Synthesis of C-glycoconjugates from readily available unprotected C-allyl glycosides by chemoselective ligation

Full text of DOI:10.1080/07328300802082457

This article was downloaded by: [Uppsala universitetsbibliotek]
On: 11 October 2014, At: 14:11
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office:
Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Carbohydrate Chemistry
Publication details, including instructions for authors and subscription
information:
http://www.tandfonline.com/loi/lcar20
Synthesis of C‐Glycoconjugates from Readily
Available Unprotected C‐Allyl Glycosides by
Chemoselective Ligation
Francisco Cardona a & Barbara La Ferla a
a Department of Biotechnology and Bioscience , University of Milano
Bicocca , Milano, Italy
Published online: 27 Jun 2008.
To cite this article: Francisco Cardona & Barbara La Ferla (2008) Synthesis of C‐Glycoconjugates from Readily
Available Unprotected C‐Allyl Glycosides by Chemoselective Ligation, Journal of Carbohydrate Chemistry,
27:4, 203-213
To link to this article: http://dx.doi.org/10.1080/07328300802082457
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”)
contained in the publications on our platform. However, Taylor & Francis, our agents, and our
licensors make no representations or warranties whatsoever as to the accuracy, completeness, or
suitability for any purpose of the Content. Any opinions and views expressed in this publication
are the opinions and views of the authors, and are not the views of or endorsed by Taylor &
Francis. The accuracy of the Content should not be relied upon and should be independently
verified with primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities
whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or
arising out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any substantial
or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or
distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use
can be found at http://www.tandfonline.com/page/terms-and-conditions

Journal of Carbohydrate Chemistry, 27:203–213, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0732-8303 print 1532-2327 online
DOI: 10.1080/07328300802082457
Synthesis of
C-Glycoconjugates from
Readily Available
Unprotected C-Allyl
Glycosides by
Chemoselective Ligation
Francisco Cardona and Barbara La Ferla
Department of Biotechnology and Bioscience, University of Milano Bicocca,
Milano, Italy
Keywords C-glycosides, Neoglycoconjugates, Chemoselective ligation
INTRODUCTION
Glycoconjugates such as glycoproteins, glycolipids, and proteoglycans are key
components of the living system and are involved in various recognition pro-
cesses such as cell adhesion, migration, and signaling,[1] and in many patho-
logical events such as autoimmune disease,[2] bacterial and viral invasion of
the host,[3] and tumor-cell motility and progression.[4] Understanding how
and why these highly specific interactions come about is a hard task due to
the difficulties associated with the “microheterogenity” of natural glycoconju-
gates. Thus, there is an increasing demand for synthetic glycoconjugates for
a better comprehension of these biological processes and to expedite the devel-
opment of therapeutic agents.
Received March 20, 2008; accepted March 26, 2008.
Address correspondence to Barbara La Ferla, Department of Biotechnology and
Bioscience, University of Milano Bicocca, Piazza della Scienza 2, I-20126 Milano,
Italy. E-mail: barbara.laferla@unimib.it
203

F. Cardona and B. La Ferla
204
The synthesis of glycoconjugates presents two main problems: the complexity
of the glycidic entity, which requires stereochemical and regiochemical control,
and the glycosylation of a polyfunctionalized aglycon, such as a peptide or a
protein, which requires chemoselectivity. This last problem has been faced in
different ways, among which is the reductive amination that allows one to
link the anomeric center of an aldose to primary amines such as the residues
of lysine (Sch. 1). Since no aldehydo or keto groups are present in natural
amino acids, this process is chemoselective, and the conjugation is metaboli-
cally and chemically stable. The procedure, however, generates glycoconjugate
mimics (neoglycoconjugates) where the sugar directly linked to the amino
group loses its natural cyclic structure.[5]
This problem can be avoided through a laborious manipulation of the
carbohydrate moiety to introduce a linker at the reducing end bearing a
terminal aldehyde group.[6]
RESULTS AND DISCUSSION
In order to generate neoglycoconjugates maintaining the cyclic structure of
the sugar, by exploiting the chemoselective reductive amination approach,
we speculated that instead of using the anomeric aldehydes, the sugar
should contain an anomeric appendage with the aldehyde. Furthermore, if
the aldehyde generates a hemiacetal with the hydroxyl group at C-2, the
structures would be more stable. Following this idea we synthesized com-
pounds 2 (Sch. 2) bearing a masked aldehyde linked to the anomeric center
through a carbon chain (a C-glycoside). Such hemiacetals have already
been synthesized from C-glycosides in order to generate amphiphilic liposac-
charides[7] and their reactivity investigated.[8] The reaction of compounds 2
with an amino acid, a peptide, or a dendrimer containing a primary amino
group, under reductive amination conditions, afforded neoglycoconjugates
3. It is interesting to note that the glycoconjugation process can be performed
on fully deprotected substrates in media that are compatible with biomater-
ials, and the synthesis of the glycidic structures 2 does not require protec-
tion-deprotection steps.
Scheme 1: Glycoconjugation by reductive amination.

Synthesis of C-glycoconjugates
205
Scheme 2: Synthesis of bicyclic hemiacetals 2 and their conjugation.
Deprotected C-allyl a-D-glucoside (1a), a-D-mannoside (1b), and a-D-galac-
toside (1c) were stereoselectively synthesized according to a procedure
described by Gray and coworkers.[9]
The hemiacetals gluco, manno, and galacto derivatives 2 were readily
obtained from the corresponding C-allyl glycosides 1, a solution of which
(7.3 mmol) in MeOH/H2O (100 mL) was cooled to –788C and saturated with
ozone. After 75 min the pale blue solution was purged with oxygen and
then with nitrogen until colorless. Then Me2S (10 equiv.) was added and the
reaction mixture was warmed to rt and left stirring overnight. The solvent
was then removed under reduced pressure affording compounds 2 (78–81%
yield) as a diastereoisomeric mixture of the bicyclic hemiacetalic structure,
along with compounds 2 1H NMR, which showed the formation of the
methyl acetal derivatives as minor products (22–19%). Surprisingly, despite
the unfavorable orientation of the C-2 OH, also the C-allyl a-D-mannoside
afforded the hemiacetals as major product, probably with a distorted confor-
mation (Sch. 3) in equilibrium with the monocyclic aldehyde, as evidenced
by the 1H NMR aldehyde signal at 9.4 ppm. To better understand this
behavior, we reacted compound 2b with N-iodosuccinimide in MeOH and
the reaction afforded the product of the iodocyclization 12 (Sch. 3) as evi-
denced by the chemical shift at 4.1 ppm of H1 confirmed through COSY
experiments.
Scheme 3: Conformational change for mannose derivatives.

F. Cardona and B. La Ferla
206
Reductive amination of compounds 2 (MeOH or MeOH/H2O, NaBH3CN
and AcOH) with the amino group of protected lysine 4, with peptide 5, and
with PAMAM G0 dendrimer 6 generated the corresponding neoglycosyl ami-
noacids 7a, 7b, and 7c, neoglycosyl peptide 8, and neoglycodendrimers 9a
and 9b (Sch. 4).
The neoglycosyl aminoacids 7 were obtained heating crude 2 (0.48 mmol) at
608C with N-acetyl L-lysine methyl ester 4 (0.24 mmol) in MeOH (2 mL) AcOH
(28 mL, 2 equiv.) and then adding NaCNBH3 (0.48 mmol). After 3 h, usual
workup and chromatography (AcOEt/MeOH/H2O/AcOH v/v 6/2/1/1)
afforded compounds 7 (7a 54%, 7b 70%, and 7c 55% yield). The neoglycosyl
peptide 8 was generated by adding 2b (0.019 mmol) dissolved in MeOH
(100 mL) to a solution of peptide 5 (0.0018 mmol) in degassed MeOH (100 mL),
and then by adding a solution of NaCNBH3 (0.048 mmol) in MeOH (50 mL)
and heating at 508C for 1 h. The reaction was monitored by HPLC and the
product characterized by mass spectrometry (Fig. 1).
The neoglycodendrimers 9a and 9b were obtained by reaction of PAMAM
(G0) dendrimer 6 (0.04 mmol) and crude 2a (0.24 mmol) in acetate buffer pH
4 (2 mL) with NaCNBH3 (0.26 mmol) for 1 h. After workup, the recovered
solid was subjected to two more reaction cycles. After the third cycle the solid
was purified by dialysis against water for 48 h and then lyophilized. Glucoden-
drimer 9a (98% yield) presented an average of 7.7 sugar moieties around 1.9 for
each terminal amino group, as determined by 1H NMR signal integration
(Fig. 2), while mannodendrimer 9b (76% yield) carried an average of 6.4
sugar residues.
An alternative chemoselective approach for the synthesis of neoglycoconju-
gates relies on the radical reaction between the thiol group and a terminal
olefinic double bond. This reaction has already been used for the generation
of glycodendrimers,[10] using thioglycosides and dendrimer cores bearing
Scheme 4: Synthesis of derivatives 7, 8, and 9 by reductive amination. Reagents and
conditions: a) MeOH, NaCNBH3, AcOH; b) MeOH/H2O, NaCNBH3, AcOH.

Synthesis of C-glycoconjugates
207
Figure 1: Mass spectra of glycopeptide 8. Calculated mass ¼ 1258.57512 Da, observed
mass ¼ 1258.60324 Da.
Figure 2: 1H NMR of signal integration of glucodendrimer 9a.

F. Cardona and B. La Ferla
208
olefinic terminal groups, or in the synthesis of carbohydrate microarray.[11] The
availability of allyl C-glycosides 1 suggested to us that we perform the reaction
with aglycons containing a thiol group, such as a cysteine residue (Sch. 5).
This reaction was carried out by irradiation (hn ¼ 254 nm) of compounds
1 (0.49 mmol) and N-acetyl L-cysteine methyl ester 10 (0.98 mmol), in
degassed MeOH/H2O (3 mL). After 1 h the solvent was removed under
reduced pressure and the product purified by flash chromatography (AcOEt/
MeOH v/v 9/1) affording 11 (11a 86%, 11b 87%, and 11c 84% yield) as
amorphous white solids.
CONCLUSION
In summary, we have presented an efficient and direct method for the
generation of neoglycoconjugates without the use of protecting groups, and
exploited two chemoselective approaches, the reductive amination and photo-
chemical addition of a thiol to a double bond. Both methods take advantage
of the easy and stereoselective preparation of deprotected C-allyl glycosides 1.
EXPERIMENTAL SECTION
General Remarks
All solvents were dried with molecular sieves, for at least 24 h prior to use.
Thin layer chromatography (TLC) was performed on silica gel 60 F254 plates
(Merck) with detection using UV light when possible, or by charring with a
solution of concd. H2SO4/EtOH/H2O (5:45:45) or a solution of (NH4)6Mo7O24
(21 g), Ce(SO4)2 (1 g), and concd. H2SO4 (31 mL) in water (500 mL). Flash
column chromatography was performed on silica gel 230–400 mesh (Merck).
1H, 13C NMR spectra were recorded at 258C with a Varian Mercury
400 MHz instrument using CDCl3 as the solvent unless otherwise stated.
Chemical shift assignments, reported in ppm, are referenced to the correspond-
ing solvent peaks. Peptide coupling was performed on reversed phase analyti-
cal HPLC on Waters HPLC system equipped with a Merck LiChrospher 100
Scheme 5: Chemoselective synthesis of cystein conjugates 11.

Synthesis of C-glycoconjugates
209
RP18 column (250 ꢀ 4 mm; 5 mm), eluting at a flow rate 1 mL/min. Detection
was at 214 and 280 nm with an absorbance detector Waters 2487 dual l.
Mass spectra were recorded with an ESI positive Fourier Transform Ion
Ciclotron Resonance Mass Spectrometer APEX II (Bruker Daltonics) — 4.7T
magnet (Magnex). Optical rotations were measured at rt using a Kru¨ss
P3002 electronic polarimeter and are reported in units of 1021 deg/cm2/g21
.
Peptide 5 was prepared with SPPS approach using Fmoc protected amino
acids and 2-chlorotrityl chloride resin as solid support. HBTU and DIPEA
were used as coupling agents, a solution of piperidine 20% in DMF was used
for Fmoc deprotection, and the terminal amino group was acetylated prior to
deprotection and cleavage from the resin. PAMAM Dendrimer (G0) 1,4-diami-
nobutane core was purchased from Sigma-Aldrich.
3,7-Anhydro-2-deoxy-a,b-D-glycero-D-ido-octofuranose
(1,4) (2a)
A solution of allyl-C-glucoside 1a (1.5 g, 7.3 mmol) in MeOH/H2O (100 mL)
was cooled to –788C and saturated with ozone. After 75 min the pale blue
solution was purged with oxygen and then with nitrogen until colorless.
Then Me2S (73 mmol, 10 equiv.) was added and the reaction mixture was
warmed to rt and left stirring overnight. The solvent was then removed
under reduced pressure affording crude compound 2a as a colorless oil.
Crude compound 2a, a mixture of hemiacetalic diastereoisomers, was used
without purification.
3,7-Anhydro-2-deoxy-a,b-D-glycero-D-talo-octofuranose
(1,4) (2b)
The same procedure was used as for the synthesis of 2a. Starting material
allyl-C-mannoside 1b (1.8 g, 8.8 mmol) afforded crude compound 2b as a color-
less oil. Crude compound 2b, a mixture of hemiacetalic diastereoisomer con-
taining also the aldehyde form, was used without purification.
3,7-Anhydro-2-deoxy-a,b-D-glycero-l-gluco-octofuranose
(1,4) (2c)
The same procedure was used as for the synthesis of 2a. Starting material
allyl-C-galactoside 1c (2.0 g, 9.8 mmol) afforded crude compound 2c as a color-
less oil. The crude 2c, a mixture of hemiacetalic diastereoisomer containing
also the two methyl acetal derivatives, was used without purification.

F. Cardona and B. La Ferla
210
N2-Acetyl-N5-[(2-glucopyranosyl)ethyl]-L-lysine Methyl
Ester (7a)
To a solution of crude 2a (100 mg, 0.48 mmol) and Ac-Lys-OMe 4 (57 mg,
0.24 mmol) in MeOH (2 mL), AcOH (28 mL, 2 equiv.) was added and the
reaction was heated to 608C. Then NaCNBH3 (30 mg, 0.48 mmol) was added
and the mixture was stirred at 608C for 3 h. The solvent was then removed
under reduced pressure and the product purified by flash chromatography
(AcOEt/MeOH/H2O/AcOH v/v 6/2/1/1) yielding 7a (50 mg, 54% yield) as
1
amorphous white solid. [a]d25 þ13.6 (c ¼ 0.25, CH3OH); H NMR (400 MHz,
D2O) d: 4.33 (dd, 1H, J ¼ 9.0, J ¼ 5.1 Hz), 4.12–4.04 (m, 1H), 3.80 (dd,
1H, J ¼ 12.0, J ¼ 2.1 Hz), 3.71–3.68 (m, 4H), 3.63 (dd, 1H, J ¼ 12.3,
J ¼ 6.3 Hz), 3.55 (t, 1H, J ¼ 9.0 Hz), 3.48–3.43 (m, 1H), 3.29 (t, 1H,
J ¼ 9.0 Hz), 3.13–3.08 (m, 2H), 3.02 (bt, 2H), 2.12–2.00 (m, 1H), 2.00–1.78
(m, 5H), 1.77–1.60 (m, 3H), 1.48–1.35 (m, 2H); 13C NMR (100 MHz) d:
174.4 (C), 174.3 (C), 73.64 (CH), 73.03 (CH), 73.03 (CH), 70.51 (CH), 69.99
(CH), 60.97 (CH2), 52.90, 52.54 (CH, CH3), 47.44 (CH2), 44.92 (CH2), 29.86
(CH2), 24.95 (CH2), 22.07 (CH2), 21.53 (CH3), 21.22 (CH2); HRMS calcd for
C17H32N2O8 (MHþ) 393.22314, found 393.22246; calcd (MNaþ) 415.20509,
found 415.20514.
N2-Acetyl-N5-[(2-mannopyranosyl)ethyl]-L-lysine Methyl
Ester (7b)
The same procedure was used as for the synthesis of 7a. Starting material
2b (100 mg, 0.48 mmol). Product obtained after purification by flash chromato-
graphy (AcOEt/MeOH/H2O/AcOH v/v 6/2/1/1) 7b (65 mg, 70% yield) as
1
amorphous white solid. [a]d25 þ6.5 (c ¼ 0.4, H2O); H NMR (400 MHz, D2O) d:
4.33 (dd, 1H, J ¼ 9.1, J ¼ 5.0 Hz), 4.00–3.96 (m, 1H); 3.86–3.68 (m, 7H),
3.60 (t, 1H, J ¼ 8.7 Hz), 3.53–3.46 (m, 1H), 3.12, (bt, 2H), 3.01 (bt, 2H),
2.24–2.10 (m, 1H), 2.00 (s, 3H), 1.90–1.80 (m, 2H), 1.78–1.60 (m, 3H), 1.45,
1.35 (m, 2H); 13C NMR (100 MHz) d: 176.9 (C), 176.8 (C), 77.88 (CH), 77.14
(CH), 73.45 (CH), 73.21 (CH), 70.12 (CH), 63.62 (CH2), 55.33, 55.69 (CH,
CH3), 50.28 (CH2), 47.79 (CH2), 32.70 (CH2), 27.85 (CH2), 27.24 (CH2), 24.96
(CH2), 24.38 (CH3); HRMS calcd for C17H32N2O8 (MHþ) 393.22314, found
393.22251; calcd (MNaþ) 415.20509, found 415.20512.
N2-Acetyl-N5-[(2-galactopyranosyl)ethyl]-L-lysine Methyl
Ester (7c)
The same procedure was used as for the synthesis of 7a. Starting material
2c (50 mg, 0.24 mmol). Product obtained after purification by flash chromato-
graphy (AcOEt/MeOH/H2O/AcOH v/v 6/2/1/1) 7c (30 mg, 55% yield) as

Synthesis of C-glycoconjugates
211
1
amorphous white solid. [a]d25 þ26.7 (c ¼ 0.15, CH3OH); H NMR (400 MHz,
D2O) d: 4.37 (dd, 1H, J ¼ 9.1, J ¼ 5.2 Hz), 4.18–4.12 (m, 1H), 4.00–3.95
(m, 2H), 3.79–3.69 (m, 7H), 3.16, (bt, 1H), 3.04 (bt, 1H), 2.14–2.05 (m, 1H),
2.02 (s, 3H), 2.02–1.94 (m, 1H), 1.93–1.84 (m, 1H), 1.79–1.65 (m, 3H), 1.44–
1.38 (m, 2H); 13C NMR (100 MHz) d: 174.4 (C), 174.3 (C), 73.61 (CH), 72.51
(CH), 69.75 (CH), 68.93 (CH), 67.93 (CH), 61.28 (CH2), 53.15, 52.83 (CH,
CH3), 48.91 (CH2), 47.73 (CH2), 30.15 (CH2), 26.49 (CH2), 25.29 (CH2), 22.35
(CH2), 21.86 (CH3); HRMS calcd for C17H32N2O8 (MNaþ) 415.20509, found
415.20515.
C-Glycopeptide (8)
Peptide 5 (2 mg, 0.0018 mmol) was dissolved in degassed MeOH (100 mL)
and 2b (4 mg, 0.019 mmol) dissolved in MeOH (100 mL) was added. Then a
solution of NaCNBH3 (3 mg, 0.048 mmol) in MeOH (50 mL) was added and
the reaction mixture was heated to 508C for 1 h. HPLC profile using
gradient 10% A, 90% B to 50% A, 50% B in 30 min (A ¼ MeCN/H2O/TFA
90/10/0.01 and B ¼ H2O/TFA 0.1%) showed complete conversion of peptide
5 to glycopeptide 8 (retention time 17, 35 min) and small amount of a
second peak not identified. 8 HRMS calcd for C53H86N12O21S (Mþ)
1258.57512, found 1258.60324.
Glucodendrimer (9a)
PAMAM Dendrimer (G0) 1,4-diaminobutane core (22 mg, 0.04 mmol) was
dissolved in acetate buffer pH 4 (2 mL) and crude 2a (50 mg, 0.24 mmol, 6
equiv.) was added. Then NaCNBH3 (16 mg, 0.26 mmol) was added and the
mixture was stirred for 1 h. The solvent was removed under reduced
pressure and the solid dissolved in MeOH, precipitated with cold Et2O, and
then filtered. The solid recovered was subjected to two more equivalent
reaction cycles. After the third cycle the solid was purified by dialysis against
water for 48 h. The final product was lyophilized affording 79 mg of glucoden-
drimer with 7.7 sugar moieties (98% yield). 1H NMR (400 MHz, D2O) d: 3.95–
3.86 (m, 7.7H), 3.85–3.82 (m, 8.4H), 3.82–3.76 (m, 11.5H), 3.72–3.64 (m, 8.8H),
3.63–3.55 (m, 9.2H), 3.53–3.46 (m, 8H), 3.48–3.26 (m, 8.3H), 2.85–2.76
(m, 7.2H), 2.73–2.64 (m, 13.3H), 2.63–2.49 (m, 9.5H), 2.48–2.33 (m, 11.3H),
2.07–1.87 (m, 6.2H), 1.77–1.61 (m, 7.7H), 1.52–1.40 (bs, 4H).
Mannodendrimer (9b)
The same procedure was used as for the synthesis of 9a. Final lyophiliza-
tion afforded 50 mg of mannodendrimer with an average of 6.4 sugar
moieties (76% yield). 1H NMR (400 MHz, D2O) d: 4.04–3.96 (m, 6.4H),

F. Cardona and B. La Ferla
212
3.87–3.78 (m, 7.0H), 3.72–3.57 (m, 23.7H), 3.55–3.47 (m, 5.7H), 3.39–3.29
(m, 12.6H), 2.86–2.78 (m, 7.8H), 2.76–2.55 (m, 17.3H), 2.54–2.49 (m, 4.6H),
2.48–2.38 (m, 8.1H), 2.38–2.32 (m, 4.4H), 1.93–1.80 (m, 12.2H), 1.51–1.42
(bs, 4H).
N-Acetyl-S-[(3-glucopyranosyl)propyl]-L-cysteine Methyl
Ester (11a)
Compound 1a (100 mg, 0.49 mmol) and cysteine L-methyl ester (174 mg,
0.98 mmol) was dissolved in degassed MeOH/H2O (3 mL) and irradiated
with UV lamp hn ¼ 254 nm. After 1 h the solvent was removed under
reduced pressure and the product purified by flash chromatography (AcOEt/
MeOH v/v 9/1) affording 11a (160 mg, 86% yield) as amorphous white solid.
[a]2d5 þ24.4 (c ¼ 0.5, CH3OH); 1H NMR (400 MHz, D2O) d: 4.63 (dd, 1H,
J ¼ 8.1, J ¼ 5.0 Hz), 4.01–3.96 (m, 1H); 3.82 (dd, 1H, J ¼ 12.2, J ¼ 2.2 Hz),
3.77 (s, 3H), 3.71–3.63 (m, 2H), 3.61 (t, 1H, J ¼ 8.1 Hz), 3.52–3.46 (m, 1H),
3.32, (bt, 1H), 3.07 (dd, 1H, J ¼ 14.7, J ¼ 5.0 Hz), 3.92 (dd, 1H, J ¼ 14.7,
J ¼ 8.1 Hz), 2.70–2.60 (m, 2H), 2.05 (s, 3H), 1.72–1.53 (m, 4H); 13C NMR
(100 MHz) d: 176.7 (C), 175.3 (C), 78.20 (CH), 76.07 (CH), 75.25 (CH), 74.00
(CH), 73.10 (CH), 63.90 (CH2), 55.96, 55.47 (CH, CH3), 35.17 (CH2), 34.23
(CH2), 27.60 (CH2), 25.60 (CH2), 24.57 (CH3); HRMS calcd for C15H27NO8S
(MNaþ) 404.13496, found 404.13425.
N-Acetyl-S-[(3-mannopyranosyl)propyl]-L-cysteine Methyl
Ester (11b)
The same procedure was used as for the synthesis of 11a starting from 1b.
Purification by flash chromatography (AcOEt/MeOH v/v 9/1) afforded 11b
(162 mg, 87% yield) as amorphous white solid. [a]2d5 þ24.4 (c ¼ 0.25, CH3OH);
1H NMR (400 MHz, D2O) d: 4.61 (dd, 1H, J ¼ 8.2, J ¼ 5.0 Hz), 3.95–3.89
(m, 1H), 3.88–3.77 (m, 6H), 3.71 (dd, 1H, J ¼ 12.1, J ¼ 6.1 Hz), 3.62 (t, 1H,
J ¼ 9.3 Hz), 3.53–3.48 (m, 1H), 3.07 (dd, 1H, J ¼ 14.0, J ¼ 5.0 Hz), 2.92 (dd,
1H, J ¼ 14.0, J ¼ 8.2 Hz), 2.63 (bt, 2H), 1.90–1.80 (m, 1H), 1.80–1.53-1.53
(m, 3H); 13C NMR (100 MHz) d: 176.7 (C), 175.3 (C), 80.70 (CH), 76.34 (CH),
74.30 (CH), 73.62 (CH), 70.13 (CH), 64.10 (CH2), 55.97, 55.47 (CH, CH3),
35.19 (CH2), 34.16 (CH2), 29.29 (CH2), 27.97 (CH2), 24.59 (CH3); HRMS calcd
for C15H27NO8S (MNaþ) 404.13496, found 404.13440.
N-Acetyl-S-[(3-glucopyranosyl)propyl]-L-cysteine Methyl
Ester (11c)
The same procedure was used as for the synthesis of 11a starting from
1c. Purification by flash chromatography (AcOEt/MeOH v/v 8/2) afforded

Synthesis of C-glycoconjugates
213
11c (156 mg, 84% yield) as amorphous white solid. [a]2d5 þ65.3 (c ¼ 0.15, CH3OH);
1H NMR (400 MHz, D2O) d: 4.61 (dd, 1H, J ¼ 8.2, J ¼ 5.0 Hz), 4.06–3.99 (m, 1H);
3.98–3.90 (m, 2H), 3.79–3.67 (m, 7H), 3.06 (dd, 1H, J ¼ 14.0, J ¼ 5.0 Hz), 2.90 (dd,
1H, J ¼ 14.0, J ¼ 8.2 Hz), 2.68–2.55 (m, 2H), 2.06 (s, 3H), 1.80–1.50 (m, 4H); 13
C
NMR (100 MHz) d: 176.7 (C), 175.3 (C), 77.86 (CH), 74.43 (CH), 72.46 (CH), 71.90
(CH), 71.05 (CH), 63.99 (CH2), 55.93, 55.44 (CH, CH3), 35.10 (CH2), 34.24 (CH2),
27.73 (CH2), 25.46 (CH2), 24.52 (CH3); HRMS calcd for C15H27NO8S (MNaþ)
404.13496, found 404.13483.
3,7-Anhydro-2-deoxy-C-iodomethyl-a,b-D-glycero-D-talo-
octofuranoside (1,4) (12) Major Isomer
1H NMR (400 MHz, CD3OD) d: 4.18–4.00 (m, 4H), 3.94–3.86 (m, 2H,), 3.76
(d, 1H, J ¼ 3.0 Hz), 3.58 (dd, 1H, J ¼ 12.0, J ¼ 4.6 Hz), 3.41–3.37 (m, 2H),
2.46–2.36 (m, 1H), 1.80–1.61 (m, 1H); 13C NMR (100 MHz) d: 86.12 (CH),
81.67 (CH), 80.89 (CH), 74.13 (CH), 73.00 (CH), 70.97 (CH), 63.65 (CH2),
40.45 (CH2), 13.95 (CH2); MS calcd for C9H16IO5 (MHþ) 331.0, found 331.3.
REFERENCES
[1] (a) Dwek, R.A. Chem. Rev. 1996, 96, 683–720; (b) Fukuda, M. Bioorg. Med. Chem.
1995, 3, 207–215; (c) Varki, A. Glycobiology 1993, 3, 97–130; (d) Feizi, T. Glyco-
conj. J. 2000, 17, 553–565; (e) Bertozzi, C.; Kiessling, L. Science 2001, 291,
2357–2364; (f) Varki, A.; Cummings, R.; Esko, J.; Freeze, H.; Hart, G.; Marth, J.
Essentials of Glycobiology; Cold Spring Harbor Laboratory Press: Cold Spring
Harbor, NY, 1999.
[2] Lowe, J.B. Cell 2001, 104, 809–812.
[3] Karlsson, K.A. Curr. Opin. Struct. Biol. 1995, 5, 622–635.
[4] Hakomori, S.; Zhang, Y. Chem. Biol. 1997, 4, 97–104.
[5] (a) Wang, P.; Hill, T.G.; Wartchow, A.; Huston, M.E.; Oehler, L.M.; Bradley
Smith, M.; Bednarski, M.D.; Callstrom, M.R. J. Am. Chem. Soc. 1992, 114,
378–380; (b) Wartchow, C.A.; Wang, P.; Bednarski, M.D.; Callstrom, M.R. J. Org.
Chem. 1995, 60, 2216–2226.
[6] (a) Wong, C.-H.; Moris-Varas, F.; Hung, S.-C.; Marron, T.G.; Lin, C.C.; Gong, K.W.;
Weitz-Schmidt, G. J. Am. Chem. Soc. 1997, 119, 8152–8158; (b) Arya, P.;
Kutterer, K.M.K.; Barkley, A. J. Comb. Chem. 2000, 2, 120–126; (c) Arya, P.;
Barkley, A.; Randell, K.D. J. Comb. Chem. 2002, 4, 193–198; (d) Clausen, M.H.;
Madsen, R. Carbohydr. Res. 2004, 339, 2159–2169.
[7] Cabaret, D.; Wakselman, M. Carbohydr. Res. 1989, 189, 341–348.
[8] Cabaret, D.; Wakselman, M. Can. J. Chem. 1990, 68, 2253–2257.
[9] Bennek, J.A.; Gray, G.R. J. Org. Chem. 1987, 52, 892–897.
[10] Lubineau, A.; Malleron, A.; Le Narvor, C. Tetrahedron Lett. 2000, 41, 8887–8891.
[11] Qian, X.; Metallo, S.J.; Choi, I.S.; Wu, H.; Liang, M.N.; Whitesides, G.M. Anal.
Chem. 2002, 74, 1805–1810.