Studies on the sialylation of galactoses with different C-5 modified sialyl donors

Article abstract of DOI:10.1016/j.carres.2012.08.007

Synthetic sialylated glycans provide useful tools to study carbohydrate-mediated biological recognition; however chemical sialylation is the most challenging practice in preparative carbohydrate chemistry, which is often associated with low yields and poor stereoselectivity. Herein, we conducted extensive studies on sialylation with five types of 5-N-modified sialyl donors and four types of galactosyl acceptors. Our studies have shown that a good combination between the donor and the acceptor seems necessary to achieve high yield and stereoselectivity. None of the donors or acceptors showed 'universal' utility toward the sialylation reaction.

Full text of DOI:10.1016/j.carres.2012.08.007

Carbohydrate Research 361 (2012) 91–99
Contents lists available at SciVerse ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Studies on the sialylation of galactoses with different C-5 modified sialyl donors
Jianzhi Gong a, Han Liu a, John M. Nicholls b, Xuechen Li a,
⇑
a Department of Chemistry, The University of Hong Kong, Hong Kong, China
b Department of Pathology, Li Ka-Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 May 2012
Received in revised form 14 July 2012
Accepted 14 August 2012
Available online 20 August 2012
Synthetic sialylated glycans provide useful tools to study carbohydrate-mediated biological recognition;
however chemical sialylation is the most challenging practice in preparative carbohydrate chemistry,
which is often associated with low yields and poor stereoselectivity. Herein, we conducted extensive
studies on sialylation with five types of 5-N-modified sialyl donors and four types of galactosyl acceptors.
Our studies have shown that a good combination between the donor and the acceptor seems necessary to
achieve high yield and stereoselectivity. None of the donors or acceptors showed ‘universal’ utility
toward the sialylation reaction.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
For a research program toward the development of a practical
synthesis of N-glycan structures, we started to evaluate the various
Sialic acids (Neu5Ac, N-acetyl-neuraminic acid) are present in
many cell-surfaced glycoconjugates and secreted glycoproteins.
They are involved in many cellular events, such as viral infection,
inflammation and cell-cell adhesion.1 Sialic acids reside in the ter-
mini of glycans and they serve as the essential determinant for
glycan–protein interactions. Thus, synthetic homogeneous sialic
acid-containing glycans are valuable tools to unravel the glycan’s
cellular functions.2 Naturally occurring glycosidic linkage between
sialic acid donors with C-5 modifications and different acceptors.
The N-glycan present on glycoproteins via the asparagine side
chain is important for correct protein folding and also mediates
many cellular events.7 The most common motif in N-glycan struc-
tures is that sialic acid is linked to a galactose via 2,6- or 2,3-link-
age, thus our studies have been focused on searching for the best
combination of the sialic acid donor and the galactosyl acceptor
to produce Neu5Ac-a-(2,3)-Gal and Neu5Ac-a-(2,6)-Gal disaccha-
sialic acids and other sugars is via
a orientation. Synthetically, the
rides (Fig. 2).
glycosylation that involves a sialic acid donor is the most challeng-
ing practice in preparative carbohydrate chemistry, often with low
yields and poor selectivity.3 The electron-withdrawing property of
the carboxylate groups at the anomeric position destabilizes the
oxocarbonium ion glycosyl intermediate generated from glycosyl-
ation, thereby challenging the coupling reaction. In addition, the
glycal derived from the elimination reaction is often the significant
byproduct.4 On the other hand, the stereoselectivity of the cou-
pling product is difficult to control, due to the lack of a directing
group at the adjacent position (C-3) (Fig. 1).
Over the past decades, many advances have been developed to
improve the stereoselectivity and coupling efficiency.3a Research-
ers have extensively studied the effect of the leaving group of the
sialic acid donor on glycosylation,3b and temporary directing
groups (i.e., I, SPh) have been introduced to enhance the stereose-
lectivity.5 More recently, it has been observed that the nature of
the 5-N-protecting group, other than 5-N-acetamido (5-NHAc),
can greatly influence the sialylation efficiency, including yields
and stereoselectivity.6
2. Results and discussion
The synthesis of sialyl donors is straightforward. We used p-tol-
uenethiosialoside as the sialyl donor due to their easy preparation
and stability,8 and four sialyl donors varying at the 5-N-protecting
groups (D1, D2, D3, and D5) were chosen. Recently, Wong and
Wu’s group reported a highly a
-selective sialyl phosphate donor,9
so we also synthesized a sialyl donor of this type (D4). The prepa-
ration of sialyl donors is shown in Scheme 1. The Neu5Ac thiogly-
coside D110 was converted into 1 by acidolysis. Acylation of 1 with
methyl trifluoroacetate, and 4-nitrophenylchloroformate produced
2,11 and 3,12 respectively, while the azido transfer reaction with
imidazole-1-sulfonyl azide hydrochloride gave 4.13 After O-acety-
lation with acetic anhydride and pyridine, 5-trifluoroacetamido
sialyl donor D2,11 and 5-azido sialyl donor D5,13 were obtained
in high yields. The O-acetylated sialoside intermediate 512 was eas-
ily converted to N-acetyl-5-N,4-O-carbonyl-protected sialyl donor
D312 and phosphate donor D49 via N-acetylation with acetyl chlo-
ride in the presence of Hunig’s base and glycosylated with dibutyl
phosphate promoted by N-iodosuccinimide (NIS) and triflic acid
(TfOH), respectively.
⇑
Corresponding author.
E-mail address: xuechenl@hku.hk (X. Li).
0008-6215/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carres.2012.08.007

92
J. Gong et al. / Carbohydrate Research 361 (2012) 91–99
OH
OAc
OAc
OH
OH
HO
AcO
HO
HO
CO2H
O
LG
CO2H
CO2H
O
OH
OH
OH
OH
O
2
O
O
CO2Me
1
O
O
O
O
5
AcHN
R
AcHN
AcHN
HO
3
HO
R'O
HO
HO
OH
O
OH
HO
O
Figure 1. Naturally occurring sialic acid and sialyl donor for the chemical synthesis.
OH
Figure 2. Neu5Ac-a-Gal components present in the N-glycan structures.
In addition, we have prepared, according to the literature proto-
col,14–16 various galactosyl acceptors, A1–A4, including 3-OH and 6-
OH building blocks. The 4-methoxyphenyl (MP) and 2-(trimethyl-
silyl)ethyl (TMSE) groups are selected for the temporary anomeric
hydroxyl protecting groups, because they could be readily removed
and modified for further elongation.17,18 For the elongation of the
resultant sialyl disaccharide to synthesize sialic acid-LacNAc, the glu-
cosamine derivative A519 was also prepared as the acceptor (Fig. 3).
The glycosylations were performed under standard conditions.
The sialyl donors and galactosyl acceptors were first mixed to-
gether with 4 Å molecular sieves and solvent (MeCN or MeCN/
CH2Cl2), and then activated with 2.0 equiv NIS and catalytic
amount of 0.20 equiv TfOH (0.30 equiv TMSOTf for D4), which
were performed at À40 °C. After the same reaction time (1 h), the
sialylation process was quenched, followed by a simple work-up.
(83% and 86%) but with low stereoselectivity (2.4:1 and 3:1). When
D1 reacted with 3-OH of A3 and A4, much lower yields (51% and
34%) were obtained with good selectivity (a only). The similar re-
sults were reported by Ito, Ando, Kiso, and Kasegawa.22,23 When
an excess amount (1.2–2.0 equiv) of donor D1 was employed, the
sialylation yield could be a little higher. In contrast with D1, 5-tri-
fluoroacetamido sialyl donor D2 gave much better stereoselectivity
when reacting with 6-OH acceptors. Both D1 and D2 suffered from
the generation of the sialyl glycal, which reduced the yield signifi-
cantly. N-Acetyl-5-N,4-O-carbonyl-protected sialyl donor D3 and
phosphate donor D4 can be coupled to both primary and secondary
hydroxyl groups in moderate to high yields (77–99% vs 55–98%),
but the glycosylation lost the stereoselectivity for 3-OH of A3 and
A4. This behavioral difference of D3 was also observed by Crich
and Xing.12,26 The sialyl donor D4 without the N-acetyl group is dif-
ferent from that phosphate donor Wong and Wu used for model
studies.9a The reaction temperature (À40 °C) was in accord with
the sialylation condition of the other four donors, but it is much
higher than the reported ones (À78 °C for model study and
The
a
/b ratio of desired disaccharide was determined by 1H NMR
analysis of the crude reaction mixture. The configurations of the
newly formed glycosidic bond of disaccharides were assigned by
3
the long-range JC-1, H-3ax coupling constant.20
As shown in Table 1, when glycosylating with 6-OH of A1 and
A2, C-5 unmodified sialyl donor D1 gave sialosides in good yields
OH
HO
OAc
AcO
F3C
STol
CO2Me
STol
CO2Me
OAc
OH
e
H
N
H
F3C
O
O
N
HO
O
AcO
D2
O
OAc
OAc
2
AcO
STol
CO2Me
O
AcHN
OAc
OAc
AcO
D1
AcO
STol
CO2Me
O
AcN
b
O
a
O
D3
f
OH
OH
OAc
OAc
HO
HO
AcO
AcO
STol
CO2Me
STol
O CO2Me
STol
CO2Me
OH
OH
c
e
O
O
H2N
HN
HN
HO
O
3
O
5
1
O
O
g
OAc
OAc
CO2Me
O
P
OBu
OBu
O
O
d
HN
O
O
D4
OH
OAc
OAc
HO
AcO
STol
CO2Me
STol
OH
e
O
O
CO2Me
N3
N3
HO
4
AcO
D5
Scheme 1. Preparation of sialyl donors (D1–D5). Reagents and conditions: (a) MsOH, MeOH, reflux; (b) CF3CO2Me, Et3N, MeOH; (c) 4-nitrophenylchloroformate, NaHCO3,
MeCN/H2O, 0 °C; (d) imidazole-1-sulfonyl azide hydrochloride, K2CO3, CuSO4Á5H2O, MeOH; (e) Ac2O, pyridine; (f) AcCl, DIPEA, CH2Cl2, 0 °C; (g) dibutyl phosphate, N-
iodosuccinimide, TfOH, molecular sieves (4 Å), CH2Cl2, 0 °C. Overall yields (from D1): D2 (85%), D3 (46%), D4 (36%), D5 (67%).

J. Gong et al. / Carbohydrate Research 361 (2012) 91–99
93
Table 1
Sialylation resultsa
OH
OH
OBn
Ph
O
BnO
BnO
HO
HO
O
O
O
O
O
Disaccharide yield (%)b;
a
/b (x:1)c glycal yield (%)
O
OMP
OMP
O
OBn
OBn
O
O
HO
OTMSE
OBz
OAc
D1A1d,21
83; 2.4:1
16
D1A2d
86; 3:1
10
D1A3d,22
AcO
STol
CO2Me
51;
a
only
OAc
30
O
AcHN
AcO
OAc
D2A124
95; 5:1
D2A2
63; >10:1
10
D2A3
17; 8.3:1
32
D2A425
68; 4.5:1
24
AcO
F3C
STol
CO2Me
OAc
Noneg
H
N
O
AcO
OAc
OAc
O
D3A1e,26
D3A2e
D3A3e
D3A4e
AcO
AcO
AcO
STol
CO2Me
99;
a
only
77; >10:1
79; 0.6:1
77; 0.8:1
Noneg
Noneg
Noneg
Noneg
O
AcN
O
O
OAc
OAc
D4A1f,27
98; only
D4A2f
D4A3f
D4A4f
69; 3.3:1
CO2Me
O
P
a
93;
a
only
55; 2.8:1
Noneg
Noneg
Noneg
OBu
OBu
O
O
HN
O
O
OAc
OAc
D5A1
99; 5:1
Noneg
D5A2
87; 1.7:1
5
D5A3
81; 2.5:1
12
D5A4
71; 1.1: 1
24
STol
O
CO2Me
N3
AcO
a
General condition: donor/acceptor (1:1, M/M), 4 Å MS, MeCN, À40 °C, 2.0 equiv NIS, 0.20 equiv TfOH. The results from optimized donor/acceptor combinations are
highlighted in bold form.
b
Isolated yields.
c
Determined by 1H NMR analysis of the crude reaction mixture.
d
1.0 equiv TfOH (the reaction with 0.20 equiv TfOH gave no product).
Reaction solvent: CH2Cl2/MeCN (3:2, v/v).
e
f
Reaction solvent: CH2Cl2/MeCN (2:1, v/v); 0.30 equiv trimethylsilyl triflate (TMSOTf).
g
Not detected from crude 1H NMR analysis.
À60 °C for
a
(2,9) polysialic acid).9 The different reaction tempera-
With D2A4 in hand, we first converted 4,6-benzylidene to acet-
yl groups, which were more stable under anomeric TMSE cleavage
conditions. After TCA donor was synthesized, it was coupled with
glucosamine acceptor A5 to afford trans-b-linkage of trisaccharide
exclusively, which is the precursor of natural 3’-sialyl-N-acetyllac-
tosamine (Scheme 2).
In summary, we have comparably studied the sialylation with five
types of 5-N-modified sialyl donors and four types of galactosyl accep-
tors. It was observed that the matching partner of the sialyl donor and
ture may account for the low selectivity of D4 toward the secondary
hydroxyl of A3 and A4. The stereoselectivity of the 5-azido sialyl
donor D5 in glycosylating the selected acceptors is rather poor.
A good combination between the donor and the acceptor seems
necessary to achieve high yield and selectivity. None of the donors
or acceptors showed ‘universal’ reactivity toward sialylation
reactions.
For the synthesis of Neu5Ac-
bination of D3 or D4 with A1 gave a much better yield (99% with
only isomer), while the disaccharide D3A1 is hard for further
elongation. D4 can be glycosylated with A2 to afford a Neu5Ac-
-(2,6)-Gal disaccharide D4A2 in 93% yield with only -sialoside.
a-(2,6)-Gal disaccharides, the com-
the galatosyl acceptor is critical to afford Neu5Ac-
high yield and good selectivity. The combination, D3/A1 and D4/A2
gave the best glycosylation to produce Neu5Ac- -(2,6)-Gal disaccha-
rides, while D1/A3 and D2/A4 produced Neu5Ac- -(2,3)-Gal disaccha-
a-Gal disaccharide in
a
a
a
a
a
Furthermore, the anomeric MP group of the resultant disaccharide
can be removed and subjected to further elongation.
rides in a reasonable yield. The utility of TMSE at the reducing end
would enable the transformation into TCA donors for further elonga-
tion toward the synthesis of the full N-glycan structure.
For the synthesis of Neu5Ac-
bination of D2 and A4 gave a relatively better overall yield (68%
with -sialoside preferred). Disaccharide D2A4 will be an impor-
a-(2,3)-Gal disaccharides, the com-
a
3. Experimental
3.1. General
tant substrate for the synthesis of a more complex sialylated gly-
can, since its anomeric TMSE group can be readily removed and
modified into glycosyl trichloroacetimidates (TCA) and the benzoyl
(Bz) group at C-2 position can ensure the trans-b-linkage formation
for the elongating glycosylation.
1H and 13C NMR (CDCl3) spectral analyses were performed on a
Bruker 400 NMR spectrometer at room temperature using TMS as

94
J. Gong et al. / Carbohydrate Research 361 (2012) 91–99
OAc
OAc
AcO
AcO
F3C
CO2Me
CO2Me
O
OAc
OAc
OBz
O
OBz
O
a
b
H
N
H
N
F3C
O
O
OTMSE
OTMSE
O
AcO
AcO
O
AcO
O
O
OAc
O
6
D2A4
Ph
NH
Cl
OAc
OAc
OBn
AcO
F3C
AcO
F3C
CO2Me
O
O
CO2Me
O
OAc
OAc
BzO
BzO
O
Cl
c
Cl
O
H
N
H
N
O
O
O
STol
NPhth
O
BzO
AcO
AcO
O
O
AcO
AcO
OAc
OAc
7
8
Scheme 2. Preparation of trisaccharide (8). Reagents and conditions: (a) 60% HOAc, 70 °C; then Ac2O, pyridine (88%); (b) boron trifluoride etherate (BF3ÁOEt2), CH2Cl2, 0 °C;
then trichloroacetonitrile, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), CH2Cl2, 0 °C (70%); (c) A5, TMSOTf, 4 Å Mol. Sieves, MeCN, À40 °C (57%).
an internal standard. High resolution electrospray ionization mass
spectrometry (ESI-HRMS, positive mode, ion-source acceleration
4.5 kV, ion-source temperature 275 °C, sheath gas flow rate was
6 (arb. unit), methanol as solvent) mass spectra were recorded
with a LTQ Orbitrap Velos spectrometer from Thermo Scientific.
Analytical TLC was performed on Kieselgel 60 F254 (Merck). Column
chromatographic purification was carried out using Kieselgel 60
(230–400 mesh, Merck). Commercial reagents were used as re-
ceived, unless otherwise indicated. Molecular sieves were freshly
activated under high vacuum by flame. Dichloromethane (CH2Cl2)
was freshly distilled from calcium hydride (CaH2). All reagents
were of analytical reagent grade.
70.70, 68.3, 68.0, 66.6, 63.3, 61.9, 60.1, 52.9, 37.4, 26.2, 26.1, 25.0,
24.8, 21.1, 21.0, 20.9. ESI-HRMS: Calcd for
C30H47N4O17
[M+NH4]+: 735.2931. Found: 735.2941.
3.2.1.1. Methyl 4,7,8,9-tetra-O-acetyl-5-azido-3,5-dideoxy-
cero-b- -galacto-non-2-ulopyranosylonate-(2?6)-1,2;3,4-di-O-
isopropylidene- -galacotopyranoside (D5A1b).
1H NMR
(CDCl3, 400 MHz): 5.61 (dd, J = 1.7, 4.8 Hz, 1H), 5.47 (d,
D-gly-
D
a
d
J = 5.0 Hz, 1H), 5.24–5.32 (m, 1H), 4.70 (dd, J = 2.3, 12.6 Hz, 1H),
4.63 (dd, J = 2.2, 8.1 Hz, 1H), 4.34 (dd, J = 1.6, 8.1 Hz, 1H), 4.24–
4.31 (m, 2H), 4.06 (dd, J = 1.6, 10.4 Hz, 1H), 3.98–4.01 (m, 1H),
3.80 (s, 3H), 3.54 (t, J = 8.8 Hz, 1H), 3.47 (dd, J = 5.8, 8.3 Hz, 1H),
3.21 (t, J = 10.1 Hz, 1H), 2.60 (dd, J = 5.0, 12.9 Hz, 1H), 2.20 (s,
3H), 2.10 (s, 3H), 2.07 (s, 3H), 2.04 (s, 6H), 1.70 (dd, J = 11.7,
12.6 Hz, 1H), 1.55 (s, 3H), 1.48 (s, 3H), 1.41 (s, 3H), 1.33 (s, 3H);
13C NMR (CDCl3, 100 MHz): d 170.8, 170.3, 170.1, 169.8, 167.0
3.2. General procedure for sialylation of sialyl donors (D1–D5)
with galactosyl acceptors (A1–A4)
3
A mixture of sialyl donor (D1–D5, 1.0 equiv), galactosyl acceptor
(A1–A4, 1.0 equiv) and activated 4 Å molecular sieves (2.0 g/mmol)
in dry MeCN (for D1, D2 and D5) or CH2Cl2/MeCN (2:1, v/v, for D3) or
CH2Cl2/MeCN (3:2, v/v, for D4), making the final concentration
50 mM, was stirred under argon atmosphere at room temperature
for 1 h to remove any trace amounts of water. The reaction mixture
was then cooled to À40 °C (MeCN in liquid N2). N-Iodosuccinimide
(2.0 equiv) was added followed by catalytic amount of triflic acid
(0.20 equiv) to promote the sialylation process (0.30 equiv TMSOTf
for D4). After being stirred at À40 °C for 1 h, the mixture was quenched
with triethylamine, diluted with CH2Cl2, and filtered through a pad of
Celite. The resulting filtrate was washed with 1 M aqueous Na2S2O3
solution, dried over anhydrous Na2SO4, filtered, and concentrated un-
(C-1, JC-1, H-3ax = 0 Hz), 109.5, 108.8, 98.1, 96.2, 71.6, 70.9, 70.7,
70.6, 70.4, 70.2, 69.3, 65.4, 62.4, 61.5, 60.2, 53.0, 36.8, 26.3, 25.9,
25.0, 24.1, 21.13, 21.11, 20.95, 20.88. ESI-HRMS: Calcd for
C
30H44N3O17 [M+H]+: 718.2665. Found: 718.2667.
3.2.2. 4-Methoxyphenyl (methyl 5-acetamido-4,7,8,9-tetra-O-
acetyl-3,5-dideoxy- -glycero- -galacto-non-2-
ulopyranosylonate-(2?6)-2,3,4-tri-O-benzyl-b-
galacotopyranoside (D1A2
D
a-D
a)
1H NMR (CDCl3, 400 MHz): d 7.27–7.39 (m, 15H), 7.07–7.09 (m,
2H), 6.79–6.82 (m, 2H), 5.35–5.39 (m, 1H), 5.29 (dd, J = 1.9, 8.1 Hz,
1H), 5.12 (d, J = 9.4 Hz, 1H), 4.97–5.02 (m, 2H), 4.67–4.90 (m, 7H),
4.30 (dd, J = 2.6, 12.4 Hz, 1H), 4.04–4.12 (m, 4H), 3.95 (d, J = 2.6 Hz,
1H), 3.90 (dd, J = 6.1, 9.4 Hz, 1H), 3.77 (s, 3H), 3.70 (t, J = 6.8 Hz,
1H), 3.66 (s, 3H), 3.63 (dd, J = 2.9, 9.8 Hz, 1H), 3.58 (dd, J = 7.6,
9.3 Hz, 1H), 2.58 (dd, J = 4.7, 12.8 Hz, 1H), 2.13 (s, 3H), 2.08 (s,
3H), 2.03 (s, 3H), 1.96 (s, 3H); 13C NMR (CDCl3, 100 MHz): d
der reduced pressure. The a
/b ratio was determined by 1H NMR anal-
ysis of the crude reaction mixture. The residue was purified by
column chromatography on silica gel with toluene/acetone or hex-
ane/EtOAc as eluent to give the respective disaccharide.
The disaccharides D1A1, D1A3, D1A4, D2A1, D2A4, D3A1, and
D4A1 were known compounds. The 1H and 13C NMR data have
good consistence with those reported in references.21–27 Following
are the NMR and HRMS data for all new disaccharides.
3
171.1, 170.8, 170.4, 170.3, 170.0, 168.2 (C-1, JC-1, H-3ax = 5.6 Hz),
155.2, 151.9, 139.0, 138.8, 138.6, 128.5, 128.43, 128.37, 128.28,
127.9, 127.7, 127.6, 127.5, 118.6, 114.6, 103.1, 99.0, 82.3, 79.4,
75.5, 73.4, 73.2, 73.0, 72.8, 69.1, 68.8, 67.5, 63.2, 62.6, 55.8, 53.0,
49.6, 38.0, 23.4, 21.2, 21.0, 20.9, 20.8. ESI-HRMS: Calcd for
3.2.1. Methyl 4,7,8,9-tetra-O-acetyl-5-azido-3,5-dideoxy-
glycero- -galacto-non-2-ulopyranosylonate-(2?6)-1,2;3,4-
di-O-isopropylidene- -galacotopyranoside (D5A1
D-
C
54H64NO19 [M+H]+: 1030.4067. Found: 1030.4118.
a-D
a
a)
3.2.2.1. 4-Methoxyphenyl (methyl 5-acetamido-4,7,8,9-tetra-O-
acetyl-3,5-dideoxy- -glycero-b- -galacto-non-2-ulopyranosylo-
nate-(2?6)-2,3,4-tri-O-benzyl-b-galacotopyranoside
(D1A2b).
1H NMR (CDCl3, 400 MHz): d 7.28–7.53 (m, 15H),
1H NMR (CDCl3, 400 MHz): d 5.49–5.52 (m, 2H), 5.37–5.41 (m,
1H), 4.83 (ddd, J = 4.7, 9.7, 14.4 Hz 1H), 4.58 (dd, J = 2.4, 7.9 Hz,
1H), 4.24–4.33 (m, 2H), 4.27 (d, J = 4.0 Hz, 1H), 4.20 (dd, J = 1.5,
7.9 Hz, 1H), 3.80–3.88 (m, 3H), 3.78 (s, 3H), 3.55 (dd, J = 6.4,
8.9 Hz, 1H), 3.22 (t, J = 10.2 Hz, 1H), 2.74 (dd, J = 4.8, 12.8 Hz, 1H),
2.18 (s, 3H), 2.14 (s, 3H), 2.11 (s, 3H), 2.07 (s, 3H), 1.78 (t,
J = 12.5 Hz, 1H), 1.54 (s, 3H), 1.42 (s, 3H), 1.33 (s, 6H); 13C NMR
D
D
7.02–7.05 (m, 2H), 6.84–6.86 (m, 2H), 5.43–5.46 (m, 1H), 5.19–
5.23 (m, 1H), 5.12 (dd, J = 2.2, 6.4 Hz, 1H), 4.97–5.02 (m, 2H),
4.68–4.90 (m, 7H), 4.57 (dd, J = 2.5, 12.5 Hz, 1H), 3.86–4.12 (m,
6H), 3.78 (s, 3H), 3.77 (s, 3H), 3.68–3.71 (m, 1H), 3.56–3.64
(m, 2H), 2.30 (dd, J = 4.8, 12.8 Hz, 1H), 2.17 (s, 3H), 2.07 (s,
3H), 2.03 (s, 3H), 1.98 (s, 3H), 1.71 (s, 3H); 13C NMR (CDCl3,
3
(CDCl3, 100 MHz): d 170.9, 170.0, 169.85, 169.81, 167.8 (C-1, JC-
H-3ax = 5.8 Hz), 109.4, 108.7, 98.5, 96.4, 71.7, 71.3, 70.8, 70.73,
1,

J. Gong et al. / Carbohydrate Research 361 (2012) 91–99
95
Ph
O
OBn
OH
OH
OBn
O
O
BnO
BnO
HO
HO
O
O
O
O
O
O
HO
STol
NPhth
A5
OMP
HO
OTMSE
O
OMP
BzO
OBn
OBn
A3
OBz
A4
O
A1
A2
Figure 3. Galactosyl acceptors A1–A4 and glucosamine acceptor A5 used in the study (MP = 4-methoxyphenyl, TMSE = 2-(trimethylsilyl)ethyl, STol = 4-methylphenylthio,
Phth = phthalimido).
3
100 MHz): d 170.71, 170.68, 170.4, 170.2, 170.0, 167.7 (C-1, JC-1,
H-3ax = 0 Hz), 155.4, 151.7, 140.0, 138.6, 138.3, 128.4, 128.2,
127.8, 127.76, 127.75, 127.4, 127.1, 126.3, 118.8, 114.6, 103.4,
99.0, 82.1, 79.4, 75.6, 74.8, 74.1, 73.3, 72.2, 71.7, 70.6, 68.9, 67.2,
62.1, 62.0, 53.1, 52.9, 48.3, 37.2, 23.3, 23.1, 21.4, 20.9, 20.8.
(dd, J = 1.8, 9.7 Hz, 1H), 5.98–5.03 (m, 2H), 4.84–4.87 (m, 2H),
4.71–4.81 (m, 3H), 4.21–4.26 (m, 3H), 4.09 (dd, J = 7.8, 9.7 Hz,
1H), 3.89–3.96 (m, 3H), 3.76 (s, 3H), 3.65 (s, 3H), 3.62–3.64 (m,
1H), 3.60 (dd, J = 2.8, 9.7 Hz, 1H), 3.50 (dd, J = 6.6, 9.5 Hz, 1H),
3.02 (dt, J = 1.1, 10.4 Hz, 1H), 2.17 (s, 3H), 2.07 (s, 3H), 2.02 (s,
3H), 2.01–2.04 (m, 1H); 13C NMR (100 MHz, CDCl3): d 171.6,
ESI-HRMS: Calcd for
1030.4090.
C
54H64NO19 [M+H]+: 1030.4067. Found:
3
170.6, 169.6, 168.2 (C-1, JC-1, H-3ax = 6.5 Hz), 159.4, 155.3, 151.9,
138.7, 138.6, 138.5, 128.5, 128.4, 128.34, 128.25, 128.0, 127.8,
127.7, 127.54, 127.50, 118.6, 114.5, 103.2, 100.1, 82.2, 79.3, 75.5,
74.3, 73.8, 73.2, 73.1, 68.9, 67.1, 63.8, 61.8, 58.0, 55.7, 53.1, 37.4,
21.1, 20.76, 20.73. ESI-HRMS: Calcd for
972.3648. Found: 972.3677.
3.2.3. 4-Methoxyphenyl (methyl 4,7,8,9-tetra-O-acetyl-3,5-
dideoxy-5-trifluoroacetamido- -glycero- -galacto-non-2-
ulopyranosylonate-(2?6)- 2,3,4-tri-O-benzyl-b-
galacotopyranoside (D2A2
D
a-D
C
51H58NO18 [M+H]+:
a)
1H NMR (CDCl3, 400 MHz): d 7.26–7.38 (m, 15H), 7.07–7.09 (m,
2H), 6.78–6.83 (m, 2H), 6.55 (d, J = 9.8 Hz, 1H), 5.33–5.37 (m, 1H),
5.26 (dd, J = 2.1, 7.8 Hz, 1H), 4.98–5.05 (m, 3H), 4.67–4.89 (m, 5H),
4.32 (dd, J = 2.5, 12.5 Hz, 1H), 4.26 (dd, J = 2.0, 10.7 Hz, 1H), 4.05–
4.12 (m, 2H), 3.90–4.01 (m, 3H), 3.77 (s, 3H), 3.66 (s, 3H), 3.65–
3.70 (m, 1H), 3.62 (dd, J = 2.8, 9.8 Hz, 1H), 3.55 (dd, J = 7.1, 9.3 Hz,
1H), 2.62 (dd, J = 4.8, 13.0 Hz, 1H), 2.13 (s, 3H), 2.08 (s, 3H), 2.02
3.2.6. 4-Methoxyphenyl (methyl 4,7,8,9-tetra-O-acetyl-5-azido-
3,5-dideoxy- -glycero- -galacto-non-2-ulopyranosylonate)-
(2?6)-2,3,4-tri-O-benzyl-b- -galacotopyranoside (D5A2
D
a-D
D
a)
1H NMR (CDCl3, 400 MHz): d 7.27–7.39 (m, 15H), 7.06 (d,
J = 9.1 Hz, 2H), 6.80 (d, J = 9.1 Hz, 2H), 5.47 (dd, J = 1.5, 9.1 Hz,
1H), 5.33–5.37 (m, 1H), 4.96–5.02 (m, 2H), 4.68–4.87 (m, 7H),
4.29 (dd, J = 2.4, 12.6 Hz, 1H), 4.15 (dd, J = 4.4, 12.6 Hz, 1H), 4.07
(dd, J = 7.7, 9.7 Hz, 1H), 3.89–3.93 (m, 2H), 3.80 (dd, J = 1.6,
10.6 Hz, 1H), 3.77 (s, 3H), 3.67 (s, 3H), 3.50–3.64 (m, 3H), 3.20 (t,
J = 10.2 Hz, 1H), 2.71 (dd, J = 4.8, 12.8 Hz, 1H), 2.13 (s, 3H), 2.10
(s, 3H), 2.09 (s, 3H), 2.02 (s, 3H), 1.74 (t, J = 12.5 Hz, 1H); 13C
NMR (100 MHz, CDCl3): d 170.8, 169.9, 169.8, 169.7, 167.6 (C-1,
3JC-1, H-3ax = 4.6 Hz), 155.2, 151.9, 138.8, 138.7, 138.5, 128.5,
128.43, 128.37, 128.3, 128.0, 127.8, 127.7, 127.6, 127.5, 118.6,
114.5, 103.1, 98.6, 82.2, 79.4, 75.4, 74.4, 73.4, 73.2, 71.8, 71.1,
68.1, 68.0, 63.4, 62.0, 60.0, 55.8, 53.1, 37.4, 21.1, 21.0, 20.9, 20.8.
ESI-HRMS: Calcd for C52H60N3O18 [M+H]+: 1014.3866. Found:
1014.3896.
(s, 3H), 1.96 (s, 3H), 1.96 (t, J = 10.2 Hz, 1H); 13C NMR (CDCl3,
3
100 MHz):
d
171.0, 170.8, 170.2, 170.1, 167.9 (C-1, JC-1,
H-3ax = 6.0 Hz), 157.9, 157.5, 155.3, 151.9, 138.9, 138.7, 138.6,
128.52, 128.48, 128.36, 128.29, 127.9, 127.8, 127.6, 127.5, 118.6,
114.6, 103.2, 98.9, 82.2, 79.4, 75.5, 73.4, 73.2, 73.1, 71.9, 69.0,
68.4, 67.4, 63.4, 62.3, 55.8, 53.1, 50.4, 37.8, 21.2, 20.75, 20.73,
20.70. ESI-HRMS: Calcd for C54H64F3N2O19 [M+NH4]+: 1101.4050.
Found: 1101.4069.
3.2.4. 4-Methoxyphenyl (methyl 5-acetamido-7,8,9-tri-O-acetyl-
5-N,4-O-carbonyl-3,5-dideoxy-
ulopyranosylonate)-(2?6)-2,3,4-tri-O-benzyl-b-
galacotopyranoside (D3A2
D-glycero-a-D-galacto-non-2-
D
-
a)
1H NMR (CDCl3, 400 MHz): d 7.27–7.41 (m, 15H), 7.05–7.07 (m,
2H), 6.78–6.81 (m, 2H), 5.55 (dd, J = 1.6, 7.4 Hz, 1H), 5.40 (dt,
J = 3.2, 7.0 Hz, 1H), 4.99–5.02 (m, 2H), 4.70–4.89 (m, 6H), 4.57
(dd, J = 1.7, 9.4 Hz, 1H), 4.33 (dd, J = 3.0, 12.3 Hz, 1H), 4.01–4.10
(m, 3H), 3.92–3.98 (m, 3H), 3.76 (s, 3H), 3.67 (s, 3H), 3.57–3.66
(m, 2H), 2.84 (dd, J = 3.6, 12.1 Hz, 1H), 2.48 (s, 3H), 2.11 (s, 3H),
3.2.6.1. 4-Methoxyphenyl (methyl 4,7,8,9-tetra-O-acetyl-5-
azido-3,5-dideoxy-
nate)-(2?6)-2,3,4-tri-O-benzyl-b-
(D5A2b).
1H NMR (CDCl3, 400 MHz): d 7.28–7.41 (m, 15H),
D
-glycero-b-
D-galacto-non-2-ulopyranosylo-
D-galacotopyranoside
7.01–7.03 (m, 2H), 6.84–6.86 (m, 2H), 5.54 (dd, J = 1.4, 7.2 Hz,
1H), 5.24–5.30 (m, 2H), 5.10 (d, J = 10.9 Hz, 1H), 4.98–5.03 (m,
2H), 4.76–4.90 (m, 7H), 4.67 (d, J = 11.8 Hz, 1H), 5.64 (d,
J = 10.9 Hz, 1H), 4.50 (dd, J = 2.2, 12.6 Hz, 1H), 4.16 (dd, J = 5.1,
12.6 Hz, 1H), 4.10 (dd, J = 7.7, 9.7 Hz, 1H), 4.02–4.06 (m, 2H),
3.83 (d, J = 2.8 Hz, 1H), 3.78 (s, 3H), 3.70 (s, 3H), 3.58–3.65
(m, 4H), 3.47–3.56 (m, 3H), 3.30 (t, J = 10.2 Hz, 1H), 2.59 (dd,
J = 5.1, 12.9 Hz, 1H), 2.20 (s,3H), 2.12 (s,3H), 2.01 (s,3H), 1.89
(s,3H), 1.72 (dd, J = 11.6, 12.8 Hz, 1H); 13C NMR (100 MHz,
2.08–2.09 (m, 1H), 2.03 (s, 3H), 1.93 (s, 3H); 13C NMR (CDCl3,
3
100 MHz):
d
172.1, 170.8, 170.2, 170.1, 168.5 (C-1, JC-1,
H-3ax = 5.0 Hz), 155.3, 153.8, 151.9, 138.9, 138.7, 138.6, 128.51,
128.43, 128.36, 128.29, 127.9, 127.8, 127.7, 127.6, 118.6, 114.6,
103.2, 99.3, 82.2, 79.4, 75.9, 75.5, 75.0, 74.4, 73.4, 73.25, 73.20,
72.0, 69.5, 64.0, 63.0, 59.2, 55.8, 53.2, 36.5, 24.8, 21.2, 20.9, 20.8.
ESI-HRMS: Calcd for C53H63N2O19 [M+H]+: 1031.4020. Found:
1031.4052.
CDCl3):
d
170.8, 170.4, 170.0, 169.7, 167.3 (C-1, 3JC-1,
H-3ax = 0 Hz), 155.5, 151.8, 138.8, 138.7, 138.5, 128.8, 128.6,
128.5, 128.45, 128.36, 127.8, 127.7, 127.65, 119.1, 114.7,
103.5, 98.9, 82.3, 79.4, 75.5, 74.9, 73.7, 73.2, 72.8, 70.9, 70.6,
69.7, 68.6, 62.7, 61.9, 60.1, 55.8, 53.0, 21.1, 21.0, 20.9, 20.8.
ESI-HRMS: Calcd for C52H60N3O18 [M+H]+: 1014.3866. Found:
1014.3862.
3.2.5. 4-Methoxyphenyl (methyl 7,8,9-tri-O-acetyl-5-N,4-O-
carbonyl-3,5-dideoxy-D-glycero-a-D-galacto-non-2-
ulopyranosylonate)-(2?6)-2,3,4-tri-O-benzyl-b-
D
-
galacotopyranoside (D4A2a)
1H NMR (CDCl3, 400 MHz): d 7.24–7.40 (m, 15H), 7.08 (d,
J = 9.1 Hz, 2H), 6.80 (d, J = 9.1 Hz, 2H), 5.40–5.43 (m, 2H), 5.09

96
J. Gong et al. / Carbohydrate Research 361 (2012) 91–99
3
3.2.7. 4-Methoxyphenyl (methyl 4,7,8,9-tetra-O-acetyl-3,5-
dideoxy-5-trifluoroacetamido- -glycero- -galacto-non-2-
ulopyranosylonate-(2?3)-2,6-di-O-benzyl-b-
galacotopyranoside (D2A3
(C-1, JC-1, H-3ax = 5.0 Hz), 159.3, 155.4, 151.6, 138.9, 138.2, 128.6,
128.5, 128.4, 128.3, 127.8, 127.7, 127.7, 118.6, 114.6, 102.9, 99.2,
76.4, 75.0, 73.9, 73.7., 73.0, 69.3, 69.0, 68.1, 67.2, 62.0, 57.9, 55.8,
53.3, 36.6, 21.2, 20.8, 20.6. ESI-HRMS: Calcd for C44H52NO18
[M+H]+: 882.3179. Found: 882.4072.
D
a-D
a)
1H NMR (CDCl3, 400 MHz): d 7.29–7.40 (m, 10H), 7.00–7.04 (m,
2H), 6.77–6.81 (m, 2H), 6.53 (d, J = 10.2 Hz, 1H), 5.28–5.38 (m, 3H),
4.99 (d, J = 10.9 Hz, 1H), 4.88–4.91 (m, 2H), 4.74 (d, J = 11.0 Hz, 1H),
4.56–4.59 (m, 2H), 4.47 (dd, J = 2.2, 10.6 Hz, 1H), 4.08–4.18 (m, 2H),
3.97–4.02 (m, 2H), 3.78–3.93 (m, 3H), 3.77 (s, 3H), 3.58–3.63 (m,
2H), 3.50 (s, 3H), 2.67 (dd, J = 4.6, 13.4 Hz, 1H), 2.31 (d, J = 7.7 Hz,
1H), 2.11 (s, 3H), 2.09 (s, 3H), 2.01 (s, 3H), 2.00 (s, 3H), 1.94–1.98
(m, 1H); 13C NMR (100 MHz, CDCl3): d 170.9, 170.8, 170.7, 169.9,
3.2.9.1. 4-Methoxyphenyl (methyl 7,8,9-tri-O-acetyl-5-N,4-O-
carbonyl-3,5-dideoxy-
sylonate)-(2?3)-2,6-di-O-benzyl-b-galacotopyranoside
(D4A3b).
Selected 1H NMR (CDCl3, 400 MHz): d 7.27–7.38 (m,
10H), 7.02–7.04 (m, 2H), 6.78–6.81 (m, 2H), 5.32–5.35 (m, 1H),
5.16 (t, J = 3.4 Hz, 1H), 4.40 (dd, J = 3.1, 9.8 Hz, 1H), 3.22 (brs, 3H),
3.09 (t, J = 10.6 Hz, 1H), 2.83 (dd, J = 3.7, 12.5 Hz, 1H), 2.14 (s,
3H), 2.08 (s, 3H), 2.00 (s, 3H); 13C NMR (100 MHz, CDCl3): d
D-glycero-b-D-galacto-non-2-ulopyrano-
3
166.9 (C-1, JC-1, H-3ax = 4.9 Hz), 158.0, 157.7, 155.5, 151.5, 138.5,
137.9, 133.8, 131.8, 130.3, 130.2, 128.64, 128.56, 128.4, 128.0,
127.91, 127.85, 118.6, 114.7, 103.1, 99.8, 75.5, 73.9, 73.0, 71.6,
70.1, 69.6, 69.0, 68.5, 62.7, 55.8, 53.0, 49.8, 37.0, 29.9, 21.1, 20.9,
3
171.1, 170.8, 170.4, 166.4 (C-1, JC-1, H-3ax = 0 Hz), 159.5, 155.4,
151.5, 138.0, 134.6, 128.6, 128.5, 128.4, 128.0, 127.8, 127.6,
127.5, 118.5, 114.6, 103.1, 100.5, 76.5, 75.4, 73.8, 73.6, 73.2, 71.8,
70.5, 70.1, 69.6, 62.4, 58.4, 55.8, 52.9, 37.1, 21.0, 20.8, 20.7. ESI-
HRMS: Calcd for C44H52NO18 [M+H]+: 882.3179. Found: 882.4072.
20.8, 20.7. ESI-HRMS: Calcd for
1011.3580. Found: 1011.3604.
C
47H58N2O19 [M+NH4]+:
3.2.8. 4-Methoxyphenyl (methyl 5-acetamido-7,8,9-tri-O-acetyl-
5-N,4-O-carbonyl-3,5-dideoxy- -glycero- -galacto-non-2-
ulopyranosylonate)-(2?3)-2,6-di-O-benzyl-b-
galacotopyranoside (D3A3
D
a-
D
3.2.10. 4-Methoxyphenyl (methyl 4,7,8,9-tetra-O-acetyl-5-
azido-3,5-dideoxy-
ulopyranosylonate)-(2?3)-2,6-di-O-benzyl-b-
galacotopyranoside (D5A3
D-glycero-a-D-galacto-non-2-
a)
1H NMR (CDCl3, 400 MHz): d 7.28–7.40 (m, 10H), 7.00–7.04 (m,
2H), 6.78–6.82 (m, 2H), 5.50–5.52 (m, 1H), 5.40–5.42 (m, 2H), 5.01
(s, 2H), 4.94 (d, J = 11.1 Hz, 1H), 4.88 (d, J = 7.7 Hz, 1H), 4.72 (d,
J = 11.1 Hz, 1H), 4.66 (dd, J = 2.4, 12.1 Hz, 1H), 4.55–4.62 (m, 3H),
4.51 (dd, J = 2.6, 9.2 Hz, 1H), 4.07 (brs, 1H), 3.96–4.01 (m, 2H),
3.83–3.88 (m, 3H), 3.77 (s, 3H), 3.68–3.73 (m, 2H), 3.48 (s, 3H),
3.36–3.38 (m, 1H), 2.86 (dd, J = 3.6, 12.5 Hz, 1H), 2.48 (s, 3H),
2.09 (s, 3H), 2.08 (s, 3H), 2.00 (s, 3H); 13C NMR (100 MHz, CDCl3):
a)
1H NMR (CDCl3, 400 MHz): d 7.27–7.39 (m, 10H), 7.02–7.04 (m,
2H), 6.78–6.80 (m, 2H), 5.48 (dd, J = 1.6, 8.8 Hz, 1H), 5.38–5.42 (m,
1H), 4.91 (d, J = 7.7 Hz, 1H), 4.77–4.92 (m, 4H), 4.57 (s, 2H), 4.29 (dd,
J = 2.3, 12.6 Hz, 1H), 4.14 (dd, J = 3.3, 9.6 Hz, 1H), 4.05 (dd, J = 4.7,
12.6 Hz, 1H), 3.83–3.86 (m, 1H), 3.82 (s, 3H), 3.78–3.80 (m, 2H),
3.77 (s, 3H), 3.71–3.76 (m, 2H), 3.20 (t, J = 10.1 Hz, 1H), 2.72 (dd,
J = 4.8, 13.0 Hz, 1H), 2.11 (s, 3H), 2.07 (s, 3H), 2.04 (s, 3H), 1.95 (s,
3H), 1.83 (t, J = 12.5 Hz, 1H); 13C NMR (100 MHz, CDCl3): d 170.8,
3
d 172.8, 171.1, 170.8, 169.9, 166.5 (C-1, JC-1, H-3ax = 6.2 Hz), 155.5,
3
153.9, 151.5, 138.2, 137.9, 135.9, 129.1, 128.8, 128.6, 128.5, 128.4,
128.0, 127.9, 127.8, 118.5, 114.7, 103.2, 99.4, 79.4, 75.8, 75.4, 74.5,
73.9, 73.3, 73.2, 71.2, 70.2, 69.6, 63.4, 59.4, 55.8, 53.0, 36.1, 29.8,
24.9, 21.2, 21.0, 20.9. ESI-HRMS: Calcd for C46H54NO19 [M+H]+:
924.3285. Found: 924.3295.
170.0, 169.7, 169.6, 168.2 (C-1, JC-1, H-3ax = 5.0 Hz), 155.4, 151.7,
138.9, 138.2, 128.5, 123.4, 128.1, 127.85, 127.80, 127.7, 118.7,
114.6, 102.9, 98.0, 75.9, 75.2, 73.8, 73.3, 72.0, 69.5, 68.5, 68.2,
68.1, 62.2, 59.9, 55.8, 53.3, 36.4, 21.2, 21.0, 20.9, 20.6. ESI-HRMS:
Calcd for C45H57N4O18 [M+NH4]+: 941.3662. Found: 941.3669.
3.2.8.1. 4-Methoxyphenyl (methyl 5-acetamido-7,8,9-tri-O-
3.2.10.1. 4-Methoxyphenyl (methyl 4,7,8,9-tetra-O-acetyl-5-
acetyl-5-N,4-O-carbonyl-3,5-dideoxy-
non-2-ulopyranosylonate)-(2?3)-2,6-di-O-benzyl-b-galacoto-
pyranoside (D3A3b).
1H NMR (CDCl3, 400 MHz): d 7.27–7.40
D
-glycero-b-
D
-galacto-
azido-3,5-dideoxy-
D
-glycero-b-
D-galacto-non-2-ulopyranosylo-
nate)-(2?3)-2,6-di-O-benzyl-b-galacotopyranoside
(D5A3b).
1H NMR (CDCl3, 400 MHz): d 7.27–7.41 (m, 10H),
(m, 10H), 7.03–7.06 (m, 2H), 6.79–6.83 (m, 2H), 5.57 (dd, J = 1.5,
7.6 Hz, 1H), 5.46 (dt, J = 2.7, 7.2 Hz, 1H), 4.77–5.08 (m, 5H), 4.56–
4.59 (m, 3H), 4.50 (dd, J = 1.6, 9.4 Hz, 1H), 4.43 (dd, J = 2.7,
12.3 Hz, 1H), 4.15 (dd, J = 3.2, 9.6 Hz, 1H), 3.90–4.06 (m, 3H),
3.82–3.87 (m, 2H), 3.81 (s, 3H), 3.65–3.78 (m, 5H), 3.77 (s, 3H),
2.82 (dd, J = 3.5, 12.4 Hz, 1H), 2.48(s, 3H), 2.23 (t, J = 12.9 Hz, 1H),
2.11 (s, 3H), 2.00 (s, 3H), 1.88 (s, 3H); 13C NMR (100 MHz, CDCl3):
6.98–7.03 (m, 2H), 6.76–6.80 (m, 2H), 5.51 (dd, J = 2.1, 4.5 Hz,
1H), 5.37–5.44 (m, 1H), 5.31–5.35 (m, 1H), 4.95 (d, J = 11.0 Hz,
1H), 4.87 (d, J = 7.0 Hz, 1H), 4.81 (d, J = 11.0 Hz, 1H), 4.77 (dd,
J = 2.5, 12.4 Hz, 1H), 4.58 (s, 2H), 4.20 (dd, J = 2.1, 10.4 Hz, 1H),
4.10 (dd, J = 7.5, 12.4 Hz, 1H), 3.95 (brs, 1H), 3.78–3.86 (m, 4H),
3.76 (s, 3H), 3.71–3.75 (m, 1H), 3.53 (s, 3H), 3.30 (t, J = 10.1 Hz,
1H), 3.01 (d, J = 3.8 Hz, 1H), 2.81 (dd, J = 4.8, 13.3 Hz, 1H), 2.18 (s,
3H), 2.11 (s, 3H), 2.03 (s, 3H), 2.01 (s, 3H), 1.78 (dd, J = 11.7,
13.3 Hz, 1H); 13C NMR (100 MHz, CDCl3): d 170.8, 170.4, 169.9,
3
d 172.2, 170.9, 170.5, 169.9, 168.5 (C-1, JC-1, H-3ax = 0 Hz), 155.4,
153.7, 151.7, 138.8, 138.2, 128.8, 128.6, 128.5, 128.4, 128.1,
127.9, 127.8, 118.8, 114.6, 103.1, 98.9, 79.0, 76.3, 75.9, 75.2, 75.1,
75.0, 73.9, 73.8, 73.3, 72.1, 69.7, 69.3, 68.5, 63.3, 59.0, 55.8, 53.5,
35.1, 29.7, 24.8, 21.3, 20.9, 20.7. ESI-HRMS: Calcd for C46H54NO19
[M+H]+: 924.3285. Found: 924.3289.
3
169.8, 167.0 (C-1, JC-1, H-3ax = 0 Hz), 155.3, 151.5, 138.3, 138.1,
128.7, 128.5, 128.3, 127.9, 127.80, 127.78, 118.5, 114.6, 102.9,
99.5, 78.0, 75.3, 73.8, 73.4, 71.2, 71.0, 70.7, 70.1, 69.9, 68.9, 62.6,
60.2, 55.8, 53.0, 36.6, 29.8, 21.1, 20.9, 20.8. ESI-HRMS: Calcd for
C
45H57N4O18 [M+NH4]+: 941.3662. Found: 941.3679.
3.2.9. 4-Methoxyphenyl (methyl 7,8,9-tri-O-acetyl-5-N,4-O-
carbonyl-3,5-dideoxy-
ulopyranosylonate)-(2?3)-2,6-di-O-benzyl-b-
galacotopyranoside (D4A3
D
-glycero-
a
-
D
-galacto-non-2-
3.2.11. 2-(Trimethylsilyl)ethyl (methyl 5-acetamido-7,8,9-tri-O-
acetyl-5-N,4-O-carbonyl-3,5-dideoxy- -glycero- -galacto-
non-2-ulopyranosylonate)-(2?3)-2-O-benzoyl-4,6-O-
benzylidene-b- -galacotopyranoside (D3A4
D
a-D
a)
Selected 1H NMR (CDCl3, 400 MHz): d 7.27–7.38 (m, 10H), 7.01–
7.04 (m, 2H), 6.78–6.80 (m, 2H), 5.50–5.54 (m, 1H), 5.10 (dd, J = 1.8,
9.4 Hz, 1H), 4.93 (d, J = 7.8 Hz, 1H), 7.81–7.91 (m, 4H), 4.25 (dd,
J = 1.9, 12.7 Hz, 1H), 3.04 (t, J = 10.2 Hz, 1H), 2.91 (dd, J = 3.4,
12.2 Hz, 1H), 2.70 (brs, 3H), 2.13 (s, 3H), 2.03 (s, 3H), 1.90 (s,
3H); 13C NMR (100 MHz, CDCl3): d 171.6, 170.6, 169.9, 168.8
D
a)
1H NMR (CDCl3, 400 MHz): d 8.11–8.13 (m, 2H), 7.54–7.59 (m,
3H), 7.43–7.47 (m, 2H), 7.34–7.39 (m, 3H), 5.57 (d, J = 2.7 Hz,
1H), 5.47 (dd, J = 8.0, 10.1 Hz, 1H), 5.39 (s, 1H), 4.73 (d, J = 8.0 Hz,
1H), 4.56 (dd, J = 3.7, 10.1 Hz, 1H), 4.44–4.50 (m, 2H), 4.32 (dd,
J = 1.3, 12.2 Hz, 1H), 4.17 (dd, J = 1.4, 12.2 Hz, 1H), 4.07 (d,

J. Gong et al. / Carbohydrate Research 361 (2012) 91–99
97
J = 3.5 Hz, 1H), 3.98–4.04 (m, 2H), 3.71–3.75 (m, 1H), 3.51–3.61 (m,
20.8, 20.5, 18.1, À1.36. ESI-HRMS: Calcd for
C
42H57N2O18Si
3H), 3.47 (s, 3H), 2.95 (dd, J = 3.2, 12.0 Hz, 1H), 2.44 (s, 3H), 2.20 (s,
3H), 2.06 (s, 3H), 1.82 (s, 3H), 1.80 (dd, J = 12.1, 13.4 Hz, 1H), 0.82–
0.90 (m, 2H), À0.10 (s, 9H); 13C NMR (100 MHz, CDCl3): d 172.1,
[M+NH4]+: 905.3370. Found: 905.3390.
3.2.13. 2-(Trimethylsilyl)ethyl (methyl 4,7,8,9-tetra-O-acetyl-5-
azido-3,5-dideoxy- -glycero- -galacto-non-2-
ulopyranosylonate)-(2?3)-2-O-benzoyl-4,6-O-benzylidene-b-
galacotopyranoside (D5A4
3
171.1, 170.6, 170.2, 168.9 (C-1, JC-1, H-3ax = 4.7 Hz), 165.4, 137.9,
D
a-D
133.1, 130.7, 130.0, 129.1, 128.5, 126.7, 101.0, 100.7, 97.0, 75.2,
75.0, 73.2, 72.9, 71.6, 70.6, 69.2, 68.2, 67.1, 66.2, 63.9, 59.0, 53.0,
37.2, 24.8, 21.5, 21.0, 20.7, 18.1, À1.36. ESI-HRMS: Calcd for
D-
a)
1H NMR (CDCl3, 400 MHz): d 8.10 (d, J = 7.2 Hz, 2H), 7.58 (t,
J = 7.3 Hz, 1H), 7.52–7.54 (m, 2H), 7.46 (t, J = 7.8 Hz, 2H), 7.33–
7.39 (m, 3H), 5.49–5.53 (m, 1H), 5.40–5.46 (m, 2H), 5.36 (s, 1H),
4.71 (d, J = 7.9 Hz, 1H), 4.67–4.72 (m, 1H), 4.49 (dd, J = 3.7,
10.1 Hz, 1H), 4.31–4.35 (m, 2H), 4.10–4.14 (m, 2H), 3.97–4.03 (m,
2H), 3.68 (dd, J = 1.6, 10.6 Hz, 1H), 3.55 (s, 3H), 3.52–3.59 (m,
2H), 3.04 (t, J = 10.1 Hz, 1H), 2.75 (dd, J = 4.5, 12.7 Hz, 1H), 2.22
(s, 3H), 2.09 (s, 3H), 2.02 (s, 3H), 1.82 (s, 3H), 1.51 (t, J = 12.6 Hz,
C
44H59N2O19Si [M+NH4]+: 947.3476. Found: 947.3498.
3.2.11.1. 2-(Trimethylsilyl)ethyl (methyl 5-acetamido-7,8,9-tri-
O-acetyl-5-N,4-O-carbonyl-3,5-dideoxy- -glycero-b- -galacto-
non-2-ulopyranosylonate)-(2?3)-2-O-benzoyl-4,6-O-benzyli-
dene-b- -galacotopyranoside (D3A4b).
1H NMR (CDCl3,
D
D
D
400 MHz): d 8.01–8.03 (m, 2H), 7.44–7.59 (m, 5H), 7.34–7.37 (m,
3H), 5.83 (t, J = 2.0 Hz, 1H), 5.67 (s, 1H), 5.58 (dt, J = 1.8, 8.8 Hz,
1H), 5.45 (dd, J = 8.2, 9.8 Hz, 1H), 5.10 (dd, J = 2.5, 12.1 Hz, 1H),
4.66 (d, J = 8.2 Hz, 1H), 4.58–4.65 (m, 1H), 4.52 (dd, J = 2.1,
9.5 Hz, 1H), 4.47 (d, J = 3.6 Hz, 1H), 4.32–4.36 (m, 2H), 4.20 (dd,
J = 1.5, 12.3 Hz, 1H), 3.97–4.04 (m, 1H), 3.92 (dd, J = 9.2, 12.1 Hz,
1H), 3.64 (s, 1H), 3.47–3.59 (m, 2H), 3.27 (s, 3H), 2.66 (dd, J = 3.6,
12.1 Hz, 1H), 2.30 (s, 3H), 2.15 (s, 3H), 2.08 (s, 3H), 2.05 (s, 3H),
1.87 (t, J = 12.3 Hz, 1H), 0.82–0.92 (m, 2H), À0.08 (s, 9H); 13C
NMR (100 MHz, CDCl3): d 171.7, 171.2, 171.1, 169.5, 166.0 (C-1,
3JC-1, H-3ax = 0 Hz), 165.3, 137.8, 133.1, 130.6, 130.0, 129.9, 129.3,
128.43, 128.35, 126.5, 101.2, 100.3, 99.5, 76.3, 75.3, 74.6, 74.4,
74.2, 72.0, 70.8, 69.2, 67.0, 66.5, 63.3, 59.2, 52.9, 36.9, 29.8, 24.5,
21.2, 21.1, 20.8, 18.2, À1.35. ESI-HRMS: Calcd for C44H59N2O19Si
[M+NH4]+: 947.3476. Found: 947.3494.
1H), 0.77–0.92 (m, 2H), À0.11 (s, 9H); 13C NMR (CDCl3,
3
100 MHz):
d
171.0, 170.5, 169.65, 169.60, 168.6 (C-1, JC-1,
H-3ax = 6.6 Hz), 165.3, 137.8, 133.0, 130.8, 130.0, 129.1, 128.4,
128.3, 126.6, 73.4, 72.5, 71.6, 70.8, 70.6, 69.3, 67.7, 67.3, 67.0,
66.2, 62.3, 59.8, 53.0, 38.1, 29.8, 21.5, 21.0, 20.9, 20.4, 18.1,
À1.36. ESI-HRMS: Calcd for C43H59N4O18Si [M+NH4]+: 947.3588.
Found: 947.3596.
3.2.13.1. 2-(Trimethylsilyl)ethyl (methyl 4,7,8,9-tetra-O-acetyl-
5-azido-3,5-dideoxy-
onate)-(2?3)-2-O-benzoyl-4,6-O-benzylidene-b-
anoside (D5A4b).
1H NMR (CDCl3, 400 MHz): d 8.03–8.05 (m,
D
-glycero-b-
D
-galacto-non-2-ulopyranosyl-
D
-galacotopyr-
2H), 7.52–7.59 (m, 3H), 7.33–7.46 (m, 5H), 5.60 (s, 1H), 5.48 (d,
J = 8.8 Hz, 1H), 5.40–5.42 (m, 1H), 5.33–5.36 (m, 1H), 5.23–5.30
(m, 1H), 4.94 (dd, J = 2.6, 12.4 Hz, 1H), 4.68 (d, J = 8.1 Hz, 1H),
4.34–4.37 (m, 2H), 4.26 (dd, J = 3.8, 9.8 Hz, 1H), 4.12 (d,
J = 11.2 Hz, 1H), 3.92–4.02 (m, 3H), 3.62 (s, 1H), 3.51–3.58 (m,
2H), 3.32 (s, 3H), 3.18 (t, J = 10.0 Hz, 1H), 2.72 (dd, J = 4.6,
13.4 Hz, 1H), 2.14 (s, 3H), 2.08 (s, 6H), 2.04 (s, 3H), 1.63 (dd,
3.2.12. 2-(Trimethylsilyl)ethyl (methyl 7,8,9-tri-O-acetyl-5-N,4-
O-carbonyl-3,5-dideoxy-
ulopyranosylonate)-(2?3)-2-O-benzoyl-4,6-O-benzylidene-b-
galacotopyranoside (D4A4
D-glycero-a-D-galacto-non-2-
D
-
a)
1H NMR (CDCl3, 400 MHz): d 8.01–8.03 (m, 2H), 7.52–7.57 (m,
3H), 7.43–7.47 (m, 2H), 7.35–7.41 (m, 3H), 5.64 (s, 1H), 5.54 (dt,
J = 2.0, 9.3 Hz, 1H), 5.46 (dd, J =8.4, 9.5 Hz, 1H), 5.20 (s, 1H), 5.17
(t, J = 2.3 Hz, 1H), 5.09 (dd, J = 2.3, 12.4 Hz, 1H), 4.67 (d, J = 8.1 Hz,
1H), 4.59 (dt, J = 2.9, 12.0 Hz, 1H), 4.36–4.39 (m, 2H), 4.25–4.28
(m, 2H), 4.15 (d, J = 11.5 Hz, 1H), 3.98–4.08 (m, 2H), 3.67 (s, 1H),
3.50–3.58 (m, 1H), 3.30 (s, 3H), 3.07 (t, J = 10.5 Hz, 1H), 2.68 (dd,
J = 3.6, 12.2 Hz, 1H), 2.10 (s, 3H), 2.09 (s, 3H), 2.04 (s, 3H), 1.90 (t,
J = 12.3 Hz, 1H), 0.82–0.90 (m, 2H), À0.09 (s, 9H); 13C NMR (CDCl3,
J = 12.0, 13.1 Hz, 1H), 0.83–0.88 (m, 2H), À0.10 (s, 9H); 13C NMR
3
(CDCl3, 100 MHz):
d
171.1, 170.5, 169.6, 167.3 (C-1, JC-1,
H-3ax = 1.6 Hz), 165.1, 137.5, 133.0, 130.5, 130.0, 129.0, 128.31,
128.30, 126.4, 100.7, 100.5, 99.1, 75.0, 74.4, 71.7, 71.1, 70.7, 70.4,
70.2, 69.0, 66.9, 66.4, 62.6, 59.6, 52.8, 35.8, 29.8, 21.01, 20.97,
20.92, 20.73, 18.1, À1.37. ESI-HRMS: Calcd for C43H59N4O18Si
[M+NH4]+: 947.3588. Found: 947.3580.
3.2.14. 2-(Trimethylsilyl)ethyl (methyl 4,7,8,9-tetra-O-acetyl-
3,5-dideoxy-5-trifluoroacetamido-D-glycero-a-D-galacto-non-2-
3
100 MHz): d 171.1, 170.9, 170.5, 166.2 (C-1, JC-1, H-3ax = 5.8 Hz),
165.3, 159.4, 137.6, 133.1, 130.6, 129.9, 129.2, 128.5, 128.4,
126.2, 100.9, 100.7, 100.3, 76.1, 75.5, 75.0, 74.8, 72.3, 70.9, 70.6,
69.1, 67.0, 66.3, 62.7, 58.0, 52.9, 37.8, 29.8, 20.9, 20.7, 18.1,
À1.36. ESI-HRMS: Calcd for C42H57N2O18Si [M+NH4]+: 905.3370.
Found: 905.3385.
ulopyranosylonate-(2?3)-4,6-di-O-acetyl-2-O-benzoyl-b-D-
galacotopyranoside (6)
The disaccharide D2A4 (100 mg, 0.10 mmol) was suspended in
aqueous 60% HOAc (5 mL) and stirred at 80 °C for 2 h. The reaction
mixture was concentrated and co-evaporated with toluene three
times. The concentrate was dissolved in Ac2O–pyridine (2:3, v/v,
5 mL). After overnight stirring at room temperature, the reaction
mixture was diluted withEtOAc, and thenwashed with 1 N HCl solu-
tion, aqueous CuSO4 solution, saturated aqueous NaHCO3 solution
and brine. The organic layer was dried over anhydrous Na2SO4 and
concentrated. The residue was purified by column chromatography
on silica gel (CH2Cl2–EtOAc 5:1–1:1) to give 6 (87.7 mg, 0.088 mmol,
88%). 1H NMR (CDCl3, 400 MHz): d 8.16 (d, J = 7.7 Hz, 1H), 7.58 (t,
J = 7.1 Hz, 1H), 7.48 (t, J = 7.6 Hz, 1H), 6.45 (d, J = 7.4 Hz, 1H), 5.56–
5.59 (m, 1H), 5.26 (dd, J = 8.2, 9.7 Hz, 1H), 5.18 (d, J = 9.1 Hz, 1H),
5.00 (d, J = 3.0 Hz, 1H), 4.76 (d, J = 7.9 Hz, 1H), 4.69 (dd, J = 3.2,
10.1 Hz, 1H), 4.35 (d, J = 10.9 Hz, 1H), 4.11 (d, J = 6.4 Hz, 1H), 3.90–
3.99 (m, 2H), 3.86 (s, 3H), 3.58–3.65 (m, 1H), 2.60 (dd, J = 4.6,
12.6 Hz, 1H), 2.22 (s, 3H), 2.14 (s, 3H), 2.07 (s, 3H), 2.06 (s, 3H),
1.96 (s, 3H), 1.74 (t, J = 12.5 Hz, 1H),1.42 (s, 3H), 0.76–0.94 (m, 2H),
À0.11 (s, 9H); 13C NMR (CDCl3, 100 MHz): d 170.9, 170.8, 170.77,
170.6, 170.56, 170.49, 169.9, 168.0, 165.4, 158.2, 157.8, 157.5,
3.2.12.1. 2-(Trimethylsilyl)ethyl (methyl 7,8,9-tri-O-acetyl-5-
N,4-O-carbonyl-3,5-dideoxy-
pyranosylonate)-(2?3)-2-O-benzoyl-4,6-O-benzylidene-b-
galacotopyranoside (D4A4b).
1H NMR (CDCl3, 400 MHz): d
D-glycero-b-D-galacto-non-2-ulo-
D-
8.07–8.09 (m, 2H), 7.52–7.59 (m, 3H), 7.44–7.48 (m, 2H), 7.35–
7.40 (m, 3H), 5.54–5.58 (m, 1H), 5.41–5.46 (m,1H), 5.36 (s, 1H),
5.21 (brs, 1H), 5.11 (dd, J = 1.9, 10.1 Hz, 1H), 4.74 (d, J = 8.0 Hz,
1H), 4.48 (dd, J = 3.7, 10.1 Hz, 1H), 4.27–4.35 (m, 3H), 4.15 (dd,
J = 1.5, 12.2 Hz, 1H), 4.07 (dd, J = 2.0, 10.0 Hz, 1H), 3.97–4.02 (m,
2H), 3.57 (dd, J = 3.6, 10.1 Hz, 1H), 3.49 (s, 3H), 2.99 (dd, J = 3.1,
12.1 Hz, 1H), 2.85 (t, J = 10.4 Hz, 1H), 2.26 (s, 3H), 2.08 (s, 3H),
1.84 (s, 3H), 1.78 (dd, J = 12.2, 13.2 Hz, 1H), 0.81–0.91 (m, 2H),
À0.10 (s, 9H); 13C NMR (CDCl3, 100 MHz): d 171.4, 170.7, 170.4,
3
168.8 (C-1, JC-1, H-3ax = 0 Hz), 165.3, 159.2, 137.8, 133.1, 130.7,
129.9, 129.2, 128.5, 128.3, 126.6, 101.1, 100.6, 98.2, 73.6, 73.3,
72.9, 70.6, 69.3, 68.7, 67.0, 66.7, 66.2, 62.0, 57.8, 53.0, 38.1, 29.8,

98
J. Gong et al. / Carbohydrate Research 361 (2012) 91–99
157.1, 133.2, 130.5, 130.3, 128.5, 100.9, 96.9, 71.7, 71.4, 71.1, 70.6,
68.8, 67.91, 67.88, 67.82, 66.4, 62.3, 62.2, 53.4, 49.7, 37.4, 29.8,
21.6, 20.9, 20.8, 20.6, 20.1, 18.2, À1.47. ESI-HRMS: Calcd for
1.92 (s, 3H), 1.86 (s, 3H), 1.68 (t, J = 14.7 Hz, 2H), 1.41 (s, 3H); 13C
NMR (CDCl3, 100 MHz): d 170.8, 170.7, 170.5, 170.3, 170.0, 169.9,
167.9, 167.8, 167.3, 165.3, 164.8, 157.8, 157.5, 138.6, 138.4,
134.3, 134.1, 133.6, 133.5, 133.1, 131.9, 131.4, 130.4, 130.1,
129.9, 129.7, 128.7, 128.4, 128.3, 127.9, 127.6, 123.8, 123.6,
100.5, 96.9, 83.4, 78.7, 75.4, 73.0, 72.9, 71.7, 71.0, 70.4, 68.7, 68.6,
67.1, 66.4, 62.2, 61.0, 54.1, 53.4, 49.8, 37.3, 29.8, 21.5, 21.3, 20.9,
C
42H56F3NO21SiNa [M+Na]+: 1018.2958. Found: 1018.2978.
3.3. 2,2,2-Trichloroacetimidate (methyl 4,7,8,9-tetra-O-acetyl-
3,5-dideoxy-5-trifluoroacetamido- -glycero- -galacto-non-2-
D
a-D
ulopyranosylonate-(2?3)-4,6-di-O-acetyl-2-O-benzoyl-
galacotopyranoside (7)
a-
D-
20.7, 20.6, 20.5, 20.2. ESI-HRMS: Calcd for
C72H74F3N2O27S
[M+H]+ 1487.4146. Found: 1487.4176.
The disaccharide 6 (98.2 mg, 0.099 mmol) was dissolved in
CH2Cl2 (5 mL). To the stirred solution was added boron trifluoride
etherate (1.1 mL, 8.7 Â 10À3 mmol, 0.15 equiv) at 0 °C and the
reaction process was monitored by TLC. When the reaction was
completed, the mixture was quenched by saturated aqueous NaH-
CO3 solution, and diluted with CH2Cl2. After separation, the organic
layer was dried over anhydrous Na2SO4 and concentrated. The res-
idue was purified by flash column chromatography on silica gel
(CH2Cl2/MeOH 100:1–50:1) to afford the lactal, which was directly
dissolved in dry CH2Cl2 (3 mL) for the next step. To the stirred solu-
tion of lactal, cooled to 0 °C, were added trichloroacetonitrile
(0.15 mL, 1.5 mmol), and 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU, 5 drops). The dark brown mixture was stirred for 2 h, then
concentrated to get a syrup, which was purified by column chro-
matography on silica gel (CH2Cl2/MeOH 100:1–60:1) to give tri-
chloroacetimidate donor 7 (72.5 mg, 0.070 mmol, 70%). 1H NMR
(CDCl3, 400 MHz): d 8.59 (s, 3H), 8.14 (d, J = 7.1 Hz, 1H), 7.62 (t,
J = 7.4 Hz, 1H), 7.51 (t, J = 7.8 Hz, 1H), 6.72 (d, J = 3.8 Hz, 1H), 6.37
(d, J = 9.4 Hz, 1H), 5.55–5.59 (m, 1H), 5.50 (dd, J = 3.8, 10.5 Hz,
1H), 5.38 (dd, J = 1.9, 9.5 Hz, 1H), 5.32 (dd, J = 3.1, 9.8 Hz, 1H),
5.29 (dd, J = 3.1, 10.5 Hz, 1H), 4.98–5.02 (m, 1H), 4.58
(t, J = 6.4 Hz, 1H), 4.14–4.22 (m, 2H), 4.07 (dd, J = 7.0, 11.5 Hz,
1H), 4.00 (dd, J = 1.9, 10.7 Hz, 1H), 3.87–3.98 (m, 1H), 3.83
(s, 3H), 2.58 (dd, J = 4.7, 12.8 Hz, 1H), 2.18 (s, 3H), 2.14 (s, 3H),
2.07 (s, 3H), 2.05 (s, 3H), 1.94 (s, 3H), 1.93 (s, 3H); 13C NMR (CDCl3,
100 MHz): d 170.83, 170.78, 1706, 170.1, 169.9, 169.6, 167.9, 165.9,
161.0, 158.4, 158.0, 157.6, 157.3, 133.8, 130.1, 129.6, 128.7, 96.7,
94.3, 71.9, 69.9, 68.7, 68.6, 67.7, 67.6, 66.7, 62.2, 61.9, 53.5, 50.4,
37.4, 29.8, 21.5, 20.89, 20.85, 20.82, 20.7, 20.6.
Acknowledgments
We would like to thank Dr. Guang Zhu and Dr. Qinglin Wu, Divi-
sion of Life Science at the Hong Kong University of Science and
Technology, for the determination of long-range JC-1,
pling constant. We also thank Dr. Eva Fung of the Department of
Chemistry at the University of Hong Kong for ESI-HRMS measure-
ments. The support from the area of Excellence Scheme of the Uni-
versity Grants Committee (Grant AoE/M-12/06) and a seed grant
support from the University of Hong Kong (HKU200912159008)
are acknowledged.
3
cou-
H-3ax
Supplementary data
Supplementary data (1H and 13C NMR spectra of new com-
pounds) associated with this article can be found, in the online ver-
sion, at http://dx.doi.org/10.1016/j.carres.2012.08.007.
References
1. (a) Schauer, R. In Sialic Acid: Chemistry, Metabolism and Function; Spring-Verlag:
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The trichloroacetimidate donor 7 (50.6 mg, 0.049 mmol) and
glycosyl acceptor A5 (67.1 mg, 0.11 mmol) were dissolved in dry
CH2Cl2 (4 mL). The mixture was stirred at room temperature for
3 h in the presence of activated 4 Å molecular sieves (205 mg).
After cooling to À40 °C, trimethylsilyl triflate (TMSOTf, 10
lL,
0.051 mmol) was added to initiate the glycosylation process. After
stirring at À40 °C for 1 h, the reaction was quenched by NaHCO3,
diluted with CH2Cl2, and filtered through a pad of Celite. The
resulting filtrate was concentrated and purified by column chro-
matography on silica gel (Hexane/EtOAc 3:1 to 1:1) to give trisac-
charide 8 (41.0 mg, 0.028 mmol, 57%). 1H NMR (CDCl3, 400 MHz): d
8.20–8.22 (m, 2H), 7.87–7.89 (m, 2H), 7.83–7.85 (m, 1H), 7.57–7.70
(m, 4H), 7.47–7.52 (m, 3H), 7.32–7.39 (m, 7H), 7.25–7.27 (m, 2H),
6.93–6.95 (m, 2H), 5.97–6.02 (m, 2H), 5.60–5.64 (m, 2H), 5.10–5.16
(m, 2H), 4.93–4.95 (m, 2H), 4.73 (d, J = 3.3 Hz, 1H), 4.54 (dd, J = 3.4,
10.0 Hz, 1H), 4.34–4.44 (m, 2H), 4.28 (dd, J = 2.3, 12.5 Hz, 1H), 4.17
(t, J = 9.3 Hz, 1H), 3.97 (dd, J = 5.3, 12.5 Hz, 1H), 3.90 (d, J = 4.4 Hz,
1H), 3.79 (s, 1H), 3.65–3.70 (m, 1H), 3.52–3.62 (m, 2H), 3.45–
3.49 (m, 1H), 3.33 (dd, J = 5.6, 10.6 Hz, 1H), 2.52 (dd, J = 4.7,
12.7 Hz, 1H), 2.26 (s, 3H), 2.13 (s, 3H), 2.03 (s, 3H), 1.94 (s, 3H),
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