A~-Pyrroline-5-carboxylic acid, an intermediate in both the biosynthesis and degradation of L-proline, has been synthesized by the periodate oxidation of hydroxylysine and isolated as a pure compound, as indicated by enzymatic assay with pyrroline-5-carboxylate reductase from Escherichia coli. Some features of the instability in solution of 2x~-pyrroline-5-carboxylic acid have been studied, leading to the conclusion that the rate of decomposition is sensitive to concentration of the compound. Colorimetric assay with o-aminobenzaldehyde was found to be an inadequate measure of the pyrroline compound in partially decomposed solutions.
In a wide range of species, Al-pyrroline-5-carboxylic acid (P5C) 2 is an intermediate both in the biosynthesis and aerobic catabolism of L-proline (1)_ The compound was first recognized as a metabolic intermediate by Vogel and Davis (2) who also described its chemical synthesis and its reactivity with o-aminobenzaldehyde (o-AB)_ This reaction, following Strecker (3), has been widely used as a quantitative assay for P5C.
Although Good and Mitchell (4) described a synthesis of P5C as its diethylacetal, all workers requiring the compound have employed the Vogel and Davis procedure_ In this procedure, subsequently refined by Strecker (3), glutamic semialdehyde was generated by acid hydrolysis of y, y-dicarbethoxy-y-acetamidobutyraldehyde. The semialdehyde exists in solution primarily as its cyclic aldimine, P5C (2). Strecker (3) purified P5C by chromatography on Dowex 50: elution with HCI yielded the hydrochloride as a solid. While this solid could be stored, its purity was only 80% by enzymatic assay with P5C dehydrogenase. Strecker found, as did Vogel and Davis, that P5C is rather unstable in solution.
A need for frequent preparation of P5C led us (5) to examine a faster and simpler synthetic route: the periodate oxidation of 6-hydroxylysine.