Synthesis of propyl and 2-aminoethyl glycosides of α-D-galactosyl-(1→3′)-β-lactoside

Propyl and 3-aminoethyl alpha -D-galactopyranosy1-(1 -->3 ')-beta -lactosides (1 and 2) were prepared from the corresponding perbenzylated trisaccharide allyl glycoside 6 which, in turn, was obtained by methyl triflate promoted a-galactosylation of benzylated allyl lactoside acceptor 4 with thiogalactoside 3. Transformation of the allyl moiety in compound 6 into 2-azidoethyl one was achieved by cleavage of the double bond followed by reduction into alcohol 9, subsequent mesylation, and mesylate --> azide substitution. Alternatively trisaccharide 2 was synthesized using cr-galactosylation of selectively benzoylated 2-azidoethyl lactoside 19 with 3 as the key step. (C) 2001 Elsevier Science Ltd. All rights reserved.