SYNTHESIS OF A NOVEL CELLULOSE-TYPE HEXOPYRANAN 6-DEOXY-(1-]4)-ALPHA-L-TALOPYRANAN BY SELECTIVE RING-OPENING POLYMERIZATION OF 1,4-ANHYDRO SUGAR-DERIVATIVES

Selective ring-opening polymerization of 1,4-anhydro-6-deoxy-beta-L-talopyranose derivatives was investigated. 2,3-O-Isopropylidene monomer (AIDT) was polymerized in a stereoregular manner by both phosphorus pentafluoride and antimony pentachloride as catalysts at -40-degrees-C to give a 6-deoxy-2,3-O-isopropylidene-(1 --> 4)-alpha-L-talopyranan, i.e., a cellulose-type polysaccharide. The structure of poly(AIDT) was determined by specific rotation and C-13 NMR spectroscopy. 2,3-O-Cyclohexylidene monomer (ACDT) was also stereoselectively polymerized by phosphorus pentafluoride to give a (1 --> 4)-linked talopyranan derivative. Deisopropylidenation of the stereoregular poly(AIDT) and decyclohexylidenation of the stereoregular poly-(ACDT) gave 6-deoxy-(1 --> 4)-alpha-L-talopyranan, which is the first synthetic hexopyranan with cellulose-type structure. On the other hand, the polymerization of 2,3-O-benzylidene monomer (ABDT) gave an irregular polymer, containing the mixture of (1 --> 4)-alpha-L-talopyranosidic and (1 --> 5)-beta-L-talofuranosidic units. Poly-(ABDT) has deprotected by reduction. The mechanism of ring-opening polymerizations of 1,4-anhydrodeoxytalose derivatives is discussed.