Monoamine oxidase (MAO) is the enzyme responsible for the oxidative deamination of endogenous amines and neurotransmitters. Two isoforms of MAO are known – MAO-A and B. MAO-A inhibitors are used as antidepressants, while MAO-B inhibitors are established therapeutics for Parkinson's disease (PD). Currently, three MAO-B inhibitors are approved for the treatment of PD, the irreversible inhibitors selegiline and rasagiline, and the reversible inhibitor safinamide, while the reversible MAO-B inhibitor KDS2010 is in preclinical development. MAO-B mediates increased synthesis of γ-aminobutyric acid (GABA) and hydrogen peroxide (H2O2) in reactive astrocytes, where both substances inhibit normal function of dopamine neurons and accelerate their degeneration. MAO-B inhibitors reduce reactive astrogliosis and restore dopaminergic activity, alleviating PD symptoms.
The aim of the MSc thesis was to establish a synthetic route for the resynthesis of the hit compound and to synthesize and evaluate analogues of the hit compound. We investigated the influence of meta and para substitution on the central phenyl ring and the effect of different substituents (amines/esters) on the inhibition of hMAO-B. The starting point for the work was a hit compound identified by ligand-based virtual screening – cyclopropylamide, which inhibits human (h)MAO-B with an IC50 value of 0.034 ± 0.001 µM. The synthesis of derivatives started with para- and meta-coumaric acid, and after the introduction of the ester and the preparation of O-benzyl ether, Johnson-Corey–Chaykovsky cyclopropanation was carried out with sulfur ylide prepared in situ from trimethylsulfoxonium oxide in the presence of a strong base – sodium hydride. Due to problems with hydrolysis of the ester under the reaction conditions, we adapted the synthetic procedure and performed the cyclopropanation on the primary N-methylamide. Biochemical assays were performed with 21 isolated and purified cyclopropanamides and coumaric acid derivatives, and ten compounds selectively inhibited hMAO-B. The most potent inhibitor of hMAO-B was N-methylamide of para-coumaric acid 8 with an IC50 value of 0.025 ± 0.001 µM. Compounds 4 (IC50 = 1.617 ± 0.057 µM), 10 (IC50 = 1.390 ± 0.055 µM) and 12 (IC50 = 4.439 ± 0.205 µM) were also among the most potent inhibitors. Structure–activity relationships showed that: i) para-substituted derivatives are more potent MAO-B inhibitors than meta-substituted analogues; ii) amides are more potent inhibitors than esters, and iii) the introduction of structurally larger substituents (benzyl, tert-butyl) leads to loss of inhibitory activity. The chemical space of coumaric acid-based cyclopropanamides is rather unexplored, so further research would include the preparation of analogues using computational drug design approaches, which could lead to the identification of potent hMAO-B inhibitors.
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