Scheme 2 Reagents and conditions: (e) tacrine hydrochloride (9), H₂O, K₂CO₃, 1 hr; (f) tacrine (10), 1,7-dibromoheptane (11), CH₃CN, KOH, rt, overnight; (g) N-(7-bromoheptyl)-1,2,3,4-tetrahydroacridin-9-amine (12), tryptoline (13), DMF, K₂CO₃, KI, microwave 160 ⁰C, 250 PSI, 200 W, 1h, giving the tacrine-tryptoline hybrid (14); (h), tryptoline (13), 1,2-dibromoethane (15), KOH, CH₃CN, microwave 100 ⁰C, 250 PSI, 130 W, 1 hr, giving the bistryptoline dimer (16).