(2S,4S)-2-{[2-(allyloxycarbonylamino)ethyl]carbamoyl}-4-tritylthio-1-(allyloxycarbonyl)pyrrolidine

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

(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