S 2238 Chromogenic substrate S-2238 D-Phenylalanyl-L-2-piperidinecarbonyl-N-(4-nitro phenyl)-L-argininamide H-D-Phenylalanyl-L-pipecolyl-arginine-nitroanilide H-D-Phenylalanyl-pip-Arg-p-nitroanilide H-D-Phe-pip-Arg-pna H-Phe-pip-Arg-pna H-Phe-pip-Arg-p-nitroanilide