Synthesis of 10‐deazariboflavin and related 2,4‐Dioxopyrimido[4,5‐b]quinolines

Condensation of substituted anthranilaldehydes with barbituric acid results in the formation of 2,4‐dioxopyrimido[4,5‐b]quinolines. Using this general synthetic approach, 7,8‐dimethyl‐2,4‐dioxo‐10‐ribityl‐2,3,4,10‐tetrahydropyrimido[4,5‐b]quinoline (10‐deazariboflavin) was prepared by the condensation of barbituric acid with 4,5‐dimethyl‐N‐ribitylanthranilaldehyde. The latter was obtainedin situby the treatment of 1‐[4,5‐dimethyl‐N‐(ribityl)anthraniloyl]‐2‐(p‐toluenesulfonyl)hydrazine, prepared from 4,5‐dimethylanthranilic acid with anhydrous sodium carbonate.