Four isomeric ethyl 1-thioglycosides from 2-amino-2-deoxy-D-arabinose

Ethyl 2-amino-2-deoxy-1-thio-alpha- and -beta-D-arabinopyranoside (2 and 4) were obtained by direct ethanethiolation of 2-amino-2-deoxy-D-arabinose (1), and their structures were determined by mass and p.m.r. spectrometry. Ethyl 2-amino-2-deoxy-1-thio-alpha- and -beta-D-arabinofuranoside (11 and 13) were prepared by partial demercaptalation of 2-amino-2-deoxy-D-arabinose diethyl dithioacetal (6) with mercuric chloride (or, preferably, with bromine), with or without protection of the 5-hydroxyl group. Demercaptalation with mercuric chloride gave the beta-D anomers almost exclusively, and treatment with bromine gave a mixture of the alpha and beta anomer in the ratio of similar to 1:1. Alternatively, direct ethanethiolation of 1 in trifluoracetic acid yielded the alpha-D anomer. The structures of 11 and 13 were determined by mass spectrometry, by direct comparison of their N-acetyl derivatives with an authentic enantiomorph (15b), and by p.m.r. spectroscopy. The physicochemical properties of the four 1-thioglycosides (2,4,11, and 13) were compared with those of the O-GLYCOSIDES of D-arabinose.