Synthesis of 5-ethynyl-1-beta-D-ribofuranosyl-1H-[1,2,3]triazole-4-carboxylic acid amide (isosteric to EICAR) and its derivatives.

The synthesis of 5-ethynyl-1H-[1,2,3]triazole-4-carboxylic acid amide riboside 1 and its derivatives exploits Pd(0)-catalyzed cross-coupling reactions. The iodinated key intermediate 3a, when coupled with alkynes affords 5-alkynylated products 1b,c,e,f in diverse yields. Methanolysis of 1b and 1c provides the title compound 1 and the 5-propynyl derivative 1d, respectively. When coupled with methyl acrylate, 3a gives the E-isomer 4c, although in low yield, while the other 5-iodo precursor 3b undergoes reduction to 4b.