LETTER
Release Strategy for Rapid Oligosaccharide Construction
981
Financial supports for Grant-in-Aid for Scientific Research
(No. 13480191) and for Encouragement of Young Scientists
(No. 13771350) from Ministry of Education, Culture, Sports, Sci-
ence and Technology, Mitsubishi Chemical Corporation Fund,
Grant-in-Aid from the Tokyo Biochemical Research Foundation
and Mizutani Foundation are greatly acknowledged. We thank Ms.
A. Takahashi for technical assistance. We thank Dr. Chihara and his
staff for elemental analysis and Ms. Chijimatsu for 1H NMR mea-
surements.
analysis, it was revealed that the deprotection of chloro-
acetyl group was completed within 10 minutes. Then the
disaccharide acceptor was subjected to the glycosylation
using 12 as a donor.13
As shown in Scheme 3, having completed the synthesis of
trisaccharide 13 on the polymer support, the capture-re-
lease purification using resin bound Boc protected cys-
teine was examined. The desired PEG supported
trisaccharide 13 was captured by 5.0 equivalents of poly-
styrene resin bound Boc-Cys derivative 14 in the presence
of i-Pr2NEt.14 After filtration of the resins and washing,
the trisaccharide product was released by successive treat-
ment with TFA (to remove Boc) and piperidine (to gener-
ate free NH2). The compound 16 was obtained
successfully in a substantially pure form in 47% yield
from 8.15
References
(1) (a) Ito, Y.; Manabe, S. Curr. Opin. Chem. Biol. 1998, 2,
701. (b) Seeberger, P. H.; Haase, W.-C. Chem. Rev. 2000,
100, 4349. (c) Sears, P.; Wong, C.-H. Science 2001, 291,
2344.
(2) (a) Ando, H.; Manabe, S.; Nakahara, Y.; Ito, Y. J. Am.
Chem, Soc. 2001, 123, 3848. (b) Ando, H.; Manabe, S.;
Nakahara, Y.; Ito, Y. Angew. Chem. Int. Ed. 2001, 40, 4725.
(c) Ito, Y.; Manabe, S. Chem.–Eur. J. 2002, 8, 3076.
(3) (a) Kanie, O.; Crawley, S. C.; Palcic, M. M.; Hindsgaul, O.
Carbohydr. Res. 1993, 243, 139. (b) Lu, P. P.; Hindsgaul,
O.; Compston, C. A.; Palcic, M. M. Bioorg. Med. Chem.
1996, 4, 2011.
(4) (a) Granovsky, M.; Fata, J.; Pawling, J.; Muller, W. J.;
Khokha, R.; Dennis, J. W. Nature Medicine 2000, 6, 306.
(b) Sasai, K.; Ikeda, Y.; Fujii, T.; Tsuda, T.; Taniguchi, N.
Glycobiology 2002, 12, 119.
(5) (a) Hodosi, G.; Kováč, P. J. Am. Chem. Soc. 1997, 119,
2335. (b) Hodosi, G.; Kováč, P. Carbohydr. Res. 1998, 308,
63.
(6) (a) Separation of b-mannoside and 3-O-alkylated
regioisomer was difficult at this stage. For easier separation,
the remained hydroxy groups were acetylated and the
anomeric acetyl group of the regio isomer was removed by
piperidine. The linkage of stereochemistry of anomeric
position of 6 was confirmed by 1H NMR analysis
(JCH = 156.6 Hz in C6D6) and NOE experiment between H-1
and H-5. (b) Bock, K.; Pedersen, C. J. Chem. Soc., Perkin
Trans. 2 1974, 293.
(7) During the benzylation, the methyl group was changed to
benzyl ether (7.9%) and carboxylic acid (9.5%). As the
separation of methyl ester and benzyl ester was difficult, the
mixture of the ester was hydrolyzed.
O
O
BocHN
HS
N
H
O
14
13
a
O
O
BocHN
S
PhthN
N
O
OBn
O
H
O
BnO
BnO
BnO
O
O
OBn
O
OBn
O
O
BnO
BnO
O(CH2)8CO2PEG
15
PhthN
OBn
OH
O
BnO
BnO
BnO
O
O
OBn
OBn
b
c
1
O
BnO
BnO
O
O(CH2)8CO2PEG
16
Scheme 3 Reagents and conditions: (a) i-Pr2NEt, CH3CN, CH2Cl2;
(b) i) TFA, CH2Cl2; ii) 10% piperidine, CH2Cl2; (c) i) 1 M KOH,
EtOH, benzene; ii) ethylenediamine, 1-BuOH, then Ac2O, pyridine,
91% (2 steps); iii) TMSCHN2, MeOH, benzene (85%); iv) H2, 20%
Pd(OH)2, HOAc, MeOH (88%).
(8) Previously, the average molecular weight 550 PEG was used
as a polymer support and it works as ‘tag’ efficiently.
However, in this case, its molecular weight is not sufficient
for the ‘tag’ for the purification because of lack of enough
polarity.
(9) Inanaga, J.; Hirai, K.; Saeki, H.; Katsuki, T.; Yamaguchi, M.
Bull. Chem. Soc. Jpn. 1979, 52, 1989.
(10) Boons, G.-J.; Bowers, S.; Coe, D. M. Tetrahedron Lett.
1997, 38, 3773.
(11) Although the characteristic ‘mountain’ like shape of the
spectra of monosaccharide and disaccharide were not
completely separated, the monitoring of progress of the
reaction was possible. After the reaction, quite high purity of
PEG-bound disaccharide was confirmed by 1H NMR
spectroscopy.
Trisaccharide was then cleaved from PEG under alkaline
conditions, and deprotected. Thus, the phthalimide group
was converted to acetamide and the acid was esterified by
(trimethylsilyl)diazomethane.16 Finally, the benzyl
groups were removed under catalytic hydrogenation con-
ditions to afford 1 in 88% yield.17
In summary, we demonstrate the utility of the refined cap-
ture-release strategy by successfully synthesizing trisac-
charide 1 on polymer support rapidly in a pure form.
(12) Van Boeckel, C. A. A.; Beetz, T. Tetrahedron Lett. 1983, 24,
3775.
(13) The ratio of a:b at the newly formed anomeric carbon is
1:9.9.
Acknowledgment
(14) Compound 14 was prepared from Boc-b-Ala-Merrifield
resin (0.66 mmol/g) in 2 steps. i) TFA, CH2Cl2, then Et3N;
ii) Boc-S-tert-butylmercapto-L-cysteine, HOBt, N, N¢-
We thank to Prof. Fumio Sugawara for his generous support. S. H.
was supported by Junior Research Associate Program at RIKEN.
Synlett 2003, No. 7, 979–982 ISSN 1234-567-89 © Thieme Stuttgart · New York