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

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

(2S,3R)-3-(Benzyloxycarbonyl-methyl-amino)-2-methanesulfonyloxy-butyric acid methyl ester

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

(2S,3R)-3-(benzyloxycarbonyl-N-methylamino)-2-hydroxybutyric acid