Anomalous Zemplén deacylation reactions of 2-O-acyl-3-O-alkyl or -3-O-glycosyl derivatives of d-galactose and d-glucose: synthesis of O-α-d-mannopyranosyl-(1→4)-O-α-l-rhamnopyranosyl-(1→3)-d-galactose and an intermediate for the preparation of 2-O-glycosyl-3-O-(α-d-mannopyranosyl)-d-glucoses

Add time:08/18/2019    Source:sciencedirect.com

Treatment of 2-O-benzoyl (1) and 2-O-acetyl (5) derivatives of benzyl 4,6-O-benzylidene-3-O-(2,3,4-tri-O-acetyl-α-l-rhamnopyranosyl)-β-d-galactopyranoside under Zemplén conditions (catalytic amount of sodium methoxide in methanol) gave partially deacylated disaccharides in which the 2-O-acyl groups were retained. Likewise, a similar result was obtained with the β-l-rhamnopyranosyl analogue (3) of 1. This anomalous reaction was used in a synthesis of the title trisaccharide (17) and of methyl 4,6-O-benzylidene-3-O-(2,3:4,6-di-O-isopropylidene-α-d-mannopyranosyl)-α-d-glucopyranoside, an intermediate for the synthesis of 2-O-glycosyl-3-O-(α-d-mannopyranosyl)-d-glucoses.

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