{(1S,2S)-1-Benzyl-3-[(R)-5,5-dimethyl-4-(1-methyl-1-phenyl-ethylcarbamoyl)-thiazolidin-3-yl]-2-hydroxy-3-oxo-propyl}-carbamic acid tert-butyl ester

{(1S,2S)-1-Benzyl-3-[(R)-4-(2-ethoxy-benzylcarbamoyl)-5,5-dimethyl-thiazolidin-3-yl]-2-hydroxy-3-oxo-propyl}-carbamic acid tert-butyl ester

(R)-N-tert-butyl-3-[(2S,3S)-3-[(S)-2-(tert-butoxycarbonyl)amino-3,3-dimethylbutanoyl]amino-2-hydroxy-4-phenylbutanoyl]-1,3-thiazolidine-4-carboxamide

(R)-N-tert-butyl-3-[(2S,3S)-3-[(S)-2-(tert-butoxycarbonyl)aminosuccinamyl]amino-2-hydroxy-4-phenylbutanoyl]-1,3-thiazolidine-4-carboxamide

{(1S,2S)-1-Benzyl-3-[(R)-4-(4-carbamoyl-benzylcarbamoyl)-5,5-dimethyl-thiazolidin-3-yl]-2-hydroxy-3-oxo-propyl}-carbamic acid tert-butyl ester