Amino acid relative transamination rates

Thus we designed and synthesized a bicyclic pyridoxamine derivative carrying an oriented catalytic side arm (16) [11], Rates for conversion of the ketimine Schiff base into the aldimine, formed with 26 (below) and a-ketovaleric acid, indolepyruvic acid, or pyruvic acid, were enhanced 20-30 times relative to those carried out in the presence of the corresponding pyridoxamine derivatives without the catalytic side arm. With a-ketovaleric acid, 16 underwent transamination to afford D-norvaline with 90% ee. The formation of tryptophan and alanine from indolepyruvic acid and pyruvic acid, respectively, showed a similar preference. A control compound (17), with a propylthio group at the same stereochemical position as the aminothiol side arm in 16, produced a 1.5 1 excess of L-norvaline, in contrast to the large preference for D-amino acids with 16. Therefore, extremely preferential protonation seems to take place on the si face when the catalytic side arm is present as in 16. 

D-Amino acids vary in availability with the species. For example d-phenylalanine is used by rat, mouse, and man (15, 35, 727, 730, 962), whereas D-tryptophan is used by the rat (53, 54, 759, 895), is partially used by the mouse and pig (139, 867), and is not used by man (7, 29). The utilization of the D-amino acids is probably determined by the relative rates of absorption of the D-amino acid from the intestine, and of conversion of d- to L-amino acid in the liver (288). The conversion of d- to L-phenylalanine is reduced in vitamin-Be deficiency (52), as is to be expected for a transformation involving transamination to phenylpyruvic acid. Phenylpyruvic and indolepyruvic acids, the a-keto acids corresponding to phenylalanine and tryptophan, may also, to an extent varying with the species, satisfy growTh requirements (e.g., 55, 109, 436, 725, 911). 

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