Multi-targeted anti-Alzheimer's agents: Synthesis, biological evaluation, and molecular modeling study of some pyrazolopyridine hybrids.

A new series of compounds bearing a pyrazolopyridine scaffold was synthesized as integrated anti-Alzheimer's disease (AD) multi-targeted ligands. Compounds 49 and 51 showed remarkable activity as hAChE inhibitors with IC50 values of 0.17 and 0.16 µM, respectively; and proved to be active hBuChE inhibitors with IC50 values 0.17 and 0.69 µM, eight and two-fold more active than the reference compound rivastigmine, respectively. Compounds 49 and 51 showed potent GSK3ß inhibition with IC50 values of 0.21 and 0.26 µM, respectively compared to L807mts. Also, 49 and 51 showed 66.0 and 60.0% as tau protein aggregation inhibitors; and Aß1-42 self-aggregation inhibitors with 79.0 and 75.0% respectively. Furthermore, 49 and 51 could bind virtually with the PAS affecting Aß aggregation, thus preventing Aß-dependent neurotoxicity. They proved to have the ability to chelate bio-metals such as Fe2+, Cu2+, and Zn2+ preventing their oxidative damage in the brain of AD patients, in addition to their safety upon WI-38 cell line. Both compounds could virtually penetrate BBB and obeyed Lipinski's rule of five. Compounds 49 and 51 could be considered as MTDLs for AD patients and the obtained model and pattern of substitution could be used for further development of new multi-targeted anti-Alzheimer's agents.

Synthesis, biological evaluation, and molecular modeling simulations of new heterocyclic hybrids as multi-targeted anti-Alzheimer's agents.

The widespread and the recognition of the multifactorial nature of Alzheimer disease (AD) increased the demands for multi-targeted directed ligands (MTDLs) to overcome possible drug-drug interactions of the combination therapy, and to acquire superior therapeutic profile than single targeted molecules. Two main scaffolds namely: pyrazolopyridine and tetrahydroacridine (THA) were used to synthesize four different series of integrated multi-targeted synthons possessing ChE (hAChE or hBuChE), Aß1-42 aggregation inhibition potency, in addition to optimum metal chelating capability. Structure modifications were performed to 9-amino function of THA core of tacrine and the pyrazolopyridine scaffolds linked to a variety of cyclic secondary amines directly or using amide spacers or ethylamine bridge or engaging THA with pyrazolopyridine to produce hybrid compounds. Different 9-amino substitutions improved the in vitro hAChE activity of 7- or 6,7-disubstituted THA derivatives. Compounds 16 and 28 proved to be multimodal anti-AD agents as they were potent hAChE inhibitors, in addition, they could bind with the amino acids of the peripheral anionic site (PAS) affecting Aß aggregation and hence Aß-dependent neurotoxicity especially compound 16 which was almost twofold more active than donepezil. Furthermore, both compounds directly inhibited Aß1-42 self-aggregation and chelated bio-metals such as Fe2+, Zn2+ and Cu2+ preventing reactive oxygen species (ROS) generation by Aß and its oxidative damage in the brain regions of AD patients. Compound 28 had superior privilege by its dual ChE activity resulting in better cognitive improvement. Compounds 16 and 28 showed acceptable relative safety upon hepG2 cell line and excellent BBB penetration with wide safety margin as their LD50 were higher than 120 mg/kg.