Synthesis, Design and Biological Evaluation of Novel Photomodulable Azoderivatives as Cholinesterase Inhibitors

Photopharmacology has emerged as an innovative approach for the development of therapeutics whose biological activity can be reversibly modulated by light. In order to develop new multitarget compounds with photomodulable properties, a series of molecular hybrids was designed by conjugating a photoisomerizable azobenzene scaffold with pharmacophores inspired by drugs used in the treatment of neurodegenerative diseases, such as donepezil, selegiline, and rivastigmine.

Prior to synthesis, biological activity predictions were performed using SwissTargetPrediction and SuperPred platforms, complemented by a quantitative structure–activity relationship (QSAR) model developed through Python-based cheminformatics tools as a virtual screening strategy. In addition, pharmacokinetic, toxicological, and synthetic accessibility properties were assessed using SwissADME, Deep-PK, and ADMETLab 3.0.

The synthesis was accomplished in two steps. First, 4-hydroxyazobenzene was reacted with 1,6-dibromohexane to afford an alkyl bromide intermediate, which was subsequently functionalized under microwave irradiation with 4-amino-N-benzylpiperidine, tetrahydroisoquinoline, N-methylpropargylamine, and 1-(2-aminoethyl)piperidine. The synthesized derivatives were evaluated as AChE and BChE inhibitors using Ellman's spectrophotometric method. In agreement with the in silico predictions, AZO-C6-NH-C2-pipe, ((E)-6-(4-(phenyldiazenyl)phenoxy)-N-(2-(piperidin-1-yl)ethyl)hexan-1-amine), emerged as the most active derivative, exhibiting IC₅₀ values of 1.6 μM against AChE and 2.1 μM against BChE. Its photomodulable properties were confirmed by UV–Vis and ¹H/¹³C NMR spectroscopy, achieving 90% conversion to the Z isomer after 90 minutes of irradiation at 254 nm.