Anthracycline oligosaccharides: facile stereoselective synthesis of 2,6-dideoxy-alpha-L-lyxo-hexopyranosides.

Glycosylation of benzyl-2,3,6-trideoxy-3-trifluoroacetamido-alpha-L-lyxo-h exopyranoside (6) with 3,4-di-O-acetyl-1,5-anhydro-2,6-dideoxy-L-lyxo-hex-1-enitol (1) or 4-O-acetyl-1,5-anhydro-3-O-benzyl-2,6-dideoxy-L-lyxo-hex-1-enit ol (2) in the presence of trimethylsilyl triflate/triethylamine gave alpha-(1----4)-linked disaccharide derivatives 7 and 8, respectively. In the presence of trimethylsilyl triflate only, 3,4-di-O-acetyl-1-O-tert-butyldimethylsilyl-2,6-dideoxy-beta-L-lyxo++ +-hexopyranose (3) and 6 gave mainly 7. Condensation of 1 or 2 with 9, obtained by O-deacylation of 8, afforded benzyl [O-(3,4-di-O-acetyl-2,6-dideoxy-alpha-L-lyso-hexopyranosyl)-(1----4)-O-( 3-O-benzyl-2,6-dideoxy-2,6-alpha-L-hexopyranosyl)-(1----4)-(2,3,6-tri deo xy-3-trifluoroacetamido-alpha-L-lyxo-hexopyranoside)] (11) and its 3''-benzyl analogue 12, respectively.