THE α-KETO ANALOGUES OF ARGININE, ORNITHINE, AND LYSINE

Abstract

Although the cr-keto analogues of most of the common natural amino acids have been prepared, there are apparently no reports describing the preparation of the cr-keto acids corresponding to arginine (or-ketod-guanidinovaleric acid), ornithine (oc-keto-&aminovaleric acid), and lysine (CXketo-e-aminocaproic acid).The 2,4-dinitrophenylhydrazones of ac-keto-daminovaleric (l-3) and cr-keto-&guanidinovaleric (4) acids have been isolated; however, the free acids were not obtained.In the present communication the preparation of ar-keto-6-guanidinovaleric acid, as well as a-keto-&nitroguanidinovaleric acid, by enzymatic oxidative deamination (5) of the corresponding L-amino acids is described.Since lysine and ornithine were oxidized relatively slowly, the cr-keto acids corresponding to these amino acids were therefore obtained as the w-N-carbobenzoxy derivatives, by enzymatic oxidation of the more susceptible w-N-carbobenzoxyamino acids.The carbobenzoxy groups were then removed from the resulting cr-keto acids by treatment with hydrobromic acid in acetic acid solution (6), yielding the hydrobromides of the desired compounds.The a-keto analogues of lysine and ornithine would be expected to exhibit tendency to cyclize by condensation of the cY-keto and w-amino groups.However, the properties of the keto analogues of lysine and ornithine include ability to form 2,4-dinitrophenylhydrazones, decarboxylation with hydrogen peroxide to the corresponding w-amino acids, and non-enzymatic transamination with pyridoxamine to form lysine and ornithine, respectively.On the other hand, hydrogenation of these keto acids, or their w-N-carbobenzoxy derivatives, resulted in the formation of pipecolic acid and proline, respectively, a finding compatible mith the expected tendency to cyclization.EXPERIMENTAL Methods-Arginase (7), arginine decarboxylase (8),l lysine decarboxylase (9),* and ornithine decarboxylase (lO)l were prepared as described.Ascending paper chromatographic studies on Whatman No. 4 paper were 1 Cultures of the organisms possessing specific decarboxylase activity were obtained through the courtesy of Dr. E. F.