Synthesis of oligosaccharides using per-O-trimethylsilyl-glycosyl iodides as glycosyl donor

Article abstract of DOI:10.1016/j.carres.2016.03.019

Trimethylsilyl (TMS) protecting group has been found to be very useful for the simultaneous protection of both the glycosyl donor- and the acceptor-substrates in oligosaccharide synthesis. Thus, while the per-O-trimethylsilylated glycosyl iodides served a

Full text of DOI:10.1016/j.carres.2016.03.019

Carbohydrate Research 427 (2016) 1–5
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Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Synthesis of oligosaccharides using per-O-trimethylsilyl-glycosyl
iodides as glycosyl donor
Hong Wang b, Yanli Cui a,*, Rong Zou a, Zhaodong Cheng a, Weirong Yao b, Yangyi Mao c,
Yongmin Zhang d
a Department of Chemistry, Zhejiang University, Hangzhou 310027, PR China
b Carbohydrate Chemistry and Biotechnology, Jiangnan University Key Laboratory of Ministry of Education, Wuxi 214122, PR China
c Hangzhou Yanqing Biotechnology Co., Ltd, Hangzhou 310052, PR China
d Institut Parisien de Chimie Moleculaire, UMR CNRS 8232, Universite Pierre et Marie Curie-Paris 6, 75005 Paris, France
A R T I C L E
I N F O
A B S T R A C T
Article history:
Received 12 October 2015
Received in revised form 21 March 2016
Accepted 22 March 2016
Available online 29 March 2016
Trimethylsilyl (TMS) protecting group has been found to be very useful for the simultaneous protection
of both the glycosyl donor- and the acceptor-substrates in oligosaccharide synthesis. Thus, while the per-
O-trimethylsilylated glycosyl iodides served as the glycosyl donor, those bearing selectively exposed primary
hydroxyl groups were found suitable as the glycosyl acceptor for the reaction. The cheap and commer-
cially available trialkylamine, triethylamine was found to be an effective promoter for the glycosylation.
Importantly, the reaction was α-stereospecific and gave the products in 58%–78% yields.
© 2016 Elsevier Ltd. All rights reserved.
Keywords:
Glycosyl iodide
α-Glycosylation
Trimethylsilyl group
Triethylamine
1. Introduction
carbohydrate is easy to prepare and deprotect.15 Recently, glycosyl
iodide,16–18 especially per-O-trimethylsilylated glycosyl iodide,16 was
Efficient formation of glycosidic linkages is a pivotal step for the
synthesis of oligosaccharides. The influencing factors for glycosylation
involve leaving groups of the glycosyl donor, catalyst, promoter,
solvent, protecting groups for the donor and the acceptor, etc.1,2
Among the various classes of glycosyl halides used for glycosylation,
glycosyl iodides, initially considered to be thermally unstable,
were largely substituted by the more stable bromide- and
chloride-analogues.3 Then in 1972, glycosyl iodides were applied
for forming O-glycosides.4 Shortly thereafter, Kronzer and Schuerch5
found that glycosyl iodides offered more advantages than glycosyl
chlorides and bromides, including less reaction time and higher
stereoselectivity. Stachulski6 and co-workers stated that glycosyl
iodides have remarkable stability at room temperature. Glycosyl
iodides attracted more attention as glycosyl donors and have been
widely utilized since then.7–9
applied for preparing several biologically active glycolipids by
Gervay-Hague and co-workers. Glycosyl iodides were prepared and
directly used as the donor. The whole process from unprotected car-
bohydrate to the donor lacked purification and only needed simple
post-processing when glycosyl iodides were prepared as the
donor.
α-Linkage formation is more difficult than β-linkage in most situ-
ations. Inspired by α-galactosyl ceramide coupling through per-O-
trimethylsilylated galactosyl iodide donor,16,19 also based on our
earlier results20 wherein 6-hydroxy trimethylsilylated monosac-
charide or 6′-hydroxy trimethylsilylated disaccharide was directly
gained by mild ammonium acetate, we envisaged the synthesis of
saccharide using per-O-trimethylsilylated glycosyl iodide as donor
and 6-hydroxy trimethylsilylated monosaccharide or 6′-hydroxy
trimethylsilylated disaccharide as acceptor. In 2002, 1,6-α-linked oli-
gosaccharides were synthesized using glycosyl iodide, but the
protecting groups for the donors and the acceptors were benzyl
groups.21 Obviously the glycosylation would be affected when the
protecting groups were trimethylsilyl groups which had different
electron and spatial effect with other types of protecting groups.
The simultaneous application of trimethylsilyl groups in the donors
and the acceptors for oligosaccharide synthesis has not yet been re-
ported. It would be worthy to observe if α-glycosidic bond could
be formed in a new structural environment and the influence of
trimethylsilyl groups on the glycosylation involved.
As protecting group, benzyl10–12 and acyl11,13,14 groups are more
stable than trimethylsilyl groups, but their protection and
deprotection go through multistep, tedious operation or chroma-
tography purification. In comparison, a per-O-trimethylsilylated
Abbreviations: MS, molecular sieves; DCM, CH2Cl2.
*
Corresponding author. Department of Chemistry, Zhejiang University, Hangzhou
310027, China. Tel.: +86 13858036095; fax: +86 57188486676.
E-mail address: cuiyl@zju.edu.cn (Y. Cui).
http://dx.doi.org/10.1016/j.carres.2016.03.019
0008-6215/© 2016 Elsevier Ltd. All rights reserved.

2
H. Wang et al./Carbohydrate Research 427 (2016) 1–5
Table 1
The effect of diverse catalysts on the yield of compound 5
Entry
Catalyst
A:B (mol ratio)a
Yield (%)
α-Isomer
1
2
3
4
5
2,6-di-tert-butylpyridine
Triethylamine
DIPEA
DMAP
DBU
1:3
1:3
1:3
1:3
1:3
70
64
60
15
10
Single
Single
Single
Single
Single
a
A:B = n (compound 4):n (compound 1).
not produce higher yield. Therefore, a 3:1 molar ratio of the donor
to the acceptor was appropriate for the reaction.
Another feature of the method is the usage of catalyst NH4OAc.
After removing the 6-O-trimethylsilyl group, the neutral mixture
was concentrated under reduced pressure and could be directly used
in glycosylation without any purification because the residual per-
O-trimethylsilylated sugar did not affect the glycosylation reaction.
In addition, the strategy had been extended to the crucial step
of α-galactosylceramide (α-GC) synthesis (Scheme 2). Previously Bz,
TBDMS and other groups were used for protecting the HO-3 and
the HO-4 of the phytoceramide for enhancing the glycosylation.16,22,23
We planned to use the trimethylsilyl groups for protecting the
phytoceramide hydroxyls. The primary trimethylsilyl group of per-
O-trimethylsilylated phytoceramide was removed by NH4OAc.20 Other
hydroxyls of the phytoceramide were protected by trimethylsilyl
groups. The trimethylsilyl groups on the HO-3 and the HO-4 of com-
pound 10 did not influence the α-glycosidic bond formation.
In order to explore the application range,
a series of
Scheme 1. Reagents: (a) 1 (0.37 mmol), TMSI (0.37 mmol), CH2Cl2 (3.70 mL); (b) 3
(0.14 mmol), NH4OAc (0.28 mmol), CH2Cl2 (1 mL), MeOH (1 mL), 86%; (c) 2
(0.37 mmol), 4 (0.12 mmol), nBu4NI (0.81 mmol), triethylamine (0.37 mmol), 4 Å MS
(100 mg), CH2Cl2 (3.70 mL), 64%; (d) Ac2O (0.37 mmol), DMAP (4.0 mg), DMF (1.5 mL),
98%.
trimethylsilylated glycosyl iodide and per-O- trimethylsilylated sugar
alcohol were subjected to glycosylation and the results are pre-
sented in Table 2. Glucosyl iodide and fucosyl iodide had similar
reactivity leading to almost identical yields. Surprisingly, practical
2. Results and discussion
Firstly, per-O-trimethylsilylated glucose 1 was synthesized by
treating glucose with a mixture of TMSCl and hexamethyldisilazane
(HMDS) in pyridine overnight at 80 °C,15 which was then con-
verted to per-O-trimethylsilylated glucosyl iodide 2 by direct reaction
with TMSI in CH2Cl2 (Scheme 1). Subsequently, active intermedi-
ate 2 was added dropwise to a mixture of alcohol 4, nBu4NI,
triethylamine and 4 Å MS in CH2Cl2. The resulting mixture was stirred
overnight and the reaction was monitored by TLC. We noticed that
the unreacted compound 2, 4 and the by-products were difficult to
analyze. So the compound 5 should be purified by flash column chro-
matography. At the beginning of our experiment, complete
detrimethylsilylation of 5 was carried out by 40% acetic acid solu-
tion, and we found that the product was a mixture of α/β anomers,
which was complicated to analyze by NMR spectrum. For concise
structural analysis, the trimethylsilyl groups were changed to acetyl
groups using Ac2O/DMAP in DMF. A good yield of fully acetylated
glycoside 6 was obtained.
Firstly, glycosylation was realized by DIPEA. To explore a more
effective promoter for this reaction, different amino catalysts were
chosen as shown in Table 1. 2,6-Di-tert-butylpyridine yielded several
by-products which were difficult to separate. The yield by trieth-
ylamine was slightly higher than by DIPEA. DMAP and DBU were
unsuitable for this reaction because of their low reaction-promoting
activity. Under the same conditions, DBU also caused trimethylsilyl
groups to fall off during the reaction. Ultimately, cheap triethyl-
amine was proved to be most advantageous as a promoter.
In the previous application, glycosyl iodides were often exces-
sively used. The ratio of the donor and the acceptor was worthy of
investigation. Screening experiments proved that higher ratio did
Scheme 2. Reagents: (a) 7 (0.37 mmol), TMSI (0.37 mmol), CH2Cl2 (3.70 mL); (b) 9
(0.15 mmol), NH4OAc (0.30 mmol), CH2Cl2 (1 mL), MeOH (1 mL), 82%; (c) 8
(0.37 mmol), 10 (0.12 mmol), nBu4NI (0.81 mmol), triethylamine (0.37 mmol), 4 Å MS
(100 mg), CH2Cl2 (3.70 mL),,79%; (d) 40% acetic acid solution (5 mL), 98%.

H. Wang et al./Carbohydrate Research 427 (2016) 1–5
3
Table 2
Formation of α-glycosidic bond
Entry
1
Donor
Acceptor
Product
Time (h)
12
Yielda (%)
63%
28
420
6
2
12
66%
14
2
15
3
12
70%
139
4
16
17
4
5
12
12
74%
60%
14
13
13
1820
19
6
12
58%
13
2020
21
7
8
—
12
12
0
14
228
77%
1020
88
12
a
Yields based on the acceptors.
glycosyl coupling did not happen in any substrates. When the donor
was per-O-trimethylsilylated lactosyl iodide, the reaction did not
proceed while using 6-monohydroxy trimethylsilylated monosac-
charide 14 as the acceptor (Table 2, entry 7), which implied that the
monosaccharide donor iodide had sufficient activity to attack
the acceptor. Other new disaccharides, trisaccharide and
α-galactosylceramide (α-GC) were obtained by the above accessi-
ble procedures. The outcomes were confirmed by NMR, formed

4
H. Wang et al./Carbohydrate Research 427 (2016) 1–5
α-glycosidic bond, which was inferred from the chemical shifts and
coupling constants of the anomeric proton signals. The other
anomeric bonds connected to the acetyl group on compound 6, 16,
19, and 21 were confirmed as α-glycosidic bonds.
4.3. α-D-Galactopyranosyl-(1→1)-(2S,3R,4R)-2-azido-octadecane-
1,3,4-triol (12)
TMSI (50 μL, 0.37 mmol) was added to a solution of 7 (0.2 g,
0.37 mmol) in CH2Cl2 (3.7 mL) at 0 °C. The reaction mixture was
stirred under an argon atmosphere for 15 min. In a separate flask,
a mixture of activated 4 Å molecular sieves (100 mg), nBu4NI (0.30 g,
0.81 mmol), triethylamine (51 μL, 0.37 mmol), and alcohol 10
(58.5 mg, 0.12 mmol) in CH2Cl2 (3.70 mL) was prepared and stirred
under argon for 20 min. The solution of glycosyl iodide was then
added dropwise over 20 min to this mixture, and the resulting
mixture was stirred overnight. After removal of the solvent under
reduced pressure, the mixture was purified by flash column chro-
matography (petroleum ether/ethyl acetate = 17:3) to afford glycoside
11. Then treating the glycoside 11 with 40% acetic acid solution 5 mL
overnight provided the fully deprotected glycoside 12 (single
3. Conclusion
In summary, we report a novel and efficient pathway for the syn-
thesis of oligosaccharides with exclusive α-stereoselectivity. The
trimethylsilyl groups as protecting groups for the acceptor did not
affect the α-glycosidic bond formation with the trimethylsilylated
monosaccharide iodide as the donor. Given the mild conditions and
the easy operation of trimethylsilyl groups, this method is labor-
saving, eco-friendly and economic. It provides rapid access to
biologically relevant carbohydrates.
[ ]
α D20
=−7.6
(c = 1.2 in
α-anomer) as a white solid (46.7 mg, 77%).
CHCl3:MeOH(1:1)). 1H NMR (DMSO–d6, 400 MHz,) δ 4.70 (d, 1H,
J = 4.0 Hz, anomeric proton), 3.94 (d, 1H, J = 8.0 Hz), 3.71 (s, 1H), 3.66–
3.58 (m, 3H), 3.54–3.50 (m, 1H), 3.47–3.41 (m, 1H), 3.35 (s, 4H), 1.59
(s, 1H), 1.45 (s, 1H), 1.24 (s, 24H), 0.85 (t, 3H, J = 4.0 Hz); 13C NMR
(DMSO–d6, 101 MHz) δ 99.89 (C–1, anomeric carbon), 74.77, 71.42,
70.66, 69.41, 68.69, 68.13, 66.87, 62.44, 60.42, 33.09, 31.27, 29.23,
29.11, 29.04, 28.99, 28.69, 25.04, 22.07, 13.93. HRMS (ESI) calcd for
C24H47N3O8 [M + Na]+ 528.3255, found 528.3254.
4. Experimental methods
4.1. General
All reagents were obtained from commercial sources (some from
Adamas-beta, PRC) and used without further purification. Sol-
vents were dried using standard methods. Reactions were monitored
by TLC using a silica gel 60 F 254 precoated plate (Merk, Darm-
stadt, Germany), and detection was performed by charring with
sulfuric acid. Flash column chromatography was performed on silica
gel 60 (100–400 mesh, Qingdao Marine Chemical Ltd., Qingdao, PRC).
NMR spectra were recorded at ambient temperature (400 MHz for
1H NMR and 101 MHz for 13C NMR) on a Bruker DRX 400 (Karlsruhe,
Germany). Mass spectral data were determined by LTQ FT Ultra
(Thermo Fisher Scientific, USA).
4.4. Methyl 2,3,4-tri-O-trimethylsilyl-β-D-galactopyranoside (14)
Compound 14 was afforded according to the method described
in previous literature20 as a white solid (33.5 mg, 85%). Rf = 0.52 (pe-
troleum ether/ethyl acetate = 8:1). 1H NMR (400 MHz, CDCl3) δ 4.11
(d, J = 8.0 Hz, 1H), 3.86 (dd, 1H), 3.77 (d, J = 3.2 Hz, 1H), 3.66–3.62
(m, 2H), 3.52 (s, 3H), 3.50–3.47 (m, 1H), 3.42 (dd, 1H), 0.16 (s, 9H),
0.15 (s, 18H). 13C NMR (101 MHz, CDCl3) δ 104.63, 74.67, 74.49, 71.89,
71.59, 62.40, 56.83, 0.23, 0.17, 0.00. HRMS (DART) calcd for C16H38O6Si3
[M + H]+ 411.2048, found 411.2048.
4.2. O-(2,3,4,6-Tetra-O-acetyl-α-D-glucopyranosyl)-(1→6)-
1,2,3,4-tetra-O-acetyl-α-D-galactopyranose (6)
TMSI (50 μL, 0.37 mmol) was added to a solution of 1 (0.20 g,
0.37 mmol) in CH2Cl2 (3.70 mL) at 0 °C. The reaction mixture was
stirred under an argon atmosphere for 15 min. In a separate flask,
a mixture of activated 4 Å molecular sieves (100 mg), nBu4NI (0.30 g,
0.81 mmol), triethylamine (51 μL, 0.37 mmol), and alcohol 4 (34.8 mg,
0.12 mmol) in CH2Cl2 (3.70 mL) was prepared and stirred under argon
for 20 min. The solution of glycosyl iodide was then added dropwise
over 20 min to this mixture, and the resulting mixture was stirred
overnight. After removal of the solvent under reduced pressure, the
mixture was purified by flash column chromatography (petro-
leum ether/ethyl acetate = 15:1) to afford glycoside 5. Then DMAP
(4.0 mg) and Ac2O (35 μL, 0.37 mmol) were added to a solution of
glycoside 5 in DMF (1.50 mL) and stirred overnight providing the
fully acetylated glycoside, and then concentrated under reduced pres-
sure. The resulting solid was purified by flash column
chromatography (petroleum ether/ethyl acetate = 2:1) to afford gly-
coside 6 (single α-anomer) as a white solid (51.2 mg, 63%). Rf = 0.55
4.5. O-(2,3,4,6-Tetra-O-acetyl-α-D-glucopyranosyl)-(1→6)-
1-O-methyl-2,3,4-tri-O-acetyl-β-D-glycosides (15)
The procedure was the same as that for compound 6. Com-
pound 15 was afforded from glycosyl iodide 2 and alcohol 14 as a
white solid (51.6 mg, 66%): Rf = 0.60 (petroleum ether/ethyl
[ ]
α D20
= +20.1
(c = 0.5, DCM). 1H NMR(CDCl3, 400 MHz)
acetate = 1:1).
δ 5.46 (d, 1H, J = 8.0 Hz), 5.42 (d, 1H, J = 4.0 Hz), 5.19 (dd, 1H), 5.07
(d, 1H, J = 8.0 Hz), 5.03–5.00 (m, 1H), 4.94 (d, 1H, J = 4.0 Hz, anomeric
proton), 4.88 (dd, 1H), 4.42 (d, 1H, J = 8.0 Hz, H–1′ β), 4.25 (dd, 1H),
4.15–4.11 (m, 2H), 4.09–4.04 (m, 1H), 3.90 (t, 1H), 3.80 (dd, 1H), 3.52
(s, 3H), 2.14 (s, 3H), 2.10 (s, 3H), 2.08 (s, 3H), 2.07 (s, 3H), 2.01 (d,
6H), 1.97 (s, 3H); 13C NMR(CDCl3, 101 MHz) δ170.64, 170.36, 170.18,
170.16, 170.11, 169.58, 169.54, 102.17 (C–1′ β anomer), 96.00 (C–
1, anomeric carbon), 71.50, 71.06, 70.26, 70.00, 68.82, 68.37, 67.52,
67.39, 65.83, 61.67, 57.05, 20.83, 20.72, 20.69, 20.63, 20.59. HRMS
(ESI) calcd for C27H38O18 [M + Na]+ 673.1950, found 673.1941.
[ ]
α D20
= +22.6
(c = 0.5, DCM).
(petroleum ether/ethyl acetate = 1:1).
1H NMR(CDCl3, 400 MHz) δ 6.36 (d, 1H, J = 3.2 Hz, H–1′ α), 5.53 (s,
1H), 5.43 (t, 1H), 5.33 (d, 2H), 5.04 (t, 1H), 4.90 (d, 1H, J = 4.0 Hz,
anomeric proton), 4.86 (dd, 1H), 4.33 (t, 1H), 4.25 (dd, 1H), 4.11 (dd,
1H), 4.03–3.99 (m, 1H), 3.73–3.69 (m, 1H), 3.45–3.41 (m, 1H), 2.21
(s, 3H), 2.15 (s, 3H), 2.10 (s, 3H),2.08 (s, 3H), 2.04 (s, 6H), 2.01 (s,
3H), 2.00 (s, 3H); 13C NMR(CDCl3, 101 MHz) δ 170.66, 170.41, 170.14,
170.06, 170.00, 169.94, 169.61, 169.08, 96.13 (C–1, anomeric carbon),
89.63 (C–1′ α anomer), 70.23, 69.95, 69.26, 68.32, 67.58, 67.58, 67.53,
66.47, 65.67, 61.70, 20.95, 20.73, 20.68, 20.63, 20.62, 20.57, 20.55,
20.55. HRMS (ESI) calcd for C28H38O19 [M + Na]+ 701.1899,found
701.1898.
4.6. O-(2,3,4-Tri-O-acetyl-α-L-fucopyranosyl)-(1→6)-
1,2,3,4-tetra-O-acetyl-α-D-galactopyranose (16)
The procedure was the same as that for compound 6. Com-
pound 16 was afforded from the glycosyl iodide 13 and alcohol 4
as a white solid (52.1 mg, 70%): Rf = 0.63 (petroleum ether/ethyl
[ ]
α D20
=−62.1
(c = 0.5, DCM). 1H NMR(CDCl3, 400 MHz)
acetate = 1:1).
δ 6.38 (d, 1H, J = 3.2 Hz, H–1′ α), 5.52 (s, 1H), 5.36–5.38 (m, 2H), 5.31–
5.27 (m, 2H), 5.10–5.08 (m, 1H), 5.06 (d, 1H, J = 2.8 Hz, anomeric
proton), 4.28 (t, 1H), 4.06–4.02 (m, 1H), 3.66 (dd, 1H), 3.57–3.52 (m,
1H), 2.18 (s, 3H), 2.17 (s, 3H), 2.16 (s, 3H), 2.08 (s, 3H), 2.03 (s, 3H),

H. Wang et al./Carbohydrate Research 427 (2016) 1–5
5
2.01 (s, 3H), 1.98 (s, 3H), 1.12 (d, 3H, J = 8.0 Hz); 13C NMR(CDCl3,
101 MHz) δ 170.68, 170.58, 170.08, 170.00, 169.92, 169.42, 169.03,
96.59 (C–1, anomeric carbon), 89.74 (C–1′ α anomer), 70.96, 69.58,
67.96, 67.89, 67.75, 67.47, 66.53, 66.15, 64.77, 20.98, 20.71, 20.65,
20.57, 19.78, 15.87. HRMS (ESI) calcd for C26H36O17 [M + Na]+ 643.1844,
found 643.1844.
as a white solid (63.2 mg, 58%). Rf = 0.50 (petroleum ether/ethyl
α D20
= +42.4 (c = 0.5, DCM). 1H NMR(CDCl3, 400 MHz)
acetate = 1:1).
[
]
δ 6.26 (d, 1H, J = 3.6 Hz, H–1″ α), 5.46 (t, 1H), 5.38 (d, 1H, J = 3.2 Hz),
5.30–5.26 (m, 2H), 5.16–5.10 (m, 1H), 5.11 (s, 1H, J = 3.2 Hz, anomeric
proton), 5.09–5.06 (m, 1H), 5.04–4.95 (m, 2H), 4.48 (d, 1H, J = 8.0 Hz,
H–1′ β), 4.45 (d, 1H, J = 2.0 Hz), 4.13–4.08 (m, 1H), 4.05–3.98 (m,
2H), 3.85–3.78 (m, 2H), 3.64–3.59 (m, 2H), 2.18–2.16 (m, 9H), 2.13
(s, 3H), 2.10 (s, 3H), 2.06 (s, 6H), 2.01 (m, 3H), 1.98 (s, 3H), 1.96 (s,
3H), 1.13 (d, 3H, J = 8.0 Hz); 13C NMR(CDCl3, 101 MHz) δ 170.62,
170.51, 170.33, 170.03, 169.98, 169.90, 169.87, 169.58, 169.20, 168.95,
101.28 (C–1′ β anomer), 96.31 (C–1, anomeric carbon), 89.03 (C–
1″ α anomer), 75.73, 71.60, 71.06, 70.87, 70.75, 69.69, 69.33, 69.19,
68.07, 67.59, 67.07, 65.00, 64.96, 61.51, 20.97, 20.87, 20.85, 20.79,
20.69, 20.65, 20.51, 19.78, 15.95. HRMS (ESI) calcd for C38H52O25
[M + Na]+ 931.2689, found 931.2692.
4.7. O-(2,3,4-Tri-O-acetyl-α-L-fucopyranosyl)-(1→6)-
1-O-methyl-2,3,4-tri-O-acetyl-β-D-glycosides (17)
The procedure was the same as that for compound 6. Com-
pound 17 was afforded from the glycosyl iodide 13 and alcohol 14
as a white solid (52.6 mg, 74%). Rf = 0.65 (petroleum ether/ethyl
acetate = 1:1).
[ ]
α D20
=−58.1 (c = 0.5, DCM). 1H NMR(CDCl3, 400 MHz)
δ 5.40 (d, 1H, J = 3.6 Hz), 5.33–5.27 (m, 2H), 5.20 (dd, 1H), 5.11 (d,
1H, J = 2.8 Hz), 5.09 (d, 1H, J = 2.8 Hz, anomeric proton), 5.02 (dd,
1H), 4.40 (d, 1H, J = 8.0 Hz, H–1′ β), 4.06 (dd, 1H), 3.87 (t, 1H), 3.72–
3.61 (m, 2H), 3.52 (s, 3H), 2.16 (d, 6H, J = 1.2 Hz), 2.07 (d, 6H,
J = 2.4 Hz), 1.98 (s, 6H), 1.12 (d, 3H, J = 8.0 Hz); 13C NMR(CDCl3,
101 MHz) δ 170.58, 170.52, 170.25, 170.13, 169.99, 169.56, 102.02
(C–1′ β anomer), 96.52 (C–1, anomeric carbon), 71.74, 71.02, 70.97,
68.84, 68.00, 67.78, 67.65, 66.19, 64.73, 56.88, 20.83, 20.76, 20.71,
20.66, 20.60, 19.77, 15.90. HRMS (ESI) calcd for C25H36O16 [M + Na]+
615.1895, found 615.1893.
Acknowledgments
The financial support from the National Natural Science Foun-
dation of China under Grant No. 30870553, the International Science
& Technology Cooperation Program of China under Grant No.
2010DFA34370 and the International S&T Cooperation Program of
Zhejiang under Grant No. 2013C14012 for this work is greatly
appreciated.
4.8. O-(2,3,4-Tri-O-acetyl-α-L-fucopyranosyl)-(1→6)-
1,2,3,4-tetra-O-acetyl-α-D-glucopyranoside (19)
Supplementary material
The procedure was the same as that for compound 6. Com-
pound 19 was afforded from the glycosyl iodide 13 and alcohol 18
as a white solid (44.7 mg, 60%). Rf = 0.63 (petroleum ether/ethyl
General information and analytical data for compound 6,
12, 14-17, 19-21 to this article can be found online at
doi:10.1016/j.carres.2016.03.019.
acetate = 1:1).
[ ]
α D20
= +18.6 (c = 0.5, DCM). 1H NMR(CDCl3, 400 MHz)
δ 6.34 (d, 1H, J = 3.2 Hz, H–1′ α), 5.46 (t, 1H), 5.35–5.32 (m, 2H), 5.22
(t, 1H), 5.15–5.09 (m, 2H), 4.98 (d, 1H, J = 2.8 Hz, anomeric proton),
4.14 (dd, 1H), 4.04–4.00 (m, 1H), 3.79–3.75 (m, 1H), 3.42 (dd, 1H),
2.18 (s, 3H), 2.16 (s, 3H), 2.11 (s, 3H), 2.02 (m, 9H), 1.99 (s, 3H), 1.13
(d, 3H, J = 8.0 Hz); 13C NMR(CDCl3, 101 MHz) δ 170.86, 170.61, 170.37,
170.03, 169.60, 169.16, 168.83, 96.72 (C–1, anomeric carbon), 89.16
(C–1′ α anomer), 71.03, 70.63, 70.12, 69.14, 68.11, 68.00, 67.86, 65.66,
64.49, 20.92, 20.76, 20.73, 20.70, 20.68, 20.61, 20.48, 15.89. HRMS
(ESI) calcd for C26H36O17 [M + Na]+ 643.1844, found 643.1843.
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4.9. Trimethylsilyl 1,2,3,6,2′,3′,4′-hepta-O-trimethylsilyl-α-D-
lactoside (20)
Compound 20 was afforded according to the method described
in previous literature20 as a white solid (76 mg, 52.7%). Rf = 0.38 (pe-
troleum ether/ethyl acetate = 8:1). 1H NMR (400 MHz, CDCl3) δ 5.02
(d, J = 3.1 Hz, 1H), 4.28 (t, J = 8.7 Hz, 1H), 4.00 (dd, 1H), 3.83 (dd, 1H),
3.73 (q, J = 8.6 Hz, 2H), 3.70–3.56 (m, 4H), 3.50 (dd, 1H), 3.44–3.29
(m, 3H), 0.13 (s, 9H), 0.12 (s, 27H), 0.08 (s, 18H), 0.07 (s, 9H). 13C
NMR (101 MHz, CDCl3) δ 102.47, 94.19, 75.82, 75.65, 74.90, 74.01,
72.43, 72.24, 71.85, 71.15, 62.53, 60.73, 0.91, 0.83, 0.69, 0.51, 0.47,
0.29, 0.02. HRMS (DART) calcd for C33H78O11Si7 [M + H]+ 847.4001,
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4.10. O-(2,3,4-Tri-O-acetyl-α-L-fucopyranosyl)-(1→6)-
2,3,4-tri-O-acetyl-β-D-galactopyranosyl-(1→4)-1,2,3,6-tetra-O-
acetyl-α-D-glucopyranoside (21)
The procedure was the same as that for compound 6. Com-
pound 21 was afforded from the glycosyl iodide 13 and alcohol 20