Design, synthesis and evaluation of novel tacrine-(ß-carboline) hybrids as multifunctional agents for the treatment of Alzheimer's disease.

A series of tacrine-(ß-carboline) hybrids (11a-q) were designed, synthesized and evaluated as multifunctional cholinesterase inhibitors against Alzheimer's disease (AD). In vitro studies showed that most of them exhibited significant potency to inhibit acetylcholinesterase (eeAChE and hAChE), butyrylcholinesterase (BuChE) and self-induced ß-amyloid (Aß) aggregation, Cu(2+)-induced Aß (1-42) aggregation, and to chelate metal ions. Especially, 11 l presented the greatest ability to inhibit cholinesterase (IC50, 21.6 nM for eeAChE, 63.2 nM for hAChE and 39.8 nM for BuChE), good inhibition of Aß aggregation (65.8% at 20 µM) and good antioxidant activity (1.57 trolox equivalents). Kinetic and molecular modeling studies indicated that 11 l was a mixed-type inhibitor, binding simultaneously to the catalytic anionic site (CAS) and the peripheral anionic site (PAS) of AChE. In addition, 11 l could chelate metal ions, reduce PC12 cells death induced by oxidative stress and penetrate the blood-brain barrier (BBB). These results suggested that 11 l might be an excellent multifunctional agent for AD treatment.