Hybrids of methylxanthines or azoderivatives as acetylcholinesterase inhibitors: preliminary structure-activity relationship analysis

Cholinesterase inhibitors play a crucial role in enhancing cerebral cholinergic activity, fundamental for treating neurodegenerative diseases. An innovative strategy involves enriching these molecules with additional biological properties to develop multifunctional compounds that can offer broader and enhanced pharmacological effects, especially in the treatment of multifactorial pathologies such as Alzheimer's disease.

In previous work, we demonstrated that caffeine-pyrrolidine hybrids can inhibit acetylcholinesterase (AChE) and activate nicotinic acetylcholine receptors (nAChR). Particularly, the hybrid linked by a seven-methylene hydrocarbon chain (caffeine-C7-pyrrolidine) showed the highest potency.

In this study, we synthesized a series of new derivatives by linking a fragment of methylxanthine with a secondary amine using a seven-carbon linker. We used alkyl bromides of theophylline and theobromine as starting reagents, and diethylamine and N-benzylmethylamine as secondary amines. Additionally, we synthesized two new compounds by replacing the methylxanthine fragment with azobenzene (Ph-N=N-Ph), known for its photo-modulable properties. The primary objective of this research was to conduct a structure-activity analysis to assess the impact of the pharmacophore (azobenzene or methylxanthine) and the amino group (diethylamine or N-benzylmethylamine) on biological activity efficacy. All synthesized compounds demonstrated inhibitory capacity against AChE. Among the azobenzene derivatives, the most active hybrid was AZO-C7-DEA ((E)-N,N-diethyl-7-(4-(phenyldiazenyl)phenoxy)heptan-1-amine) with an IC₅₀ of 1.1 µM. Furthermore, among the methylxanthine derivatives, theobromine-C7-DEA (7-(7-(benzyl(methyl)amino)heptyl)-1,3-dimethyl-1H-purine-2,6(3H,7H)-dione) emerged as the most potent inhibitor with an IC₅₀ of 0.188 µM.