Synthesis of a set of highly clustered monosulfated galactopyranosides

There are several biological events that are known to involve certain sulfated saccharides. In many such cases, however, clustered ligands have been shown to be more effective than monovalent saccharides. A set of 6-aminohexyl glycosides of 2,3,4 or 6-monosulfated galactose have been synthesized and linked to polyglutamic acid. Because of the bulky aglycon employed, the 2-OH group of the key compound, 6-benzyloxycarbonylaminohexyl 4,6-O-benzylidene-beta-D-galactopyranoside was markedly less reactive than 3-OH. Thus, site-specific acetylation of 3-OH was readily carried out to obtain 2-O-sulfated galactosides, and even the direct sulfation of 3-OH afforded the 3-sulfate in a reasonable yield. On the other hand, the key compound was unexpectedly resistant to 2,3-O-dibenzylation or 2,3-O-dibenzoylation, both of which were meant for regioselective cleavage of 4,6-benzylidene to obtain the 4-sulfate.