No abstract

A new method for the preparation of t-butyloxycarbonyl amino acids and p-methoxybenzyloxycarbonyl amino acids has been devised. The former was obtained in satisfactory yields from amino acids and t-butyl S-4,6-dimethylpyrimid-2-ylthiocarbonate prepared from t-butyl alcohol and (4,6-dimethylpyrimid-2-ylthio)corbonyl chloride in dry pyridine, and the latter was also obtained from amino acids and p-methoxybenzyl S-4,6-dimethylpyrimid-2-ylthiocarbonate from p-methoxybenzyl alcohol and (S-4,6-dimethylpyrimid-2-ylthio)carbonyl chloride. These t-butyloxycarbonylation and p-methoxybenzyloxycarbonylation of amino acids are more convenient than the usual methods.

N δ-Tosyl-Nδ-benzyloxy-Dl-ornithine was synthesized starting from γ-(N-tosyl-N-benzyloxy)-aminopropyl bromide and diethyl acetamidomalonate and resolved enzymatically to give the l- and d-isomers. Removal of one or both of protecting groups gave Nδ-benzyloxyornithine or Nδ-hydroxyornithine. The reduction product of Nδ-hydroxy-l-ornithine was identical with authentic l-ornithine.

Nagarse, papain, pepsin and thermolysin were found to catalyze the peptide bond formation between two amino acids or peptides, one protected with a suitable group at the amino group and the other at the carboxyl group. Experiments with various combinations of amino acids and dipeptides show specificity in the catalytic action in varying degree which depending on the nature of the enzyme. Since the condensation takes place efficiently under mild conditions, this method opens up a useful way for the synthesis of peptides.

An example of the use of proteolytic enzymes to facilitate the peptide synthesis by fragment condensation is provided for the preparation of protected valine-5 angiotensin II amide-1 using t-butoxycarbonylpeptides as a carboxyl component and a peptide ethyl ester as an amine component. The proteolytic enzymes used are papain, nagarse (subtilisin BPN′) and microbial metalloenzyme isolated from St. caespitosus. Papain-catalyzed condensation reaction afforded the corresponding oligopeptide in the ester form, whereas nagarse and microbial metalloenzyme-catalyzed condensation reactions afforded the products in the carboxyl free form. Assignment of the product was made on the basis of a comparison of physical properties with those of the peptide prepared by the solution method.