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

(2S,4S)-4-Acetylsulfanyl-2-(5-hydroxymethyl-isoxazol-3-yl)-pyrrolidine-1-carboxylic acid 4-nitro-benzyl ester

(2S,4S)-2-(5-Hydroxymethyl-isoxazol-3-yl)-4-mercapto-pyrrolidine-1-carboxylic acid 4-nitro-benzyl ester

(2S,4R)-2-(5-Hydroxymethyl-isoxazol-3-yl)-4-methanesulfonyloxy-pyrrolidine-1-carboxylic acid 4-nitro-benzyl ester

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