L-Pro-D-Phe

3-benzylhexahydropyrrolo[1,2-a]pyrazin-1,4-dione

(5-(((S)-1-amino-1-oxopropan-2-yl)amino)-2,4-dinitrophenyl)-D-phenylalanine

[(S)-1-((S)-3-Benzyl-1,4-dioxo-hexahydro-pyrrolo[1,2-a]pyrazine-2-carbonyl)-2-methyl-propyl]-carbamic acid benzyl ester