Facile synthesis of a comb-like mannohexaose: A trimer of the disaccharide repeating unit of the cell-wall mannans of Aphanoascus mephitatus and related species

Article abstract of DOI:10.1016/S0008-6215(01)00059-3

An efficient method for the preparation of a comb-like mannohexaose having α-(1→6) and α-(1→2) linkages has been described using 6-O-acetyl-2-O-benzoyl-3,4-di-O-benzyl-α-D-mannopyranosyl trichloroacetimidate as the key glycosyl donor in an 'inverse Schmidt' procedure.

Full text of DOI:10.1016/S0008-6215(01)00059-3

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Carbohydrate Research 331 (2001) 431–437
Facile synthesis of a comb-like mannohexaose: a trimer
of the disaccharide repeating unit of the cell-wall
mannans of Aphanoascus mephitatus and related species
Linsen Heng, Jun Ning, Fanzuo Kong*
Research Center for Eco-En6ironmental Sciences, Chinese Academy of Sciences, PO Box 2871,
Beijing 100085, People’s Republic of China
Received 27 November 2000; accepted 16 February 2001
Abstract
An efficient method for the preparation of a comb-like mannohexaose having a-(1“6) and a-(1“2) linkages has
been described using 6-O-acetyl-2-O-benzoyl-3,4-di-O-benzyl-a-D-mannopyranosyl trichloroacetimidate as the key
glycosyl donor in an ‘inverse Schmidt’ procedure. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Comb-like oligosaccharide; Synthesis; Mannose
1. Introduction
phosphatase to the cell-wall,1 and they may
participate in cell–cell recognition as well as
in the adhesion of the microorganism to host
cells.
Mannans are constituents of many fungal
cell-walls. They are considered to have impor-
tant physiological functions. Besides physical
protection of the cell-wall, they may serve to
anchor such enzymes as invertase and acid
In 1993 Jime´nez-Barbero and co-workers2
investigated the structures of cell-wall man-
nans isolated from Aphanoascus mephitatus,
Aphanoascus ful6escens, Aphanoascus 6erruco-
sus, and Aphanoascus reticulisporus, and found
that they invariably consist of a relatively
simple comb-like structure of a disaccharide
repeating block {“6}-[a-Man p-(1“2)]-a-
Man p-(1“). It would be helpful to synthe-
size its fragments for the elucidation of the
biological functions of the cell-wall polysac-
charides. In a previous communication,3 we
described an efficient method to construct a
mannooligosaccharide having a-(1“6) and a-
(1“2) linkages. In this paper, as a part of our
continuing effort to develop new synthetic
approaches directed toward oligosaccharide
fragments of fungal cell-wall mannans, we
report the synthesis of a comb-like haxasac-
Scheme 1. Reagents and conditions: (a) 6:1:0.05 (v/v) AcOH–
Ac2O–H2SO4, rt, 16 h, 90%; (b) anhyd Et2O satd with dry
NH3, rt, 24 h, 97%; (c) CCl3CN (1.2 equiv), DBU (0.2 equiv),
0 °C, 2 h, 92%.
* Corresponding author. Tel.: +86-10-62936613; fax: +
86-10-62923563.
E-mail address: fzkong@mail.rcees.ac.cn (F. Kong).
0008-6215/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(01)00059-3

432
L. Heng et al. / Carbohydrate Research 331 (2001) 431–437
lated in high yield at the anomeric position
with benzylamine in THF to the correspond-
ing 6-O-acetyl-2,3,4-tri-O-benzoyl- -manno-
D
pyranose (8). Subsequent reaction of 8 with
CCl3CN–DBU in CH2Cl2 afforded another
glycosyl donor 9.
With the synthons 5 and 9 in hand, con-
struction of the target compound was readily
carried out. As shown in Scheme 3, allyl 6-O-
Scheme 2. Reagents and conditions: (a) (i) TrCl (1.2 equiv),
pyridine, 50 °C, 32 h; (ii) BzCl (4.4 equiv), 40 °C, 24 h; (iii)
1:1:0.6:0.175 (v/v) CH2Cl2–HOAc–Ac2O–H2SO4, rt, 20 h,
71.3%. (b) THF, BnNH2 (4.2 equiv), rt, 24 h, 86.2%. (c)
CCl3CN (2.8 equiv), DBU (0.22 equiv), 0 °C, 2 h, 88.1%.
acetyl - 2 - O - benzoyl - 3,4 - di - O - benzyl - a - -
D
mannopyranoside (10) was prepared by the
Helferich reaction8 using 3 as the glycosyl
donor and allyl alcohol as the acceptor. Selec-
tive removal of the acetyl group of 10 using a
0.5% methanolic HCl quantitatively gave the
glycosyl acceptor 11. The disaccharide 12 was
prepared using the ‘inverse Schmidt’ strategy.9
Thus the glycosyl acceptor 11 and the catalyst
TMSOTf were mixed first in dry CH2Cl2, and
after stirring for 15 min, the glycosyl donor 5
was added dropwise within 30 min. Selective
removal of the acetyl group of 12 gave the
glycosyl acceptor 13, ‘inverse Schmidt’ cou-
pling of which with 2-O-acetyl-3,4,6-tri-O-
charide 1, which is a trimer of the disaccharide
repeating unit of mannans isolated from A.
mephitatus and related species.
benzyl-a- -mannopyranosyl trichloro-acetimi-
D
date10 afforded the trisaccharide 14 in 85%
1
yield. The H NMR spectrum of 14 showed
one acetyl signal (l 2.14), one allyl methine
signal (5.87) and three downfield H-2 signals
(l 5.78, 5.67, and 5.52), characteristic of the
structure of the trisaccharide 14. Removal of
the acetyl and benzoyl groups of 14 with NH3
in MeOH quantitatively gave the glycosyl ac-
ceptor 15 having free 2-OH, 2%-OH, and 2%%-
OH groups. The fully protected comb-like
hexasaccharide 16 was smoothly obtained by
coupling of 15 with 6-O-acetyl-2,3,4-tri-O-
2. Results and discussion
First we synthesized the synthons 5 and 9.
Thus, methyl 2-O-benzoyl-3,4,6-tri-O-benzyl-
a-
65% overall yield according to the literature4
using -mannose as the starting material. Se-
lective acetolysis of 2 using 6:1:0.05 HOAc–
D
-mannopyranoside (2) was prepared in
D
5
Ac2O–H2SO4
gave the corresponding
benzoyl-a-
D
-mannopyranosyl
trichloroacet-
diacetate 3 (Scheme 1). Compound 4 was ob-
tained in nearly quantitative yield by
amonolysis of 3 in anhydrous ether saturated
with dry NH3 according to Lemieux and
Howard.6 Subsequent reaction of 4 with
CCl3CN–DBU in CH2Cl2 afforded the key
glycosyl donor 5. Tritylation of the mannose
(6),7 followed by benzoylation in one pot,
1
13
imidate (9). The H and C NMR data of 16
contained structural information, i.e., three
acetyl signals (l 1.91, 1.93, and 1.98) and one
allyl methine signal (l 5.93), and six anomeric
carbon signals (l 99.6, 99.4, 99.3, 99.2. 99.1,
and 98.3). The use of 6-O-acetyl-2,3,4-tri-O-
benzoyl-a-
D
-mannopyranosyl
trichloroacet-
imidate (9) as the glycosyl donor afforded
three hydroxy groups at C-6 for potential
further transformation. Deprotection of 16
gave the title mannohexaose 1.
gave the 1,2,3,4-tetra-O-benzoyl-6-O-trityl- -
D
mannopyranose (Scheme 2), selective acetoly-
sis of which using 1:1:0.6:0.175 CH2Cl2–
AcOH–Ac2O–H2SO4 afforded the corre-
sponding 1,6-diacetate 7 in 85% yield (three
steps). The diacetate 7 was selectively deacety-
In summary, we have successfully developed
a highly efficient strategy for the preparation

L. Heng et al. / Carbohydrate Research 331 (2001) 431–437
433
of a comb-like mannohexaose containing a-
(1“6) and a-(1“2) linkages. It is anticipated
that octa- and higher comb-like oligosaccha-
rides can be synthesized by this strategy.
the eluent. Solutions were concentrated at B
60 °C under diminished pressure.
1,6-Di-O-acetyl-2-O-benzoyl-3,4-di-O-ben-
zyl-h- -mannopyranose (3).—A solution of
D
compound 24 (6 g, 10.55 mmol) in AcOH (36
mL) and Ac2O (6 mL) cooled to 0 °C in an ice
bath, and H2SO4 (0.3 mL) was added drop-
wise over 10 min. The ice bath was removed,
and the reaction was allowed to continue for
16 h at rt, then poured into ice water (100
mL). Stirring was continued for an additional
15 min, at the end of which time it was
extracted with CHCl3 (3×30 mL). The com-
bined CHCl3 extracts were washed with 10%
aq NaHCO3 (3×60 mL), dried over Na2SO4,
and concentrated to a syrup. The crude
product was then subjected to column chro-
matography with 3:1 petroleum ether–EtOAc
as the eluent. Compound 3 was obtained as
crystals (5.21 g, 90%,); mp 102–104 °C; [h]D
3. Experimental
General methods.—Optical rotations were
determined at 25 °C with a Perkin–Elmer
model 241-MC automatic polarimeter. Melt-
ing points were determined with a ‘Mel-Temp’
1
apparatus. H NMR spectra were recorded in
CDCl3 with Bruker ARX 400 spectrometers.
Chemical shifts are given in parts per million
(ppm) downfield from internal Me4Si. Mass
spectra were recorded with a JMS-D300S
mass spectrometer using a sample probe.
Thin-layer chromatography (TLC) was per-
formed on Silica Gel HF254 (E. Merck) with
detection by charring with 30% (v/v) H2SO4 in
MeOH or in some cases by UV detection.
Column chromatography utilized silica gel
with EtOAc–petroleum ether (60–90 °C) as
1
+3.2° (c 1.4, CHCl3); H NMR (CDCl3, 400
MHz): l 8.20–7.20 (m, 15 H, 3 PhH), 6.20 (d,
1 H, J1,2 2.1 Hz, H-1), 5.62 (dd, 1 H, J1,2 2.1,
J2,3 2.9 Hz, H-2), 4.89, 4.60 (ABq, 2 H, J 10.7
Scheme 3. Reagents and conditions: (a) allyl alcohol (1.9 equiv), TMSOTf (0.24 equiv), CH2Cl2, rt, 1 h, 88%. (b) MeOH–0.5%
HCl, rt, 14–18 h, 95.6–98.1%. (c) 5 (1.4 equiv), CH2Cl2, TMSOTf (0.1 equiv), rt, 3 h, 86.5%. (d) 2-O-Acetyl-3,4,6-tri-O-benzyl-a-
D
-mannopyranosyl trichloroacetimidate (1.5 equiv), CH2Cl2, TMSOTf (0.1 equiv), rt, 3 h, 85.7%. (e) MeOH satd with dry NH3,
rt, 72 h, 97%. (f) 9 (6.0 equiv), CH2Cl2, TMSOTf (0.2 equiv), rt, 3 h, 75.8%. (g) (i) PdCl2, MeOH, rt, 8 h; (ii) MeOH satd with
dry NH3; (iii) H2, Pd(OH)2/C 20%, MeOH, rt, 24 h, 61.8%.

434
L. Heng et al. / Carbohydrate Research 331 (2001) 431–437
for C31H30Cl3NO8: C, 57.20; H, 4.65. Found:
C, 57.42; H, 4.60.
Hz, PhCH2), 4.83, 4.61 (ABq, 2 H, J 11.9 Hz,
PhCH2), 4.34 (m, 2 H, H-6, 6%), 4.11 (m, 1 H,
H-5), 3.96 (m, 2 H, H-3,4), 2.10, 2.06 (2 s, 6
H, 2 COCH3). Anal. Calcd for C31H32O9: C,
67.87; H, 5.88. Found: C, 67.95; H, 5.79.
6-O-Acetyl-2-O-benzoyl-3,4-di-O-benzyl-h-
1,6-Di-O-acetyl-2,3,4-tri-O-benzoyl-h- -
D
mannopyranose (7).—A solution of mannose 6
(15 g, 83.3 mmol) and chlorotriphenylmethane
(28 g, 100.5 mmol) in pyridine (60 mL) was
stirred at 50 °C for 32 h until TLC (4:1
EtOAc–MeOH) indicated that the reaction
was complete. The reaction mixture was
cooled to 0 °C, and BzCl (46.5 mL, 370 mmol)
was then added over 30 min keeping the reac-
tion temperature under 40 °C. After 24 h,
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), and the extract was washed
sequentially with HCl (1 N) and satd aq
NaHCO3 solution, dried (Na2SO4), and con-
centrated. Without further separation, the
residue was redissolved with CH2Cl2 (50 mL),
Ac2O (50 mL) and AcOH (30 mL), and cooled
to 10 °C in an ice bath. Concd H2SO4 (8.8
mL) was added dropwise over 20 min, then
held for 20 h at rt. The reaction solution was
poured into ice water (400 mL), stirred for an
additional 15 min, and extracted with CHCl3
(3×100 mL). Combined extracts were washed
with 10% aq NaHCO3 (3×60 mL), dried, and
concentrated to give a syrup. Column chro-
matography with 4:1 petroleum ether–EtOAc
as the eluent afforded compound 7 as a syrup
D
-mannopyranose (4).—A solution of com-
pound 3 (3 g, 5.47 mmol) in anhyd ether (100
mL) saturated with dry NH3 was stirred for 24
h at rt. TLC (2:1 petroleum ether–EtOAc)
indicated that the reaction was complete. The
solution was concentrated, and purification of
the crude product by flash-column chromatog-
raphy on silica gel (2:1 petroleum ether–
EtOAc) gave compound 4 as crystals (2.69 g,
97%,); mp 108–110 °C; [h]D +6.9° (c 2.1,
CHCl3); 1H NMR (CDCl3, 400 MHz): l
8.07–7.23 (m, 15 H, 3 PhH), 5.60 (dd, 1 H,
J1,2 1.8, J3,2 2.8 Hz, H-2), 5.31 (d, 1 H, J2,1 1.8
Hz, H-1), 4.89, 4.59 (ABq, 2 H, J 10.9 Hz,
PhCH2), 4.79, 4.58 (ABq, 2 H, J 11.3 Hz,
PhCH2), 4.38 (dd, 1 H, J6b,6a 11.9, J5,6a 2.2 Hz,
H-6a), 4.27 (dd, 1 H, J6a,6b 11.9, J5,6b 4.4 Hz,
H-6b), 4.18 (dd, 1 H, J2,3 2.8, J4,3 9.1 Hz, H-3),
4.12 (m, 1 H, J6a,5 2.2, J6b,5 4.4, J4,5 9.1 Hz,
H-5), 3.90 (t, 1 H, J3,4 =J5,4=9.1 Hz, H-4),
2.04 (s, 3 H, COCH3). Anal. Calcd for
C29H30O8: C, 68.76; H, 5.97. Found: C, 68.61;
H, 5.92.
6-O-Acetyl-2-O-benzoyl-3,4-di-O-benzyl-h-
-mannopyranosyl trichloroacetimidate (5).—
D
1
A mixture of 4 (4.5 g, 8.88 mmol), CCl3CN
(1.05 mL, 10.5 mmol), and 1,8-diazabicy-
clo[5,4,0]undecene (DBU) (0.27 mL, 1.8
mmol) in dry CH2Cl2 (30 mL) was stirred
under N2 for 2 h at 0 °C and then concen-
trated in vacuo. The residue was purified by
flash chromatography (3:1 petroleum ether–
EtOAc) to give 5 (5.32 g, 92%) as crystals; mp
(34.2 g, 71.3%); [h]D +9.5° (c 1.0, CHCl3); H
NMR (400 MHz, CDCl3): l 8.11–7.28 (m, 15
H, 3 PhH), 6.36 (d, 1 H, J1,2 2.0 Hz, H–1),
6.01 (t, 1 H, J3,4 =J4,5=10.2 Hz, H-4), 5.88
(dd, 1 H, J2,3 3.2, J3,4 10.2 Hz, H-3), 5.70 (dd,
1 H, J1,2 2.0, J2,3 3.2 Hz, H-2), 4.34 (m, 2 H,
H-5, 6a), 4.27 (dd, 1 H, J6a,6b 13.4, J5,6b 4.2
Hz, H-6b), 2.28, 2.08 (2 s, 6 H, 2COCH3).
Anal. Calcd for C31H28O11: C, 64.58; H, 4.89.
Found: C, 64.67; H, 4.94.
1
91–93 °C; [h]D +16.9° (c 2.6, CHCl3); H
NMR (CDCl3, 400 MHz): l 8.72 (s, 1 H,
OC(NH)CCl3), 8.10–7.10 (m, 15 H, 3 PhH),
6.36 (d, 1 H, J1,2 2.1 Hz, H-1), 5.73 (t, 1 H,
J1,2=J2,3=2.1 Hz, H-2), 4.90, 4.64 (ABq, 2
H, J 10.8 Hz, PhCH2), 4.82, 4.61 (ABq, 2 H,
J 11.3 Hz, PhCH2), 4.35 (dd, 1 H, J6,6% 11.9,
J5,6 1.7 Hz, H-6), 4.30 (dd, 1 H, J6,6% 11.9, J5,6%
3.4 Hz, H-6%), 4.17 (dd, 1 H, J2,3 2.1, J3,4 8.7
Hz, H-3), 4.1 (t, 1 H, J3,4=J4,5 =8.7 Hz,
H-4), 4.02 (m, 1 H, J5,6 1.7, J5,6% 3.4, J4,5 8.7
Hz, H-5), 2.03 (s, 3 H, COCH3). Anal. Calcd
6-O-Acetyl-2,3,4-tri-O-benzoyl-h- -manno-
D
pyranose (8).—A solution of compound 7 (5
g, 8.67 mmol) and benzylamine (4 mL, 36.6
mmol) in anhyd THF (30 mL) was stirred at
rt for 24 h until TLC (3:1 petroleum ether–
EtOAc) indicated that the reaction was com-
plete. The solution was concentrated, and the
crude product was purified by flash-column
chromatography on silica gel (3:1 petroleum
ether–EtOAc) to give compound 8 as a syrup

L. Heng et al. / Carbohydrate Research 331 (2001) 431–437
435
1
CH3). Anal. Calcd for C32H34O8: C, 70.31; H,
(4.0 g, 86.2%); [h]D +16.8° (c 1.0, CHCl3); H
NMR (400 MHz, CDCl3): l 8.11–7.27 (m, 15
H, 3 PhH), 5.98 (m, 2 H, H-3, 4), 5.71 (dd, 1
H, J1,2 1.6, J2,3 2.4 Hz, H-2), 5.53 (d, 1 H, J1,2
1.6 Hz, H-1), 4.55 (m, 1 H, H-5), 4.33 (m, 2
H, H-6a, 6b), 2.09 (s, 3 H,COCH3). Anal.
Calcd for C29H26O10: C, 65.16; H, 4.90.
Found: C, 65.36; H, 4.84.
6.27. Found: C, 70.24; H, 6.31.
Allyl 2 - O - benzoyl - 3,4 - di - O - benzyl - h - -
D
mannopyranoside (11).—A solution of 10 (1.6 g,
2.93 mmol) in MeOH (80 mL) containing
0.5% HCl was stirred at rt for 18 h, neutral-
ized with Et3N, and then evaporated to dry-
ness. The residue was partitioned between
water and CH2Cl2, and the organic layer was
dried and concentrated to a syrup. Purifica-
tion of the residue by flash chromatography
(2:1 petroleum ether–EtOAc) gave 11 as a
syrup (1.45 g, 98.1%); [h]D +9.2° (c 1.0,
CHCl3); 1H NMR (400 MHz, CDCl3): l
8.08–7.23 (m, 15 H, 3 PhH), 5.88 (m, 1 H,
CH2CHꢀCH2), 5.61 (dd, J1,2 1.8, J2,3 3.6 Hz,
6-O-Acetyl-2,3,4-tri-O-benzoyl-h- -manno-
D
pyranosyl trichloroacetimidate (9).—A mixture
of 8 (4.0 g, 7.48 mmol), CCl3CN (2.1 mL, 20.9
mmol), and 1,8-diazabicyclo[5,4,0]undecene
(DBU) (0.25 mL, 1.67 mmol) in dry CH2Cl2
(25 mL) was stirred under N2 for 2 h at 0 °C
and then concentrated in vacuo. The residue
was purified by flash chromatography (4:1
petroleum ether–EtOAc) to give 9 (4.47 g,
88.1%) as crystals; mp 88–91 °C; [h]D +20.3°
2
3
H-2), 5.28 (dd, 1 H, J 1.6, Jtrans 17.2 Hz,
2
3
CH2CHꢀCH2), 5.21 (dd, 1 H, J 1.6, Jcis 10.4
Hz, CH2CHꢀCH2), 4.97 (d, J1,2 1.8 Hz, H-1),
4.92, 4.65 (ABq, 2 H, J 10.8 Hz, PhCH2),
4.78, 4.58 (ABq, 2 H, J 11.2 Hz, PhCH2),
4.15–3.78 (m, 7 H, H-3, 4, 5, 6a, 6b,
CH2CHꢀCH2). Anal. Calcd for C30H32O7: C,
71.41; H, 6.39. Found: C, 71.04; H, 6.35.
Allyl 6-O-acetyl-2-O-benzoyl-3,4-di-O-ben-
1
(c 1.0, CHCl3); H NMR (400 MHz, CDCl3):
l 8.87 (s, 1 H, OC(NH)CCI3), 8.12–7.27 (m,
15 H, 3 PhH), 6.55 (d, 1 H, J1,2 2.0 Hz, H-1),
6.06 (t, 1 H, J3,4 =J4,5=10.0 Hz, H-4), 5.93
(dd, 1 H, J2,3 3.2, J3,4 10.0 Hz, H-3), 5.90 (dd,
1 H, J1,2 2.0, J2,3 3.2 Hz, H-2), 4.49 (m, 1 H,
H-5), 4.34 (m, 2 H, H-6a, 6b), 2.07 (s, 3 H,
COCH3). Anal. Calcd for C31H26Cl3NO10: C,
54.84; H, 3.86. Found: C, 54.72; H, 3.90.
Allyl 6-O-acetyl-2-O-benzoyl-3,4-di-O-ben-
zyl-h-
D
-mannopyranosyl-(1“6)-2-O-benzoyl-
-mannopyranoside (12).—
3,4-di-O-benzyl-h-
D
A solution of 11 (0.37 g, 0.73 mmol) and
trimethylsilyl trifluoromethanesulfonate (13
mL, 0.073 mmol) in dry CH2Cl2 (6 mL) was
zyl-h- -mannopyranoside (10).—A solution of
D
3 (2.5 g, 4.56 mmol) and allyl alcohol (0.6 mL,
,
stirred with dried molecular sieves (4 A, 0.4 g)
8.8 mmol) in dry CH2Cl2 (40 mL) was stirred
under N2 for 15 min, and then 5 (0.65 g, 1.0
mmol) in CH2Cl2 (4 mL) was added over 20
min at rt. After 3 h, the reaction mixture was
diluted with CH2Cl2 (30 mL) and washed with
satd aq NaHCO3 solution (5 mL). The or-
ganic layer was dried and concentrated in
vacuo. Purification of the residue by flash
chromatography (2:1 petroleum ether–
EtOAc) gave 12 as a syrup (0.63 g, 86.5%);
,
with dried molecular sieves (4 A, 1 g) under
N2 for 15 min, and then trimethylsilyl tri-
fluoromethanesulfonate (0.2 mL, 1.1 mmol)
was added dropwise. After 1 h, the reaction
mixture was diluted with CH2Cl2 (50 mL) and
washed with satd aq NaHCO3 solution (15
mL). The organic layer was dried and concen-
trated in vacuo. Purification of the residue by
flash chromatography (3:1 petroleum ether–
EtOAc) gave 10 as a syrup (2.19 g, 88%); [h]D
1
[h]D +19.3° (c 1.0, CHCl3); H NMR (400
MHz, CDCl3): l 8.11–7.22 (m, 30 H, 6 PhH),
5.88 (m, 1 H, CH2CHꢀCH2), 5.73 (dd, 1 H,
J1,2 1.6, J2,3 3.2 Hz, H-2), 5.67 (dd, 1 H, J1%,2%
1
+5.9° (c 1.0, CHCl3); H NMR (400 MHz,
CDCl3): l 8.09–7.24 (m, 15 H, 3 PhH), 5.88
(m, 1 H, CH2CHꢀCH2), 5.63 (dd, J1,2 2.0, J3,2
2
1.6, J2%,3% 3.2 Hz, H-2%), 5.28 (dd, 1 H, J 1.6,
2
3
3Jtrans 17.2 Hz, CH2CHꢀCH2), 5.21 (dd, 1 H,
3.0 Hz, H-2), 5.28 (dd, 1 H, J 1.6, Jtrans
=
2
3
2J 1.6, Jcis=10.4 Hz, CH2CHꢀCH2), 5.08 (d,
17.2 Hz, CH2CHꢀCH2), 5.21 (dd, 1 H, J 1.6,
3Jcis 10.4 Hz, CH2CHꢀCH2), 4.98 (d, J1,2 2.0
Hz, H-1), 4.88, 4.59 (ABq, 2 H, J 10.8 Hz,
PhCH2), 4.80, 4.58 (ABq, J 11.2 Hz, PhCH2),
4.36 (m, 2 H, H-6a, 6b), 4.20–3.90 (m, 5 H,
H-3, 4, 5, CH2CHꢀCH2), 2.07 (s, 3 H,CO-
1 H, J1,2 1.6 Hz, H-1), 4.97 (d, 1 H, J1%,2% 1.6
Hz, H-1%), 4.90–4.45 (m, 8 H, 4 PhCH2),
4.28–3.76 (m, 12 H), 1.99 (s, 3 H, COCH3).
Anal. Calcd for C59H60O14: C, 71.36; H, 6.09.
Found: C, 71.45; H, 6.11.

436
L. Heng et al. / Carbohydrate Research 331 (2001) 431–437
H-1), 4.98 (d, 1 H, J1%,2% 1.6 Hz, H-1%), 4.96 (d,
1 H, J1%%,2%% 1.6 Hz, H-1%%), 4.87–4.37 (m, 14 H,
7 PhCH2), 4.14–3.61 (m, 17 H), 2.14 (s, 3 H,
COCH3). Anal. Calcd for C86H88O19: C, 72.46;
H, 6.22. Found: C, 72.53; H, 6.17.
Allyl 2 - O - benzoyl - 3,4 - di - O - benzyl - h -
mannopyranosyl-(1“6)-2-O-benzoyl-3,4-di-
O-benzyl-h- -mannopyranoside (13).—A solu-
D
-
D
tion of 12 (0.55 g, 0.55 mmol) in MeOH (25
mL) containing 0.5% HCl was stirred at rt for
14 h. The mixture was carefully neutralized
with Et3N, and then evaporated to dryness.
The residue was partitioned between water
and CH2Cl2, then the organic layer was dried
and evaporated to a syrup. Purification of the
residue by flash chromatography (2:1
petroleum ether–EtOAc) gave 13 as a syrup
(0.50 g, 95.6%); [h]D +13.0° (c 1.5, CHCl3);
1H NMR (400 MHz, CDCl3): l 8.08–7.15 (m,
30 H, 6 PhH), 5.87 (m, 1 H, CH2CHꢀCH2),
5.72 (dd, 1 H, J1,2 1.6, J2,3 3.2 Hz, H-2), 5.66
(dd, 1 H, J1%,2% 1.6, J2%,3% 3.2 Hz, H-2%), 5.28 (dd,
1 H, 2J 1.6, 3Jtrans 17.2 Hz, CH2CHꢀCH2), 5.20
Allyl 3,4,6-tri-O-benzyl-h-
osyl-(1“6)-3,4-di-O-benzyl-h-
ranosyl-(1“6)-3,4-di-O-benzyl-h-
D
-mannopyran-
-mannopy-
-manno-
D
D
pyranoside (15).—A solution of 14 (0.45 g,
0.32 mmol) in MeOH (50 mL) saturated with
dry NH3 was stirred at rt for 72 h, until TLC
(1:1.5 petroleum ether–EtOAc) indicated that
the reaction was complete. The solution was
concentrated to afford compound 15 (0.36 g,
97%) as a syrup; [h]D+21.4° (c 1.0, CHCl3);
1H NMR (400 MHz, CDCl3): l 7.81–7.15 (m,
35 H, 7 PhH), 5.85 (m, 1 H, CH2CHꢀCH2),
3
5.23 (dd, 1 H, 2J 1.6, Jtrans 17.2 Hz,
2
3
2
3
(dd, 1 H, J 1.6, Jcis 10.4 Hz, CH2CHꢀCH2),
5.07 (d, 1 H, J1,2 1.6 Hz, H-1), 4.96 (d, 1 H,
J1%,2% 1.6 Hz, H-1%), 4.90–4.45 (m, 8 H, 4
PhCH2), 4.14–3.71 (m, 12 H). Anal. Calcd for
C57H58O13: C, 71.98; H, 6.15. Found: C, 71.87;
H, 6.18.
CH2CHꢀCH2), 5.12 (dd, 1 H, J 1.6, Jcis 10.4
Hz, CH2CHꢀCH2), 4.96 (1 H, J1,2 2.0 Hz,
H-1), 4.90 (d, 1 H, J1%,2% 2.0 Hz, H-1%), 4.85 (d,
1 H, J1%%,2%% 2.0 Hz, H-1%%), 4.82–4.46 (m, 14 H,
7 PhCH2), 4.07–3.64 (m, 20 H). Anal. Calcd
for C70H78O16: C, 71.53; H, 6.69. Found: C,
71.61; H, 6.73.
Allyl 2-O-acetyl-3,4,6-tri-O-benzyl-h-
mannopyranosyl-(1“6)-2-O-benzoyl-3,4-di-
O-benzyl-h- -mannopyranosyl-(1“6)-2-O-
benzoyl-3,4-di-O-benzyl-h- -mannopyranoside
D
-
Allyl 6-O-acetyl-2,3,4-tri-O-benzoyl-h-
mannopyranosyl-(1“2)-3,4,6-tri-O-benzyl-h-
-mannopyranosyl-(1“6)-[(6-O-acetyl-2,3,4-
tri-O-benzoyl-h- -mannopyranosyl)-(1“2)]-
(3,4-di-O-benzyl-h- -mannopyranosyl)-(1“6)-
[(6-O-acetyl-2,3,4-tri-O-benzoyl-h- -manno-
pyranosyl) - (1“2)] - 3,4 - di - O - benzyl - h - -
D
-
D
D
D
(14).—A solution of 13 (0.25 g, 0.26 mmol)
and trimethylsilyl trifluoromethanesulfonate
(5 mL, 0.028 mmol) in dry CH2Cl2 (20 mL)
D
D
D
,
was stirred with dried molecular sieves (4 A, 1
D
g) under N2 for 15 min, and then 2-O-acetyl-
mannopyranoside (16).—A solution of 15
(0.13 g, 0.11 mmol) and trimethylsilyl trifl-
uoromethanesulfonate (4 mL, 0.022 mmol) in
dry CH2Cl2 (15 mL) was stirred with dried
3,4,6-tri-O-benzyl-a-
D
-mannopyranosyl
tri-
chloroacetimidate (12) (0.25 g, 0.39 mmol) in
dry CH2Cl2 (10 mL) was added over 30 min at
rt. After 3 h the reaction mixture was diluted
with CH2Cl2 (20 mL) and washed with satd aq
NaHCO3 solution (8 mL). The organic layer
was dried and concentrated in vacuo. Purifica-
tion of the residue by column chromatography
(2:1 petroleum ether–EtOAc) gave 14 as a
syrup (0.32 g, 85.7%); [h]D +30.7° (c 1.0,
CHCl3); 1H NMR (400 MHz, CDCl3): l
8.12–7.13 (m, 45 H, 9 PhH), 5.87 (m, 1 H,
CH2CHꢀCH2), 5.78 (dd, 1 H, J1,2 1.6, J2,3 3.2
Hz, H-2), 5.67 (dd, 1 H, J1%,2% 1.6, J2%,3% 3.2 Hz,
H-2%), 5.52 (dd, 1 H, J1%%,2%% 1.6, J2%%,3%% 3.2 Hz,
,
molecular sieves (4 A, 0.4 g) under N2 for 15
min, and then 6-O-acetyl-2,3,4-tri-O-benzoyl-
a- -mannopyranosyl trichloroacetimidate (9)
D
(0.45 g, 0.66 mmol) in dry CH2Cl2 (10 mL)
was added dropwise for 30 min at rt. After
3 h the reaction mixture was diluted with
CH2Cl2 (30 mL) and washed with satd aq
NaHCO3 solution (5 mL). The organic layer
was dried and concentrated in vacuo. Purifica-
tion of the residue by column chromatography
(2:1 petroleum ether–EtOAc) gave 16 as a
syrup (0.23 g, 75.8%); [h]D +13.3° (c 1.0,
CHCl3); 1H NMR (400 MHz, CDCl3): l
8.03–7.14 (m, 80 H, 16 PhH), 6.02–5.92 (m,
10 H, 2B, 2D, 2F, 3B, 3D, 3F, 4B, 4D, 4F,
2
3
H-2%%), 5.28 (dd, 1 H, J 1.6, Jtrans17.2 Hz,
2
3
CH2CHꢀCH2), 5.19 (dd, 1 H, J 1.6, Jcis 10.4
Hz, CH2CHꢀCH2), 5.07 (d, 1 H, J1,2 1.6 Hz,

L. Heng et al. / Carbohydrate Research 331 (2001) 431–437
437
CH2CHꢀCH2), 5.56 (d, 1 H, J2,1 1.1 Hz, HB-
1), 5.46 (d, 1 H, J2,1 1.1 Hz, HD-1), 5.40 (d, 1
hadex LH-20 to afford 1 (0.022 g, 61.8%) as
an amorphous mass; [h]D +1.4° (c 0.1,
MeOH); ESMS for C36H62O31 (990.87): 989.5
[M−H].
2
H, J2,1 1.1 Hz, HF-1), 5.28 (dd, 1 H, J 1.6,
3Jtrans 17.2 Hz, CH2CHꢀCH2), 5.21 (d, 1 H,
2
3
J2,1 1.1 Hz, HA-1), 5.18 (dd, 1 H, J 1.6, Jcis
10.4 Hz, CH2CHꢀCH2), 5.14 (d, 1 H, J2,1 1.1
Hz, HC-1), 4.97 (d, 1 H, J2,1 1.1 Hz, HE-1),
2.07, 1.99, 1.97 (3 s, 9 H, 3 COCH3); 13C
NMR (400 MHz, CDCI3): l 170.5–170.4
(CH3CO), 165.7–164.8 (9 PhCO), 138.8–137.7
(7 PhCH2, C-1), 133.4–132.7 (7 PhCO, C-1,
CH2ꢀCHꢁCH2), 129.9–127.2 (aromatic C),
117.5 (CH2ꢀCHꢁCH2), 99.6, 99.4, 99.3, 99.2,
99.1, 98.3 (C-1A,, 1B, 1C, 1D, 1E, 1F), 80.2, 80.0,
79.0 (C-2B, 2C, 2E), 67.9 (CH2ꢀCHꢁCH2),
20.61, 20.58, 20.53 (3 CH3CO); Anal. Calcd
for C157H150O43: C, 69.20; H, 5.55. Found: C,
69.14; H, 5.59.
Acknowledgements
This work was supported by Chinese
Academy of Sciences (KJ952J1510 and
KIPRCEES9904) and The National Natural
Science Foundation of China (59973026 and
29905004). Mr Linsen Heng is a visiting
scholar from Da Xian Normal College, De-
partment of Chemistry, Si Chuan, People’s
Republic of China.
h-
pyranosyl - (1“6) - [h -
(1“2)] - h - - mannopyranosyl - (1“6) - [(h -
mannopyranose) - (1“2)] - - mannopyranose
D
-Mannopyranosyl-(1“2)-h-
D
-manno-
References
D
- mannopyranosyl-
D
D
-
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