Preparation of 3-methoxycarbonylpropyl α-D- and 7-methoxycarbonylhexyl β-D-galactopyranosides: spacer-arm glycosides for branched oligosaccharide synthesis

Abstract

7-Methoxycarbonylheptyl β-D-galactopyranoside (7), 3-methoxycarbonylpropyl α-D-galactopyranoside (18), and its 6-O-pivaloloyl derivative (20), suitable for coupling to proteins or functionalised solid supports, have been synthesised from galactopyranosyloxyalkanals (4), (9), and (11) by sequential application of Wittig condensations, hydrogenations and, for the first example, deacetylation. Glycoside (2), prepared by galactosylation of the abundant ω-functionalised alcohol (1), was readily transformed into aldehyde (4) by chlorochromate oxidation of the ω-hydroxyglycoside (3) obtained upon debenzylation of (2). Aldehydes (9) and (11), obtained by ozonolysis of the allyl galactosides (8) and (10), were readily converted into enoates (12) and (13) respectively.