Synthesis, design and biological evaluation of novel highly potent tacrine congeners for the treatment of Alzheimer's disease

New tacrine derivatives 5a–d, 6a–d with piperazino-ethyl spacer linked with corresponding secondary amines and tacrine homodimer 8 were synthesized and tested as cholinesterase inhibitors on human acetylcholinesterase (hAChE) and human plasmatic butyrylcholinesterase (hBChE). In most cases the majority of synthesized derivatives exhibit a high AChE and BChE inhibitory activity with IC50 values in the low-nanomolar range, being clearly more potent than the reference standard tacrine (9-amino-1,2,3,4-tetrahydroacridine, 1) and 7-MEOTA (7-methoxy-9-amino-1,2,3,4-tetrahydroacridine). Among them, inhibitors 8 and 5c, showed a strong inhibitory activity against hAChE, with an IC50 value of 4.49 nM and 4.97, nM resp., and a high selectivity to hAChE. The compound 5d acted as the most potent inhibitor against hBChE with an IC50 value of 33.7 nM and exhibited also a good selectivity towards hBChE. The dissociation constants Ki of the selected inhibitors were compared with their IC50 values. Molecular modeling studies were performed to predict the binding modes between individual derivatives and hAChE/hBChE.

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► Novel tacrine derivatives have been synthesized.
► The inhibition activity against acetylcholinesterase and butyrylcholinesterase of new compounds have been screened.
► Most of the tested hybrids exhibited significant inhibition activity with IC50 values in the nanomolar range.
► Docking studies performed using some of the compounds are presented.