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

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

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

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