C O M M U N I C A T I O N S
lished. The deprotection of CAc was monitored by the PNBP
method, whereas the glycosylation was monitored by the cyanuric
chloride-Disperse Red conjugate method. It is operationally simple
and quick and does not require any special equipment. Because
PNBP and Disperse Red color tests are complementary to each
other, the combination allows one to gain a clear indication of the
progress of glycosylation, even if complete conversion is not
obtained. Several examples of fluorescence or dye based screening
methods of reaction conditions are known;14 however, to our
knowledge, this is the first example for the multistep transformation
monitored on resin, except peptide synthesis. Further application
of this methodology will be reported in due course.
Acknowledgment. This work was supported by a Grant-in-Aid
for Scientific Research (No. 13480191) and for Encouragement of
Young Scientists (No. 13771350) from the Ministry of Education,
Culture, Sports, Science, and Technology, the Mizutani Foundation,
and the Presidential Fund in RIKEN. We thank Ms. Akemi
Takahashi for her technical assistance. We thank Dr. T. Chihara
and his staff for elemental analysis.
Supporting Information Available: Detailed experimental pro-
cedures for the synthesis of all compounds, general procedure, and
1
deprotection and glycosylation reactions on solid-phase, H and 13C
NMR spectra (PDF). This material is available free of charge via the
Figure 2. Reaction monitoring by PNBP and Disperse Red method. (i)
(a) Ac2O, i-Pr2NEt, CH2Cl2, (b) HDTC, DMF; (ii) 11, BF3‚OEt2, CH2Cl2.
References
(1) Essentials of Glycobiology; Varki, A., Cummings, R., Esko, J., Freeze,
H., Hart, G., Marth, J., Eds.; Cold Spring Harbor Laboratory Press:
Plainview, NY, 1999.
(2) (a) Ito, Y.; Manabe, S. Curr. Opin. Chem. Biol. 1998, 2, 701-708. (b)
Seeberger, P. H.; Hasse, W.-C. Chem. ReV. 2000, 100, 4349-4394.
(3) Kaiser, E.; Colescott, R L.; Bossinger, C. D.; Cook, P. I. Anal. Biochem.
1970, 34, 595-598.
Figure 3. TLC profile of the crude mixture after cleavage of 13 (CHCl3:
MeOH 8:1).
(4) Seeberger, P. H.; Beebe, X.; Sukenick, G. D.; Pochapsky, S.; Danishefsky,
S. J. Angew. Chem., Int. Ed. Engl. 1997, 36, 491-493.
(5) (a) Kanemitsu, T.; Kanie, O.; Wong, C.-H. Angew. Chem., Int. Ed. 1998,
37, 3415-3418. (b) Kanemitsu, T.; Wong, C.-H.; Kanie, O. J. Am. Chem.
Soc. 2002, 124, 3591-3599.
Scheme 2
(6) Mogemark, M.; Elofsson, M.; Kihlberg, J. Org. Lett. 2001, 3, 1463-
1466.
(7) Ando, H.; Manabe, S.; Nakahara, Y.; Ito, Y. J. Am. Chem. Soc. 2001,
123, 3848-3849.
(8) Kuisle, O.; Lolo, M.; Quin˜oa´, E.; Riguera, R. Tetrahedron 1999, 55,
14807-14812.
Scheme 3
(9) (a) Attardi, M. E.; Falchi, A.; Taddei, M. Tetrahedron Lett. 2000, 41,
7395-7399. (b) Attardi, M.; Taddei, M. Tetrahedron Lett. 2001, 42, 2927.
(10) Nicolaou, K. C.; Winssinger, N.; Pastor, J.; DeRoose, F. J. Am. Chem.
Soc. 1997, 119, 449-450.
(11) (a) Manabe, S.; Nakahara, Y.; Ito, Y. Synlett 2000, 1241-1244. (b)
Manabe, S.; Ito, Y. Chem. Pharm. Bull. 2001, 49, 1241-1242. (c) Wu,
X.; Grathwohl, M.; Schmidt, R. R. Org. Lett. 2001, 3, 747-750.
(12) van Boechel, C. A. A.; Beetz, T. Tetrahedron Lett. 1983, 24, 3775-
3778.
(13) (a) Tabata, K.; Ito, W.; Kojima, T.; Kawabata, S.; Misaki, A. Carbohydr.
Res. 1981, 89, 121. (b) Nishimura, K.; Nishimura, S.; Nishi, N.; Saiki, I.;
Tokura, S.; Azuma, I. Vaccine 1984, 2, 93-99. (c) Chihara, G. Cancer
Res. 1986, 85-96. (d) Schizophyllan was demonstrated to form a triple
helix with single-stranded RNA: Sakurai, K.; Shinkai, S. J. Am. Chem.
Soc. 2000, 122, 4520-4521. (e) For a recent example of solution-phase
synthesis of immuno-active â-glycan, see: Yang, G.; Kong, F. Synlett
2000, 1423-1426.
45% yield (Scheme 2) (for TLC profile, see the Supporting
Information).
Resin-bound disaccharide 12 was subjected to the second round
of dechloroacetylation-glycosylation, and the tetrasaccharide, which
corresponds to the repeating unit of the immuno-active oligosac-
charide schizophyllan,13 was constructed successfully again with
on-resin real-time monitoring. After cleavage, the tetrasaccharide
15 was obtained in a reasonably pure form (Scheme 3, Figure 3).
After chromatographic purification, 15 was isolated in 30% overall
yield based on the initiated loading of 9 (Scheme 3, Figure 3).
In summary, a practical method for the real-time reaction
monitoring on-beads for oligosaccharide construction was estab-
(14) (a) Weingarten, M. D.; Sekanina, K.; Still, W. C. J. Am. Chem. Soc. 1998,
120, 9112-9113. (b) Shaughnessy, K. H.; Kim, P.; Hartwig, J. F. J. Am.
Chem. Soc. 1999, 121, 2123-2132. (c) Copeland, G. T.; Miller, S. J. J.
Am. Chem. Soc. 1999, 121, 4306-4307. (d) Korbel, G. A.; Lalic, G.;
Shair, M. D. J. Am. Chem. Soc. 2001, 123, 361-362.
JA020781Z
9
J. AM. CHEM. SOC. VOL. 124, NO. 43, 2002 12639