[(S)-2-((R)-1-{[(4-Carboxymethoxy-phenylcarbamoyl)-methyl]-carbamoyl}-2-phenyl-ethylcarbamoyl)-pyrrolidin-1-yl]-oxo-acetic acid methyl ester

(S)-2-[(R)-1-(4-tert-Butoxycarbonylmethoxy-phenylcarbamoyl)-2-phenyl-ethylcarbamoyl]-pyrrolidine-1-carboxylic acid benzyl ester

[(S)-2-((R)-1-{[(4-tert-Butoxycarbonylmethoxy-phenylcarbamoyl)-methyl]-carbamoyl}-2-phenyl-ethylcarbamoyl)-pyrrolidin-1-yl]-oxo-acetic acid methyl ester

(S)-1-{(2S,3S)-2-Hydroxy-3-[2-(4-nitro-phenoxy)-acetylamino]-4-phenyl-butyryl}-pyrrolidine-2-carboxylic acid tert-butylamide