(S)-5-benzyl-1-((S)-1-((S)-2-benzyl-5-oxo-2,5-dihydro-1H-pyrrol-3-yl)pyrrolidin-3-yl)-4-(tert-butoxy)-1H-pyrrol-2(5H)-one

(5S)-1-((3S)-1-(2-benzyl-5-oxo-2,5-dihydro-1H-pyrrol-3-yl)pyrrolidin-3-yl)-4-(tert-butoxy)-5-isobutyl-1H-pyrrol-2(5H)-one

(S)-2-benzyl-5-oxo-2,5-dihydro-1H-3-pyrrolyl benzoate

(S)-2-benzyl-5-oxo-2,5-dihydro-1H-3-pyrrolyl 2-methylbutanoate