188] The synthesis of N5,N10-methenyltetrahydrofolic acid

Abstract

This chapter describes the synthesis of N, N -Methenyltetrahydrofolic acid. The N, N -methenyltetrahydrofolic acid is the specific formyl donor for the third step in purine biosynthesis, the introduction of the 8-carbon atom into the purine ring by formylation of glycinamide ribonucleotide to formylglycinamide ribonucleotide. This folic acid derivative is formed in acid solution from either N -formyl- or N -formyltetrahydrofolic acid by elimination of water. An alternative procedure consists in the platinum oxide-catalyzed reduction at pH 1–2 of N -formylfolic acid, produced by formylation of folic acid. A method developed for the direct synthesis, in high yield, of the pure N, N -methenyl derivative from commercial tetrahydrofolic acid. The N -formyl derivative is the formyl donor for the formylation of 5-amino-4-imidazole carboxamide ribotide. N, N- methenyl and N -formyl derivatives of tetrahydrofolic acid are required for the biosynthesis of purines de novo in a partially purified enzyme system from pigeon liver. It is examined by descending chromatography on Whatman No.1 paper with a 1.0 M formic acid–0.01 M β -mercaptoethanol solvent system, demonstrates a single white fluorescent spot under ultraviolet light.