HCl (0.4 mL, 2 N) was added to 4-isoquinolin-3-yl-phenol (0.133 g, 0.6 mmol) in anhydrous DMF (5 mL). To this mixture 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-Diisopropylethylamine (0.233 g, 1.8 mmol) was added and the mixture was stirred at rt 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 Boc derivative 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 sold was dried under vacuum. Triturating with ether gave 200 mg of 4-(isoquinolin-3-yl)phenyl 2-amino-5-guanidinopentanoate tetrahydrochloride (86%). MS (ES) m/z: 222.96 (M+1−Arg), 221.99 (M−Arg); Mp. 198-201° C.
