(2S,4S)-4-Mercapto-2-(2-piperazin-1-yl-ethylcarbamoyl)-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

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