The Synthesis of Benzoyl-l-arginine-p-nitroanilide

Benzoyl-arginine-p-nitroanilide (BAPA) is a synthetic substrate for trypsin, papain, and other enzymes, but it has not yet been prepared in the active l-form, although the preparations of Dl-form and d-form by the trypsin digestion of the Dl-form have been reported. The optically active l-BAPA was prepared by the following route; Nα-carbobenzyloxy-Nω-nitro-l-arginine-p-nitroanilide was prepared from Nα-carbobenzyloxy-Nω-nitro-l-arginine and p-nitrophenyl isocyanate, and the subsequent decarbobenzyloxylation and the benzoylation of this compound gave Nα-benzoyl-Nω-nitro-l-arginine-p-nitroanilide. The removal of the nitro group was followed by Sakakibara’s method using hydrogen fluoride. The l-BAPA shows the same melting point and the same reversal optical rotation as those of d-BAPA. When Nα-benzoyl derivatives of l-arginine were used as starting materials in the preparation of BAPA, Dl-BAPA was always obtained with complete racemization; when Nα,Nω,Nω′-tricarbobenzyloxy-l-arginme as the starting material reacted on p-nitrophenyl isocyanate, the product had no racemization, but the desired l-BAPA was not obtained because one of the carbobenzyloxy groups on the guanido group was extraordinally stable to reagents and could not be removed completely.