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Histidine‐containing cyclic dipeptides as catalysts in the hydrolysis of carbonic acid p‐nitrophenyl esters

A histidine‐containing cyclic dipeptide, cyclo(D‐Leu‐L‐His), was almost 20 times as efficient a catalyst as imidazole in the hydrolysis of p‐nitrophenyl laurate. The effect of dioxane on the hydrolysis showed that hydrophobic interaction between the cyclic dipeptide and the ester is very important. This reaction obeyed the Michaelis‐Menten kinetics, and the Michaelis constant Km was as low as 9.98 × 10−5M. Since the linear dipeptide having D‐Leu‐L‐His sequence was nearly inactive in the hydrolysis, the functional groups of cyclo(D‐Leu‐L‐His) in a specific arrangement held by the rigid backbone must have cooperated in the fast hydrolysis. Very weak catalysis by the diasteremeric cyclic dipeptide, cyclo(L‐Leu‐L‐His), in the hydrolysis supported the above view.