Acid-catalyzed dehydrative cyclization of 4-(D-galacto-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole. Synthesis and anomeric configuration of D-lyxo-C-nucleoside analogs

Dehydration of 4-(D-galacto-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole with 20% methanolic sulfuric acid afforded the anomeric pairs of nucleosides, 4- (alpha -D-lyxopyranosyl)-2-phenyl-2H-1,2,3-triazole (major component) and i ts beta -anomer, as well as 4-(alpha -D-lyxofuranosyl)-2H-1,2,3-triazole an d its beta -anomer. The four anomeric C-nucleosides were separated by chrom atography, and their structure and anomeric configuration were determined b y periodate oxidation, acylation, and NMR spectroscopy as well as mass spec trometry. The anomeric assignment from optical rotation was not in agreemen t with final structure assignment and represented a violation of the Hudson isorotation rules. NOE studies and X-ray diffraction measurements confirme d the anomeric configuration. (C) 2001 Elsevier Science Ltd. All rights res erved.