Synthesis of 2-Amino-2-deoxy-β-D-galactopyranosyl-(1→4)-2-amino-2-deoxy-β-D-galactopyranosides: Using Various 2-Deoxy-2-phthalimido-D-galactopyranosyl Donors and Acceptors

Abstract

A systematic study is presented of the efficiency of the most common glycosylation methods using standard 2-deoxy-2-phthalimidogalactopyranosyl donors ethyl 4-O-acetyl-3,6-di-O- benzyl-2-deoxy-2-phthalimido-1-thio-β-D-galactopyranoside (3a), 4-O-Acetyl-3,6-di-O-benzyl- 2-deoxy-2-phthalimido-β-D-galactopyranosyl bromide (4), 4-O-acetyl-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-D-galactopyranosyl fluoride (5b), O-(4-O-acetyl-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-D-galactopyranosyl) trichloroacetimidate (7) and ethyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-1-thio-β-D-galactopyranoside (8), pent-4-enyl 3,6-di-O-benzyl- and 3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimido-β-D-galactopyranoside (10a) and (10b) and pent-4-enyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-4-O-(trimethylsilyl)-β-D-galactopyranoside (11) as glycosyl acceptors in the synthesis of 2-amino-2-deoxy-β-D-galactopyranosyl-(1→4)-2-amino-2-deoxy-β-D-galactopyranosides 12, 16a and 17a. It was found that due to a low reactivity of the axial OH(4) group of glycosyl acceptors, disaccharides 16b and 17b with α(1→4) bond were also formed. The unexpected intermolecular migration of ethylsufanyl group from the reducing end of glycosyl acceptor 8 the reducing end of the activated form of glycosyl donor 4 in the glycosylation step to give ethylsulfanyl derivative 3a was proved. For preparation of the glycosyl donors and glycosyl acceptors with galacto configuration an approach based on epimerization of 4-O-mesyl derivatives of appropriate synthons with gluco configuration 2a and 2b was employed.