Synthesis, biological investigation and molecular docking study of N-malonyl-1,2-dihydroisoquinoline derivatives as brain specific and shelf-stable MAO inhibitors

• Synthesis of new 1,2-dihydroisoquinoline redox chemical delivery system based MAOIs.
• In vitro stability in buffer and oxidizing agents proves shelf-life stability.
• In vitro stability in biological fluids to investigate the metabolic pathways.
• In vivo distribution in rats revealed preferential “lock-in” the brain.
• Molecular docking study to explore the binding mode to monoamine oxidase enzyme.

A group of N-malonyl-1,2-dihydroisoquinoline derivatives were synthesized and investigated as brain specific and shelf-stable MAO inhibitors. N-malonyl-1,2-dihydroisoquinoline redox carrier system was linked through amidic bond to 4-chloro and 4-nitrobenzylidenehydrazines (9a-b), as monoamine oxidase inhibitors (MAOIs), and β-phenethylamine (14), as a model drug, to afford a novel group of N-malonyl-1,2-dihydroisoquinoline chemical delivery systems (DHIQCDSs) (13a-b and 18). These systems are expected to be stable against air oxidation due to the presence of the carbonyl group close to nitrogen of the dihydroisoquinoline. The synthesized DHIQCDS (18) was subjected to various chemical and biological investigations to evaluate its stability and prove its ability to cross the blood brain barrier and “lock-in” the brain. The in vitro chemical and enzymatic oxidation studies showed reasonable stability and adequate rate of conversion of DHIQCDS (18) to its corresponding quaternary metabolites. In vivo distribution study in rats revealed preferential concentration of the active moiety in the brain. Moreover, compounds (9a-b, 12a-b and 17) were screened for their in vitro MAO inhibitory activity compared to clorgyline as a reference compound. The inhibition profile was found to be competitive for both MAO-A and MAO-B isozymes with more selectivity toward MAO-A. Molecular docking study of compounds (9a-b, 12a-b and 17) and the suggested metabolites was carried out on both MAO-A and MAO-B isozymes. Observation of the docked poses revealed many interactions with many residues previously reported to have an effect on the inhibition of MAO enzyme.

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