The diastereoselective hydrolysis of p-nitrophenyl N-(benzyloxycarbonyl)-D(L)-prolyl-L-prolinate (Z-Pro-Pro-PNP) and p-nitrophenyl N-(benzyloxycarbonyl)-D(L)-tryptophanyl-L-prolinate (Z-Trp-Pro-PNP) has been found to be controlled by changing pH, the reaction temperature, and the composition of aggregates. First, the cleavages of Z-Trp-Pro-PNP esters are DL diastereoselective below pH 9.3 in buffer solution which should be attributed to the intramolecular cyclization with diketopiperazine formation, though those are LL-diastereoselective when the nucleophile is hydroxide ion above pH 9.6 or with catalysts in the aggregate systems. Second, the highest diastereoselectivity (k(psi)(LL)/k(psi)(DL) = 13.2) was attained by regulating the temperature (20 degrees C) for the hydrolytic cleavage of Z-Pro-Pro-PNP as catalyzed by the nucleophilic 5-(2-(N-n-hexadecyl-N,N-dimethylammonio)ethyl)oxy-2-isodosylbenzoic acid chloride (16-I=O) catalyst in the vesicular (dihexadecyldimethylammonium chloride, 2C(16)Cl) system. Furthermore, the stereochemical control was attained by changing the composition of the coaggregates and the highest stereoselectivity (k(psi)(LL)/k(psi)(DL) )= 11.5) was obtained for the hydrolytic cleavage of Z-Pro-Pro-PNP with 16-I=O in the optimal coaggregate system of 77 mol % 2C(16)Cl and 23 mol % hexadecyltrimethylammonium chloride (CTACl) at 25 degrees C. It is noteworthy that the diastereoselective hydrolytic cleavage of dipeptide esters was maximized by regulating the reaction temperature and/or composition of coaggregates.