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

Article abstract of DOI:10.1016/0008-6215(93)84024-Z

Treatment of phenyl α-maltoside with an excess of α,α-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-α-maltoside (1). 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-α-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-β-maltotriose derivative. Treatment of phenyl α-maltoside with an excess of α-α-dimethoxytoluene in the presence of (+)-10-caphorsulfonic acid, followed by practical hydrolysis to remove unstable acrylic acetal substituents, gave phenyl 3,2':4', 6-di-O-benzylidence-α-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% yield 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-benzoly derivative of 1 with lithium aluminium hydride-aluminium chloride gave a 2,3,6,3'4,-penta-O-benzyl derivative, while reduction with sodium cyanoborohydride-hydrogen chloride or borane trimethylamine complex-aluminium chloride afforded a 2,3,6,3' penta-O-benzyl derivative in good yield. Similar regioselectivity was observed in the reductive cleavage of a 1,6-anhydro-3'2″-diO-benzylidene-beta-maltotriose derivative.