Convergent synthesis of the pentasaccharide repeating unit of the O-antigen of escherichia coli O36

Article abstract of DOI:10.1055/s-0034-1379952

An efficient synthesis of the pentasaccharide repeating unit of the O-antigen of Escherichia coli O36 is reported. A stereoselective [2 + 3] block glycosylation method has been exploited to obtain the target pentasaccharide derivative using thioglycoside, trichloroacetimidate, and halide-exchange glycosylation procedures. The 2-azidoethyl group has been used as the anomeric protecting group to make the glycone moiety with a readily available linker for its conjugation to a protein without destroying the cyclic structure at the reducing end. Yields were high in all the intermediate steps.

Full text of DOI:10.1055/s-0034-1379952

SYNTHESIS
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
© Georg Thieme Verlag Stuttgart · New York
2015, 47, 836–844
paper
836
P. K. Mandal
Paper
Synthesis
Convergent Synthesis of the Pentasaccharide Repeating Unit of
the O-Antigen of Escherichia coli O36
Pintu Kumar Mandal*
OH
HO
HO
O
Medicinal and Process Chemistry Division, CSIR-Central Drug
O
Research Institute, BS-10/1, Sector 10, Jankipuram extension,
Sitapur Road, Lucknow, 226 031, India
pintuchem06@gmail.com
HO
O
O
O
OH
O
OH
HO
HO
NHAc
O
O
HO
O
O
HO
OH
NH2
OH
Received: 10.09.2014
Accepted after revision: 02.12.2014
Published online: 22.12.2014
α-L-Rhap-(1→2)-α-L-Fucp
1
↓
DOI: 10.1055/s-0034-1379952; Art ID: ss-2014-n0558-op
3
→ 4)-α-D-Manp-(1→3)-α-L-Fucp-(1→3)-β-D-GlcpNAc-(1→
Abstract An efficient synthesis of the pentasaccharide repeating unit
of the O-antigen of Escherichia coli O36 is reported. A stereoselective [2
+ 3] block glycosylation method has been exploited to obtain the target
pentasaccharide derivative using thioglycoside, trichloroacetimidate,
and halide-exchange glycosylation procedures. The 2-azidoethyl group
has been used as the anomeric protecting group to make the glycone
moiety with a readily available linker for its conjugation to a protein
without destroying the cyclic structure at the reducing end. Yields were
high in all the intermediate steps.
Figure 1 Structure of the repeating unit of the cell wall O-antigen of
Escherichia coli O36
Bacterial cell wall O-antigens are unique polysaccha-
rides and play important roles in the initial stage of bacteri-
al adhesion with the host.10 Due to the antigenic character
of bacterial O-antigens in the form of glycoconjugates, biol-
ogists have made extensive efforts to develop antibacterial
agents or vaccine candidates based on the cell wall glyco-
conjugate derivatives, and a number of reports appeared in
the literature for the development of glycoconjugate vac-
cine candidates against several pathogenic bacteria.11 How-
ever, it is impossible to collect adequate amounts of bacteri-
al O-antigens from natural sources with high purity for
making suitable glycoconjugates and for detailed biological
evaluation. Therefore, the development of a chemical syn-
thetic strategy would be useful to gain access to large-scale
production of the O-antigen structure from commercially
available sugars.
Key words Escherichia coli, pentasaccharide, glycosylation, lipopoly-
saccharide, O-antigen
Escherichia coli (E. coli) are a group of gram-negative
bacteria that cause a variety of bacterial infections in hu-
mans and animals.1 There are several E. coli infections, fre-
quent in humans, including infections of the urinary tract,2
sepsis, meningitis,3 enteric/diarrheal disease blood stream,4
and other anatomical diseases.5,6
Although E. coli strains are generally nonpathogenic
members of the human colonic flora, certain clones develop
specific virulence factors and they cause a broad spectrum
of diseases in humans and animals. Based on intestinal
types of diseases, there are six well-described pathotypes:
enteropathogenic E. coli (EPEC), enterotoxigenic E. coli
(ETEC), enteroinvasive E. coli (EIEC), enterohaemorrhagic E.
coli (EHEC), enteroaggregative E. coli (EAEC), and diffusely
adherent E. coli (DAEC).7
As a part of the ongoing studies on the synthesis of bac-
terial cell wall oligosaccharides12 for their use in glycocon-
jugate preparation, the chemical synthesis of the pentasac-
charide repeating unit of the O-antigen of Escherichia coli
O36 as its 2-aminoethyl glycoside (Scheme 1) is presented
herein.
Recently, Perepelov et al. reported the structure of the
cell wall O-antigen of E. coli O36 comprising of D-glucos-
amine, L-fucose, D-mannose, and L-rhamnose (Figure 1).8 E.
coli O36 strain is associated with diarrheal infections, respi-
ratory tract disease, and broiler breeders with salpingitis.9
The retrosynthetic analysis for the synthesis of penta-
saccharide 1 showed a convergent [2 + 3] block synthetic
strategy approach to be attractive (Scheme 1). Target struc-
ture 1 may be obtained from fully protected pentasaccha-
ride 20 through a three-step deprotection sequence, includ-
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 836–844

837
P. K. Mandal
Paper
Synthesis
ing conversion of the N-phthaloyl group into the corre-
sponding acetamide, deprotection of the ester groups, and
hydrogenolysis.
dichloromethane–N,N-dimethylformamide
three days at room temperature, furnished the protected
disaccharide 4 in 56% yield.
(4:1),16 for
Synthesis of the disaccharide acceptor 4 started with
the known acceptor, 2-azidoethyl 4,6-O-benzylidene-2-de-
oxy-2-N-phthalimido-β-D-glucopyranoside (2)13 and the
halide donor 3,4-di-O-acetyl-2-O-benzyl-α-L-fucopyrano-
syl bromide,14 prepared in situ by the addition of bromine
to ethylthio fucoside 3.15 The stereoselective coupling
(Scheme 2) under halide-assisted coupling conditions be-
tween the known acceptor 2 and the halide donor 3,4-di-O-
acetyl-2-O-benzyl-α-L-fucopyranosyl bromide in the pres-
ence of tetraethylammonium bromide in the mixed solvent
Due to the low yield of this reaction an alternative
method excluding the halide donor was utilized. Thioglyco-
sides are commonly used as α-selective donors, as dis-
cussed in several reports.17 An alternative approach in-
volved the glycosylation of the thiofucoside donor 3 with
known acceptor 2 using mixed solvent diethyl ether–di-
chloromethane (4:1) in the presence of N-iodosuccinim-
ide/trimethylsilyl triflate18 furnishing disaccharide deriva-
tive 4 in 83% yield together with a small quantity (~5%) of
its other isomer, which was separated by column chroma-
tography.
OH
HO
HO
O
O
C
HO
O
D
O
O
OH
B
O
OH
HO
HO
NHAc
O
O
E
A
O
HO
O
HO
OH
NH2
OH
1
OAc
O
AcO
AcO
O
AcO
O
O
O
OBn
O
O
OAc
AcO
AcO
NPhth
O
O
O
O
O
AcO
OAc
Ph
N3
20
[2 + 3]
OAc
O
OAc
O
AcO
AcO
AcO
AcO
O
Ph
O
O
O
O
O
OPMP
L1
O
N3
O
O
O
O
NPhth
O
OAc
OAc
AcO
AcO
OBn
AcO
AcO
O
O
OH
5
AcO
AcO
AcO
OAc
18
OAc
15: L1 = SEt
O
Ph
19: L1 = OC(=NH)CCl3
O
SEt
OBn
O
O
O
HO
N3
NPhth
OAc
AcO
2
3
SEt
O
OAc
O
OAc
O
AcO
AcO
HO
OPMP
OH
AcO
AcO
HO
PMP: p-methoxyphenyl
O
AcO
OAc
AcO
10
Scheme 1 Retrosynthetic analysis of pentasaccharide 1
AcO
OAc
OPMP
SEt
9
12
11
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 836–844

838
P. K. Mandal
Paper
Synthesis
OAc
Br
O
Ph
a
OPMP
OAc
b, c, d
AcO
O
OPMP
OBn
O
O
O
O
O
c (ii)
a
OAc
O
O
N3
+ 2
2 + 3
OBn
OAc
OAc
OAc
NPhth
AcO
AcO
OAc
O
AcO
8
6
7
OBn
OAc
AcO
c (i)
In situ
e
4
b
3
OPMP
OH
O
O
Ph
O
OAc
O
AcO
O
O
N3
9
NPhth
Scheme 3 Reagents and conditions: (a) 4-methoxyphenol, BF3·OEt2,
CH2Cl2, 0 °C, 3 h, 77%; (b) 0.1 M NaOMe, MeOH, r.t., 2 h; (c) (i) 2,2-di-
methoxypropane, TsOH, DMF, r.t., 6 h; (ii) BnBr, NaOH, TBAB, THF, r.t., 5
h; (d) (i) 80% aq AcOH, 80 °C, 1.5 h; (ii) Ac2O, pyridine, r.t., 3 h, 85%
overall; (e) H2, 20% Pd(OH)2/C, MeOH, r.t., 4 h; 88%.
O
OBn
OH
AcO
5
Scheme 2 Reagents and conditions: (a) NIS, TMSOTf, Et2O–CH2Cl2 (4:1),
4 Å molecular sieves, –30 °C, 30 min, 83%; (b) (i) 0.1 M NaOMe, MeOH,
r.t., 1 h; (ii) triethyl orthoacetate, TsOH, DMF, 2 h then 80% aq AcOH,
r.t., 1 h, 90% overall; (c) (i) Br2, CH2Cl2, 0 °C; (ii) Et4NBr, CH2Cl2–DMF
(4:1), 4 Å molecular sieves, r.t., 72 h, 56%.
The stereoselective glycosylation of 4-methoxyphenyl
3,4-di-O-acetyl-β-L-fucopyranoside (9) and ethyl 2,3,4-tri-
O-acetyl-α-L-rhamnopyranoside (10) in the presence of N-
iodosuccinimide/trimethylsilyl triflate18 furnished disac-
charide derivative 13 in 88% yield. Formation of compound
13 was confirmed by spectral analysis [δ = 5.25 (br s, 1 H,
H1E), 4.86 (d, J = 7.8 Hz, 1 H, H1D) and δ = 102.8 (C1D), 97.9
(C1E) in the 1H and 13C NMR spectra, respectively] (Scheme
4).
Therefore N-iodosuccinimide/trimethylsilyl triflate me-
diated glycosylation reaction should be preferred over ha-
lide-assisted coupling glycosylation. Stereoselective forma-
tion of compound 4 was supported by its spectral analysis
[δ = 5.58 (PhCH), 5.33 (d, J = 8.5 Hz, 1 H, H1A), 4.81 (d, J = 3.3
Hz, 1 H, H1B) and at δ = 102.2 (PhCH), 99.1 (C1A), 98.9 (C1B)
9 + 10
12 + 3
in the H and 13C NMR spectra, respectively]. Compound 4
1
d
a
was treated with sodium methoxide19 in methanol followed
by selective acetylation via the formation of an orthoester
intermediate20 resulting in the formation of disaccharide
acceptor 5 in 90% yield (Scheme 2), which was used in the
block glycosylation step for the preparation of the pentasac-
charide derivative.
OAc
O
OR
O
AcO
O
AcO
OAc
O
O
AcO
AcO
OPMP
O
OBn
AcO
OAc
OAc
e
AcO
To synthesize trisaccharide 15, a number of suitable
functionalized monosaccharide intermediates 9, 10,21 and
1122 were prepared from the reducing sugars following re-
ported reaction conditions in the literature (Scheme 1).
Transformation of L-fucose tetraacetate (6) into 4-methoxy-
phenyl 2,3,4-tri-O-acetyl-β-L-fucopyranoside (7) was car-
ried out in 77% yield by treatment with 4-methoxyphenol
and boron trifluoride–diethyl ether at 0 °C. Compound 7
was subjected to a series of reactions consisting of saponifi-
cation, 3,4-O-isopropylidene ketal formation using 2,2-di-
methoxypropane in the presence of 4-toluenesulfonic
acid,23 benzylation of the remaining hydroxy group using
benzyl bromide and sodium hydroxide,24 acid hydrolysis of
the O-isopropylidene ring, and finally acetylation of the re-
maining hydroxy group to give 4-methoxyphenyl 3,4-di-O-
acetyl-2-O-benzyl-β-L-fucopyranoside (8) in 85% yield.
Compound 8 was transformed into 4-methoxyphenyl 3,4-
di-O-acetyl-β-L-fucopyranoside (9) by hydrogenolysis in
88% yield using hydrogen over Pearlman’s catalyst25
(Scheme 3).
13: R = PMP
16: R = Bn
17: R = H
b
14: R = C(=NH)CCl3
c
a
11
10
OAc
O
OAc
O
AcO
AcO
AcO
AcO
O
O
OR
SEt
O
O
O
O
OAc
OAc
AcO
AcO
O
O
AcO
AcO
AcO
AcO
OAc
OAc
15
18: R = PMP
19: R = C(=NH)CCl3
b
Scheme 4 Reagents and conditions: (a) NIS, TMSOTf, CH2Cl2, 4 Å molec-
ular sieves, –30 °C, 1 h, 88% for 13, 85% for 18; (b) (i) CAN, MeCN–H2O
(4:1), r.t., 2 h; (ii) CCl3CN, DBU, CH2Cl2, –10 °C, 1 h; (c) NOBF4, Et2O–
CH2Cl2 (4:1), – 30 °C, 30 min, 66%; (d) NIS, TMSOTf, Et2O–CH2Cl2 (4:1),
4 Å molecular sieves, –30 °C, 30 min, 76%; (e) H2, 20% Pd(OH)2/C,
MeOH, r.t., 5 h, 86%.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 836–844

839
P. K. Mandal
Paper
Synthesis
Removal of the anomeric 4-methoxyphenyl group of
compound 13 using ammonium cerium(IV) nitrate (CAN)26
in acetonitrile–water (4:1) followed by DBU27 catalyzed re-
action with trichloroacetonitrile furnished 2,3,4-tri-O-ace-
tyl-α-L-rhamnopyranosyl)-(1→2)-3,4-di-O-acetyl-β-L-fuco-
pyranosyl disaccharide trichloroacetimidate donor 14 in
84% overall yield, and it was used directly without further
purification.
Because of its high reactivity, trichloroacetimidate do-
nor 14 was coupled with ethyl 2,4,6-tri-O-acetyl-α-D-man-
nopyranosyl (11) in the presence of nitrosyl tetrafluorobo-
rate28 as a glycosyl activator in the mixed solvent diethyl
ether–dichloromethane (4:1) furnishing trisaccharide thio-
glycoside derivative 15 in 66% moderate yield. Formation of
compound 15 was confirmed from its spectral analysis [δ =
5.28 (br s, 1 H, H1C), 5.09 (d, J = 2.3 Hz, 1 H, H1D), 4.84 (br s,
1 H, H1E) and δ = 95.7 (C1E), 94.7 (C1D), 82.4 (C1C) in the 1H
and 13C NMR spectra, respectively] (Scheme 4).
pound 20 was supported by its spectral analysis [δ = 5.41 (s,
1 H, PhCH), 5.24 (d, J = 8.4 Hz, 1 H, H1A), 4.87 (d, J = 2.3 Hz, 1
H, H1D), 4.77 (d, J = 2.8 Hz, 1 H, H1B), 4.66 (br s, 2 H, H1C,
H1E) and δ = 101.4 (PhCH), 98.9 (C1A), 98.0 (C1B), 97.9 (C1C),
95.5 (C1E), 91.9 (C1D) in the 1H and 13C NMR spectra, respec-
tively]. Finally compound 20 was transformed to the target
compound 1 in overall 51% yield following a sequence of re-
actions consisting of (a) conversion of N-phthaloyl group to
the acetamido group;30 (b) hydrogenolysis using hydrogen
over Pearlmen’s catalyst,25 and (c) saponification using so-
dium methoxide.
5 + 15
5 + 19
b
a
OAc
O
AcO
AcO
O
To circumvent the degradation pathways, an alternative
retrosynthetic analysis was designed for the synthesis of
another type of trisaccharide (Scheme 1). In this approach,
another trisaccharide derivative 18 was synthesized using a
sequential glycosylation strategy via stereoselective glyco-
sylation of monosaccharide intermediates.
AcO
O
O
O
OBn
O
OAc
AcO
AcO
NPhth
O
O
O
O
O
AcO
OAc
Ph
O
N3
20
1
The stereoselective glycosylation of compound 1229
with thioglycoside derivative 3 in the presence of N-iodo-
succinimide/trimethylsilyl triflate18 in the mixed solvent
diethyl ether–dichloromethane (4:1) furnished disaccha-
ride derivative 16 in 76% yield together with a small quanti-
ty (~5%) of its other isomer, which was separated by column
chromatography. Formation of compound 16 was con-
firmed from its spectral analysis [δ = 5.43 (d, J = 1.7 Hz, 1 H,
H1C), 5.02 (d, J = 3.4 Hz, 1 H, H1D) and δ = 96.9 (2 C, C1C, C1D)
in the 1H and 13C NMR spectra, respectively] (Scheme 4).
Hydrogenolysis of compound 16 using hydrogen over
Pearlman’s catalyst25 furnished disaccharide acceptor deriv-
ative 17 in 86% yield. The following iodonium ion mediated
stereoselective coupling of compound 17 with the thiogly-
coside donor 10 in the presence of N-iodosuccinim-
ide/trimethylsilyl triflate18 furnished trisaccharide deriva-
tive 18 in 85% yield. The presence of signals in the NMR
spectra confirmed the formation of compound 18 [δ = 5.42
(d, J = 2.0 Hz, 1 H, H1C), 5.17 (d, J = 2.2 Hz, 1 H, H1D), 4.89 (d,
J = 1.3 Hz, 1 H, H1E) and δ = 96.9 (C1C), 96.5 (C1D), 96.1 (C1E)
in the 1H and 13C NMR spectra, respectively].
Finally the glycosylation of disaccharide acceptor 5 with
thioglycoside trisaccharide donor 15 in the presence of N-
iodosuccinimide/trimethylsilyl triflate18 furnished penta-
saccharide derivative 20 in 78% yield. In another approach
2,3,4-tri-O-acetyl-α-L-rhamnopyranosyl-(1→2)-3,4-di-O-
acetyl-α-L-fucopyranosyl-(1→3)-2,4,6-tri-O-acetyl-α-D-
mannopyranosyl trichloroacetimidate derivative 19 was
glycosylated with disaccharide acceptor 5 in the presence of
nitrosyl tetrafluoroborate28 furnishing pentaasaccharide
derivative 20 in 81% yield (Scheme 5). Formation of com-
c, d, e
Scheme 5 Reagents and conditions: (a) NIS, TMSOTf, CH2Cl2, 4 Å molec-
ular sieves, –10 °C, 1 h, 78%; (b) NOBF4, CH2Cl2, –10 °C, 30 min, 81%; (c)
(i) NH2NH2·H2O, EtOH, 80 °C, 8 h; (ii) Ac2O, pyridine, r.t., 1 h; (d) H2, 20%
Pd(OH)2/C, MeOH, r.t., 12 h; (e) 0.1 M NaOMe, MeOH, r.t., 3 h, 51%
overall yield.
Spectroscopic analysis of compound 1 unambiguously
confirmed its formation [δ = 5.28 (br s, 1 H, H1D), 5.03 (br s,
1 H, H1C, H1B), 5.02 (br s, 1 H, H1E), 4.47 (d, J = 7.4 Hz, 1 H,
H1A) and δ = 101.1 (C1C), 100.5 (C1A), 99.8 (C1B), 98.1 (C1E),
96.1 (C1D) in the 1H and 13C NMR spectra, respectively]
(Scheme 5).
In summary, an efficient synthetic strategy has been de-
veloped for the synthesis of a pentasaccharide (1) as its 2-
aminoethyl glycoside corresponding to the O-antigen of E.
coli O36. Two model trisaccharide donors have been used to
synthesize target compound using complementary glyco-
sylation conditions.
All reactions were monitored by TLC (silica gel coated plates) visual-
ized by warming 2% Ce(SO4)2 in 5% H2SO4 in EtOH sprayed plates on a
hot plate. Silica gel (230–400 mesh) was used for column chromatog-
raphy. 1H and 13C NMR, DEPT 135, 2D COSY, HSQC spectra were re-
corded on Bruker DPX-400 MHz spectrometers using CDCl3 and D2O
as solvents and TMS as internal reference unless stated otherwise.
ESI-MS were recorded on a Jeol spectrometer. Elementary analysis
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 836–844

840
P. K. Mandal
Paper
Synthesis
was carried out on Carlo ERBA analyzer. IR spectra were recorded on
Shimadzu spectrophotometers. Optical rotations were determined on
Autopol III polarimeter. Commercially available grades of organic sol-
vents of adequate purity were used in all reactions.
der reduced pressure and a solution of the crude product in 80% aq
AcOH (40 mL) was stirred at r.t. for 1 h. The solvents were removed
under reduced pressure and the crude product was purified by chro-
matography (silica gel; hexane–EtOAc, 3:1) to give pure 5 (0.85 g,
90%) as a yellow oil; [α]D25 +17 (c 1.0, CHCl3).
2-Azidoethyl O-(3,4-Di-O-acetyl-2-O-benzyl-α-L-fucopyranosyl)-
(1→3)-4,6-O-benzylidene-2-deoxy-2-N-phthalimido-β-D-glucopy-
ranoside (4)
IR (neat): 3429, 3011, 2827, 2127, 1734, 1555, 1323, 1248, 1133,
1102, 979, 782, 698 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.78–7.75 (m, 2 H, HAr), 7.69–7.66 (m,
2 H, HAr), 7.52–7.49 (m, 2 H, HAr), 7.39–7.35 (m, 3 H, HAr), 7.24–7.22
(m, 3 H, HAr), 6.99–6.95 (m, 2 H, HAr), 5.57 (s, 1 H, PhCH), 5.37 (d, J =
8.5 Hz, 1 H, H1A), 5.01 (dd, J = 3.2, 1.2 Hz, 1 H, H4B), 4.87 (d, J = 3.3 Hz,
1 H, H1B), 4.73 (dd, J = 8.6, 1.8 Hz, 1 H, H3A), 4.46–4.39 (m, 2 H, H2A,
H6aA), 4.26 (d, J = 12.4 Hz, 1 H, PhCH2), 4.25–4.22 (m, 1 H, H5B), 4.01–
3.97 (m, 2 H, H6bA, H3B), 3.89 (d, J = 12.5 Hz, 1 H, PhCH2), 3.88–3.84
(m, 1 H, OCH2), 3.76–3.71 (m, 2 H, H5A, H4A), 3.68–3.63 (m, 1 H,
OCH2), 3.39–3.35 (m, 2 H, H2B, CH2N3), 3.23 (ddd, J = 13.3, 4.7, 3.4 Hz,
1 H, CH2N3), 1.98 (s, 3 H, COCH3), 0.70 (d, J = 6.5 Hz, 3 H, CCH3).
13C NMR (100 MHz, CDCl3): δ = 171.0 (COCH3), 168.7, 168.3 (Phth),
137.7–123.4 (CAr), 101.9 (PhCH), 99.0 (C1A), 98.1 (C1B), 81.5 (C4A),
75.5 (C2B), 74.7 (C3A), 73.4 (C4B), 72.3 (PhCH2), 68.7 (OCH2), 68.5
(C6A), 68.0 (C3B), 66.5 (C5A), 65.4 (C5B), 55.8 (C2A), 50.5 (CH2N3), 20.7
(COCH3), 15.6 (CCH3).
Process I: Br2 (56 μL, 1.09 mmol) was added to a solution of ethyl 3,4-
di-O-acetyl-2-O-benzyl-1-thio-β-L-fucopyranoside 3 (236 mg, 0.65
mmol) in CH2Cl2 (4 mL) at 0 C. After 20 min, the solution was con-
centrated and coevaporated with toluene, to which a solution of
compound 2 (100 mg, 0.22 mmol), Et4NBr (104 mg, 0.32 mmol) and 4
Å molecular sieves (100 mg) in anhyd CH2Cl2–DMF (4:1, 1.5 mL) were
added and the mixture was stirred at r.t. After 72 h, TLC showed com-
plete conversion of the starting materials. The crude mixture was
concentrated and purified by column chromatography (silica gel;
hexane–EtOAc, 4:1) to give 4 (95 mg, 56%).
Process II: To a solution of 2 (1 g, 2.15 mmol) and 3 (0.98 g, 2.58
mmol) in anhyd Et2O–CH2Cl2 (4:1, 15 mL) was added 4 Å molecular
sieves (1 g) and the mixture was stirred at r.t. for 30 min under argon
and cooled to –30 °C. To the cooled mixture were added NIS (695 mg,
3.09 mmol) and TMSOTf (10 μL) and the mixture was stirred at this
temperature for 30 min. The mixture was diluted with CH2Cl2 (50 mL)
and filtered through Celite and it was washed with CH2Cl2. The com-
bined organic layers were successively washed with 5% Na2S2O3, sat.
NaHCO3, and water, dried (Na2SO4), and concentrated. The crude
product was purified by chromatography (silica gel; hexane–EtOAc,
4:1) to give pure 4 (1.4 g, 83%) as a yellow oil; [α]D25 +25 (c 1.0, CHCl3).
MS (ESI): m/z = 767.1 [M + Na]+.
Anal. Calcd for C38H40N4O12 (744.26): C, 61.28; H, 5.41. Found: C,
61.17; H, 5.51.
4-Methoxyphenyl 2,3,4-Tri-O-acetyl-β-fucopyranoside (7)
A solution of L-fucose tetraacetate (6, 5 g, 15.1 mmol), 4-methoxyphe-
nol (2.2 g, 18.1 mmol), and 4 Å molecular sieves (2 g) in anhyd CH2Cl2
(30 mL) was cooled to 0 °C. To the cooled reaction was dropwise add-
ed BF3·OEt2 (2.2 ml, 18.1 mmol) and the mixture was stirred this tem-
perature for 3 h. The mixture was diluted with CH2Cl2 (50 mL) and the
organic layer was washed with sat. NaHCO3 and water in succession,
dried (Na2SO4), and evaporated to dryness. The crude product was pu-
rified by chromatography (silica gel; hexane–EtOAc, 4:1) to give pure
7 (4.6 g, 77%) as a colorless liquid; [α]D25 +22 (c 1.0, CHCl3).
IR (neat): 3451, 2924, 2117, 1777, 1742, 1721, 1507, 1387, 1250,
1102, 995, 796 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.71–7.62 (m, 4 H, HAr), 7.53–7.50 (m,
2 H, HAr), 7.39–7.34 (m, 3 H, HAr), 7.22–7.19 (m, 3 H, HAr), 6.91–6.88
(m, 2 H, HAr), 5.58 (s, 1 H, PhCH), 5.33 (d, J = 8.5 Hz, 1 H, H1A), 5.12 (dd,
J = 10.5, 3.3 Hz, 1 H, H3B), 5.07 (dd, J = 3.2, 1.2 Hz, 1 H, H4B), 4.81 (d, J =
3.3 Hz, 1 H, H1B), 4.74 (dd, J = 8.6, 1.8 Hz, 1 H, H3A), 4.45–4.39 (m, 2 H,
H2A, H6aA), 4.27–4.24 (m, 1 H, H5B), 4.08 (d, J = 12.9 Hz, 1 H, PhCH2),
4.03–3.97 (m, 1 H, OCH2), 3.95 (d, J = 12.9 Hz, 1 H, PhCH2), 3.90–3.83
(m, 1 H, H6aA), 3.78–3.70 (m, 2 H, H4A, H5A), 3.69–3.62 (m, 1 H, OCH2),
3.52 (dd, J = 3.5 Hz, 1 H, H2B), 3.38 (ddd, J = 13.3, 8.4, 3.5 Hz, 1 H,
CH2N3), 3.23 (ddd, J = 13.3, 4.7, 3.4 Hz, 1 H, CH2N3), 1.95 (s, 3 H, CO-
CH3), 1.70 (s, 3 H, COCH3), 0.54 (d, J = 6.5 Hz, 3 H, CCH3).
13C NMR (100 MHz, CDCl3): δ = 170.4 (COCH3), 169.6 (COCH3), 168.6,
168.2 (Phth), 137.9–126.5 (CAr), 102.2 (PhCH), 99.1 (C1A), 98.9 (C1B),
81.3 (C4A), 75.1 (C3A), 72.8 (PhCH2), 72.7 (C2B), 71.7 (C4B), 70.4 (C3B),
68.7 (C6A), 68.4 (OCH2), 66.6 (C5A), 64.9 (C5B), 55.7 (C2A), 50.5
(CH2N3), 20.5 (COCH3), 20.4 (COCH3), 15.1 (CCH3).
IR (neat): 2925, 2239, 1750, 1633, 1595, 1440, 1373, 1212, 1048, 760
cm–1
.
1H NMR (400 MHz, CDCl3): δ = 6.95 (d, J = 9.0 Hz, 2 H, HAr), 6.82 (d, J =
9.0 Hz, 2 H, HAr), 5.43 (dd, J = 10.5, 3.0 Hz, 1 H, H3), 5.28 (d, J = 2.5 Hz,
1 H, H4), 5.09 (dd, J = 11.0, 3.5 Hz, 1 H, H2), 4.92 (d, J = 8.0 Hz, 1 H,
H1), 3.92–3.89 (m, 1 H, H5), 3.77 (s, 3 H, OCH3), 2.19 (s, 3 H, COCH3),
2.07 (s, 3 H, COCH3), 2.01 (s, 3 H, COCH3), 1.26 (d, J = 6.5 Hz, 3 H,
CCH3).
13C NMR (100 MHz, CDCl3): δ = 170.8 (COCH3), 170.3 (COCH3), 169.6
(COCH3), 155.6–114.6 (CAr), 100.7 (C1), 71.3 (C4), 70.1 (C2), 69.4 (C3),
68.9 (C5), 55.6 (OCH3), 20.8 (COCH3), 20.7 (COCH3), 20.6 (COCH3), 16.2
(CCH3).
MS (ESI): m/z = 809.1 [M + Na]+.
Anal. Calcd for C40H42N4O13 (786.27): C, 61.06; H, 5.38. Found: C,
60.92; H, 5.49.
MS (ESI): m/z = 419.0 [M + Na]+.
Anal. Calcd for C19H24O9 (396.14): C, 57.57; H, 6.10. Found: C, 57.45;
H, 6.25.
2-Azidoethyl O-(4-O-Acetyl-2-O-benzyl-α-L-fucopyranosyl)-(1→3)-
4,6-O-benzylidene-2-deoxy-2-N-phthalimido-β-D-glucopyrano-
side (5)
4-Methoxyphenyl 3,4-Di-O-acetyl-2-O-benzyl-β-L-fucopyranoside
A solution of 4 (1 g, 1.27 mmol) in 0.1 M NaOMe in MeOH (20 mL) was
stirred at r.t. for 1 h. The mixture was neutralized with Dowex 50W-
X8 (H+) resin, filtered, and evaporated to dryness. To a solution of the
de-O-acetylated product in anhyd DMF (30 mL) was added triethyl or-
thoacetate (0.35 mL, 1.91 mmol) followed by TsOH (100 mg) and the
mixture was stirred at r.t. for 2 h. The mixture was concentrated un-
(8)
A solution of 7 (4 g, 10.1 mmol) in 0.1 M NaOMe in MeOH (30 mL) was
stirred at r.t. for 2 h. The mixture was neutralized with Dowex 50W-
X8 (H+) resin, filtered, and evaporated to dryness. To a solution of the
de-O-acetylated product in anhyd DMF (30 mL) were added 2,2-di-
methoxypropane (1.9 mL, 15.2 mmol) and TsOH (150 mg) and the
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P. K. Mandal
Paper
Synthesis
mixture was stirred at r.t. for 6 h. To the mixture were added pow-
dered NaOH (804 mg, 20.1 mmol), BnBr (1.4 mL, 12.0 mmol) and
TBAB (3.9 g, 12.0 mmol) the mixture was stirred at r.t. for 5 h. The
mixture was poured into water (200 mL) and extracted with EtOAc
(100 mL). The organic layer was washed with water, dried (Na2SO4),
and concentrated. A solution of the crude product in 80% aq AcOH (80
mL) was stirred at 80 °C for 1.5 h. The solvents were removed under
reduced pressure and co-evaporated with toluene. To a solution of the
crude product in anhyd pyridine (20 mL), Ac2O (5 mL) was added and
the solution was stirred at r.t. for 3 h when TLC (hexane–EtOAc, 6:1)
showed complete conversion of the starting material to a faster mov-
ing spot. The solvents were evaporated in vacuo and co-evaporated
with toluene to remove residual pyridine. The syrupy residue thus ob-
tained was purified by chromatography (silica gel; hexane–EtOAc,
8:1) to give pure 8 (3.8 g, 85% overall) as a yellow oil; [α]D25 +37 (c 1.0,
CHCl3).
cooled to –30 °C. To the cooled mixture were added NIS (1.8 g, 8.13
mmol) and TMSOTf (30 μL) and the mixture was stirred at this tem-
perature for 1 h. The mixture was diluted with CH2Cl2 (50 mL) and fil-
tered through Celite and it was washed with CH2Cl2. The combined
organic layers were successively washed with 5% Na2S2O3, sat.
NaHCO3, and water, dried (Na2SO4), and concentrated. The crude
product was purified by chromatography (silica gel; hexane–EtOAc,
6:1) to give pure 13 (3.1 g, 88%) as a yellow oil; [α]D25–39 (c 1.0,
CHCl3).
IR (neat): 3445, 2918, 1863, 1736, 1507, 1452, 1263, 1052, 1068,
1026, 709 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.01 (d, J = 9.1 Hz, 2 H, HAr), 6.80 (d, J =
9.1 Hz, 2 H, HAr), 5.28–5.26 (m, 2 H, H3D, H3E), 5.25 (br s, 1 H, H1E),
5.17 (dd, J = 10.0, 3.2 Hz, 1 H, H4E), 5.08–5.04 (m, 1 H, H2E), 5.01 (dd,
J = 10.2, 3.3 Hz, 1 H, H4D), 4.86 (d, J = 7.8 Hz, 1 H, H1D), 4.08 (dd, J =
10.2, 7.8 Hz, 1 H, H2D), 4.03–3.96 (m, 1 H, H5E), 3.90–3.85 (m, 1 H,
H5D), 3.75 (s, 3 H, OCH3), 2.16 (s, 3 H, COCH3), 2.14 (s, 3 H, COCH3),
2.02 (s, 3 H, COCH3). 2.01 (s, 3 H, COCH3), 1.95 (s, 3 H, COCH3), 1.23 (d,
J = 6.4 Hz, 3 H, CCH3), 1.21 (d, J = 6.4 Hz, 3 H, CCH3).
13C NMR (100 MHz, CDCl3): δ = 170.6 (COCH3), 169.9 (COCH3), 169.8
(COCH3), 169.7 (2 C, COCH3), 155.8–114.6 (CAr), 102.8 (C1D), 97.9
(C1E), 73.6 (C2D), 71.9 (C4D), 70.9 (C2E), 70.4 (C3D), 69.6 (C3E), 69.1
(C5D), 68.9 (C4E), 66.6 (C5E), 55.6 (OCH3), 20.8 (COCH3), 20.7 (COCH3),
20.6 (3 C, COCH3), 17.4 (CCH3), 16.1 (CCH3).
IR (neat): 2925, 2339, 1750, 1663, 1595, 1440, 1373, 1222, 1048, 760
cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.32–7.29 (m, 5 H, HAr), 7.02 (d, J = 9.0
Hz, 2 H, HAr), 6.83 (d, J = 9.0 Hz, 2 H, HAr), 5.25 (d, J = 2.5 Hz, 1 H, H4),
5.05 (dd, J = 10.5, 3.0 Hz, 1 H, H3), 4.97 (d, J = 8.0 Hz, 1 H, H1), 4.93 (d,
J = 11.6 Hz, 1 H, PhCH2), 4.73 (d, J = 11.6 Hz, 1 H, PhCH2), 3.89–3.84 (m,
2 H, H5, H2), 3.78 (s, 3 H, OCH3), 2.16 (s, 3 H, COCH3), 1.98 (s, 3 H,
COCH3), 1.24 (d, J = 6.5 Hz, 3 H, CCH3).
13C NMR (100 MHz, CDCl3): δ = 170.6 (COCH3), 170.1 (COCH3), 155.5–
114.6 (CAr), 103.0 (C1), 76.3 (C2), 74.9 (C3), 72.7 (PhCH2), 70.6 (C4),
69.1 (C5), 55.7 (OCH3), 20.7 (2 C, COCH3), 16.2 (CCH3).
MS (ESI): m/z = 649.1 [M + Na]+.
Anal. Calcd for C29H38O15 (626.22): C, 55.59; H, 6.11. Found: C, 55.42;
H, 6.23.
MS (ESI): m/z = 467.1 [M + Na]+.
Anal. Calcd for C24H28O8 (444.17): C, 64.85; H, 6.35. Found: C, 64.72;
H, 6.47.
Ethyl O-(2,3,4-Tri-O-acetyl-α-L-rhamnopyranosyl)-(1→2)-O-(3,4-
di-O-acetyl-α-L-fucopyranosyl)-(1→3)-2,4,6-tri-O-acetyl-1-thio-α-
D-mannopyranoside (15)
4-Methoxyphenyl 3,4-Di-O-acetyl-β-L-fucopyranoside (9)
To a solution of 13 (3 g, 4.79 mmol) in MeCN–H2O (4:1, 40 mL) was
added CAN (3.2 g, 5.75 mmol) and the mixture stirred at r.t. for 2 h.
The mixture was diluted with CH2Cl2 (70 mL) and the organic layer
was washed with sat. NaHCO3 and water, dried (Na2SO4), and evapo-
rated to dryness to give disaccharide hemiacetal. To a solution of the
hemiacetal in anhyd CH2Cl2 (30 mL) was added trichloroacetonitrile
(0.72 mL, 7.2 mmol) and the mixture was cooled to –10 °C. To the
cooled mixture was added DBU (0.2 mL, 1.3 mmol) and it was stirred
at –10 °C for 1 h. The mixture was evaporated to dryness and the
crude product was passed through a short pad of silica gel to give
2,3,4-tri-O-acetyl-α-L-rhamnopyranosyl)-(1→2)-3,4-di-O-acetyl-β-L-
fucopyranosyl trichloroacetimidate (14; 2.6 g, 84%). A solution of 11
(1.0 g, 2.9 mmol) and 14 (2.3 g, 3.4 mmol) in anhyd Et2O–CH2Cl2 (4:1,
30 mL) was cooled to –30 °C. To the cooled mixture was added NOBF4
(119 mg, 1.02 mmol) and it was stirred at –30 °C for 30 min. The mix-
ture was diluted with CH2Cl2 (50 mL) and the organic layer was
washed with sat. NaHCO3 and water in succession, dried (Na2SO4),
and evaporated to dryness. The crude product was purified by chro-
matography (silica gel; hexane–EtOAc, 3:1) to give pure 15 (1.6 g,
66%) as a yellow oil; [α]D25– 28 (c 1.0, CHCl3).
To a solution of 8 (3.0 g, 6.76 mmol) in MeOH (20 mL) was added 20%
Pd(OH)2/C (100 mg) and the mixture was stirred at r.t. for 4 h under a
positive pressure of H2. The mixture was filtered through Celite, the
filter bed was washed with MeOH (20 mL), and the combined filtrates
were concentrated under reduced pressure. The crude product was
purified by chromatography (silica gel; hexane–EtOAc, 4:1) to give
pure 9 (2.1 g, 88%) as a colorless oil; [α]D25 +28 (c 1.0, CHCl3).
IR (neat): 2925, 2349, 1760, 1653, 1595, 1430, 1373, 1232, 1048, 767
cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.03 (d, J = 9.0 Hz, 2 H, HAr), 6.84 (d, J =
9.0 Hz, 2 H, HAr), 5.27 (dd, J = 10.5, 3.0 Hz, 1 H, H3), 5.00 (d, J = 2.5 Hz,
1 H, H4), 4.83 (d, J = 7.6 Hz, 1 H, H1), 4.06–4.01 (m, 1 H, H5), 3.92–3.88
(m, 1 H, H2), 3.78 (s, 3 H, OCH3), 2.18 (s, 3 H, COCH3), 2.07 (s, 3 H,
COCH3), 1.24 (d, J = 6.5 Hz, 3 H, CCH3).
13C NMR (100 MHz, CDCl3): δ = 170.7 (COCH3), 170.5 (COCH3), 155.6–
114.6 (CAr), 102.5 (C1), 72.9 (C2), 70.3 (C3), 69.4 (C4), 68.9 (C5), 55.6
(OCH3), 20.8 (COCH3), 20.6 (COCH3), 16.2 (CCH3).
MS (ESI): m/z = 377.1 [M + Na]+.
IR (neat): 3447, 2929, 2231, 1722, 1718, 1452, 1386, 1265, 1094, 957,
Anal. Calcd for C17H22O8 (354.13): C, 57.62; H, 6.26. Found: C, 57.48;
H, 6.38.
710 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 5.37–5.36 (m, 1 H, H2C), 5.31–5.29 (m,
2 H, H3D, H3E), 5.28 (br s, 1 H, H1C), 5.22–5.21 (m, 1 H, H4E), 5.20–5.12
(m, 2 H, H4C, H2E), 5.09 (d, J = 2.3 Hz, 1 H, H1D), 5.07–5.05 (m 1 H,
H4D), 4.84 (br s, 1 H, H1E), 4.30–4.26 (m, 2 H, H5C, H6aC), 4.18–4.12 (m,
2 H, H3C, H5D), 4.11–4.07 (m, 3 H, H6bC, H2D, H5E), 2.66–2.62 (m, 2 H,
SCH2CH3), 2.17 (s, 3 H, COCH3), 2.15 (s, 3 H, COCH3), 2.13 (s, 3 H, CO-
4-Methoxyphenyl O-(2,3,4-Tri-O-acetyl-α-L-rhamnopyranosyl)-
(1→2)-3,4-di-O-acetyl-α-L-fucopyranoside (13)
To a solution of 9 (2.0 g, 5.65 mmol) and 10 (2.3 g, 6.78 mmol) in an-
hyd CH2Cl2 (50 mL) was added 4 Å molecular sieves (2.0 g) and the
mixture was stirred at r.t. for 30 min under argon. The mixture was
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 836–844

842
P. K. Mandal
Paper
Synthesis
CH3), 2.12 (s, 3 H, COCH3), 2.09 (s, 3 H, COCH3), 2.02 (s, 3 H, COCH3),
1.99 (s, 3 H, COCH3), 1.96 (s, 3 H, COCH3), 1.29 (t, J = 7.4 Hz, 3 H,
SCH2CH3), 1.19 (d, J = 6.4 Hz, 3 H, CCH3), 1.12 (d, J = 6.4 Hz, 3 H, CCH3).
13C NMR (100 MHz, CDCl3): δ = 170.6 (COCH3), 170.3 (COCH3), 169.9
(2 C, COCH3), 169.8 (COCH3), 169.6 (COCH3), 169.5 (COCH3), 169.4
(COCH3), 95.7 (C1E), 94.7 (C1D), 82.4 (C1C), 73.1 (C2D), 71.4 (C3D), 70.8
(C4D), 69.8 (C2E), 69.6 (C2C), 69.3 (C4E), 69.2 (C5C), 69.0 (C3C), 68.5
(C4C), 67.6 (C3E), 66.4 (C5E), 65.1 (C5D), 62.6 (C6C), 25.5 (SCH2CH3),
20.9 (COCH3), 20.8 (COCH3), 20.7 (COCH3), 20.6 (COCH3), 20.5 (2 C, CO-
CH3), 20.5 (2 C, COCH3), 17.1 (SCH2CH3), 15.7 (CCH3), 14.8 (CCH3).
IR (neat): 3077, 2836, 1742, 1645, 1510, 1395, 1259, 1173, 1062, 989,
823, 678 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.02 (d, J = 9.2 Hz, 2 H, HAr), 6.84 (d, J =
9.2 Hz, 2 H, HAr), 5.55 (d, J = 1.6 Hz, 1 H, H2C), 5.43 (br s, 1 H, H1C), 5.32
(t, J = 9.9 Hz, 1 H, H4C), 5.22 (d, J = 2.2 Hz, 1 H, H4D), 5.07 (d, J = 3.4 Hz,
1 H, H1D), 4.94 (dd, J = 10.5, 3.3 Hz, 1 H, H3D), 4.33–4.25 (m, 2 H, H3C,
H6aC), 4.13–4.08 (m, 3 H, H5C, H5D, H6bC), 3.97–3.93 (m, 1 H, H2D),
3.79 (s, 3 H, OCH3), 2.25 (s, 3 H, COCH3), 2.17 (s, 3 H, COCH3), 2.13 (s, 3
H, COCH3), 2.07 (s, 3 H, COCH3), 2.06 (s, 3 H, COCH3), 1.13 (d, J = 6.4 Hz,
3 H, CCH3).
MS (ESI): m/z = 875.1 [M + Na]+.
13C NMR (100 MHz, CDCl3): δ = 171.6 (COCH3), 170.6 (2 C, COCH3),
170.5 (COCH3), 169.8 (COCH3), 155.5–114.7 (CAr), 98.4 (C1D), 96.9
(C1C), 77.1 (C3C), 71.3 (C4D), 70.4 (C3D), 69.5 (C2C), 68.9 (C5C), 67.4
(C4C), 66.8 (C2D), 66.1 (C5D), 62.3 (C6C), 55.7 (OCH3), 21.1 (COCH3),
20.9 (COCH3), 20.8 (COCH3), 20.7 (COCH3), 20.6 (COCH3), 15.9 (CCH3).
Anal. Calcd for C36H52O21S (852.27): C, 50.70; H, 6.15. Found: C, 50.53;
H, 6.28.
4-Methoxyphenyl O-(3,4-Di-O-acetyl-2-O-benzyl-α-L-fucopyrano-
syl)-(1→3)-2,4,6-tri-O-acetyl-α-D-mannopyranoside (16)
MS (ESI): m/z = 665.1 [M + Na]+.
Anal. Calcd for C29H38O16 (642.21): C, 54.20; H, 5.96. Found: C, 54.08;
H, 6.07.
To a solution of 12 (2 g, 4.85 mmol) and 3 (2.23 g, 5.83 mmol) in an-
hyd Et2O–CH2Cl2 (4:1, 30 mL) was added 4 Å molecular sieves (1 g)
and the mixture was stirred at r.t. for 30 min under argon and cooled
to –30 °C. To the cooled mixture were added NIS (1.6 g, 6.99 mmol)
and TMSOTf (30 μL) and it was stirred at this temperature for 30 min.
The mixture was diluted with CH2Cl2 (50 mL) and filtered through
Celite and it was washed with CH2Cl2. The combined organic layers
were successively washed with 5% Na2S2O3, sat. NaHCO3, and water,
dried (Na2SO4), and concentrated. The crude product was purified by
chromatography (silica gel; hexane–EtOAc, 4:1) to give pure 16 (2.7 g,
76%) as a yellow oil; [α]D25 –14 (c 1.0, CHCl3).
4-Methoxyphenyl O-(2,3,4-Tri-O-acetyl-α-L-rhamnopyranosyl)-
(1→2)-O-(3,4-di-O-acetyl-α-L-fucopyranosyl)-(1→3)-2,4,6-tri-O-
acetyl-α-D-mannopyranoside (18)
To a solution of 17 (1 g, 1.56 mmol) and 10 (0.62 g, 1.87 mmol) in an-
hyd CH2Cl2 (10 mL) was added 4 Å molecular sieves (500 mg) and the
mixture was stirred under argon at r.t. for 30 min and cooled to –30
°C. To the cooled mixture were added NIS (505 mg, 2.24 mmol) and
TMSOTf (10 μL) and it was stirred at this temperature for 1 h. The
mixture was filtered through Celite and it was washed with CH2Cl2
(50 mL). The combined organic layers were successively washed with
5% Na2S2O3, sat. NaHCO3, and water, dried (Na2SO4), and concentrated.
The crude product was purified by chromatography (silica gel; hex-
IR (neat): 3057, 2856, 1712, 1625, 1520, 1365, 1229, 1173, 1097, 989,
911, 823, 745, 697 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.36–7.28 (m, 5 H, HAr), 7.01 (d, J = 9.2
Hz, 2 H, HAr), 6.84 (d, J = 9.2 Hz, 2 H, HAr), 5.48–5.47 (m, 1 H, H2C), 5.43
(d, J = 1.7 Hz, 1 H, H1C), 5.37 (t, J = 9.9 Hz, 1 H, H4C), 5.28 (dd, J = 3.3,
1.2 Hz, 1 H, H4D), 5.23 (dd. J = 10.5, 3.3 Hz, 1 H, H3D), 5.02 (d, J = 3.4
Hz, 1 H, H1D), 4.62 (br s, 2 H, PhCH2), 4.29 (dd, J = 9.8, 3.4 Hz, 1 H, 3C),
4.24–4.19 (m, 2 H, 6aC, H5D), 4.14–4.04 (m, 2 H, H6bC, H5C), 3.83 (dd,
J = 10.4, 3.4 Hz, 1 H, H2D), 3.78 (s, 3 H, OCH3), 2.14 (s, 3 H, COCH3),
2.11 (s, 3 H, COCH3), 2.04 (s, 3 H, COCH3), 2.01 (s, 3 H, COCH3), 1.94 (s,
3 H, COCH3), 1.14 (d, J = 6.4 Hz, 3 H, CCH3).
13C NMR (100 MHz, CDCl3): δ = 170.6 (2 C, COCH3), 170.4 (COCH3),
169.9 (COCH3), 169.6 (COCH3), 155.4–114.6 (CAr), 96.9 (2 C, C1C, C1D),
73.4 (PhCH2), 73.2 (C2D), 73.1 (C3C), 71.5 C4D), 70.1 (C3D), 69.3 (C5C),
68.6 (C2C), 67.4 (C4C), 65.2 (C5D), 62.5 (C6C), 55.7 (OCH3), 20.8 (2 C,
COCH3), 20.7 (2 C, COCH3), 20.6 (COCH3), 15.9 (CCH3).
25
ane–EtOAc, 3:1) to give pure 18 (1.2 g, 85%) as a colorless oil; [α]D
–26 (c 1.0, CHCl3).
IR (neat): 3027, 2806, 1762, 1615, 1509, 1355, 1239, 1173, 1042, 989,
813, 677 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.01 (d, J = 9.2 Hz, 2 H, HAr), 6.81 (d, J =
9.2 Hz, 2 H, HAr), 5.54–5.53 (m, 1 H, H2C), 5.42 (d, J = 2.0 Hz, 1 H, H1C),
5.41–5.39 (m, 1 H, H4C), 5.31–5.30 (m, 1 H, H4E), 5.28–5.25 (m, 1 H,
H3E), 5.21 (dd, J = 10.5, 3.3 Hz, 1 H, H3D), 5.17 (d, J = 2.2 Hz, 1 H, H1D),
5.16–5.15 (m, 1 H, H2E), 5.10–5.05 (m, 1 H, H4D), 4.89 (d, J = 1.3 Hz, 1
H, H1E), 4.34 (dd, J = 9.8, 3.4 Hz, 1 H, 3C), 4.27–4.23 (m, 2 H, H6aC, H5D),
4.15 (dd, J = 10.4, 3.4 Hz, 1 H, H2D), 4.12–4.04 (m, 3 H, H5E, H6bC, H5C),
3.77 (s, 3 H, OCH3), 2.20 (s, 3 H, COCH3), 2.17 (s, 3 H, COCH3), 2.15 (s, 3
H, COCH3), 2.13 (s, 3 H, COCH3), 2.05 (s, 3 H, COCH3), 2.01 (s, 6 H, CO-
CH3), 1.89 (s, 3 H, COCH3), 1.21 (d, J = 6.5 Hz, 3 H, CCH3), 1.14 (d, J = 6.5
Hz, 3 H, CCH3).
13C NMR (100 MHz, CDCl3): δ = 170.6 (COCH3), 170.4 (COCH3), 170.2
(COCH3), 170.0 (COCH3), 169.9 (COCH3), 169.6 (COCH3), 155.4–114.5
(CAr), 96.9 (C1C), 96.5 (C1D), 96.1 (C1E), 74.1 (C3C), 71.5 (C4E), 70.7
(C4D), 70.5 (C2D), 69.9 (C3E), 69.4 (C5C), 68.9 (C3D), 68.8 (C2C), 68.6
(C2E), 67.5 (C4C), 66.6 (C5E), 65.5 (C5D), 62.4 (C6C), 55.6 (OCH3), 20.9 (2
C. COCH3), 20.7 (3 C, COCH3), 20.6 (2 C, COCH3), 20.5 (COCH3), 17.2
(CCH3), 15.8 (CCH3).
MS (ESI): m/z = 755.1 [M + Na]+.
Anal. Calcd for C36H44O16 (732.26): C, 59.01; H, 6.05. Found: C, 58.89;
H, 6.17.
4-Methoxyphenyl O-(3,4-Di-O-acetyl-α-L-fucopyranosyl)-(1→3)-
2,4,6-tri-O-acetyl-α-D-mannopyranoside (17)
To a solution of 16 (2.0 g, 2.73 mmol) in MeOH (50 mL) was added
20% Pd(OH)2/C (500 mg) and the mixture was stirred at r.t. for 5 h un-
der a positive pressure of H2. The mixture was filtered through Celite,
it was washed with MeOH (40 mL), and the combined filtrates were
concentrated under reduced pressure. The crude product was purified
by chromatography (silica gel; hexane–EtOAc, 3:1) to give pure 17
(1.5 g, 86%) as a colorless oil; [α]D25 –24 (c 1.0, CHCl3).
MS (ESI): m/z = 937.2 [M + Na]+.
Anal. Calcd for C41H54O23 (914.31): C, 53.83; H, 5.95. Found: C, 53.71;
H, 6.08.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 836–844

843
P. K. Mandal
Paper
Synthesis
2-Azidoethyl O-(2,3,4-Tri-O-acetyl-α-L-rhamnopyranosyl)-(1→2)-
O-(3,4-di-O-acetyl-α-L-fucopyranosyl)-(1→3)-O-(2,4,6-tri-O-ace-
tyl-α-D-mannopyranosyl)-(1→3)-O-(4-O-acetyl-2-O-benzyl-α-L-
fucopyranosyl)-(1→3)-4,6-O-benzylidene-2-deoxy-2-N-phthali-
mido-β-D-glucopyranoside (20)
68.5 (C3B), 67.8 (C3C), 66.9 (C4C), 66.5 (C3E),, 66.3 (C5A), 66.0 (C5D),
65.7 (C5B), 64.5 (C5E), 62.9 (C6C), 55.2 (C2A), 50.4 (CH2N3), 20.9 (2 C,
COCH3), 20.7 (2 C, COCH3), 20.6 (COCH3), 20.5 (2 C, COCH3), 20.5 (2 C,
COCH3), 17.1 (CCH3), 15.7 (CCH3), 15.5 (CCH3).
MS (ESI): m/z = 1557.3 [M + Na]+.
Process I: To a solution of 5 (500 mg, 0.67 mmol) and 15 (687 mg, 0.81
mmol) in anhyd CH2Cl2 (20 mL) was added 4 Å molecular sieves (500
mg) and the mixture was stirred under argon at r.t. for 30 min and
cooled to –10 °C. To the cooled mixture were added NIS (217 mg, 0.97
mmol) and TMSOTf (10 μL) and it was stirred at this temperature for 1
h. The mixture was filtered through Celite and it was washed with
CH2Cl2 (50 mL). The combined organic layers were successively
washed with 5% Na2S2O3, sat. NaHCO3, and water, dried (Na2SO4), and
concentrated. The crude product was purified by chromatography
(silica gel; hexane–EtOAc, 1:1) to give pure 20 (800 mg, 78%).
Anal. Calcd for C72H86N4O33 (1534.51): C, 56.32; H, 5.65. Found: C,
56.18; H, 5.79.
2-Aminoethyl O-(α-L-Rhamnopyranosyl)-(1→2)-O-(α-L-fucopyra-
nosyl)-O-(1→3)-(α-D-mannopyranosyl)-(1→3)-O-(α-L-fucopyrano-
syl)-(1→3)-2-acetamido-2-deoxy-β-D-glucopyranoside (1)
To a solution of 20 (300 mg, 0.19 mmol) in EtOH (10 mL) was added
hydrazine hydrate (2 mL) and the mixture was stirred at 80 °C for 8 h.
The solvents were removed under reduced pressure and a solution of
the crude mass in pyridine (5 mL) and Ac2O (5 mL) was kept at r.t. for
1 h. The solvents were evaporated and co-evaporated with toluene
under reduced pressure. To a solution of the acetylated product in
MeOH (20 mL) was added 20% Pd(OH)2/C (200 mg) and the mixture
was stirred at r.t. under a positive pressure of H2 for 12 h. The mixture
was filtered through Celite, it was washed with MeOH (20 mL), and
the combined filtrates were concentrated under reduced pressure. A
solution of the hydrogenated product in 0.1 M NaOMe in MeOH (10
mL) was stirred at r.t. for 3 h. The mixture was neutralized with
Dowex 50W-X8 (H+) resin, filtered, and concentrated. The crude prod-
uct was passed through a Sephadex LH20 column (MeOH–H2O, 3:1) to
give pure 1 (85 mg, 51%) as a white powder; [α]D25 +10 (c 1.0, H2O).
Process II: To a solution of 18 (1 g, 1.09 mmol) in MeCN–H2O (4:1, 20
mL) was added CAN (0.72 g, 1.31 mmol) and the mixture was stirred
at r.t. for 2 h. The mixture was diluted with CH2Cl2 (40 mL) and the
organic layer was washed with sat. NaHCO3 and water, dried (Na2SO4),
and evaporated to dryness to give the disaccharide hemiacetal. To a
solution of the hemiacetal in anhyd CH2Cl2 (30 mL) was added trichlo-
roacetonitrile (0.16 mL, 1.6 mmol) and the mixture was cooled to –10
°C. To the cooled mixture was added DBU (0.2 mL, 1.3 mmol) and it
was stirred at –10 °C for 1 h. The mixture was evaporated to dryness
and the crude product was passed through a short pad of silica gel to
give 2,3,4-tri-O-acetyl-α-L-rhamnopyranosyl-(1→2)-3,4-di-O-acetyl-
α-L-fucopyranosyl-(1→3)-2,4,6-tri-O-acetyl-α-D-mannopyranosyl
trichloroacetimidate (19; 0.90 g, 87%). A solution of 5 (500 mg, 0.67
mmol) and 19 (764 mg, 0.80 mmol) in anhyd CH2Cl2 (30 mL) was
cooled to –10 °C. To the cooled mixture was added NOBF4 (28 mg, 0.24
mol) and it was stirred at –10 °C for 30 min. The mixture was diluted
with CH2Cl2 (50 mL) and the organic layer was washed with sat. NaH-
CO3 and water in succession, dried (Na2SO4), and evaporated to dry-
ness. The crude product was purified by chromatography (silica gel;
hexane–EtOAc, 1:1) to give pure 20 (850 mg, 81%) as a colorless oil;
[α]D25 +12 (c 1.0, CHCl3).
IR (KBr): 3456, 2935, 2722, 2117, 1622, 1356, 1256, 1165, 1067, 697
cm–1
.
1H NMR (400 MHz, D2O): δ = 5.28 (br s, 1 H, H1D), 5.03 (br s, 1 H, H1C,
H1B), 5.02 (br s, 1 H, H1E), 4.47 (d, J = 7.4 Hz, 1 H, H1A), 4.33–4.23 (m,
2 H, H5D, H5B), 4.22–4.11 (m, 3 H, H2C, H3C, H5C), 4.10–3.84 (m, 6 H,
H3D, OCH2, H2E, H5E, H6aA, H2A), 3.78–3.70 (m, 8 H, H6bA, H6abC, OCH2,
H3A, H2D, H2B, H4D,), 3.69–3.60 (m, 3 H, H4B, H3E, H4C), 3.51–3.39 (m,
2 H, H4E, H4A), 3.35–3.25 (m, 2 H, H3B, H5A), 3.24–3.21 (m, 1 H,
CH2N3), 3.13–3.02 (m, 1 H, CH2N3), 1.95 (s, 3 H, COCH3), 1.21 (d, J = 6.4
Hz, 3 H, CCH3), 1.17 (d, J = 6.4 Hz, 3 H, CCH3), 1.12 (d, J = 6.4 Hz, 3 H,
CCH3).
IR (neat): 3029, 2834, 2210, 2127, 1849, 1628, 1415, 1322, 1250,
1042, 988, 756, 667 cm–1
.
13C NMR (100 MHz, D2O): δ = 175.9 (COCH3), 101.1 (C1C), 100.5 (C1A),
99.8 (C1B), 98.1 (C1E), 96.1 (C1D), 80.1 (C3A), 76.2 (C3B), 75.4 (C5A),
73.2 (C3C), 72.2 (2 C, C4C, C4D), 72.0 (C4E), 70.6 (C4B), 70.3 (C5C), 70.1
(C2D), 69.0 (C2E), 68.9 (2 C, C3E, C4A), 67.2 (C5B), 67.0 (C5D), 66.6 (C2B),
66.4 (C2C), 65.7 (2 C, C5E, C3D), 65.3 (OCH2), 60.8 (C6A), 60.7 (C6C), 57.2
(C2A), 39.9 (CH2N3), 23.2 (COCH3), 16.8 (CCH3), 15.1 (2 C, CCH3).
1H NMR (400 MHz, CDCl3): δ = 7.35–7.33 (m, 2 H, HAr), 7.20–7.12 (m,
8 H, HAr), 7.06–7.04 (m, 2 H, HAr), 5.41 (s, 1 H, PhCH), 5.24 (d, J = 8.4
Hz, 1 H, H1A), 5.13–5.13 (m, 2 H, H2C, H3D), 5.05 (m, 2 H, H3E, H4E),
4.93 (dd, J = 3.2, 1.2 Hz, 1 H, H4B), 4.90–4.88 (m, 1 H, H2E), 4.87 (d, J =
2.3 Hz, 1 H, H1D), 4.86–4.84 (m, 4 H, PhCH2, H4C, H4D), 4.77 (d, J = 2.8
Hz, 1 H, H1B), 4.66 (br s, 2 H, H1C, H1E), 4.42 (dd, J = 8.6, 1.8 Hz, 1 H,
H3A), 4.29–4.17 (m, 3 H, H6aA, H6aC, H2A), 4.15–4.059 (m, 4 H, H3C,
MS (ESI): m/z = 865.2 [M + H]+.
H5E, H5C, H2D), 3.99–3.91 (m, 2 H, H6bC, H5B), 3.84–3.72 (m, 5 H, H6bA
,
Anal. Calcd for C34H60N2O23 (864.36): C, 47.22; H, 6.99. Found: C,
47.08; H, 7.12.
H5D, H3B, OCH2, H5A), 3.54–3.48 (m, 2 H, H4A, OCH2), 3.35 (m, 1 H,
H2B), 3.22–3.17 (m, 1 H, CH2N3), 3.06–3.03 (m, 1 H, CH2N3), 2.02 (s, 3
H, COCH3), 1.99 (s, 3 H, COCH3), 1.96 (s, 6 H, COCH3), 1.84 (s, 9 H,
COCH3), 1.82 (s, 3 H, COCH3), 1.78 (s, 3 H, COCH3), 1.02 (d, J = 6.4 Hz, 6
H, CCH3), 0.74 (d, J = 6.4 Hz, 3 H, CCH3).
Acknowledgment
13C NMR (100 MHz, CDCl3): δ = 170.9 (COCH3), 170.7 (COCH3), 170.3
(COCH3), 169.9 (COCH3), 169.8 (2 C, COCH3), 169.7 (2 C, COCH3), 169.5
(COCH3), 168.9, 168.7 (Phth), 155.1–114.5 (CAr), 101.4 (PhCH), 98.9
(C1A), 98.0 (C1B), 97.9 (C1C), 95.5 (C1E), 91.9 (C1D), 82.2 (C4A), 76.4
(C2B), 75.9 (C3A), 73.1 (C4B), 72.5 (PhCH2), 71.7 (C2D), 70.8 (C3D), 70.7
(C4D), 69.7 (C2E), 69.5 (C2C), 69.4 (2 C, C4E, C5C), 68.6 (2 C, OCH2, C6A),
Author gratefully acknowledges financial support by Department of
Science and Technology (DST), India under Fast Track Proposal
Scheme for Young Scientists (CS-127/2012) and SAIF Division of CSIR-
CDRI for providing the spectroscopic and analytical data. CDRI com-
munication no. 8863.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 836–844

844
P. K. Mandal
Paper
Synthesis
Supporting Information
5143. (c) Mandal, P. K.; Dhara, D.; Misra, A. K. Beilstein J. Org.
Chem. 2014, 10, 293. (d) Mandal, P. K.; Dhara, D.; Misra, A. K.
Synthesis 2014, 46, 1947.
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1379952. Included are copies of 1D
and 2D NMR spectra of compounds 1, 4, 5, 7, 8, 9, 13, 15, 16, 17, 18,
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S
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p
p
ortiInfogrmoaitn
S
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p
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nrtIo
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 836–844