earticle

영어

Previously, we reported the a-directing effect due to the remote participation of 3-O-acyl and 6-O-acetyl groups of donors in mannosylations. Herein we report the a-directing effect by remote participation of 4-O-acyl groups of galactose donors in galactosylations. Galactosyldonors possessing benzylsulfonyl, benzoyl, p-methoxybenzoyl, and acetyl groups were prepared. The outcome of the stereochemistry in glycosylations of various acceptors with these donors indicated that 4-O-acyl groups of galactose donors participated during glycosylations. The outcome of the stereochemistry of the galactosylations could be interpreted either by the remoteparticipation of acylgroups or by the reaction between the acceptor and the galactosyl oxocarbeniumion in 4H3 or 3H4 comformation. Detection by the mass spectrometry of the bicyclic product with a seven-membered trichlorooxazepine ring, resulting from the activation of phenyl 1-thio-4-trichloroacetimidoyl galactoside with BSP and Tf2O, is provided a further evidence for the participation of 4-O-acyl groups in the galactosylation. Galactosylations were conducted by treatment of thioglycosides possessing electron-withdrawing groups at O-4 with BSP and Tf2O at -60℃.