NUCLEOSIDES HAVING QUINOLONE DERIVATIVES AS NITROGENATED BASE - REGIOSPECIFIC AND STEREOSPECIFIC RIBOSYLATION OF 3-CARBETHOXY-1,4-DIHYRO-4-OXOQUINOLINES

Ribosylation reactions of previously silylated 3-carbethoxy-8-methyl-1 ,4-dilhydro-4-oxoquinoline (6a) and 3-carbethoxy-6-methyl-1,4-dihydro- 4-oxoquinoline (6b) with 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofur anose (7), under Lewis acid catalysis, were studied. The method using hexamethyldisilazane (HMDS)/trimethylchlorosilane (TMCS) mixture for s ilylation and anhydrous stannic chloride as catalyst for ribosylation failed to give any nucleoside product. On the other hand, the protecte d nucleoside l-beta-D-ribofuranosyl)-1,4-dihydro-4-oxoquinoline (8b) w as obtained in good yields using bis(trimethylsilyl)trifluoroacetamide (BSTFA) containing 1% of TMCS and the same catalyst. Compound 8b was more easily isolated in higher yields with an improvement of the later method by replacing stannic chloride with trimethylsilyl trifluoromet hanesulfonate (TMSOTf). De-O-benzoylation of 8b with methanolic sodium hydroxide solution afforded the free riboside -1-beta-D-ribofuranosyl -1,4-dihydro-4-oxoquinoline (9b). The structures of the obtained produ cts were confirmed by their UV, MS IR, H-1 and C-13-NMR data.