Abstract
Treatment of 6-methylsulfonyl-9-(2, 3, 5-tri-O-benzoyl-β-D-ribofuranosyl) purine with ethyl acetoacetate and sodium hydride in tetrahydrofuran afforded, after deblocking, 6-ethoxycarbonylmethyl-9-β-D-ribofuranosylpurine. Similarly, replacement of the 6-methylsulfonyl moiety with other carbanions derived from diethyl malonate, ethyl cyanoacetate, malononitrile, nitromethane, and sodium cyanide gave the corresponding 6-C-substituted purine nucleosides. Most of these derivatives exist as the 6-(1H)-exomethylene tautomeric forms. 6-Ethoxycarbonylmethylpurine riboside was further converted to 6-methyl, ethyl, propyl, butyl, and pentyl-purine ribosides by decarboxylation or prior alkylation of the methylene group followed by de-carboxylation. This reaction sequence facilitated the preparation of hitherto almost inaccessible alkyl or C-substituted purine nucleosides.
