Chymotrypsin was modified in the zymogen form with 2,4-bis(O-methoxypolyethylene glycol)-6-chloro-s-triazine (activated PEG2), followed by activation with trypsin. The modified enzyme was soluble in benzene and retained its enzymic activity. Acid-amide bond formation by the modified enzyme proceeded efficiently in benzene: N-benzoyltyrosine butylamide was made from N-benzoyl-L-tyrosine ethyl ester and n-butyl-amine, and benzoyltyrosine(oligo)phenylalanine ethyl esters were formed from N-benzoyl-L-tyrosine ethyl ester and L-phenylalanine ethyl ester.
