C1(N=C=NC2CCCCC2)CCCCC1.[C:16]([NH:23][C@H:24]([C:29]([OH:31])=[O:30])[CH2:25][C:26](=O)[NH2:27])([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17]>CC(C)=O.N1C=CC=CC=1>[C:19]([O:18][C:16]([NH:23][C@@H:24]([CH2:25][C:26]#[N:27])[C:29]([OH:31])=[O:30])=[O:17])([CH3:22])([CH3:21])[CH3:20]A solution of dicyclohexylcarbodiimide (DCC, 8.3 g, 40 mmol) in acetone (100 ml) was added dropwise a suspension of Boc-asparagine (9.3 g, 40 mmol) in pyridine (50 mL) at 0° C. under nitrogen. The reaction mixture was stirred at ambient temperature for 3 h. The mixture was filtered and the filtrate was concentrated. The residue was dissolved in dichloromethane (400 mL) and the solution was washed with 2 N aqueous HCl (20 mL×3) and brine (200 mL), dried over anhydrous sodium sulfate, and concentrated to afford (S)-2-(tert-butoxycarbonylamino)-3-cyanopropanoic acid (5.5 g, 56% yield), which was used directly without further purification.
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