1-O-tert-butyl 2-O-methyl (2S,4S)-4-[[4-[[(3S,5S)-5-acetyl-1-[(2-methylpropan-2-yl)oxycarbonyl]pyrrolidin-3-yl]carbamoyl]benzoyl]amino]pyrrolidine-1,2-dicarboxylate;1-O-tert-butyl 2-O-methyl (2S,4S)-4-aminopyrrolidine-1,2-dicarboxylate;(2S)-3,3-dimethyl-2-[2-[(2-methylpropan-2-yl)oxy]-2-oxoethyl]butanoic acid;4-formylchloranuidylbenzoyl chloride;methyl (2S,4S)-4-[[4-[[(3S,5S)-5-acetyl-1-[(2S)-3,3-dimethyl-2-[2-[(2-methylpropan-2-yl)oxy]-2-oxoethyl]butanoyl]pyrrolidin-3-yl]carbamoyl]benzoyl]amino]-1-[(2S)-3,3-dimethyl-2-[(2-methylpropan-2-yl)oxycarbonylamino]butanoyl]pyrrolidine-2-carboxylate;methyl (2S,4S)-4-[[4-[[(3S,5S)-5-acetylpyrrolidin-3-yl]carbamoyl]benzoyl]amino]pyrrolidine-2-carboxylate