Efficient synthesis of a 6-deoxytalose tetrasaccharide related to the antigenic O-polysaccharide produced by Aggregatibacter actinomycetemcomitans serotype c

Article abstract of DOI:10.1016/j.carres.2010.04.009

Concise synthesis of a 6-deoxy-α-l-talose tetrasaccharide, 6-deoxy-α-l-Talp-(1→3)-6-deoxy-α-l-Talp-(1→2)-6-deoxy-α-l-Talp-(1→3)-6-deoxy-α-l-Talp, the dimer of the disaccharide repeating unit of the OPS from Aggregatibacter actinomycetemcomitans serotype c

Full text of DOI:10.1016/j.carres.2010.04.009

Carbohydrate Research 345 (2010) 1230–1234
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Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Note
Efficient synthesis of a 6-deoxytalose tetrasaccharide related to the antigenic
O-polysaccharide produced by Aggregatibacter actinomycetemcomitans
serotype c
*
Xiangyan Cai, Guanghui Zong, Yanjun Xu, Jianjun Zhang , Xiaomei Liang, Daoquan Wang
Key Lab of Pesticide Chemistry and Application Technology, Department of Applied Chemistry, China Agricultural University, Beijing 100193, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Concise synthesis of a 6-deoxy-
(1?2)-6-deoxy-a-L-Talp-(1?3)-6-deoxy-a-L-Talp, the dimer of the disaccharide repeating unit of the
OPS from Aggregatibacter actinomycetemcomitans serotype c, has been accomplished through suitable
protecting group manipulations and stereoselective glycosylation starting from commercially available
a
-
L
-talose tetrasaccharide, 6-deoxy-
a-L-Talp-(1?3)-6-deoxy-a-L-Talp-
Received 12 February 2010
Received in revised form 31 March 2010
Accepted 9 April 2010
Available online 10 May 2010
L
-rhamnose. The target oligosaccharide in the form of its p-methoxyphenyl glycoside is suitable for fur-
ther glycoconjugate formation via selective cleavage of this group.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Rhamnose
6-Deoxy-a-L-talose
Tetrasaccharide
Selective acylation
Aggregatibacter actinomycetemcomitans is
a
Gram-negative,
tionship of carbohydrates.21–24 In this paper, we wish to report
the first total synthesis of the 6-deoxy- -talose tetrasaccharide,
the dimer of the disaccharide repeating unit of the antigenic
O-polysaccharide produced by A. actinomycetemcomitans serotype
c, in the form of its p-methoxyphenyl glycoside (Fig. 1). The
p-methoxyphenyl group will, after cleavage, enable us to conjugate
the oligosaccharide with a suitable aglycon, if necessary.
non-motile, non-spore-forming, facultative anaerobic rod-shaped
bacterium that has been implicated in the etiology of localized
juvenile periodontitis,1–3 adult periodontitis,4 and severe non-oral
human infections.5 Normally, A. actinomycetemcomitans strains are
divided into six serotypes: a, b, c, d, e, and f, according to their
characteristic O-antigenic polysaccharides. These are forming the
outer part of the LPS that is connected to the cell surfaces of the
organism.6–9 These molecules are involved in pathogenic processes
and in mediating resistance to host defense mechanisms, and have
been regarded as an important factor in the virulence of many ani-
mal and plant pathogens.10 It was revealed that most of the poly-
saccharides in A. actinomycetemcomitans strains are made up of
a-L
Since tetrasaccharide 1 consists of a single monosaccharide
type, 6-deoxy-
the development of an efficient synthetic strategy for the large
scale preparation of a 6-deoxy- -talose building block, namely, p-
methoxyphenyl 6-deoxy- -talopyranoside 5. As shown in
Scheme 1, p-methoxyphenyl 2,3-O-isopropylidene- -rhamno-
L-talose, our interest was firstly concentrated on
L
a-L
a
-L
6-deoxysugars, including 6-deoxy-
rhamnose, and
-fucose.6–9 Among them, serotype c-specific poly-
saccharide antigen is a 6-deoxy- -talan composed of repeating
disaccharide units: ?3)-6-deoxy- -Talp-(1?2)-6-deoxy- -Talp-
(1?, which are acetylated at the O-2 position of the 1,3-linked 6-
deoxy- -talose is a key building block
-talose.5,11 Although 6-deoxy-
D
-talose, 6-deoxy-
L
-talose,
D
-
pyranoside 3 was prepared from L-rhamnose through a more con-
D
venient procedure than the previously reported one:25
L
-rhamnose
L
L
a-D
Me
L
L
of many biologically important glycopeptidolipids (GPLs)12–15 and
an essential component of numerous antigenic bacterial lipopoly-
saccharides (LPSs),16–20 polysaccharides consisting of only 6-
deoxytalose are rare. Synthetic studies on these antigenic O-poly-
saccharides are of considerable interests in view of developing
novel vaccine candidates and studying structure–bioactivity rela-
Me
Me
O
HO
O
O
OPMP
HO
HO
HO
O
Me
O
HO
O
HO
HO
HO
O
HO
1
* Corresponding author. Tel.: +86 10 62731115; fax: +86 10 62732219.
E-mail address: zhangjianjun@cau.edu.cn (J. Zhang).
Figure 1. Structure of the target tetrasaccharide.
0008-6215/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2010.04.009

X. Cai et al. / Carbohydrate Research 345 (2010) 1230–1234
1231
OPMP
OPMP
OPMP
OH
Me
O
Me
O
Me
O
Me
O
HO
b
c
a
HO
O
O
HO
OH
HO
O
Me2
O
OH
C
OH
OH
C
Me2
3
2
4
5
Scheme 1. Reagents and conditions: (a) (i) Py–Ac2O, 70 °C, 3 h; (ii) 4-methoxyphenol, BF3ꢀEt2O, CH2Cl2, 0–25 °C, 3 h; (iii) MeOH–MeONa; (iv) DMF, CH3C(OCH3)2CH3, cat.
TsOHꢀH2O, 30 °C, 24 h. 61% for four steps; (b) (i) DMSO, Et3N, PhOPOC12, CH2Cl2, ꢁ15 to ꢁ10 °C, 6–8 h; (ii) 50% CH3COOCH2CH3, H2O, NaBH4. 86% for two steps; (c) 70%AcOH,
3 h, 70 °C, 93%.
was acetylated with pyridine–Ac2O, after co-evaporated with tolu-
ene, the crude tetra-O-acetyl derivative was treated with p-
methoxyphenol and boron trifluoride diethyl etherate affording
aqueous workup. Subsequent deacetonation of 4 was accom-
plished by aqueous acetic acid to give p-methoxyphenyl
6-deoxy-
a
-L
-talopyranoside 5 in 93% yield. By far, the 6-deoxy-
a-
crude p-methoxyphenyl 2,3,4-tri-O-acetyl-
The crude product was deacetylated in MeOH–MeONa, providing
the p-methoxyphenyl -rhamnopyranoside as a white solid after
a
-
L
-rhamnopyranoside.
L
-talose derivative 5 was synthesized from L
-rhamnose efficiently
in an overall yield of 49%. The preparation could be easily scaled
up to 20 g of starting material, giving ca. 16 g of compound 5.
Subsequently, synthesis of the target tetrasaccharide 1 was
accomplished through transformation of 5 into suitably protected
building blocks 6 and 8, followed by stepwise glycosylation and
de-protection as depicted in Scheme 2. Kinetically controlled iso-
a-L
precipitating from EtOAc–petroleum ether (2:1). Isopropylidena-
tion of the solid in dry DMF with 2,2-dimethoxylpropane in the
presence of catalytic amounts of TsOHꢀH2O resulted in compound
3 that could be precipitated as a white solid when pouring the
reaction mixture into crushed ice. These four steps were carried
out in consecutive way without chromatographic separation, mak-
ing the preparation of 3 in large scale possible with high yield (61%
from 2).
propylidenation28 of p-methoxyphenyl 6-deoxy-
with 2,2-dimethoxypropane resulted in the C-2–OH acceptor, p-
methoxyphenyl 3,4-O-isopropylidene-6-deoxy- -talopyranoside
a-L-taloside 5
a
-L
(6), exclusively in 85% yield. The regioselective 3,4-O-isopropylide-
nation product was confirmed by the 1H NMR of the product,
showing characteristic large coupling constant for the anomeric
proton at d 5.31 ppm (J1,2 = 5.6 Hz).23,28 An important change of
conformation of the taloside takes place after formation of the
3,4-O-linked bicyclic acetal, and the molecule takes a boat or
twist-boat conformation of the ring instead of the more common
chair form of the precursors. The coupling constant between
H-1 and H-2 indicated an almost diaxial orientation of these protons,
and this phenomenon was also observed previously.23,28 Meanwhile,
Inversion of the configuration at the C-4 atom of L-rhamnose
derivative 3 was smoothly accomplished using the phenyl dichlo-
rophosphate (PDCP)-mediated Pfitzner–Moffat oxidation26 in
methylene chloride followed by NaBH4 reduction yielding p-
methoxyphenyl 2,3-O-isopropylidene-6-deoxy-a-L-talopyranoside
427 in 86% yield over two steps. In contrast to our previously re-
ported PDC oxidation procedure27 in which a chromatographic
separation was unavoidable, the crude oxidation product could
be isolated sufficiently pure to be used in the reduction after an
OCNHCCl3
OPMP
OPMP
Me
O
Me
Me
O
O
c
b
a
5
5
AllocO
OBz
AllocO
OBz
O
O
OBz
OCNHCCl3
OH
OBz
C
7
6
8
Me2
OPMP
OPMP
Me
O
Me
O
Me
O
O
O
AcO
OAc
O
O
O
e
O
C
d
O
f
C
Me2
Me2
6 + 8
Me
O
Me
O
Me
O
AcO
OBz
HO
OBz
AllocO
OBz
OBz
OBz
Me
OBz
9
11
10
Me
Me
Me
AcO
O
g
d
1
AcO
BzO
Me2C
+
10 11
BzO
O
O
AcO
O
O
O
O
O
O
OPMP
BzO
BzO
12
Scheme 2. Reagents and conditions: (a) DMF, CH3C(OCH3)2CH3, cat. TsOHꢀH2O, 30 °C, 24 h, 90%; (b) AllocCl, Py, DMAP, CH2Cl2; ꢁ15 to 0 °C, 3 h; then BzCl, 0–25 °C, 12 h; 73%;
(c) (i) 80% CH3CN, CAN, 35 °C, 0.5 h; (ii) CCl3CN, DBU, CH2Cl2, rt, 0.5 h, 81% for two steps; (d) TMSOTf, CH2Cl2, ꢁ10 °C to rt, 2 h, 88% for 9; 71% for 12; (e) MeOH–THF = 1:1,
NaBH4, Pd[P(C6H5)3]4, CH3COONH4, 90%; (f) (i) 70% AcOH, 3 h, 70 °C, 90%; (ii) Ac2O, Py; (iii) 80% CH3CN, CAN, 35 °C, 0.5 h; (iv) CCl3CN, DBU, CH2Cl2, rt, 0.5 h, 67% for four steps;
(g) (i) 70% AcOH, 3 h, 70 °C, (ii) satd NH3–MeOH, rt, 96 h, 75% for two steps.

1232
X. Cai et al. / Carbohydrate Research 345 (2010) 1230–1234
treatment of 5 with allyloxycarbonyl chloride in dichloromethane at
ꢁ10 °C in the presence of 10 equiv of pyridine and catalytic amounts
of DMAP, the C-3 hydroxyl group was selectively acylated to give p-
silica gel (200–300 mesh) with EtOAc–petroleum ether (bp 60–
90 °C) as the eluent. Solutions were concentrated at a temperature
<60 °C under diminished pressure.
methoxyphenyl 3-O-allyloxycarbonyl-6-deoxy-a-L-talopyranoside,
which was benzoylated with 3 equiv of benzoyl chloride to provide
1.2. p-Methoxyphenyl 2,3-O-isopropylidene-a-L-rhamnopyrano-
p-methoxyphenyl 3-O-allyloxycarbonyl-2,4-di-O-benzoyl-6-deoxy-
side (3)
a-L
-talopyranoside (7) in 73% yield. The 1H NMR of compound 7
was in accordance with our previously reported data.27,29 Since the
equatorially oriented C-3–OH is more reactive than the axial C-2–
OH or C-4–OH, the regioselectivity was not unexpected. Cleavage
of the p-methoxyphenyl group of 6 with ceric ammonium nitrate
(CAN) in CH3CN–H2O followed by trichloroacetimidation with
trichloroacetonitrile in the presence of DBU30 provided 3-O-allyloxy-
L-Rhamnose (2) (20.0 g, 0.11 mol) was dissolved in a mixture of
pyridine (100 mL) and Ac2O (80 mL), and the solution was stirred
at rt overnight. The solvents were evaporated in vacuo, and then
co-evaporated with toluene, providing the tetra-O-acetyl deriva-
tive as a syrup. Then to a cold (0 °C) solution of the syrup and p-
methoxyphenol (20.7 g, 0.17 mol) in dry CH2Cl2 (50 mL) was added
boron trifluoride diethyl etherate (70 mL, 0.55 mol) for 30 min.
Then, the mixture was agitated for 6 h at rt until TLC (petroleum
ether–EtOAc; 2:1) indicated that the reaction was complete. The
reaction mixture was poured into crushed ice, and the excess bor-
on trifluoride diethyl etherate was neutralized by the careful addi-
tion of NaHCO3. The organic layer was washed with water, dried
(Na2SO4), and concentrated in vacuo to provide a white solid. The
solid was dried under high vacuum for 2 h and then dissolved in
150 mL absolute MeOH, 200 mg MeONa was added to the reaction
mixture and stirred at rt for 3 h. Neutralization of the reaction mix-
ture was with acidic ion exchange resin (Amberlite IR-120 (H+),
Alfa Aesar) and the organic phase was concentrated to a volume
of 50 mL. Then 300 mL of EtOAc–petroleum ether (2:1) was added
to the mixture with vigorous stirring, and the target compound
was precipitated from the mixture as a white solid. Drying under
high vacuum for 2 h, the above-obtained product was dissolved
in dry DMF under nitrogen atmosphere, TsOH–H2O (0.32 g,
1.7 mmol) and 2,2-dimethoxylpropane (21 mL, 0.17 mol) were
added, and the mixture was stirred for 6 h at rt until completion
(petroleum ether–EtOAc; 2:1). The reaction mixture was poured
into 5%NaHCO3, and a white solid was obtained after standing for
12 h at rt, after filtrating and drying, p-methoxyphenyl 2,3-O-iso-
carbonyl-2,4-di-O-benzoyl-a-L-talopyranosyl trichloroacetimidate
(8) in 81% yield. Glycosylation of acceptor 6 with donor 8 was
accomplished within 40 min using TMSOTf as the catalyst at ꢁ5 °C,
giving the
a-linked disaccharide 9 in satisfactory yield (88%) after
column chromatography, and the configuration of the glycosyl bond
formed in the product was deduced from the corresponding coupling
constants (d 5.39 ppm, J1,2 = 1.1 Hz).
With disaccharide 9 in hand, assembly of the tetrasaccharide 12
was achieved through three steps: (1) the allyloxycarbonyl group
of 9 was successfully removed in MeOH–THF31 in the presence of
CH3COONH4, Pd[P(C6H5)3]4, and NaBH4, within 5 min without
affecting any of the other protecting groups, giving the desired
acceptor 10 in 90% yield; (2) preparation of disaccharide glycosyl
donor 11 as follows: firstly, removal of the isopropylidene ring of
10 with 70% HOAc at 70 °C for 3 h provided the triol intermediate,
then, acetylation of the intermediate with py-Ac2O provided p-
methoxyphenyl 3-O-acetyl-2,4-di-O-benzoyl-6-deoxy-
a-L-talopyr-
anosyl-(1?2)-3,4-di-O-acetyl-6-deoxy- -talopyranoside, which
a-L
was the corresponding disaccharide donor 11 through C-1 depro-
tection and trichloroacetimidation. Since the C-1 deprotection
was carried out in MeCN–H2O with the presence of CAN, transfor-
mation of the acidic liable isopropylidene-protecting group to rel-
atively stable acetyl groups was necessary; (3) TMSOTf-catalyzed
coupling reaction of disaccharide acceptor 10 with donor 11 took
place smoothly at 0 °C, giving fully protected tetrasaccharide 12
in 71% yield. The structure of 12 was confirmed by its 1H NMR
and 13C NMR spectra, showing the characteristic signals such as d
5.44, d 5.35, 5.34, and 5.32 ppm for H-1, d 98.8, 98.7, 96.9, and
96.2 ppm for C-1, and d 16.4, 16.3, 16.1, and 15.3 ppm for C-6.
The configuration of the glycosyl bond formed in the product
was concluded from the corresponding coupling constants (d
propylidene-
a-L-rhamnoside (3) was fulfilled (23.2 g, 61% over four
steps). The 1H NMR data were in accordance with the literature.25
1.3. p-Methoxyphenyl 6-deoxy-2,3-O-isopropylidene-a-L-talo-
pyranoside (4)
A solution of PhOPOCl2 (9.2 mL, 62 mmol) in i-PrOAc (18 mL)
was added dropwise over 1 h to a solution of p-methoxyphenyl
2,3-O-isopropylidene-a-L-rhamnoside (3) (11.4 g, 36.7 mmol),
DMSO (10.4 mL, 146 mmol), and TEA (25.6 mL, 184 mmol) in i-PrO-
Ac (192 mL) at ꢁ15 °C. The mixture was stirred for 1 h at ꢁ15 °C and
then poured into 1% aqueous H3P04. The aqueous phase was ex-
tracted with i-PrOAc (3 ꢂ 50 mL), and the combined organic phases
were washed with saturated aqueous NaHCO3 (50 mL) and evapo-
rated in vacuo to give p-methoxyphenyl 6-deoxy-2,3-O-isopropyli-
00 00
5.35 ppm, J 1 ,2 1.1 Hz). Finally, deisopropylidenation of 12 in
70% HOAc followed by deacylation in ammonium-saturated meth-
anol afforded the target tetrasaccharide 1 in 79% yield and its bio-
assay is in progress and will be reported in due course.
1. Experimental
dene-a-L-lyxohexopyranosid-4-ulose as a yellowish syrup. Then to
1.1. General methods
a cold (0 °C) solution of the syrup in 50% aq EtOAc was added NaBH4
(1.5 g, 42 mmol). The mixture was stirred at 0 °C for 15 min, and
TLC (petroleum ether–EtOAc; 4:1) indicated that the reaction was
complete. The aqueous solution was extracted with EtOAc
(3 ꢂ 150 mL), the extract was washed with M HCl and satd aq NaH-
CO3, dried (Na2SO4), and concentrated to give crude 4 as a syrup.
Purification of the crude product by crystallization (petroleum
ether–EtOAc; 4:1) provided 4 (9.8 g, 86% over two steps) as white
crystals. The 1H NMR data were in accordance with the literature.27
Optical rotations were determined with a Perkin–Elmer model
241-MC automatic polarimeter for solution in a 1-dm, jacketed
cell. 1H and 13C NMR spectra were recorded with Bruker DPX300
and Bruker AVANCE600 spectrometers in CDCl3 or D2O solutions.
Internal references: TMS (d 0.000 ppm for 1H), CDCl3 (d
77.00 ppm for 13C), HOD (d 4.700 for 1H). 1H NMR signals of some
compounds were assigned with the aid of COSY. Elemental analysis
was performed on a Yanaco CHN Corder MF-3 automatic elemental
analyzer. MALDI and ESI mass spectra were performed by the Insti-
tute of Chemistry of the Chinese Academy of Sciences. Thin-layer
chromatography (TLC) was performed on Silica Gel HF with detec-
tion by charring with 30% (v/v) H2SO4 in MeOH or by UV detection.
Column chromatography was conducted by elution of a column of
1.4. p-Methoxyphenyl 6-deoxy-a-L-talopyranoside (5)
Compound 4 (6.2 g, 20 mmol) was dissolved in 70% aq AcOH
(50 mL) and the solution was stirred at 70 °C for 3 h. The solvents
were evaporated in vacuo and then co-evaporated with toluene,

X. Cai et al. / Carbohydrate Research 345 (2010) 1230–1234
1233
which afforded the triol 5 (5.0 g, 93%) as a white solid after precip-
3-O-allyloxycarbonyl-2,4-di-O-benzoyl-a-L-6-deoxy-talopyrano-
itating from EtOAc–petroleum ether (2:1). ½a D25
ꢃ
ꢁ60 (c 1.0, CHCl3).
side as a foamy solid. A mixture of this compound, trichloroaceto-
nitrile (2.0 ml, 20 mmol), and 1,8-diazabicyclo[5.4.0] undecene
(DBU) (0.20 ml, 20 mmol) in dry CH2Cl2 (70 ml) was stirred for
0.5 h and then concentrated. The residue was purified by chroma-
tography with 5:1 petroleum ether–EtOAc as the eluent to give 8
1H NMR (300 MHz, CDCl3) d: 7.01–6.95 (m, 2H, Ar-H), 6.84–6.77
(m, 2H, Ar-H), 5.50 (s, 1H, H-1), 4.46 (s, 2H, 2 ꢂ OH), 4.11–4.00
(m, 4H), 3.77 (m, 1H), 3.76 (s, 3H, OCH3), 1.27 (d, 3H, J5,6 6.5 Hz,
C-CH3). HRMS calcd for C13H18O6Na (M+Na)+: 293.1001, found:
293.1030.
(2.6 g, 81%). ½a 2D5
ꢃ
ꢁ51 (c 1.0, CHCl3). 1H NMR (300 MHz, CDCl3) d:
8.81 (s, 1H, CNHCCl3), 8.15–7.20 (m, 10H, Bz-H), 6.56 (d, 1H, J1,2
1.5 Hz, H-1), 5.92 (m, 1H, CH2@HCH2OCO), 5.70 (m, 1H, H-2),
5.63 (m, 1H, H-4), 5.45 (dd, 1H, J2,3, J3,4 3.7 Hz, H-3), 5.36–5.22
(m, 2H, CH2@HCH2OCO), 4.68–4.64 (m, 2H, CH2@HCH2OCO), 4.53
(m, 1H, H-5), 1.35 (d, 3H, J5,6 6.5 Hz, H-6). Anal. Calcd for
C26H24Cl3NO9: C, 51.97; H, 4.03; N, 2.33. Found: C, 51.74; H,
4.21; N, 2.78.
1.5. p-Methoxyphenyl 6-deoxy-3,4-O-isopropylidene-a-L-talo-
pyranoside (6)
To a solution of compound 5 (4.6 g, 17 mmol) with TsOHꢀH2O
(0.048 g, 0.26 mmol) in dry DMF under an N2 atmosphere was
added 2,2-dimethoxypropane (4.1 mL) dropwise. The mixture
was allowed to stir at room temperature for 2 h when TLC (petro-
leum ether–EtOAc; 1:1) indicated that the reaction was complete.
White precipitate was formed when pouring the reaction mixture
into crushed ice. Filtration and then vacuum-drying on the filter for
1.8. p-Methoxyphenyl 3-O-allyloxycarbonyl-2,4-di-O-benzoyl-6-
deoxy-a-L-talopyranosyl-(1?2)-3,4-O-isopropylidene-6-deoxy-
a-L-talopyranoside (9)
about 1 h gave acceptor 6 (4.7 g, 90%) as a white solid. ½a D25
ꢁ20 (c
ꢃ
1.0, CHCl3). 1H NMR (300 MHz, CDCl3) d: 7.00–7.05 (m, 2H, Ar-H),
6.80–6.85 (m, 2H, Ar-H), 5.32 (d, 1H, J1,2 5.6 Hz, H-1), 4.61 (dd,
1H, J3,4 7.5 Hz, J4,5 3.4 Hz, H-4), 4.18 (dd, 1H, J2,3 2.0 Hz, J3,4
7.5 Hz, H-3), 4.00–3.92 (m, 2H, H-2, H-5), 3.77 (s, 3H, OCH3), 2.43
(s, 1H, OH), 1.54, 1.39 (2s, 6H, C(CH3)2), 1.26 (d, J5,6 6.5 Hz, 3H, C-
CH3). Anal. Calcd for C16H22O6: C, 61.92; H, 7.15. Found: C, 61.80;
H, 7.28.
To a cooled (ꢁ10 °C) solution of 6 (1.1 g, 3.6 mmol) and 8 (2.4 g,
4.0 mmol) in anhydrous, redistilled CH2Cl2 (40 mL) was added 4 Å
molecular sieves (2.0 g) and the mixture was stirred under an N2
atmosphere for 30 min. Then TMSOTf (36 lL, 0.2 mmol) was added
to the mixture. The reaction mixture was stirred at ꢁ10 °C for 0.5 h,
during which time the mixture was allowed to gradually warm to
ambient temperature. TLC (petroleum ether–EtOAc; 4:1) indicated
that the reaction was complete. Then the reaction mixture was
neutralized with Et3N (two drops) and filtrated. The filtrate was
evaporated in vacuo to give a residue, which was purified by silica
gel column chromatography (petroleum ether–EtOAc; 6:1) to give
1.6. p-Methoxyphenyl 3-O-allyloxycarbonyl-2,4-di-O-benzoyl-6-
deoxy-a-L-talopyranoside (7)
To a cold (ꢁ10 °C) solution of compound 5 (2.3 g, 8.5 mmol) in
dry CH2Cl2 (20 mL) containing dry pyridine (5.6 mL, 68 mmol) was
added slowly allyl chloroformate (0.85 mL, 8.9 mmol) in anhyd
CH2Cl2 (5 mL) under an N2 atmosphere. After complete addition,
the mixture was allowed to stir at rt for 1 h when TLC (petroleum
ether–EtOAc; 1:1) showed complete conversion of the starting
material to a faster moving spot. Then benzoyl chloride (2.2 mL,
19 mmol) in pyridine (5 mL) was added dropwise to the solution
over 30 min at ꢁ0 °C. The reaction mixture was slowly raised to
rt and stirred overnight, at the end of which time TLC (petroleum
ether–EtOAc; 2:1) indicated that the reaction was complete. The
reaction mixture was diluted with CH2Cl2 (50 mL), washed with
ice-water, M HCl, and dried (Na2SO4). The solution was concen-
trated, and purification of the residue by column chromatography
on silica gel (petroleum ether–EtOAc; 4:1) gave compound 7 (3.5 g,
disaccharide 9 (1.5 g, 88%). ½a D25
ꢃ
ꢁ73 (c 1.0, CHCl3). 1H NMR
(300 MHz, CDCl3) d: 8.14–7.17(m, 10H, Bz-H), 7.07–6.98 (m, 2H,
Ar-H), 6.87–6.84 (m, 2H, Ar-H), 5.90 (m, 1H, CH2@HCH2OCO),
5.59 (m, 1H, H-20), 5.53 (m, 1H, H-30), 5.45 (d, 1H, J1,2 6.4 Hz, H-
1), 5.39 (d, 1H, J1,2 1.1 Hz, H-1), 5.38 (m, 1H, H-4), 5.34–5.20 (m,
2H, CH2@HCH2OCO), 4.72 (dd, 1H, J2,3 2.5 Hz, J3,4 7.6 Hz, H-3),
4.63–4.59 (m, 3H, H-50, CH2@HCH2OCO), 4.17 (dd, 1H, J3,4 7.6 Hz,
J4,5 1.7 Hz, H-4), 4.15 (dd, 1H, J1,2 6.4 Hz, J2,3 2.5 Hz, H-2), 3.94
(m, 1H, H-5), 3.78 (s, 3H, CH3O), 1.56, 1.42 (2s, 6H, C(CH3)2), 1.31,
1.23 (2d, 6H, J 6.5 Hz, H-6, H-60). 13C NMR (300 MHz, CDCl3) d:
166.4, 166.1 (2 ꢂ COPh), 155.1, 153.9 (OCOO), 150.8, 118.9, 118.8,
118.5, 118.4(2), 114.7(2), 110.7 (C(CH3)2), 98.7, 96.2 (2 ꢂ C-1),
55.7 (CH3O), 26.2, 25.5 (C(CH3)2), 16.2, 15.3 (2 ꢂ C-6). Anal. Calcd
for C40H44O14: C, 64.16; H, 5.92. Found: C, 64.37; H, 5.98.
73%) as a white solid.27,29
½
a 2D5
ꢃ
ꢁ88 (c 1.0, CHCl3). 1H NMR
1.9. p-Methoxyphenyl 2,4-di-O-benzoyl-6-deoxy-
a
-L
-talopyran-
(300 MHz, CDCl3) d: 8.17–7.17 (m, 10H, Bz-H), 7.08–7.05 (m, 2H,
Ar-H), 6.87–6.84 (m, 2H, Ar-H), 5.93 (m, 1H, CH2@CHCH2OCO),
5.71 (m, 1H, H-2), 5.67 (m, 1H, H-4), 5.59–5.56 (m, 2H, H-1, H-3),
5.38–5.22 (m, 2H, CH2@HCH2OCO), 4.69–4.65 (m, 2H,
CH2@HCH2OCO), 4.46 (m, 1H, H-5), 3.78 (s, 3H, CH3O), 1.29 (d,
3H, J5,6 6.5 Hz, H-6). Anal. Calcd for C31H30O10: C, 66.18; H, 5.38.
Found: C, 66.40; H, 5.52.
osyl-(1?2)-3,4-O-isopropylidene-6-deoxy-a-L-talopyranoside
(10)
To a cooled (ꢁ5 °C) solution of compound 9 (1.2 g, 2.5 mmol) in
1:1 MeOH–THF (40 mL) was added CH3COONH4 (1.9 g, 25 mmol).
With vigorous stirring, NaBH4 (0.027 g, 0.75 mmol), Pd[P(C6H5)3]4
(0.12 g, 0.10 mmol), and NaBH4 (0.11 g, 3.0 mmol) were added in
three portions immediately one after another. One minute after
the addition of the second portion of NaBH4, TLC (petroleum
ether–EtOAc; 3:1) indicated that the reaction was complete. The
reaction mixture was concentrated under vacuum, and the residue
was dissolved in CH2Cl2 (20 mL) and washed with brine (10 mL),
then the organic phase was dried over Na2SO4. Evaporation and
purification by flash column chromatography (petroleum ether–
EtOAc; 5:1) afforded compound 10 as a white solid (1.5 g, 90%).
1.7. 3-O-Allyloxycarbonyl-2,4-di-O-benzoyl-6-deoxy-a-L-
talopyranosyl trichloroacetimidate (8)
To a solution of compound 7 (3.0 g, 5.3 mmol) in acetonitrile
(80 mL) and water (20 mL) was added CAN (11.6 g, 21.2 mmol).
The mixture was stirred for 20 min at 30 °C, at the end of which
time TLC (petroleum ether–EtOAc; 3:1) indicated that the reaction
was complete. The solvent was evaporated under diminished pres-
sure at 50 °C to give a residue, and then the residue was dissolved
in CH2Cl2 and washed with water. The organic phase was dried
(Na2SO4) and concentrated. Purification by silica gel chromatogra-
phy with 4:1 petroleum ether–EtOAc as the eluent afforded
½
a 2D5
ꢃ
ꢁ62 (c 1.0, CHCl3). 1H NMR (300 MHz, CDCl3) d: 8.12–7.22
(m, 10H, Bz-H), 7.00–6.97 (m, 2H, Ar-H), 6.87–6.84 (m, 2H, Ar-H),
5.44–5.39 (m, 3H, H-20, H-40, H-1), 5.38 (s, 1H, H-10), 4.74 (dd,
1H, J2,3 2.3 Hz, J3,4 7.6 Hz, H-3), 4.54 (m, 1H, H-50), 4.45 (t, 1H,
J3 ,4 , J4 ,5 3.8 Hz, H-30), 4.18 (dd, 1H, J3,4 7.6 Hz, J4,5 1.4 Hz, H-4),
0
0
0
0

1234
X. Cai et al. / Carbohydrate Research 345 (2010) 1230–1234
4.15 (dd, 1H, J2,3 2.3 Hz, J1,2 6.4 Hz, H-2), 3.95 (m, 1H, H-5), 3.79 (s,
3H, CH3O), 1.56, 1.42 (2s, 6H, C(CH3)2), 1.32, 1.23 (2d, 6H, J 6.5 Hz,
H-6, H-60). Anal. Calcd for C36H40O12: C, 65.05; H, 6.07. Found: C,
64.82; H, 6.31.
uene. The crude mixture thus obtained was purified by flash
chromatography using petroleum ether–EtOAc (3:1) to get a white
foam. Then the white foam was dissolved in satd NH3–MeOH
(40 mL). After 96 h at rt, the reaction mixture was concentrated,
and the residue was purified by chromatography on Sephadex
LH-20 (MeOH) to afford 1 (0.21 g, 75% over two steps) as a foamy
1.10. p-Methoxyphenyl 3-O-acetyl-2,4-di-O-benzoyl-6-deoxy-
-talopyranosyl-(1?2)-3,4-di-O-acetyl-6-deoxy- -talopyran-
osyl trichloroacetimidate (11)
a-
L
a
-L
solid. ½a 2D5
ꢃ
ꢁ70 (c 1.0, H2O). 1H NMR (300 MHz, D2O) d: 6.99–6.86
(2d, 4H, J 9.0 Hz, C6H4OCH3), 5.40, 5.13, 5.06, 5.02 (4s, 4H, 4 ꢂ H-
1), 4.11–3.87 (m, 13H), 3.71 (s, 3H, CH3O), 3.69–3.66 (m, 3H),
1.20, 1.18, 1.16, 1.13 (4d, 12H, J 6.5 Hz, 4 ꢂ C-CH3). 13C NMR
(300 MHz, D2O) d: 157.2, 152.1, 121.0(2), 117.3(2) (Ar-C), 105.9,
105.7, 101.2, 99.4 (4 ꢂ C-1), 57.9 (C6H4OCH3), 18.0(2), 17.9, 17.8
(4 ꢂ C-CH3). HRMS calcd for C31H48O18Na (M+Na)+: 731.2738,
found: 731.2716.
Deisopropylidenation of compound 10 (1.3 g, 2.0 mmol) was
carried out in 70% aq AcOH (30 mL) at 70 °C for 3 h, at the end of
which time TLC (petroleum ether–EtOAc; 2:1) indicated comple-
tion of the reaction. The mixture was concentrated under dimin-
ished pressure and then co-evaporated with toluene (2 ꢂ 20 mL)
to give the crude product. The crude product was then acetylated
with Ac2O (5 mL) in pyridine (20 mL) without purification to ob-
tain its acetylated derivative. The disaccharide trichloroacetimi-
date 11 was prepared by following the same procedure as
described above for the preparation of compound 8. After purifica-
tion by column chromatography on silica gel (petroleum ether–
EtOAc; 4:1), 11 (0.97 g, 66% over four steps) was obtained as a
Acknowledgments
This work was supported by the Innovation Experiment Pro-
gram for University Students of CAU (No. 0810010929), the Na-
tional Basic Research Program of China (2010CB126105), and
NSFC (No. 20902108) of China.
white foam. ½a 2D5
ꢃ
ꢁ43 (c 1.0, CHCl3). 1H NMR (300 MHz, CDCl3) d:
8.68 (s, 1H, CNHCCl3), 8.18–7.15 (m, 10H, Bz-H), 6.47 (d, 1H, J1,2
References
1.4 Hz, H-1), 5.62 (t, 1H, J2 ,3 , J3 ,4 3.8 Hz, H-30), 5.55 (m, 1H, H-
20), 5.37 (m, 1H, H-4), 5.32–5.30 (m, 2H, H-10, H-40), 5.30 (t, 1H,
J2,3, J3,4 3.6 Hz, H-3), 4.55 (m, 1H, H-5), 4.39 (m, 1H, H-50), 4.12
(m, 1H, H-2), 2.28, 2.10, 2.00 (3s, 9H, 3 ꢂ CH3CO), 1.34, 1.27 (2d,
0
0
0
0
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3,4-O-isopropylidene-6-deoxy- -talopyranoside (12)
a-L-
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Glycosylation between disaccharide acceptor 10 (0.40 g,
0.60 mmol) and donor 11 (0.77 g, 0.96 mmol) was accomplished
by following the same procedure as described above for the prep-
aration of disaccharide 9. After purification, tetrasaccharide 12
(0.94 g, 74%) was afforded as a white foamy solid. ½a D25
ꢁ10 (c
ꢃ
1.0, CHCl3). 1H NMR (300 MHz, CDCl3) d: 8.17–7.16 (m, 20H, Bz-
H), 7.02–6.98 (m, 2H, Ar-H), 6.88–6.85 (m, 2H, Ar-H), 5.61 (t, 1H,
J
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3.7 Hz, H-3000), 5.54–5.45 (m, 3H, H-40, H-4000, H-2000),
2000,3000
3000,4000
5.44 (d, 1H, J1,2 6.4 Hz, H-1), 5.35 (d, 1H, J 1 ,2 1.1 Hz, H-100), d
00 00
5.34 (d, 1H, J1 ,2 0.8 Hz, H-10), 5.31 (m, 1H, H-20), 5.32 (d, 1H, J
0
0
1000,2000
1.0 Hz, H-1000), 5.19 (m, 1H, H-400), 4.95 (m, 1H, J 2 ,3 , J 3 ,4 , 3.6 Hz,
00 00
00 00
H-300), 4.73 (dd, 1H, J2,3 2.4 Hz, J3,4 7.5 Hz, H-3), 4.56–4.51 (m, 2H,
0
0
0
0
0
2 ꢂ H-5), 4.45 (t, 1H, J2 ,3 , J3 ,4 , 3.9 Hz, H-3 ), 4.28 (m, 1H, H-5),
4.18 (dd, 1H, J3,4 7.5 Hz, J4,5 1.7 Hz, H-4), 4.15 (dd, 1H, J1,2 6.4 Hz,
J2,3 2.4 Hz, H-2), 3.98 (m, 1H, H-5), 3.79 (s, 3H, CH3O), 3.66 (m,
1H, H-200), 2.23, 1.97, 1.92 (3s, 9H, 3 ꢂ CH3CO), 1.58, 1.42 (2s, 6H,
C(CH3)2), 1.38, 1.34, 1.24, 1.20 (4d, 12H, J 6.5 Hz, 4 ꢂ C-CH3). 13C
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166.4, 166.2, 165.9 (4 ꢂ COPh), 110.6 (C(CH3)2), 98.8, 98.7, 96.9,
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1.12. p-Methoxyphenyl 6-deoxy-
deoxy- -talopyranosyl-(1?3)-6-deoxy-
(1?2)-6-deoxy- -talopyranoside (1)
a
-
L
-talopyranosyl-(1?2)-6-
a-L
a-L-talopyranosyl-
a-L
Compound 12 (0.51 g, 0.39 mmol) was dissolved in 70% aq
AcOH (25 mL) and the solution was stirred at 70 °C for 3 h. The sol-
vents were evaporated in vacuo and then co-evaporated with tol-