A number of citrullinep-nitroanilides have been synthesised as potential substrates for proteolytic enzymes. N∝-Benzyloxycarbonyl-l-citrullinep-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 ...