Synthetic Studies on the Isomeric<i>N</i>-Methyl Derivatives of<i>C</i>-Ribavirin

Abstract The syntheses of all three of the mono-N-methy1 derivatives of C-ribavirin (3-β-D-ribofuranosyl-1, 2, 4-triazole-5-carboxamide, 2) have been accomplished. Reaction of 1-(β-D-ribofuranosyliminomethyl)-2-methyl-hydrazine ( 7 ) with ethyl oxamate (8) in boiling ethanol gave the N′-methyl-C-ribavirin ( 3 ). A similar treatment of β-D-ribofuranosyl-1-carboximidic acid methyl ester ( 6 ) with N′-methyloxamic hydrazide ( 10 ) furnished the N2-methyl-C-ribavirin ( 4 ). Direct methylation of unprotected 2 with methyl iodide in the presence of potassium carbonate in dimethyl sulfoxide gave N 4-methyl isomer ( 5 ) as the major product. Structural assignments of 3 , 4 , and 5 were based on the unequivocal synthetic sequences, 1H and 13C NMR data and confirmed by single crystal X-ray diffraction analysis.