To a solution of 4-isoquinolin-3-yl-phenol (0.133 g, 0.6 mmol) in anhydrous DMF (5 mL) were added HOBt (0.081 g, 0.6 mmol), Boc-Arg-(Boc)2-OH (0.285 g, 0.6 mmol), and EDCl (0.115 g, 0.6 mmol). N,N-Diisopropyl ethyl amine (0.233 g, 1.8 mmol) was added and the mixture was stirred at room temperature for 24 h. Water (15 mL) was added and the white precipitate was filtered off, washed with water and dried under vacuum to give 0.3 g (74%) of the Boc-arginine derivative. The above compound (0.3 g) was dissolved in anhydrous dichloromethane (10 mL). HCl gas was bubbled into the solution at 0° C. for 4 h. A yellow precipitate was formed. The solvent was removed and the resulting solid was dried under vacuum. Triturating with ether gave 4-(isoquinolin-3-yl)phenyl 2-amino-5-guanidinopentanoate tetrahydrochloride (0.2 g, 86%). Selected data: MS (ES) m/z: 222.96 (M+1−Arg), 221.99 (M−Arg); MP 198-201° C.
