Monoamine oxidase (MAO) is a flavoenzyme bound to the outer mitochondrial membrane, which catalyzes the oxidative deamination of amines. MAO regulates homeostasis and neurotransmission of important monoamine neurotransmitters like serotonin, dopamine and noradrenalin. There are two isoenzymes, monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B), which differ in their substrate specificities, inhibitor sensitivities and tissue localization.
Increased activity of MAO, followed by decreased concentrations of monoamine neurotransmitters, is related to numerous neurological disorders. During the reaction of oxidative deamination several neurotoxic species are produced, which contribute to the oxidative damage. MAO inhibitors have been therefore used for decades in the treatment of numerous diseases like depression, Parkinson’s disease and Alzheimer’s disease. The first MAO inhibitors were non-selective and irreversible, but recently the research focused on the development of reversible and selective MAO inhibitors due to the lower degree of adverse effects.
The laboratory work involved the synthesis and evaluation of nitro derivatives of 5-styrylnicotinonitrile. Compounds were designed based on previous research of potential MAO inhibitors at the Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Ljubljana, and based on the structure of known reversible MAO-B inhibitor safinamide. The inhibitory activity of compounds was evaluated with biological tests on human MAO-A and MAO-B enzymes. Out of a total of 16 tested compounds, the half maximal inhibitory concentration (IC50) in nanomolar region was determined by eight compounds in the case of MAO-B and by one compound in the case of MAO-A isoenzyme. Two compounds showed the best inhibitory properties: (E)-2-chloro-5-(4-methoxy-2-nitrostyryl)nicotinonitrile (IC50 = 42.2 ± 4.9 nM) and etil (E)-2-(4-(2-(5-cyanopyridin-3-yl)vinyl)-3-nitrophenoxy)acetate (IC50 = 42.3 ± 3.4 nM) on MAO-B isoenzyme. These values exceed the inhibitory property of safinamide (IC50 = 98 nM) and present a basis of further research of MAO inhibitors.
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