Potential inhibitors of polyamine biosynthesis. 2. alpha-Alkyl- and benzyl-(+/-)-ornithine

Alpha-Methyl-(+/-)-ornithine hydrochloride was not a substrate for ornithine decarboxylase from rat prostate glands. It produced equal inhibition of ornithine decarboxylase obtained from rat prostate glands, spleens of mice inoculated with L1210 leukemic cells, and regenerating rat liver indicating its lack of selectivity for any of these tissues. In these three tissues the inhibition was competitive with L-ornithine. A number of alpha-alkyl- and alpha-aralkyl-substituted analogs of (+/-)-ornithine were synthesized and evaluated in vitro as inhibitors of the enzyme L-ornithine decarboxylase obtained from prostate glands of rats. These compounds were obtained by the reaction of alkyl iodide or benzyl bromide with the anion obtained by treatment of 3-(benzalimino)piperidin-2-one with sodium hydride. The following alpha-substituted analogs of (+/-)-ornithine were obtained: ethyl, n-propyl, n-butyl, n-hexyl, n-octyl, and benzyl. The synthesized compounds were found to be much less active than alpha-methyl-(+/-)-ornithine as competitive inhibitors of ornithine decarboxylase in vitro. The most active compound in the series was alpha-n-octyl-(+/-)-ornithine which was 60-fold less active than alpha-methyl-(+/-)-ornithine and the least active analog was alpha-n-butyl-(+/-)-ornithine which was 270-fold less active than the alpha-methyl-(+/-)-ornithine.