Carboxamides vs. methanimines: Crystal structures, binding interactions, photophysical studies, and biological evaluation of (indazole-5-yl)methanimines as monoamine oxidase B and acetylcholinesterase inhibitors.

A comprehensive study was performed for the first time to compare two structurally related substance classes, namely indazole-5-carboxamides (11-16) and (indazole-5-yl)methanimines (17-22). Both chemical entities are potent, selective and reversible MAO-B inhibitors and, therefore, may serve as promising lead structures for the development of drug candidates against Parkinson's disease (PD) and other neurological disorders. Compounds 15 (Ki = 170 pM, SI = 25907) and 17 (Ki = 270 pM, SI = 16340) were the most potent and selective MAO-B inhibitors in both series. To investigate the multi-target inhibitory activity, all compounds were further screened for their potency against human AChE and BuChE enzymes. Compound 15 was found to be the most potent and selective AChE inhibitor in all series (hAChE IC50 = 78.3 ±â€¯1.7 µM). Moreover, compounds 11 and 17 showed no risk of drug-induced hepatotoxicity and a wider safety window, as determined in preliminary cytotoxicity screening. Molecular modeling studies into the human MAO-B enzyme-binding site supported by a HYDE analysis suggested that the imine linker similarly contributes to the total binding energy in methanimines 17-22 as the amide spacer in their carboxamide analogs 11-16. Amplified photophysical evaluation of compounds 17 and 20, including single X-ray analysis, photochemical experiments, and quantum-chemical calculations, provided insights into their more favourable isomeric forms and structural features, which contribute to their biologically active form and promising drug-like properties.

(Pyrrolo-pyridin-5-yl)benzamides: BBB permeable monoamine oxidase B inhibitors with neuroprotective effect on cortical neurons.

An extensive study was performed to develop a series of (pyrrolo-pyridin-5-yl)benzamides as reversible MAO-B inhibitors. Compounds 14 (NTZ-2020, hMAO-B IC50 = 1.11 nM, Ki = 0.56 nM, >9000-fold selective versus MAO-A) and 15 (NTZ-2027, hMAO-B IC50 = 3.27 nM, Ki = 1.45 nM, SI > 3058) are identified as the most promising BBB permeable derivatives within the series of (1H-pyrrolo[3,2-b]pyridine-5-yl)benzamides, combining both high potency and selectivity with optimal physicochemical and drug-like properties required for CNS active drugs. Extended photophysical analysis, including single X-ray analysis, quantum-chemical calculations and spectroscopic experiments provided insights into their tautomerism and structural behavioral, which relates to their biologically active form. The reversible MAO-B inhibitor 14 (NTZ-2020) exhibits a neuroprotective effect on cortical neuron survival and induces neurite network outgrowth. These effects are associated with a good BBB penetration of 14 that was confirmed in a triple cell neurovascular unit (NVU) model.

Crystal structures, binding interactions, and ADME evaluation of brain penetrant N-substituted indazole-5-carboxamides as subnanomolar, selective monoamine oxidase B and dual MAO-A/B inhibitors.

The pharmacological and physicochemical analysis of structurally optimized N-alkyl-substituted indazole-5-carboxamides, developed as potential drug and radioligand candidates for the treatment and diagnosis of Parkinson's disease (PD) and other neurological disorders, is reported. Recent efforts have been focused on the development of subnanomolar potent, selective MAO-B (N1-alkyl-substituted compounds 12a-14a and 15) and dual active MAO-A/B (N2-methylated compounds 12b-14b) inhibitors with nanomolar potency towards MAO-B and moderately active against MAO-A enzyme, respectively. The most promising drug-like derivatives in both series were N-(3-chloro-4-fluorophenyl)-1-methyl-1H-indazole-5-carboxamide (13a, NTZ-1441, IC50 hMAO-B 0.662 nM, >15000-fold selective versus MAO-A) and N-(3-chloro-4-fluorophenyl)-2-methyl-2H-indazole-5-carboxamide (13b, NTZ-1442, IC50 hMAO-B 8.08 nM, IC50 hMAO-A 0.56 µM, SI = 70). Moreover, compounds 13a and 13b were predicted to cross both the gastrointestinal tract (at pH 2.0, 5.5, and 7,4) and the blood-brain barrier (BBB) in vitro with appropriate drug-like properties required for CNS active drugs. Combined single X-ray/molecular modeling studies provided insights into the enzyme-inhibitor interactions within both MAO isoforms and the rationale for their inhibitory activity with controlled MAO-A/B selectivity - despite their small structural differences. The binding modes of 12a,b and 13a,b confirmed that the major interactions with hMAO-B were established via the flexible carbonyl group of the carboxamide linkage and the electron-donating nitrogens N1 or N2 of the indazole moiety, allowing further exploration of the alkyl side chain for next step lead optimization efforts.