Branched-chain sugar nucleosides: stereocontrolled synthesis and bioevaluation of novel 3′-C-trifluoromethyl and 3′-C-methyl pyranonucleosides

A new series of 3 '-C-trifluoromethyl- and 3 '-C-methyl-beta-D-allopyranonucleosides of 5-fluorouracil and their deoxy derivatives has been designed and synthesized. Treatment of ketosugar 1 with trifluoromethyltrimethylsilane under catalytic fluoride activation and methyl magnesium bromide, gave 1,2:5,6-di-O-isopropylidene-3-C-trifluoromethyl (2a) and 3-C-methyl (2b)-alpha-D-allofuranose, respectively, in a virtually quantitative yield and with complete stereoselectivity. Hydrolysis followed by acetylation led to the 1,2,4,6-tetra-O-acetyl-3-C-trifluoromethyl (3a) and 3-C-methyl (3b)-beta-D-allopyranose. Compounds 3a,b were then condensed with silylated 5-fluorouracil and deacetylated to afford the target nucleosides 5a,b. Deoxygenation of the peracylated allopyranoses 3a,b followed by condensation with silylated 5-fluorouracil and subsequent deacetylation yielded the target 3 '-deoxy-3 '-C-trifluoromethyl and 3 '-deoxy-3 '-C-methyl-beta-D-glucopyranonucleosides 14a,b. The newly synthesized compounds were evaluated for their potential antiviral and cytostatic activities. The 3 '-deoxy-3 '-C-methyl-ribonucleoside 11b showed significant cytotoxic activity (similar to 7 mu M) almost equally active against a variety of tumor cell lines. (C) 2015 Elsevier Ltd. All rights reserved.