To a solution of 6,7-dimethoxy-1-propylisoquinolin-3-ol RBO 35134 (316 mg, 1.3 mmol) in THF (13 mL) in a 20 mL microwave vial equipped with a magnetic stirrer was added a 3-(chloromethyl)-6-methoxyquinoline hydrochloride SLA 47088B (265 mg, 1.1 mmol) and a 2 N aq. LiOH solution (1.3 mL, 2.6 mmol) and the mixture was stirred at 160° C. for 1.5 h under microwave irradiation. After cooling to RT, THF was then removed at 40° C. under vacuum and the residue was then taken up in CH2Cl2 (50 mL), washed with brine (10 mL), dried over Na2SO4, filtered, and concentrated under vacuum. Purification by column chromatography (SiO2, eluent CH2Cl2:MeOH=100:0 to 94:6) gave 89 mg of 6,7-dimethoxy-4-((6-methoxyquinolin-3-yl)methyl)-1-propylisoquinolin-3-ol. This free base was dissolved in MeOH (2 mL) in a 10 mL round-bottomed flask equipped with a magnetic stirrer before addition of a 0.149 M HCl solution in MeOH (3.0 mL). The reaction mixture was stirred for 5 min at RT and concentrated at 40° C. under vacuum to afford 6,7-dimethoxy-4-((6-methoxyquinolin-3-yl)methyl)-1-propylisoquinolin-3-ol dihydrochloride 84 as a brown solid (93 mg, 17% yield).
