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

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

allyl (2S,4S)-2-((2-((Z)-2,3-bis((allyloxy)carbonyl)guanidino)ethyl)carbamoyl)-4-mercaptopyrrolidine-1-carboxylate

(2S,4S)-2-[2-(3-methylthioureido)ethylcarbamoyl]-4-tritylthio-1-(allyloxycarbonyl)pyrrolidine

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