3-[[[(2S, 4S)-4-mercapto-1-(4-nitrobenzyloxy)carbonyl-2-pyrrolidinyl]carbonyl]amino]benzoic acid or (2S, 4S)-2-[[(3-carboxyphenyl)amino]carbonyl]-4-mercapto-1-(4-nitrobenzyl)pyrrolidinecarboxylate

≥98%(HPLC,　外标法)