Wang resin-type linker containing a nitro group for polymer support oligosaccharide synthesis: Polymer-supported glycosyl donor

Article abstract of DOI:10.1248/cpb.49.1234

A nitro-introduced Wang resin-type linker for soluble and insoluble polymer support oligosaccharide synthesis is described. The linker was used for connecting glycosyl donors and polymer supports, and was completely stable under the glycosylation conditions tested. The cleavage of the linker was performed under reductive conditions without affecting the protecting groups to release disaccharides.

Full text of DOI:10.1248/cpb.49.1234

1234
Communications to the Editor
Chem. Pharm. Bull. 49(9) 1234—1235 (2001)
Vol. 49, No. 9
romethanesulfonate was also compatible with this type of
linker, and disaccharide 15 was obtained in 59% yield from
glucose-derived donor 8 (Chart 4).
Next, the suitability of the linker for solid-phase oligosac-
charide synthesis was examined. To minimize the steric hin-
drance imposed by solid support, spacer 16 was incorporated
between Merrifield resin and the linker (Chart 5). The degree
of loading was quantified by elemental analysis. For exam-
ple, the immobilization of 16 was calculated by the decrease
Wang Resin-Type Linker Containing a
Nitro Group for Polymer Support
Oligosaccharide Synthesis:
Polymer-Supported Glycosyl Donor
Shino MANABE and Yukishige ITO*
RIKEN (The Institute of Physical and Chemical Research), Wako,
Saitama, 351–0198 Japan.
Received May 14, 2001; accepted June 28, 2001
A nitro-introduced Wang resin-type linker for soluble and in-
soluble polymer support oligosaccharide synthesis is described.
The linker was used for connecting glycosyl donors and polymer
supports, and was completely stable under the glycosylation
conditions tested. The cleavage of the linker was performed
under reductive conditions without affecting the protecting
groups to release disaccharides.
Key words solid-phase synthesis; oligosaccharide; linker
Solid-phase synthesis is now widely recognized as the
leading-edge technology for rapid and efficient oligosaccha-
ride construction.1) The design of linker that connects the
first sugar unit to the polymeric support is of crucial impor-
tance for the ultimate success of the synthesis.2,3) We have re-
cently reported a nitro group-introduced Wang resin-type
linker, which was useful for connecting soluble polymer sup-
port and the glycosyl acceptor.2) An electron-withdrawing
nitro group was introduced to attenuate the acid susceptibil-
ity of the p-alkoxybenzyl ether linkage resin and this linker
was proved to be completely stable under typical glycosyla-
tion conditions using trimethylsilyl trifluoromethanesulfonate
or Cp2HfCl2–AgOTf. The products were released with reduc-
tion of the nitro group via the intramolecular cyclization re-
action as hydroxamic acid derivatives. Complete removal of
the cyclic hydroxamic acid from the linker was carried out
with acid treatment. In this paper, we describe the renewed
use of the nitro-modified linker. It connects glycosyl donors
and polymer supports, and was designed to be “traceless.”
That is, cleavage under reductive conditions directly affords a
product with a free hydroxy group at the position originally
connected to the linker (Chart 1).
Chart 1
Reagents and conditions: i, Cl3CCN, DBU, CH2Cl2, room temperature (r.t.),
2 h; ii, PEGOH, TMSOTf, CH2Cl2, 0 °C, 12 h; iii, LiOH, MeOH, H2O, r.t.,
12 h, quant., 3 steps; PEGϭpoly(ethylene glycol) methyl ether.
Chart 2
Table 1. Immobilization of Glycosyl Donor to Polymer Support
i
2ϩsugar unit (3, 4, or 5) → polymer-supported glycosyl donor (6, 7, or 8)
The linker 12) was first immobilized via ether linkage to
poly(ethylene glycol) methyl ether (PEG, average MW 5000)
using the imidate method (Chart 2). After hydrolysis of the
methyl ester, glycosyl donors 3—5 were attached with 1-ethyl-
3-1-ethyl-3-(3-dimethylaminopropyl)carbodiimide · HCl
(WSCDI) and DMAP to afford 6—8 in high yields (Table 1).
The soluble PEG-supported thioglycoside 6 was activated
by dimethyl(methylthio)sulfonium triflate (DMTST)4) in the
presence of 4 eq of acceptor 9. After reduction of the nitro
group by Sn(SPh)2–PhSH–Et3N,5) product 11 was obtained in
87% overall yield. This structure corresponds to O-linked N-
acetyl-D-glucosamine, which has been found in a variety of
nuclear and cytoplasmic proteins.6) Reaction with the toluoyl
group-protected glucose 10 afforded disaccharide 12 in 86%
overall yield after cleavage from the polymer (Table 2). Gly-
cosyl fluoride 7 was reacted with benzyl protected-acceptor
13 by Cp2HfCl2–AgOTf7) to give 14 in high yield (Chart 3).
A combination of N-iodosuccinimide-triethylsilyl trifluo-
Sugar unit
Product
Yield (%)
3
6
Quant.
4
5
7
8
94
96
Reagents and conditions: i, sugar unit (2 eq), WSCDI, DMAP, CH2Cl2, r.t., overnight.
PhthϭPhtalimide.
To whom correspondence should be addressed. e-mail: yukito@postman.riken.go.jp
© 2001 Pharmaceutical Society of Japan

September 2001
1235
Table 2. Reaction of Soluble Polymer-Supported Glycosyl Donor
i, ii
Table 3. Reaction of Insoluble Resin-Immobilized Glycosyl Donor
Sn(SPh) ,PhSH
2
6ϩacceptor
→ product
glycosylation
Et3N,PhH
18 or 19
product
→
→
Acceptor
Product
Yield (%)
Glycosylation
conditions
Donor Acceptor
Product
Yield (%)
87
NIS, TESOTf
CH2Cl2, r.t., 15 h
18
10
20
12
21
74a) (38)b)
66d) (60)b)
NIS, TESOTf
CH2Cl2, r.t., 16 h
18c)
Cp2HfCl2, AgOTf
MS 4A, CH2Cl2
0 °C—r.t., 15 h
86
19
20
21
56a) (29)b)
Reagents and conditions: i, DMTST, MS 3A, CH2Cl2, 0 °C—r.t., overnight;
ii, Sn(SPh)2, PhSH, Et3N, PhH, r.t., overnight; MBzϭ4-methylbenzoyl, MPϭ4-
methoxyphenyl.
a) Based on 18 or 19 (0.33 mmol/g), b) overall yields from Merrifield resin (0.64
mmol/g), c) high loading 18 (thioglycoside content 0.58 mmol/g) was used, d) based on
18 (0.58 mmol).
52% (0.33 mmol/g), which was in close proximity to the
value obtained after releasing thioglycoside 3 (NaOMe,
MeOH, 51% overall yield).8) The glycosylation of 18 with 10
was effected by DMTST, and disaccharide 12 was obtained
in 74% yield (Table 3). Not only thioglycoside, but also fluo-
ride 19 was activated under Suzuki conditions (Hf2CpCl2–
AgOTf) to give disaccharide 21.
Reagent and conditions: i, Cp2HfCl2, AgOTf, MS 4A, CH2Cl2, 0 °C—r.t.,
overnight; ii, Sn(SPh)2, PhSH, Et3N, PhH, r.t., overnight, 82%.
Chart 3
In conclusion, the nitro-modified Wang resin-type linker
proved to be useful for immobilizing glycosyl donors onto
soluble and insoluble polymer supports. Thoughout the reac-
tion sequence, the linker was stable and cleavage can be per-
formed under mild conditions without affecting commonly
used protecting groups. As a result, direct use of the
oligosaccharide products for block condensation can be con-
sidered.
Reagent and conditions: i, NIS, TESOTf, 0 °C—r.t., overnight; ii, Sn(SPh)2,
PhSH, Et3N, PhH, r.t., overnight, 59% (2 steps).
Chart 4
Acknowledgments This work was supported by a Grant-in-Aid for En-
couragement of Young Scientists from the Ministry of Education, Science,
Sports and Culture, the Presidential Fund of RIKEN (S. M.), and the New
Energy and Industrial Technology Development Organization. We thank Dr.
T. Chihara and his staff for elemental analysis, and Ms. A. Takahashi for
technical assistance.
References and Notes
1) For recent reviews, see Ito Y., Manabe S., Curr. Opin. Chem. Biol., 2,
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4349—4394 (2000).
2) Manabe S., Nakahara Y., Ito Y., Synlett, 2000, 1241—1244, and refer-
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3) Melean L. G., Hasse W.-C., Seeberger P. H., Tetrahedron Lett., 41,
4329—4333 (2000); Tolborg J. F., Jensen K. J., Chem. Commun.,
2000, 147—148; Wu X., Grathwohl M., Schmidt R. R., Org. Lett., 3,
747—750 (2001).
Reagents and conditions: i, Cs2CO3, DMF, 40 °C, 2 d; ii, 17, BF3·OEt2,
CH2Cl2, 0 °C, overnight; iii, aq. NaOH, THF, r.t., overnight; iv, 3 or 4,
WSCDI, HOBt, DMAP, r.t., overnight; or 3 or 4, PPh3, DEAD, THF, r.t.,
overnight.
4) Fügedi P., Garegg P. J., Carbohydr. Res., 149, c9—c12 (1986).
5) Bartra M., Romea P., Urpí F., Vilarrasa J., Tetrahedron, 46, 587—594
(1990).
6) Hart G. W., Kreppel L. K., Comer F. I., Arnold C. S., Snow D. M., Ye
Z., Cheng X., Dellamanna D., Caine D. S., Earlesm B. J., Akimoto Y.,
Cole R. N., Haynes B. K., Glycobiology, 6, 711—716 (1996); Comer
F. I., Hart G. W., J. Biol. Chem., 275, 29179—29182 (2000).
7) Suzuki K., Maeta H., Matsumoto T., Tetrahedron Lett., 30, 4853—
4856 (1989).
8) It was possible to increase loading thioglycoside loading up to 0.58
mmol/g (calculated after cleavage; elemental analysis calculation for
S; 1.22%) by repeating the addition reaction of phenol 16 to Merrifield
resin twice.
Chart 5
in chlorine content which correlated with the increase in the
value for nitrogen, after reaction with 17. Furthermore, the
thioglycoside content was determined by the sulfur atom per-
centage. From the elemental analysis (S; 0.70%), the yield
(from Merrifield resin to 18, four steps) was calculated to be