Novel potent and selective dual acetylcholinesterase inhibitors: N-substituted theobromine and theophylline derivatives.

Methylxanthines and their derivatives are of great interest due to their diverse biological activities. In this work, a new series of twenty-eight semisynthetic theobromine and theophylline derived compounds were designed and synthesized by applying a simple and efficient strategy. First, the corresponding methylxanthine was reacted with a dibromoalkane (n = 3, 5-8) and subsequently, the brominated intermediate was reacted with an amine, including pyrrolidine, piperidine, diethylamine, methylpiperazine, 1-(2-aminoethyl)pyrrolidine, 1-(2-aminoethyl)piperidine, 2-(1-methylpyrrolidin-2-yl)ethanamine, 1-benzylpiperidin-4-amine, 1-benzylpiperidin-4-yl-methanamine, and 2-(1-benzylpiperidin-4-yl)ethan-1-amine. The two synthetic steps were carried out in very short times using a microwave reactor. The biological activity of the new compounds was evaluated on acetylcholinesterase (AChE), butyrylcholinesterase (BChE), monoamine oxidases (MAO-A, MAO-B) and beta-secretase (BACE-1). The majority of the new derivatives showed potent and selective in vitro AChE inhibition. Compounds 21, 28 and 30 exhibited the strongest effect on both electric eel and human AChE enzyme, with IC₅₀ values on the low nanomolar scale. The kinetic study of compound 28 in hAChE displayed a mixed inhibition mechanism, suggesting a simultaneous interaction with both the CAS and PAS of the enzyme. This experimental binding mode is consistent with the results of docking and molecular dynamics modelling studies, where it was observed that the piperidinium fragment of 16, 21, 28 and 32 was located at the CAS, whereas the xanthine fragment of each inhibitor interacted with Trp286 in the PAS. These results indicate that these novel xanthine analogues act as selective and potent AChE inhibitors that could also prevent the precipitation of the aberrant Aβ peptide. These properties, in conjunction with their in silico good pharmacokinetic profiles, make these molecules promising lead compounds for the development of new effective drugs against several forms of dementia.