To a stirred solution of 6,7-dimethoxy-1-propylisoquinolin-3-ol RBO 35142 (250 mg, 1.01 mmol) in toluene (15 mL) in a 20 mL microwave vial equipped with a magnetic stirrer was added 3-(chloromethyl)-6-methoxy-N-methylquinolin-2-amine hydrochloride SLA 28154 (276 mg, 1.01 mmol) followed by a 2 N aq. LiOH solution (1.01 mL, 2.02 mmol) and the mixture was stirred at 150° C. for 1.5 h under microwave irradiation. After cooling to RT, the mixture was diluted with a CH2Cl2:MeOH=9:1 mixture (150 mL), washed with brine (20 mL), dried over Na2SO4, filtered and concentrated at 40° C. under vacuum. Purification by column chromatography (SiO2, eluent CH2Cl2:MeOH=100:0 to 92:8) provided, after evaporation and drying, 39 mg of 6,7-dimethoxy-4-((6-methoxy-2-(methylamino)quinolin-3-yl)methyl)-1-propylisoquinolin-3-ol as a brown solid. This free base was dissolved in CH2Cl2 (2 mL) in a 10 mL round-bottomed flask equipped with a magnetic stirrer before addition of a 0.49 M HCl solution in MeOH (0.40 mL). The reaction mixture was stirred for 5 min at RT and concentrated at 40° C. under vacuum to give 6,7-dimethoxy-4-((6-methoxy-2-(methylamino)quinolin-3-yl)methyl)-1-propylisoquinolin-3-ol dihydrochloride 48 as a yellow solid (31 mg, 6% yield).
