THE SYNTHESIS AND BACITRACIN-CATALYSED HYDROLYSIS OF ARYL ESTERS OF N-ACYLAMINO ACIDS.

1. A new method for synthesizing aryl esters of N-acylamino acids is described. The unsymmetrical anhydride resulting from the interaction of an N-acylamino acid and diphenylketen is allowed to react with a phenol. Cleavage of the anhydride by the phenol usually occurs in the desired direction. 2. Bacitracin has been examined as an enzyme model by determining its catalytic activity towards the hydrolysis of aryl esters. In general, it is less effective than imidazole. The variation of the catalytic constant with pH, together with other evidence, suggests that the histidine residue in bacitracin is the effective catalytic centre. 3. The stereoisomers of N-methoxycarbonylalanine p-nitrophenyl ester were hydrolysed at the same rate, but bacitracin was stereoselective towards the stereoisomers of the corresponding phenylalanine derivative.