Practical preparation of 2-azido-2-deoxy-β-d-mannopyranosyl carbonates and their application in the synthesis of oligosaccharides

Article abstract of DOI:10.1016/j.carres.2007.09.001

1-O-Allyloxycarbonyl (or ethyloxycarbonyl)-2-azido-2-deoxy-3-O-benzyl (or allyl, or benzoyl)-4,6-O-isopropylidene-β-d-mannopyranose derivatives were prepared from the corresponding 2-hydroxy-β-d-glucopyranosyl carbonates in high yields via triflation of t

Full text of DOI:10.1016/j.carres.2007.09.001

Available online at www.sciencedirect.com
Carbohydrate Research 342 (2007) 2810–2817
Note
Practical preparation of 2-azido-2-deoxy-b-D-mannopyranosyl
carbonates and their application in the synthesis of oligosaccharides
Jianjun Zhang,a Shiqiang Yan,a Xiaomei Liang,a Jingping Wu,a
Daoquan Wanga,* and Fanzuo Kongb
aKey Lab of Pesticide Chemistry and Application Technology, Department of Applied Chemistry,
China Agricultural University, Beijing 100094, China
bResearch Center for Eco-Environmental Sciences, Academia Sinica, PO Box 2871, Beijing 100085, China
Received 9 July 2007; received in revised form 30 August 2007; accepted 2 September 2007
Available online 7 September 2007
Abstract—1-O-Allyloxycarbonyl (or ethyloxycarbonyl)-2-azido-2-deoxy-3-O-benzyl (or allyl, or benzoyl)-4,6-O-isopropylidene-b-D-
mannopyranose derivatives were prepared from the corresponding 2-hydroxy-b-D-glucopyranosyl carbonates in high yields via tri-
flation of the 2-hydroxyl group and subsequent SN2 displacement with azide ion. An N-acetyl-mannosamine-containing trisaccha-
ride, a fragment of the putative O10 antigen from Acinetobacter baumannii, was efficiently synthesized using these derivatives.
ꢀ 2007 Published by Elsevier Ltd.
Keywords: 2-Azido-2-deoxy-b-D-mannopyranose; Triflation; Azide displacement
N-Acetyl-mannosamine (ManNAc) is the biosynthetic
precursor of sialic acids, N-acetyl-neuraminic acid,1
and is as a high-affinity ligand for the natural killer cell
activating protein NKR-P1.2 The ManNAc unit has
been found in many bacterial polysaccharides,3 and
some oligosaccharides containing ManNAc have been
found to possess immunostimulatory activity.4 Because
of the biological significance and utility of this monosac-
charide, the synthesis of ManNAc and corresponding
analogues has been an interesting topic in carbohydrate
chemistry. As a synthetic intermediate, the correspond-
ing azido derivative has been used extensively. Usually,
the azido derivative is prepared by either azidonitra-
tion of glucal derivatives5 or SN2 inversion of the
configuration at the C-2 atom of D-glucose deriva-
tives.6a–h
the instability of the target compound during work-up
process is a major limitation of these approaches.
Although the reasons for the instability of the product
and the breakdown mechanism remain unclear, we spec-
ulate that the decomposition may be partially due to the
interaction of azido group with the cis-3-O-acetyl group,
as the corresponding 2-azido-2-deoxy-glucose6c and 3-
O-unprotected 2-azido-2-deoxy-mannose derivatives6g
are relatively stable. A previous study demonstrated
the regio- and stereoselective esterification of 3-O-allyl
(or benzyl, or benzoyl)-4,6-O-isopropylidene-D-gluco-
pyranose with allyl (or ethyl) chloroformate, to afford
the corresponding 2-hydroxy-b-D-glucopyranosyl carbo-
nates in good yields.7 With these compounds in hand,
we envisioned that the corresponding 2-azido-2-deoxy-
mannose derivatives could be conveniently prepared
from these intermediates. We report here the results
we recently obtained on this approach, which provides
a new and practical method for the synthesis of 2-azi-
do-2-deoxy-mannose derivatives. As an example of the
methodology, it was used to synthesize efficiently a
ManNAc-containing trisaccharide, a fragment of the
putative O10 antigen from Acinetobacter baumannii.8
There have been several publications regarding the
preparation of 1,3,4,6-tetra-O-acetyl-2-azido-2-deoxy-
a-D-mannopyranose from 1,3,4,6-tetra-O-acetyl-a-D-
glucopyranose via a two-step process.6c,g,h However,
*
Corresponding author. Tel./fax: +86 10 62732219; e-mail: wangdq@
cau.edu.cn
0008-6215/$ - see front matter ꢀ 2007 Published by Elsevier Ltd.
doi:10.1016/j.carres.2007.09.001

J. Zhang et al. / Carbohydrate Research 342 (2007) 2810–2817
Me2C
Me2C
2811
Me2C
O
O
O
N3
O
R2O
O
c
O
a
O
OTf
O
R2O
O
R2O
O
O
O
OH
COOR1
COOR1
COOR1
R1 = All; Et
R2 = Bn; All; Bz
R1 = All; Et
R2 = Bn; All; Bz
R1 = All; Et
R2 = Bn; All; Bz
3
2
1
b
HO
HO
R2O
N3
O
O
COOR1
4 R1 =All; R2 = Bn
Scheme 1. Synthesis of 2-azido-2-deoxy-b-D-mannopyranoside derivatives. Reagents and conditions: (a) Tf2O, pyridine; (b) NaN3, DMF, 70 ꢁC; (c)
NaN3, DMF, Et3N, 70 ꢁC.
As shown in Scheme 1, the preparation of the target 2-
azido-2-deoxy-b-D-mannopyranose derivative, 3, was
achieved via SN2 inversion by azide ion of triflate, 2,
which was prepared from the corresponding 2-hydr-
oxy-glucopyranosyl carbonate 1. The results of the
reaction using different glucopyranosyl carbonate deriv-
atives (1a–e) as the starting materials are listed in Table
1.
It was found that triflation of 1a–e with triflic anhy-
dride (2.2 equiv) in dichloromethane in the presence of
pyridine (2.4 equiv) at ꢀ15 ꢁC proceeded smoothly.
Complete esterification occurred and intermediates
Table 1. Results of triflation and azide displacement reactions
Entry
Reactant 1a–e
Triflate 2a–e (yield)a
Product 3a–e (yield)a
J1,2 (Hz)
Me2C
O
Me2C
O
Me2C
O
2a (8.2)
3a (1.6)
N3
O
AllO
O
O
O
O
1
O
O
O
AllO
AllO
COOEt
COOAll
COOEt
O
OTf
OH
3a (83%)
1a
COOEt
2a (96%)
Me2C
Me2C
O
Me2C
O
O
N3
O
BzO
O
O
O
O
BzO
O
O
2
2b (8.1)
3b (1.5)
O
BzO
O
OTf
2b (94%)
OH
COOAll
1b
COOAll
3b (59%)
Me2C
Me2C
O
Me2C
O
O
N3
O
O
O
O
O
O
AllO
O
O
O
O
3
4
2c (8.2)
3c (1.6)
AllO
AllO
COOAll
COOEt
COOAll
COOAll
O
OTf
2c (95%)
OH
3c (72%)
1c
COOAll
Me2C
Me2C
Me2C
O
O
O
N3
O
O
O
O
O
BnO
O
BnO
2d (8.2)
3d (1.6)
O
BnO
O
OTf
2d (93%)
OH
COOEt
3d (84%)
1d
COOEt
Me2C
Me2C
O
Me2C
O
O
N3
O
O
O
O
O
BnO
O
BnO
5
2e (8.2)
3e (1.5)
O
BnO
O
OTf
2e (95%)
OH
COOAll
3e (80%)
1e
COOAll
a Isolated yield.

2812
J. Zhang et al. / Carbohydrate Research 342 (2007) 2810–2817
2a–e were obtained in high yields after a simple work-up
procedure and silica gel column chromatography (8:1
petroleum ether–EtOAc, containing 0.5% of Et3N).
The use of low reaction temperatures was necessary to
ensure the high yields. The H NMR spectra of all tri-
flates provided clear information to support the assigned
structures.
chloroacetimidate, with acceptor 7 was accomplished
within 40 min at room temperature using TMSOTf as
the catalyst, giving the a-linked disaccharide 12 after sil-
ica gel column chromatography. Second, deallyloxy-
carbonylation of 12 under the same conditions as
those used for the deallyloxycarbonylation of 3b affor-
ded the disaccharide acceptor 13 in 73% yield. Finally,
TMSOTf-catalyzed coupling of the 2-azido-2-deoxy-a-
D-mannopyranosyl donor 5 with 13 proceeded smoothly
at 0 ꢁC. However, some byproducts with identical chro-
matographic mobilities to trisaccharide 13 were pro-
duced and purification of the product was difficult.
Therefore, a solution of 0.3% acetyl chloride in metha-
nol was added to the reaction mixture immediately after
completion of the coupling reaction, which, after stirring
for 6 h at room temperature, led to the successful
removal of the isopropylidene acetal furnishing the
trisaccharide diol 15 (71% for 2 steps) as an amorphous
solid. Subsequent acetylation with acetic anhydride in
pyridine readily gave acetylated trisaccharide 16 (88%).
The azido groups were transformed into the correspond-
ing acetamido groups by reduction of 16 with activated
zinc in a mixture of acetic anhydride, acetic acid, and
THF,14 and then the O-acyl groups were cleaved with
a catalytic amount of sodium methoxide in methanol,
furnishing the desired trisaccharide (56% for 2 steps).
Construction of the (1!6)-linked dimer and trimer of
this trisaccharide is in progress.
1
These triflates were quite unstable and turned dark
brown after 3–4 days of storage in a refrigerator, even
at ꢀ15 ꢁC. Therefore, to minimize decomposition, the
triflates were used in the next step soon after purifica-
tion. When the displacement reaction of 2a with sodium
azide was carried out in DMF at an elevated tempera-
ture (70 ꢁC), the desired product, 3a, was formed within
4 h in very low yield (17%) due to the removal of the 4,6-
O-isopropylidene group under these conditions, thus
giving 4 as the main product (61%). To solve this prob-
lem, several drops of Et3N were added to the reaction
mixture, and using this modification, 3a was obtained
in a high yield (83%). Under these optimized conditions,
the triflates 2b–e were converted to the corresponding
azido derivatives in good yields (72–84%) except for 2b
(59%), presumably because of the instability of 3-O-ben-
zoyl group under the basic reaction conditions. The
inversion of configuration at C-2 was readily identified
1
by comparison of H NMR spectral data as indicated
in Table 1 As expected, compounds with the b-gluco
configuration showed large coupling constants for H-1
(J1,2 8.1–8.2 Hz), while those with the b-manno configu-
ration showed small coupling constants (J1,2 1.5–
1.6 Hz).
These 2-azido-2-deoxy-b-D-mannopyranose deriva-
tives are useful building blocks for the preparation of
ManNAc-containing oligosaccharides and glycoconju-
gates, as they can be readily converted either to 2-azido-
2-deoxy-a-D-mannopyranosyl donors or to 2-azido-2-
deoxy-b-D-mannopyranosyl carbonate acceptors. As
an example, a trisaccharide containing 2-acetamido-2-
deoxy-a-D-mannose was synthesized efficiently (Scheme
2). This trisaccharide is the core structure of the
repeating unit of the putative O10 antigen from A.
baumannii.8
Thus, dealloxycarbonylation of 3b with the palladium
catalyst, Pd[P(C6H5)3]4, (0.05 equiv), in the presence of
triphenylphosphine (0.3 equiv) and triethylamine
(2 equiv) in THF,9 followed by C-1 activation with tri-
chloroacetonitrile,10 furnished the 2-azido-2-deoxy-a-D-
mannopyranosyl donor 5 in 73% yield over the two
steps. When rhamnose diol 611 was treated with allyl
chloroformate in dichloromethane at ꢀ15 ꢁC in the
presence of 4 equiv of pyridine, the C-3 hydroxyl group
was selectively blocked, giving acceptor 7 in 92% yield.12
Assembly of trisaccharide 14 was achieved in three
steps. First, glycosylation of 11, which was prepared
from 2-azido-2-deoxy-glucopyranose 813 through benzo-
ylation, C-1 debenzoylation, and conversion to the tri-
In conclusion, an efficient and practical method was
developed for the synthesis of 2-azido-2-deoxy-b-D-
mannopyranoside derivatives. Large-scale preparation
of these building blocks is possible thus providing a
valuable supplement to the present efforts for the syn-
thesis of 2-azido-2-deoxymannose derivatives.
1. Experimental
1.1. General methods
Optical rotations were determined with a Perkin–Elmer
model 241-MC automatic polarimeter for solution in a
1-dm, jacketed cell. NMR spectra were recorded in
CDCl3 solution on a Bruker DPX300 spectrometer,
using tetramethylsilane as the internal standard. Ele-
mental analysis was performed on a Yanaco CHN Cor-
der MF-3 automatic elemental analyzer. Thin-layer
chromatography (TLC) was performed on Silica Gel
HF with detection by charring with 30% (v/v) H2SO4
in MeOH or by UV detection. Column chromatography
was conducted by elution of a column (8 · 100 mm,
16 · 240 mm, 18 · 300 mm, or 35 · 400 mm) of silica
gel (200–300 mesh) with mixtures of EtOAc–petroleum
ether (bp 60–90 ꢁC) as the eluent. Solutions were con-
centrated at a temperature <60 ꢁC under diminished
pressure.

J. Zhang et al. / Carbohydrate Research 342 (2007) 2810–2817
2813
OPMP
OPMP
Me2C
O
Me2C
O
O
N3
N3
Me
BzO
Me
BzO
O
BzO
O
O
O
O
a
b
BzO
O
HO
AllocO
OH
OH
COOAll
7
6
5
OCNHCCl3
3b
OBz
OBz
HO
O
BzO
O
O
BzO
BzO
HO
HO
e
c
BzO
N3
N3
R = Bz
N3
OCNHCCl3
OR
OH
9
11
8
d
10 R = OH
OPMP
Me
O
12 R = Alloc
13 R = H
BzO
g
f
RO
O
N3
+
11
7
OBz
OBz
O
OPMP
OBz
Me
HO
OPMP
O
Me
BzO
O
O
O
O
N3
j
f
O
O
+
13
5
OBz
OBz
OBz
NHAc
O
O
O
AcHN
N3
OBz
OR
OH
OH
OH
OH
OR
OH
OH
14 R = isopropylidene
h
i
15 R = H
17
16 R = Ac
Scheme 2. Synthesis of antigenic trisaccharide 17. Reagents and conditions: (a) Pd[P(C6H5)3]4, P(C6H5)3, Et3N, THF, rt then Cl3CCN, DBU,
CH2Cl2, 0 ꢁC, 73% for 2 steps; (b) AllocCl, pyridine, CH2Cl2, ꢀ15 ꢁC, 89%; (c) BzCl, pyridine; (d) MeOH, THF, NH3; (e) Cl3CCN, DBU, CH2Cl2,
0 ꢁC, 62% from 8; (f) TMSOTf, CH2Cl2, rt, 67% for 12; (g) Pd[P(C6H5)3]4, P(C6H5)3, Et3N, THF, rt, 69%; (h) 0.3% CH3COCl–MeOH, 71% for two
steps; (i) Ac2O–pyridine, 88%; (j) Zn, THF–Ac2O–HOAc (3:2:1); then NaOMe, MeOH, 56%.
1.2. General procedure for the preparation of the triflates
2a–e
of CH2Cl2. The combined organic layer and extracts
were dried over Na2SO4 and the solution was concen-
trated under diminished pressure to give a residue,
which was subjected to silica gel column chromato-
graphy (8:1–10:1 petroleum ether–EtOAc, containing
0.5% Et3N) to give the desired triflates in almost quan-
titative yield.
A 100-mL two-neck round-bottom flask equipped with
two addition funnels was charged with pyridine
(0.90 mL, 11 mmol) and dry CH2Cl2 (40 mL). A solu-
tion of triflic anhydride (1.65 mL, 10.0 mmol) in dry
CH2Cl2 (10 mL) was placed in a funnel and a solution
of 1a–e (5.0 mmol) in dry CH2Cl2 (20 mL) was placed
in the other funnel. The flask was cooled to ꢀ15 ꢁC in
an ice-salt-acetone bath and the triflic anhydride solu-
tion was added dropwise. A thick white precipitate be-
gan to form during the addition. After addition was
complete, the suspension was allowed to stir for an addi-
tional 10 min. The sugar solution was added dropwise
and stirring continued for an additional 0.5 h. The reac-
tion mixture was poured into 50 mL of ice-water; the
aqueous layer was extracted with two 30 mL portions
1.3. 3-O-Allyl-1-O-ethyloxycarbonyl-4,6-O-isopropylid-
ene-2-O-trifluoromethanesulfonyl-b-D-glucopyranose (2a)
25
2.15 g (96%), syrup. ½aꢁD +27.2 (c 1.0, CHCl3); 1H NMR
(CDCl3, 300 MHz): d 5.95–5.87 (m, 1H, CH2@CH–
CH2O), 5.63 (d, 1H, J = 8.2 Hz, H-1), 5.31–5.20 (m,
2H, CH2@CH–CH2O), 4.66 (dd, J = 8.2, 8.8 Hz, 1H,
H-2), 4.40–4.15 (m, 4H, CH2@CH–CH2O, CH3CH2O),
3.98 (dd, 1H, J = 5.4, 10.9 Hz, H-6a), 3.80–3.66 (m,
3H, H-3, H-4, H-6b), 3.46–3.73 (m, 1H, H-5), 1.50,

2814
J. Zhang et al. / Carbohydrate Research 342 (2007) 2810–2817
1.43 (2s, 6H, Me2C), 1.30 (t, 3H, 7.14, CH3CH2). Anal.
Calcd for C16H23F3O10S: C, 41.38; H, 4.99. Found: C,
41.19; H, 5.02.
(2s, 6H, Me2C). Anal. Calcd for C21H25F3O10S: C,
47.91; H, 4.79. Found: C, 48.16; H, 5.04.
1.8. General procedure for the preparation of azides 3a–e
1.4. 1-O-Allyloxycarbonyl-3-O-benzoyl-4,6-O-isopropyl-
idene-2-O-trifluoromethanesulfonyl-b-D-glucopyranose
(2b)
A mixture of 2a–e (2.50 mmol) and NaN3 (0.81 g,
12.5 mmol) in dry DMF (15 mL, containing four drops
of Et3N) was stirred under N2 atmosphere at 70 ꢁC for
4 h, at which time TLC (8:1–10:1 petroleum ether–
EtOAc) indicated that the reaction was complete. The
reaction mixture was diluted with CH2Cl2 (100 mL),
washed with satd aq NaHCO3, and the organic layer
was dried over Na2SO4. The solution was concentrated
under diminished pressure, and the residue was purified
by column chromatography on a silica gel column (8:1–
10:1 petroleum ether–EtOAc) to give 3a–e.
25
1
2.54 g (94%), white solid. ½aꢁD +7.8 (c 2.0, CHCl3); H
NMR (CDCl3, 300 MHz): d 8.08–7.44 (m, 5H, Bz-H),
5.97–5.88 (m, 1H, CH2@CH–CH2OCO), 5.78 (d, 1H,
J = 8.1 Hz, H-1), 5.66 (dd, 1H, J = 9.5 Hz, H-3), 5.42–
5.29 (m, 2H, CH2@CH–CH2OCO), 4.97 (dd, 1H,
J = 8.1, 9.5 Hz, H-2), 4.73–4.69 (m, 2H, CH2@CH–
CH2OCO), 4.07–3.65 (m, 3H, H-4, H-6a, H-6b), 3.63
(m, 1H, H-5), 1.45, 1.36 (2s, 6H, Me2C). Anal. Calcd
for C21H23F3O11S: C, 46.67; H, 4.29. Found: C, 46.55;
H, 4.46.
1.9. 3-O-Allyl-2-azido-2-deoxy-1-O-ethyloxycarbonyl-
4,6-O-isopropylidene-b-D-mannopyranose (3a)
1.5. 3-O-Allyl-1-O-allyloxycarbonyl-4,6-O-isopropylid-
ene-2-O-trifluoromethanesulfonyl-b-D-glucopyranose (2c)
25
740 mg (83%), white solid. ½aꢁD +68.0 (c 1.0, CHCl3); 1H
NMR (CDCl3, 300 MHz):
d 5.92–5.86 (m, 1H,
25
2.26 g (95%), colorless oil. ½aꢁD +19.6 (c 1.9, CHCl3); 1H
CH2@CH–CH2O), 5.59 (d, 1H, J = 1.6 Hz, H-1), 5.37–
5.20 (m, 2H, CH2@CH–CH2O), 4.31–3.80 (m, 8H),
3.67–3.63 (m, 1H, H-6b), 3.33–3.23 (m, 1H, H-5), 1.55,
1.41 (2s, 6H, Me2C), 1.28 (t, 3H, J = 7.2 Hz, CH3CH2).
Anal. Calcd for C15H23N3O7: C, 50.41; H, 6.49; N,
11.76. Found: C, 50.58; H, 6.35; N, 11.26.
NMR (CDCl3, 300 MHz):
d 5.96–5.86 (m, 2H,
CH2@CH–CH2O, CH2@CH–CH2OCO), 5.66 (d, 1H,
J = 8.2 Hz, H-1), 5.41–5.20 (m, 4H, CH2@CH–CH2O,
CH2@CH–CH2OCO), 4.71–4.67 (m, 3H, CH2@CH–
CH2OCO, H-2), 4.40–4.10 (m, 2H, CH2@CH–CH2O),
3.97 (dd, 1H, J = 5.4, 10.9 Hz, H-6a), 3.80–3.61 (m,
3H, H-3, H-4, H-6b), 3.42 (m, 1H, H-5), 1.50, 1.43 (2s,
6H, Me2C). Anal. Calcd for C17H23F3O10S: C, 42.86;
H, 4.87. Found: C, 42.90; H, 5.00.
1.10. 1-O-Allyloxycarbonyl-2-azido-3-O-benzoyl-2-
deoxy-4,6-O-isopropylidene-b-D-mannopyranose (3b)
25
1
640 mg (59%), white solid. ½aꢁD +9.3 (c 1.5, CHCl3); H
NMR (CDCl3, 300 MHz): d 8.11–7.45 (m, 5H, Bz-H),
5.98–5.89 (m, 1H, CH2@CH–CH2OCO), 5.79 (d, 1H,
J = 1.5 Hz, H-1), 5.42–5.25 (m, 3H, CH2@CH–CH2O-
CO, H-3), 4.70–4.68 (m, 2H, CH2@CH–CH2OCO),
4.38 (dd, 1H, J = 1.5, 3.7 Hz, H-2), 4.16 (dd, 1H, J
9.7, 9.7 Hz, H-4), 4.01–3.84 (m, 2H, H-6), 3.49 (m,
1H, H-5), 1.53, 1.37 (2s, 6H, Me2C). Anal. Calcd for
C20H23N3O8: C, 55.42; H, 5.35; N, 9.70. Found: C,
55.76; H, 5.40; N, 9.47.
1.6. 3-O-Benzyl-1-O-ethoxycarbonyl-4,6-O-isopropylid-
ene-2-O-trifluoromethanesulfonyl-b-D-glucopyranose (2d)
25
1
2.40 g (93%), white solid. ½aꢁD +9.0 (c 1.0, CHCl3); H
NMR (CDCl3, 300 MHz): d 7.36–7.25 (m, 5H, Ar-H),
5.66 (d, 1H, J = 8.2 Hz, H-1), 4.86–4.69 (m, 3H, PhCH2,
H-2), 4.32–4.21 (m, 2H, CH3CH2OCO), 3.99 (dd, 1H,
J = 5.4, 10.9 Hz, H-6a), 3.82–3.73 (m, 3H, H-3, H-4,
H-6b), 3.43 (m, 1H, H-5), 1.48, 1.43 (2s, 6H, Me2C),
1.32 (t, 3H, J = 7.1 Hz, CH3CH2OCO). Anal. Calcd
for C20H25F3O10S: C, 46.69; H, 4.90. Found: C, 46.33;
H, 4.66.
1.11. 3-O-Allyl-1-O-allyloxycarbonyl-2-azido-2-deoxy-
4,6-O-isopropylidene-b-D-mannopyranose (3c)
25
1.7. 1-O-Allyloxycarbonyl-3-O-benzyl-4,6-O-isopropylid-
ene-2-O-trifluoromethanesulfonyl-b-D-glucopyranose (2e)
670 mg (73%), colorless oil. ½aꢁD ꢀ5.7 (c 1.7, CHCl3); 1H
NMR (CDCl3, 300 MHz):
d 5.97–5.87 (m, 2H,
CH2@CH–CH2O, CH2@CH–CH2OCO), 5.59 (d, 1H,
J = 1.6 Hz, H-1), 5.42–5.20 (m, 4H, CH2@CH–CH2O,
CH2@CH–CH2OCO), 4.69–4.67 (m, 2H, CH2@CH–
CH2OCO), 4.30–4.12 (m, 2H, CH2@CH–CH2O), 4.10
(dd, 1H, J = 1.5, 3.6 Hz, H-2), 4.010–3.33 (m, 4H, H-
3, H-4, H-6), 3.30 (m, 1H, H-5), 1.52, 1.41 (2s, 6H,
Me2C). Anal. Calcd for C16H23N3O7: C, 52.03; H,
6.28; N, 11.38. Found: C, 52.29; H, 6.36; N, 11.51.
25
1
2.50 g (95%), white solid. ½aꢁD +3.9 (c 1.0, CHCl3); H
NMR (CDCl3, 300 MHz): d 7.39–7.32 (m, 5H, Ar-H),
5.92–5.86 (m, 1H, CH2@CH–CH2OCO), 5.65 (d, 1H,
J = 8.2 Hz, H-1), 5.40–5.28 (m, 2H, CH2@CH–CH2O-
CO), 4.86–4.66 (m, 5H, H-2, PhCH2, CH2@CH–CH2O-
CO), 3.95 (dd, 1H, J = 5.4, 10.9 Hz, H-6a), 4.07–3.65
(m, 3H, H-3, H-4, H-6b), 3.44 (m, 1H, H-5), 1.47, 1.44

J. Zhang et al. / Carbohydrate Research 342 (2007) 2810–2817
2815
1.12. 2-Azido-3-O-benzyl-2-deoxy-1-O-ethoxycarbonyl-
4,6-O-isopropylidene-b-D-mannopyranose (3d)
Bz-H), 6.26 (d, 1H, J = 1.6 Hz, H-1), 5.63 (dd, 1H,
J = 3.9, 10.1 Hz, H-3), 4.46 (dd, 1H, J = 1.6, 3.9 Hz,
H-2), 4.33 (dd, 1H, J = 10.1, 10.1 Hz, H-4), 4.04–3.82
(m, 3H, H-5, H-6), 1.56, 1.39 (2s, 6H, Me2C). Anal.
Calcd for C18H19Cl3N4O6: C, 43.79; H, 3.88; N, 11.35.
Found: C, 43.53; H, 3.67; N, 11.62.
25
860 mg (84%), white solid. ½aꢁD ꢀ17.0 (c 2.5, CHCl3); 1H
NMR (CDCl3, 300 MHz): d 7.39–7.28 (m, 5H, Ar-H),
5.52 (d, 1H, J = 1.6 Hz, H-1), 4.88 (d, 1H, J = 12.3,
PhCH2), 4.71 (d, 1H, J = 12.3, PhCH2), 4.23 (m, 2H,
CH3CH2OCO), 4.06 (d, 1H, J = 9.5, H-4), 3.98 (dd,
1H, J = 1.6, 3.4 Hz, H-2), 3.94–3.77 (m, 2H, H-6),
3.66 (dd, 1H, J = 3.4, 9.5 Hz, H-3), 3.26 (m, 1H, H-5),
1.51, 1.41 (2s, 6H, Me2C), 1.30 (t, 3H, J = 7.2 Hz,
CH3CH2OCO). Anal. Calcd for C19H25N3O7: C,
56.01; H, 6.18; N, 10.31. Found: C, 56.05; H, 6.46; N,
10.19.
1.15. 4-Methoxylphenyl 3-O-allyloxycarbonyl-4-O-benzo-
yl-a-L-rhamnopyranoside (7)
Compound 6 (3.74 g, 10 mmol) was dissolved in dry
CH2Cl2 (40 mL) containing pyridine (8.1 mL,
100 mmol), then under N2 atmosphere, allyl chlorofor-
mate (1.2 mL, 11 mmol) in anhyd CH2Cl2 (10 mL) was
added dropwise to the solution over 30 min at 0 ꢁC.
The reaction mixture was slowly raised to room temper-
ature and stirred for 2 h, at the end of which time TLC
(3:1 petroleum ether–EtOAc) indicated that the reaction
was complete. The reaction mixture was diluted with
CH2Cl2 (100 mL), washed with water, 1 M HCl, and
dried (Na2SO4). The solution was concentrated, and
purification of the residue by column chromatography
on silica gel (3:1 petroleum ether–EtOAc) gave com-
1.13. 1-O-Allyloxycarbonyl-2-azido-3-O-benzyl-2-deoxy-
4,6-O-isopropylidene-b-D-mannopyranose (3e)
25
840 mg (80%), white solid. ½aꢁD +10.2 (c 1.0, CHCl3); 1H
NMR (CDCl3, 300 MHz): d 7.38–7.28 (m, 5H, Ar-H),
5.98–5.87 (m, 1H, CH2@CH–CH2OCO), 5.53 (d, 1H,
J = 1.5 Hz, H-1), 5.41–5.21 (m, 2H, CH2@CH–CH2O-
CO), 4.89 (d, 1H, J = 12.2 Hz, PhCH2), 4.73 (d, 1H,
J = 12.2 Hz, PhCH2), 4.70–4.65 (m, 2H, CH2@CH–
CH2OCO), 4.06 (dd, 1H, J = 9.5, 9.5 Hz, H-4), 3.98
(dd, 1H, J = 9.5 Hz, H-4), 3.95 (dd, 1H, J = 1.5,
3.6 Hz, H-2), 3.94–3.79 (m, 2H, H-6), 3.67 (dd, 1H,
J = 3.6, 9.5 Hz, H-3), 3.26 (m, 1H, H-5), 1.55, 1.51 (2s,
6H, Me2C). Anal. Calcd for C20H25N3O7: C, 57.27; H,
6.01; N, 10.02. Found: C, 57.50; H, 5.88; N, 9.89.
25
pound 7 (4.21 g, 92%) as a syrup; ½aꢁD ꢀ50.3 (c 1.1,
1
CHCl3); H NMR (CDCl3, 300 MHz): d 8.05–7.41 (m,
5H, Bz-H), 7.07–6.83 (m, 4H, Ar-H), 5.76–5.67 (m,
1H, CH2@CH–CH2OCO), 5.54–5.47 (m, 3H, H-1, H-
3, H-4), 5.21–5.04 (m, 2H, CH2@CH–CH2OCO), 4.51–
4.48 (m, 2H, CH2@CH–CH2OCO), 4.38 (dd, 1H,
J = 0.5, 2.7 Hz, H-2), 4.13 (m, 1H, H-5), 3.77 (s, 3H,
CH3O), 1.25 (d, 3H, J = 6.3 Hz, H-6). Anal. Calcd
for C24H26O9: C, 62.88; H, 5.72. Found: C, 63.03; H,
5.66.
1.14. 2-Azido-3-O-benzoyl-2-deoxy-4,6-O-isopropylidene-
a-D-mannopyranosyl trichloroacetimidate (5)
A
solution of the allyloxycarbonate 3b (600 mg,
1.16. 2-Azido-3,4,6-tri-O-benzoyl-2-deoxy-a,b-D-gluco-
pyranosyl trichloroacetimidate (11)
1.4 mmol) and Et3N (0.39 mL, 2.77 mmol) in THF
(10 mL) was mixed with PPh3 (110 mg 0.42 mmol) and
Pd[P(C6H5)3]4 (80 mg, 0.07 mmol), and the mixture
was stirred at 25 ꢁC until TLC (6:1 petroleum ether–
EtOAc) indicated the completion of the reaction. The
reaction mixture was concentrated under diminished
pressure and the residue was purified by flash chroma-
tography on a silica gel column (7:1 petroleum ether–
EtOAc) to give the deallyloxycarbonation product as a
white solid. This solid was dried under high vacuum
for 4 h and then was dissolved in CH2Cl2 (10 mL). Un-
der N2 atmosphere, CCl3CN (0.5 mL, 5 mmol) and
DBU (70 lL, 0.5 mmol) were added, the mixture was
stirred for 2 h, at which time TLC (6:1 petroleum
ether–EtOAc) indicated that the reaction was complete.
The mixture was concentrated under diminished pres-
sure to give a residue that was purified on a silica gel col-
umn with 8:1 petroleum ether–EtOAc as the eluent to
give the desired compound (500 mg, 73%) as a foamy so-
To a solution of 2-azido-2-deoxy-a,b-D-glucopyranose 8
(6.20 g, 30 mmol) in pyridine (100 mL) was added ben-
zoyl chloride (21 mL, 180 mmol) at ꢀ5 ꢁC. The reaction
mixture was slowly warmed to room temperature and
stirred for 12 h, at which time TLC (4:1 petroleum
ether–EtOAc) indicated that the reaction was complete.
Water (300 mL) was added to the reaction mixture, and
stirring was continued for 30 min. The aq solution was
extracted with CH2Cl2 (3 · 100 mL), the combined ex-
tracts were washed with 1 M HCl and satd aq NaHCO3,
dried (Na2SO4), and concentrated to give 9 (18.1 g, 97%)
as a white solid. Compound 9 (15.54 g, 25.0 mmol) was
dissolved in a 2 M solution of ammonia–MeOH
(200 mL) and stirred for 4 h, at which time TLC (3:1
petroleum ether–EtOAc) indicated that the reaction
was complete. The solution was concentrated, and puri-
fication of the residue by flash chromatography on a sil-
ica gel column (3:1 petroleum ether–EtOAc) gave
compound 10 (10.5 g, 81%) as a syrup. A mixture of
25
lid: ½aꢁD +100.0 (c 1.0, CHCl3); 1H NMR (CDCl3,
300 MHz): d 8.7 (s, 1H, CNHCCl3), 8.11–7.45 (m, 5H,

2816
J. Zhang et al. / Carbohydrate Research 342 (2007) 2810–2817
10 (10.3 g, 20 mmol), trichloroacetonitrile (8.0 mL,
80 mmol), and 1,8-diazabicyclo[5.4.0]undecene (DBU)
(0.50 mL, 4.04 mmol) in dry CH2Cl2 (50 mL) was stirred
under N2 atmosphere for 5 h and then concentrated in
vacuo. The residue was purified by flash chromatogra-
phy (4:1 petroleum ether–EtOAc) to give 11 (10.5 g,
79%) as a foamy solid; ½aꢁD +31.3 (c 1.0, CHCl3); H
NMR (CDCl3, 300 MHz): d 8.7 (2s, 1H, a,b-CNHCCl3),
8.00–7.31 (m, 15H, Bz-H), 6.63 (d, 0.17H, J = 3.6 Hz, a-
H-1), 6.11 (dd, 0.17H, J = 9.7, 9.7 Hz, a-H-3), 5.96 (d,
0.83 H, J = 8.3, b-H-1), 5.69–5.59 (m, 1.83 H, b-H-3,
a, b-H-4), 4.62–4.45 (m, 2H), 4.23–4.06 (m, 2 H). Anal.
Calcd for C29H23Cl3N4O8: C, 52.62; H, 3.50; N, 8.46.
Found: C, 52.58; H, 3.71; N, 8.60.
20H, Bz-H), 7.06–6.84 (m, 4H, Ar-H), 6.08 (dd, 1H,
J = 9.4, 10.6 Hz), 5.69 (dd, 1H, J = 10.2, 10.2 Hz),
5.59 (d, 1H, J = 1.0 Hz, H-1), 5.32 (d, 1H, J = 3.8 Hz,
H-10), 5.28 (dd, 1H, J = 9.7 Hz), 4.88 (m, 1H), 4.68–
4.30 (m, 4H), 4.16 (m, 1H, H-5), 3.78 (s, 3H, CH3O),
3.55 (dd, 1H, J = 3.7, 10.7 Hz), 1.34 (d, 3H,
J = 6.2 Hz, H-6); 13C NMR d 167.1, 166.1, 165.5,
165.4, 155.2, 150.3, 133.4, 133.4, 133.3, 133.0, 129.9,
129.8, 129.8, 129.7, 129.5, 129.5, 129.0, 128.7, 128.6,
128.5, 128.4, 128.4, 128.3, 97.9, 96.2, 78.1, 75.6, 70.3,
69.6, 69.3, 68.8, 67.2, 62.6, 61.4, 55.6, 29.3, 17.5. Anal.
Calcd for C47H43N3O14: C, 64.60; H, 4.96; N, 4.81.
Found: C, 64.44; H, 5.08; N, 5.11.
25
1
1.19. 4-Methoxylphenyl 2-azido-3-O-benzoyl-2-deoxy-a-
D-mannopyranosyl-(1!3)-[2-azido-3,4,6-tri-O-benzoyl-2-
deoxy-a-D-glucopyranosyl-(1!2)-]4-O-benzoyl-a-L-
rhamnopyranoside (15)
1.17. 4-Methoxylphenyl 2-azido-3,4,6-tri-O-benzoyl-2-
deoxy-a-D-glucopyranosyl-(1!2)-3-O-allyloxycarbonyl-
4-O-benzoyl-a-L-rhamnopyranoside (12)
Compounds 7 (275 mg, 0.60 mmol) and 11 (437 mg,
0.66 mmol) were dried together under high vacuum for
4 h, then dissolved in anhyd CH2Cl2 (10 mL). TMSOTf
(7.0 lL, 0.04 mmol) was added at 25 ꢁC under a N2
atmosphere. The reaction mixture was stirred for 2 h,
neutralized with Et3N, concentrated to dryness under
diminished pressure, and the residue was purified by
flash chromatography (4:1 petroleum ether–EtOAc) to
To a cooled solution (0 ꢁC) of 13 (350 mg, 0.4 mmol)
and
2-azido-3-O-benzoyl-2-deoxy-4,6-O-isopropylid-
ene-a-D-mannopyranosyl
trichloroacetimidate
(5)
(237 mg, 4.8 mmol) in anhyd CH2Cl2 (30 mL) was
added TMSOTf (7.2 lL, 0.04 mmol). The mixture was
stirred at this temperature for 2 h, then MeOH
(30 mL) and CH3COCl (0.1 mL) were subsequently
added to the reaction mixture. The mixture was stirred
at room temperature for 6 h, and then concentrated.
The residue was purified by silica gel column chroma-
tography to give 15 (340 mg, 73%) as a foamy solid;
25
give 12 (380 mg, 66%) as a syrup; ½aꢁD ꢀ30.7 (c 0.9,
1
CHCl3); H NMR (CDCl3, 300 MHz): d 8.08–7.36 (m,
20H, Bz-H), 7.01–6.84 (m, 4H, Ar-H), 6.04 (dd, 1H,
J = 9.4, 10.7 Hz), 5.77–5.59 (m, 4H), 5.55 (d, 1H,
J = 1.3 Hz, H-1), 5.21 (d, 1H, J = 3.8 Hz, H-10), 5.15–
4.92 (m, 2H, CH2@CH–CH2OCO), 4.80–4.76 (m, 1H,
CH2@CH–CHHOCO), 4.63 (dd, 1H, J = 2.7, 12.7 Hz),
4.48–4.41 (m, 3H), 4.31 (dd, 1H, J = 3.7, 12.6 Hz),
4.15 (m, 1H, H-5), 3.78 (s, 3H, CH3O), 3.49 (dd, 1H,
J = 3.8, 10.6 Hz), 1.34 (d, 3H, J = 6.2 Hz, H-6). Anal.
Calcd for C51H47N3O16: C, 63.94; H, 4.95; N, 4.39.
Found: C, 63.83; H, 5.10; N, 4.54.
25
1
½aꢁD +19 (c 1.2, CHCl3); H NMR (CDCl3, 300 MHz):
d 813–7.15 (m, 25H, Bz-H), 7.07–6.84 (m, 4H, Ar-H),
6.11 (dd, 1H, J = 9.8 Hz), 5.71 (dd, 1H, J = 9.9,
9.9 Hz), 5.70 (d, 1H, J = 1.9 Hz, H-1), 5.63 (dd, 1H,
J = 9.5 Hz), 5.46 (dd, 1H, J = 3.6, 10.0 Hz), 5.43 (d,
1H, J = 2.5 Hz, H-1), 5.15 (d, 1H, J = 1.5 Hz, H-1),
5.01 (dd, 1H, J = 1.5, 10.8 Hz), 4.72 (m, 1H), 4.57–
4.44 (m, 3H), 4.30 (d, 1H, J = 1.80, 3.50 Hz, H-2),
4.16–4.02 (m, 2H), 3.89 (m, 1H), 3.71 (m, 1H), 1.33 (d,
3H, J = 6.3 Hz, H-6); 13C NMR (characteristic signals
given) d 166.4, 166.2, 165.9, 165.8, 165.5, 155.4, 150.1,
98.3, 97.4, 95.8, 17.6. Anal. Calcd for C60H56N6O19:
C, 61.85; H, 4.84, N, 7.21. Found: C, 61.77; H, 4.69;
N, 7.53.
1.18. 4-Methoxylphenyl 2-azido-3,4,6-tri-O-benzoyl-2-
deoxy-a-D-glucopyranosyl-(1!2)-4-O-benzoyl-a-L-
rhamnopyranoside (13)
A solution of compound 12 (770 mg, 0.8 mmol) and
Et3N (0.22 mL, 1.6 mmol) in THF (15 mL) was mixed
with PPh3 (63 mg, 0.24 mmol) and Pd[P(C6H5)3]4
(46 mg, 0.04 mmol) and the mixture was stirred at
25 ꢁC until TLC (2:1 petroleum ether–EtOAc) indicated
the completion of the reaction. The reaction mixture was
concentrated under diminished pressure, and the residue
was purified by flash chromatography on a silica gel col-
umn (3:1 petroleum ether–EtOAc) to give compound 13
1.20. 4-Methoxyphenyl 4,6-di-O-acetyl-2-azido-3-O-benz-
oyl-2-deoxy-a-D-mannopyranosyl-(1!3)-[2-azido-3,4,6-
tri-O-benzoyl-2-deoxy-a-D-glucopyranosyl-(1!2)-]4-O-
benzoyl-a-L-rhamnopyranoside (16)
To a solution of 15 (312 mg, 0.250 mmol) in pyridine
(12 mL) was added Ac2O (8 mL, 8 mmol). The reaction
mixture was stirred at rt for 12 h, at which time TLC
(2:1 petroleum ether–EtOAc) indicated that the reaction
was complete. The reaction mixture was concentrated,
25
(510 mg, 73%) as a white solid; ½aꢁD ꢀ11.0 (c 1.5,
1
CHCl3); H NMR (CDCl3, 300 MHz): d 8.07–7.36 (m,

J. Zhang et al. / Carbohydrate Research 342 (2007) 2810–2817
2817
and then the residue was purified by silica gel column
Acknowledgments
chromatography (2:1 petroleum ether–EtOAc) to give
25
compound 16 (283 mg, 88%) as a foamy solid. ½aꢁD
This work was supported by the Research Foundation
of China Agricultural University, Project Number:
2006010 and The National Basic Research Program of
China (2003CB114407).
+16 (c 0.3, CHCl3); 1H NMR (CDCl3, 300 MHz): d
8.13–7.09 (m, 25 H, Bz-H), 7.09–6.85 (m, 4H, Ar-H),
6.05 (dd, 1H, J = 9.9, 9.9 Hz), 5.75 (dd, 1H, J =
10.0 Hz), 5.68 (d, 1H, J = 2.0 Hz, H-1), 5.60 (dd, 1H,
J = 9.8 Hz), 5.51–5.39 (m, 2H), 5.25 (d, 1H,
J = 3.4 Hz, H-1), 5.15 (d, 1H, J = 1.20 Hz, H-1), 4.90
(dd, 1H, J = 2.0, 10.0 Hz), 4.72 (m, 1H), 4.55–4.46 (m,
3H), 4.39 (d, 1H, J = 1.20, 3.40 Hz, H-2), 4.22–4.10
(m, 1H), 4.00–3.90 (m, 2H), 3.79 (s, 3H, OMe), 3.70
(m, 1H), 2.06 (s, 3H, OAc), 1.58 (s, 3H, OAc), 1.27 (d,
3H, J = 6.4 Hz, H-6); 13C NMR (characteristic signals
given) d 170.6, 169.4, 165.7, 165.4, 165.3, 165.2, 165.1,
117.7, 114.8, 99.4, 96.9, 95.9, 20.7, 20.3, 17.5. Anal.
Calcd for C64H60N6O21: C, 61.53; H, 4.84, N, 6.73.
Found: C, 61.70; H, 4.61; N,6.49.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.carres.
2007.09.001.
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25
56%) as a foamy solid. ½aꢁD +33 (c 1.0, H2O); 1H
NMR (CDCl3, 300 MHz) (characteristic signals given):
d 6.99–6.81 (m, 4H, Ar-H), 5.36 (d, 1H, J = 2.3 Hz,
H-1), 5.18 (d, 1H, J = 3.5 Hz, H-1), 4.98 (s, 1H, H-1),
3.37 (s, 3H, OMe), 2.02 (s, 3H, OAc), 1.96 (s, 3H,
OAc), 1.28 (d, 3H, J = 6.2 Hz, H-6); 13C NMR (charac-
teristic signals given) d 174.2, 173.7, 156.7, 151.9, 119.0,
119.0, 115.7, 115.7, 98.4, 97.6, 96.5, 22.8, 22.7, 18.5;
MALDI-TOF MS Calcd for C29H44N2O16: 676.27
[M]. Found: 699.43 [M+Na].
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