[((S)-2-Amino-3-methyl-butyryl)-(3-phenyl-propyl)-amino]-acetic acid methyl ester

[[(S)-2-Amino-3-(4-chloro-phenyl)-propionyl]-(3-phenyl-propyl)-amino]-acetic acid methyl ester

(S)-3-Phenethyl-1-(3-phenyl-propyl)-piperazine-2,5-dione

[(S)-2-Isobutyl-3,6-dioxo-4-(3-phenyl-propyl)-piperazin-1-yl]-acetic acid

(S)-3-Isopropyl-1-(3-phenyl-propyl)-piperazine-2,5-dione