A Chemically Prepared Formamidopyrimidine Derivative of Guanosine Triphosphate as a Possible Intermediate in Pteridine Biosynthesis

A nonenzymatic reaction of guanosine triphosphate, 2-mercaptoethanol, and Fe++ yields three products, each containing an acid-labile formyl group. Conditions for this reaction are described. Only one of the products, denoted as Fraction V, which is separated by diethylaminoethyl cellulose chromatography, served as a substrate for the enzymatic release of formate and the synthesis of dihydrofolate. In addition, Fraction V was converted enzymatically to 2-amino-4-hydroxy-6-substituted pteridines. Analyses of Fraction V indicated that it contains a pentose moiety, 3 phosphate residues, and an acid-labile formyl group. Treatment by glyoxal produced 2-amino-4-hydroxypteridine. The ultraviolet absorption spectra of Fraction V are also presented. These results suggest that Fraction V is identical with or similar to the immediate formamidopyrimidine derivative from GTP and may be an intermediate of pteridine biosynthesis from GTP.