The allyl ether as a protecting group in carbohydrate chemistry. Part V. Preparation of benzyl ethers of carbohydrates for use in oligosaccharide synthesis

Abstract

The four tri-O-benzyl ethers of benzyl α-D-galactopyranoside were prepared from benzyl 6-O-allyl-α-D-galactopyranoside. The stability of 4,6-O-propylidene derivatives of benzyl-α-D-galactopyranoside in acidic hydroxylic solvents was noted in this work. The condensations of 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl chloride with methanol, benzyl 2,3,4-tri-O-benzyl-α-D-galactopyranoside, and benzyl 3,4,6-tri-O-benzyl-α-D-galactopyranoside in dichloromethane containing triethylamine and tetraethylammonium chloride gave glycosides containing predominantly α-linkages. The ¹³C n.m.r. spectra of the crystalline α-linked disaccharides, benzyl 6-O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-2,3,4-tri-O-benzyl-α-D-galactopyranoside and benzyl 2-O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-3,4,6-tri-O-benzyl-α-D-galactopyranoside were compared with those of the corresponding β-linked isomers. Treatment of 2,3,4,6-tetra-O-benzyl-D-glucose dimethyl acetal with an acid catalyst in ether gave predominantly methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranoside. 3,4,6-Tri-O-benzyl-2-dibenzylamino-2-deoxy-D-glucopyranose was prepared from allyl 2-benzamido-2-deoxy-β-D-glucopyranoside, as a potential intermediate for α-glycoside synthesis in the amino-sugar series.