Carbonic acid (2S,4S)-4-tert-butoxycarbonylamino-4-methyl-5-oxo-pyrrolidin-2-ylmethyl ester tert-butyl ester

(3S,5S)-3-tert-Butoxycarbonylamino-5-tert-butoxycarbonyloxymethyl-3-methyl-2-oxo-pyrrolidine-1-carboxylic acid tert-butyl ester

((3S,5S)-5-Hydroxymethyl-3-methyl-2-oxo-pyrrolidin-3-yl)-carbamic acid tert-butyl ester

(2S,4S)-2,4-Bis-tert-butoxycarbonylamino-5-hydroxy-2-methyl-pentanoic acid methyl ester

((1S,3S)-3-tert-Butoxycarbonylamino-4-hydroxy-1-hydroxymethyl-3-methyl-butyl)-carbamic acid tert-butyl ester