Synthesis of chitotetraose and chitohexaose based on dimethylmaleoyl protection.

Abstract tert -Butyldimethylsilyl 3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranoside was readily transformed into the disaccharide glycosyl donor, 3,4,6-tri- O -acetyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranosyl-(1→4)-3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-α/β- d -glucopyranosyl trichloroacetimidate, and the disaccharide glycosyl acceptor, tert -butyldimethylsilyl 3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranosyl-(1→4)-3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- 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-β- d -glucopyranosyl-(1→4)-3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranoside was converted into donor 3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-4- O -phenoxyacetyl-β- d -glucopyranosyl-(1→4)-3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranosyl trichloroacetimidate. Its coupling with benzyl 3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranosyl-(1→4)-3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranoside, followed by dephenoxyacetylation, gave benzyl 3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranosyl-(1→4)-3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranosyl-(1→4)-3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranosyl-(1→4)-3,6-di- O -benzyl-2-deoxy-2-dimethylmaleimido-β- d -glucopyranoside, whose glycosylation furnished, after replacement of the DMM-group by the acetyl moiety and subsequent deprotection, chitohexaose.