused on the deprotec-
tion of these oligosaccharides
to form the final products as
repeating a-(1!4)-1inked N-
acetyl
galactosaminuronic
acids. As shown in Scheme 3,
disaccharide 8 was first hydro-
lyzed by using water to remove
the oxazolidinone group. It
was found that the cleavage of
the silyl ether in 8 also oc-
curred during the hydrolysis
process. Subsequent acetyla-
tion afforded compound 13,
Scheme 1. The synthesis of the monosaccharide building blocks. Reagents and conditions: i) tert-butyldimethyl-
silyl chloride (TBDMSCl), imidazole, DMF, 708C, 48 h, quantitative; ii) benzyloxycarbonyl chloride (CbzCl),
NaHCO3, H2O, 0 8C, 17 h, 85%; iii) HCl, MeOH, reflux, overnight, 80%; iv) PhCHACHTUNTRGNE(NUG OMe)2, camphorsulfonic
acid (CSA), CH3CN, RT, 10 min, quantitative; v) NaH, DMF, 08C to RT, 30 min; vi) Ac2O, pyridine, 4-dime-
thylaminopyridine (DMAP), 1 h, 75% for two steps; vii) Et3SiH, trifluoromethanesulfonic acid (TfOH),
CH2Cl2, ꢀ728C, 1 h, 73 %.
which was subjected to
a
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14519

Salmonella typhi Antigens
Vi PS itself as an inhibitor
provided a standard curve im-
plying that it provides inhibi-
tion from 0.05 to 10 mgmLꢀ1
(Figure 2), with an IC50 value
around 1 mgmLꢀ1. The inhibi-
tion by tetrasaccharide 18
gradually
0.1 mgmLꢀ1 and grew sharply
from 10 to
500 mgmLꢀ1
increased
from
(Figure 2). Its IC50 value was
around 100 mgmLꢀ1, nearly 100
times that of Vi PS. The best
inhibition it provided was
around 77%. The inhibition
curve produced for trisacchar-
ide 16 fluctuated at low con-
centrations and increased grad-
ually
from
50 mgmLꢀ1
(Figure 2). The highest inhibi-
tion was around 41% at
500 mgmLꢀ1, which is below
the IC50 value for this com-
pound. The inhibition by disac-
charide 14 was low and
changed little when the con-
centration was increased, indi-
cating that disaccharide 14 had
no distinct competitive inhibi-
tion activity, although its activi-
ty may be increased at concen-
trations
higher
than
(Figure 2,
500 mgmLꢀ1
Table 1).
In the work of Sinaꢀ and co-
workers,[8] a similar Vi PS stan-
dard curve was provided. How-
ever, the disaccharide and tri-
saccharide they synthesized
Scheme 2. The Synthesis of the di-, tri-, and tetrasaccharides. Reagents and conditions: i) Ph2SO, Tf2O, 2,4,6-
tri-tert-butylpyrimidine (TTBP), CH2Cl2, ꢀ728C to RT, ꢁ3 h; ii) tetra-n-butylammonium fluoride (TBAF)/
THF, RT, 10 min.
tandem hydrogenolysis and oxidation operation to afford
uronic acid 14 in good isolated yield. Following this conven-
ient and efficient deprotection and oxidation procedure, tri-
saccharide 10 and tetrasaccharide 12 were converted into
the corresponding uronic acids 16 and 18 in high yields
(Scheme 3).
showed no immunogenic activity in the range 0 to
500 mgmLꢀ1. Inhibition by their tetrasaccharide was detected
from 100 mgmLꢀ1 but had not reached 30% at 500 mgmLꢀ1.
The inhibition by their hexasaccharide reached nearly 90%
at 500 mgmLꢀ1, with the IC50 value being nearly 100–200
times that of Vi PS. In our case, the only change was in the
terminal protecting group of the “donor” end of the polysac-
charide, which was an acetyl group instead of a methyl, but
the competitive inhibitory ability of our tetrasaccharide 18
was much higher than that of their tetrasaccharide and was
similar to that of their hexasaccharide. Moreover, the anti-
genic activity of our synthetic trisaccharide 16 was signifi-
cant and much higher than that of their tetrasaccharide.
Studies into the immunochemical properties of the Vi anti-
gen have shown the presence of at least two antigenic deter-
minants. One of them is the O-acetyl moiety at C3, which
plays a dominant role. The other antigenic determinant in-
volves both carboxyl and N-acetyl groups.[22] It may be infer-
Antigenic assay: To explore the antigenic activity of these
synthetic saccharide moieties of the Vi antigen (compounds
14, 16, and 18), a test of the inhibition of antibody binding
by the native polysaccharide was performed by use of the
enzyme-linked immunosorbent assay (ELISA). First, 96-well
plates were coated with the Vi PS. Then, serial concentra-
tions of Vi PS, 14, 16, and 18 were separately mixed with
anti-Vi serum before addition to the coated plates. An anti-
rabbit IgG antibody labeled with horseradish peroxidase
was employed as a secondary antibody for colorimetric de-
tection (OD, optical density).
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X.-S. Ye et al.
FULL PAPER
Scheme 3. The deprotection and oxidation of the di-, tri-, and tetrasaccharides. Reagents and conditions: i) NaOH (aqueous)/1,4-dioxane (1:1), 408C,
ꢁ2–5 h; ii) Ac2O, DMAP, pyridine, 08C to RT, ꢁ2–10 h; iii) H2, Pd/C, THF/AcOH/H2O (4:2:1), ꢁ2–5 h; iv) NaIO4, RuCl3·xH2O, CCl4/CH3CN/H2O
(2:2:3), overnight.
red from our results that the antigenic activity of short oli-
gosaccharides of the Vi antigen could be strengthened great-
ly by increasing the number of acetyl groups. This could
even remedy the detrimental effects of shorter sugar chains.
that the O-acetyl moiety plays a dominant role in antigenic
determinants. It was found that the antigenic activity of
short oligosaccharides could be strengthened significantly by
increasing the number of acetyl groups. Further extension of
this protocol and evaluation of the bioactivity are now un-
derway.
Conclusion
We have developed a short and efficient approach to con-
structing fragments of the repeating a-(1!4)-1inked N-
acetyl galactosaminuronic acid of the Salmonella typhi Vi
antigen in high yields. The use of the N-acetyloxazolidinone-
protected glycosides based on a pre-activation protocol was
effective in providing exclusively a-stereoselective glycosyla-
tion and greatly reduced the number of steps in the func-
tional group transformation. Examination of the competitive
inhibition by use of the ELISA showed that the synthetic
tri- and tetrasaccharides (16 and 18) had greatly improved
antigenic activities in comparison with previous literature
reports. Our data seems to be complementary to the finding
Experimental Section
General: All chemicals purchased were reagent grade and were used
without further purification unless otherwise stated. Dichloromethane
(CH2Cl2), pyridine, and acetonitrile (CH3CN) were distilled over calcium
hydride (CaH2). Methanol was distilled from magnesium. DMF was
stirred with CaH2 and distilled under reduced pressure. All glycosylation
reactions were carried out under anhydrous conditions with freshly dis-
tilled solvents, unless otherwise stated. Reactions were monitored by ana-
lytical thin-layer chromatography on silica gel 60 F254 precoated on alumi-
num plates (E. Merck). Spots were detected under UV (254 nm) light
and/or by staining with acidic ceric ammonium molybdate. Solvents were
evaporated under reduced pressure by use of a below 408C bath. Organic
solutions of crude products were dried over anhydrous Na2SO4. Column
Chem. Eur. J. 2011, 17, 14518 – 14526
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14521

Salmonella typhi Antigens
171.51, 152.95, 138.25, 137.77, 133.17, 129.84, 128.70, 128.37, 127.73,
127.65, 87.44, 76.90, 73.39, 71.49, 68.48, 66.54, 55.12, 25.78, 23.94, 21.10,
18.18, ꢀ4.38, ꢀ5.13 ppm; MS (ESI): m/z: 558 [M+H]+, 575 [M+NH4]+,
580 [M+Na]+, 596 [M+K]+; elemental analysis calcd (%) for
C29H39NO6SSi: C 62.45, H 7.05, N 2.51; found: C 62.34, H 7.15, N 2.38.
Methyl 2-benzyloxycarbonylamino-4,6-O-benzylidene-2-deoxy-a-d-galac-
topyranoside (5): Benzaldehyde dimethyl acetal (1.03 g, 1.02 mL,
6.78 mmol) was added dropwise to a stirred solution of compound 4[23]
(1.48 g, 4.52 mmol) and camphorsulfonic acid (105 mg, 0.45 mmol) in dry
CH3CN (15 mL) at room temperature. The pH value was about 2–3. The
solution was then stirred for 10 min, at which time TLC showed the com-
plete disappearance of 4. The reaction mixture was quenched with Et3N
to give a pH around 7 and then concentrated in vacuo. The crude product
was concentrated and the residue was purified by column chromatogra-
phy on silica gel (hexane/EtOAc, 1:2) to give 5 as a white amorphous
solid (1.87 g, quantitative). Rf =0.4 (hexane/EtOAc, 1:2); [a]2D4 = +98.3
(c=2.4 in CHCl3); 1H NMR (CDCl3, 400 MHz): d=7.51 (d, 2H, J=
4.8 Hz; Ar), 7.38–7.31 (m, 8H; Ar), 5.58 (s, 1H; PhCH), 5.13 (d, 1H, J=
12.0 Hz; PhCH2), 5.08 (d, 1H, J=12.0 Hz; PhCH2), 5.06 (d, 1H, J=
8.8 Hz; NH), 4.86 (d, 1H,
12.4 Hz; H6a), 4.23 (d, 1H, J4,3 =3.2 Hz; H4), 4.21–4.16 (m, 1H; H2),
4.08 (dd, 1H, J=1.2, 12.4 Hz; H6b), 3.82 (td, 1H, J3,2 =J3,OH =11.2, J3,4
3.2 Hz; H3), 3.68 (s, 1H; H5), 3.39 (s, 3H; CH3), 2.51 ppm (d, 1H, J=
11.2 Hz; 3OH); 13C NMR (CDCl3, 100 MHz): d=156.88, 137.47, 136.26,
129.16, 128.53, 128.22, 126.30, 101.26, 99.70, 75.48, 69.32, 69.12, 67.06,
62.82, 55.52, 52.18 ppm; HRMS (ESI): m/z calcd for C22H25NO7Na:
438.1523 [M+Na]+; found: 438.1532.
J1,2 =3.2 Hz; H1), 4.29 (dd, 1H, J=0.8,
Figure 2. The results of the ELISA for the competitive inhibition of
Vi PS and the synthetic oligosaccharides. The 96-well plates were coated
with Vi PS (0.5 mgmLꢀ1). Anti-Vi serum (1:250 dilution) was first mixed
with an equivalent volume of saccharides 14, 16, and 18 (0.05–
500 mgmLꢀ1) before being applied to coated plates. The data are reported
as the mean ꢂSD of measurements performed in triplicate.
=
Methyl 2-acetamido-4,6-O-benzylidene-2,3-N,O-carbonyl-2-deoxy-a-d-
galactopyranoside (6): Compound 5 (4.0 g, 9.63 mmol) was dissolved in
dry DMF (100 mL) and cooled to 08C under a nitrogen atmosphere.
NaH (0.28 g, 11.6 mmol) was added carefully to the solution. Once the
bubbles had vanished, the reaction was gradually warmed to room tem-
perature and stirred for a further 30 min. After the TLC showed the
complete disappearance of 5, the mixture was dropped slowly into a
large amount of iced water and then extracted with EtOAc. The com-
bined organic layers were dried over Na2SO4 and concentrated in vacuo.
After addition of DMAP (58.8 mg, 0.48 mmol), the mixture was dis-
solved in pyridine (20 mL). The solution was cooled to 08C and acetic
anhydride (9.8 g, 9.05 mL, 96.1 mmol) was added dropwise. The result-
ing mixture was gradually warmed to room temperature and stirred for
a further 1 h. The mixture was concentrated, and the residue purified by
column chromatography on silica gel (hexane/EtOAc, 2:1) to give 6 as a
white amorphous solid (2.52 g, 75% for two steps). Rf =0.4 (hexane/
EtOAc, 1:1); [a]2D4 = +91.4 (c=2.8 in CHCl3); 1H NMR (CDCl3,
400 MHz): d=7.52–7.49 (m, 2H; Ar), 7.39–7.36 (m, 3H; Ar), 5.70 (d,
Table 1. The competitive percentage inhibition for the ELISA.
Concentration Vi PS
[mgmLꢀ1
Disaccharide Trisaccharide Tetrasaccharide
G
]
14
16
18
0.05
0.1
0.5
1
10
50
7.53ꢂ5.46
19.39ꢂ4.20 ꢀ2.02ꢂ7.76
39.06ꢂ2.44 ꢀ0.47ꢂ15.45 14.87ꢂ0.70 16.06ꢂ2.75
–
–
–
8.05ꢂ3.68 13.27ꢂ0.62
51.39ꢂ11.76 7.28ꢂ2.30
9.81ꢂ3.41 19.85ꢂ7.71
92.06ꢂ6.38
5.87ꢂ9.75 11.01ꢂ3.95 22.06ꢂ14.16
9.85ꢂ4.36 16.01ꢂ2.16 32.27ꢂ10.92
4.55ꢂ3.94 20.67ꢂ4.31 47.61ꢂ4.93
15.46ꢂ4.78 40.95ꢂ9.59 77.00ꢂ5.84
–
–
–
100
500
chromatography was performed on silica gel (200–300 mesh). 1H NMR
spectra were recorded on a Varian INOVA-500 or an Advance DRX
Bruker-400 spectrometer at 258C. Chemical shifts (in ppm) were refer-
enced to tetramethylsilane (d=0 ppm) in deuterated chloroform.
13C NMR spectra were obtained by using the same NMR spectrometers
and were calibrated with CDCl3 (d=77.00 ppm). Mass spectra were re-
corded by using a PE SCLEX QSTAR spectrometer. Elemental analysis
data were recorded on a Vario EL-III elemental analyzer.
1H, J1,2 =2.8 Hz; H1), 5.62 (s, 1H; PhCH), 4.72 (dd, 1H, J3,4 =2.4, J3,2
=
12.4 Hz; H3), 4.60 (s, 1H; H4), 4,51 (dd, 1H, J2,1 =2.8, J2,3 =12.4 Hz; H2),
4.35 (dd, 1H, J=0.8, 12.8 Hz; H6a), 4.23 (dd, 1H, J=1.6, 12.8 Hz; H6b),
4.12 (s, 1H; H5), 3.66 (s, 3H; CH3), 2.49 ppm (s, 3H; CH3); 13C NMR
(CDCl3, 100 MHz): d=171.41, 152.97, 136.97, 129.28, 128.26, 126.18,
100.36, 98.31, 72.99, 71.77, 69.89, 63.16, 56.15, 55.17, 23.85 ppm; MS
(ESI): m/z: 350 [M+H]+, 367 [M+NH4]+, 372 [M+Na]+, 388 [M+K]+;
elemental analysis calcd (%) for C17H19NO7: C 58.45, H 5.48, N 4.01;
found: C 58.19, H 5.48, N 3.94.
para-Tolyl 2-acetamido-4-O-tert-butyldimethylsilyl-6-O-benzyl-2,3-N,O-
carbonyl-2-deoxy-1-thio-a-d-galactopyranoside (2): A mixture of com-
pound 1[16] (1.5 g, 3.39 mmol), tert-butyldimethylsilyl chloride (4.09 g,
27.1 mmol), and imidazole (0.69 g, 10.2 mmol) in dry DMF (8.2 mL) was
heated at 708C for 48 h. After the TLC showed the complete disappear-
ance of 1, the reaction mixture was extracted with EtOAc (90 mL), and
the organic layer was washed with saturated aqueous NH4Cl (30 mLꢂ2)
and water (30 mL). The combined organic layers were dried over Na2SO4
and concentrated in vacuo. The crude product was purified by column
chromatography on silica gel (hexane/EtOAc, 15:1) to give 2 as a color-
less viscous oil (1.89 g, quantitative). Rf =0.8 (hexane/EtOAc, 3:1);
[a]2D4 = +177.0 (c=2.9 in CHCl3); 1H NMR (CDCl3, 400 MHz): d=7.37–
7.29 (m, 7H; Ar), 7.05 (d, 2H, J=8.0 Hz; Ar), 6.10 (d, 1H, J1,2 =4.4 Hz;
H1), 4.62 (dd, 1H, J2,1 =4.4, J2,3 =12.4 Hz; H2), 4.55 (d, 1H, J=11.6 Hz;
PhCH2), 4.50 (d, 1H, J=11.6 Hz; PhCH2), 4.42–4.38 (m, 3H; H3, H4,
H5), 3.70 (dd, 1H, J=6.8, 9.6 Hz; H6a), 3.58 (dd, 1H, J=6.0, 9.2 Hz;
H6b), 2.54 (s, 3H; CH3), 2.30 (s, 3H; CH3), 0.90 (s, 9H; tBu), 0.11 (s,
3H; CH3), 0.10 ppm (s, 3H; CH3); 13C NMR (CDCl3, 100 MHz): d=
Methyl 2-acetamido-6-O-benzyl-2,3-N,O-carbonyl-2-deoxy-a-d-galacto-
pyranoside (7): Et3SiH (205 mg, 281 mL, 1.76 mmol) and TfOH (177 mg,
104 mL, 1.18 mmol) were added to
a stirred mixture of 6 (206 mg,
0.59 mmol) and activated 4 ꢃ molecular sieves (830 mg, powder) in
CH2Cl2 (8.3 mL) at ꢀ728C under a nitrogen atmosphere. After being
stirred for 1 h at ꢀ728C, Et3N (1 mL) and MeOH (1 mL) were added
successively. The mixture was then filtered and the filtrate was concen-
trated. The residue was purified by column chromatography on silica gel
(hexane/EtOAc, 2.5:1) to give 7 as a colorless viscous oil (151 mg, 73%).
Rf =0.5 (hexane/EtOAc, 1:1); [a]2D4 = +98.0 (c=2.5 in CHCl3); 1H NMR
(CDCl3, 400 MHz): d=7.39–7.30 (m, 5H; Ar), 5.60 (d, 1H, J1,2 =2.4 Hz;
H1), 4.64–4.56 (m, 3H; PhCH2 ꢂ2, H3), 4.47 (s, 1H; H4), 4.20 (dd, 1H,
J
2,1 =2.4, J2,3 =12.4 Hz; H2), 3.85 (t, 1H, J=4.4 Hz; H5), 3.80–3.77 (m,
2H; H6a, H6b), 3.42 (s, 3H; CH3), 3.28 (d, 1H, J=2.0 Hz; 4-OH),
14522
www.chemeurj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14518 – 14526

X.-S. Ye et al.
FULL PAPER
2.49 ppm (s, 3H; CH3); 13C NMR (CDCl3, 100 MHz): d=171.56, 153.19,
137.21, 128.47, 127.94, 127.70, 97.69, 74.92, 73.75, 69.67, 69.50, 66.49,
55.91, 54.83, 23.79 ppm; HRMS (ESI): m/z calcd for C17H22NO7: 352.1391
[M+H]+; found: 352.1395.
concentrated. The residue was purified by column chromatography on
silica gel (hexane/EtOAc, 4:1) to give 10 as a colorless foam (29 mg,
61%). Rf =0.5 (hexane/EtOAc, 2:1); [a]2D4 = +106.7 (c=1.2 in CHCl3);
1H NMR (CDCl3, 400 MHz): d=7.37–7.26 (m, 15H; Ar), 5.82 (d, 2H, J=
2.8 Hz; H1’’, H1’), 5.54 (d, 1H, J1,2 =2.8 Hz; H1), 4.70 (d, 1H, J=
11.6 Hz; PhCH2), 4.67–4.62 (m, 3H; PhCH2, H3’’, H3’), 4.57–4.50 (m,
6H; PhCH2 ꢂ4, H3, H4’’), 4.47 (s, 1H; H4’), 4.38 (s, 1H; H4), 4.35 (dd,
Methyl (2-acetamido-4-O-tert-butyldimethylsilyl-6-O-benzyl-2,3-N,O-car-
bonyl-2-deoxy-a-d-galactopyranosyl)-(1!4)-2-acetamido-6-O-benzyl-2,3-
N,O-carbonyl-2-deoxy-a-d-galactopyranoside (8): Tf2O (14.3 mg, 8.4 mL,
0.051 mmol) was added to a stirred mixture of 2 (24.8 mg, 0.044 mmol),
Ph2SO (9.6 mg, 0.048 mmol), TTBP (22.0 mg, 0.88 mmol), and activated
4 ꢃ molecular sieves (500 mg, powder) in CH2Cl2 (5 mL) at ꢀ728C under
a nitrogen atmosphere. The reaction mixture was stirred for 5 min and,
after the complete disappearance of 2 as detected by TLC, a solution of
acceptor 7 (10.4 mg, 0.030 mmol) in CH2Cl2 (1.0 mL) was added dropwise
to the mixture. The mixture was slowly warmed to room temperature,
stirred for a further 2 h and quenched with Et3N (0.1 mL). The precipi-
tate was filtered off and the filtrate was concentrated. The residue was
purified by column chromatography on silica gel (hexane/EtOAc, 5:1) to
give 8 as a colorless foam (16.7 mg, 72%). Rf =0.5 (hexane/EtOAc, 2:1);
[a]2D4 = +92.7 (c=3.7 in CHCl3); 1H NMR (CDCl3, 400 MHz): d=7.36–
1H,
J2’’,1’’ =2.8, J2’’,3’’ =12.4 Hz; H2’’), 4.25 (dd, 1H, J2’,1’ =2.8, J2’,3’ =
12.4 Hz; H2’), 4.18 (dd, 1H, J2,1 =2.8, J2,3 =12.4 Hz; H2), 4.15 (t, 1H, J=
6.8 Hz; H5’’), 4.06 (t, 1H, J=6.4 Hz; H5’), 3.91 (t, 1H, J=6.8 Hz; H5),
3.61–3.57 (m, 1H; H6a’’), 3.53–3.44 (m, 5H; H6b’’, H6a’, H6b’, H6a,
H6b), 3.41 (s, 3H; CH3), 2.47 (s, 3H; CH3), 2.45 (s, 3H; CH3), 2.42 (s,
3H; CH3), 0.88 (s, 9H; tBu), 0.07 ppm (d, 6H, J=2.8 Hz; CH3 ꢂ2);
13C NMR (CDCl3, 100 MHz): d=171.93, 171.43, 152.98, 152.54, 137.98,
137.85, 137.80, 128.43, 128.37, 127.76, 127.66, 127.57, 97.42, 96.71, 96.53,
74.69, 73.68, 73.34, 73.22, 73.06, 72.88, 71.34, 71.18, 70.83, 70.39, 69.92,
67.65, 67.20, 66.65, 66.36, 56.07, 55.80, 55.69, 55.01, 25.80, 23.80, 18.18,
ꢀ4.50, ꢀ5.13 ppm; HRMS (ESI): m/z calcd for C55H70N3O19Si: 1104.4367
[M+H]+; found: 1104.4343.
Methyl (2-acetamido-6-O-benzyl-2,3-N,O-carbonyl-2-deoxy-a-d-galacto-
pyranosyl)-(1!4)-(2-acetamido-6-O-benzyl-2,3-N,O-carbonyl-2-deoxy-a-
d-galactopyranosyl)-(1!4)-2-acetamido-6-O-benzyl-2,3-N,O-carbonyl-2-
deoxy-a-d-galactopyranoside (11): Compound 10 (34.5 mg, 0.03 mmol)
was dissolved in TBAF/THF (1m; 2 mL). The solution was then stirred
for 10 min, at which time TLC showed the complete disappearance of 10.
The reaction mixture was extracted with EtOAc (50 mL) and the organic
layer was washed with saturated aqueous NH4Cl (15 mLꢂ2) and water
(10 mL). The combined organic layers were dried over Na2SO4 and con-
centrated in vacuo. The crude product was purified by column chroma-
tography on silica gel (hexane/EtOAc, 2:1) to give 11 as a colorless foam
(27.8 mg, 90%). Rf =0.4 (hexane/EtOAc, 1:1); [a]2D4 = +96.2 (c=1.6 in
7.27 (m, 10H; Ar), 5.80 (d, 1H, J1’,2’ =2.4 Hz; H1’), 5.55 (d, 1H, J1,2
2.8 Hz; H1), 4.69 (d, 1H, J=11.6 Hz; PhCH2), 4.65 (dd, 1H, J3’,2’ =12.4,
3’.4’ =1.6 Hz; H3’), 4.58 (dd, 1H, J3,2 =12.4, J3,4 =1.6 Hz; H3), 4.53–4.51
(m, 3H; PhCH2 ꢂ3), 4.47 (s, 1H; H4’), 4.40 (s, 1H; H4), 4.36 (dd, 1H,
2’,1’ =2.4, J2,3 =12.0 Hz; H2), 4.19 (dd, 1H, J2,1 =2.8, J2,3 =12.4 Hz; H2),
4.10 (t, 1H, J=6.4 Hz; H5’), 3.91 (t, 1H, J=6.4 Hz; H5), 3.64–3.59 (m,
1H; H6a’), 3.53–3.43 (m, 3H; H6b’, H6a, H6b), 3.41 (s, 3H; CH3), 2.48
(s, 3H; CH3), 2.46 (s, 3H; CH3), 0.89 (s, 9H; tBu), 0.08 ppm (s, 6H;
CH3 ꢂ2); 13C NMR (CDCl3, 100 MHz): d=172.01, 171.41, 152.97, 152.66,
137.82, 137.80, 128.41, 128.34, 127.78, 127.75, 127.71, 127.62, 97.36, 96.78,
74.71, 73.78, 73.22, 73.06, 71.23 (2C), 70.09, 67.53, 67.35, 66.27, 56.04,
55.80, 55.01, 25.80, 23.83, 18.17, ꢀ4.51, ꢀ5.13 ppm; HRMS (ESI): m/z
calcd for C39H52N2O13SiNa: 807.3131 [M+Na]+; found: 807.3131.
=
J
J
1
CHCl3); H NMR (CDCl3, 400 MHz): d=7.40–7.27 (m, 15H; Ar), 5.92 (s,
1H; H1’’), 5.81 (d, 1H, J1’,2’ =2.0 Hz; H1’), 5.53 (d, 1H, J1,2 =2.0 Hz; H1),
4.72–4.46 (m, 13H; PhCH2 ꢂ6, H2’’, H3’’, H3’, H3, H4’’, H4’, H4), 4.25
(dd, 1H, J2’,1’ =2.0, J2’,3’ =12.4 Hz; H2’), 4.18–4.12 (m, 2H; H2, H5’’), 4.01
(s, 1H; H5’), 3.90 (t, 1H, J=6.8 Hz; H5), 3.78 (d, 2H, J=4.0 Hz; H6a’’,
H6b’’), 3.52–3.43 (m, 5H; 4’’-OH, H6a’,H6b’, H6a, H6b), 3.40 (s, 3H;
CH3), 2.48 (s, 3H; CH3), 2.46 ppm (s, 6H; CH3 ꢂ2); 13C NMR (CDCl3,
100 MHz): d=172.00, 171.89, 171.49, 153.06, 152.63, 152.56, 137.95,
137.79, 137.14, 128.61, 128.45, 128.41, 128.06, 127.81, 127.80, 127.69,
127.62, 97.41, 96.83, 96.50, 74.30, 73.90, 73.67, 73.28, 73.08, 72.92, 71.25,
70.25, 69.97, 69.90, 69.81, 67.18, 67.06, 66.38, 56.11, 55.82, 55.76, 54.62,
23.84, 23.80 ppm; HRMS (ESI): m/z calcd for C49H59N4O19: 1007.3768
[M+NH4]+; found: 1007.3789.
Methyl (2-acetamido-6-O-benzyl-2,3-N,O-carbonyl-2-deoxy-a-d-galacto-
pyranosyl)-(1!4)-2-acetamido-6-O-benzyl-2,3-N,O-carbonyl-2-deoxy-a-
d-galactopyranoside (9): Compound 8 (149 mg, 0.19 mmol) was dissolved
in TBAF/THF (1m; 2 mL). The solution was then stirred for 10 min, at
which time TLC showed the complete disappearance of 8. The reaction
mixture was extracted with EtOAc (50 mL) and the organic layer was
washed with satutated aqueous NH4Cl (15 mLꢂ2) and water (10 mL).
The combined organic layers were dried over Na2SO4 and concentrated
in vacuo. The crude product was purified by column chromatography on
silica gel (hexane/EtOAc, 2:1) to give 9 as a colorless foam (114 mg,
90%). Rf =0.4 (hexane/EtOAc, 1:1); [a]2D4 = +125.7 (c=1.4 in CHCl3);
1H NMR (CDCl3, 400 MHz): d=7.37–7.29 (m, 10H; Ar), 5.89 (d, 1H,
Methyl (2-acetamido-4-O-tert-butyldimethylsilyl-6-O-benzyl-2,3-N,O-car-
bonyl-2-deoxy-a-d-galactopyranosyl)-(1!4)-(2-acetamido-6-O-benzyl-
2,3-N,O-carbonyl-2-deoxy-a-d-galactopyranosyl)-(1!4)-(2-acetamido-6-
O-benzyl-2,3-N,O-carbonyl-2-deoxy-a-d-galactopyranosyl)-(1!4)-2-acet-
amido-6-O-benzyl-2,3-N,O-carbonyl-2-deoxy-a-d-galactopyranoside (12):
Tf2O (56.1 mg, 33 mL, 0.20 mmol) was added to a stirred mixture of 2
(106 mg, 0.19 mmol), Ph2SO (38.4 mg, 0.19 mmol), TTBP (94.4 mg,
0.38 mmol), and activated 4 ꢃ molecular sieves (1.5 g, powder) in CH2Cl2
(15 mL) at ꢀ728C under a nitrogen atmosphere. The reaction mixture
was stirred for 5 min and, after the complete disappearance of 2 as de-
tected by TLC, a solution of acceptor 11 (94.2 mg, 0.095 mmol) in
CH2Cl2 (3.0 mL) was added dropwise to the mixture. The mixture was
slowly warmed to room temperature, stirred for a further 2 h, and
quenched with Et3N (0.1 mL). The precipitate was filtered off and the fil-
trate was concentrated. The residue was purified by column chromatogra-
phy on silica gel (hexane/EtOAc, 3:1) to give 12 as a colorless foam
(72 mg, 53%). Rf =0.4 (hexane/EtOAc, 2:1); [a]2D1 = +110.9 (c=2.6 in
CHCl3); 1H NMR (CDCl3, 500 MHz): d=7.38–7.26 (m, 20H; Ar), 5.84
(d, 1H, J1’’’,2’’’ =3.0 Hz; H1’’’), 5.82 (d, 1H, J1’’,2’’ =3.0 Hz; H1’’), 5.80 (d,
1H, J1’,2’ =3.0 Hz; H1’), 5.54 (d, 1H, J1,2 =2.5 Hz; H1), 4.72–4.46 (m,
15H; PhCH2 ꢂ8, H3’’’, H3’’, H3’, H3, H4’’’, H4’’, H4’), 4.38 (s, 1H; H4),
4.33 (dd, 1H, J2’’’,1’’’ =3.0, J2’’’,3’’’ =12.5 Hz; H2’’’), 4.25–4.22 (m, 2H; H2’’,
H2’), 4.19–4.10 (m, 3H; H2, H5’’’, H5’’) 4.05 (t, 1H, J=6.5 Hz; H5’), 3.90
(t, 1H, J=6.5 Hz; H5), 3.58 (dd, 1H, J=2.5, 9.0 Hz; H6a’’’), 3.52–3.42
(m, 7H; H6b’’’, H6a’’, H6b’’, H6a’, H6b’, H6a, H6b), 3.40 (s, 3H; CH3),
J
1’,2’ =1.2 Hz; H1’), 5.54 (d, 1H, J1,2 =2.8 Hz; H1), 4.73 (d, 1H, J=
11.6 Hz; PhCH2), 4.66–4.50 (m, 8H; PhCH2 ꢂ3, H3’, H3, H4’, H4, H2’),
4.19 (dd, 1H, J2,1 =2.8, J2,3 =12.4 Hz; H2), 4.05 (t, 1H, J=4.0 Hz; H5’),
3.91 (t, 1H, J=6.8 Hz; H5), 3.81 (d, 2H, J=4.0 Hz; H6a’, H6b’), 3.58 (s,
1H; 4’-OH), 3.56–3.51 (m, 1H; H6a), 3.47 (dd, 1H, J=6.4, 9.2 Hz; H6b),
3.40 (s, 3H; CH3), 2.49 (s, 3H; CH3), 2.48 ppm (s, 3H; CH3); 13C NMR
(CDCl3, 100 MHz): d=172.09, 171.35, 153.03, 152.77, 137.82, 137.10,
128.62, 128.45, 128.10, 127.88, 127.85, 127.81, 97.33, 96.96, 74.32, 73.98,
73.79, 73.11, 70.75, 69.93, 67.16, 67.08, 56.09, 55.93, 54.63, 23.83 ppm;
HRMS (ESI): m/z calcd for C33H38N2O13Na: 693.2266 [M+Na]+; found:
693.2264.
Methyl (2-acetamido-4-O-tert-butyldimethylsilyl-6-O-benzyl-2,3-N,O-car-
bonyl-2-deoxy-a-d-galactopyranosyl)-(1!4)-(2-acetamido-6-O-benzyl-
2,3-N,O-carbonyl-2-deoxy-a-d-galactopyranosyl)-(1!4)-2-acetamido-6-
O-benzyl-2,3-N,O-carbonyl-2-deoxy-a-d-galactopyranoside (10): Tf2O
(20.7 mg, 12.2 mL, 0.073 mmol) was added to a stirred mixture of 2
(36.2 mg, 0.065 mmol), Ph2SO (14 mg, 0.069 mmol), TTBP (32.0 mg,
0.13 mmol), and activated 4 ꢃ molecular sieves (500 mg, powder) in
CH2Cl2 (5 mL) at ꢀ728C under a nitrogen atmosphere. The reaction mix-
ture was stirred for 5 min and, after the complete disappearance of 2 as
detected by TLC, a solution of acceptor 9 (29 mg, 0.043 mmol) in CH2Cl2
(1.0 mL) was added dropwise to the mixture. The mixture was slowly
warmed to room temperature, stirred for a further 2 h, and quenched
with Et3N (0.1 mL). The precipitate was filtered off and the filtrate was
Chem. Eur. J. 2011, 17, 14518 – 14526
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14523

Salmonella typhi Antigens
2.47 (s, 3H; CH3), 2.44 (s, 3H; CH3), 2.41 (s, 6H; CH3 ꢂ2), 0.87 (s, 9H;
tBu), 0.07 (s, 3H; CH3), 0.06 ppm (s, 3H; CH3); 13C NMR (CDCl3,
100 MHz): d=171.95, 171.93, 171.82, 171.41, 152.96, 152.55, 152.41,
137.97, 137.88, 137.82, 128.44, 128.41, 128.39, 128.37, 127.79, 127.76,
127.67, 127.61, 97.43, 96.77, 96.56, 96.49, 74.69, 73.69, 73.31, 73.23, 73.09,
72.89, 72.87, 71.38, 71.21, 70.97, 70.82, 70.51, 70.20, 69.92, 67.69, 67.18,
66.76, 66.53, 66.40, 56.09, 55.83, 55.68, 55.03, 25.81, 23.79, 23.73, 23.68,
18.19, ꢀ4.49, ꢀ5.13 ppm; HRMS (ESI): m/z calcd for C71H90N5O25Si:
1440.5689 [M+NH4]+; found: 1440.5702.
hydrochloric acid to give a pH around 7 and concentrated in vacuo.
After addition of DMAP (0.19 mg, 1.6 mmol), the mixture was dissolved
in pyridine (2 mL). The solution was cooled to 08C and acetic anhydride
(1.0 mL) was then added dropwise. The resulting mixture was gradually
warmed to room temperature and stirred for a further 2 h. The crude
product was purified by column chromatography on silica gel (MeOH/
EtOAc, 1:50) to give 15 as a colorless viscous oil (27.2 mg, 80% for two
steps). Rf =0.7 (MeOH/EtOAc, 1:10); [a]2D4 = +145.9 (c=0.4 in MeOH);
1H NMR (CDCl3, 400 MHz): d=7.34–7.23 (m, 15H; Ar), 6.05 (d, 1H, J=
9.2 Hz; NH), 6.02 (d, 1H, J=9.6 Hz; NH), 5.61 (d, 1H, J=9.6 Hz; NH),
5.56 (d, 1H, J=2.8 Hz; H4’’), 5.34 (dd, 1H, J3’’,4’’ =2.8, J3’’,2’’ =11.6 Hz;
H2’’), 5.23 (dd, 1H, J3’,4’ =2.8, J3’,2’ =11.6 Hz; H2’), 5.16 (dd, 1H, J3,4 =2.4,
Methyl (2-acetamido-3,4-di-O-acetyl-6-O-benzyl-2-deoxy-a-d-galactopyr-
anosyl)-(1!4)-2-acetamido-3-O-acetyl-6-O-benzyl-2-deoxy-a-d-galacto-
pyranoside (13): Compound 8 (10.5 mg, 0.013 mmol) was dissolved in a
mixed solvent consisting of aqueous NaOH (1m) and 1,4-dioxane
(1.6 mL, 1:1) and then heated at 408C for 2 h. After the TLC showed the
complete disappearance of 8, the reaction mixture was quenched with hy-
drochloric acid to give a pH around 7 and then concentrated in vacuo.
After the addition of DMAP (0.08 mg, 0.65 mmol), the mixture was dis-
solved in pyridine (1 mL). The solution was cooled to 08C and acetic an-
hydride (0.5 mL) was added dropwise. The resulting mixture was gradual-
ly warmed to room temperature and stirred for a further 2 h. The crude
product was purified by column chromatography on silica gel (MeOH/
EtOAc, 1:50) to give 13 as a colorless viscous oil (8.9 mg, 89% for two
steps). Rf =0.8 (MeOH/EtOAc, 1:10); [a]2D4 = +110.7 (c=1.4 in MeOH);
1H NMR (CDCl3, 400 MHz): d=7.36–7.22 (m, 10H; Ar), 5.99 (d, 1H, J=
9.6 Hz; NH), 5.70 (d, 1H, J=9.2 Hz; NH), 5.54 (d, 1H, J=1.6 Hz; H4’),
5.22–5.19 (m, 2H; H3’, H3), 5.04 (d, 1H, J1’,2’ =3.6 Hz; H1’), 4.78 (d, 1H,
J
3,2 =11.2 Hz; H2), 5.05 (s, 2H; H1’’, H1’), 4.74 (d, 1H, J1,2 =3.2 Hz; H1),
4.65–4.35 (m, 12H; PhCH2 ꢂ6, H2’’, H2’, H2, H4’, H5’’, H5’), 4.13 (d, 1H,
J=2.4 Hz; H4), 3.95 (t, 1H, J=7.2 Hz; H5), 3.49–3.41 (m, 6H; H6a’’,
H6b’’, H6a’, H6b’, H6a, H6b), 3.39 (s, 3H; CH3), 2.05 (s, 3H; CH3), 2.04
(s, 3H; CH3), 2.00 (s, 3H; CH3), 1.95 (s, 3H; CH3), 1.92 (s, 3H; CH3),
1.91 (s, 3H; CH3), 1.86 ppm (s, 3H; CH3); 13C NMR (CDCl3, 100 MHz):
d=171.47, 171.27, 170.65, 170.18, 170.13, 170.07, 169.70, 137.37, 136.89,
128.47, 128.42, 128.38, 128.09, 128.08, 127.96, 127.91, 127.78, 98.60, 97.43,
97.38, 73.61, 73.35, 73.27, 71.84, 71.48, 69.80, 69.04, 68.83, 68.37, 67.74,
67.60, 67.29, 66.75, 66.33, 55.41, 49.09, 48.54, 47.97, 23.32, 23.27, 23.22,
20.81, 20.74, 20.59, 20.45 ppm; HRMS (ESI): m/z calcd for
C54H69N3O20Na: 1102.4367 [M+Na]+; found: 1102.4379.
Methyl (2-acetamido-3,4-di-O-acetyl-2-deoxy-a-d-galactopyranosyluro-
nate)-(1!4)-(2-acetamido-3-O-acetyl-2-deoxy-a-d-galactopyranosyluro-
nate)-(1!4)-2-acetamido-3-O-acetyl-2-deoxy-a-d-galactopyranosideuro-
nate (16): Compound 15 (26 mg, 0.024 mmol) was dissolved in a mixed
solvent consisting of THF, AcOH, and water (3.5 mL, 4:2:1) and then
Pd/C (10%; 26 mg) was added. The mixture was stirred under a hydro-
gen atmosphere. After stirring for 2 h, the catalyst was removed by filtra-
tion and the filtrate was concentrated. The residue was dissolved in a
mixed solvent consisting of CCl4, CH3CN, and water (3.5 mL, 2:2:3), and
then sodium periodate (77.2 mg, 0.36 mmol) and hydrated ruthenium tri-
chloride (0.33 mg, 1.6 mmol) were added to the mixture. The mixture was
stirred overnight and then concentrated in vacuo. The residue was sub-
jected to C18 reverse-phase column chromatography (MeOH/H2O, 1:12)
to give 16 as a colorless foam (13.3 mg, 66% for two steps). Rf =0.1
(MeOH/EtOAc, 1:1); [a]D24 = +298.0 (c=0.4 in MeOH); 1H NMR (D2O,
500 MHz): d=5.79 (s, 1H; H4’’), 5.42 (dd, 1H, J3’’,2’’ =12.0, J3’’,4’’ =2.5 Hz;
H3’’), 5.37–5.32 (m, 2H; H3’, H3), 5.22 (d, 1H, J1’’,2’’ =3.5 Hz; H1’’), 5.20
(d, 1H, J1’,2’ =3.5 Hz; H1’), 5.09 (s, 1H; H5’’), 5.07 (s, 1H; H4’), 4.96 (d,
1H, J1,2 =3.5 Hz; H1), 4.75 (s, 2H; H5’, H5), 4.70 (d, 1H, J=2.0 Hz; H4),
J
1,2 =3.6 Hz; H1), 4.63–4.35 (m, 7H; PhCH2 ꢂ4, H2’, H2, H5’), 4.20 (d,
1H, J=2.0 Hz; H4), 3.97 (t, 1H, J=7.2 Hz; H5), 3.49 (d, 2H, J=7.2 Hz;
H6a, H6b), 3.41 (d, 2H, J=6.4 Hz; H6a’, H6b’), 3.38 (s, 3H; CH3), 2.05
(s, 3H; CH3), 2.01 (s, 3H; CH3), 2.00 (s, 3H; CH3), 1.95 (s, 3H; CH3),
1.94 ppm (s, 3H; CH3); 13C NMR (CDCl3, 100 MHz): d=171.67, 170.55,
170.13, 170.08, 169.83, 137.35, 137.22, 128.47, 128.34, 128.01, 127.90,
127.78, 127.72, 98.37, 97.50, 73.61, 73.29, 71.75, 69.35, 68.70, 68.37, 67.86,
67.61, 67.42, 66.81, 55.42, 48.91, 47.91, 23.29, 23.26, 20.76, 20.71,
20.60 ppm; HRMS (ESI): m/z calcd for C37H48N2O14Na: 767.2998
[M+Na]+; found: 767.2994.
Methyl (2-acetamido-3,4-di-O-acetyl-2-deoxy-a-d-galactopyranosyluro-
nate)-(1!4)-2-acetamido-3-O-acetyl-2-deoxy-a-d-galactopyranosideuro-
nate (14): Compound 13 (15 mg, 0.020 mmol) was dissolved in a mixed
solvent consisting of THF, AcOH, and water (2.8 mL, 4:2:1) and then
Pd/C (10%; 15 mg) was added. The mixture was stirred under a hydro-
gen atmosphere. After stirring for 2 h, the catalyst was removed by filtra-
tion and the filtrate was concentrated. The residue was dissolved in a
mixed solvent consisting of CCl4, CH3CN, and water (1.75 mL, 2:2:3),
and then sodium periodate (42.8 mg, 0.2 mmol) and hydrated ruthenium
trichloride (0.18 mg, 0.88 mmol) were added to the mixture. The mixture
was stirred overnight and then concentrated in vacuo. The residue was
subjected to C18 reverse-phase column chromatography (MeOH/H2O,
1:10) to give 14 as a colorless foam (9.0 mg, 75% for two steps). Rf =0.2
(MeOH/EtOAc, 1:1); [a]D24 = +116.7 (c=0.3 in MeOH); 1H NMR (D2O,
500 MHz): d=5.81 (dd, 1H, J4’,3’ =3.0, J4’,5’ =1.5 Hz; H4’), 5.39 (dd, 1H,
4.53 (dd, 1H, J2,1 =3.5, J2,3 =11.5 Hz; H2), 4.50 (dd, 1H, J2’,1’ =3.5, J2’,3’
=
11.5 Hz; H2’), 4.44 (dd, 1H, J2’’,1’’ =3.5, J2’’,3’’ =11.5 Hz; H2’’), 3.44 (s, 3H;
CH3), 2.16 (s, 3H; CH3), 2.02 (s, 3H; CH3), 2.00 (s, 9H; CH3 ꢂ3), 1.97 (s,
3H; CH3), 1.96 ppm (s, 3H; CH3); 13C NMR (D2O, 100 MHz): d=174.58,
174.40, 173.00, 172.70, 172.47, 171.45, 171.29, 171.13, 99.11, 98.71, 98.27,
76.48, 75.95, 70.42, 69.61, 69.42, 69.34, 68.91, 68.60, 67.56, 55.76, 47.83,
47.43, 47.07, 21.99, 21.91, 21.66, 19.92, 19.83, 19.75 ppm; HRMS (ESI): m/
z calcd for C33H45N3O23Na: 874.2336 [M+Na]+; found: 874.2296.
Methyl (2-acetamido-3,4-di-O-acetyl-6-O-benzyl-2-deoxy-a-d-galactopyr-
anosyl)-(1!4)-(2-acetamido-3-O-acetyl-6-O-benzyl-2-deoxy-a-d-galacto-
pyranosyl)-(1!4)-(2-acetamido-3-O-acetyl-6-O-benzyl-2-deoxy-a-d-gal-
actopyranosyl)-(1!4)-2-acetamido-3-O-acetyl-6-O-benzyl-2-deoxy-a-d-
galactopyranoside (17): Compound 12 (46 mg, 0.032 mmol) was dissolved
in a mixed solvent consisting of aqueous NaOH (1m) and 1,4-dioxane
(4.0 mL, 1:1) and then heated at 408C for 10 h. After the TLC showed
the complete disappearance of 12, the reaction mixture was quenched
with hydrochloric acid to give a pH around 7 and concentrated in vacuo.
After addition of DMAP (0.19 mg, 1.6 mmol), the mixture was dissolved
in pyridine (2 mL). The solution was cooled to 08C and acetic anhydride
(1.0 mL) was added dropwise. The resulting mixture was gradually
warmed to room temperature and stirred for a further 10 h. The crude
product was purified by column chromatography on silica gel (MeOH/
EtOAc, 1:20) to give 17 viscous oil (32.0 mg, 70% for two steps). Rf =0.6
(MeOH/EtOAc, 1:10); [a]2D3 = +175.4 (c=0.5 in MeOH); 1H NMR
(CDCl3, 500 MHz): d=7.35–7.23 (m, 20H; Ar), 6.14 (d, 1H, J=9.5 Hz;
NH), 6.11 (d, 1H, J=9.5 Hz; NH), 6.00 (d, 1H, J=10.0 Hz; NH), 5.60
J
3’,2’ =11.5, J3’,4’ =3.0 Hz; H3’), 5.33 (dd, 1H, J3,2 =11.5, J3,4 =2.5 Hz; H3),
5.22 (d, 1H, J1’,2’ =3.5 Hz; H1’), 5.14 (d, 1H, J=1.5 Hz; H5’), 4.98 (d, 1H,
1,2 =4.0 Hz; H1), 4.75 (s, 1H; H5), 4.68 (d, 1H, J=2.0 Hz; H4), 4.52 (dd,
J
1H, J2,1 =3.5, J2,3 =11.5 Hz; H2), 4.44 (dd, 1H, J2’,1’ =4.0, J2’,3’ =11.5 Hz;
H2’), 3.45 (s, 3H; CH3), 2.17 (s, 3H; CH3), 2.02 (d, 6H, J=2.5 Hz; CH3 ꢂ
2), 1.99 ppm (d, 6H, J=0.5 Hz; CH3 ꢂ2); 13C NMR (D2O, 100 MHz): d=
174.57, 174.42, 173.04 (2C), 172.71, 171.68, 171.14, 99.04, 98.28, 76.42,
69.59, 69.41, 69.38, 69.03, 67.65, 55.74, 47.81, 47.10, 21.97, 21.67, 19.93,
19.85, 19.78 ppm; HRMS (ESI): m/z calcd for C23H33N2O16: 593.1825
[M+H]+; found: 593.1824.
Methyl (2-acetamido-3,4-di-O-acetyl-6-O-benzyl-2-deoxy-a-d-galactopyr-
anosyl)-(1!4)-(2-acetamido-3-O-acetyl-6-O-benzyl-2-deoxy-a-d-galacto-
pyranosyl)-(1!4)-2-acetamido-3-O-acetyl-6-O-benzyl-2-deoxy-a-d-galac-
topyranoside (15): Compound 10 (35 mg, 0.032 mmol) was dissolved in a
mixed solvent consisting of aqueous NaOH (1m) and 1,4-dioxane
(4.0 mL, 1:1) and then heated at 408C for 2 h. After the TLC showed the
complete disappearance of 10, the reaction mixture was quenched with
14524
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14518 – 14526

X.-S. Ye et al.
FULL PAPER
(d, 1H, J=9.5 Hz; NH), 5.55 (d, 1H, J=1.5 Hz; H4’’’), 5.36 (dd, 1H,
goat-anti-rabbit LgG-HRP, Santa cruz) diluted 5000 fold in diluent buffer
was added. The plates were incubated for 1 h at 378C. After three
washes with PBS, the reaction was developed with O-phenylenediamine
(OPD; 100 mL per well) in the dark for 15 min and stopped with H2SO4
(2m; 100 mL per well). Optical density (OD) values were measured at
490 nm with an ELISA plate reader (TECAN, sunrise). The control con-
sisted of Vi PS coated wells incubated without the inhibitors (serum
(50 mL)+diluent buffer (50 mL)) and had the maximum optical density
(ODm). The percentage inhibition was calculated by using the equation:
J
3’’’,4’’’ =2.5, J3’’’,2’’’ =11.5 Hz; H3’’’), 5.28 (dd, 1H, J3’’,4’’ =2.5, J3’’,2’’ =11.5 Hz;
H3’’), 5.24 (dd, 1H, J3’,4’ =3.0, J3’,2’ =11.5 Hz; H3’), 5.15 (dd, 1H, J3,4 =2.5,
3,2 =11.5 Hz; H3), 5.05 (d, 1H, J1’’’,2’’’ =4.0 Hz; H1’’’), 5.03 (d, 1H, J1’’,2’’
J
=
3.5 Hz; H1’’), 4.99 (d, 1H, J1’,2’ =4.0 Hz; H1’), 4.73 (d, 1H, J1,2 =3.5 Hz;
H1), 4.67–4.29 (m, 16H; PhCH2 ꢂ8, H4’’, H2’’’, H2’’, H2’, H2, H5’’’, H5’’,
H5’), 4.25 (d, 1H, J=2.5 Hz; H4’), 4.13 (d, 1H, J=2.5 Hz; H4), 3.95 (t,
1H, J=7.0 Hz; H5), 3.51–3.35 (m, 8H; H6a’’’, H6b’’’, H6a’’, H6b’’, H6a’,
H6b’, H6a, H6b), 3.34 (s, 3H; CH3), 2.05 (s, 3H; CH3), 2.04 (s, 3H; CH3),
2.00 (s, 3H; CH3), 1.96 (s, 3H; CH3), 1.92 (s, 3H; CH3), 1.91 (s, 3H;
CH3), 1.88 (s, 3H; CH3), 1.86 (s, 3H; CH3), 1.85 ppm (s, 3H; CH3);
13C NMR (CDCl3, 125 MHz): d=171.47, 171.26, 171.05, 170.66, 170.37,
170.28, 170.21, 170.16, 169.86, 137.37, 137.28, 137.01, 136.86, 128.49,
128.42, 128.38, 128.12, 128.06, 127.96, 127.85, 127.79, 98.56, 97.47, 97.35,
97.11, 73.60, 73.36, 73.32, 71.71, 71.29, 71.23, 69.72, 69.37, 69.12, 69.02,
68.92, 68.86, 68.34, 67.69, 67.59, 67.32, 66.86, 66.31, 55.40, 49.03, 48.69,
48.58, 47.87, 23.24, 23.18, 23.13, 20.80, 20.72, 20.61, 20.42 ppm; HRMS
(ESI): m/z calcd for C71H90N4O26Na: 1437.5736 [M+Na]+; found:
1437.5745.
X%=100%ꢂ(ODmꢀODx)/(ODmꢀODo). ODo is the optical density
G
of blank wells. Every concentration was tested in triplicate. The data
were reported as the mean ꢂSD of the measurements performed in trip-
licate.
Acknowledgements
This work was financially supported by the National Natural Science
Foundation of China (Grant No. 20732001).
Methyl (2-acetamido-3,4-di-O-acetyl-2-deoxy-a-d-galactopyranosyluro-
nate)-(1!4)-(2-acetamido-3-O-acetyl-2-deoxy-a-d-galactopyranosyluro-
nate)-(1!4)-(2-acetamido-3-O-acetyl-2-deoxy-a-d-galactopyranosyluro-
nate)-(1!4)-2-acetamido-3-O-acetyl-2-deoxy-a-d-galactopyranosideuro-
nate (18): Compound 17 (19.1 mg, 0.013 mmol) was dissolved in a mixed
solvent consisting of THF, AcOH, and water (3.5 mL, 4:2:1) and then
Pd/C (10%; 19.1 mg) was added. The mixture was stirred under a hydro-
gen atmosphere. After stirring for 5 h, the catalyst was removed by filtra-
tion and the filtrate was concentrated. The residue was dissolved in a
mixed solvent consisting of CCl4, CH3CN, and water (3.5 mL, 2:2:3), and
then sodium periodate (57.6 mg, 0.27 mmol) and hydrated ruthenium tri-
chloride (0.25 mg, 1.2 mmol) were added to the mixture. The mixture was
stirred overnight and then concentrated in vacuo. The residue was sub-
jected to C18 reverse-phase column chromatography (MeOH/H2O, 1:12)
to give 18 as a colorless foam (10.0 mg, 67% for two steps). Rf =0.1
(MeOH/EtOAc, 1:1.5); [a]2D3 = +192.3 (c=0.3 in MeOH); 1H NMR
(D2O, 400 MHz): d=5.78 (dd, 1H, J4’,5’ =1.6, J4’,3’ =1.6 Hz; H4’’’), 5.43
(dd, 1H, J3,2 =11.6, J3,4 =2.8 Hz; H3), 5.40–5.32 (m, 3H; H3’, H3’’, H3’’’),
5.21 (d, 1H, J1’,2’ =4.0 Hz; H1’), 5.20 (d, 1H, J1’’,2’’ =3.6 Hz; H1’’), 5.18 (d,
1H, J1’’’,2’’’ =3.6 Hz; H1’’’), 5.04 (s, 2H; H5’’’, H5’’), 4.99 (s, 1H; H5’), 4.96
(d, 1H, J1,2 =3.6 Hz; H1), 4.73–4.72 (m, 2H; H4’’, H4’), 4.69 (d, 1H, J=
2.4 Hz; H4), 4.55–4.48 (m, 3H; H2, H2’, H2’’), 4.43 (dd, 1H, J2’’’,3’’’ =11.6,
[1] B. Ivanoff, M. M. Levine, Bull. Inst. Pasteur. 1997, 95, 129–142.
[2] a) A. Gupta, Pediatr. Infect. Dis. J. 1994, 13, 134–140; b) Z. A.
Bhutta, S. H. Naqvi, R. A. Razzaq, B. J. Farooqui, Rev. Infect. Dis.
1991, 13, 832–836; c) C. Parry, J. Wain, N. T. Chinh, H. Vinh, J. J.
Farrar, Lancet 1998, 351, 1289; d) I. Stephens, M. M. Levine, Pediatr.
Infect. Dis. J. 2002, 21, 157–158.
[3] a) A. Felix, R. M. Pitt, Lancet 1934, 224, 186–191; b) A. Felix, R. M.
Pitt, Br. J. Exp. Pathol. 1936, 17, 81–86; c) E. E. Baker, R. E. White-
side, R. Basch, M. A. Derow, J. Immunol. 1959, 83, 680–686; d) I.
Virlogeux-Payant, M. Y. Popoff, Bull. Inst. Pasteur. 1996, 94, 237–
250.
[4] a) K. Heyns, G. Kiessling, Carbohydr. Res. 1967, 3, 340–352;
b) E. M. Daniels, R. Schneerson, W. M. Egan, S. C. Szu, J. B. Rob-
bins, Infect. Immun. 1989, 57, 3159–3164.
[5] a) R. E. Kossack, R. L. Guerrant, P. Densen, J. Schadelin, G. L.
Mandell, Infect. Immun. 1981, 31, 674–678; b) R. M. Miller, J.
Garbus, R. B. Hornick, Science 1972, 175, 1010–1011.
[6] a) R. J. Looney, R. T. Steigbigel, J. Lab. Clin. Med. 1986, 108, 506–
516; b) J. D. Robbins, J. B. Robbins, J. Infect. Dis. 1984, 150, 436–
449.
J
2’’’,1’’’ =3.6 Hz; H2’’’), 3.43 (s, 3H; CH3), 2.15 (s, 3H; CH3), 2.01–1.97 ppm
(m, 24H; CH3 ꢂ8); 13C NMR (D2O, 125 MHz): d=175.37, 175.19, 173.82,
173.53, 173.35, 172.60, 172.36, 172.22, 172.09, 99.92, 99.52 (2C), 99.05,
77.28, 76.78, 71.42, 70.50, 70.21, 69.85, 69.52, 69.46, 68.53, 56.51, 48.63,
48.27, 48.20, 47.87, 22.80, 22.74, 22.70, 22.44, 20.71, 20.64, 20.57 ppm;
HRMS (ESI): m/z calcd for C43H58N4O30Na: 1133.3028 [M+Na]+; found:
1133.3038.
[7] a) I. L. Acharya, C. U. Lowe, R. Thapa, V. L. Gurubacharya, M. B.
Shrestha, M. Cadoz, D. Schulz, J. Armand, D. A. Bryla, B. Trollfors,
T. Cramton, R. Schneerson, J. B. Robbins, N. Engl. J. Med. 1987,
317, 1101–1104; b) K. P. Klugman, H. J. Koornshof, R. Schneerson,
M. Cadoz, I. T. Gilbertson, J. B. Robbins, D. Schulz, J. Armand,
Lancet 1987, 2, 1165–1169; c) L. Hessel, H. Debois, M. Fletcher, R.
Dumas, Eur. J. Clin. Microbiol. Infect. Dis. 1999, 18, 609–620.
[8] L. K. Shi-Shun, J. M. Mallet, M. Moreau, P. Sinaꢀ, Tetrahedron 1999,
55, 14043–14068.
Antibody-binding analyses: The investigation into the ability of the syn-
thetic oligosaccharides to inhibit binding of the antibody to its native
polysaccharide was performed by use of the enzyme-linked immunosorb-
ent assay (ELISA). Briefly, high-binding flat-bottom 96-well EIA/RIA
plates (corning-costar, NY14831) were coated with 100 mL of Vi PS (Vi
polysaccharide vaccine, lot: 20100101, CDC, Beijing, China) per well at a
concentration of 0.5 mgmLꢀ1 in CBC coating buffer (Na2CO3 (15 mm)
and NaHCO3 (35 mm); pH 9.6). After incubation at 48C overnight, the
plates were washed three times with PBS (200 mL per well). After addi-
tion of blocking solution (PBS, 3% BSA; 200 mL per well), the plates
were incubated for 1 h at 378C. Vi PS, compounds 14, 16, and 18 were di-
luted with the diluent buffer (PBS, 1% BSA) to a series of concentra-
tions (0–10 mgmLꢀ1 for Vi PS; 0–500 mgmLꢀ1 for the synthetic saccha-
rides). The anti-Vi serum (serum of rabbit immunized by the Vi PS vac-
cine, Institute of Biological Products, Lanzhou, China) was diluted
250 fold in the diluent buffer. The plates were then washed three times
with PBS after incubation. The serial concentrations of Vi PS, 14, 16, and
18 were mixed with anti-Vi serum separately (50 mL+50 mL per well)
before being added to the coated plates, which were then incubated for
1 h at 378C. The plates were washed three times with PBS and a secon-
dary antibody labeled with horseradish peroxidase (100 mL per well;
[9] K. Benakli, C. Zha, R. J. Kerns, J. Am. Chem. Soc. 2001, 123, 9461–
9462.
[10] a) P. Wei, R. J. Kerns, J. Org. Chem. 2005, 70, 4195–4198; b) M.
Boysen, E. Gemma, M. Lahmann, S. Oscarson, Chem. Commun.
2005, 3044–3046; c) S. Manabe, K. Ishii, Y. Ito, J. Am. Chem. Soc.
2006, 128, 10666–10667; d) S. Manabe, K. Ishii, Y. Ito, Eur. J. Org.
Chem. 2011, 497–516; e) S. Manabe, Y. Aihara, Y. Ito, Chem.
Commun. 2011, 47, 9720–9722.
[11] a) D. Crich, A. U. Vinod, Org. Lett. 2003, 5, 1297–1300; b) D. Crich,
A. U. Vinod, J. Org. Chem. 2005, 70, 1291–1296.
[12] H. Paulsen, Angew. Chem. 1982, 94, 184–201; Angew. Chem. Int.
Ed. Engl. 1982, 21, 155–173.
[13] R. J. Kerns, C. Zha, K. Benakli, Y.-Z. Liang, Tetrahedron Lett. 2003,
44, 8069–8072.
[14] D. Crich, V. Dudkin, J. Am. Chem. Soc. 2001, 123, 6819–6825.
[15] a) Y. Q. Geng, L. H. Zhang, X.-S. Ye, Chem. Commun. 2008, 597–
599; b) Y. Q. Geng, L. H. Zhang, X.-S. Ye, Tetrahedron 2008, 64,
4949–4958; c) Y. Q. Geng, X.-S. Ye, Synlett 2010, 16, 2506–2512.
Chem. Eur. J. 2011, 17, 14518 – 14526
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14525

Salmonella typhi Antigens
[16] L. Yang, X.-S. Ye, Carbohydr. Res. 2010, 345, 1713–1721.
[17] P. Wei, R. J. Kerns, Tetrahedron Lett. 2005, 46, 6901–6905.
[18] M. Sakagami, H. Hamana, Tetrahedron Lett. 2000, 41, 5547–5551.
[19] a) X. Huang, L. Huang, H. Wang, X.-S. Ye, Angew. Chem. 2004,
116, 5333–5336; Angew. Chem. Int. Ed. 2004, 43, 5221–5224; b) Y.
Wang, X.-S. Ye, L. H. Zhang, Org. Biomol. Chem. 2007, 5, 2189–
2200; c) D. Crich, S. Sun, J. Org. Chem. 1996, 61, 4506–4507;
d) J. D. C. Codꢄe, L. J. van den Bos, R. E. J. N. Litjens, H. S. Over-
kleeft, J. H. van Boom, G. A. van der Marel, Org. Lett. 2003, 5,
1947–1950; e) S. Yamago, T. Yamada, T. Maruyama, J. I. Yoshida,
Angew. Chem. 2004, 116, 2197–2200; Angew. Chem. Int. Ed. 2004,
43, 2145–2148; f) H. M. Nguyen, J. L. Poole, D. Y. Gin, Angew.
Chem. 2001, 113, 428–431; Angew. Chem. Int. Ed. 2001, 40, 414–
417.
kleeft, J. H. van Boom, G. A. van der Marel, Org. Lett. 2003, 5,
1519–1522.
[21] a) H. C. van der Plas, A. Koudijs, Recl. Trav. Chim. Pays-Bas, 1978,
97, 159–161; b) D. Crich, M. Smith, Q. Yao, J. Picione, Synthesis
2001, 0323–0326.
[22] a) B. Szewezyk, A. Taylor, Infect. Immun. 1980, 29, 539–544;
b) D. G. Martin, F. G. Jarvis, K. C. Milner, J. Bacteriol. 1967, 94,
1411–1416; c) S. C. Szu, X. R. Li, A. L. Stone, J. B. Robbins, Infect.
Immun. 1991, 59, 4555–4561.
[23] a) R. Kaifu, L. C. Plantefaber, I. J. Goldstein, Carbohydr. Res. 1985,
140, 37–49; b) Y. Fukuda, H. Sasai, T. Suami, Bull. Chem. Soc. Jpn.
1982, 55, 1574–1578.
[20] a) B. A. Garcia, D. Y. Gin, J. Am. Chem. Soc. 2000, 122, 4269–4279;
b) J. D. C. Codꢄe, R. E. J. N. Litjens, R. den Heeten, H. S. Over-
Received: August 22, 2011
Published online: November 17, 2011
14526
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14518 – 14526