(R)-N1-[(2R,3S)-3-((2S,3R)-2-Amino-3-hydroxy-butyrylamino)-2-hydroxy-4-phenyl-butyl]-2-tert-butyl-N4-(1-ethyl-propyl)-succinamide

(R)-N1-[(2R,3S)-3-((S)-2-Amino-3-methyl-butyrylamino)-2-hydroxy-4-phenyl-butyl]-2-tert-butyl-N4-(1-ethyl-propyl)-succinamide

(R)-N-[(2R,3S)-3-((S)-2-Amino-3-carbamoyl-propionylamino)-2-hydroxy-4-phenyl-butyl]-2-[(1-ethyl-propylcarbamoyl)-methyl]-3,3-dimethyl-butyramide

[(S)-1-((1S,2R)-1-Benzyl-3-{(R)-2-[(1-ethyl-propylcarbamoyl)-methyl]-3,3-dimethyl-butyrylamino}-2-hydroxy-propylcarbamoyl)-2-methyl-propyl]-carbamic acid benzyl ester

[(S)-1-((1S,2R)-1-Benzyl-3-{(R)-2-[(1-ethyl-propylcarbamoyl)-methyl]-3,3-dimethyl-butyrylamino}-2-hydroxy-propylcarbamoyl)-2-carbamoyl-ethyl]-carbamic acid benzyl ester