Design, synthesis and in vitro evaluation of new cholinesterase inhibitors with metal-chelating and antioxidant properties as multitarget compounds for Alzheimer’s disease

Alzheimer’s disease (AD) is a multifactorial neurodegenerative syndrome, as many factors are involved in its pathogenesis, including: cholinergic system alterations; hyperproduction and aggregation of β-amyloid (Aβ) neurotoxic peptide; increased oxidative stress; dyshomeostasis of some bio-metals, which promote aggregation of the Aβ peptide and catalyze the formation of reactive oxygen species (ROS). Based on these considerations, series of pyrimidine, pyridine and deferiprone derivatives have been designed, synthesized and evaluated in vitro with the hypothesis that they can restore the cholinergic tone, contrast the toxicity and deposition of the β-amyloid peptide, attenuate the dyshomeostasis of the metals mainly involved in the pathology and reduce the oxidative stress, in order to obtain multitarget molecules for Alzheimer’s therapy. Specifically, the compounds were designed as potential cholinesterases inhibitors able to interact with both the active catalytic site (CAS) and the peripheral anionic site (PAS) of the enzyme, inserting two small aromatic groups separated by an aliphatic linker. Metal ions chelating groups and, in some cases, antioxidant moieties were incorporated into these compounds, in order to obtain molecules potentially able to chelate bio-metals colocalized in Aβ plaques and involved in the generation of radical species and to reduce the oxidative stress. Totally, 74 new compounds were synthesized, which were tested by enzymatic inhibition studies towards EeAChE and eqBChE by Ellman’s method. Among the tested compounds the most potent inhibitor of EeAChE showed a mixed-type inhibition mechanism with a Ki = 0.312 ± 0.108 uM, while the most potent inhibitor of eqBChE showed a mixed-type inhibition mechanism with a Ki = 0.099 ± 0.071 uM. For the most potent cholinesterases inhibitors, the ability to chelate iron, copper and zinc ions was assessed through UV-vis spectrophotometry. The tested compounds showed chelating capacities towards metal ions mainly involved in the pathogenesis of AD (all towards Fe3+, many towards Cu2+ and some towards Zn2+). On the most potent cholinesterases inhibitors among phenolic derivatives, the antioxidant activity assay was carried out according to DPPH spectrophotometric method. Biological studies for the evaluation of the anti-aggregating activity towards Aβ42 and Tau and of the cytotoxicity are still ongoing and the relative results will be useful to identify the best compounds among those synthesized and to deepen the assessments regarding the optimal structural characteristics in order to obtain multitarget compounds for AD.