(S)-2-tert-Butylcarbamoyl-4-oxo-piperidine-1-carboxylic acid tert-butyl ester

(S)-6-tert-Butylcarbamoyl-4-oxo-5,6-dihydro-4H-pyridine-1,3-dicarboxylic acid 3-benzyl ester 1-tert-butyl ester

(5S)-tert-butoxycarbonylamino-5-tert-butylcarbamoyl-3-oxopentanoic acid benzyl ester

2-(3-(S)-tert-butoxycarbonylamino-3-tert-butylcarbamoylpropionyl)-3-dimethylamino acrylic acid benzyl ester

(S)-2-(tert-butoxycarbonyl-(2-methoxycarbonyl-ethyl)-amino)-succinic acid 4-methyl ester