(2R,3R)-tert-Butyl 2-azido-3-(N-benzyloxycarbonyl-N-methyl)aminobutanoate

(2R,3R)-2-tert-Butoxycarbonylamino-3-methylamino-butyric acid methyl ester

(2R,3R)-3-Methylamino-2-(4-methyl-benzyloxycarbonylamino)-butyric acid methyl ester

(2R,3R)-2-tert-Butoxycarbonylamino-3-[(9H-fluoren-9-ylmethoxycarbonyl)-methyl-amino]-butyric acid methyl ester

(2R,3R)-3-[(9H-Fluoren-9-ylmethoxycarbonyl)-methyl-amino]-2-(4-methyl-benzyloxycarbonylamino)-butyric acid methyl ester