(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

(4S)-isobutyl-(5S)-(2-methoxycarbonyl-1-methyl-5-oxo-4-(toluene-4-sulfonyl)-pyrrolidin-3-yl)-2,2-dimethyl-oxazolidine-3-carboxylic acid tert-butyl ester

(4S)-isobutyl-(5S)-(2-methoxycarbonyl-(1S)-nitro-methyl-ethyl)-2,2-dimethyl-oxazolidine-3-carboxylic acid tert-butyl ester

(4S)-isobutyl-2,2-dimethyl-(5S)-(5-oxo-pyrrolidin-(3S)-yl)-oxazolidine-3-carboxylic acid tert-butyl ester