The multitarget therapeutic strategy, as opposed to the more traditional ‘one disease-one tar-get-one drug’, may hold promise in treating multifactorial neurodegenerative syndromes, such as Alzheimer’s disease (AD) and related dementias. Recently, combining a photopharmacology approach with the multitarget-directed ligand (MTDL) design strategy, we disclosed a novel donepezil-like compound, namely 2-(4-((diethylamino)methyl)benzylidene)-5-methoxy- 2,3-dihydro-1H-inden-1-one (1a), which in the E diastereomeric form (and about tenfold less in the UV-B photo-induced isomer Z) showed the best activity as dual inhibitor of the AD-related targets acetylcholinesterase (AChE) and monoamine oxidase B (MAO-B). Herein, we investigated further photoisomerizable 2-benzylideneindan-1-one analogs 1b-h with the unconjugated tertiary amino moiety bearing alkyls of different bulkiness and lipophilicity. For each compound the thermal stable E diastereoisomer, along with the E/Z mixture as produced by UV-B light irradia-tion in the photostationary state (PSS, 75% Z), was investigated for the inhibition of human ChEs and MAOs. The pure E-diastereoisomer of the N-benzyl(ethyl)amino analog 1h achieved low nanomolar AChE and high nanomolar MAO-B inhibition potencies (IC50s 39 and 355 nM, re-spectively), whereas photoisomerization to the Z isomer (75% Z in the PSS mixture) resulted in a decrease (about 30%) of AChE inhibitory potency, and not in the MAO-B one. Molecular docking studies were performed to rationalize the different E/Z diastereoselectivity of 1h toward the two target enzymes.

Previous studies showed that some lamellarin-resembling annelated azaheterocyclic carbaldehydes and related imino adducts, sharing the 1-phenyl-5,6-dihydropyrrolo[2,1-a]isoquinoline (1-Ph-DHPIQ) scaffold, are cytotoxic in tumor cells and may reverse multidrug resistance (MDR) mediated by P-glycoprotein (P-gp). Herein, we synthesized and evaluated for their antiproliferative activity in four tumor cell lines (RD, HCT116, HeLa, A549) and ability of inhibiting P-gp-mediated MDR some ten diversely substituted 1-Ph-DHPIQ derivatives bearing at position 2 carboxylate groups (COOH, COOEt), nitriles (CN) and Mannich bases (e.g., morpholinomethyl derivatives). Lipophilicity parametrization and molecular docking calculations improved the understanding of the structure-activity relationships in cytotoxicity and P-gp inhibition of the investigated 1-Ph-DHPIQs, which led us to disclose a novel Mannich base HCl salt (8b’), which proved to be cytotoxic to all the tested tumor cell lines in the low micromolar range (IC50 < 20 M) and to inhibit in-vitro the efflux pumps P-gp and MRP1 responsible for MDR, with IC50s of 0.45 and 12.1 M, respectively.