| 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-Obenzyl-2- deoxy-2-phthalimido-1-thio-beta-D-galactopyranoside (3a), 4-O-Acetyl- 3,6-di-O-benzyl-2- deoxy-2-phthalimido-beta-D-galactopyranosyl bromide ( 4), 4-O-acetyl-3,6-di-O-benzyl-2-deoxy- 2-phthalimido-beta-D-galactopyranosyl fluoride (5b), O-(4-O-acetyl-3,6-di-O-benzyl-2-deoxy- 2-phthalimido-beta-D-galactopyranosyl) trichloroacetimidate ( 7) and ethyl 3,6-di-Obenzyl-2- deoxy-2-phthalimido-1-thio-beta-D-galactopyranoside (8), pent-4-enyl 3,6-di-O-benzyland 3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimido-beta-D-galactopyranoside(10a) and (10b) and pent-4-enyl 3,6-di-O-benzyl-2- deoxy-2-phthalimido-4-O-(trimethylsilyl)-beta-D-galactopyranoside ( 11) as glycosyl acceptors in the synthesis of 2-amino-2-deoxy-beta-D-galactopyranosyl( 1 --> 4)-2-amino-2-deoxy-beta-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 alpha( 1 --> 4) bond were also formed. The unexpected intermolecular migration of ethyl-sufanyl 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. |
