Inhibitory Activity of N- and S-Functionalized Monoterpene Diols Towards Monoamine Oxidases A and B

Monoamine oxidase B (MAO-B) inhibitors are widely used as part of combination drug therapy for Parkinson's disease. As demonstrated in both in vitro and in vivo experiments, the monoterpenoid Prottremine and some of its derivatives exhibit high antiparkinsonian activity. In this study, the inhibitory activity of Prottremine and its derivatives (including 14 new 9-N- and S-derivatives) against MAO-A and MAO-B enzymes has been investigated for the first time. Compounds containing fragments of substituted anilines have demonstrated the highest activity against MAO-A; for example, compound 28 had an IC₅₀ of 178 ± 44 μM. A significant proportion of the compounds tested, including Prottremine, exhibited moderate inhibitory activity towards MAO-B, with the most active being the o-aminoacetophenone derivative, which had an IC₅₀ of 95 ± 5 μM. A molecular docking method for studying murine MAO-A and -B enzymes was developed using AlphaFold2 (v2.3.2), with further improvements. For the MAO-B enzyme, a strong correlation was observed between the molecular docking data and the measured activity of the compounds, with the maximum binding affinity registered for the most active compound. It is conceivable that the antiparkinsonian activity of Prottremine and some of its derivatives may be partially mediated, among other mechanisms, by MAO-B enzyme inhibition.