Preparation and properties of some citrulline p-nitroanilide derivatives for possible use as protease substrates

Abstract

A number of citrulline p-nitroanilides have been synthesised as potential substrates for proteolytic enzymes. N ∝-Benzyloxycarbonyl- l-citrulline p-nitroanilide, a key starting material, was prepared by the phosphoazo method. During this reaction, depending on the conditions, lactam formation and decarbamoylation took place. It is probable that decarbamoylation took place subsequent to the lactamisation step. The derivatives prepared included some protected tripeptide nitroanilides, benzyloxycarbonylglycyl- l-prolyl- l-citrullin p-nitroanilide, bezyloxycarbonyl- d-phenylalanyl- lprolyl- l-citrulline P-nitroanilide, benzyloxycarbonylglycyl- l-phenylalanyl- l-citrulline p-nitroanilide, methyloxycarbonylglycyl- l-phenylalanyl- l-citrulline p-nitroanilide and a protected tetrapeptide, benzyloxycarbonylglycyl glycyl- l-phenylalanyl-- l-citrulline p-nitroanilide. Prelimnary results have indicated that citrulline pnitroanilides are far more susceptible to hydrolysis by plant thiol enzymes such as papain, ficin and bromelain than by mammaalian serine proteases.