Synthesis and NMR elucidation of four novel 2-(trimethylsilyl)ethyl glycosides

Article abstract of DOI:10.1007/s11164-013-1060-0

Four novel 2-(trimethylsilyl)ethyl glycosides have been synthesized by a short and efficient route starting from d-glucose. Their structures were elucidated by applying high-resolution mass spectra, and one-dimensional and two-dimensional NMR techniques.

Full text of DOI:10.1007/s11164-013-1060-0

Res Chem Intermed
DOI 10.1007/s11164-013-1060-0
Synthesis and NMR elucidation of four novel
2-(trimethylsilyl)ethyl glycosides
•
Huanhuan Qu Wenji Sun Yanyan Zhang
•
•
•
Matthieu Sollogoub Yongmin Zhang
Received: 22 November 2012 / Accepted: 15 January 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract Four novel 2-(trimethylsilyl)ethyl glycosides have been synthesized by a
short and efficient route starting from D-glucose. Their structures were elucidated by
applying high-resolution mass spectra, and one-dimensional and two-dimensional
NMR techniques. These glycosides were prepared and used as intermediate building
blocks in the scheme developed for oligosaccharide construction.
Keywords Total synthesis Á Structure elucidation Á Glycosides Á NMR
spectroscopy Á Oligosaccharides
Introduction
Over the past three decades or so, carbohydrate chemistry has emerged from a fairly
self-contained and specialized field to one that has been thrust into a position of
center stage in chemical research. This shift in focus for the area, sometimes
referred to as ‘‘glycoscience’’, has arisen through the impact of carbohydrates on
many disciplines: biochemistry, immunology, medicinal chemistry, plant science,
food science, and nanomaterials, to name a few [1]. In recent years, a steadily
increasing research effort has been centered on the production of glycosides, and
particularly of oligo- and polysaccharides. Crucial impetus has come from the
increasing interest shown by biochemists in these substances [2].
H. Qu (&) Á Y. Zhang Á M. Sollogoub Á Y. Zhang
´
Institut Parisien de Chimie Moleculaire (UMR CNRS 7201), Universite Pierre et Marie Curie-Paris
6, C.181, 4 Place Jussieu, 75005 Paris, France
´
e-mail: aiby116@163.com
H. Qu Á W. Sun
Biomedicine Key Laboratory of Shaanxi Province, Northwest University, Xi’an 710069, People’s
Republic of China
123

H. Qu et al.
Since the first glycoside syntheses by Michael [3] and Fischer [4], followed by
the seminal studies of Koenigs and Knorr [5], a very large number of glycosylation
methods have been developed. Unlike proteins and nucleic acids, there is no general
synthetic route for oligosaccharide syntheses [6]. The development of efficient and
general synthetic routes for oligosaccharides remains a major challenge because of
the complexity of their structures.
The chemical synthesis of glycosides usually involves the transformation of a
sugar into a fully protected glycosyl donor with a leaving group at its anomeric
center. Glycosylation of a suitably protected glycosyl acceptor, which generally
contains only one free hydroxy group, then follows. Hence, the leaving group of the
glycosyl donor and the protecting groups are the most fundamental parameters with
respect to the yield and anomeric selectivity of glycosylation reaction [7].
Numerous novel glycosides have been synthesized in recent years to meet the
demands of glycosylation reaction [8–10].
In this article, we present the synthesis of four novel 2-(trimethylsilyl)ethyl
glycosides. High-resolution mass spectra (HRMS) as well as one-dimensional (1D)
and two-dimensional (2D) NMR experiments were used to determine their
structures and NMR spectral assignments. These new glycosides can be used as
intermediate building blocks for oligosaccharide synthesis, which will be the subject
of our further research.
Results and discussion
The total synthesis of new glycosides 1, 2, 3, and 4 was carried as reported in
Scheme 1, D-glucose was converted to its diacetonide 5 in high yields according to
standard procedures [11, 12]. Subsequent allylation of the remaining free 3-OH
group of diacetonide 5, followed by removal of the isopropylidene protecting groups
of allyl ether 6, provided 3-O-allyl-glucose 7. Acetylation of 7 with acetic anhydride
and sodium acetate [13] gave 1,2,4,6-tetra-O-acetyl-3-O-allyl-b-D-glucopyranose 8,
as colorless crystals after recrystallization from ethanol, then subsequently, via a
number of standard steps [14, 15], to a new 2-(trimethylsilyl)ethyl glycoside 1 in
95 % yield. Deacetylation, 4,6-O-benzylidenation, and 2-O-benzylidenation gave
2-(trimethylsilyl)ethyl 2-O-benzylidene-3-O-allyl-4,6-O-benzylidene-b-D-glucopy-
ranoside 2. Subsequent reductive benzylidene acetal opening with triethylsilane
and trifluoroacetic acid [15, 16] gave the desired glycoside 3 in 81 % yield. Further,
the allyl group of glycoside 3 was removed with palladium chloride in methanol
[17] to afford glycoside 4 in 96 % yield. New compounds 1, 2, 3 and 4 obtained by
these reactions were isolated by chromatography, were obtained in analytically pure
1
state, and were fully characterized by HRMS, H and 13C NMR data, and physical
constants.
The choice of the anomeric protecting group in the synthesis of oligosaccharides
is important for several reasons. It should be compatible with a series of different
reaction conditions that are to be utilized in the synthesis, it should be removable
without affecting the remaining glycosidic bonds of the oligosaccharide, and,
preferentially, it should be transformable into activated derivatives for further
123

Synthesis and NMR elucidation
O
O
O
O
O
O
OH
O
O
O
a
d
b
c
HO
HO
OH
O
O
5
6
OH
D-Glucose
HO
OAc
AllylO
OAc
OH
O
O
O
g
e,f
O
AcO
AcO
HO
AllylO
O
OAc
Ph
OH
O
Si
AllylO
AllylO
AcO
OAc
1
OH
8
7
OH
O
O
i
h
HO
O
AllylO
O
k
Si
AllylO
Si
HO
OH
OBn
O
OBn
O
O
Ph
O
j
O
HO
AllylO
HO
HO
O
O
O
Si
AllylO
Si
Si
3
OBn
OBn
OBn
4
2
Scheme 1 Reagents and conditions: a ZnCl2, 85 % phosphoric acid, acetone, r.t., 30 h; 70 %; b DMF,
NaH, AllBr, 0 °C - r.t., 1 h, 98 %; c 10 % AcOH, 80 °C, over night, quant.; d Ac2O, NaOAc, 140 °C,
0.5 h, crystallization 87 %; e CH2Cl2, HBr/AcOH, 0 °C - r.t., 1.5 h; f TMSEtOH, HgO, HgBr2, r.t., 18 h,
95 % (2 steps); g NaOMe, MeOH, r.t., over night, quant.; h C6H5CH(OCH3)2, CSA, dry CH3CN, N2, r.t.,
over night; i DMF, NaH, BnBr, 0 °C - r.t., 0.5 h, 92 % (2 steps); j CH2Cl2, TES, TFA, 0 °C - r.t., 0.5 h,
81 %; k MeOH, PdCl2, r.t., 1 h, 96 %
glycoside synthesis [14, 18]. Here, we chose 2-(trimethylsilyl)ethyl as the anomeric
protecting group which fulfills these criteria by being stable under the majority of
reaction conditions used in oligosaccharide synthesis. At the same time, both allyl
and benzyl are very common protecting groups which can be deprotected rapidly
under mild conditions.
Conclusions
The synthesis and complete elucidation of four novel 2-(trimethylsilyl)ethyl
glycosides were successfully carried out. The reactions allow the rapid construction
of glycosides with high yields from simple and commercially available substrates
and reagents. We believe the research will provide meaningful and useful references
for oligosaccharide synthesis.
Experimental
All chemicals were purchased as reagent grade and used without further
purification. Dichloromethane (CH2Cl2) was freshly distilled from P2O5. All
reactions were carried out under anhydrous conditions with freshly distilled
solvents, unless otherwise noted. Reactions were monitored by thin-layer chroma-
tography (TLC) on a precoated plate of silica gel 60 F254 (Merck), with detection by
staining with sulfuric acid. Solvents were evaporated under reduced pressure and
below 40 °C (bath). Flash column chromatography was performed on silica gel 60
(230–400 mesh; Merck). NMR spectra were recorded with a Bruker DRX 400
1
spectrometer (400 MHz for H NMR and 101 MHz for 13C NMR). The chemical
123

H. Qu et al.
shifts were referenced to the solvent peak, d = 7.26 ppm (1H) and d = 77.16 ppm
(13C) for CDCl3, at 25 °C, and coupling constants were given in Hz. High-resolution
mass spectra (HRMS) were recorded with a Bruker micrOTOF spectrometer in
electrospray ionization (ESI) mode, using Tuning-Mix as reference. Optical
rotations were measured at 589 nm (Na line) at 20 °C with a Perkin–Elmer Model
343 digital polarimeter, using a 10-cm, 1-mL cell.
1,2:5,6-Di-O-isopropylidene-a-D-glucofuranose (5)
To a well-stirred suspension of anhydrous D-glucose (5.0 g, 26.9 mmol) in
anhydrous acetone (50 mL) was added pulverized anhydrous zinc chloride (4.0 g)
followed by 0.15 mL of 85 % phosphoric acid. This mixture was stirred 30 h at
room temperature, and the unreacted sugar was collected and washed with a little
acetone. The filtrate and washings were cooled and made slightly alkaline with
2.5 N NaOH. The insoluble inorganic material was removed by filtration and
washed with acetone. The almost colorless filtrate and washings were concentrated
under reduced pressure and the residue was diluted with water (10 mL), extracted
with CH2Cl2 (3 9 50 mL), dried over MgSO4, and concentrated under reduced
pressure. Crystallization of the residue from hexane gave the desired compound as
colorless needles (5.01 g, 70 %). Rf = 0.44 (Cy-EtOAc 1:1). The NMR data were
identical to those reported in literatures [11, 19].
3-O-Allyl-1,2:5,6-di-O-isopropylidene-a-D-glucofura-nose (6)
To a solution of 5 (3.26 g, 12.5 mmol) in dry DMF (70 mL) were added NaH (60 %
in oil, 1.00 g, approximately 25.0 mmol) and allyl bromide (2.2 mL, 25.0 mmol) at
0 °C. The mixture was stirred for 1 h at 23 °C, quenched by careful addition of
MeOH, and diluted with diethyl ether and water [20]. The aqueous layer was
extracted four times with diethyl ether. The combined organic extracts were washed
with brine, dried over MgSO4, and concentrated in vacuo. The resulting residue was
purified by flash column chromatography (Cy-EtOAc 6:1). Compound 6 was
obtained (3.68 mg, 98 %) as a white amorphous solid. Rf = 0.35 (Cy-EtOAc 5:1).
The NMR spectral data were in good agreement with those reported in literature [21].
3-O-Allyl-D-glucofuranose (7)
Compound 6 (3.39 g, 11.3 mmol) was dissolved in acetic acid solution (10 %) and
stirred at 80 °C overnight. Solvent was evaporated and the resulting sugar 7 was
rendered free of water and acetic acid by repeated coevaporation with dry toluene.
Yield 2.44 g (yellow syrup, quant.). Rf = 0.33 (CH2Cl2-MeOH 6:1). The NMR data
were identical to those reported in the literature [22].
1,2,4,6-Tetra-O-acetyl-3-O-allyl-b-D-glucopyranose (8)
Compound 7 (2.44 g) was acetylated with acetic anhydride (50 mL) and sodium
acetate (2.46 g, 30.0 mmol) under reflux for 30 min. Most of the solvent was
123

Synthesis and NMR elucidation
evaporated, and the residue was poured into ice-water, and extracted with
chloroform (3 9 30 mL). The extracts were combined, washed successively with
water, sat. NaHCO3 solution, and water, dried, and evaporated. Crystallization from
ethanol gave 8 (3.74 g, 87 %) as colorless crystals. Rf = 0.49 (Cy-EtOAc 1:1). The
NMR data were identical to those reported in literature [13].
2-(Trimethylsilyl)ethyl 2,4,6-tri-O-acetyl-3-O-allyl-b-D-glucopyranoside (1,
C20H34O9Si)
To a stirred, ice-cold solution of 8 (2.55 g, 6.6 mmol) in CH2Cl2 (30 mL) was
added dropwise HBr in acetic acid (10 mL). The mixture was allowed to gradually
warm to room temperature and was stirred 1.5 h. The reaction mixture was
neutralized by careful addition of NaHCO3 and iced-water, and the aqueous solution
was extracted three times with CH2Cl2. The combined organic extracts were dried
over MgSO4 and concentrated in vacuo. The resulting residue was dissolved in dry
CH2Cl2 (40 mL), and (2-trimethylsilyl)ethanol (2.7 mL, 18.9 mmol), mercury(II)
oxide (1.50 g, 6.9 mmol) and mercury(II) bromide (377 mg, 1.0 mmol) were added.
The resulting suspension was stirred for 18 h at room temperature. The reaction
mixture was then diluted with CH2Cl2, stirred with KI and NaHCO3 solution for 2 h
at room temperature, and filtered through a pad of Celite. The aqueous eluate was
extracted three times with CH2Cl2, and the combined organic extracts were washed
with brine, dried over MgSO4, and concentrated in vacuo. The resulting residue was
purified by flash column chromatography (Cy-EtOAc 3:1). Compound 1 was
obtained (2.82 g, 95 %) as a white amorphous solid. Rf = 0.32 (Cy-EtOAc 3:1); mp
65–66 °C; [a]2D0 = -23.4 (c = 1.0, CHCl3); 1H NMR (400 MHz, CDCl3):
d = 5.81–5.70 (m, 1H, =CH), 5.23–5.15 (m, 1H, =CH2), 5.14–5.09 (m, 1H,
=CH2), 5.02 (d, J = 9.5 Hz, 1H, H-4), 4.98–4.92 (m, 1H, H-2), 4.40 (d, J = 7.9 Hz,
1H, H-1), 4.23–4.16 (dd, J = 12.2, 5.2 Hz, 1H, H-6a), 4.10 (dd, J = 12.2, 2.6 Hz,
1H, H-6b), 4.04 (dd, J = 5.6, 1.0 Hz, 2H, OCH2-CH=CH2), 3.93 (ddt, J = 13.7,
9.3, 4.6 Hz, 1H, OCHaCH2Si), 3.61–3.50 (m, 3H, H-3, H-5, OCHbCH2Si), 2.07
(s, 3H, OAc), 2.06 (s, 3H, OAc), 2.06 (s, 3H, OAc), 0.97–0.84 (m, 2H,
OCH2CH2Si),-0.01 (s, 9H, Si(CH3)3) ppm; 13C NMR (101 MHz, CDCl3):
d = 170.90 (C=O, Ac), 169.41 (C=O, Ac), 169.20 (C=O, Ac), 134.41 (=CH),
117.06 (=CH2), 100.57 (C-1), 80.05, 72.70 (OCH2-CH=CH2), 72.59 (C-2), 72.09,
69.81 (C-4), 67.32 (OCH2CH2Si), 62.56 (C-6), 21.09 (CH3, Ac), 20.97 (CH3, Ac),
20.88 (CH3, Ac), 18.04 (OCH2CH2Si),-1.32 (3C, Si(CH3)3) ppm; ESI-HRMS (m/z)
C20H34O9SiNa [M ? Na]?: calcd. 469.1870, found: 469.1887.
2-(Trimethylsilyl)ethyl 2-O-benzylidene-3-O-allyl-4,6-O-benzylidene-b-D-
glucopyranoside (2, C28H38O6Si)
To a solution of 1 (2.82 g, 6.3 mmol) in MeOH (40 mL) was added sodium
methoxide (cat.) and the mixture was stirred overnight at room temperature. The
reaction mixture was neutralized with Amberlite IR-120 (H?) ion-exchange resin,
filtered, and concentrated in vacuo. The residue (2.02 g) was dissolved in dry
CH3CN (50 mL), benzaldehyde dimethyl acetal (1.57 mL, 10.4 mmol), and
123

H. Qu et al.
camphorsulfonic acid (300 mg, 1.29 mmol) were added, and the mixture was stirred
overnight at room temperature. The reaction mixture was neutralized with sat.
NaHCO3 solution and the resulting aqueous solution was extracted three times with
EtOAc. The combined organic extracts were washed with brine, dried over MgSO4,
and concentrated in vacuo. The residue (2.57 g) was dissolved in dry DMF (50 ml),
and benzyl bromide (0.9 mL, 7.6 mmol) and NaH (60 % in oil, 504 mg,
approximately 21.0 mmol) at 0 °C. The mixture was stirred for 0.5 h, quenched
by careful addition of MeOH, and diluted with diethyl ether and water. The aqueous
layer was extracted four times with diethyl ether. The combined organic extracts
were washed with brine, dried over MgSO4, and concentrated in vacuo. The
resulting residue was purified by flash column chromatography (Cy-EtOAc 10:1).
Compound 2 was obtained (2.89 g, 92 %) as a white amorphous solid. Rf = 0.35
(Cy-EtOAc 10:1); mp 78–79 °C; [a]2D0 = -11.5 (c = 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d = 7.43–7.30 (m, 10H, Ar–H), 6.05–5.89 (m, 1H, =CH), 5.56
(s, 1H, CH-Ph), 5.30 (dd, J = 17.2, 1.6 Hz, 1H, =CH2), 5.17 (dd, J = 10.4, 1.4 Hz,
1H, =CH2), 4.91 (d, J = 11.0 Hz, 1H, OCH2-Ph), 4.80 (d, J = 11.0 Hz, 1H, OCH2-
Ph), 4.51 (d, J = 7.8 Hz, 1H, H-1), 4.45–4.34 (m, 2H, OCH2-CH=CH2, H-6a),
4.33–4.25 (m, 1H, OCH2-CH=CH2), 4.01 (dd, J = 13.5, 5.4 Hz, 1H, OCHaCH2Si),
3.79 (t, J = 10.3 Hz, 1H, H-6b), 3.71–3.60 (m, 3H, OCHbCH2Si, H-4, H-3), 3.41
(dd, J = 9.8, 6.4 Hz, 2H, H-2, H-5), 1.09–1.04 (m, 2H, OCH2CH2Si), 0.05 (s, 9H,
Si(CH3)3) ppm; 13C NMR (101 MHz, CDCl3): d = 138.66 (C aromatic), 138.21 (C
aromatic), 135.33 (=CH), 128.53 (2C, CH aromatic), 128.43 (2C, CH aromatic),
128.22 (2C, CH aromatic), 127.91 (2C, CH aromatic), 127.88 (C, CH aromatic),
127.75 (C, CH aromatic), 116.93 (=CH2), 103.77 (C-1), 101.23 (CH-Ph), 82.34 (C-
2), 81.57, 80.81, 75.51 (OCH2-Ph), 74.15 (OCH2-CH=CH2), 68.97 (C-6), 68.14
(OCH2CH2Si), 66.14 (C-5), 18.74 (OCH2CH2Si),-1.28 (3C, Si(CH3)3) ppm; ESI-
HRMS (m/z) C28H38O6SiNa [M ? Na]?: calcd. 521.2335, found: 521.2330.
2-(Trimethylsilyl)ethyl 3-O-allyl-2,6-di-O-benzyl-b-D-glucopyranoside (3,
C28H40O6Si)
To a stirred, ice-cold solution of 2 (1.00 g, 2.0 mmol) and triethylsilane (1.9 mL,
11.9 mmol) in CH2Cl2 (25 mL) was added dropwise trifluoroacetic acid (1.2 mL,
15.6 mmol). The mixture was stirred for 0.5 h. The reaction mixture was then
diluted with CH2Cl2 and neutralized with sat. NaHCO3 solution. The aqueous layer
was extracted three times with CH2Cl2, and the combined organic extracts were
washed with brine, dried over MgSO4, and concentrated in vacuo. The resulting
residue was purified by flash column chromatography (Cy-EtOAc 5:1). Compound 3
was obtained (0.81 g, 81 %) as a white amorphous solid. Rf = 0.28 (Cy-EtOAc
5:1); mp 103–106 °C; [a]D20 = -25.2 (c = 1.0, CHCl3); 1H NMR (400 MHz,
CDCl3): d = 7.41–7.27 (m, 10H, Ar–H), 6.02–5.88 (m, 1H,=CH), 5.27 (ddd,
J = 17.2, 3.3, 1.6 Hz, 1H,=CH2), 5.21–5.15 (m, 1H, =CH2), 4.94 (d, J = 11.1 Hz,
1H, OCH2-Ph), 4.71 (d, J = 11.1 Hz, 1H, OCH2-Ph), 4.60 (d, J = 3.1 Hz, 2H,
OCH2-Ph), 4.44–4.37 (m, 2H, H-1, OCH2-CH=CH2), 4.25 (ddt, J = 12.6, 6.0,
1.3 Hz, 1H, OCH2-CH=CH2), 4.01 (ddd, J = 9.6, 8.2, 6.0 Hz, 1H, OCHaCH2Si),
3.80 (dd, J = 10.4, 4.0 Hz, 1H, H-6a), 3.73 (dd, J = 10.4, 5.3 Hz, 1H, H-6b),
123

Synthesis and NMR elucidation
3.65–3.53 (m, 2H, OCHbCH2Si, H-4), 3.46 (ddd, J = 9.5, 5.3, 4.1 Hz, 1H, H-5),
3.38–3.32 (m, 2H, H-3, H-2), 2.82–2.68 (m, 1H, OH), 1.09–1.00 (m, 2H,
OCH2CH2Si), 0.04 (s, 9H, Si(CH3)3) ppm; 13C NMR (101 MHz, CDCl3):
d = 138.72 (C aromatic), 138.08 (C aromatic), 135.27 (=CH), 128.55 (2C, CH
aromatic), 128.45 (2C, CH aromatic), 128.20 (2C, CH aromatic), 127.85 (C, CH
aromatic), 127.81 (2C, CH aromatic), 127.76 (C, CH aromatic), 117.20 (=CH2),
103.29 (C-1), 83.95 (C-3), 81.91 (C-2), 74.81 (OCH2-Ph), 74.28 (OCH2-CH=CH2),
74.06 (C-5), 73.80 (OCH2-Ph), 71.90 (C-4), 70.66 (C-6), 67.66 (OCH2CH2Si),
18.69 (OCH2CH2Si),-1.29 (3C, Si(CH3)3) ppm; ESI-HRMS (m/z) C28H40O6SiNa
[M ? Na]?: calcd. 523.2492, found: 523.2487.
2-(Trimethylsilyl)ethyl 2,6-di-O-benzyl-b-D-glucopyranoside (4, C25H36O6Si)
To a mixture of 3 (0.70 g, 1.4 mmol) in MeOH (35 mL), PdCl2 (124 mg, 0.7 mmol)
was added and the solution was stirred at room temperature for 1 h, and filtered
through a pad of Celite. The solvent was removed and the crude product was
immediately charged into a column of silica gel and eluted with Cy-EtOAc 3:2.
Compound 4 was obtained (0.62 g, 96 %) as a white amorphous solid. Rf = 0.30
(Cy-EtOAc 3:2); mp 111–114 °C; [a]2D0 = -8.8 (c = 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d = 7.39–7.29 (m, 10H, Ar–H), 4.98 (d, J = 11.5 Hz, 1H,
OCH2-Ph), 4.69 (d, J = 11.5 Hz, 1H, OCH2-Ph), 4.60 (d, J = 3.3 Hz, 2H, OCH2-
Ph), 4.41 (d, J = 7.8 Hz, 1H, H-1), 4.06–3.96 (m, 1H, OCHaCH2Si), 3.77 (dd,
J = 10.4, 3.6 Hz, 1H, H-6a), 3.70 (dd, J = 10.4, 5.1 Hz, 1H, H-6b), 3.64–3.43 (m,
4H, OCHbCH2Si, H-3, H-4, H-5), 3.23 (dd, J = 8.7, 8.0 Hz, 1H, H-2), 3.16 (d,
J = 2.1 Hz, 1H, OH), 2.94 (d, J = 2.2 Hz, 1H, OH), 1.11–0.97 (m, 2H,
OCH2CH2Si), 0.04 (s, 9H, Si(CH3)3) ppm; 13C NMR (101 MHz, CDCl3):
d = 138.59 (C aromatic), 138.06 (C aromatic), 128.58 (2C, CH aromatic), 128.53
(2C, CH aromatic), 128.19 (2C, CH aromatic), 127.94 (C, CH aromatic), 127.84 (C,
CH aromatic), 127.79 (2C, CH aromatic), 102.93 (C-1), 81.04 (C-2), 76.21 (C-3),
74.45 (OCH2-Ph), 74.25 (C-5), 73.72 (OCH2-Ph), 71.60 (C-4), 70.38 (C-6), 67.56
(OCH2CH2Si), 18.63 (OCH2CH2Si),-1.30 (3C, Si(CH3)3) ppm; ESI-HRMS (m/z)
C50H72O12Si2Na [2 M ? Na]?: calcd. 943.4460, found: 943.4464.
Acknowledgments We thank Daowan Lai for his valuable advice. Financial support from the China
Scholarship Council for a PhD fellowship to Huanhuan Qu is gratefully acknowledged.
References
1. H. Pellissier, Tetrahedron 61, 2947 (2005)
¨
2. G. Wulff, G. Rohle, Angew. Chem. Int. Ed. Engl. 13, 157 (1974)
3. A. Michael, Am. Chem. J. 1, 305 (1879)
4. E. Fischer, Ber. Dtsch. Chem. Ges. 26, 24002 (1893)
5. W. Koenig, E. Knorr, Ber. Dtsch. Chem. Ges. 34, 957 (1901)
6. H. Paulsen, Angew. Chem. Int. Ed. Engl. 21, 155 (1982)
7. D.P. Galonic, D.Y. Gin, Nature 446, 1000 (2007)
8. K. Larsen, K. Worm-Leonhard, P. Olsen, A. Hoel, K.J. Jensen, Org. Biomol. Chem. 3, 3966 (2005)
9. M. Takatani, J. Nakano, M.A. Arai, A. Ishiwata, H. Ohta, Y. Ito, Tetrahedron Lett. 45, 3929 (2004)
10. A.V. Demchenko, Lett. Org. Chem. 2, 580 (2005)
123

H. Qu et al.
11. Y. Saito, T.A. Zevaco, L.A. Agrofoglio, Tetrahedron 58, 9593 (2002)
12. J. Milecki, E. Zamaratski, T.V. Maltseva, A. Foldesi, R.W. Adamiak, J. Chattopadhyaya, Tetrahe-
dron 55, 6603 (1999)
13. K. Takeo, T. Nakaji, K. Shinmitsu, Carbohydr. Res. 133, 275 (1984)
14. K. Jansson, S. Ahlfors, T. Frejd, J. Kihlberg, G. Magnusson, J. Org. Chem. 53, 5629 (1988)
15. H. Shimizu, J.M. Brown, S.W. Homans, R.A. Field, Tetrahedron 54, 9489 (1998)
16. M.P. DeNinno, J.B. Etienne, K.C. Duplantie, Tetrahedron Lett. 36, 669 (1995)
17. B. Mukhopadhyay, N. Roy, Carbohydr. Res. 338, 589 (2003)
18. K. Jansson, G. Noori, G. Magnusson, J. Org. Chem. 55, 3181 (1990)
19. C. Adelwohrer, T. Takano, F. Nakatsubo, T. Rosenau, Biomacromolecules 10, 2817 (2009)
20. V. Pozsgay, E.P. Dubois, L. Pannell, J. Org. Chem. 62, 2832 (1997)
21. A.B. Smith III, R.A. Rivero, K.J. Hale, H.A. Vaccaro, J. Am. Chem. Soc. 113, 2092 (1991)
22. H. Ito, R. Eby, S. Kramer, C. Schuerch, Carbohydr. Res. 86, 193 (1980)
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