Efficient synthesis of an allose-containing analogue of the phytoalexin- Elicitor glucohexaose and its dodecyl glycoside

Article abstract of DOI:10.1055/s-0028-1083292

An allose-containing analogue 2 of the phytoalexin elic- itor β-(1→3)-branched β-(1→6)-linked glucohexatose and its dode- cyl glycoside 3 has been regio- and stereospecifically synthesized. As a typical example of the method, the synthesis of 2 was achiev

Full text of DOI:10.1055/s-0028-1083292

PAPER
199
Efficient Synthesis of an Allose-Containing Analogue of the Phytoalexin-
Elicitor Glucohexaose and Its Dodecyl Glycoside
Efficient
S
ynthese
o
s
of
O
ligosac
n
charides gju Ma, Dewen Qiu, Xiangdong Mei,* Jun Ning,* Qianfei Zhao, Yonghong Li
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection,
Chinese Academy of Agricultural Sciences, Beijing 100193, P. R. of China
Fax +86(10)62899142; E-mail: meixiangdong@gmail.com; E-mail: jning@ippcaas.cn
Received 28 July 2008; revised 18 September 2008
Glcp
Glcp
1,3
Abstract: An allose-containing analogue 2 of the phytoalexin elic-
β
1,3
β
itor b-(1→3)-branched b-(1→6)-linked glucohexatose and its dode-
cyl glycoside 3 has been regio- and stereospecifically synthesized.
As a typical example of the method, the synthesis of 2 was achieved
via coupling of the trisaccharide donor 2,3,4,6-tetra-O-benzoyl-b-
D-glucopyranosyl-(1→3)-[2,3,4,6-tetra-O-benzoyl-b-D-glucopyra-
nosyl-(1→6)]-1,2-O-isopropylidene-a-D-allopyranosyl trichloro-
acetimidate (9) with a trisaccharide acceptor. The donor was
prepared easily from 1,2:5,6-di-O-isopropylidene-a-D-allofuranose
(5) and 2,3,4,6-tetra-O-benzoyl-a-D-glucopyranosyl trichloroace-
timidate (4) in a regio- and stereoselective manner.
1,6
1,6
1,6
Glcp
Glcp
Glcp
Glcp
Glcp
Glcp
Glcp
β
β
1
β
Glcp
1,3
1,6
Glcp
1,3
β
β
1,6
1,6
Allp
Glcp
β
β
β
2
Glcp
1,3
Glcp
1,3
β
β
1,6
1,6
1,6
Key words: oligosaccharides, synthesis, glycosides, glycosyla-
tions, stereoselectivity
Allp
Glcp
Glcp
ODodecyl
β
β
β
β
3
Figure 1 D-Glucohexatose (1) and its allose-containing glycosides
2 and 3
Increased appreciation of the role of carbohydrates in
biological and pharmaceutical science has resulted in a re-
vival of interest in carbohydrate chemistry. However,
compared with other biopolymers such as peptides and
nucleic acids, the role of the saccharide structure in func-
tion has received minimal attention. This can be attributed
mainly to the difficulty of synthesizing saccharides. Al-
though over the past few decades, considerable progress
has been made in this field,1 currently there is still no gen-
eral route for saccharide synthesis, and glycosylation
chemistry is still not predicable or generally accessible.
functions. For detailed elucidation of the molecular struc-
ture responsible for the biological properties of the b-
(1→3)-branched b-(1→6)-linked glucose oligomers, it
would be necessary to synthesize a variety of model com-
pounds. We have previously found that a hexasaccharide
analogue of the repeating unit of lentinan, which was not
fully b-linked but contained one a-linkage between the
two trisaccharide moieties, had better activity and lower
toxicity.9 Inspired by this, we designed and synthesized
the allose-containing analogue 2 of the phytoalexin-elici-
tor b-(1→3)-branched b-(1→6)-linked glucohexatose.
In addition, some studies showed that modification of oli-
gosaccharides with hydrophobic long alkyls at the reduc-
ing terminal can increase their biological activity.10 The
reason is that the newly formed compounds are composed
both of a hydrophilic oligosaccharide portion and a hydro-
phobic long alkyl portion and have the characteristic of a
surface-active agent, able to coagulate together. But some
reports showed that modifications of the reducing termi-
nal glucosyl residue of elicitor-active glucans had no sig-
nificant effect on their elicitor activities.5b,11 Therefore, in
order to find out whether the modification of 2 with hy-
drophobic long alkyls at the reducing terminal have a sig-
nificant effect on the elicitor activity, further the study of
structure–bioactivity relationships, and the search for oli-
gosaccharides of higher elicitor performance, we present
herein the synthesis of lauryl glycoside 3 of allose-con-
taining glucohexaose. Also the bioassay results of the
compounds 2 and 3 as phytoaleaxin elicitors are given.
The
b-(1→3)-branched
b-(1→6)-linked
glucose
oligomers2 derived from the cell walls of fungus Phytoph-
thora megasperma f. sp. Glycinea by enzymatic or chem-
ical hydrolysis is an effective phytoalexin elicitor, which
can induce the biosynthesis of different phytoalexins in a
wide range of plant species,3 such as soybean.4 A biolog-
ical analysis reported that the minimum structure element
required for high elicitor activity is D-glucohexatose (1)5
(Figure 1). These significant discoveries stimulated the
interest of scientists. Since these elicitors were isolated
and identified, the glucan elictors had been prepared by
different groups6,7 through employing various methods
and strategies including the elegant solid-phase strate-
gies.8
Providing sufficient quantities of a sample is a basic pre-
requisite for detailed studies on a compound’s fundamen-
tal biochemical properties and possible biological
SYNTHESIS 2009, No. 2, pp 0199–0204
x
x
.
x
x
.2
0
0
8
Advanced online publication: 19.12.2008
DOI: 10.1055/s-0028-1083292; Art ID: F17108SS
© Georg Thieme Verlag Stuttgart · New York

200
H. Ma et al.
PAPER
In our synthesis, 2,3,4,6-tetra-O-benzoyl-a-D-glucopyra- trimethylsilyl triflate as the catalyst in 86% yield. The 1H
nosyl trichloroacetimidate (4) and 1,2:5,6-di-O-isopropyl- NMR data of compound 11 contained structurally charac-
idene-a-D-allofuranose (5) were the starting materials. teristic information, for instance, two acetyl signals (d =
Compound 4 was prepared from D-glucose according to 1.83, 1.38), and six H1 signals (d = 5.43, 5.20, 5.01, 4.98,
the standard procedure.12 Compound 5 could be obtained 4.86, 4.92). The 13C NMR spectrum of 11 gave six signals
from oxidation of 1,2:5,6-di-O-isopropylidene-a-D-glu- for C1 (d = 105.95, 104.88, 101.20, 100.99, 100.97,
cofuranose with dimethyl sulfoxide, followed by ste- 100.71). Acid-catalyzed (80% AcOH) removal of the 1,2-
reospecific reduction with sodium borohydride in one O-isopropylidene group of 11, followed by deprotection
pot.13 Condensation of 4 and 5 with trimethylsilyl triflate in ammonia-saturated methanol yielded the target com-
as catalyst and 4 Å molecular sieves in dichloromethane pound 2. The chemical shifts of anomeric carbons of 2 re-
at room temperature smoothly afforded the b-(1→3)- vealed by 13C NMR spectrum were at d = 107.55, 102.96,
linked disaccharide
6
in excellent yield (94%) 102.88, 102.61, 101.64, and 100.97, confirming the struc-
(Scheme 1). Selective removal of the 5,6-O-isopropy- ture of 2.
lidene group of 6 with 90% acetic acid at 40 °C afforded
Removal of the 1,2-O-isopropylidene group of 11 in 80%
disaccharide 7 as crystals in a high yield (96%). Conden-
sation of 7 with 4 catalyzed by trimethylsilyl triflate regio-
and stereoselectively gave the key intermediate, the 3,6-
branched trisaccharide 8, in 56% yield. The structure of 8
was unambiguously confirmed by 1H and 13C NMR data.
acetic acid followed acetylation with acetic anhydride in
pyridine, selective 1-O-deacetylation with benzylamine in
tetrahydrofuran, and subsequent treatment with trichloro-
acetonitrile in the presence of potassium carbonate gave
the desired hexasaccharide glycosyl donor 12. The struc-
ture of 12 was confirmed by 1H NMR spectral analysis as
follows: d = 8.35 (s, 1 H, CNHCCl3), and by 13C NMR
spectrum giving six signals for anomer carbons at d =
106.04, 101.26, 101.25, 101.20, 101.04, and 100.63. Cou-
pling 12 with dodecyl alcohol gave compound 13. Depro-
tection in ammonia-saturated methanol afforded another
1
The three anomeric proton signals in the H NMR spec-
trum of 8 were located at d = 5.59 as a doublet with
J1,2 = 3.8 Hz, at d = 4.94 as a doublet with J1,2 = 8.0 Hz,
and at d = 4.92 as a doublet with J1,2 = 8.0 Hz, respective-
ly, whereas the 13C NMR spectrum revealed anomeric car-
bons at d = 103.6, 101.6, and 101.5. The de-
isopropylidenation of 8 in chloroform–trifluoroacetic acid
(10:1) at room temperature, followed by acetylation with
acetic anhydride in pyridine, selective 1-O-deacetylation
with benzylamine in tetrahydrofuran, and subsequent
treatment with trichloroacetonitrile in the presence of po-
tassium carbonate afforded the desired trisaccharide glyc-
osyl donor 9 in good yield (68% for 4 steps).
1
target 3. The signals of the H NMR spectrum of 3 were
not distinguishable. However, the chemical shifts of ano-
meric carbons of 3 were at d = 107.55, 103.24, 103.06,
102.65, 102.35, and 100.90, confirming the structure of 3.
The bioassay was carried out according to the method de-
vised by Ayers et al.15 The phytoalexin-elicitor sugars can
stimulate glyceollin accumulation in cotyledons of soy-
bean seedlings. The activity of the synthesized oligosac-
charides was determined by the concentration required to
elicit half-maximal accumulation of glyceollin (C50). The
test results showed that C50 of the dodecyl b-(1→3)-
branched b-(1→6)-linked hexaglucoside 3 and underiva-
With the glycosyl donor 9 and 2,3,4,6-tetra-O-benzoyl-b-
D-glucopyranosyl-(1→3)-[2,3,4-tri-O-benzoyl-b-D-gluco-
pyranosyl-(1→6)]-1,2-O-isopropylidene-a-D-glucofuran-
ose (10)14 in hand, construction of the target compound
was readily carried out. As shown in Scheme 2, hexasac-
charide 11 was obtained by coupling of 9 with 10 using
O
O
HO
HO
O
O
O
BzO
BzO
O
O
O
O
O
O
O
a
b
BzO
BzO
BzO
BzO
BzO
+
O
O
O
O
O
O
OBz
BzO
BzO
HO
OC(NH)CCl3
OBz
OBz
6
4
5
7
4
c
BzO
BzO
BzO
O
O
HO
O
O
O
BzO
O
BzO
BzO
AcO
OBz
OBz
BzO
OAc
d
O
O
OC(NH)CCl3
BzO
O
O
O
O
BzO
BzO
BzO
BzO
OBz
OBz
8
9
Scheme 1 Reagents and conditions: (a) TMSOTf (cat.), CH2Cl2, MS 4 Å powder, r.t., 4 h, 94%; (b) 90% aq AcOH, 40 °C, 10 h, 96%; (c)
TMSOTf (cat.), CH2Cl2, MS 4 Å powder, –45 °C to r.t., 2 h, 56%; (d) (i) CHCl3–TFA (10:1), r.t., 5 h; (ii) Ac2O, pyridine, r.t., 3 h; (iii) BnNH2
(4.0 equiv), THF, r.t., 24 h; (iv) Cl3CCN (2.0 equiv), K2CO3 (2.0 equiv), CH2Cl2, r.t., 12 h, 68% (for 4 steps).
Synthesis 2009, No. 2, 199–204 © Thieme Stuttgart · New York

PAPER
Efficient Syntheses of Oligosaccharides
201
HO
O
O
BzO
BzO
O
O
BzO
BzO
O
O
O
HO
HO
O
O
O
AcO
O
9
BzO
BzO
OBz
O
OBz
O
O
O
OAc
BzO
O
O
a
OBz
O
O
BzO
O
BzO
BzO
BzO
OBz
OBz
OBz
BzO
11
BzO
BzO
BzO
BzO
10
c
b
O
O
O
BzO
BzO
O
O
OAc
O
O
2
BzO
BzO
BzO
AcO
O
AcO
O
O
OAc
OBz
OBz
BzO
OC(NH)CCl3
BzO
O
BzO
BzO
BzO
12
BzO
OBz
OBz
d
O
BzO
O
O
O
O
OC12H25
OAc
BzO
O
O
AcO
BzO
BzO
BzO
e
OBz
O
AcO
O
OAc
3
OBz
BzO
BzO
O
O
BzO
BzO
BzO
BzO
OBz
OBz
13
Scheme 2 Reagents and conditions: (a) TMSOTf (cat.), CH2Cl2, MS 4 Å powder, r.t., 2 h, 86%; (b) (i) 80% AcOH, reflux, 5 h; (ii) CH2Cl2–
MeOH saturated with NH3, r.t., 24 h, 91% (for 2 steps); (c) (i) 80% AcOH, reflux, 5 h; (ii) Ac2O, pyridine, r.t., 3 h; (iii) BnNH2 (4.0 equiv),
THF, r.t., 24 h; (iv) Cl3CCN (2.0 equiv), K2CO3 (2.0 equiv), CH2Cl2, r.t., 12 h, 58% (for 4 steps); (d) C12H25OH (1.5 equiv), TMSOTf (cat.),
CH2Cl2, MS 4 Å powder, r.t., 2 h, 87%; (e) CH2Cl2–MeOH saturated with NH3, r.t., 24 h, 97%.
HRMS were obtained with Bruker Apex II. FT-ICR MS spectro-
photometer. TLC was performed on silica gel HF254 with detection
tized 2 are about 7 nM and 9 nM respectively, indicating
that the two compounds have similar activities compared
to that of glucohexaose and modification of the reducing
end of oligosaccharide 2 does not have a significant effect
on its biological activity. Although the biological test did
not show a remarkable result, this kind of information
would be significant for the further study of structure–
activity relationships.
by charring with 30% (v/v) H2SO4 in MeOH or in some cases by a
UV detector. Column chromatography was conducted by elution of
a column (16 × 240 mm, 18 × 300 mm, 35 × 400 mm) of silica gel
(100–200 mesh) with EtOAc–petroleum ether (bp 60–90 °C) (PE)
as the eluent. Solns were concentrated at <60 °C under reduced
pressure.
2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1→3)-1,2:5,6-di-
O-isopropylidene-a-D-allofuranose (6)
In summary, an efficient method for the preparation of
allose-containing analogue of the phytoalexin-elicitor b-
(1→3)-branched b-(1→6)-linked glucohexatose and its
dodecyl glycoside has been developed by regio- and
stereoselective glycosylation using glycosyl trichloroacet-
imidates as the donors and partially protected sugars as
the acceptor. All new compounds involved in this study
A soln of 4 (5.1 g, 6.9 mmol) and 5 (1.5 g, 5.8 mmol) in anhyd
CH2Cl2 (80 mL) was stirred with activated 4 Å molecular sieves
(2.1 g) at r.t. under an atmosphere of N2 for 10 min. Then TMSOTf
(55 mL, 0.28 mmol) was added. After ~4 h (TLC monitoring, PE–
EtOAc, 1.5:1), the mixture was neutralized with Et3N and filtered
and the filtrate was concentrated. The resultant residue was subject-
ed to column chromatography (PE–EtOAc, 1.5:1) to afford 6 (4.5 g,
94%).
1
were identified by optical rotations, H NMR or/and 13C
NMR spectroscopy, and elemental analyses or MALDI–
TOF MS. This method can be used to synthesize both ho-
mo- and hetero-saccharide structures, which are used for
the further assembly of advanced bioactive sugar chains.
The sole use of acyl groups in the synthesis substantially
simplified the procedure.
[a]D +11 (c 1.0, CHCl3).
1H NMR (400 MHz, CDCl3): d = 8.02–7.25 (m, 20 H, 4 PhH), 5.89
(dd, J2¢,3¢ = J3¢,4¢ = 9.7 Hz, 1 H, H3¢), 5.72 (dd, J3¢,4¢ = J4¢,5¢ = 9.7 Hz,
1 H, H4¢), 5.67 (dd, J1¢,2¢ = 7.9 Hz, J2¢,3¢ = 9.7 Hz, 1 H, H2¢), 5.57 (d,
J1,2 = 3.8 Hz, 1 H, H1), 5.11 (d, J1¢,2¢ = 7.9 Hz, 1 H, H1¢), 4.68 (dd,
J5¢,6¢a = 3.2 Hz, J6¢a,6¢b = 11.9 Hz, 1 H, H6¢a), 4.62 (dd, J1,2 = 3.8 Hz,
J2,3 = 5.1 Hz, 1 H, H2), 4.56 (dd, J5¢,6¢b = 6.0 Hz, J6¢a,6¢b = 11.9 Hz, 1
H, H6¢b), 4.25 (ddd, J5,6a = 4.9 Hz, J5,6b = 6.6 Hz, J4,5 = 6.6 Hz, 1 H,
H5), 4.22–4.19 (m, 1 H, H5¢), 4.07–4.02 (m, 2 H, H3, H4), 3.74 (dd,
J5,6a = 4.9 Hz, J6a,6b = 8.8 Hz, 1 H, H6a), 3.69 (dd, J5,6b = 6.6 Hz,
J6a,6b = 8.8 Hz, 1 H, H6b), 1.50, 1.41 [2 s, 6 H, C(CH3)2], 1.26, 1.24
[2 s, 6 H, C(CH3)2].
Optical rotations were determined at 20 °C with a Perkin-Elmer
Model 241-Mc automatic polarimeter. 1H NMR and 13C NMR spec-
tra were recorded with Bruker ARX 400 spectrometers (400 MHz
for 1H, 100 MHz for 13C) for solns in CDCl3 or D2O as indicated.
Chemical shifts are given in ppm downfield from internal TMS.
Synthesis 2009, No. 2, 199–204 © Thieme Stuttgart · New York

202
H. Ma et al.
PAPER
Anal. Calcd for C46H46O15: C, 65.86; H, 5.53. Found: C, 65.78; H,
5.49.
ture was diluted with toluene (150 mL) and then it was concentrated
under vacuum. The residue was acetylated with Ac2O (10 mL) in
pyridine (30 mL) at r.t. for 3 h. The resultant trisaccharide was dis-
solved in BnNH2 (14 mL) in THF (250 mL) and the mixture was
kept in dark at r.t. for 24 h (TLC monitoring, PE–EtOAc, 1.5:1). The
soln was concentrated and the resultant residue, without purifica-
tion, was dissolved in anhyd CH2Cl2 (50 mL) and trichloroacetoni-
trile (0.73 mL, 6.4 mmol) and anhyd K2CO3 (1 g, 7.2 mmol) were
added. The mixture was stirred at r.t. for 12 h, the solid material was
filtered off, and the filtrate was concentrated. Purification by col-
umn chromatography (silica gel, PE–EtOAc, 1:1) gave 9 (3.4 g,
68%).
2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1→3)-1,2-O-iso-
propylidene-a-D-allofuranose (7)
A soln of 6 (5 g, 5.9 mmol) in 90% aq AcOH (250 mL) was kept at
40 °C for 10 h (TLC monitoring, PE–EtOAc, 1:1). The mixture was
concentrated under reduced pressure, the residue was subjected to
column chromatography (PE–EtOAc, 1:1) to give 7 (4.6 g, 96%) as
white crystals.
[a]D +15 (c 1.0, CHCl3).
1H NMR (400 MHz, CDCl3): d = 8.04–7.26 (m, 20 H, 4 PhH), 5.89
(dd, J2¢,3¢ = J3¢,4¢ = 9.5 Hz, 1 H, H3¢), 5.71 (dd, J3¢,4¢ = J4¢,5¢ = 9.5 Hz,
1 H, H4¢), 5.66 (dd, J1¢,2¢ = 7.9 Hz, J2¢,3¢ = 9.5 Hz, 1 H, H2¢), 5.56 (d,
J1,2 = 3.8 Hz, 1 H, H1), 5.09 (d, J1¢,2¢ = 7.9 Hz, 1 H, H1¢), 4.69 (dd,
J5¢,6¢a = 3.2 Hz, J6¢a,6¢b = 11.9 Hz, 1 H, H6¢a), 4.62 (dd, J1,2 = 3.8 Hz,
J2,3 = 6.2 Hz, 1 H, H2), 4.55 (dd, J5¢,6¢b = 6.0 Hz, J6¢a,6¢b = 11.9 Hz, 1
H, H6¢b), 4.23–4.20 (m, 1 H, H5¢), 4.09 (dd, J2,3 = 6.2 Hz, J3,4 = 8.8
Hz, 1 H, H3), 4.01 (dd, J4,5 = 2.8 Hz, J3,4 = 8.8 Hz, 1 H, H4), 3.93–
3.91–4.02 (m, 1 H, H5¢), 3.39 (dd, J5,6a = 7.6 Hz, J6a,6b = 11.2 Hz, 1
H, H6a), 3.31 (dd, J5,6b = 4.3 Hz, J6a,6b = 11.2 Hz, 1 H, H6b), 1.49,
1.18 [2 s, 6 H, C(CH3)2].
[a]D +38.2 (c 1.0, CHCl3).
1H NMR (400 MHz, CDCl3): d = 8.52 [s, 1 H, O(NH)CCl3], 8.05–
7.26 (m, 40 H, 8 PhH), 6.19 (d, J1,2 = 3.6 Hz, 1 H, H1), 6.09 (dd,
J2,3 = J3,4 = 9.6 Hz, 1 H, H3¢), 5.80 (dd, J2,3 = J3,4 = 9.6 Hz, 1 H,
H3¢¢), 5.75 (dd, J3,4 = J4,5 = 9.6 Hz, 1 H, H4¢), 5.70 (dd,
J3,4 = J4,5 = 9.6 Hz, 1 H, H4¢¢), 5.48 (dd, J1,2 = 8 Hz, J2,3 = 9.6 Hz, 1
H, H2¢), 5.47 (d, J1,2 = 8 Hz, 1 H, H1¢), 5.48–5.43 (m, 1 H), 5.13 (d,
J1,2 = 8 Hz, 1 H, H1¢¢), 4.76–4.63 (m, 3 H), 4.53–4.43 (m, 3 H),
4.38–4.28 (m, 3 H), 4.06 (m, 1 H, H5¢¢), 3.93 (dd, 1 H), 3.82 (dd,
J5,6b = 5.2 Hz, J6a,6b = 12 Hz, 1 H, H6b), 1.98, 1.57 (2 s, 6 H, 2
CH3CO).
Anal. Calcd for C43H42O15: C, 64.66; H, 5.30. Found: C, 64.79; H,
5.25.
Anal. Calcd for C80H68Cl3NO26: C, 61.37; H, 4.38. Found : C, 61.53;
H, 4.41.
2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1→3)-[2,3,4,6-
tetra-O-benzoyl-b-D-glucopyranosyl-(1→6)]-1,2-O-isopropy-
lidene-a-v-allofuranose (8)
2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1→6)-[2,3,4,6-
tetra-O-benzoyl-b-D-glucopyranosyl-(1→3)]-2,4-di-O-acetyl-b-
D-allopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-b-D-glucopyrano-
syl-(1→6)-[2,3,4,6-tetra-O-benzoyl-b-D-glucopyranosyl-
(1→3)]-1,2-O-isopropylidene-a-D-glucofuranose (11)
A soln of 9 (1.5 g, 0.96 mmol) and 10 (1.1 g, 0.87 mmol) in anhyd
CH2Cl2 (50 mL) was stirred with activated 4 Å molecular sieves
(1.5 g) at r.t. under an atmosphere of N2 for 10 min. Then TMSOTf
(35 mL, 0.18 mmol) was added; the reaction was complete in ~2 h
(TLC monitoring, PE–EtOAc, 1.5:1). The mixture was neutralized
with Et3N and filtered and the filtrate was concentrated. The result-
ant residue was subjected to the column chromatography (PE–
EtOAc, 1.5:1) to afford 11 (2.0 g, 86%).
A soln of 4 (2.5 g, 3.4 mmol) and 7 (3 g, 3.7 mmol) in anhyd CH2Cl2
(200 mL) was stirred with activated 4 Å MS (2.5 g) at r.t. under an
atmosphere of N2 for 10 min. The mixture was cooled to –45 °C and
TMSOTf (45 mL, 0.23 mmol) was added, after 30 min the tempera-
ture was allowed to rise to r.t. and the mixture was stirred for a fur-
ther 1.5 h (TLC monitoring, PE–EtOAc, 1.5:1). The mixture was
neutralized with Et3N and filtered, and the filtrate was concentrated
under vacuum. The residue was purified by flash chromatography
(PE–EtOAc, 1.5:1) to afford 8 (2.6 g, 56%).
[a]D +30.3 (c 1.0, CHCl3).
1H NMR (400 MHz, CDCl3): d = 8.07–7.26 (m, 40 H, 8 PhH), 5.86
(dd, J2,3 = J3,4 = 9.6 Hz, 1 H, H3¢), 5.83 (dd, J2,3 = J3,4 = 9.6 Hz, 1 H,
H3¢¢), 5.70 (dd, J3,4 = J4,5 = 9.6 Hz, 1 H, H4¢), 5.69 (dd,
J3,4 = J4,5 = 9.6 Hz, 1 H, H4¢¢), 5.59 (dd, J1,2 = 8.0 Hz, J2,3 = 9.6 Hz,
1 H, H2¢), 5.59 (d, J1,2 = 3.8 Hz, 1 H, H1), 5.47 (dd, J1,2 = 8.0 Hz,
J2,3 = 9.6 Hz, 1 H, H2¢¢), 4.94 (d, J1,2 = 8.0 Hz, 1 H, H1¢), 4.92 (d,
J1,2 = 8.0 Hz, 1 H, H1¢¢), 4.74 (dd, J5,6a = 3.6 Hz, J6a,6b = 12.0 Hz, 1
H, H6a¢), 4.70 (dd, J5,6a = 3.6 Hz, J6a,6b = 12.0 Hz, 1 H, H6a¢¢), 4.63
(dd, J1,2 = 3.8 Hz, J2,3 = 5.1 Hz, 1 H, H2), 4.55 (dd, J5,6b = 5.2 Hz,
J6a,6b = 12.0 Hz, 1 H, H6b¢), 4.55 (dd, J5,6b = 4.8 Hz, J6a,6b = 12.0 Hz,
1 H, H6b¢¢), 4.26–4.23 (m, 1 H, H5), 4.21 (dd, J2,3 = 5.1 Hz,
J3,4 = 8.8 Hz, 1 H, H3), 4.05–3.98 (m, 3 H, H4, H5¢, H5¢¢), 3.26 (dd,
J5,6a = 7.9 Hz, J6a,6b = 12 Hz, 1 H, H6a), 3.31 (dd, J5,6b = 3.6 Hz,
J6a,6b = 12 Hz, 1 H, H6b), 1.47, 1.18 [2 s, 6 H, C(CH3)2].
[a]D +28.6 (c 1.0, CHCl3).
1H NMR (400 MHz, CDCl3): d = 8.11–7.23 (m, 75 H, 15 PhH), 5.97
(dd, J2,3 = J3,4 = 9.6 Hz, 1 H, H3), 5.90 (dd, J2,3 = J3,4 = 9.6 Hz, 1 H,
H3), 5.82 (dd, J2,3 = J3,4 = 9.6 Hz,
1 H, H3), 5.71 (dd,
J2,3 = J3,4 = 9.6 Hz, 1 H, H3), 5.68 (dd, J2,3 = J3,4 = 9.6 Hz, 1 H, H3),
5.63 (dd, J2,3 = J3,4 = 9.6 Hz, 1 H, H4), 5.20 (d, J1,2 = 5.2 Hz, 1 H,
H1), 5.43 (d, J1,2 = 3.6 Hz, 1 H, H1), 5.01, 4.98, 4.86, 4.92 (4 d,
J1,2 = 8.1 Hz, 1 H, H1), 1.83, 1.38 (2 s, 6 H, 2 CH3CO).
13C NMR (100 MHz, CDCl3): d = 170.55, 169.49 (2 CH3CO),
166.06, 165.97, 165.87, 165.72, 165.62, 165.60, 165.50, 165.07,
165.04, 165.00, 164.97, 164.94, 164.61, 164.59, 164.57 (15 PhCO),
111.89 [C(CH3)2], 105.95, 104.88, 101.20, 100.99, 100.97, 100.71
(6 C1), 82.83, 82.40, 81.28, 78.99, 78.95, 77.31, 74.87, 73.96,
73.34, 72.95, 72.85, 72.77, 72.65, 72.53, 72.41, 71.96, 71.90, 71.71,
71.43, 71.34, 71.06, 69.69, 69.60, 69.51, 69.33, 67.96, 66.74, 63.20,
62.74, 62.64 (6 C2, C3, C4, C5, C6), 26.52, 25.1 [2 C(CH3)2], 20.46,
19.88 (2 CH3CO).
13C NMR (100 MHz, CDCl3): d = 166.01, 165.92, 165.66, 165.55,
165.39, 165.16, 165.14, 164.51 (8 COPh), 113.11 [C(CH3)2],
103.55, 101.59, 101.47 (3 C1), 80.22, 79.59, 78.84, 77.17, 73.10,
72.61, 72.44, 72.37, 72.19, 71.56, 69.85, 69.45, 62.98, 62.65, 62.07,
26.80, 26.17 [C(CH3)].
Anal. Calcd for C148H130O48: C, 66.41; H, 4.90. Found : C, 66.50; H,
4.87.
Anal. Calcd for C77H68O24: C, 67.15; H, 4.98. Found : C, 67.19; H,
5.01.
b-D-Glucopyranosyl-(1→6)-[b-D-glucopyranosyl-(1→3)]-b-D-
allopyranosyl-(1→6)-b-D-glucopyranosyl-(1→6)-[b-D-glucopy-
ranosyl-(1→3)]-D-glucopyranose (2)
Compound 11 (4.1 g, 1.5 mmol) was added to 80% aq AcOH (80
mL) and the mixture was refluxed for 5 h (TLC monitoring, PE–
EtOAc, 1:1). The mixture was concentrated under vacuum, the res-
2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1→3)-[2,3,4,6-
tetra-O-benzoyl-b-D-glucopyranosyl-(1→6)]-2,4-di-O-acetyl-a-
D-allopyranosyl Trichloroacetimidate (9)
Compound 8 (4.3 g, 3.2 mmol) was treated with CHCl3–TFA (10:1,
50 mL) at r.t. for 5 h (TLC monitoring, PE–EtOAc, 1:1). The mix-
Synthesis 2009, No. 2, 199–204 © Thieme Stuttgart · New York

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Efficient Syntheses of Oligosaccharides
203
idue was dissolved in NH3-saturated CH2Cl2–MeOH (1:9, 200 mL)
at r.t. After 24 h, the mixture was concentrated to ~20 mL, then
CH2Cl2 (150 mL) was added. The resultant precipitate was filtered
and washed with CH2Cl2 to give free hexasaccharide 2 (1.3 g, 91%
for 2 steps) as a white powder.
1H NMR (400 MHz, CDCl3): d = 8.10–7.22 (m, 75 H, 15 PhH), 5.10
(d, J1,2 = 5.2 Hz, 1 H, H1), 4.94, 4.91, 4.87, 4.86, 4.76 (5 d, J1,2 = 8.0
Hz, 1 H, H1), 1.99, 1.93. 1.86. 1.82 (4 s, 12 H, 4 CH3CO), 1.40–0.79
(m, 23 H, CH2C11H23).
13C NMR (100 MHz, CDCl3): d = 170.34, 169.55, 169.49, 167.96
(4 CH3CO), 166.00, 165.94, 165.83, 165.76, 165.70, 165.69,
165.56, 165.48, 165.04, 164.93, 164.95, 164.96, 164.78, 164.53,
164.52 (15 PhCO), 105.86, 101.14, 101.02, 100.95, 100.90, 100.34
(6 C1), 81.29, 78.70, 78.63, 77.09, 74.70, 73.76, 73.35, 73.29,
72.87, 72.78, 72.72, 72.58, 72.41, 72.10, 71.90, 71.83, 71.77, 71.62,
71.43, 71.36, 69.62, 69.50, 69.18, 68.75, 68.47, 66.98, 63.04, 62.98,
62.58, 62.49 (6 C2, C3, C4, C5, C6), 31.78, 29.57, 29.52, 29.48,
29.36, 29.23, 29.10, 25.86, 25.71, 22.56, 20.57, 20.47, 20.38, 19.98
(4 CH3CO), 13.99.
[a]D –43.6 (c 0.3, H2O).
13C NMR (100 MHz, D2O): d = 107.55, 102.96, 102.88, 102.61,
101.64, 100.97 (6 C1), 84.65, 82.36 (2 C3), 69.83, 69.44, 68.94,
68.78, 60.83, 60.56 (6 C6).
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C36H62NaO31:
1013.3198; found: 1013.3198.
2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1→6)-[2,3,4,6-
tetra-O-benzoyl-b-D-glucopyranosyl-(1→3)]-2,4-di-O-acetyl-b-
D-allopyranosyl-(1→6)-2,3,4-tri-O-benzoyl-b-D-glucopyrano-
syl-(1→6)-[2,3,4,6-tetra-O-benzoyl-b-D-glucopyranosyl-
(1→3)]-2,4-di-O-acetyl-a-D-glucopyranosyl Trichloroacetimi-
date (12)
Compound 11 (4.1 g, 1.5 mmol) was added to 80% aq AcOH (80
mL) and the mixture was refluxed for 5 h (TLC monitoring, PE–
EtOAc, 1:1). The mixture was concentrated under vacuum and the
residue was acetylated with Ac2O (10 mL) in pyridine (35 mL) at
r.t. for 3 h. The resultant trisaccharide was dissolved in BnNH2 (14
mL) in THF (250 mL) and the mixture was kept in dark at r.t. for 24
h (TLC monitoring, PE–EtOAc, 1.5:1). The soln was concentrated
and the resultant residue, without purification, was dissolved in an-
hyd CH2Cl2 (50 mL) and trichloroacetonitrile (0.5 mL, 4.3 mmol)
and anhyd K2CO3 (1 g, 7.2 mmol) were added. The mixture was
stirred at r.t. for 12 h and the solid material was filtered off. Concen-
tration of the filtrate followed by purification by column chroma-
tography (silica gel, PE–EtOAc, 1:1) gave 12 (2.5 g, 58%).
Anal. Calcd for C161H154O50: C, 66.94; H, 5.37. Found : C, 66.86; H,
5.53.
Dodecyl b-D-Glucopyranosyl-(1→6)-[b-D-glucopyranosyl-
(1→3)]-b-D-allopyranosyl-(1→6)-b-D-glucopyranosyl-(1→6)-
[b-D-glucopyranosyl-(1→3)]-b-D-glucopyranoside (3)
Compound 13 (1.0 g, 0.35 mmol) was dissolved in NH3-saturated
CH2Cl2–MeOH (1:9, 100 mL) at r.t. After 24 h, the mixture was
concentrated to ~10 mL and CH2Cl2 (120 mL) was added. The re-
sultant precipitate was filtered and washed with CH2Cl2 to afford 3
(0.39g, 97%) as a white solid.
[a]D –25.3 (c 1.0, H2O).
13C NMR (100 MHz, D2O): d = 107.55, 103.24, 103.06, 102.65,
102.35, 100.90 (6 C6), 85.16, 81.76 (2 C3), 31.96, 29.74, 29.47,
29.39, 25.77, 22.64, 14.01.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C48H86NaO31:
1181.5098; found: 1181.5096.
[a]D +28.6 (c 1.0, CHCl3).
1H NMR (400 MHz, CDCl3): d = 8.35 [s, 1 H, CNHCCl3], 8.15–
7.26 (m, 75 H, 15 PhH), 6.25 (d, J1,2 = 3.6 Hz, 1 H, H1), 5.14 (d,
J1,2 = 5.2 Hz, 1 H, H1), 4.96, 4.93, 4.86, 4.74 (4 d, J1,2 = 8.0 Hz, 1
H, H1), 1.95, 1.83, 1.77. 1.40 (4 CH3CO).
13C NMR (100 MHz, CDCl3): d = 170.47, 169.64, 169.44, 169.02
(4 CH3CO), 166.13, 166.12, 165.95, 165.86, 165.80, 165.72,
165.61, 165.18, 165.11, 165.09, 165.06, 164.93, 164.66, 164.65,
160.30 (15 PhCO), 106.04, 101.26, 101.25, 101.20, 101.04, 100.63
(6 C1), 92.73, 90.65, 81.35, 78.85, 77.23, 76.39, 74.96, 73.69,
72.94, 72.93, 72.81, 72.25, 72.08, 71.99, 71.78, 71.67, 71.57, 71.51,
69.87, 69.68, 69.60, 69.55, 67.76, 67.68, 67.03, 67.00, 63.18, 63.14,
62.81, 62.68 (6 C2, C3, C4, C5, C6), 22.69, 20.54, 20.31, 19.98 (4
CH3CO).
Acknowledgment
This work was supported by 863 high-tech key project of China
(2006AA10A203), the Major State Basic Research Development
Program of China (No. 2006CB101907 and No. 2003CB114407),
and the Excellent Scientist Project from the Chinese Academy of
Agricultural Sciences. Beijing municipal science and technology
project (D706005040431).
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