(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

(2S,4R)-2-{[(1R,2R)-2-Methoxycarbonyl-1-methyl-2-(4-methyl-benzyloxycarbonylamino)-ethyl]-methyl-carbamoyl}-4-((Z)-propenyl)-pyrrolidine-1-carboxylic acid tert-butyl ester