p-Nitrophenyl acetate and other esters except formates, will acylate the unprotected diamino acids homolysine, lysine, and ornithine, exclusively at the ω-amino group at pH 11. At lower alkaline pH's, the reaction is preferential but not selective. The reaction with diaminobutyric acid and diaminopropionic acid is not selective at any alkaline pH. ε-N-Acetyllysine can be prepared directly by the action of excess phenyl acetate on lysine at pH 11.

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e-N-Acetyl-L-lysinamide, a-N-glycyl-e-N-acetyl-L-lysine, E-N-acetyl-L-lysylglycine, a-iVglycyl-e-N-acetyl-L-lysylglycine, and E-N-acetylglycyl-L-lysine have been synthesized for testing as substrates for the enzyme e-lysine acylase.Several years ago, the enzyme E-lysine acylase was identified and partially purified from rat kidney (1). We have now purified 6-lysine acylase from a much more convenient source, hog kidney, and have tested its hydrolytic action on several derivatives of lysine including some peptides of E-N-acetyl-L-lysine (2). This paper describes the synthesis of the peptides.The compounds 111, V, VII, and I X , and the synthetic routes employed, are illustrated in the accompanying scheme. In addition, the isomeric peptide E-N-acetylglycyl-L-lysine was also prepared. E-N-Acetyl-L-lysine, prepared by acetylation of the copper salt of lysine (3), was carbobenzoxylated to the disubstituted derivative I , which was crystallized as the dicyclohexylammonium salt. I was also prepared by acetylation of a-N-carbobenzoxy-Llysine, obtained through the E-N-benzylidene derivative (4) ; however, our inability to obtain the reported yields for a-N-carbobenzoxy-L-lysine rendered this route less attractive. The mixed anhydride (5) of I, by treatment with anhydrous ammonia or glycine benzyl ester, gave the protected amide I1 and dipeptide SV respectively. Catalytic hydrogenolysis of these provided the E-N-acetyl-L-lysine amide IS1 and the E-N-acetyl-L-lysine dipeptide

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ω-N-Acyl-diamino acids have been tested as substrates for ε-lysine acylase from animal sources. Chicken and pigeon kidney enzyme preparations hydrolyzed derivatives of lysine homologues as well as of lysine, the best substrates tested being ε-N-propionyl-lysine and ε-N-propionyl-ornithine. A modified procedure for purifying the enzyme from rat and hog kidney is presented. Some of its properties are different from those previously reported.