Syntheses of alpha-D-galactosamine neoglycolipids

Abstract

Several N-acetyl-alpha-d-galactosamine neoglycolipids, as well as hydrophobized T and T(N) antigen analogues, were prepared for embedment onto liposomes. Three different lipidic structures were used for the anchoring, that is cholesterol, 1,3-bis(undecyloxy)propan-2-ol and 1,3-bis(3,7,11,15-tetramethylhexadecyloxy)propan-2-ol. Oligoethyleneglycol spacers were used to link the carbohydrate and the hydrophobic moieties; their lengths were varied in order to obtain model compounds for the selective recognition by sialyl transferases involved in cancer processes. Glycosylation reactions were optimized to sluggish amphiphilic acceptor alcohols, in order to reach good 1,2-cis-stereoselectivities and acceptable yields. This aim was achieved by using 3,4,6-tri-O-acetyl-2-azido-2-deoxy-d-galactopyranosyl trichloroacetimidate as the donor, trimethylsilyl trifluoromethanesulfonate as the promoter and diethyl ether or mixtures of diethyl ether and dichloromethane as solvents.