Syntheses of alkenylated carbohydrate derivatives toward the preparation of monolayers on silicon surfaces

Article abstract of DOI:10.1016/j.carres.2004.09.004

This note describes the synthesis of different alkenylated carbohydrate derivatives suitable for direct attachment to hydrogen-terminated silicon surfaces. The derivatives were alkenylated at the C-1 position, while the remaining hydroxyl groups were protected. The development of such new carbohydrate-based sensing elements opens the access to new classes of biosensors.

Full text of DOI:10.1016/j.carres.2004.09.004

Carbohydrate
RESEARCH
Carbohydrate Research 339 (2004) 2599–2605
Note
Syntheses of alkenylated carbohydrate derivatives toward
the preparation of monolayers on silicon surfaces
Louis C. P. M. de Smet,a Aliaksei V. Pukin,a Gerrit A. Stork,a C. H. Ric de Vos,b
Gerben M. Visser,a,* Han Zuilhof a and Ernst J. R. Sudho¨ltera
aLaboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB Wageningen, The Netherlands
bPlant Research International, PO Box 16, 6700 AA Wageningen, The Netherlands
Received 17 June 2004; accepted 1 September 2004
Abstract—This note describes the synthesis of different alkenylated carbohydrate derivatives suitable for direct attachment to hydro-
gen-terminated silicon surfaces. The derivatives were alkenylated at the C-1 position, while the remaining hydroxyl groups were pro-
tected. The development of such new carbohydrate-based sensing elements opens the access to new classes of biosensors.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Mono- and disaccharides; Alkenylation; Hydrosilylation; Receptors; Biosensors
Only very recently the construction of carbohydrate
arrays on glass has been reported.1,2 This allows for
optical or spectroscopic detection of specific carbo-
hydrate–protein interactions. Given the essential role
of carbohydrates in many biological processes, the
development of new carbohydrate sensing elements will
likely provide a tremendous stimulus to this field. The
application of modified silicon in this area can open
up a whole new field of research, as the semiconducting
nature of the substrate provides a unique feature in
silicon-based biosensing.3–5 This latter property allows
for detection of selective recognition of, for example,
antibodies to oligosaccharide receptors via changes in
capacitance. An example of this principle can be found
in a recent study in which real-time capacitance mea-
surements were performed to monitor DNA hybridiza-
tion on oligodeoxynucleotide-modified silicon.6
ricinus communis agglutinin (RCA120) molecules from
a contacting solution as well as nonspecific adsorption
on the Si–O area. The other paper8 presents our work
on the functionalization of Si(100)–H with well-defined,
covalently attached heterogeneous monolayers contain-
ing carbohydrates (Fig. 1). The monosaccharides we
have chosen in this study do not have properties regard-
ing any specific adsorption, but were used to develop
different methods and conditions to produce the first
case of well-defined, carbohydrate-substituted monolay-
ers. Two methods were used to attain this aim: a thermal
method (refluxing in mesitylene) and an extremely mild
photochemical method9 (irradiation with 447nm at
room temperature).
In 2003 two papers on the attachment of monosaccha-
rides to crystalline silicon appeared in the literature.
One7 describes the preparation of homogeneous mono-
layers of allyl a-D-galactopyranoside on the Si(100)–H
surface. The authors observed specific adsorption of
Figure 1. Formation of
a well-defined, carbohydrate-substituted
*
monolayer on the silicon surface. The ellipses and wavy bonds
represent a protected carbohydrate and alkyl spacers, respectively.
Corresponding author. Tel.: +31 317 484810; fax: +31 317 484914;
e-mail: gerben.visser@wur.nl
0008-6215/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2004.09.004

2600
L. C. P. M. de Smet et al. / Carbohydrate Research 339 (2004) 2599–2605
For the preparation of such well-defined monolayers
Due to the twisted conformation of the bonds closest to
the Si surface (Si–C–C–C), a rapidly deteriorating
monolayer quality is observed for alkenes with alkyl
chains that are shorter than 12 atoms.14 For this reason
the use of 10-undecen-1-ol (the longest x-alkene-1-ol
commercially available) to alkenylate carbohydrates is
advocated and applied in the present work.
SnCl4 was also used to attach 10-undecen-1-ol (3) to
octa-O-acetyl-b-lactose (2), a commercially available
peracetylated disaccharide. The resulting product 5
was attached to crystalline silicon surfaces, and the anal-
ysis of the resulting mixed monolayers is in progress.
Apart from the direct attachment to the silicon sur-
face, compound 4 was also applied in the three-step
synthesis of compound 8 (Scheme 1, steps b–d, respec-
tively). In the first step the acetyl groups are removed
of carbohydrate derivatives on silicon surfaces, at least
two structure properties are required: (a) presence of
an x-alkenyl tail in order to perform the hydrosilylation
reaction, and (b) protection of the hydroxyl groups—of
both alcohols and acids—in order to prevent the inter-
fering reaction between these groups and the hydro-
gen-terminated silicon surface.10–12 In this note we
report the synthesis of several monosaccharides and
one disaccharide with those properties.
Using SnCl4 as a Lewis acid catalyst,13 10-undecen-1-
ol (3) was attached to penta-O-acetyl-b-D-glucopyranose
(1) resulting in compound 4 (Scheme 1, step a). After
purification via column chromatography, compound 4
was directly available for the attachment on the hydro-
gen-terminated surface. It is obvious that all remaining
hydroxyl groups need to be protected in order to avoid
random binding of the alkenylated carbohydrate deriva-
tives via either the 1-alkene or hydroxyl functionality.10
Shirahata et al. used allyl a-D-galactopyranoside to
modify the Si(100)–H surface.7 Although free hydroxyl
groups will also react with this surface, the authors did
not discuss the resulting aspecificity of the hydrosilyl-
ation. Another relevant difference between allyl a-D-gal-
actopyranoside and the carbohydrate derivatives
presented in this Note is the length of the alkenyl chain.
according to the general deacetylation method devel-
´
15
oped by Zemplen and Pascu. The use of NaOCH3 in
MeOH afforded compound 6 in an almost quantitative
yield. Using trityl chloride,16 the primary hydroxyl
group at C-6 was tritylated yielding compound 7. Subse-
quently, the remaining three free hydroxyl groups were
protected with trifluoromethylbenzoyl groups,16 giving
compound 8 in a good yield.
In the synthesis of compound 8 the trityl group was
introduced in order to have a handle to synthesize
AcO
AcO
O
O
R1O
AcO
R1O
AcO
a
β
OAc
HO
O
+
9
9
OAc
OAc
1 R1 = Ac
4 R1 = Ac
3
2 R1 = tetra-O-acetyl-β-D-galactosyl
5 R1 = tetra-O-acetyl-β-D-galactosyl
HO
TrO
O
O
HO
b
HO
HO
c
O
O
HO
OH
6
9
9
OH
7
O
TrO
R2 =
O
OR2
R2O
d
R2O
O
CF3
9
8
Scheme 1. Reagents and conditions: (a) SnCl4 in dry CH2Cl2, rt, 38–56%; (b) NaOCH3 in MeOH, rt, 96%; (c) Ph3CCl, DMAP in pyridine, rt, 64%;
(d) 3-(trifluoromethyl)benzoylchloride, DMAP in pyridine, rt, 77%.

L. C. P. M. de Smet et al. / Carbohydrate Research 339 (2004) 2599–2605
2601
oligosaccharides. Detritylation17 would result in a glucose
derivative with only one free hydroxyl group at C-6,
which can be linked with a glycosyl donor yielding an
oligosaccharide. The trifluoromethylbenzoyl protection
group was chosen since the fluorine atom proved to be
a good probe for XPS studies of monolayers with com-
pound 8.8,9
In the second part of this report we focus on the der-
ivatization of sialic acids, which are a crucial component
in oligosaccharides that play a role in cell recognition
processes.16,18,19 Their chemistry frequently requires
more subtle procedures for regio- and stereoselective
introduction of glycosidic linkages.16,18,20–22 Sialic acid-
containing carbohydrates display a diminished thermal
stability, but can in combination with our recently
developed photochemical approach nevertheless be
linked smoothly to the Si surface.8,9
Protection of the hydroxyl groups that are present in
commercially available sialic acid (compound 9) took
place in two steps (Scheme 2, steps a and b, respec-
tively). Treatment of 9 with acidified MeOH gave the
methyl glycoside 10.23 Acetylation of 10 with AcCl23
acetylates all the hydroxyl groups including the one at
C-1. At C-1 this is followed by the in situ formation of
the a/b chloride at the anomeric centre yielding 11.
The glycosylation conditions used in step c of Scheme
2 were obtained from the work of Tomoo et al.24 The
alkenylation was promoted with AgOTf, and according
to the NMR spectrum, the crude product was a mixture
containing the a:b isomers of compound 12 in a ratio of
3:2. The total yield was 79%.
In conclusion, the syntheses of three different pro-
tected alkenylated monosaccharides (compounds 4, 8,
and 12) and one disaccharide (compound 5) are re-
ported. The monosaccharide derivatives have been used
successfully in the modification of silicon surfaces as de-
scribed recently in our paper ÔCovalently attached sac-
charides on silicon surfacesÕ.8 The development of new
1-alkenyl-derivatized carbohydrate-based sensing ele-
ments plays a crucial role in the development of capac-
itance-based biosensors on silicon. Future work will
focus on the derivatization and embedding of larger
oligosaccharides.
1. Experimental
1.1. General methods
CH2Cl2 and CH3CN were distilled over CaH2. Distilled
˚
MeOH was dried over 3A molecular sieves. Pyridine
was dried over KOH. All solvents for extractions and
chromatography were distilled. Petroleum ether refers
to the bp 40–60ꢁC fraction. All reactions were carried
out under a nitrogen or argon atmosphere with glass-
ware dried at P120ꢁC. Thin-layer chromatography
(TLC) was performed on E. Merck Silica Gel 60F254
plastic sheets, and detection was realized by either of
the following methods: charring with a solution of
KMnO4 (aq), molybdenum reagents (ammonium
molybdate (21g), ammonium cesium(IV) sulfate (1.8),
water (469mL), and H2SO4 (31mL)), 5% (v/v) sulfuric
acid in MeOH and subsequent heating or UV detection.
Column chromatography was conducted by elution of a
column of E. Merck Kieselgel (230–400mesh) using elu-
ents as specified below. NMR spectra were recorded on
a Bruker AC-E 200 or a Bruker DPX 400 spectrometer
in solvents as specified below at room temperature.
Samples of compounds 4, 5, 8, and 12 were subjected
to accurate-mass LC–MS on a high-resolution time-of-
flight mass spectrometer with lock mass correction.25
The ESIMS (Q-TOF Ultima, Waters Corporation)
was calibrated with 0.05% phosphoric acid in 50%
acetonitrile. The carbohydrate derivatives were dis-
solved and diluted in 75% acetonitrile and subsequently
injected at 10lL/min using a syringe pump (Harvard
Apparatus PHD2000). The following settings were ap-
plied: desolvation temperature of 250ꢁC with a nitrogen
gas flow of 300L/h, capillary spray at 2.5kV, source
temperature of 120ꢁC, cone voltage at 35eV with
OR1
R3
OAc
O
9
R1O
OR2
+
AcO
OCH3
O
O
c
AcHN
R1O
HO
AcHN
AcO
9
O
O
R1O
AcO
3
12
R1
R2
R3
9
10
11
H
H
OH
OH
Cl
a
b
H
Me
Me
Ac
Scheme 2. Reagents and conditions: (a) MeOH, (H+) resin, rt; (b) AcCl, rt, 48h, 66%; (c) dry CH3CN (dark), rt, 1h; AgOTf, stirred at 35–45ꢁC for
48h, 79%.

2602
L. C. P. M. de Smet et al. / Carbohydrate Research 339 (2004) 2599–2605
50L/h nitrogen gas flow, collision energy ranging from 3
to 10eV (depending on compound). Ions in the m/z range
70–1500 were detected in the centroid mode, using a
scan time of 0.9s and an interscan delay of 0.1s. In case
the mass signal was not detectable or too low for reliable
accurate mass measurements, HCO2H (0.1%) or
NH4OAc (2mM) was added to enhance the signal. Leu-
cine enkaphalin in 50% acetonitrile plus 2mM NH4OAc
was used as a lock mass (recorded every 10s), injected at
a flow rate of 10lL/min using a separate syringe pump.
MassLynx software version 4.0 (Waters) was used to
control the MS and to calculate accurate masses.
After the formation of gas stopped, the solution was fil-
tered over Hyflo. The precipitate was washed thoroughly
with CH2Cl2. The combined organic phase was evapo-
rated to give 4.2g of residue. Column chromatography
(gradient of 2:1 petroleum ether–EtOAc to 100% EtOAc)
yielded 5 (1.95g, 56%) as a white solid.
1
TLC Rf 0.63 (1:1 petroleum ether–EtOAc); H NMR
(400MHz, C6D6): d 5.97–5.87(m, 1H, –CH@CH2), 5.61
(dd, 1H, J2 ,3 10.5Hz, J1 ,2 7.9Hz, H-20), 5.57 (dd, 1H,
0
0
0
0
J3 ,4 3.4Hz, J4 ,5 0.8Hz, H-40), 5.52 (t, 1H, J2,3 = J3,4
9.0Hz, H-3), 5.34 (dd, 1H, J2,3 9.0Hz, J1,2 7.5Hz, H-
0
0
0
0
2), 5.21 (dd, 1H, J2 ,3 10.5Hz, J3 ,4 3.4Hz, H-30), 5.20–
0
0
0
0
5.09 (m, 2H, –CH@CH2), 4.64 (dd, 1H, J6a,6b 11.5Hz,
J5,6a 2.0Hz, H-6a), 4.48 (d, 1H, J1 ,2 7.9Hz, H-10),
4.38 (d, 1H, J1,2 7.5Hz, H-1), 4.30–4.19 (m, 3H, H-6b,
H-60a, H-60b), 3.91 (dt, 1H, 2J 9.5Hz, 3J 6.5Hz,
–OCHa–), 3.79 (ꢁt, 1H, J4,5 9.5Hz, J3,4 9.0Hz, H-4),
3.60–3.57 (m, 1H, H-50), 3.48 (dt, 1H, 2J 9.5Hz, 3J
6.5Hz, –OCHb–), 3.40 (ddd, 1H, J4,5 9.5Hz, J5,6b
5.5Hz, J5,6a 2.0Hz, H-5), 2.17–2.07 (m, 5H, –CH2–
CH@CH2, Ac at 2.09), 2.05 (s, 3H, Ac), 1.95 (s, 3H,
Ac), 1.86 (s, 3H, Ac), 1.84 (s, 3H, Ac), 1.80 (s, 3H,
Ac), 1.70 (s, 3H, Ac), 1.69–1.26 (m, 14H, –(CH2)7–);
13C NMR (100MHz, CDCl3): d 170.3, 170.2, 170.0,
169.9, 169.6, 169.4, 169.2 (7 · C@O), 139.4
(–CH@CH2), 114.7 (–CH@CH2), 101.9 (C-10), 101.0
(C-1), 77.5 (C-4), 74.0 (C-3), 73.0 (C-5), 72.6 (C-2),
71.7 (C-30), 71.0 (C-50), 70.0 (–OCH2–), 69.9 (C-20),
67.1 (C-40), 62.9 (C-6), 61.1 (C-60), 34.4 (–CH2–
CH@CH2), 30.1, 30.0, 29.9, 29.8, 29.7, 29.5, 29.4
(–(CH2)7–), 21.0, 20.7, 20.6, 20.5, 20.4, 20.3, 20.0
(7 · CH3–C(O)–). QTOFMS [MꢀH]ꢀ 787.3405 (calcd
0
0
1.2. 10-Undecenyl 2,3,4,6-tetra-O-acetyl-b-D-glucopyr-
anoside (4)
A solution of penta-O-acetyl-b-D-glucopyranose (1)
(6.59g, 16.9mmol), 10-undecen-1-ol (3) (7.5mL,
˚
37.2mmol), and 4A molecular sieves (3.5g) in CH2Cl2
(dry, 30mL) was stirred at room temperature. Subse-
quently, SnCl4 (2.0mL) was added in one portion by
syringe. After 6.5h NaHCO3 (2.5g) and MgSO4 (2.5g)
were added. The solution was filtered over a Celite layer,
and the filtrate was concentrated under reduced pres-
sure. Column chromatography (4:1 petroleum ether–
EtOAc) yielded 4 (3.20g, 38%) as a colorless oil.
1
TLC Rf 0.44 (1:1 EtOAc–petroleum ether); H NMR
(200MHz, CDCl3): d 5.90–5.69 (m, 1H, –CH@CH2),
5.20 (t, 1H, J 9.3Hz, H-3), 5.07 (t, 1H, J 9.5Hz, H-2),
5.05–4.85 (m, 2H, –CH@CH2), 4.47 (d, 1H, J 7.9Hz,
0
H-1), 4.30–4.22 (dd, J6,6 12.3Hz, J5,6 4.6Hz, 1H, H-
0
6), 4.15–4.08 (dd, 1H, J6,6 12.2Hz, J5,6 2.4Hz, H-60),
0
2
3
3.91–3.80 (dt, 1H, J 9.6Hz, J 6.3Hz, –OCHa), 3.72–
3.63 (m, 1H, H-5), 3.38–3.52 (dt, 1H, 2J 9.6Hz, 3J
6.7Hz, –OCHb), 2.07–1.98 (m, 14H, –CH2CH@CH2 +
4 · –OCH3 at 2.07, 2.03, 2.01, 1.99), 1.70–1.47 (m, 2H,
–OCH2CH2–), 1.25 (s, 12H, –(CH2)6–); 13C NMR
787.3389; D
ppm = 2.1); [M+H]+ 789.3572 (calcd
789.3545; D ppm = 3.4).
1.4. 10-Undecenyl b-D-glucopyranoside (6)
(50MHz, CDCl3):
d
170.7, 170.4, 169.4, 169.3
Compound 4 (2.62g, 5.23mmol) was dissolved in
MeOH (dry, 30mL) and freshly prepared 1M NaOCH3
(150lL) was added. The solution was stirred at room
temperature, and the conversion was followed by TLC
(EtOAc). After ꢁ2h the starting material (Rf ꢁ 0.5)
was converted into a more polar compound (Rf ꢁ 0.2).
The reaction was quenched by adding Dowex-50 [H+]
resin. After standing overnight, the mixture was filtered,
and the filtrate was concentrated, yielding 6 (1.66g,
96%) as a colorless viscous oil.
(4 · C@O), 139.2 (–CH@CH2), 114.1 (–CH@CH2),
100.8 (C-1), 72.9 (C-3), 71.7 (C-5), 71.3 (C-2), 70.3
(OCH2–), 68.5 (C-4), 62.0 (C-6), 33.8 (–CH2CH@CH2),
29.5, 29.4, 29.4, 29.3, 29.1, 28.9 (6 · –CH2–), 25.8
(–OCH2CH2–), 20.8 (CH3), 20.7 (3 · CH3). QTOFMS
[MꢀH]ꢀ 499.2541 (calcd 499.2543; D ppm = ꢀ0.4);
[M+H]+ 501.2711 (calcd 501.2699; D ppm = 2.3).
1.3. 10-Undecenyl 2,3,6,20,30,40,60-hepta-O-acetyl-b-
lactoside (5)
1
TLC Rf ꢁ0 (1:1 petroleum ether–EtOAc); H NMR
(200MHz, CD3OD): d 5.90–5.70 (m, 1H, –CH@CH2),
5.02–4.88 (m, 2H, –CH@CH2), 4.23 (d, 1H, J 7.7Hz,
H-1), 3.95–3.83 (m,2H), 3.69–4.46 (m,2H), 3.39–3.03
(m, 6H), 2.05–1.97 (q, 2H, J ꢁ 6.7Hz, CH2CH@CH2),
1.64–1.55 (m, 2H, –OCH2CH2–), 1.31 (s, 12H,
–(CH2)6–); 13C NMR (50MHz, CD3OD): d 140.2
(–CH@CH2), 114.7 (–CH@CH2), 104.2 (C-1), 78.1, 77.9,
75.1, 71.6 (C-3, C-5, C-2, and C-4), 70.9 (–OCH2–),
A solution of octa-O-acetyl-b-D-lactose (2) (3.00g,
4.42mmol), 10-undecen-1-ol (3) (1.5g, 8.84mmol), and
˚
4A molecular sieves (1.0g) in CH2Cl2 (dry, 30mL) was
stirred at room temperature. Subsequently, SnCl4
(0.52mL) was added in one portion by syringe. The
mixture was stirred overnight. Then NaHCO3 (2.5g),
Na2SO4 (2g), and water (ꢁ5mL) were added portionwise.

L. C. P. M. de Smet et al. / Carbohydrate Research 339 (2004) 2599–2605
2603
62.7 (C-6), 34.9 (–CH2CH@CH2), 30.6, 30.2, 30.1, 29.0,
27.5, 27.1 (6 · –CH2– and –OCH2CH2–).
9.7Hz, 3J 6.3Hz, –OCHa–), 3.83–3.78 (m, 1H, H-5),
3.58–3.53 (dt, 1H, 2J 9.7Hz, 3J 6.7Hz, –OCHb–),
0
3.38–3.32 (dd, 1H, J6,6 10.5Hz, J5,6 2.2Hz, H-6),
1.5. 10-Undecenyl 6-O-trityl-b-D-glucopyranoside (7)
3.19–3.11 (dd, 1H, J6,6 10.6Hz, J5,6 4.6Hz, H-60),
1.98–1.87 (q, 2H, J ꢁ 7.0Hz, CH2CH@CH2), 1.23–
1.13 (m, 12H, –(CH2)6–); 13C NMR (50MHz, CDCl3):
d 164.8, 163.9, 163.5 (3 · C@O), 143.4 (–C-6-OCC–),
139.2 (–CH@CH2), 132.9, 132.8, 131.5, 130.7, 130.2,
129.9, 129.6, 129.0, 128.6, 127.7, 127.0, 126.7 (aromatic
C atoms, quaternary C atoms in italics), ꢁ120.8 and
ꢁ115.4 (2 · 3 signals from quartet, JC,F 273Hz, CF3.
N.B. Only two signals of each quartet were observed,
since the other two overlap with the signals from the
aromatic region; the shift of each quartet is about
3Hz), 114.1 (–CH@CH2), 101.0 (C-1), 86.7 (C(phen-
yl)3), 74.1, 73.5, 72.7, 69.9 (C-2, C-3, C-4, and C-5),
70.1 (–OCH2), 62.2 (C-6), 33.8 (–CH2CH@CH2), 29.5,
29.4, 29.3, 29.1, 28.9 (6 · –CH2–), 26.0 (–OCH2CH2–).
QTOFMS [MꢀH]ꢀ not found (calcd 1089.3624),
0
0
Compound 6 (1.66g, 5.01mmol) was dissolved in pyr-
idine (dry, 19mL). Trityl chloride (1.67g, 6.00mmol)
and a catalytic amount of DMAP were added. The mix-
ture was stirred at room temperature. The reaction was
followed by TLC (2:1 petroleum ether–EtOAc; Rf prod-
uct ꢁ0.8). After 24h the reaction mixture was poured
into ice water (ca. 150mL). The mixture was extracted
with CH2Cl2 (2 · 60mL and 2 · 30mL, respectively).
The combined organic layers were washed with NaH-
CO3 (3 · 50mL). The organic layer was dried over
MgSO4, filtered, and concentrated. Traces of pyridine
were co-evaporated with toluene (3·). Column chroma-
tography (19:1 CH2Cl2–MeOH with one drop of TEA
per 100mL) yielded 7 (1.84g, 64%).
TLC Rf ꢁ0.3 (19:1 CH2Cl2–MeOH); 1H NMR
(200MHz, CDCl3): d 7.47–7.23 (m, 15H, aromatic H),
5.91–5.70 (m, 1H, –CH@CH2), 5.02–4.90 (m, 2H,
–CH@CH2), 4.26 (d, 1H, J 7.5Hz, H-1), 3.55–3.39
(m,7H), 3.27 (br s, 1H), 3.10 (br s, 1H), 2.76 (br s,
1H), 2.07–1.97 (q, 2H, J ꢁ 6.8Hz, CH2CH@CH2),
1.72–1.57 (m, 2H, –OCH2CH2–), 1.27 (s, 12H,
–(CH2)6–); 13C NMR (50MHz, CDCl3): d 143.5 (–C-6-
OCC–), 139.2 (–CH@CH2), 128.6, 127.9, 127.1
(aromatic C), 114.1 (–CH@CH2), 102.4 (C-1), 87.1
(C(phenyl)3), 76.2, 73.6, 73.6, 72.2 (C-2, C-3, C-4, and
C-5), 70.1 (–OCH2–), 64.4 (C-6), 33.8 (–CH2CH@CH2),
29.6, 29.5, 29.4, 29.1, 28.9 (–CH2–), 26.0 (–OCH2CH2–).
[MꢀH+HCOOH]ꢀ 1135.3696 (calcd 1135.3679;
D
ppm = 1.5); [M+H]+ 1091.3823 (calcd 1091.3780; D
ppm = 3.7).
1.7. Methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-
dideoxy-D-glycero-b-D-galacto-nonulopyranosylchlor-
ide)onate (11)
A suspension of compound 9 (1.5g, 4.85mmol) in 50mL
of MeOH, containing 1.5g of Amberlite IR-120 (H+)
resin was stirred overnight at room temperature. After
that second portion of 1.5g of Amberlite IR-120 (H+)
resin was added. After stirring for another 7h a clear
solution was obtained. The resin was filtered off, and
the solution was evaporated giving a dark viscous oil.
The latter was dissolved in a minimal amount of MeOH,
and Et2O was added to turbidity. Upon standing methyl
N-acetyl-a-D-neuraminate (10) crystallized (1.6g).
1.6. 10-Undecenyl 2,3,4-O-(3-trifluoromethylbenzoyl)-6-
O-trityl-b-D-glucopyranoside (8)
Compound 7 (0.91g, 1.58mmol) was dissolved in pyr-
idine (dry, ꢁ10mL). The solution was stirred at 0ꢁC, and
3-(trifluoromethyl)benzoylchloride (1.46mL, 9.66mmol)
and a catalytic amount of DMAP were added. The reac-
tion was followed by TLC. After 44h the mixture was
poured into ice water (ꢁ135mL). The mixture was sepa-
rated, and the layer was extracted with CH2Cl2 (50, 25,
and 25mL, respectively). The combined organic layers
were washed successively with satd NaHCO3 (50mL)
and twice with water (50 and 35mL, respectively). The
organic layer was dried over MgSO4. The solution was
concentrated under reduced pressure, and traces of
pyridine were removed by co-evaporation with small
volumes of toluene (4·). Column chromatography
(1:1 petroleum ether–CH2Cl2) yielded 8 (1.33g, 77%).
TLC Rf 0.41 (1:1 petroleum ether–CH2Cl2); Rf 0.25
(1:1 petroleum ether–EtOAc); 1H NMR (200MHz,
CDCl3): d 8.15–6.98 (m, 27H, aromatic H), 5.9–5.5 (m,
1H, –CH@CH2), 5.79–5.59 (m, 4H), 4.95–4.74 (m,
Freshly distilled AcCl (30mL) was added dropwise to
ice-cooled methyl N-acetyl-a-D-neuraminate (10) (0.8g,
2.47mmol) over 15min. The suspension was allowed
to warm to room temperature and was stirred for 48h.
The reaction mixture was evaporated to dryness and
co-evaporated a few times with dry toluene at 35ꢁC.
The residue was crystallized from a benzene–hexane–
Et2O mixture to give compound 11 (0.83g, 66%) as a
1
colorless solid. The H NMR and 13C NMR spectra
of compound 10 and 11 data were in accordance with
those in the literature.26
1.8. Methyl (undec-10-enyl 5-acetamido-4,7,8,9-tetra-O-
acetyl-3,5-dideoxy-D-glycero-D-galacto-nonulopyranosyl
chloride)onate (12)
Compound 11 (0.15g, 0.294mmol) was dissolved in dry
acetonitrile (5mL) containing 10-undecen-1-ol (3) (0.1g,
˚
0.588mmol) and 4A molecular sieves (1g). The mixture
3
2
3H), 4.76 (d, 1H, J 7.8Hz, H-1), 3.96–3.92 (dt, 1H, J

2604
L. C. P. M. de Smet et al. / Carbohydrate Research 339 (2004) 2599–2605
was stirred for 1h at room temperature in the dark, and
then silver triflate (0.15g, 0.588mmol) was added in one
portion. The mixture was stirred at 35–45ꢁC for 48h.
After cooling to room temperature, the solids were fil-
tered off through Celite, and washed thoroughly with
acetonitrile. The filtrate was diluted with EtOAc
(15mL), washed successively with 5% NaHCO3, satd
aq Na2S2O3, and finally with brine. The organic layer
was dried over Na2SO4, and the solvent removed in
vacuo at 35ꢁC. According to the NMR spectrum, the
residue was a mixture containing the a:b isomers in a
ratio of 3:2. Chromatography (gradient of 1:1 petroleum
ether–EtOAc to 100% EtOAc) of the residue on a col-
umn of silica gel afforded (in order of elution) b glyco-
side 12 (0.04g, 21%), a/b glycoside 12 (0.04, 21%), and
a glycoside 12 (0.07g, 37%).
29.50, 29.45, 29.4, 29.1, 28.9, 26.5 (–(CH2)6–), 23.6,
21.4, 21.3, 21.2 (5 · CH3–C(O)–).
QTOFMS [MꢀH]ꢀ 642.3124 (calcd 642.3126; D
ppm = ꢀ0.3); [M+H]+ 644.3311 (calcd 644.3262; D
ppm = 4.4).
Acknowledgements
The authors thank The Netherlands Technology Foun-
dation (NWO-STW), the graduate school VLAG, and
ASML for financial support. Furthermore, we thank
Jan Blaas, Harry Jonker, Barend van Lagen, Huseyin
¨
Topal, Beb van Veldhuizen, and Patrick Vronen for
instrumental or synthetic assistance.
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