o-Methoxycarbonylphenyl 1-thio-β-d-galactopyranoside, a non-malodorous thio glycosylation donor for the synthesis of globosyl α (1-4)-linkages

Article abstract of DOI:10.1055/s-2001-16803

o-Methoxycarbonylphenyl 2,3,4,6-tetra-O-benzyl-1-thio-β-D-galactoside 1 was designed and demonstrated to serve as a non-malodorous thioglycosyl donor in α-selective glycosylation reactions with 4-OH galactoside and 4′-OH lactoside to give globosyl Gb

Full text of DOI:10.1055/s-2001-16803

1446
LETTER
o-Methoxycarbonylphenyl 1-Thio- -D-Galactopyranoside, A Non-malodorous
Thio Glycosylation Donor for the Synthesis of Globosyl (1-4)-Linkages
Hirofumi Dohi, Yoshihiro Nishida,* Hidehiko Tanaka, Kazukiyo Kobayashi*
Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603,
Japan
Received 7 June 2001
could be kept as an active glycosyl donor for months with-
Abstract: o-Methoxycarbonylphenyl 2,3,4,6-tetra-O-benzyl-1-
out decomposition. Reactivity and stereoselectivity of 1
were examined preliminarily using cetyl alcohol as an ac-
thio- -D-galactoside 1 was designed and demonstrated to serve as a
non-malodorous thioglycosyl donor in -selective glycosylation re-
ceptor (1.5 mol) and NIS/trifluorosulfonic acid (TfOH) as
an activator18 in CH2Cl2. The reaction gave a mixture of
- and -galactosides ( / = 45:55) at 0 C, and -galac-
toside predominantly ( / = 30:70) at 40 C. It may be
noted that the higher -selectivity of the glycosylation at
lower temperature is a unique phenomenon. We assume
that this unique tendency is attributable to the o-carboxy-
late function in the leaving group as shown in Scheme 2.
The sulfur atom of 1 is activated by the iodonium cation
to generate the intermediate a which affords the -glyco-
side. The carbonyl oxygen atom of the o-carboxylate
group interacts with the anomeric carbon in an intramo-
lecular fashion to generate the ortho ester-type intermedi-
ate b which affords the -glycoside. The presence of the
intermediate b was suggested by the finding that cetyl
thiosalicylate was obtained as a byproduct which may be
produced via transesterification of b with cetyl alcohol.
Since the electron-withdrawing o-carboxylate group re-
duces the leaving activity of the phenylthio group, the in-
termediate a is less reactive at low temperature, and the
contribution of the intermediate b becomes predominant,
which results in favored formation of -galactoside.
actions with 4-OH galactoside and 4’-OH lactoside to give globosyl
Gb2 and Gb3 saccharides, respectively.
Key words: stereoselective glycosylations, thioglycosides, globo-
syl oligosaccharides, glycoconjugate polymers, carbohydrates
Globosyl ceramides (Gb2- and Gb3-ceramide) are natural
ligands of Shiga-like toxins (Stx-I and Stx-II) produced by
Escherichia coli O-157: H-7 and other pathogenic E. coli
species.1 Intensive efforts have been directed to the devel-
opment of artificial Stx ligands such as Gb3-embedded
glycoconjugate polymers,2 dendrimers,3 starfish-like
models,4 liposomes,5 and so on.6 In these and other syn-
thetic studies on globosyl oligosaccharides, stereoselec-
tive and high-yield construction of the Gal 1 4Gal
linkage was the key investigative step.7 Among many syn-
thetic protocols for -galactosylation, thioglycosylation
methods seem to be the most preferentially employed.8,9
This is mainly because thioglycoside donors are highly
stable for storage and are chemo-selective under glycosy-
lation conditions. These favorable properties have provid-
ed a key basis to the recent methodologies termed
“orthogonal syntheses”10 and “armed/disarmed glycosyla-
tions”11, which have significantly extended the utility of
thioglycosylation methods12 including the syntheses of
globosyl Gb2 and Gb3 oligosaccharides.13,14
In our continuous efforts to develop glycoconjugate poly-
mers carrying Gb3 and iso-Gb3 trisaccharides2 and other
biologically active oligosaccharides,15 we have hesitated
to use the thioglycosylation method because it evolves un-
pleasant odor in the process of preparing the thioglycosyl
donors and isolating the glycosyl products. The malodor
of mercaptanes should be unbearable even if the reaction
achieves an excellent outcome. This communication re-
ports the convenient use of a new thiogalactosyl donor 116
that enables us to prepare both Gb2 and Gb3 linkages and
their cluster models in high yields without suffering from
the malodor in the laboratory.
The donor 117 was synthesized as a colorless crystal in
90% yield via the SN2 reaction of penta-O-acetyl- -D-ga-
lactopyranosyl bromide 2 with methyl thiosalicylate 3 that
smells faintly like a blend of methyl salicylate and
thiophenol (Scheme 1). Compound 1 evolved little un-
pleasant odor during its preparation and treatment and
Scheme 1 Preparation of o-methoxycarbonylphenyl thiogalactosyl
donor 1
Reagents and Conditions: (a) 3, K2CO3, DMF, r.t., 2 h, 90%; (b) NaO-
Me, MeOH, r.t., 3 h, 99%; (c) NaH, BnBr, DMF, 16 h, 91%.
Though -selective galactosylation was unsuccessful with
cetyl alcohol, we attempted to apply the donor 1 to the
more hindered and less reactive p-nitrophenyl (pNP) 6-O-
benzyl-2,3-di-O-acetyl- -D-galactopyranoside 520 which
Synlett 2001, No. 9, 1446–1448 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
o-Methoxycarbonylphenyl 1-Thio- -D-Galactopyranoside
1447
Scheme 2 Proposed mechanism of glycosylation of 1 with cetyl
alcohol.
was prepared in a conventional way from pNP -D-galac-
topyranoside via benzylidenation, acetylation, and regi-
oselective cleavage of the benzylidene acetal21 (Scheme
3). Although the glycosylation was conducted under the
same conditions as for cetyl alcohol (CH2Cl2 at 0 C),
much higher -selectively ( / = 83/17, 89% yield) was
achieved. Use of the Et2O - CH2Cl2 mixture as the solvent
at 10 C could improve the -selectivity up to 99% to
give the desired Gal 1 4Gal linkage 6 in 83% yield (Ta-
ble 1). The high -selectivity may be explained similarly
as that of the other glycosylations on the basis of the ano-
meric effect22 and also by solvent effect of Et2O.23 De-
acetylation and the subsequent catalytic hydrogenolysis
gave p-aminophenyl galabioside 7, which was converted
to a Gb2 glycoconjugate polymer 8 via radical copolymer-
ization with acrylamide (Mn = 4.4 105 (SEC analysis,
pullulan standard), the molar ratio of Gb2
unit:acrylamide = 0.20:0.80). Thus, the novel galactosyl
donor 1 enabled us to prepare 8 from pNP -D-galactoside
totally in 40% yield (8 steps). The same pathway was ex-
tended to the synthesis of a Gb3 derivative 10 via -galac-
tosylation ( : = >99:1, 79%) using 1 of pNP lactoside
derivative 924 (Scheme 4).
Scheme 3 Synthesis of glycoconjugate polymer carrying Gb2
bioside 8
Reagents and Conditions: (d) 1, NIS, TfOH, CH2Cl2, Et2O, -10 C, 30
min, 86%; (e) NaOMe, MeOH, r.t., 3 h, 99%; (f) Pd(OH)2/C, H2, Me-
OH, r.t., 2 h, 95%; (g) acryloyl chloride, Et3N, CH2Cl2, MeOH,
0 C r.t., 2 h, 91%; (h) acrylamide (4 eq.), 2, 2’-azobis (2-amidino-
propane) dihydrochloride (1% mol against all monomers), H2O,
60 C, 8 h, 72%.
Table Coupling reaction between 1 and 5a
Scheme 4 Synthesis of Gb3 trioside derivative 10
Reagents and Conditions: (i) 1, NIS, TfOH, CH2Cl2, Et2O, -10 C, 3
h, 79%.
aThe glycosylations of 1 and 5 (1.5 eq) were carried out in the
presence of N-iodosuccinimide (NIS, 2 eq.) and cat. TfOH for 1 h.
Synlett 2001, No. 9, 1446–1448 ISSN 0936-5214 © Thieme Stuttgart · New York

1448
H. Dohi et al.
LETTER
(15) Dohi, H.; Nishida, Y.; Mizuno, M.; Shinkai, M.; Kobayashi,
T.; Takeda, T.; Uzawa, H.; Kobayashi, K. Bioorg. Med. Chem.
1999, 7, 2053.
(16) Some groups already synthesized o-methoxycarbonylphenyl
thioglycosides, but the glycosides were not employed as
glycosyl donors. See: Li, P.; Sun, L.; Landry, D. W.; Zhao, K.
Carbohydr. Res. 1995, 275, 179. Per-O-benzylated
o-methoxycarbonylphenyl thiogalactoside 1 is a new
compound,.
(17) Compound 1: [ ]D -3.0 (c 0.05, CHCl3, 24 C). mp = 93-94 C.
IR (cm-1): 1720, 1249 (CO2Me), 1290, 1128 (OBn). 1H NMR
( ppm, 500 MHz, CDCl3, 22 C): 7.26-7.37 (m, 20H,
aromatic-H of Bn), 7.13, 7.17, 7.78, 7.86 (ddd 2 and dd 2,
1H 4, aromatic-H of o-methoxycarbonylphenyl group), 4.99
(d, 1H, J = 8.0 Hz, H-1), 4.42, 4.49, 4.62, and 4.72-4.80 (d 3
and m, 1H 3 and 5H, methylene of Bn), 4.04 (dd, 1H, J = 9.0
Hz, H-2), 4.00 (d, 1H, J = 2.6 Hz, H-4), 3.86 (s, 3H, H of Me),
3.61-3.69 (m, 4H, H-3, H-5, and H-6). Anal. calcd. for
C42H42O7S: C, 73.02; H, 6.13%; found C, 73.15; H, 6.11%.
(18) Sasaki, M.; Tachibana, K.; Nakanishi, H. Tetrahedron Lett.
1991, 32, 6873.
In conclusion, we have designed a thiogalactosyl donor 1
with an o-methoxycarbonylphenyl thio leaving group and
demonstrated its highly synthetic potential as a non-mal-
odorous thioglycosyl agent to construct the (1-4) linkage
in Gb2 and Gb3 derivatives. Extension of the o-methoxy-
carbonylphenyl thio leaving group to other glycosyla-
tions, elucidation of its reaction mechanism, and
biological applications25 of the resulting substances are
now in progress.
Acknowledgement
This work was carried out with support of the Japan Society for the
Promotion Science Research Fellowship (DC) to H. D.
References and Notes
(1) (a) Lingwood, C. A.; Law, H.; Richardson, S.; Petric, M.;
Brunton, J. L.; Grandis, S. D.; Karamali, M. J. Biol. Chem.
1987, 262, 8834. (b) Lindberg, A. A.; Brown, J. E.;
Strömberg, N.; Westling-Ryd, M.; Schultz, J. E.; Karlsson, K.
A. J. Biol. Chem. 1987, 262, 1779. (c) Arab, S.; Lingwood, C.
A. Glycoconjugate J. 1996, 13, 159. (d) Karlsson, K. A. Annu.
Rev. Biochem. 1989, 58, 309.
(19) Leaving group participation similar to that described here was
previously reported. See: Shimizu, H.; Ito, Y.; Ogawa, T.
Synlett 1994, 7, 535.
(20) Compound 5: [ ]D = -16.4 (c 0.05, CHCl3, 24 C). mp = 144-
146 C. IR (cm-1): 3513 (OH), 1745, 1241 (Ac), 1513 (NO2),
1338, 1220 (OBn). 1H NMR ( ppm, 500MHz, CDCl3, 22 C):
8.18 (d, 2H, J = 9.3 Hz, H-meta of pNP), 7.28-7.37 (m, 5H,
aromatic-H of Bn), 7.10 (d, 2H, J = 9.3 Hz, H-ortho of pNP),
5.60 (dd, 1H, J = 8.6 and 11.4 Hz, H-2), 5.16 (d, 1H, J = 8.6
Hz, H-1), 5.06 (dd, 1H, J = 2.9 and 11.4 Hz, H-3), 4.56 and
4.58 (s 2, 1H 2, methylene of Bn), 4.24 (s, 1H, H-4), 3.90
(dd, 1H, H-5), 3.82 (m, 2H, H-6), 2.06 and 2.14 (s 2, 3H 2, H
of Ac). Anal. calcd. for C23H25NO10: C, 58.10; H, 5.30; N,
2.95%; found C, 57.46; H, 5.22; N, 2.85%.
(2) Nishida, Y.; Dohi, H.; Uzawa, H.; Kobayashi, K. Tetrahedron
Lett. 1998, 39, 8681.
(3) Matsuoka, K.; Terabatake, M.; Esumi, Y.; Terunuma, D.;
Kuzuhara, H. Tetrahedron Lett. 1999, 40, 7839.
(4) Kitov, P. I.; Sadowska, J. M.; Mulvey, G.; Armstrong, G. D.;
Ling, H.; Pannu, N. S.; Read, R. J.; Bundle, D. R. Nature
2000, 403, 669.
(5) (5) Arab, S.; Lingwood, C. A. Glycoconjugate J. 1996, 2,
159.
(6) (6) Lundquist, J. J.; Debenham, S. D.; Toone, E. J. J. Org.
Chem. 2000, 65, 8245.
(21) DeNinno, M. P.; Etienne, J. B.; Duplantier, K. C. Tetrahedron
Lett. 1995, 36, 669.
(22) (a) Osborn, H.; Khan, T., In Oligosaccharides, Oxford
University Press, 2000, p 58. (b) Oscarson, S., In
Carbohydrates in Chemistry and Biology, Part 1: Chemistry
of Saccharides; Ernst, B.; Hart, G. W.; Sinay, P., Ed.; Wiley-
VCH: Weinheim, 1999, p 93.
(7) For the recent synthesis Gb2 derivative, see Ohlsson, J.;
Magnusson, G. Carbohydr. Res. 2000, 329, 49.
(8) (8) Barresi, F.; Hindsgaul, O. J. Carbohydr. Chem. 1995, 14,
1043.
(9) (9) Medgyes, A.; Bajza, I.; Farkas, E.; Pozsgay, V.; Liptàk,
A. J. Carbohydr. Chem. 2000, 19, 285.
(10) Kanie, O.; Ito, Y.; Ogawa, T. Tetrahedron Lett. 1996, 37,
4551.
(11) Mootoo, D. R.; Konradsson, P.; Uododong, U.; Fraser-Reid,
B. J. Am. Chem. Soc. 1988, 110, 5583.
(23) Garegg, P. J.; Helland, A. C. J. Carbohydr. Chem. 1993, 12,
105.
(24) Glycosylation of 9 with 6-O-acetyl-2,3,4-tri-O-benzyl-D-
galactopyranosyl fluoride and the subsequent preparation of
the glycoconjugate polymers were previously reported.2, 15
(25) Dohi, H.; Nishida, Y.; Furuta, Y.; Uzawa, T.; Yokoyama, S.;
Mori, H.; Kobayashi, K. to be submitted.
(12) Fraser-Reid, B.; Wu, Z.; Uododong, U.; Ottoson, H. J. Org.
Chem. 1990, 55, 6068.
(13) Qiu, D.; Schmidt, R. R. Liebigs Ann. Chem. 1992, 217.
(14) Hashimoto, S.; Sakamoto, H.; Honda, T.; Abe, H.; Nakamura,
S.; Ikegami, S. Tetrahedron Lett. 1997, 52, 8969.
Article Identifier:
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Synlett 2001, No. 9, 1446–1448 ISSN 0936-5214 © Thieme Stuttgart · New York