Biosynthesis of L-Azetidine-2-Carboxylic Acid In Actinoplanes ferrugineus

L-Azetidine-2-carboxylic acid (A-2-C), a four-membered cyclic imino acid has been identified in certain plants, and the microorganism Actinoplanes ferrugineus. The imino acid A-2-C has a physiological significance as an antgaonist of proline during peptide synthesis. The biosynthetic mechanism for the formation of A-2-C has not been studied in any detail. By using various amino acids such as methionine and S-adenosyl-L-methionine labeled with deuterium or carbon-14, the details of the biosynthetic pathway and a possible mechanism for the formation of L-A-2-C in .4. ferrugineus have been unravelled, Both in vivo and in vitro experimental results suggest the biosynthesis of L-A-2-C is mediated by a confactor containing a carbonyl group, probably pyridoxal Phosphate. S-Adenosyl-L-methionine, which seems to be the direct biosynthetic substrate, has undergone a f-displacement by an ${\alpha}$-amino group of the amino acid portion of the substrate S-adenosyl-L-methionine potentially via a vinylglycine intermediate. The overall stereochemical events at the ${\beta}$-carbon of the substrate have been shown to inversion of configuration. The overall stereochemical events at the -position of the sub- strate have also been shown to occur with inversion of configuration. The ${\beta}$, ${\gamma}$-elimination reaction of the substrate seems to follow a cisoidal-type mechanism and the addition portion of the reaction a transoidal-type mechanism . The assignment of the proton NMR of A-2-C has been deduced by apply- ing NOE difference experiments, Gd(III) line-broadening experiments and 2D-NOESY experiments of regio-and stereospecificially deuterated A-2-C's.