CHEMICAL EVOLUTION .33. PHOTO-CHEMICAL DECARBOXYLATION OF OROTIC-ACID, OROTIDINE, AND OROTIDINE 5'-PHOSPHATE

Orotic acid, orotidine, and orotidine 5ʹ-phosphate are photochemically converted to uracil, uridine, and uridine 5ʹ-phosphate in chemical yields of 13, 45, and 23%, respectively. The chemical yields for uracil and uridine formation are 1.6 X 10-5 and 1.7 X 10-2, respectively. The chemical yield of uracil increases 2.5-fold when the orotic acid concentration is decreased 10-fold, indicating that bimolecular reactions limit the uracil yield. The reaction proceeds from the singlet excited state as shown by the absence of quenching by paramagnetic ions and the absence of sensitization by benzophenone and acetone. The Fe(III)- and Cu(II)-promoted photochemical formation of uracil from orotic acid proceeds in up to 17% yield. Small amounts of barbituric acid are also observed. A plausible pathway for the prebiological formation of uracil and its derivatives from HCN via orotic acid and its derivatives is discussed. © 1979, American Chemical Society. All rights reserved.