Synthesis of new sugar amino acid derivatives of D-glucosamine

Article abstract of DOI:10.1016/S0008-6215(02)00487-1

The synthesis of several new sugar amino acid derivatives of 2-acetamido-2-deoxy-D-glucose, bearing a C-glycosyl functionality as building blocks for the design and synthesis of natural glycoconjugates mimetics, is described. These compounds were prepared from the readily accessible per-benzylated amino C-allyl glucopyranosyl compounds, with TMSOTf/Ac₂O-mediated selective acetolysis of the 6-O-benzyl group as the key step.

Full text of DOI:10.1016/S0008-6215(02)00487-1

Carbohydrate Research 338 (2003) 399–406
www.elsevier.com/locate/carres
Synthesis of new sugar amino acid derivatives of
D-glucosamine
Juan Xie*
Laboratoire de Chimie des Glucides, CNRS UMR 7613, Uni6ersite´ Pierre et Marie Curie, 4 Place Jussieu, F-75005 Paris, France
Received 27 May 2002; received in revised form 21 October 2002; accepted 15 November 2002
Abstract
The synthesis of several new sugar amino acid derivatives of 2-acetamido-2-deoxy-
D
-glucose, bearing a C-glycosyl functionality
as building blocks for the design and synthesis of natural glycoconjugates mimetics, is described. These compounds were prepared
from the readily accessible per-benzylated amino C-allyl glucopyranosyl compounds, with TMSOTf/Ac2O-mediated selective
acetolysis of the 6-O-benzyl group as the key step. © 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Sugar amino acids; 2-Acetamido-2-deoxy-D-glucose; Amino C-glycosyl compounds
1. Introduction
D-glucosamine bearing the carboxylic acid functionality
at either the C-1, C-3 or C-6 position of a pyranose
backbone have been reported.10 In this work, we report
an easy preparation of several new SAAs derivatives of
GlcNAc, containing a functional carbon chain at the
anomeric position, with the amine and carboxylic func-
tion at either C-1 or C-6 position of the sugar moiety
(Compounds 6, 9, 12, 15 and 19).
Amino sugars are widely distributed in biological sys-
tems.1,2 Glycosides of 2-acetamido-2-deoxy-
-glucose
D
are of particular importance because they are funda-
mental constituents of N-glycoproteins2c and mucin-
type O-glycoproteins.3 Recently, it has been shown that
O-linked GlcNAc (O-GlcNAc) nucleoplasmic and cy-
toplasmic proteins4 are implicated in signal transduc-
tion, transcription, translation, cancer, neuronal
pathology and other biological process.5 There is also
evidence of a link between aberrant O-GlcNAc modifi-
cation and diabetes.5 Consequently, structural modifi-
cation of GlcNAc and its conjugates would constitute
useful glycomimetics of interest as inhibitors of Glc-
NAc processing enzymes.
2. Results and discussion
Per-benzylated C-allyl glycosyl compounds are readily
accessible8 and can be easily converted into other func-
tional groups (aldehyde, amine, carboxylic acid, hy-
droxyl group). Recently, Kobertz et al.11 described a
one-pot TMSOTf/Ac2O mediated debenzylation/acety-
lation of the 6-O-benzyl group of per-benzylated gly-
cosides. Application of this procedure to per-benzylated
C-allyl glycosyl compounds should allow the further
functionalization of these derivatives.12 We then de-
cided to use the per-benzylated amino a- and b-C-allyl
glucopyranosyl compounds 1 and 16 as starting materi-
als to prepare diversely functionalized amino C-gluco-
syl compounds.
C-Glycosyl compounds of GlcNAc6 and a-GlcNAc
thioconjugates7 have recently been prepared as stable
analogs of O-GlcNAc. It is known that C-glycosyl
analogs of natural carbohydrates are good mimetics,
resistant to glycosidase-catalyzed hydrolysis.8 More-
over, efficient synthesis of functional amino C-glycosyl
compounds is attractive for the generation of more
complex carbohydrates. Of particular interest are sugar
amino acids (SAAs), which have been successfully used
in the design and synthesis of peptidomimetics, enzyme
inhibitors, oligomers and polymers.9 Several SAAs of
The amino a-C-allyl glucosyl derivative 1 was pre-
pared as described.13 Acetolysis of the 6-O-benzyl
group of 1 required 2 equiv of TMSOTf as catalyst
instead of 1 equiv in the case of methyl tetra-O-benzyl-
* Tel.: +33-1-44275893; fax: +33-1-44275513
E-mail address: xie@ccr.jussieu.fr (J. Xie).
a-D
-glucopyranoside11 (Scheme 1). The resulting acetate
0008-6215/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(02)00487-1

400
J. Xie / Carbohydrate Research 338 (2003) 399–406
2 was deacetylated under Zemple´n conditions to give
the alcohol 3 which was transformed into azide 4 by
displacement of the mesylate. The following oxidative
conversion of alkene to carboxylic acid was more prob-
functional groups (amine, epoxide, carbonyl or hy-
droxyl groups etc). These multifunctional compounds
could be used to increase the diversity of the SAA-
14
lematic. Oxidation with KMnO4 led to a mixture of
several compounds. The best result was achieved using
a combination of OsO4/Jones reagent.15 The corre-
sponding methyl ester 5 was obtained in 33% yield.
Comparison of the l values for H-1, H-2, NH, C-1 and
C-2 with compounds with similar structure (see Table
1) clearly indicates the a configuration of 5. Compared
to the b isomers, the chemical shifts of the signals for
H-1,18 H-2 and NH are at lower field in the a isomer.
However, a highfield shift for C-1 and C-2 for the a
isomer is observed. Finally, compound 5 was reduced
to the amine 6 using the Staudinger reaction.
Compounds 9 and 12 were prepared in a similar way
(Scheme 2). Oxidation of primary alcohol function of 3
with Jones reagent followed by esterification furnished
the SAA 9. Oxidative cleavage (OsO4/NaIO4) of the
double bond followed by reduction (NaBH4) afforded
the alcohol 10. As before, the azide was introduced via
a mesylate, then reduced to the amine 12.
In order to get access to other derivatives, we decided
to isomerize the terminal olefin of 1 (Scheme 3). The
reaction was catalyzed by PdCl2 in benzene under
reflux.19 Compound 13 was obtained as a mixture of
two diastereoisomers (E/Z 21:4) in 71% yield. Selective
acetolysis of 13 followed by deacetylation gave alcohol
14, which was converted to the methyl ester 15 as for 9.
The amino b-C-glucosyl compound 19 was generated
by an analogous procedure (Scheme 4). The amino
b-C-glucosyl compound 1613b,13c was first protected as
its benzyl ether 17, followed by selective acetolysis,
deacetylation, oxidation and esterification.
Scheme 1.
In summary, this work describes a convenient synthe-
sis of several new sugar aminoacids derivatives of N-
acetylglucosamine, by using the common starting
materials. Compounds 9, 15 and 19 which contain a
CꢀC double bond, could be easily converted into other
Scheme 2.
Table 1
NMR data for some amino C-
D
-glucopyranosyl compounds
Compound
Configuration
l H-1
l H-2
l NH
l C-1
l C-2 (ppm)
5
a
b
b
4.45–4.48
3.70
3.63
4.27–4.31
3.85
3.85
6.61
5.45
5.00
65.0
75.8
76.7
46.9
54.5
55.2
716
817

J. Xie / Carbohydrate Research 338 (2003) 399–406
401
Silica Gel 60 (230–400 mesh). Analytical thin-layer
chromatography was performed on E. Merck alu-
minum percolated plates of Silica Gel 60F-254 with
detection by UV and by spraying with 6 N H2SO4 and
heating about 2 min at 300 °C. Dichloromethane was
distilled over CaH2. Microanalyses were performed at
the Service de Microanalyse de l’Universite´ Pierre et
Marie Curie.
3.2. 3-(6%-O-Acetyl-2%-N-acetylamino-3%,4%-di-O-benzyl-
2%-deoxy-a-D-glucopyranosyl)-1-propene (2)
To a soln of 3-(2%-N-acetylamino-3%,4%,6%-tri-O-benzyl-
2%-deoxy-a-
-glucopyranosyl)-1-propene (1)13a (515 mg,
D
1 mmol) in anhyd CH2Cl2 (4 mL) and Ac2O (4 mL),
was added a solution of TMSOTf (362 mL, 2 mmol) in
CH2Cl2 (2 mL) at −40 °C under argon. After 1 h, the
reaction was quenched with satd NaHCO3. The aq
layer was extracted with CH2Cl2 (2×20 mL) and the
combined organic layers were washed with water, dried
over MgSO4, filtered, evaporated and purified by
column chromatography (1:3 then 1:2 EtOAc–cyclo-
hexane) to afford 2 as a white solid (427 mg, 91%): mp
136–139 °C; [h]D +11.0 (c 1.0, CH2Cl2); Rf 0.38 (1:1
EtOAc–cyclohexane); IR (KBr) 3325, 3107, 3083, 3035,
1757, 1640 cm−1. 1H NMR: l 7.33–7.16 (m, 10 H, Ph),
6.81–6.65 (m, 1 H, H-2), 6.42 (d, J2%,NH 9.5 Hz, 1 H,
NH), 5.06–4.95 (m, 2 H, H-1), 4.63 (dd, J5%,6¦ 4.0, Jgem
11.8 Hz, 1 H, H-6¦), 4.60 (d, Jgem 11.5 Hz, 1 H,
OCHPh), 4.49 (d, Jgem 9.5 Hz, 1 H, OCHPh), 4.44 (d,
Jgem 9.5 Hz, 1 H, OCHPh), 4.35 (d, Jgem 11.5 Hz, 1 H,
OCHPh), 4.20–4.15 (m, 2 H, H-2%,5%), 4.04 (dd, J5%,6% 4.8
Hz, 1 H, H-6%), 4.00–3.96 (m, 1 H, H-1%), 3.64–3.62 (m,
1 H, H-3%), 3.32 (m, 1 H, H-4%), 2.17–2.09 (m, 2 H,
H-3), 1.99 (s, 3 H, Ac), 1.77 (s, 3 H, Ac). 13C NMR: l
170.8, 159.9 (CO), 137.5, 137.2 (Cipso), 134.4 (C-2),
128.7, 128.3, 128.2, 127.9 (Ph), 117.2 (C-1), 74.3 (C-5%),
73.9 (C-3%), 73.5 (C-4%), 72.4, 72.0 (OCH2), 67.4 (C-1%),
61.3 (C-6%), 47.3 (C-2%), 35.8 (C-3), 23.5, 21.0 (Me).
Anal. Calcd for C27H33NO6: C, 69.36; H, 7.11; N, 3.00.
Found: C, 69.21; H, 7.09; N, 3.05.
Scheme 3.
Scheme 4.
building blocks and may find applications as potential
glycomimetics, peptidomimetics or as building blocks
for the synthesis of novel glycoconjugates.
3.3. 3-(2%-N-Acetylamino-3%,4%-di-O-benzyl-2%-deoxy-a-D-
glucopyranosyl)-1-propene (3)
3. Experimental
3.1. General procedures
To a soln of 2 (271 mg, 0.580 mmol) in MeOH (10 mL)
was added MeONa (1 M, 0.58 mL). After 20 h stirring
at room temperature (rt), the reaction mixture was
neutralized with 10% HCl at 0 °C and MeOH was
removed under diminished pressure. The resulting
residue was dissolved in CH2Cl2 (30 mL) and washed
with water and brine. The organic layer was dried over
MgSO4, filtered and evaporated. Purification by column
chromatography (1:3 to 1:1 EtOAc–cyclohexane) af-
forded 3 as a white solid (241 mg, 98%): mp 127–
131 °C; [h]D +2.0 (c 1, CH2Cl2); Rf 0.27 (1:1
Melting points were measured with a Thomas-Hoover
1
apparatus. H and 13C NMR spectra were recorded on
a Bruker AGH-250 spectrometer in CDCl3 solution.
1
1
Assignments were confirmed by H/1H, H/13C correla-
tions and Dept 135. Optical rotations were measured
using a Perkin–Elmer 141 polarimeter and a 10-cm cell.
Column chromatography was performed on E. Merck

402
J. Xie / Carbohydrate Research 338 (2003) 399–406
EtOAc–cyclohexane); IR (KBr) 3301, 3107, 3083, 3035,
1709, 1660 cm−1. 1H NMR: l 7.32–7.18 (m, 10 H, Ph),
6.36 (d, J2%,NH 9.8 Hz, 1 H, NH), 5.83–5.65 (m, 1 H,
H-2), 5.08–4.99 (m, 2 H, H-1), 4.62 (d, Jgem 11.5 Hz, 1
H, OCHPh), 4.51 (d, Jgem 11.3 Hz, 1 H, OCHPh), 4.47
(d, Jgem 11.3 Hz, 1 H, OCHPh), 4.39 (d, Jgem 11.5 Hz,
1 H, OCHPh), 4.19–4.12 (m, 1 H, H-2%), 4.05–3.95 (m,
3 H, H-1%,5%,6¦), 3.65–3.62 (m, 1 H, H-3%), 3.52–3.44
(m, 1 H, H-6%), 3.34–3.32 (m, 1 H, H-4%), 2.11–1.96 (m,
2 H, H-3), 1.96 (dd, J6%,OH 3.0, J6¦,OH 7.3 Hz, 1 H, OH),
1.77 (s, 3 H, Ac). 13C NMR: l 171.1 (CO), 137.6, 137.4
(Cipso), 135.3 (C-2), 128.8, 128.4, 128.3, 128.0 (Ph),
117.9 (C-1), 76.9, 74.4, 74.0 (CH), 72.6, 72.3 (OCH2),
67.6 (C-1%), 60.1 (C-6%), 48.0 (C-2%), 35.5 (C-3), 23.5
(Me). Anal. Calcd for C25H31NO5: C, 70.57; H, 7.34; N,
3.29. Found: C, 70.76; H, 7.41; N, 3.19.
3.5. Methyl (2%-N-acetylamino-6%-azido-3%,4%-di-O-ben-
zyl-2%,6%-dideoxy-a- -glucopyranosyl) ethanoate (5)
D
To a soln of 4 (71 mg, 0.158 mmol) in acetone (1 mL)
was added a 4 (wt)% soln of OsO4 in tBuOH (63 mL)
and Jones reagent (1 M, 0.79 mL). After stirring 20 h at
rt, the mixture was concentrated, dissolved in EtOAc
(10 mL) and washed successively with water and brine.
The organic layer was dried over MgSO4, filtered and
concentrated to an oil, which was dissolved in DMF
(0.5 mL). Sodium hydrogenocarbonate (20 mg, 0.238
mmol) was added to the solution, followed by methyl
iodide (20 mL, 0.321 mmol). After 20 h, the mixture was
concentrated and diluted in EtOAc. The organic solu-
tion was washed successively with water, brine, dried
over MgSO4, filtered, concentrated and purified by
preparative TLC with 1:1 EtOAc–cyclohexane as elu-
ent to afford 5 (25 mg, 33%): mp 128 °C; [h]D +6.5 (c
1.2, CH2Cl2); Rf 0.25 (1:1 EtOAc–cyclohexane); IR
3.4. 3-(2%-N-Acetylamino-6%-azido-3%,4%-di-O-benzyl-2%,6%-
1
dideoxy-a-D-glucopyranosyl)-1-propene (4)
(KBr) 2119, 1757, 1685 cm−1. H NMR: l 7.36–7.25
(m, 10 H, Ph), 6.61 (d, J2%,NH 9.5 Hz, 1 H, NH), 4.70 (d,
Jgem 11.5 Hz, 1 H, OCHPh), 4.56 (d, Jgem 11.3 Hz, 1 H,
OCHPh), 4.50 (d, Jgem 11.5 Hz, 1 H, OCHPh), 4.48–
4.45 (m, 1 H, H-1%), 4.41 (d, Jgem 11.3 Hz, 1 H,
OCHPh), 4.31–4.27 (m, 1 H, H-2%), 4.12 (t, J 7.0 Hz, 1
H, H-5%), 3.83 (dd, J5%,6¦ 8.0, Jgem 12.8 Hz, 1 H, H-6¦),
3.73–3.70 (m, 1 H, H-3%), 3.68 (s, 3 H, OMe), 3.43 (dd,
J5%,6% 6.5 Hz, 1 H, H-6%), 3.42–3.41 (m, 1 H, H-4%),
2.48–2.45 (m, 2 H, H-2), 1.82 (s, 3 H, Ac). 13C NMR:
l 171.3, 170.0 (CO), 137.2, 137.0 (Cipso), 128.8, 128.4,
128.3, 127.9 (Ph), 75.3 (C-5%), 73.8 (C-3%), 73.4 (C-4%),
72.4, 72.2 (OCH2), 65.0 (C-1%), 52.0 (OMe), 49.5 (C-6%),
46.9 (C-2%), 36.7 (C-2), 23.3 (Me). Anal. Calcd for
C25H30N4O6: C, 62.23; H, 6.27; N, 11.61. Found: C,
62.36; H, 6.34; N, 11.81.
Methanesulfonyl chloride (122 mL, 1.584 mmol) was
added to a 0 °C soln of alcohol 3 (468 mg, 1.100 mmol)
and TEA (282 mL, 2.024 mmol) in CH2Cl2 (4.8 mL).
The ice bath was removed, and stirring was continued
for 18 h before MeOH (63 mL) was added. The solution
was concentrated, the residue dissolved in EtOAc (20
mL) and washed successively with water, NaHCO3 5%
and brine. The organic layer was dried over MgSO4,
filtered and concentrated to an oil, which was used
directly without purification. The mesylate was dis-
solved in DMF (5 mL) and added to NaN3 (367 mg,
5.654 mmol). The reaction was heated at 90 °C for 20 h.
After evaporation, the residue was diluted in EtOAc (20
mL), washed successively with water, brine, dried over
MgSO4, filtered, concentrated and purified by flash
chromatography (1:4 to 2:5 EtOAc–cyclohexane) to
afford 4 as a white solid (394 mg, 80%): mp 146 °C;
[h]D +7.0 (c 1.0, CH2Cl2); Rf 0.17 (1:3 EtOAc–cyclo-
hexane); IR (KBr) 3325, 3107, 3083, 3035, 2119, 1660
3.6. Methyl (2%-N-acetylamino-6%-amino-3%,4%-di-O-ben-
zyl-2%,6%-dideoxy-a-D-glucopyranosyl) ethanoate (6)
To a soln of 5 (40 mg, 0.083 mmol) in THF (1 mL),
was added Ph3P (24 mg, 0.091 mmol) and water (16 mL,
0.889 mmol). The mixture was stirred at rt for 20 h.
After concentration, the residue was purified by prepar-
ative TLC with 1:9 MeOH–CH2Cl2 as eluent to afford
6 as a white solid (27 mg, 69%): mp 116 °C; [h]D +17.6
(c 0.5, CH2Cl2); Rf 0.38 (1:9 MeOH–CH2Cl2); IR (KBr)
1
cm−1. H NMR: l 7.32–7.17 (m, 10 H, Ph), 6.38 (d,
J2%,NH 9.8 Hz, 1 H, NH), 5.76–5.69 (m, 1 H, H-2),
5.05–4.96 (m, 2 H, H-1), 4.60 (d, Jgem 11.5 Hz, 1 H,
OCHPh), 4.48 (d, Jgem 11.3 Hz, 1 H, OCHPh), 4.44 (d,
Jgem 11.5 Hz, 1 H, OCHPh), 4.36 (d, Jgem 11.3 Hz, 1 H,
OCHPh), 4.19–4.15 (m, 1 H, H-2%), 4.09–4.03 (m, 1 H,
H-5%), 3.93–3.89 (m, 1 H, H-1%), 3.76 (dd, J5%,6¦ 8.8, Jgem
13.0 Hz, 1 H, H-6¦), 3.65–3.63 (m, 1 H, H-4%), 3.33–
3.31 (m, 1 H, H-3%), 3.24 (dd, J5%,6% 5.8 Hz, 1 H, H-6%),
2.23–2.08 (m, 2 H, H-3), 1.76 (s, 3 H, Ac). 13C NMR:
l 170.2 (CO), 137.7, 137.4 (Cipso), 134.3 (C-2), 129.1,
128.7, 128.6, 128.2 (Ph), 118.0 (C-1), 75.5 (C-5%), 74.5
(C-4%), 74.1 (C-3%), 72.8, 72.5 (OCH2), 68.0 (C-1%), 49.8
(C-6%), 47.4 (C-2%), 35.9 (C-3), 23.7 (Me). Anal. Calcd
for C25H30N4O4: C, 66.65; H, 6.71; N, 12.44. Found: C,
66.56; H, 6.79; N, 12.69.
1
3421, 3324, 3300, 1757, 1685, 1660 cm−1. H NMR: l
7.38–7.22 (m, 10 H, Ph), 6.69 (d, J2%,NH 9.5 Hz, 1 H,
NH), 4.66 (d, Jgem 11.8 Hz, 1 H, OCHPh), 4.57 (d, Jgem
11.5 Hz, 1 H, OCHPh), 4.48 (d, Jgem 11.8 Hz, 1 H,
OCHPh), 4.44–4.41 (m, 1 H, H-1%), 4.39 (d, Jgem 11.5
Hz, 1 H, OCHPh), 4.37–4.30 (m, 1 H, H-2%), 4.07–4.01
(m, 1 H, H-5%), 3.67 (s, 3 H, OMe), 3.66–3.64 (m, 1 H,
H-3%), 3.33–3.32 (m, 1 H, H-4%), 2.61–2.46 (m, 4 H,
H-2,6%), 2.41 (s, 2 H, NH2), 1.83 (s, 3 H, Ac). 13C
NMR: l 172.6, 170.3 (CO), 137.7, 137.6 (Cipso), 129.0,

J. Xie / Carbohydrate Research 338 (2003) 399–406
403
128.6, 128.4, 128.1, 128.0 (Ph), 78.2, 74.5, 74.3 (C-
3%,4%,5%), 72.7, 72.6 (OCH2), 63.5 (C-1%), 52.3 (OMe), 47.7
(C-2%), 40.1 (C-6%), 36.9 (C-2), 23.7 (Me). Anal. Calcd for
C25H32N2O6: C, 65.77; H, 7.06; N, 6.14. Found: C,
65.89; H, 7.09; N, 6.03.
OCHPh), 4.53 (d, Jgem 11.8 Hz, 1 H, OCHPh), 4.51–
4.40 (m, 2 H, H-2,6), 4.47 (d, Jgem 11.3 Hz, 1 H,
OCHPh), 4.41 (d, Jgem 11.8 Hz, 1 H, OCHPh), 4.18–
4.11 (m, 1 H, H-5), 4.09–4.07 (m, 1 H), 3.76–3.73 (m,
2 H, H-8), 3.67–3.64 (m, 1 H), 3.54 (s, 3 H, OMe), 3.01
(s, 1 H, OH), 1.78 (s, 3 H, Ac), 1.66–1.59 (m, 2 H, H-7).
13C NMR: l 170.7, 170.3 (CO), 137.6, 137.2 (Cipso),
129.1, 128.8, 128.3, 128.2, 127.7 (Ph), 74.7, 74.3, 73.1
(CH), 72.7, 72.1 (OCH2), 68.9 (CH), 60.1 (C-8), 52.7
(OMe), 48.3 (C-5), 33.8 (C-7), 23.7 (Me). Anal. Calcd
for C25H31NO7: C, 65.63; H, 6.83; N, 3.06. Found: C,
65.50; H, 6.89; N, 3.12.
3.7. Methyl 5-N-acetylamino-2,6-anhydro-3,4-di-O-ben-
zyl-8,9-didehydro-5,7,8,9-tetradeoxy-
D
-glycero- -gluco-
L
nonuronate (9)
To a soln of alcohol 3 (84 mg, 0.2 mmol) in acetone (5
mL), was added Jones reagent (1 M, 0.6 mL, 0.6 mmol).
The mixture was stirred 48 h at rt. After concentration,
the residue was dissolved in EtOAc (10 mL), washed
successively with water, Na2S2O3 5%, HCl 5%, brine,
dried over MgSO4, filtered and concentrated. The corre-
sponding acid was then esterified as for 5. Purification
by preparative TLC with 3:2 EtOAc–cyclohexane as
eluent afforded 9 as an oil (62 mg, 68%): [h]D +38 (c
0.5, CH2Cl2); Rf 0.60 (2:1 EtOAc–cyclohexane); IR
3.9. Methyl 5-N-acetylamino-2,6-anhydro-8-azido-3,4-
di-O-benzyl-5,7,8-trideoxy-
D
-glycero- -gluco-octuronate
L
(11)
Alcohol 10 was transformed to the azide 11 as described
for 4. The product was purified by preparative TLC
with 1:1 EtOAc–cyclohexane as eluent to afford 11
(71%) as an oil: [h]D +30 (c 0.3, CH2Cl2); Rf 0.72
1
(KBr) 3421, 3083, 3035, 1757, 1685 cm−1. H NMR: l
1
(EtOAc); IR (KBr) 3421, 2119, 1757, 1685 cm−1. H
7.30–7.14 (m, 10 H, Ph), 6.59 (d, J2%,NH 10.0 Hz, 1 H,
NH), 5.92–5.76 (m, 1 H, H-8), 5.13–4.98 (m, 2 H, H-9),
4.63 (d, Jgem 11.3 Hz, 1 H, OCHPh), 4.52 (d, Jgem 11.3
Hz, 1 H, OCHPh), 4.44 (d, Jgem 11.3 Hz, 1 H, OCHPh),
4.51–4.38 (m, 2 H, H-2,6), 4.39 (d, Jgem 11.3 Hz, 1 H,
OCHPh), 4.20–4.15 (m, 1 H, H-5), 4.09–4.07 (m, 1 H),
3.64 (t, J 3.0 Hz, 1 H), 3.50 (s, 3 H, OMe), 2.23–2.13
(m, 2 H, H-7), 1.76 (s, 3 H, Ac). 13C NMR: l 170.0,
169.9 (CO), 137.4, 137.1 (Cipso), 134.4 (C-8), 128.8,
128.5, 128.0, 127.9, 127.5 (Ph), 117.2 (C-9), 74.5, 74.1,
73.1 (CH), 72.3, 71.8 (OCH2), 69.7 (C-6), 52.1 (OMe),
47.3 (C-5), 36.0 (C-7), 23.4 (Me). Anal. Calcd for
C26H31NO6: C, 68.86; H, 6.89; N, 3.09. Found: C, 68.66;
H, 6.77; N, 3.02.
NMR: l 7.31–7.15 (m, 10 H, Ph), 6.65 (d, J2%,NH 10.0
Hz, 1 H, NH), 4.65 (d, Jgem 11.3 Hz, 1 H, OCHPh), 4.45
(d, Jgem 11.3 Hz, 1 H, OCHPh), 4.41–4.38 (m, 4 H,
H-2,6, 2×OCHPh), 4.15–4.09 (m, 3 H), 3.63 (t, J 3.0
Hz, 1 H), 3.53 (s, 3 H, OMe), 3.46–3.39 (m, 2 H, H-8),
1.76 (s, 3 H, Ac), 1.73–1.56 (m, 2 H, H-7). 13C NMR:
l 170.2 (CO), 137.6, 137.2 (Cipso), 129.1, 128.8, 128.3,
128.2, 127.8 (Ph), 74.8, 74.2, 73.2 (CH), 72.7, 72.1
(OCH2), 68.0 (C-6), 52.5 (OMe), 48.4 (C-8), 48.0 (C-5),
31.6 (C-7), 23.7 (Ac). Anal. Calcd for C25H30N4O6: C,
62.23; H, 6.27; N, 11.61. Found: C, 62.39; H, 6.18; N,
11.80.
3.10. Methyl 5-N-acetylamino-8-amino-2,6-anhydro-3,4-
di-O-benzyl-5,7,8-trideoxy-
(12)
D
-glycero- -gluco-octuronate
L
3.8. Methyl 5-N-acetylamino-2,6-anhydro-3,4-di-O-ben-
zyl-5,7-dideoxy-
D
-glycero- -gluco-octuronate (10)
L
The azide 11 was reduced to the amine 12 as described
for 6. Purification by preparative TLC with 1:9 MeOH–
CH2Cl2 as eluent afforded 12 as an oil in 46% yield: [h]D
+42.5 (c 0.4, CH2Cl2); Rf 0.25 (1:19 MeOH–CH2Cl2);
IR (KBr) 3421, 3035, 1757, 1733, 1685 cm−1. 1H NMR:
l 7.38–7.23 (m, 10 H, Ph), 6.76 (d, J2%,NH 9.8 Hz, 1 H,
NH), 4.72 (d, Jgem 11.3 Hz, 1 H, OCHPh), 4.59 (d, Jgem
11.3 Hz, 1 H, OCHPh), 4.55 (d, Jgem 11.5 Hz, 1 H,
OCHPh), 4.48 (d, Jgem 11.5 Hz, 1 H, OCHPh), 4.61–
4.45 (m, 2 H, H-2,6), 4.22–4.13 (m, 3 H), 3.72 (t, J 3.0
Hz, 1 H), 3.60 (s, 3 H, OMe), 3.45 (s, 2 H, NH2),
3.04–2.96 (m, 2 H, H-8), 1.86 (s, 3 H, Ac), 1.80–1.52
(m, 2 H, H-7). 13C NMR: l 170.6, 170.4 (CO), 137.6,
137.2 (Cipso), 129.1, 128.8, 128.3, 128.2, 127.8 (Ph), 74.5,
74.1, 73.1 (CH), 72.6, 72.2 (OCH2), 68.8 (CH), 52.7
(OMe), 48.2 (C-5), 38.6 (C-8), 30.1 (C-7), 23.7 (Me).
Anal. Calcd for C25H32N2O6: C, 65.77; H, 7.06; N, 6.14.
Found: C, 65.66; H, 7.00; N, 6.21.
Osmium tetraoxyde (4% soln in tBuOH, 93 mL) and
NaIO4 (146 mg, 0.684 mmol) were added to a soln of 9
(155 mg, 0.342 mmol) in a mixture of THF–water (2:1,
1.5 mL). After 20 h stirring at rt, the mixture was
concentrated, diluted in EtOAc (30 mL), washed with
water, Na2S2O3 5%, brine, dried over MgSO4, filtered
and concentrated to an oil which was dissolved in
MeOH (1 mL). Sodium borohydride (26 mg, 0.684
mmol) was added and the mixture was stirred for 20 h
at rt. The solution was concentrated, dissolved in
EtOAc (30 mL), washed with water, dried over MgSO4,
filtered and concentrated. The residue was purified by
preparative TLC with 2:1 EtOAc–cyclohexane as eluent
to afford 10 (66 mg, 42%) as an oil: [h]D +63.3 (c 0.3,
CH2Cl2); Rf 0.67 (EtOAc); IR (KBr) 3397, 3083, 1757,
1
1685 cm−1. H NMR: l 7.33–7.15 (m, 10 H, Ph), 6.65
(d, J2%,NH 9.3 Hz, 1 H, NH), 4.65 (d, Jgem 11.3 Hz, 1 H,

404
J. Xie / Carbohydrate Research 338 (2003) 399–406
3.11. (E)-1-(2%-N-Acetylamino-3%,4%,6%-tri-O-benzyl-2%-
deoxy-a- -glucopyranosyl)-1-propene (13)
45%) as a mixture of two diastereoisomers (E/Z=
21:4): [h]D +38.2 (c 1.1, CH2Cl2); Rf 0.72 (EtOAc); IR
D
1
(KBr) 3445, 3348, 1757, 1685 cm−1. H NMR of the
To a soln of 1 (500 mg, 0.971 mmol) in benzene (5 mL),
was added PdCl2 (50 mg, 0.282 mmol). The mixture
was heated at reflux for 23 h, then concentrated. Purifi-
cation by column chromatography (1:3 to 2:1 EtOAc–
hexane) afforded 13 (356 mg, 71%) as a mixture of two
major isomer E: l 7.33–7.15 (m, 10 H, Ph), 6.55 (d,
J2%,NH 10.0 Hz, 1 H, NH), 5.81 (qd, J7,8 15.3, J8,9 6.5 Hz,
1 H, H-8), 5.35 (ddq, J6,7 6.5, J7,9 1.5 Hz, 1 H, H-7),
4.82–4.80 (m, 1 H, H-6), 4.68–4.38 (m, 5 H, H-2,
2×OCH2Ph), 4.21–4.17 (m, 1 H, H-5), 4.08–4.07 (m,
1 H, H-4), 3.67 (t, J2,3=J3,4=3.0 Hz, 1 H, H-3), 3.51
(s, 3 H, OMe), 1.75 (s, 3 H, Ac), 1.62 (d, 3 H, H-9). 13C
NMR of the major isomer E: l 170.4, 170.1 (CO),
137.7, 137.4 (Cipso), 130.4 (C-8), 129.1, 128.8, 128.7,
128.2, 127.8 (Ph), 127.4 (C-7), 74.6 (C-4), 74.4 (C-2),
73.1 (C-3), 72.6, 72.1 (OCH2), 70.9 (C-6), 52.5 (OMe),
48.3 (C-5), 23.7 (Ac), 18.5 (C-9). Anal. Calcd for
C26H31NO6: C, 68.86; H, 6.89; N, 3.09. Found: C,
68.69; H, 6.95; N, 3.16.
diastereoisomers (E/Z=21:4): mp 98–100 °C; [h]D
+
27.0 (c 1.2, CH2Cl2); Rf 0.36 (1:1 EtOAc–cyclohexane);
1
IR (KBr) 3325, 3060, 3035, 1733 cm−1. H NMR of
the major isomer E: l 7.27–7.15 (m, 15 H, Ph), 6.12 (d,
J2%,NH 9.5 Hz, 1 H, NH), 5.70 (qd, J1,2 15.4, J2,3 6.5 Hz,
1 H, H-2), 5.33 (ddq, J1,1% 6.3, J1,3 1.6 Hz, 1 H, H-1),
4.59–4.33 (m, 6 H, 3×OCH2Ph), 4.35–4.33 (m, 1 H,
H-1%), 4.15–4.10 (m, 2 H), 3.77–3.51 (m, 4 H), 1.74 (s,
3 H, Ac), 1.61 (m, 3 H, H-3). 13C NMR of the major
isomer E: l 168.2 (CO), 136.6, 136.2, 136.0 (Cipso),
128.5 (CHꢁ), 127.0, 126.8, 126.4, 126.3, 126.1, 125.2
(Ph), 125.2 (CHꢁ), 73.7, 73.2, 72.4 (CH), 67.9 (CH),
66.4 (C-6%), 47.3 (C-2%), 21.7, 16.5 (Me). Anal. Calcd for
C32H37NO5: C, 74.53; H, 7.23; N, 2.71. Found: C,
74.46; H, 7.11; N, 2.69.
3.14. 3-(2%-N-Acetylamino-3%,4%,6%-tri-O-benzyl-2%-deoxy-
b-D-glucopyranosyl)-1-propene (17)
A soln of 3-(2%-N-acetylamino-2%-deoxy-b-
D
-glucopy-
13b,13c
ranosyl)-1-propene (16)
(488 mg, 0.200 mmol) in
anhyd DMF (10 mL) was added dropwise to a suspen-
sion of NaH (1.3 equiv/OH) in DMF (2 mL) at 0 °C.
Benzyl bromide (0.75 mL, 0.623 mmol) was added
dropwise after 30 min of further stirring at 0 °C and the
mixture stirred for additional 16 h at rt. Methanol (2
mL) was then added and the mixture was concentrated
under diminished pressure. The residue was dissolved in
EtOAc (30 mL), washed with water, brine, dried over
MgSO4, filtered and concentrated. Purification by
column chromatography (1:1 EtOAc–hexane) gave 17
(700 mg, 70%) as a white solid: mp 128 °C; [h]D +10.0
(c 1, CH2Cl2); Rf 0.54 (2:1 EtOAc–hexane); IR (KBr)
3.12. (E)-1-(2%-N-Acetylamino-3%,4%-di-O-benzyl-2%-de-
oxy-a-D-glucopyranosyl)-1-propene (14)
Compound 13 was acetolyzed as described for 1 and
deacetylated as described for 2. Purification by column
chromatography (1:1 to 2:1 EtOAc–cyclohexane) af-
forded 14 (white solid, 51%) as a mixture of two
diastereoisomers (E/Z=21:4): mp 140 °C; [h]D +35.0
(c 1.0, CH2Cl2); Rf 0.31 (2:1 EtOAc–cyclohexane); IR
1
(KBr) 3300, 3083, 3035, 1733, 1660 cm−1. H NMR of
the major isomer E: l 7.29–7.17 (m, 10 H, Ph), 5.99 (d,
J2%,NH 9.0 Hz, 1 H, NH), 5.69 (qd, J1,2 15.0, J2,3 6.8 Hz,
1 H, H-2), 5.38 (ddq, J1,1% 6.8, J1,3% 1.0 Hz, 1 H, H-1),
4.63–4.50 (m, 4 H, 2×OCH2Ph), 4.43–4.40 (m, 1 H,
H-1%), 4.15–4.08 (m, 1 H, H-2%), 3.94–3.83 (m, 2 H,
1
3325, 3107, 3083, 3035, 1660, 1612 cm−1. H NMR: l
7.28–7.13 (m, 15 H, Ph), 5.90–5.72 (m, 1 H, H-2),
5.12–4.93 (m, 2 H, H-1), 4.87 (d, J2%,NH 9.8 Hz, 1 H,
NH), 4.76 (t, Jgem 12.0 Hz, 2 H, OCH2Ph), 4.59–4.51
(m, 4 H, 2×OCH2Ph), 3.70–3.55 (m, 5 H), 3.38–3.22
(m, 2 H), 2.23–2.10 (m, 2 H, H-3), 1.73 (s, 3 H, Ac).
13C NMR: l 170.0 (CO), 138.4, 138.3, 138.0 (Cipso),
134.7 (C-2), 128.5, 128.4, 128.3, 128.2, 128.0, 127.8,
127.7, 127.5 (Ph), 116.8 (C-1), 83.0, 79.1, 78.9, 78.4
(CH), 74.8, 74.3, 73.4 (OCH2Ph), 68.9 (C-6%), 54.9
(C-2%), 36.5 (C-3), 23.5 (Ac). Anal. Calcd for
C32H37NO5: C, 74.53; H, 7.23; N, 2.71. Found: C,
74.46; H, 7.12; N, 2.79.
H-5%,6¦), 3.63–3.58 (m, 2 H, H-3%,6%), 3.43 (t, J3%,4%
=
J4%,5%=4.0 Hz, 1 H, H-4%), 2.60 (s, 1 H, OH), 1.72 (s, 3
H, Ac), 1.60 (d, J2,3 6.3 Hz, 3 H, H-3). 13C NMR of the
major isomer E: l 170.4 (CO), 138.2, 137.9 (Cipso),
131.3 (CHꢁ), 129.0, 128.5, 128.3 (Ph), 126.5 (CHꢁ), 76.2
(C-5%), 76.1 (C-3%), 75.6 (C-4%), 73.4, 73.3 (OCH2), 70.5
(C-1%), 61.1 (C-6%), 50.0 (C-2%), 23.7, 18.5 (Me). Anal.
Calcd for C25H31NO5: C, 70.57; H, 7.34; N, 3.29.
Found: C, 70.45; H, 7.31; N, 3.37.
3.13. Methyl (E)-5-N-acetylamino-2,6-anhydro-3,4-di-
O-benzyl-7,8-didehydro-5,7,8,9-tetradeoxy-
D-glycero-
L
-
3.15. 3-(2%-N-Acetylamino-3%,4%-di-O-benzyl-2%-deoxy-b-
gluco-nonuronate (15)
D-glucopyranosyl)-1-propene (18)
The alcohol 14 was oxidized and esterified as described
for 9 to afford, after purification by preparative TLC
with 1:1 EtOAc–cyclohexane as eluent, the ester 15 (oil,
Compound 17 was acetolyzed as described for 1 and
deacetylated as described for 2. Purification by column
chromatography (1:1 to 2:1 EtOAc–cyclohexane) af-

J. Xie / Carbohydrate Research 338 (2003) 399–406
405
(b) Cipolla, L.; La Ferla, B.; Lay, L.; Peri, F.; Nicotra, F.
Tetrahedron: Asymmetry 2000, 11, 295–303;
(c) SanMartin, R.; Tavassoli, B.; Walsh, K. E.; Walter,
D. S.; Gallagher, T. Org. Lett. 2000, 2, 4051–4054;
(d) Yang, G.; Franck, R. W.; Bittman, R.; Samadder, P.;
Arthur, G. Org. Lett. 2001, 3, 197–200;
(e) Ohnishi, Y.; Ichikawa, Y. Bioorg. Med. Chem. Lett.
2002, 12, 997–999;
(f) Wakabayashi, T.; Shiozaki, M.; Kurakata, S. Carbo-
hydr. Res. 2002, 337, 97–104;
(g) Pachamuthu, K.; Gupta, A.; Das, J.; Schmidt, R.
R.; Vankar, Y. D. Eur. J. Org. Chem. 2002, 1479–
1483.
forded 18 as a white solid (43%): mp 158–160 °C; [h]D
−1.8 (c 1, CH2Cl2); Rf 0.35 (2:1 EtOAc–cyclohexane).
1H NMR: l 7.26–7.20 (m, 10 H, Ph), 5.85–5.68 (m, 1
H, H-2), 5.57 (d, J2%,NH 8.8 Hz, 1 H, NH), 5.02–4.95
(m, 2 H, H-1), 4.77 (d, Jgem 10.8 Hz, 1 H, OCHPh),
4.74 (d, Jgem 12.5 Hz, 1 H, OCHPh), 4.61 (d, Jgem 11.5
Hz, 1 H, OCHPh), 4.59 (d, Jgem 10.8 Hz, 1 H, OCHPh),
3.81–3.47 (m, 5 H), 3.37–3.28 (m, 2 H, H-1%+CH),
2.27–2.10 (m, 3 H, H-3, OH), 1.76 (s, 3 H, Ac). 13C
NMR: l 170.4 (CO), 138.5, 138.0 (Cipso), 134.5 (C-2),
128.6, 128.3, 128.1, 128.0, 127.9 (Ph), 117.1 (C-1), 83.1,
79.1, 78.9, 78.2 (CH), 75.0, 74.6 (OCH2), 62.2 (C-6%),
54.9 (C-2%), 36.5 (C-3), 23.5 (Me). Anal. Calcd for
C25H31NO5: C, 70.57; H, 7.34; N, 3.29. Found: C,
70.73; H, 7.45; N, 3.40.
7. Knapp, S.; Myers, D. S. J. Org. Chem. 2001, 66, 3636–
3638.
8. (a) Postema, M. H. D. Tetrahedron 1992, 48, 8545–8599;
(b) Levy, D. E.; Tang, C. In The Chemistry of C-gly-
cosides; Baldwin, J. E.; Magnus, P. D., Eds.; Elsevier
Science: Oxford, 1995;
(c) Du, Y.; Linhardt, R. J. Tetrahedron 1998, 54, 9913–
9959;
3.16. Methyl 5-N-acetylamino-2,6-anhydro-3,4-di-O-
benzyl-8,9-didehydro-5,7,8,9-tetradeoxy-
L-glycero-L-
(d) Nicotra, F. Top. Curr. Chem. 1997, 187, 55–83.
9. For recent reviews on this subjet, see:
(a) Gruner, S. A. W.; Locardi, E.; Lohof, E.; Kessler, H.
Chem. Re6. 2002, 102, 491–514;(b) Schweizer, F. Angew.
Chem., Int. Ed. 2002, 41, 230–253.
10. (a) Irvine, J. C.; McNicoll, D.; Hynd, A. J. Chem. Soc.
1911, 11, 250–261;
gluco-nonuronate (19)
Ester 19 was prepared as described for 9. Purification
by preparative TLC with 3:2 EtOAc–cyclohexane as
eluent afforded 19 as a white solid (49%): mp 146 °C;
[h]D −1.0 (c 0.8, CH2Cl2); Rf 0.53 (3:2 EtOAc–cyclo-
(b) Heyns, K.; Paulsen, H. Chem. Ber. 1955, 88, 188–
195;
1
hexane). H NMR: l 7.27–7.20 (m, 10 H, Ph), 5.84–
5.68 (m, 1 H, H-8), 5.09 (d, J2%,NH 7.5 Hz, 1 H, NH),
5.01–4.94 (m, 2 H, H-9), 4.79 (d, Jgem 11.5 Hz, 1 H,
OCHPh), 4.71 (d, Jgem 11.0 Hz, 1 H, OCHPh), 4.57 (d,
Jgem 11.8 Hz, 1 H, OCHPh), 4.54 (d, Jgem 10.8 Hz, 1 H,
OCHPh), 3.85–3.62 (m, 4 H), 3.66 (s, 3 H, OMe),
3.47–3.37 (m, 1 H, H-6), 2.27–2.15 (m, 2 H, H-7), 1.73
(s, 3 H, Ac). 13C NMR: l 170.2, 169.4 (CO), 138.3,
137.8 (Cipso), 134.2 (C-8), 128.7, 128.6, 128.4, 128.2,
128.1 (Ph), 117.3 (C-9), 81.8, 80.7, 78.9, 78.4 (C-
2,3,4,6), 75.0, 74.6 (OCH2), 54.9, 52.6 (C-5, OMe), 36.5
(C-7), 23.6 (Me). Anal. Calcd for C26H31NO6: C, 68.86;
H, 6.89; N, 3.09. Found: C, 68.99; H, 6.74; N, 2.99.
(c) Fodor, G.; Otvos, L. Chem. Ber. 1956, 89, 701–
708;
(d) Yoshimura, J.; Sato, T.; Ando, H. Bull. Chem. Soc.
Jpn. 1969, 42, 2352–2356;
(e) Mu¨ller, C.; Kitas, E.; Wessel, H. P. J. Chem. Soc.,
Chem. Commun. 1995, 2425–2426;
(f) Wessel, H. P.; Mitchell, C. M.; Lobato, C. M.;
Schmid, G. Angew. Chem., Int. Ed. 1995, 34, 2712–2713;
(g) Suhara, Y.; Hildreth, J. E. K.; Ichikawa, Y. Tetra-
hedron Lett. 1996, 37, 1575–1578;
(h) Suhara, Y.; Ichikawa, M.; Hildreth, J. E. K.;
Ichikawa, Y. Tetrahedron Lett. 1996, 37, 2549–2552;
(i) Graf von Roedern, E.; Lohof, E.; Hessler, G.; Hoff-
mann, M.; Kessler, H. J. Am. Chem. Soc. 1996, 118,
10156–10167;
(j) Hoffmann, M.; Burkhart, F.; Hessler, G.; Kessler, H.
Hel6. Chim. Acta 1996, 79, 1519–1532;
(k) Burkhart, F.; Kessler, H. Tetrahedron Lett. 1998, 39,
References
255–256;
1. Kennedy, J. F. Carbohydrate Chemistry; Oxford Univer-
sity Press: Oxford, 1988.
2. (a) Bahl, O. P. An Introduction to Glycoproteins; Marcel
Dekker: New York, 1992;
(l) Sofia, M. J.; Hunter, R.; Chan, T. Y.; Vaughan, A.;
Dulina, R.; Wang, H.; Gange, D. J. Org. Chem. 1998, 63,
2802–2803;
(m) Ghosh, M.; Dulina, R. R.; Kakarla, R.; Sofia, M. J.
J. Org. Chem. 2000, 65, 8387–8390.
(b) Kobata, A. Acc. Chem. Res. 1993, 26, 319–324;
(c) Arsequell, G.; Valencia, G. Tetrahedron: Asymmetry
1999, 10, 3045–3094.
11. Kobertz, W. R.; Bertozzi, C. R.; Bednarski, M. D. J.
Org. Chem. 1996, 61, 1894–1897.
12. Xie, J. Eur. J. Org. Chem. 2002, 3411–3418.
13. (a) Grugier, J.; Xie, J.; Duarte, I.; Vale´ry, J. M. J. Org.
Chem. 2000, 65, 979–984;
3. Taylor, C. M. Tetrahedron 1998, 54, 11317–11362.
4. Haltiwanger, R. S.; Kelly, W. G.; Roquemore, E. P.;
Blomberg, M. A.; Dong, L. Y. D.; Kreppel, L.; Chou, T.
Y.; Hart, G. W. Biochem. Soc. Trans. 1992, 20, 264–269.
5. (a) Wells, L.; Vosseller, K.; Hart, G. W. Science 2001,
291, 2376–2378;
(b) Roe, B. A.; Boojamra, C. G.; Griggs, J. L.; Bertozzi,
C. R. J. Org. Chem. 1996, 61, 6442–6445;
(c) Cui, J.; Horton, D. Carbohydr. Res. 1998, 309, 319–
330.
(b) Zachara, N. E.; Hart, G. W. Chem. Re6. 2002, 102,
431–438.
14. McDevitt J.P.; Lansbury Jr., P.T. J. Am. Chem. Soc.
1996, 118, 3818–3828.
6. (a) Reviewed in Xie, J. Recent Res. De6el. Org. Chem.
1999, 3, 505–523;

406
J. Xie / Carbohydrate Research 338 (2003) 399–406
15. Henry, W. R.; Weinreb, S. M. J. Org. Chem. 1993, 58,
4745.
16. Mbongo, A.; Fre´chou, C.; Beaupe`re, D.; Uzan, R.; De-
mailly, G. Carbohydr. Res. 1993, 246, 361–370.
17. Xie, J.; Molina, A.; Czernecki, S. J. Carbohydr. Chem.
1999, 18, 481–498.
18. Shao, H.; Wang, Z.; Lacroix, E.; Wu, S.-H.; Jennings,
H. J.; Zou, W. J. Am. Chem. Soc 2002, 124, 2130–
2131.
19. 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.