Synthesis and Cholinesterase Inhibitory Activity of N-Phosphorylated/ N-Tiophosphorylated Tacrine

Alzheimer's disease (AD) is progressive and irreversible neurodegenerative disorder. Current pharmacotherapy is not able to stop progression of the disease and can only improve cognitive functions. Therefore, new drugs are being sought that will slow down the development of the disease.

Novel phosphorus and thiophosphorus tacrine derivatives 7-14 were designed, synthesized and their biological activity and molecular modeling was investigated as a new potential anti- Alzheimer's disease (AD) agents.

9-Chlorotacrine was treated with propane-1,3-diamine in the presence of sodium iodide to yield N1-(1,2,3,4-tetrahydroacridin-9-yl)propane-1,3-diamine 6. Finally, it was treated with corresponding acid ester or thioester to give phosphorus or thiophosphorus tacrine derivative 7-14. All of the obtained final structures were characterized by 1H NMR, 13C NMR, 31P NMR and MS.

The results of the docking studies showed that the newly designed phosphorus and thiophosphorus tacrine analogs, theoretically possess AChE and BChE-binding ability. Kinetic study showed that 8 and 12 in the series proved to be more potent electric eel AChE (eeAChE) and human (hAChE) inhibitors than tacrine, where 8 inhibited eeAChE three times more than the referenced drug. The highest BChE inhibition revealed 11 and 13. The most active compounds against eeAChE, hAChE and BChE showed mixed type of inhibition.

All new synthesized compound exhibited lower toxicity against neuroblastoma.cell line (SH-SY5Y) in comparison with tacrine. Two analogues in the series, 7 and 9, demonstrated lack of cytotoxicity against hepatocellular cells (hepG2).