Chemical behavior of benzylidene acetal groups bridging the contiguous glucose residues in malto-oligosaccharide derivatives.

Treatment of phenyl alpha-maltoside with an excess of alpha, alpha-dimethoxytoluene in the presence of (+)-10-camphorsulfonic acid, followed by partial hydrolysis to remove unstable acyclic acetal substituents, gave phenyl 3,2':4',6'-di-O-benzylidene-alpha-maltoside. Thus, one of the benzylidene groups formed an eight-membered cyclic acetal ring bridging the two monosaccharide components. This acetal function was stable under conventional acylation and alkylation conditions, but was selectively hydrolyzed by 80% acetic acid at room temperature. Treatment of a per-O-benzoyl derivative of 1 with N-bromosuccinimide-barium carbonate afforded phenyl 2,6,3', 4'-tetra-O-benzoyl-6'-bromo-6'-deoxy-alpha-maltoside in 80% yield. Reductive ring opening of the tri-O-benzyl derivative of 1 with lithium aluminum hydride-aluminum chloride gave a 2,3,6,3',4'-penta-O-benzyl derivative, while reduction with sodium cyanoborohydride-hydrogen chloride or borane trimethylamine complex-aluminum chloride afforded a 2,3,6,3',6'-penta-O-benzyl derivative in good yield. Similar regioselectivity was observed in the reductive cleavage of a 1,6-anhydro-3',2'':4'',6''-di-O-benzylidene-beta- maltotriose derivative.