Design, Synthesis, and Evaluation of 9-<scp>d</scp>-Ribityl-1,3,7-trihydro-2,6,8-purinetrione, a Potent Inhibitor of Riboflavin Synthase and Lumazine Synthase

Abstract

Reduction of 5-nitro-6-d-ribitylaminouracil (9) afforded 5-amino-6-d-ribitylaminouracil (1), which reacted with ethyl chloroformate to yield 5-ethylcarbamoyl-6-d-ribitylaminouracil (12). The latter compound was cyclized to 9-d-ribityl-1,3,7-trihydropurine-2,6,8-trione (13), which was found to be a relatively potent inhibitor of both Escherichia coli riboflavin synthase (Ki 0.61 μM) and Bacillus subtilis lumazine synthase (Ki 46 μM). Molecular modeling of the lumazine synthase−inhibitor complex indicated the possibility for hydrogen bonding between the Lys135 ε-amino group of the enzyme and both the 8-keto group and the 4‘-hydroxyl group of the ligand. A bisubstrate analogue of the riboflavin synthase-catalyzed reaction, 1,4-bis[1-(9-d-ribityl-1,3,7-trihydropurine-2,6,8-trionyl)]butane (18), was also synthesized using a similar route and was found to be inactive as an inhibitor of both riboflavin synthase and lumazine synthase.