Nucleophilic displacement reactions in carbohydrates. Part XVIII. Syntheses of derivatives of 3,5-diacetamido-3,5-dideoxy-L-arabinose and 3,5-diacetamido-3,5-dideoxy-L-lyxose

Abstract

3,5-Diacetamido-3,5-dideoxy-L-arabinose has been synthesized by way of an azide-exchange reaction on 3-acetamido-3-deoxy-1,2-O-isopropylidene-5-O-p-tolysulphonyl-β-L-arabinose (7), which was conveniently prepared from 3-acetamido-3-deoxy-1,2:5,6-di-O-isopropylidene-α-D-galactofuranose (3). The replacement reaction of 1,2-O-isopropylidene-3,5-di-O-p-tolysulphonyl-β-L-arabinofuranose (17) with anhydrous hydrazine yielded 3,5-dideoxy-3,5-hydrazino-1,2-O-isopropylidene-β-L-lyxofuranose (19) as product, which was ultimately converted into 3,5-diacetamido-3,5-dideoxy-L-lyxose following hydrogenolysis over Raney nickel, N-acetylation, and acid hydrolysis. The free sugars were shown to favour the furanoid (10) and the six-membered (22) ring forms, respectively, at equilibrium in aqueous solution.