SYNTHESES AND COUPLING REACTIONS OF 1,2-ANHYDRO-3,5-DI-O-BENZYL-ALPHA-L-RIBOFURANOSE AND ANHYDRO-5-O-BENZYL-3-O-METHYL-ALPHA-L-RIBOFURANOSE

1,2-Anhydro-3,5-di-O-benzyl-alpha-L-ribofuranose (7) and anhydro-5-O-b enzyl-3-O-methyl-alpha-L-ribofuranose (20) were synthesized from L-ara binose via the key intermediates 3,5-di-O-benzyl-2-O-tosyl- (5) and 5- O-benzyl-3-O-methyl-2-O-tosyl-L-arabinofuranose (18) respectively. Con densation of the anhydro sugars with silylated uracil in the absence o f catalyst gave the corresponding nucleoside derivatives with free 2'- OH in high yield. Selective glycosylation of 1,2-O-isopropylidene-alph a-D-xylofuranose with 7 afforded (1-->5)-beta-linked disaccharide pred ominantly in a good yield.