(2S,4S)-4-Mercapto-2-(2-methanesulfonylamino-ethylcarbamoyl)-pyrrolidine-1-carboxylic acid allyl ester

(2S,4S)-2-[2-(3,3-Dimethyl-ureido)-ethylcarbamoyl]-4-mercapto-pyrrolidine-1-carboxylic acid allyl ester

(2S,4S)-2-(2-Allyloxycarbonylamino-ethylcarbamoyl)-4-mercapto-pyrrolidine-1-carboxylic acid allyl ester

(2S,4S)-2-(2-{[(E)-Allyloxycarbonylimino-methyl]-amino}-ethylcarbamoyl)-4-mercapto-pyrrolidine-1-carboxylic acid allyl ester

(2S,4S)-4-Mercapto-2-{2-[(morpholine-4-carbonyl)-amino]-ethylcarbamoyl}-pyrrolidine-1-carboxylic acid allyl ester