Further SAR studies on natural template based neuroprotective molecules for the treatment of Alzheimer's disease

In our earlier paper, we described ferulic acid (FA) template based novel series of multifunctional cholinesterase (ChE) inhibitors for the management of AD. This report has further extended the structure-activity relationship (SAR) studies of this series of molecules in a calibrated manner to improve upon the ChEs inhibition and antioxidant property to identify the novel potent multifunctional molecules. To investigate the effect of replacement of phenylpiperazine ring with benzylpiperazine, increase in the linker length between FA and substituted phenyl ring, and replacement of indole moiety with tryptamine on this molecular template, three series of novel molecules were developed. All synthesized compounds were tested for their acetyl and butyryl cholinestrases (AChE and BChE) inhibitory properties. Enzyme inhibition and PAS binding studies identified compound 13b as a lead molecule with potent inhibitor property towards AChE/BChE (AChE IC₅₀ = 0.96 ± 0.14 µM, BChE IC₅₀ = 1.23 ± 0.23 µM) compared to earlier identified lead molecule EJMC-G (AChE IC₅₀ = 5.74 ± 0.13 μM, BChE IC₅₀ = 14.05 ± 0.10 μM, respectively). Molecular docking and dynamics studies revealed that 13b fits well into the active sites of AChE and BChE, forming stable and strong interactions with key residues Trp86, Ser125, Glu202, Trp 286, Phe295, Tyr 337 in AChE, and with Trp 82, Gly115, Tyr128, and Ser287 in BChE. The compound, 13b was found to be three times more potent antioxidant in a DPPH assay (IC₅₀ = 20.25 ± 0.26 µM) over the earlier identified EJMC-B (IC₅₀ = 61.98 ± 0.30 µM) and it also was able to chelate iron. Co-treatment of 13b with H₂O₂, significantly attenuated and reversed H₂O₂-induced toxicity in the SH-SY5Y cells. The parallel artificial membrane permeability assay-blood brain barrier (PAMPA-BBB) revealed that 13b could cross BBB efficiently. Finally, the in-vivo efficacy of 13b at dose of 10 mg/kg in scopolamine AD model has been demonstrated. The present study strongly suggests that the naturally inspired multifunctional molecule 13b may behave as a potential novel therapeutic agent for AD management.