SYNTHESIS AND PROPERTIES OF O-GLYCOSYL CALIX[4]ARENES (CALIXSUGARS)

Model O-glycosylation reactions at either rim of calix[il]arenes are d escribed with the aim of providing access to a new family of carbohydr ate-containing calixarene derivatives named calixsugars. One or two su gar moieties (D-mannofuranose and D-glucopyranose) were introduced at the lower rim of the parent calix[4]arene by glycosylation of the phen olic hydroxyl groups by means of a Mitsunobu reaction, Tetrapropoxy ca lix[4]arenes bearing two or four hydroxymethyl groups at the upper rim were coupled with perbenzoylated thioethyl D-galactoside and D-lactos ide in the presence of the thiophilic promoter copper(Ir) triflate. In this way beta-linked bis-and tetrakis-O-galactosyl calix[4]arenes wer e obtained in good yield, the latter showing some solubility in water. For the O-lactosyl derivatives only the bis-substituted compound coul d be obtained because of the competing formation of an intramolecular ether linkage between 1,3-hydroxymethyl groups. Preliminary binding st udies showed some affinity of the galactose-containing calixsugars tow ard charged carbohydrates and dihydrogen phosphate anion.