Synthesis of allyl 3-deoxy- and 4-deoxy-beta-D-galactopyranoside and simultaneous preparations of Gal(1-->2)- and Gal(1-->3)-linked disaccharide glycosides

Syntheses of galactose derivatives that are useful in probing the binding specificity of galactose-specific lectins are reported. These include allyl 3-deoxy- and 4-deoxy-beta-D-xylo-hexopyranoside and several disaccharide glycosides having Gal(1-->2) and Gal(1-->3) linkages. The beta-linked Gal disaccharide isomers were produced using 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide as glycosyl donor and the 4,6-O-benzylidene derivatives of allyl beta-D-galactopyranoside, alpha-D-glucopyranoside, alpha-D-mannopyranoside, and 2-acetamido-2-deoxy-alpha-D-galactopyranoside as acceptors. Only the Gal(1-->3)-linked disaccharide was obtained when the benzylidene derivatives of the mannopyranoside and 2-acetamido-2-deoxygalactopyranoside were used. Attempts at the preparation of Gal(alpha, 1-->2)Gal and Gal(alpha, 1-->3)Gal disaccharide glycosides were made using the same strategy, but employing the 1-trichloro-acetimidate or 1-N-methylacetimidate of 2,3,4,6-tetra-O-benzyl-D-galactopyranose as the glycosyl donor. The latter imidate produced a mixture of Gal(alpha, 1-->2)Gal and Gal(alpha, 1-->3)Gal derivatives as major products, but the former gave the Gal(beta, 1-->2)Gal isomer as the major product.