Reductive cleavage of permethylated polysaccharides with borane-methyl sulfide complex and butyltin trichloride

Several per-O-methylated monosaccharides and polysaccharides were used as models in an attempt to identify more convenient reagents for accomplishing reductive cleavage of glycosidic linkages. Included in the model studies were methyl α- and β-d-glucopyranoside, methyl α- and β-d-mannopyranoside, and methyl α- and β-d-ribofuranoside. These studies led to the identification of a new promoter, butyltin trichloride, for carrying out reductive cleavage when borane-methyl sulfide complex was used as the reducing agent. These reagents were found to accomplish the reductive cleavage of per-O-methylated amylose, cellulose, and pullulan to give only the expected derivatives of 1,5-anhydro-d-glucitol. These reagents also accomplished reductive cleavage of per-O-methylated inulin to give only the expected derivatives of 2,5-anhydro-d-mannitol and 2,5-anhydro-d-glucitol. Reductive cleavage using these reagents is easy to perform, and subsequent acetylation of the products is readily accomplished in situ.Mixtures of borane-methyl sulfide complex and boron trifluoride etherate were found to accomplish the reductive cleavage of several fully methylated methyl glycosides as well as fully methylated amylose, cellulose, pullulan, and inulin to given only the expected products.