4-β-D-Ribofuranosyl-1,2,4-triazin-3,5(2H,4H)-dione and 4-β-D-ribofuranosyl-6-methyl-1,2,4-triazin-3,5(2H, 4H)-dione

4-β-D-Ribofuranosyl-1,2,4-triazin-3,5(2H,4H)-dione (IX) and 4-β-D-ribofuranosyl-6-methyl-1,2,4,-triazin-3,5(2H,4H)-dione (XI) were prepared by cyclization of (Z)-4-β-D-ribofuranosyl-semicarbazones of methyl glyoxylate (VI) and methyl pyruvate (VIII) in the methanolic solution of sodium methoxide. A mixture of (E)- and (Z)-ribosylsemicarbazones III and IV was prepared by condensation of the ribosylsemicarbazide I with methyl dimethoxyacetate and a mixture of (E)-and (Z)-isomers V and VIII was obtained on condensation of I with methyl pyruvate. The (Z) isomer VI was prepared on acid-catalyzed isomerisation of the (E)-isomer III while the (Z)-isomer VIII was obtained on the UV-irradiation of isomer V.