Synthesis of chitotetraose and chitohexaose based on dimethylmaleoyl protection

tert-Butyldimethylsilyl 3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido-beta -D-glucopyranoside was readily transformed into the disaccharide glycosyl donor, 3,4,6-tri-O-acetyl-2-deoxy-2-dimethylmaleimido-beta -D-glucopyranosyl-(1 --> 4)-3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido-alpha/beta -D-glucopyranosyl trichloroacetimidate, and the disaccharide glycosyl acceptor, tert-butyldimethylsilyl 3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido-beta -D-glucopyranosyl-(1 --> 4)-3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido-beta -D-glucopyranoside. A TMSOTf-catalysed coupling of the acceptor with the donor afforded the respective tetrasaccharide derivative, which can be transformed to chitotetraose. tert-Butyldimethylsilyl 3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido-4-O-phenoxyacetyl-beta -D-glucopyranosyl-(1 --> 4)-3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido-beta -D-glucopyranoside was converted into donor 3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido-4-O-phenoxyacetyl-beta -D-glucopyranosyl- (1 --> 4)-3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido-beta -D-glucopyranosyl trichloroacetimidate. Its coupling with benzyl 3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido- beta -D-glucopyranosyl-(1 --> 4)-3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido-beta -D-glucopyranoside, followed by dephenoxyacetylation, gave benzyl 3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimiido-beta -D-glucopyranosyl- (1 --> 4)-3,6-di-O-benzyl-2-deoxy-2-dimethyimaleimido-beta -D-glucopyranosyl-(1 --> 4)- 3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido- beta -D-glucopyranosyl-(1 --> 4)-3.6-di-O-benzyl-2-deoxy-2-dimethylmaleimido-beta -D-glucopyranoside, whose glycosylation furnished, after replacement of the DMM-group by the acetyl moiety and subsequent deprotection, chitohexaose. (C) 2001 Elsevier Science Ltd. All rights reserved.