Synthesis of a derivative of a pentasaccharide repeating unit of the O-antigenic polysaccharide of the bacterium Klebsiella pneumoniae O3 as a benzoylated 2-methoxycarbonylethyl thioglycoside

Article abstract of DOI:10.1007/s11172-010-0033-3

Block synthesis of a fully benzoylated derivative of the pentasaccharide α-d-Manp-(1→3)-α-d-Manp-(1→2)-α-d-Manp-(1→2) -α-d-Manp-(1→2)-α-d-Manp-SCH₂CH₂CO ₂Me, the glycoside of the repeating unit of the O-antigenic polysaccharide of the bacterium Klebsiella pneumoniae O3, was performed.

Full text of DOI:10.1007/s11172-010-0033-3

Russian Chemical Bulletin, International Edition, Vol. 58, No. 2, pp. 457—467, February, 2009
457
Synthesis of a derivative of a pentasaccharide repeating unit
of the Oꢀantigenic polysaccharide of the bacterium
Klebsiella pneumoniae O3
as a benzoylated 2ꢀmethoxycarbonylethyl thioglycoside*
P. I. Abronina,a K. I. Galkin,b L. V. Backinowsky,a and A. A. Gracheva
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499)135 5328. Eꢀmail: polinaꢀabronina@yandex.ru
bHigher Chemical College of the Russian Academy of Sciences,
9 Miusskaya pl., 125047 Moscow, Russian Federation.
Block synthesis of a fully benzoylated derivative of the pentasaccharide αꢀDꢀManpꢀ(1→3)ꢀ
αꢀDꢀManpꢀ(1→2)ꢀαꢀDꢀManpꢀ(1→2)ꢀαꢀDꢀManpꢀ(1→2)ꢀαꢀDꢀManpꢀSCH2CH2CO2Me, the
glycoside of the repeating unit of the Oꢀantigenic polysaccharide of the bacterium Klebsiella
pneumoniae O3, was performed.
Key words: pentasaccharide, mannooligosaccharides, repeating unit of the Oꢀantigenic
polysaccharide of the bacterium Klebsiella pneumoniae O3, block synthesis, NMR spectroscopy.
as thioglycoside donors for the construction of neoglycoꢀ
peptides using automated solidꢀphase peptide synthesis10,11
and glycodendrimers with the polypropyleneimine core
and peripheral galactose sulfate residues.12 An attractive
feature of Sꢀglycosides is their higher hydrolytic stability
compared to Oꢀglycosides in a living organism. However,
no data on the possible use of 3ꢀmercaptopropionic acid
glycosides as glycosyl acceptors have been reported.
Here we describe the synthesis of a derivative of linear
mannopentaoside having the structure of the repeating unit
of the Oꢀantigenic polysaccharide of Klebsiella pneumoniae
O3 as the Sꢀglycoside of 3ꢀmercaptopropionic acid for its
subsequent transformation to neoglycoconjugates.
Lipopolysaccharide of the bacterium K. pneumoniae
O3 (see Ref. 13) is an effective adjuvant (compound that
enhance the immune response of the organism to antiꢀ
gens). The Oꢀspecific polysaccharide of this lipopolysacꢀ
charide responsible for the adjuvant effect is a linear reguꢀ
lar αꢀDꢀmannan composed of pentasaccharide repeating
units with the 1→2 and 1→3 linkages.14 The same
structure is inherent in Oꢀantigenic polysaccharides of
Escherichia coli O9 (see Ref. 15) and Hafnia alvei PCM
1223 (see Ref. 16); as regards the adjuvant action, the
lipopolysaccharide from E. coli O9 is comparable with
the Klebsiella O3 lipopolysaccharide (see Ref. 17).
Covalent bonding of monoꢀ or oligosaccharide fragꢀ
ments of natural highꢀmolecularꢀweight carbohydrates to
natural or synthetic polymers is a popular method for the
synthesis of neoglycoconjugates that combine specific bioꢀ
logical activity of the carbohydrate component and high
molecular weight of the carrier.1 If immobilization is to be
performed for a synthetic oligosaccharide, it is desirable
to use its glycoside containing a certain function, for
example, a carboxy group, in the аglycone.
Oligosaccharide glycosides of 9ꢀhydroxynonanoic acid
(as the methyl ester) have become popular.2 The conjuꢀ
gates were prepared by converting the ester to hydrazide
and then to reactive acyl azide, which was employed
to acylate free amino groups of a protein. Glycosides of
lower and higher homologs of this spacer (4ꢀhydroxyꢀC4ꢀ,
7ꢀhydroxyꢀC7ꢀ, 12ꢀhydroxyꢀC12ꢀ, 15ꢀhydroxyꢀC15ꢀacid,3
6ꢀhydroxyꢀC6ꢀacid4) and its heteroatomic analogs, esters
of 10ꢀhydroxyꢀ5,8ꢀdioxadecanoic, 9ꢀhydroxyꢀ6ꢀoxoꢀ7ꢀazaꢀ
nonanoic, 8ꢀhydroxyꢀ3,6ꢀdioxaoctanoic, and 6ꢀhydroxyꢀ
4ꢀthiahexanoic acid,3—7 were also synthesized. The latter
were obtained by the reaction of 2ꢀbromoethyl glycosides
with methyl 3ꢀmercaptopropionate. Glycosylation of the
proper 3ꢀmercaptopropionic acid with fully acetylated
monoꢀ and disaccharides in the presence of Lewis acids
gave the corresponding thioglycosides,8,9 which were used
The synthesis of the repeating unit of the Oꢀantigenic
polysaccharide of K. pneumoniae O3 as a reducing pentaꢀ
saccharide (A) was reported in the literature.18
* On the occasion of the 75th anniversary of the foundation
of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 448—458, February, 2009.
1066ꢀ5285/09/5802ꢀ0457 © 2009 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
Abronina et al.
Scheme 1
A
This synthesis was based on the use of partly Oꢀbenꢀ
zylated derivatives of monoꢀ and oligosaccharides as
glycosyl donors and glycosyl acceptors; the final synthetic
stage is the removal of Oꢀbenzyl protecting groups by
catalytic hydrogenolysis. This is inapplicable to thioglyꢀ
cosides, hence, the route to pentasaccharide derivative
that we propose should not include hydrogenolysis.
Hence, other protecting groups for monosaccharides
should be used.
A number of publications describe the targeted prepaꢀ
ration of linear and branched oligomannosides, mainly as
methyl and allyl glycosides (see, for example, a review19).
Recently,20 oligomannosides with an аglycone containing
a free amino group were synthesized; they were effectively
converted to conjugates with bovine serum albumin.
Retrosynthetic analysis of the target pentasaccharide
derivative suggests the following synthetic route: stepꢀ
wise construction of the 1→2ꢀlinked trisaccharide and
1→3ꢀlinked disaccharide and their coupling (Scheme 1).
The presence of 1→2 and 1→3 intermonomer bonds
in the pentasaccharide molecule allows the use of two
types of building blocks for the synthesis
Scheme 2
where R1 is a “temporary” protecting group at O(2) or
O(3), R2 is a “permanent” protecting group, and Х is a
leaving group of the glycosyl donor or an аglycone in the
glycosyl acceptor. Since the Oꢀacetyl protecting group in
carbohydrates can selectively be removed in the presence
of Oꢀbenzoyl groups by mild acid methanolysis,21 we
decided to use this combination of protecting groups for
the assembly of oligosaccharide structures.
Thus a possible precursor of the 2ꢀsubstituted
mannose residue in oligosaccharides is 1,2ꢀdiꢀOꢀacetylꢀ
3,4,6ꢀtriꢀOꢀbenzoylꢀDꢀmannopyranose, which is easily
obtained from Dꢀmannose (Scheme 2).
Reagents: i. 1) BzCl, pyridine; 2) HBr/AcOH;
ii. NaBH4/MeCN; iii. 1) 90% CF3CO2H; 2) Ac2O, pyridine.
The key step of this route, namely, the conversion of
readily accessible perꢀOꢀbenzoylꢀαꢀDꢀmannopyranosyl
bromide to 1,2ꢀOꢀbenzylidene derivative by treatment with
sodium borohydride in acetonitrile at room temperature,
i.e., under conditions described previously,22 or on heatꢀ

Mannopentaoside
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
459
Scheme 3
Reagents: i. BzCl, pyridine; ii. 80% AcOH, reflux; iii. PhC(OAlk)3 (Alk = Me or Et), TsOH, MeCN;
iv. 90% CF3CO2H; v. Ac2O—AcOH, H2SO4.
ing,23 smoothly gave crystalline benzylidene derivative 1
in high yield. The structure of this previously unknown
compound followed unambiguously from 1H and 13C NMR
spectra. A comparison of the chemical shifts of the acetal
H atoms in the 1H NMR spectra of compound 1 (δH 6.03),
3,4ꢀdiꢀOꢀacetylꢀ1,2ꢀOꢀ[(R)ꢀbenzylidene]ꢀβꢀLꢀrhamnoꢀ
pyranose (δH 5.91),22 and 3,4ꢀdiꢀOꢀacetylꢀ1,2ꢀOꢀ[(S)ꢀ
benzylidene]ꢀβꢀLꢀrhamnopyranose (δH 6.36)22 provides
the conclusion of (S)ꢀconfiguration of the new chiral cenꢀ
ter, i.e., the exoꢀposition of the acetal H atom. Data from
the difference 1D ROESY spectrum confirm this concluꢀ
sion: preꢀirradiation of the proton signal at δH 6.03 (acetal
H atom) induces enhancement of the proton signal at
δH 4.74 (H(2)). Judging by the spin—spin coupling
constants of the ring H atoms, the pyranose ring has the
4C1ꢀconformation.
version to glycosyl bromide and then to 1,2ꢀOꢀethylidene
derivative by a known procedure,22 saponification of the
Oꢀacetyl groups, Oꢀbenzoylation, acidꢀinduced deacetalꢀ
ation, and Oꢀacetylation of 1,2ꢀdiol.
It was decided to use isomeric 1,3ꢀdiꢀOꢀacetylꢀ2,4,6ꢀ
triꢀOꢀbenzoylꢀDꢀmannopyranose (3) for introducing
3ꢀsubstituted Dꢀmannose residue. Known26 methyl
2,3ꢀOꢀisopropylideneꢀαꢀDꢀmannopyranoside (4) served as
the starting compound for its synthesis. By simple operaꢀ
tions (benzoylation, deacetonation, transꢀorthoesterifiꢀ
cation, and regiospecific27 hydrolysis), this compound
was converted to methyl 2,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannoꢀ
pyranoside (5), which was then subjected to acetolysis
(Scheme 3). The structure of the acetolysis product (3)
was established unambiguously by spectroscopic and
analytical data.
Acid hydrolysis of acetal 1 and acetylation of 1,2ꢀdiol
thus formed (Ac2O in pyridine) gave the target diacetate 2
as an anomeric mixture (~2.5 : 1, 1H and 13C NMR data).
The major component is the αꢀanomer, as the signals of
its C(3) and C(5) atoms are located in the higher field
than the signals of the same atoms of the minor βꢀanomer
(cf. Ref. 24). The spin—spin coupling constants of the
vicinal H atoms of compound 2 (and other monoꢀ and
oligosaccharide derivatives) have standard values:
H(1) resonates as a broadened singlet or doublet with
J1,2 ≈ 2 Hz, the H(2) atom resonates as a broadened
singlet or broadened doublet, H(3) forms a doublet of
doublets with J2,3 ≈ 3, J3,4 ≈ 10 Hz, and H(4) is a triplet
with J4,3 = J4,5 ≈ 10 Hz.
The proposed route to tribenzoate 5 appears more
effective than the approaches comprising selective benꢀ
zoylation, with benzoyl cyanide (see Refs 28, 29), of
methyl 4,6ꢀOꢀbenzylideneꢀαꢀDꢀmannopyranoside or
methyl 2,4ꢀdiꢀOꢀbenzoylꢀαꢀDꢀmannopyranoside whose
synthesis was reported previously.30
Acetolysis of the lastꢀmentioned methyl glycoside was
also investigated.30 Treatment with an Ac2O—AcOH—
H2SO4 mixture (100 : 50 : 3) at room temperature resulted
only in 3,6ꢀdiꢀOꢀacetylation; at 40 °C, smooth replaceꢀ
ment of the MeO group by the AcO group in high yield
took place. Under the same conditions, acetolysis of
methyl glycoside 5 gave 1,3ꢀdiacetate 3 in ~90% yield.
1,2ꢀDiacetate 2 was made to react with 3ꢀmercaptoꢀ
propionic acid in the presence of BF3•Et2O under therꢀ
modynamic control (16 h, ~20 °C) and the thiolysis
product was treated with hydrogen chloride in methanol.
The αꢀanomer of the same compound was reported.25
It was synthesized by a longer route that comprised the
preparation of Dꢀmannopyranose pentaacetate, its conꢀ

460
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
Abronina et al.
Scheme 4
Data from NMR spectra unambiguously prove the
structure of this compound. In particular, the relatively
highꢀfield position of the H(2) signal in the 1H NMR
spectrum (δH(2) 4.44, cf. δH(2) 5.55 in the spectrum of the
acetate) attested to the presence of a free hydroxy group at
O(2), while lowꢀfield signals for H(3), H(4), and H(6)
implied that the benzoyl groups at the corresponding
oxygen atoms have been retained. The anomeric C atom
of thiomannoside 6 appeared as a higherꢀfield signal
(δC 84.7) than the C(1) atom of Oꢀmannosides (δC ~100);
we used this feature in interpreting the NMR spectra of
the thioglycosides of the oligosaccharides obtained subꢀ
sequently. The spectra exhibited also signals for the
CO2CH3 group (δH 3.70, δC 171.9 and 51.8).
1,2ꢀDiacetate 2 was converted to the corresponding
mannosyl bromide by the conventional route. This
product was used as the glycosyl donor in the glycosylation
of acceptor 6 in the presence of silver trifluoromethaneꢀ
sulfonate (triflate), the yield of disaccharide 7 was ~70%. The
Oꢀacetyl group of the disaccharide was removed selectively;
however, the yield of product 8 was rather low (~40%).
Glycosylation of acceptor 8 under the same condiꢀ
tions as in the synthesis of disaccharide 7 afforded fully
protected trisaccharide 9 in a relatively high yield (82%).
OꢀDeacetylation gave the target trisaccharide glycosyl
acceptor, compound 10 (Scheme 5).
Reagents: i. HSCH2CH2CO2H, BF3•Et2O;
ii. HCl/MeOH; iii. HSCH2CH2CO2Me, BF3•Et2O
This resulted in esterification of the carboxyl group and
selective Oꢀdeacetylation. The target thioglycoside 6
(primary glycosyl acceptor) was isolated by column chroꢀ
matography in 42% yield (Scheme 4). The same product
was obtained in the reaction of diacetate 2 with methyl
3ꢀmercaptopropionate followed by Oꢀdeacetylation.
Scheme 5
Reagents: i. HBr/AcOH; ii. HCl/MeOH.

Mannopentaoside
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
461
The glycosylation pattern (the formation of 1→2ꢀglyꢀ
cosidic bonds) followed from NMR data, in particular,
from the downfield shift of the C(2) and C(2´) signals in
the 13C NMR spectra and the highꢀfield position of the
benzoylꢀαꢀDꢀmannopyranoside under the action of PdCl2
in MeOH; the H NMR spectral data for the compound
1
we synthesized are similar to those reported. The same
publication32 gives characterization of disaccharide deꢀ
rivative 13. The [α]D value of our glycoside 13 (–34.6) is
similar to the reported value (–42.6). Relying on the analyꢀ
sis of the COSY spectrum (Fig. 1), we changed the earꢀ
lier32 assignment of the signals of H(1a,b), H(2a,b), and
H(4a,b) protons in the 1H NMR spectrum (Table 1).
The final step of the synthesis was coupling of glycosyl
acceptor 10 (trisaccharide) with glycosyl donor 16 (disacꢀ
charide). This reaction was carried out in the presence of
silver triflate to give the target pentasaccharide derivative
17 in 43% yield (Scheme 7).
The structure of the condensation product (17) folꢀ
lowed from spectroscopic data. The ESI mass spectrum
exhibited an ion peak with m/z 1320.9, which corꢀ
responded to [M + 2 Na]2+ of the protected pentasacꢀ
charide (calculated for z = 2, C146H122O43SNa2 (2594.71 +
+ 2•22.99) : 2 = 1320.345).
The 1H and 13C NMR signals were assigned (see Tables
1 and 2) by means of 2D NMR spectroscopy (COSY,
TOCSY, HSQC); the HMBC and ROESY procedures
provided unambiguous proof for the types of linkage (one
1→3ꢀ and three 1→2ꢀlinkages) and the sequence of
monosaccharide units in the chain. Thus the assumed
sequence is supported by the presence of δH/δC correlaꢀ
tion peaks between the monosaccharide residues in the
HMBC spectrum (δ): 5.33 (H(1e))/75.67 (C(3d)), 5.00
(H(1d))/77.48 (C(2c)), 5.33 (H(1c))/76.50 (C(2b)) и 5.45
1
H(2) and H(2´) signals in the H NMR spectra of disacꢀ
charide 7 and trisaccharide 9, respectively. Deacetylation
of the glycosylation products (7 → 8; 9 → 10) was accomꢀ
panied by an upfield shift of the signals of H(2´) and
1
H(2″) in the H NMR spectra and a downfield shift of
the signals of C(2´) and C(2″) in the 13C NMR spectra
of diꢀ and trisaccharide glycosyl acceptors 8 and 10.
It was found31 that the signals for the carbon atoms of Oꢀ
and Sꢀmannosides with the same pattern of substitution
(except for the signals for the anomeric carbons) occur in
similar spectral regions. Analysis of the 13C NMR spectra of
diꢀ and trisaccharides showed similarity of the chemical shifts
of the characteristic C(3) and C(5) atoms, which is indicaꢀ
tive of the same αꢀconfiguration of the anomeric centers.
For constructing the 1→3ꢀlinked disaccharide fragment
of the pentasaccharide, 1,3ꢀdiacetate 3 was converted to
pꢀmethoxyphenyl αꢀglycoside (11), the 3ꢀOꢀacetyl group
was selectively removed (→ 12), and the second mannoꢀ
pyranose residue was introduced. The oxidative removal
of the аglycone, pꢀmethoxyphenyl group, in the glycoside
of disaccharide 13 by treatment with cerium ammonium
nitrate resulted in reducing disaccharide 14, which was
converted to disaccharide glycosyl donor (→ 15 → 16) by
a standard procedure (Scheme 6).
Compound 12 has been obtained previously32 by
deallylation of 4ꢀmethoxyphenyl 3ꢀOꢀallylꢀ2,4,6ꢀtriꢀOꢀ
Scheme 6
Reagents: i. pꢀMeOC6H4OH, BF3•Et2O; ii. HCl/MeOH; iii. (NH4)2Ce(NO3)6, MeCNꢀH2O; iv. Ac2O/pyridine;
v. HBr/AcOH.

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Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
Abronina et al.
Scheme 7
1
Table 1. Data of the H NMR spectra of derivatives of diꢀ and trisaccharides 7—10, 13—15 and pentasaccharide 17
Comꢀ
pound
Residue
δ
Н(1)
Н(2)
Н(3)
Н(4)
Н(5)
Н(6)
Н(6´)
7
8
9
a
b
5.70 (br.s)
5.13 (br.s)
4.51 (m)
5.70 (br.s)
5.79 (dd)
5.91 (m)
6.03 (t)
5.90 (t)
4.79 (ddd)
4.60 (m)
4.66 (dd)
4.60 (m)
4.51 (m)
4.59 (m)
4.58 (m) 4.51 (m)
a
b
5.66 (br.s)
5.14 (br.s)
4.51 (m)
4.46 (br.s)
5.70 (dd)
5.77 (dd)
5.98 (t)
5.91 (t)
4.75 (ddd)
4.55 (m)
a
b
c
5.71 (br.s)
5.49 (br.s)
4.96 (br.s)
4.55 (br.s)
4.53 (br.s)
5.64 (br.t)
5.73 (m)
6.01 (m)
5.87 (dd)
6.00 (m)
6.07 (t)
5.83 (t)
4.81 (ddd)
4.65 (m)
4.46 (m)
4.68 (m)
4.62 (m)
4.29 (dd)
4.62 (m)
4.58 (m)
4.16 (dd)
10
13
a
b
c
5.63 (br.s)
5.44 (br.s)
4.93 (br.s)
4.46 (br.s)
4.51 (br.s)
4.37 (br.s)
5.67 (dd)
5.89 (dd)
5.68 (dd)
5.96 (t)
5.99 (t)
5.78 (t)
4.75 (ddd)
4.57 (m)
4.37 (m)
4.19 (dd)
4.06 (dd)
a
*
b
*
5.68 (br.s)
5.42
5.41 (br.s)
5.69
5.86 (br.s)
5.36
5.35 (br.s)
5.87
4.84 (dd)
4.84
5.72 (dd)
5.72
6.03 (t)
6.01
5.99 (t)
6.05
4.44 (m)
4.62 (m)
4.46 (m)
4.52 (br.dt)
4.59 (br.d)
4.36 (dd)
14
a
b
5.50 (br.s)
5.33 (br.s)
5.72 (br.s)
5.41 (br.s)
4.73 (br.d)
5.70 (dd)
6.08 (t)
5.98 (t)
4.52 (m)
4.52 (m)
4.73 (br.d)
4.62 (br.d)
4.39 (dd)
4.34 (dd)
15
17
a
b
a
b
c
6.38 (d)
5.70 (m)
5.35 (d)
4.65 (dd)
5.70 (m)
5.74 (dd)
5.85 (dd)
5.84 (dd)
4.65 (m)
5.70 (dd)
6.11 (t)
6.01 (t)
5.99 (t)
6.02 (t)
5.98 (t)
5.97 (t)
6.10 (t)
4.35 (m)
4.51 (m)
4.79 (m)
4.65 (m)
4.41 (m)
4.25 (m)
4.44 (m)
4.69 (dd)
4.56 (m)
4.65 (m)
4.58 (m)
4.35 (dd)
4.48 (m)
4.42 (dd)
4.61 (dd)
5.37 (br.s)
5.72 (br.s)
5.45 (br.s)
5.33 (br.s)
5.00 (br.s)
5.33 (br.s)
4.58 (m)
4.63 (br.d)
4.52 (br.s)
5.72 (m)
5.38 (br.s)
4.23 (dd)
4.33 (dd)
d
e
4.19 (br.s)
4.52 (br.d)
* Data from Ref. 32.
Note. Other signals, δ: 2.1 (s, CH3CO), 2.6 (m, SCH2), 2.9 (m, CH2COOMe), 3.7 (s, C6H4OCH3, CO2CH3). Spin—spin coupling
constants: J1,2 ≈ 2 Hz, J2,3 ≈ 3 Hz, J3,4 ≈ 10 Hz, J4,5 ≈ 10 Hz, J5,6 ≈ 3 Hz, J5,6´ ≈ 4 Hz, and J6,6´ ≈ 12 Hz.
δ
H(1)/δC(3) and δH(1)/δC(5) correlation peaks of particular
(H(1b))/78.00 (C(2a)). The spin—spin coupling constants
1JH(1),C(1)O = 175 Hz and 1JH(1),C(1)S = 169 Hz (see Ref. 33)
pointed to the αꢀconfiguration of all anomeric centers.
The same conclusion follows from the presence of intense
monosaccharide residues [5.72/71.00 and 5.72/69.46 (unit
a), 5.45/71.26 and 5.45/69.89 (unit b), 5.33/70.69 and
5.33/69.73 (unit c), 5.00/75.67 and 5.00/69.53 (unit d)]

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463
δ
3.6
3.8
4.0
4.2
4.4
4.6
4.8
5.0
5.2
5.4
5.6
5.8
6.0
6.2
6.4 6.2 6.0 5.8 5.6 5.4 5.2 5.0
4.8 4.6 4.4 4.2 4.0
3.8 3.6
δ
Fig. 1. Fragment of the COSY spectrum of disaccharide derivative 13.
Table 2. 13C NMR data for derivatives of diꢀ and trisaccharides 7—10, 13—15 and pentasaccharide 17
Comꢀ
pound
Residue
δ
С(1)
С(2)
С(3)
С(4)
С(5)
С(6)
7
8
9
a
b
a
b
a
b
c
a
b
c
a
b
a
b
a
b
a
b
c
84.25
99.50
84.27
101.52
84.13
99.86
99.56
84.32
100.08
101.72
96.44
99.66
92.21
99.44
91.8
77.85
69.48
77.73
69.38
77.42
77.42
69.32
77.39
77.39
69.68
71.72
70.23
72.21
70.19
72.2
71.12
69.49
71.20
71.59
71.20
70.25
69.42
72.19
70.76
71.26
76.23
69.32
75.62
69.34
77.3
67.60
67.23
67.52
67.03
67.56
67.36
66.91
67.69
67.41
66.85
68.37
66.51
68.48
66.59
69.3
69.49
69.88
69.33
69.82
69.22
69.60
69.42
69.36
69.46
69.25
69.78
69.48
68.86
69.59
72.1
63.56
63.44
63.58
63.58
63.43
63.73
63.21
63.58
63.89
63.46
62.99
62.64
62.79
62.66
64.1
10
13
14
15
17
100.9
84.17
100.37
100.43
99.55
99.34
71.7
71.0
67.7
71.5
64.1
78.00
76.50
77.48
71.34
70.10
71.00
71.26
70.69
75.67
69.46
67.29*
67.23*
67.90**
67.95**
66.11
69.46
69.89
69.73
69.53
69.46
63.72
63.72
63.54
62.62
62.00
d
e
* The assignment may be opposite. ** The assignment may be opposite.
Note. Other signals, δ: 26.6 (SCH2), 34.6 (CH2CO2CH3), 55.6 (C6H4OCH3), 51.8 (CO2CH3).

464
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
Abronina et al.
saturated aqueous solution of NaHCO3, and the solvent was
evaporated. Chromatography gave 0.895 g (97%) of 1,2ꢀdiacetate
2. 1H NMR, δ: 6.25 (d, 0.72 H, H(1α), J1,2 = 1.4 Hz); 6.15
(br.s, 0.28 H, H(1β)); 6.05 (t, 0.72 H, H(4α), J4,3= J4,5 = 9.9 Hz);
5.85 (t, 0.28 H, H(4β), J4,3 = J4,5 = 9.9 Hz); 5.80 (dd, 0.72 H,
H(3α), J3,2 = 3.3 Hz, J3,4 = 10.2 Hz); 5.75 (br.d, 0.28 H, H(2β),
J = 2.7 Hz); 5.65 (dd, 0.28 H, H(3β), J3,2 = 3.1 Hz, J3,4 = 9.9 Hz);
5.55 (br.d, 0.72 H, H(2α), J = 2.1 Hz); 4.64 (m, 1 H, H(6α),
H(6β)); 4.53 (dd, 0.28 H, H(6´β), J6 ,5 = 5.4 Hz, J6 ,6α = 12.2 Hz);
in the HMВC spectrum (the H(1)—C(1)—C(2)—C(3)
and H(1)—C(1)—O—C(5) dihedral angles are 180°).
Thus, we synthesized a functionalized thioglycoside
of the protected pentasaccharide with the structure of the
chemical repeating unit of the Oꢀantigenic polysacchaꢀ
ride of the bacterium Klebsiella pneumoniae O3.
Experimental
β
β
4.55—4.45 (m, 1.44 H, H(5α), H(6´α)); 4.25 (ddd, 0.28 H,
H(5β), J5,6α = 3.1 Hz). 13C NMR, δ: 90.59 (C(1α, 1β)); 73.28
(C(5β)); 71.24 (C(3β)); 70.84 (C(5α)); 69.49 (C(3α)); 68.70
(C(2α)); 68.37 (C(2β)); 66.51 (C(4β)); 66.43 (C(4α)); 63.06
(C(6β)); 62.82 (C(6α)).
Optical rotation was measured in CH2Cl2 on a PUꢀ07
polarimeter (Russia) at ~20 °C. The melting points were
measured on a Koffler hot stage. ESI mass spectrum was
recorded on an LCQ Finnigan MAT instrument. NMR spectra
were measured on Bruker ACꢀ200, Bruker AMꢀ300, Bruker
DRXꢀ500, and Avance II 600 spectrometers in CDCl3. The
1H NMR chemical shifts were referred to the residual CHCl3
signal (δH 7.27), 13C{1H} NMR chemical shifts were referred to
the CDCl3 signal (δ 77.0); the most important signals are
presented. Data of theCNMR spectra of diꢀ and trisaccharide and
pentasaccharide derivatives are summarized in Tables 1 and 2.
Column chromatography was carried out using silica gel Merck
(type 9385, 230—400 mesh, 60 Å); elution was carried out with
toluene—ethyl acetate solvent mixtures with increasing conꢀ
centration of the latter, TLC was performed on DCꢀAlufolien
Kieselgel 60 F254 plates (Merck); the compounds were visualized
under UV light and/or by wetting the plates with an ethanol—
85% H3PO4 mixture (9 : 1 v/v) followed by heating on a hot
plate at ~150 °C. Anhydrous solvents were prepared by convenꢀ
tional procedures. Acylmannopyranosyl bromides were prepared
by treating the corresponding fully acylated derivatives with a
solution of HBr in AcOH according to a previously reported
procedure.34
1,2ꢀOꢀ[(S)ꢀBenzylidene]ꢀ3,4,6ꢀtriꢀOꢀbenzoylꢀβꢀDꢀmannoꢀ
pyranose (1). A solution of tetraꢀOꢀbenzoylꢀαꢀDꢀmannoꢀ
pyranosyl bromide (3.71 g, 5.3 mmol) in anhydrous MeCN
(10 mL) was stirred with NaBH4 (0.311 g, 8.18 mmol) for 48 h at
~20 °C. The reaction mixture was diluted with chloroform
and washed with water, the organic layer was concentrated, and
the residue was crystallized from an ethyl acetate—light petroꢀ
leum mixture to give 2.4 g (77%) of benzylidene derivative 1,
m.p. 173—174 °C, [α]D –3.4 (c 0.8). Found (%): C, 70.13;
H, 4.96. C34H28O9. Calculated (%): C, 70.34; H, 4.86. 1H NMR,
δ: 6.20 (t, 1 H, H(4), J = 9.9 Hz); 6.03 (s, 1 H, Ph—C—H);
5.78 (dd, 1 H, H(3), J3,2 = 3.9 Hz, J3,4 = 10.0 Hz); 5.66 (d,
1 H, H(1), J1,2 = 2.0 Hz); 4.77 (dd, 1 H, H(6), J6,5 = 2.6 Hz,
2ꢀMethoxycarbonylethyl
3,4,6ꢀtriꢀOꢀbenzoylꢀ1ꢀthioꢀ
αꢀDꢀmannopyranoside (6). A. 3ꢀMercaptopropionic acid (6.1 g,
5.7 mL, 57.6 mmol) (Fluka) was dissolved in MeOH (10 mL),
AcCl (0.4 mL) was added, and the mixture was kept for ~14 h at
~20 °C. The solution was diluted with dichloromethane and
washed with an aqueous solution of NaHCO3, and the solvent
was evaporated at 30 °C. The residue was distilled in vacuo to
give methyl 3ꢀmercaptopropionate, b.p. 70 °C (20 Torr) (lit.:35
b.p. 54—55 °C (14 Torr); lit.:36 b.p. 79—80 °C (27 Torr)), yield
3.8 g (55%). At 0 °C, HSCH2CH2CO2Me (2.6 mL, 23.3 mmol)
and BF3•OEt2 (1.7 mL, 13.4 mmol) were added to a solution of
1,2ꢀdiacetate 2 (4 g, 6.9 mmol) in CH2Cl2 (20 mL). The reaction
mixture was kept for 48 h at ~20 °C. After completion of the
reaction (TLC monitoring, toluene—ethyl acetate, 1 : 1), the
reaction mixture was diluted with chloroform, washed with water
and a saturated aqueous solution of NaHCO3, filtered through
cotton, and concentrated in vacuo. Column chromatography
gave 3.55 g (83%) of 2ꢀmethoxycarbonylethyl 2ꢀOꢀacetylꢀ3,4,6ꢀ
triꢀOꢀbenzoylꢀ1ꢀthioꢀαꢀDꢀmannopyranoside, [α]D +69.4 (c 1.43).
1H NMR, δ: 5.92 (t, 1 H, H(4), J4,3 = J4,5 = 10.0 Hz); 5.67 (dd,
1 H, H(3), J3,2 = 3.2 Hz, J3,4 =10.0 Hz); 5.55 (br.d, 1 H, H(2));
5.42 (br.s, 1 H, H(1)); 4.73 (ddd, 1 H, H(5), J5,6 = 2.6 Hz,
J
5,6´ = 5.2 Hz, J5,4 = 9.5 Hz); 4.60 (dd, 1 H, H(6), J6,5 = 2.6
Hz, J6,6´ = 12.1 Hz); 4.50 (dd, 1 H, H(6´), J6´,5 = 5.4 Hz,
J
6,6´ = 12.1 Hz); 3.65 (s, 3 H, OCH3); 2.95 (m, 2 H, SCH2);
2.70 (t, 2 H, CH2COO); 2.12 (s, 3 H, CH3COO). 13C NMR, δ:
82.72 (C(1)); 71.28 (C(2)); 70.20 (C(3)); 69.46 (C(5)); 67.17
(C(4)); 63.19 (C(6)); 51.84 (OCH3); 34.48 (SCH2); 26.47
(CH2COO); 20.72 (CH3CO).
The whole amount of obtained 2ꢀacetate (3.55 g, 5.58 mmol)
was dissolved in CH2Cl2 (10 mL), and a solution of HCl in
MeOH (obtained by adding acetyl chloride (1 mL) to methanol
(50 mL) at 0 °C) was added. The solution was kept for 14 h at
~20 °C, and, after completion of the reaction (TLC monitoring,
toluene—ethyl acetate, 1 : 1), an aqueous solution of KHCO3
was added, and the mixture was stirred for 30 min. Then the
reaction mixture was concentrated, diluted with chloroform,
and washed with water, and the solvent was evaporated. Crysꢀ
tallization from an ether—petroleum ether mixture gave 2.5 g
(75%) of compound 6, m.p. 114—116 °C, [α]D +85.4 (c 0.69).
J6,6´ = 12.2 Hz); 4.74 (dd, 1 H, H(2), J2,1 = 2.1 Hz, J2,3 = 3.8 Hz);
4.50 (dd, 1 H, H(6´), J6´,5 = 3.7 Hz, J6,6´ = 12.2 Hz); 4.16 (br.dt,
1 H, H(5)). 13C NMR, δ: 107.17 (Ph—C—H); 96.53 (C(1));
78.36 (C(2)); 71.70 (C(3)); 71.64 (C(5)); 66.43 (C(4)); 62.68 (C(6)).
1,2ꢀDiꢀOꢀacetylꢀ3,4,6ꢀtriꢀOꢀbenzoylꢀDꢀmannopyranose (2).
A solution of benzylidene derivative 1 (0.93 g, 1.6 mmol) in 90%
CF3CO2H (9 mL) was kept for 1 h at ~20 °C. After completion
of the reaction (TLC monitoring, toluene—ethyl acetate, 20 : 1),
the reaction mixture was diluted with chloroform, washed with
water and a saturated aqueous solution of NaHCO3, filtered
through cotton, and concentrated in vacuo. The 1,2ꢀdiol thus
obtained was acetylated with Ac2O (0.82 g, 8 mmol) in pyridine
(5 mL) at ~20 °C. After 14 h, the excess of Ac2O was quenched
by adding water (0.2 mL), the reaction mixture was diluted with
chloroform, the solution was washed with water, 1 M HCl, and a
Found (%): C, 63.04; H, 5.01. C31H30O10S. Calculated (%):
1
C, 62.62; H, 5.09. H NMR, δ: 5.96 (t, 1 H, H(4), J4,3 = J4,5
=
= 9.9 Hz); 5.59 (dd, 1 H, H(3), J3,2 = 3.1 Hz, J3,4 = 9.9 Hz);
5.48 (br.s, 1 H, H(1)); 4.76 (ddd, 1 H, H(5), J5,6 = 2.8 Hz,
J
5, 6´ = 5.4 Hz, J5,4 = 9.5 Hz); 4.61 (dd, 1 H, H(6), J6,5 = 2.7 Hz,
J6,6´ = 12.1 Hz); 4.54 (dd, 1 H, H(6´), J6´,5 = 5.6 Hz,
6,6´ = 12.2 Hz); 4.44 (br.s, 1 H, H(2)); 3.70 (s, 3 H, OCH3);
J

Mannopentaoside
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
465
3.00 (m, 2 H, SCH2); 2.71 (t, 2 H, CH2COO). 13C NMR, δ:
84.76 (C(1)); 72.82 (C(3)); 70.49 (C(2)); 69. 30 (C(5)), 67.15
(C(4)); 63.41 (C(6)).
(0.07 g, 64% relative to the converted trisaccharide acetate),
[α]D –10 (c 0.58).
Methyl 4,6ꢀdiꢀOꢀbenzoylꢀαꢀDꢀmannopyranoside. Benzoyl
chloride (9 mL, 78 mmol) was added with stirring to a solution
of methyl 2,3ꢀOꢀisopropylideneꢀαꢀDꢀmannopyranoside26
(3.7 g, 15.6 mmol) in pyridine (10 mL). After 40 min, TLC
analysis (CHCl3—MeOH, 19 : 1) showed the absence of the
starting compound. The excess of BzCl was decomposed by
dropwise addition of water to the reaction mixture, and the
reaction mixture was diluted with chloroform, washed with
water, 1 M HCl, and a saturated aqueous solution of NaHCO3,
and concentrated to give methyl 4,6ꢀdiꢀOꢀbenzoylꢀ2,3ꢀOꢀisoꢀ
propylideneꢀαꢀDꢀmannopyranoside, yield 6.1 g (91%), [α]D +28.0
(c 1.45), m.p. 87—88 °C (from ethanol). Found (%): C, 65.26;
H, 5.98. C24H26O8. Calculated (%): C, 65.15; H, 5.92. 1H NMR,
δ: 5.42 (dd, 1 H, H(4), J4,3 = 7.6 Hz, J4,5 = 10.2 Hz); 5.03 (s,
1 H, H(1)); 4.55 (dd, 1 H, H(6), J6,5 = 3.0 Hz, J6,6´ = 12.0 Hz);
4.43 (m, 2 H, H(3), H(6´)); 4.23 (d, 1 H, H(2), J2,3 = 5.5 Hz);
4.15 (sept, 1 H, H(5), J5,6 = 3.0 Hz, J5, 6´ = 6.2 Hz, J5,4 = 9.8 Hz),
3.45 (s, 3 H, OCH3), 1.65, 1.38 (both s, 3 H each, 2 CH3).
13C NMR, δ: 110.12 (C(CH3)2, 98.26 (C(1)); 75.99 (C(3));
75.77 (C(2)); 70.68 (C(4)); 66.35 (C(5)); 63.67 (C(6)); 55.09
(OCH3); 27.66, 26.29 (C(CH3)2).
The resulting isopropylidene derivative was dissolved in 80%
AcOH (50 mL), the solution was refluxed for 1 h, the solvent
was evaporated in vacuo, and the remaining AcOH was
coꢀevaporated with toluene. Column chromatography in a
CHCl3—MeOH system (methanol concentration gradient from
5 to 10%) gave methyl 4,6ꢀdiꢀOꢀbenzoylꢀαꢀDꢀmannopyranoside,
yield 4.95 g (80%), [α]D +72.1 (c 0.70), m.p. 84ꢀ85 °C (from an
ether—petroleum ether mixture). Found (%): C, 62.89; H, 5.65.
C21H22O8. Calculated (%): C, 62.68; H, 5.51. 1H NMR, δ: 5.41
(t, 1 H, H(4), J4,3 = J4,5 = 9.8 Hz); 4.80 (s, 1 H, H(1)); 4.53 (dd,
1 H, H(6), J6,5 = 2.7 Hz, J6,6´ = 12.0 Hz); 4.44 (dd, 1 H, H(6´),
J6´,5 = 6.1 Hz, J6,6´ = 12.0 Hz); 4.16 (sept, 1 H, H(5), J5,6 = 2.6 Hz,
B. 1,2ꢀDiacetate 2 (1.17 g, 2 mmol) was dissolved in CH2Cl2
(2 mL), and HSCH2CH2CO2H (0.7 mL, 8 mmol) and BF3•OEt2
(0.17 mL) were added at 0 °C. After 14 h at ~20 °C (TLC
monitoring in the toluene—ethyl acetate system, 1 : 1), the
reaction mixture was diluted with CHCl3, washed with water
and 1 M HCl, and filtered through cotton, and the solvent was
evaporated. The product thus obtained was dissolved in 10 mL
of a 0.6 M solution of HCl in MeOH (prepared by adding acetyl
chloride (0.4 mL) to methanol (10 mL) at 0 °C). The solution
was kept for 14 h at ~20 °C. Evaporation of the solvent and
chromatography gave 0.5 g (42%) of product 6 identical to that
obtained by procedure A.
2ꢀMethoxycarbonylethyl
2ꢀOꢀ(2ꢀOꢀacetylꢀ3,4,6ꢀtriꢀ
OꢀbenzoylꢀαꢀDꢀmannopyranosyl)ꢀ3,4,6ꢀtriꢀOꢀbenzoylꢀ1ꢀthioꢀ
αꢀDꢀmannopyranoside (7). Calcined molecular sieves 4 Å were
added to a solution of glycosyl acceptor 6 (0.43 g, 0.72 mmol)
and 2ꢀOꢀacetylꢀ3,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannopyranosyl bromide
(obtained from 1.09 mmol of diacetate 2) in CH2Cl2 (10 mL)
(here and below, the weight of molecular sieves is approximately
equal to the sum of weights of the glycosyl acceptor and the
glycosyl donor), the mixture was stirred for 1 h at 0 °C, a solution
of AgOTf (0.334 g, 1.3 mmol) in toluene (5 mL) was added, and
the mixture was stirred for an additional 40 min. The reaction
mixture was diluted with chloroform, filtered through a layer of
Celite HyFlo, and washed with a solution of Na2S2O3, and
the solvent was evaporated. Column chromatography
gave disaccharide 7, yield 0.53 g (66%), [α]D +29 (c 2.08).
Found (%): C, 65.00; H, 4.69. C60H54O19S. Calculated (%):
C, 64.86; H, 4.90.
2ꢀMethoxycarbonylethyl
2ꢀOꢀ(3,4,6ꢀtriꢀOꢀbenzoylꢀ
αꢀDꢀmannopyranosyl)ꢀ3,4,6ꢀtriꢀOꢀbenzoylꢀ1ꢀthioꢀαꢀDꢀmannoꢀ
pyranoside (8). MonoꢀOꢀacetate 7 (0.65 g, 0.59 mmol) was
dissolved in 3 mL of a 0.6 M solution of HCl in MeOH (prepared
by adding acetyl chloride (0.4 mL) to methanol (10 mL) at
0 °C). The solution was kept for 14 h at ~20 °C. Evaporation of
the solvent and chromatography in a toluene—ethyl acetate
system gave 0.12 g of unreacted disaccharide 7 and 0.22 g
of glycosyl acceptor 8 (43% relative to the converted disacchaꢀ
ride 7), [α]D +27.2 (c 0.93). Found (%): C, 65.37; H, 4.95.
C58H54O18S. Calculated (%): C, 65.16; H, 4.90.
2ꢀMethoxycarbonylethyl (2ꢀOꢀacetylꢀ3,4,6ꢀtriꢀOꢀbenzoylꢀ
αꢀDꢀmannopyranosyl)ꢀ(1→2)ꢀ(3,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannoꢀ
pyranosyl)ꢀ(1→2)ꢀ3,4,6ꢀtriꢀOꢀbenzoylꢀ1ꢀthioꢀαꢀDꢀmannopyraꢀ
noside (9). The condensation of disaccharide glycosyl acceptor 8
(0.156 g, 0.146 mmol) with 2ꢀOꢀacetylꢀ3,4,6ꢀtriꢀOꢀbenzoylꢀ
αꢀDꢀmannopyranosyl bromide (prepared from 0.218 mmol of
diacetate 2) in the presence of AgOTf (0.057 g, 0.22 mmol) and
molecular sieves 4 Å in a CH2Cl2—toluene mixture was carried
out similarly to the above described synthesis of protected
disaccharide 7 to give trisaccharide 9 (0.19 g, 82%), [α]D +4.7
(c 1.0).
J
5, 6´ = 6.0 Hz, J5,4 = 9.6 Hz); 4.07 (br.d, 1 H, H(3)); 4.00 (br.s,
1 H, H(2)); 3.38 (s, 3 H, OCH3). 13C NMR, δ: 100.62 (C(1));
71.04 (C(4)); 70.64 (C(2)); 70.27 (C(3)); 67.96 (C(5)); 63.82
(C(6)); 55.10 (OCH3).
Methyl 2,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannopyranoside (5). A.
A solution of methyl 2,4ꢀdiꢀOꢀbenzoylꢀαꢀDꢀmannopyranoside30
(0.55 g, 1.35 mmol) and BzCN (0.18 g, 1.35 mmol) in MeCN
(2 mL) was stirred for 30 min at ~20 °C in the presence of
catalytic amount of Et3N. After completion of the reaction (TLC
monitoring, toluene—ethyl acetate, 4 : 1), anhydrous MeOH
(5 mL) was added, the mixture was stirred for 30 min, and the
solvents were evaporated. Column chromatography gave methyl
2,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannopyranoside (327 mg, 48%),
[α]D +6.2 (c 0.42). Found (%): C, 66.39; H, 5.24. C28H26O9.
Calculated (%): C, 66.39; H, 5.17. 1H NMR, δ: 5.68 (t, 1 H,
H(4), J4,3 = J4,5 = 10 Hz); 5.41 (dd, 1 H, H(2), J2,1 = 1.6 Hz,
J2,3 = 3.3 Hz); 4.93 (d, 1 H, H(1), J1,2 = 1.5 Hz); 4.67 (dd, 1 H,
H(6), J6,5= 2.5 Hz, J6,6´ = 12.0 Hz); 4.50 (dd, 1 H, H(6´),
J6´,5 = 4.7 Hz, J6,6´ = 12.1 Hz); 4.39 (br.d, 1 H, H(3)); 4.27 (ddd,
1 H, H(5), J5,6 = 2.5 Hz, J5,6´ = 4.4 Hz, J5,4 = 10 Hz); 3.48 (s,
3 H, OCH3). 13C NMR, δ: 98.51 (C(1)), 72.75 (C(2)), 70.39
(C(4)), 68.91 (C(3)), 60.88 (C(5)), 62.99 (C(6)), 55.44 (OCH3).
B. A solution of methyl 4,6ꢀdiꢀOꢀbenzoylꢀαꢀDꢀmannopyraꢀ
noside (1.034 g, 2.5 mmol), PhC(OMe)3 (2 mL, 10.278 mmol),
and TsOH•H2O (0.05 g) in anhydrous MeCN (8 mL) was stirred
at ~20 °C. After 1 h (TLC monitoring, CHCl3—MeOH, 19 : 1),
2ꢀMethoxycarbonylethyl (3,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannoꢀ
pyranosyl)ꢀ(1→2)ꢀ(3,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannopyranosyl)ꢀ
(1→2)ꢀ3,4,6ꢀtriꢀOꢀbenzoylꢀ1ꢀthioꢀαꢀDꢀmannopyranoside (10).
The prepared trisaccharide 9 (0.17 g, 0.11 mmol) was treated
with 3 mL of a 0.6 M solution HCl in MeOH as described above.
Evaporation of the solvent and chromatography gave 0.06 g
of the initial trisaccharide and its deacetylation product 10

466
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
Abronina et al.
90% CF3COOH (2 mL) was added to the obtained bicyclic
orthoester. After 30 min, the solvents were evaporated, the
remaining acid was coꢀevaporated with toluene. Column chroꢀ
matography gave 0.849 g (67%) of tribenzoate 5 identical to that
obtained by method A, [α] + 4.5 (lit28: [α] +4.9).
chloroform, the solution was filtered through a layer of Celite
HyFlo and washed with an aqueous solution of Na2S2O3, and
the solvent was evaporated. Column chromatography gave the
glycoside of disaccharide 13, yield 0.490 g (69%), [α]D –34.6
(c 0.13); lit.:32 [α]D –42.6 (c 1.0, CHCl3).
D
D
1,3ꢀDiꢀOꢀacetylꢀ2,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannopyranose
(3). A cooled solution of conc. H2SO4 (0.08 mL) in Ac2O
(1.9 mL) was added to a cooled (0 °C) solution of glycoside 5
(0.307 g, 0.61 mmol) in AcOH (1.9 mL) and Ac2O (1.9 mL).
The mixture was heated for 2 h at 40 °C. After completion of
the reaction (TLC monitoring, toluene—ethyl acetate, 4 : 1),
the solution was cooled to 20 °C, cold water was added dropwise,
and the solution was concentrated in vacuo to ~1 mL. The
residue was diluted with chloroform, and the solution was washed
with a saturated aqueous solution of NaHCO3 to give diacetate
3ꢀOꢀ(2,3,4,6ꢀTetraꢀOꢀbenzoylꢀαꢀDꢀmannopyranosyl)ꢀ2,4,6ꢀ
triꢀOꢀbenzoylꢀDꢀmannopyranose (14). A mixture of bioside 13
(0.48 g, 0.408 mmol) and (NH4)2Ce(NO3)6 (0.447 g, 0.816 mmol)
in an acetonitrile—water mixture (4.5 : 0.5 mL) was stirred for
15 min at ~20 °C and diluted with ethyl acetate. The organic
layer was washed with water and an aqueous solution of Na2S2O3
and concentrated. Column chromatography of the residue gave
disaccharide 14, yield 0.185 g (42%).
1ꢀOꢀAcetylꢀ3ꢀOꢀ(2,3,4,6ꢀtetraꢀOꢀbenzoylꢀαꢀDꢀmannopyraꢀ
nosyl)ꢀ2,4,6ꢀtriꢀOꢀbenzoylꢀDꢀmannopyranose (15). The obtained
disaccharide 14 (0.15 g, 0.14 mmol) was dissolved in pyridine
(2 mL), Ac2O (0.1 mL) was added, and the mixture was left for
14 h at ~20 °C. Water (0.5 mL) was added dropwise, and the
mixture was diluted with chloroform, washed with water, 1 M
HCl, water, and an aqueous solution of NaHCO3. The organic
layer was concentrated in vacuo, and chromatography of the
residue gave 140 mg (90%) of disaccharide 15, [α]D –44.6
(c 0.125).
3, yield 0.32 g (91%). Found (%): C, 64.76; H, 4.86. C31H28O11
Calculated (%): C, 64.58; H, 4.90. 1H NMR (200 MHz), δ: 6.33
(d, 1 H, H(1), J1,2 = 1.9 Hz); 6.01 (t, 1 H, H(4), J4,3 = J4,5
.
=
= 10.1 Hz); 5.72 (dd, 1 H, H(3), J3,2 = 3.3 Hz, J3,4 = 10.2 Hz);
5.61 (dd, 1 H, H(2), J2,1 = 2.0 Hz, J2,3 = 3.2 Hz); 4.69 (dd, 1 H,
H(6), J6,5 = 2.6, J6,6´ = 12.2); 4.47—4.36 (m, 2 H, H(5), H(6´));
1.93, 2.28 (both s, 3 H each, 2 CH3COO). 13C NMR (δ: 90.82
(C(1)); 70.92 (C(5)); 69.06 (C(2)); 68.75 (C(3)); 66.30 (C(4));
62.50 (C(6)).
2ꢀMethoxycarbonylethyl
(2,3,4,6ꢀtetraꢀOꢀbenzoylꢀ
4ꢀMethoxyphenyl
3ꢀOꢀacetylꢀ2,4,6ꢀtriꢀOꢀbenzoylꢀαꢀ
αꢀDꢀmannopyranosyl)ꢀ(1→3)ꢀ(2,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannoꢀ
pyranosyl)ꢀ(1→2)ꢀ(3,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannopyranosyl)ꢀ
(1→2)ꢀ(3,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannopyranosyl)ꢀ(1→2)ꢀ3,4,6ꢀ
triꢀOꢀbenzoylꢀ1ꢀthioꢀαꢀDꢀmannopyranoside (17). 1ꢀOꢀAcetate 15
(28 mg, 0.025 mmol) was dissolved in CH2Cl2 (0.5 mL), and
AcOH (0.05 mL) and AcBr (0.02 mL) were added. On cooling
with ice water, AcOH (0.05 mL) and water (0.01 mL) were
added, and the mixture was kept for 2 h. The reaction mixture
was diluted with chloroform and washed with ice water and a
saturated aqueous solution of NaHCO3 to give 2,4,6ꢀtriꢀ
Oꢀbenzoylꢀ3ꢀOꢀ(2,3,4,6ꢀtetraꢀOꢀbenzoylꢀαꢀDꢀmannopyranoꢀ
syl)ꢀαꢀDꢀmannopyranosyl bromide (16).
Calcined molecular sieves 4 Å were added to a solution of
2ꢀmethoxycarbonylethyl (3,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannoꢀ
pyranosyl)ꢀ(1→2)ꢀ(3,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannopyranosyl)ꢀ
(1→2)ꢀ3,4,6ꢀtriꢀOꢀbenzoylꢀ1ꢀthioꢀαꢀDꢀmannopyranoside (10)
(41 mg, 0.027 mmol) and biosyl bromide 16 in CH2Cl2 (1 mL),
and the mixture was stirred for 1 h at 0 °C. Then a solution of
AgOTf (0.01 g) in toluene (0.5 mL) was added, and the mixture
was stirred for additional 40 min. The reaction mixture was
diluted with chloroform, filtered through a layer of Celite HyFlo,
and washed with an aqueous solution of Na2S2O3, and the solvent
was evaporated. Gel permeation chromatography on a column
(40Ѕ1.3 cm) with gel SXꢀ1 in toluene gave pentasaccharide 17
Dꢀmannopyranoside (11). 4ꢀMethoxyphenol (0.24 g, 1.94 mmol)
and BF3•Et2O (0.28 g, 0.25 mL, 1.94 mmol) were added at
~20 °C to a solution of 1,3ꢀdiacetate 3 (0.56 g, 0.97 mmol) in
anhydrous CH2Cl2 (3 mL). After 14 h, the reaction mixture was
diluted with chloroform and washed with water and a saturated
aqueous solution of NaHCO3. Column chromatography gave
glycoside 11, yield 0.44 g (70%), [α]D –11.5 (c 0.46). 1H NMR,
δ: 5.94—5.93 (m, 2 H, H(3), H(4)); 5.78 (br.s, 1 H, H(2));
5.63 (br.s, 1 H, H(1)); 4.62 (dd, 1 H, H(6), J6,5 = 2.0 Hz,
J
6,6´ = 12.0 Hz); 4.52 (m, 1 H, H(5)); 4.45 (dd, 1 H, H(6´),
J6´,5 = 5.0 Hz, J6,6´ = 12.0 Hz); 3.76 (s, 3 H, OCH3); 1.93 (s,
3 H, CH3COO). 13C NMR, δ: 96.70 (C(1)); 70.18 (C(2)); 69.39
(C(5)); 69.10 (C(3)); 67.05 (C(4)); 62.94 (C(6)); 55.59 (OCH3);
20.69 (CH3COO).
4ꢀMethoxyphenyl 2,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannopyranoside
(12). Glycoside 11 (0.41 g, 0.65 mmol) was dissolved in 7 mL of
a 0.6 M solution of HCl in MeOH (prepared by adding acetyl
chloride (0.4 mL) to methanol (10 mL) at 0 °C). The solution
was kept for 14 h at ~20 °C. Evaporation of the solvent and
column chromatography gave 0.3 g (77%) of glycosyl acceptor
12, [α]D +46 (c 0.46) (lit.:32 [α]D +10.3 (c 1.0, CHCl3)). 1H NMR,
δ: 5.71 (t, 1 H, H(4), J4,3 = J4,5 = 9.8 Hz) ; 5.64 (d, 1 H, H(1),
J1,2 = 1.7 Hz); 5.60 (dd, 1 H, H(2), J2,3 = 3.2 Hz, J2,1 = 1.7 Hz);
4.63—4.60 (m, 2 H, H(3), H(6)); 4.49—4.43 (m, 2 H, H(5),
H(6´)); 3.75 (s, 3 H, OCH3). 13C NMR, δ: 96.47 (C(1)); 72.67
(C(2)); 70.30 (C(4)); 69.01 (C(5)), 68.90 (C(3)); 63.05 (C(6));
55.60 (OCH3).
(30 mg, 43%), [α] +48.3 (c 1).
D
The authors are grateful to a student of the Higher
Chemical College S. V. Stefanyuk for participation in the
synthesis of compound 1.
4ꢀMethoxyphenyl
3ꢀOꢀ(2,3,4,6ꢀtetraꢀOꢀbenzoylꢀαꢀ
Dꢀmannopyranosyl)ꢀ2,4,6ꢀtriꢀOꢀbenzoylꢀαꢀDꢀmannopyranoside
(13). Calcined molecular sieves 4 Å were added to a solution of
glycoside 12 (0.360 g, 0.602 mmol) and 2,3,4,6ꢀtetraꢀOꢀbenzoylꢀ
αꢀDꢀmannopyranosyl bromide (prepared from 0.96 mmol of
Dꢀmannose pentabenzoate) in CH2Cl2 (5 mL), the mixture was
stirred for 1 h at 0 °C, a solution of AgOTf (0.247 g, 0.96 mmol)
in toluene (2 mL) was added, and the mixture was stirred for
additional 40 min. The reaction mixture was diluted with
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Received November 11, 2008;
in revised form January 13, 2009