(4R)-N-(Tert-Butyloxycarbonyl)-4-(Cyanomethyl)-L-Glutamic Acid 1,5-Dimethyl Ester; Dimethyl (2R,4S)-2-(Cyanomethyl)-4-[(2-Methylpropan-2-Yl)Oxycarbonylamino]Pentanedioate