(4S,5S)-5-[(1R,2R)-2-((S)-1-Benzyloxycarbonyl-ethylcarbamoyl)-cyclopentyl]-4-isobutyl-2,2-dimethyl-oxazolidine-3-carboxylic acid tert-butyl ester

(4S,5S)-4-Isobutyl-2,2-dimethyl-5-{(1R,2R)-2-[(S)-1-(2,2,2-trichloro-ethoxycarbonyl)-ethylcarbamoyl]-cyclopentyl}-oxazolidine-3-carboxylic acid tert-butyl ester

tert-butyl (4S,5S)-4-isobutyl-5-((1R,2R)-2-(methoxycarbonyl)-4-(2-tosylhydrazineylidene)cyclopentyl)-2,2-dimethyloxazolidine-3-carboxylate

(4S,5S)-5-[(1R,2R)-2-((S)-1-Butylcarbamoyl-ethylcarbamoyl)-cyclopentyl]-4-isobutyl-2,2-dimethyl-oxazolidine-3-carboxylic acid tert-butyl ester

(4S,5S)-4-Isobutyl-2,2-dimethyl-5-{(1R,2R)-4-oxo-2-[(S)-1-(2,2,2-trichloro-ethoxycarbonyl)-ethylcarbamoyl]-cyclopentyl}-oxazolidine-3-carboxylic acid tert-butyl ester