We synthesized eleven new
amiridine-
piperazine hybrids 5a-j and 7 as potential multifunctional agents for
Alzheimer's disease (AD) treatment by reacting N-chloroacetylamiridine with
piperazines. The compounds displayed mixed-type reversible inhibition of
acetylcholinesterase (AChE) and
butyrylcholinesterase (BChE). Conjugates were moderate inhibitors of equine and human BChE with negligible fluctuation in anti-BChE activity, whereas anti-AChE activity was substantially dependent on N4-substitution of the
piperazine ring. Compounds with para-substituted aromatic moieties (5g, 5h, and bis-
amiridine 7) had the highest anti-AChE activity in the low micromolar range. Top-ranked compound 5h, N-(2,3,5,6,7,8-hexahydro-1H-cyclopenta[b]quinolin-9-yl)-2-[4-(4-nitro-phenyl)-piperazin-1-yl]-
acetamide, had an IC50 for AChE = 1.83 ± 0.03 μM (Ki = 1.50 ± 0.12 and αKi = 2.58 ± 0.23 μM). The conjugates possessed low activity against
carboxylesterase, indicating a likely absence of unwanted drug-drug interactions in clinical use. In agreement with analysis of inhibition kinetics and molecular modeling studies, the lead compounds were found to bind effectively to the peripheral anionic site of AChE and displace
propidium, indicating their potential to block AChE-induced β-
amyloid aggregation. Similar
propidium displacement activity was first shown for
amiridine. Two compounds, 5c (R = cyclohexyl) and 5e (R = 2-MeO-Ph), exhibited appreciable
antioxidant capability with
Trolox equivalent
antioxidant capacity values of 0.47 ± 0.03 and 0.39 ± 0.02, respectively. Molecular docking and molecular dynamics simulations provided insights into the structure-activity relationships for AChE and BChE inhibition, including the observation that inhibitory potencies and computed pKa values of hybrids were generally lower than those of the parent molecules. Predicted ADMET and physicochemical properties of conjugates indicated good CNS bioavailability and safety parameters comparable to those of
amiridine and therefore acceptable for potential lead compounds at the early stages of anti-AD drug development.