Lead optimization of rivastigmine-like hybrids: Impact of nitro group and halogen substitution on multi-target anti-Alzheimer's activity

The multifactorial profile of Alzheimer's disease has led researchers to adopt a multi-target strategy for the design of new small molecules. In this context, starting from the structure of ROS151, a novel series of seventeen rivastigmine-like hybrids was developed. Structural modification involved the aryloxy-methylene portion, with the substitution of the nitro group with other groups and the variation of type and position of the halogen atom. The nitro group was confirmed to be essential for high anti-ChE activity, with compound 3 showing the most balanced profile, superior to that of the lead compound (IC50 = 0.827 ± 0.012 μM and 4.58 ± 0.01 μM against hAChE and eqBChE, respectively). Hybrid 2 showed inhibitory activity against hAChE close to that of donepezil (IC50 = 0.029 ± 0.005 μM), while 7 had better activity against eqBChE than the parent drug rivastigmine (IC50 = 0.45 ± 0.02 μM). In silico experiments were performed to corroborate these results. When the nitro group was reduced to amine, as for compound 10, relevant antioxidant activity (ABTS, IC50 = 25.2 ± 1.2 μM) and remarkable chelating properties toward Fe3+ (pM = 15.6) and Cu2+ (pM = 11.4), with a good selectivity over Zn2+ (pM = 6.0) were observed. Inhibition of fatty acid amide hydrolase (hFAAH) resulted less relevant but still appreciable. Cyano-derivative 8 appears to be the only compound with preserved multi-enzymatic inhibitory potential, even without nitro-group in its structure and can be used as starting point for further series. Finally, many hybrids demonstrated interesting experimental pharmacokinetic properties, evaluated using bioanalytical methods.