(2S,4R)-4-Hydroxy-2-(2-methyl-isoxazolidin-5-yl)-pyrrolidine-1-carboxylic acid 4-nitro-benzyl ester

(2S,4S)-4-Mercapto-2-(2-methyl-isoxazolidin-5-yl)-pyrrolidine-1-carboxylic acid 4-nitro-benzyl ester

(4R,5S,6S)-6-((R)-1-Hydroxy-ethyl)-4-methyl-3-[(3S,5S)-5-(2-methyl-isoxazolidin-5-yl)-1-(4-nitro-benzyloxycarbonyl)-pyrrolidin-3-ylsulfanyl]-7-oxo-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid 4-nitro-benzyl ester

5-[(2S,4S)-4-Acetylsulfanyl-1-(4-nitro-benzyloxycarbonyl)-pyrrolidin-2-yl]-4,5-dihydro-isoxazole-3-carboxylic acid ethyl ester

5-[(2S,4S)-4-Mercapto-1-(4-nitro-benzyloxycarbonyl)-pyrrolidin-2-yl]-4,5-dihydro-isoxazole-3-carboxylic acid ethyl ester