Isolation of Acacetin from Calea urticifolia with Inhibitory Properties against Human Monoamine Oxidase-A and -B

Natural Products as Monoamine Oxidase Inhibitors: Potential Agents for Neurological Disorders

The role of medicinal plants has been advantageous due to their manifestation through various cellular and molecular mechanisms. Inhibition of the monoamine oxidase enzyme is suspected to be a highly effective treatment for various neurological illnesses like Alzheimer's disease, Parkinson's disease, depression, social phobia, and panic disorders. The study of phytochemicals and plant extracts used as a traditional source of medication revealed that they possess the vast potential for monoamine oxidase inhibition. Thus, the article focuses on the potential use of plant extracts and phytochemicals as sources of novel MAO inhibitors for treating neurological disorders. Exhaustive literature search revealed that a variety of phytochemicals from the categories such as flavonoids, alkaloids, glycosides, alkyl phenyl ketones, coumarin derivatives and essential oils have displayed potential MAO inhibition. This review highlights the progress made in the discovery and development of plant-based MAO inhibitors and aims to provide medicinal chemists with an overview of this information to aid in the development of clinically viable drugs.

Recent advances in the discovery of plant-derived antimicrobial natural products to combat antimicrobial resistant pathogens: insights from 2018-2022

Covering: 2018 to 2022Antimicrobial resistance (AMR) poses a significant global health threat. There is a rising demand for innovative drug scaffolds and new targets to combat multidrug-resistant bacteria. Before the advent of antibiotics, infections were treated with plants chosen from traditional medicine practices. Of Earth's 374 000 plant species, approximately 9% have been used medicinally, but most species remain to be investigated. This review illuminates discoveries of antimicrobial natural products from plants covering 2018 to 2022. It highlights plant-derived natural products with antibacterial, antivirulence, and antibiofilm activity documented in lab studies. Additionally, this review examines the development of novel derivatives from well-studied parent natural products, as natural product derivatives have often served as scaffolds for anti-infective agents.

Ternifolipyrons A-J: new cytotoxic α-pyrones from Isodon ternifolius (D. Don) Kudô

Isodon ternifolius (D.Don) Kudô is an important Asian herb used in traditional medicine against several diseases. Nineteen compounds were isolated from the dichloromethane-methanol (1 : 1) extract of I. ternifolius roots, including ten new α-pyrone derivatives, named ternifolipyrons A-J. The chemical structures of the isolates were determined by a combination of 1D and 2D NMR, along with LR- and HRMS spectroscopy. The absolute configurations of the α-pyrone derivatives were constructed based upon the X-ray signal crystal of the bromobenzoyl derivative of 1 as well as the electronic circular dichroism (ECD). All isolates (1-19) were investigated for their growth-inhibitory potential towards CCRF-CEM-leukemia cells at a fixed concentration of 30 μM. The compounds which exerted more than 50% inhibition at this concentration, compounds (7, 10, 12, 15-17), were tested at a different concentration range to determine their IC₅₀ values in CCRF-CEM leukemia, MDA-MB-231 triple-negative breast cancer, and MCF7 breast cancer cell lines. Ursolic acid (16) showed the most potent activity against the three cancer cell lines with IC₅₀ values of 8.37, 18.04, and 18.93 μM, respectively.

Roles of selected non-P450 human oxidoreductase enzymes in protective and toxic effects of chemicals: review and compilation of reactions

This is an overview of the metabolic reactions of drugs, natural products, physiological compounds, and other (general) chemicals catalyzed by flavin monooxygenase (FMO), monoamine oxidase (MAO), NAD(P)H quinone oxidoreductase (NQO), and molybdenum hydroxylase enzymes (aldehyde oxidase (AOX) and xanthine oxidoreductase (XOR)), including roles as substrates, inducers, and inhibitors of the enzymes. The metabolism and bioactivation of selected examples of each group (i.e., drugs, "general chemicals," natural products, and physiological compounds) are discussed. We identified a higher fraction of bioactivation reactions for FMO enzymes compared to other enzymes, predominately involving drugs and general chemicals. With MAO enzymes, physiological compounds predominate as substrates, and some products lead to unwanted side effects or illness. AOX and XOR enzymes are molybdenum hydroxylases that catalyze the oxidation of various heteroaromatic rings and aldehydes and the reduction of a number of different functional groups. While neither of these two enzymes contributes substantially to the metabolism of currently marketed drugs, AOX has become a frequently encountered route of metabolism among drug discovery programs in the past 10-15 years. XOR has even less of a role in the metabolism of clinical drugs and preclinical drug candidates than AOX, likely due to narrower substrate specificity.

Bioguided isolation of a selective compound from Calea phyllolepis leaves against breast cancer cells

Plants of the Calea genus have been reported to contain lipophilic compounds, such as sesquiterpene lactones, with cytotoxic effect against different cancer cell lines. The aim of this manuscript was to investigate the chemical profile and cytotoxic activity of different fractions from Calea phylolepis leaves on different human cancer cell lines. The fractions were prepared using solvent extraction of increasing polarity, yielding hexane, ethyl acetate and methanolic fractions. All fractions were chemically analysed by thin layer chromatography (TLC), and their cytotoxic activity against HT-29 (colon adenocarcinoma), MCF-7 (breast cancer), U-251MG (malignant glioblastoma) and L929 (mouse fibroblast) cell lines was investigated. Among these, the hexane and ethyl acetate fractions showed higher cytotoxic effects, while the methanolic fraction did not show any cytotoxic effects. The major bioactive compound from the hexane fraction (12.15%) was isolated using chromatographic methods and was identified by nuclear magnetic resonance spectroscopy (NMR) and gas chromatography-mass spectrometry (GC-MS) analysis as 6-epi-β-verbesinol coumarate. This compound showed activity against breast cancer cells (IC₅₀  = 5.8 ± 1.0 μg/ml), similar to etoposide. Furthermore, 6-epi-β-verbesinol coumarate showed low cytotoxicity to normal fibroblast cells, suggesting a high selectivity index (SI = 7.39) against breast cancer cells.

Computationally Assisted Lead Optimization of Novel Potent and Selective MAO-B Inhibitors

A series of dietary flavonoid acacetin 7-O-methyl ether derivatives were computationally designed aiming to improve the selectivity and potency profiles against monoamine oxidase (MAO) B. The designed compounds were evaluated for their potential to inhibit human MAO-A and -B. Compounds 1c, 2c, 3c, and 4c were the most potent with a Ki of 37 to 68 nM against MAO-B. Compounds 1c–4c displayed more than a thousand-fold selectivity index towards MAO-B compared with MAO-A. Moreover, compounds 1c and 2c showed reversible inhibition of MAO-B. These results provide a basis for further studies on the potential application of these modified flavonoids for the treatment of Parkinson’s Disease and other neurological disorders.

Cardiac senescence is alleviated by the natural flavone acacetin via enhancing mitophagy

Cardiac senescence is associated with cardiomyopathy which is a degenerative disease in the aging process of the elderly. The present study investigates using multiple experimental approaches whether the natural flavone acacetin could attenuate myocardial senescence in C57/BL6 mice and H9C2 rat cardiac cells induced by D-galactose. We found that the impaired heart function in D-galactose-induced accelerated aging mice was improved by oral acacetin treatment in a dose-dependent manner. Acacetin significantly countered the increased serum advanced glycation end products, the myocardial telomere length shortening, the increased cellular senescence marker proteins p21 and p53, and the reduced mitophagy signaling proteins PINK1/Parkin and Sirt6 expression in aging mice. In H9C2 rat cardiac cells, acacetin alleviated cell senescence induced by D-galactose in a concentration-dependent manner. Acacetin decreased p21 and p53 expression, up-regulated PINK1/Parkin, LC3II/LC3I ratio, pLKB1, pAMPK and Sirt6, and reversed the depolarized mitochondrial membrane potential in aging cardiac cells. Mitophagy inhibition with 3-methyladenine or silencing Sirt6 abolished the protective effects of acacetin against cardiac senescence. Further analysis revealed that acacetin effect on Sirt6 was mediated by Sirt1 activation and increase of NAD+/NADH ratio. These results demonstrate that acacetin significantly inhibits in vivo and in vitro cardiac senescence induced by D-galactose via Sirt1-mediated activation of Sirt6/AMPK signaling pathway, thereby enhancing mitophagy and preserving mitochondrial function, which suggests that acacetin may be a drug candidate for treating cardiovascular disorders related to aging.

Selective Interactions of O-Methylated Flavonoid Natural Products with Human Monoamine Oxidase-A and -B

A set of structurally related O-methylated flavonoid natural products isolated from Senecio roseiflorus (1), Polygonum senegalense (2 and 3), Bhaphia macrocalyx (4), Gardenia ternifolia (5), and Psiadia punctulata (6) plant species were characterized for their interaction with human monoamine oxidases (MAO-A and -B) in vitro. Compounds 1, 2, and 5 showed selective inhibition of MAO-A, while 4 and 6 showed selective inhibition of MAO-B. Compound 3 showed ~2-fold selectivity towards inhibition of MAO-A. Binding of compounds 1-3 and 5 with MAO-A, and compounds 3 and 6 with MAO-B was reversible and not time-independent. The analysis of enzyme-inhibition kinetics suggested a reversible-competitive mechanism for inhibition of MAO-A by 1 and 3, while a partially-reversible mixed-type inhibition by 5. Similarly, enzyme inhibition-kinetics analysis with compounds 3, 4, and 6, suggested a competitive reversible inhibition of MAO-B. The molecular docking study suggested that 1 selectively interacts with the active-site of human MAO-A near N5 of FAD. The calculated binding free energies of the O-methylated flavonoids (1 and 4-6) and chalcones (2 and 3) to MAO-A matched closely with the trend in the experimental IC_50's. Analysis of the binding free-energies suggested better interaction of 4 and 6 with MAO-B than with MAO-A. The natural O-methylated flavonoid (1) with highly potent inhibition (IC₅₀ 33 nM; Ki 37.9 nM) and >292 fold selectivity against human MAO-A (vs. MAO-B) provides a new drug lead for the treatment of neurological disorders.

Promising selective MAO-B inhibition by sesamin, a lignan from Zanthoxylum flavum stems

Monoamine oxidase inhibition is an important therapeutic approach for various neurodegenerative disorders. Reversible MAO inhibitors selectively targeting only one isoform possess substantial merit in terms of safety, efficacy, and side effect profile. This study aimed to isolate the secondary metabolites of Zanthoxylum flavum stems and evaluate their recombinant human MAO inhibition, antimicrobial, and antiprotozoal activities. As a result, fourteen compounds were isolated and identified (nine of them were reported from Z. flavum for the first time). Compound 3 (sesamin) exhibited potent selective MAO-B inhibition (IC₅₀ value of 1.45 ± 0.05 µM) which reported herein for the first time. Compound 2 showed selective MAO-A inhibition activity, compound 5 exhibited good trypanocidal activity, and compound 7 displayed moderate antibacterial activity. The promising MAO-B inhibitory activity of sesamin provoked us to further explore the kinetic properties, the binding mode, and the underlying mechanism of MAO-B inhibition by this lignan. This detailed investigation substantiated a reversible binding and mixed MAO-B catalytic function inhibition via sesamin (K_i: 0.473 ± 0.076 μM). Selectivity and reversibility of sesamin on MAO-B provide exciting prerequisites for further in vivo investigation to confirm its therapeutic potentiality.

Novel approaches to the discovery of selective human monoamine oxidase-B inhibitors: is there room for improvement?

Introduction: Selective monoamine oxidase-B (MAO-B) inhibitors are currently used as coadjuvants for the treatment of early motor symptoms in Parkinson's disease. They can, based on their chemical structure and mechanism of inhibition, be categorized into reversible and irreversible agents. Areas covered: This review provides a comprehensive update on the development state of selective MAO-B inhibitors describing the results, structures, structure-activity relationships (SARs) and Medicinal chemistry strategies as well as the related shortcomings over the past five years. Expert opinion: Researchers have explored and implemented new and old chemical scaffolds achieving high inhibitory potencies and isoform selectivity. Most of them were characterized and proposed as multitarget agents able to act at different levels (including AChE inhibition, H3R or A_2AR antagonism, antioxidant and chelating properties, Aβ_1-42 aggregation reduction) in the network of aetiologies of neurodegenerative disorders. These results can also be used to avoid 'cheese-reaction' effects and the occurrence of serotonergic syndrome in patients.

Selective Inhibition of Human Monoamine Oxidase B by Acacetin 7-Methyl Ether Isolated from Turnera diffusa (Damiana)

The investigation of the constituents that were isolated from Turnera diffusa (damiana) for their inhibitory activities against recombinant human monoamine oxidases (MAO-A and MAO-B) in vitro identified acacetin 7-methyl ether as a potent selective inhibitor of MAO-B (IC₅₀ = 198 nM). Acacetin 7-methyl ether (also known as 5-hydroxy-4′, 7-dimethoxyflavone) is a naturally occurring flavone that is present in many plants and vegetables. Acacetin 7-methyl ether was four-fold less potent as an inhibitor of MAO-B when compared to acacetin (IC₅₀ = 50 nM). However, acacetin 7-methyl ether was >500-fold selective against MAO-B over MAO-A as compared to only two-fold selectivity shown by acacetin. Even though the IC₅₀ for inhibition of MAO-B by acacetin 7-methyl ether was ~four-fold higher than that of the standard drug deprenyl (i.e., Selegiline^TM or Zelapar^TM, a selective MAO-B inhibitor), acacetin 7-methyl ether’s selectivity for MAO-B over MAO-A inhibition was greater than that of deprenyl (>500- vs. 450-fold). The binding of acacetin 7-methyl ether to MAO-B was reversible and time-independent, as revealed by enzyme-inhibitor complex equilibrium dialysis assays. The investigation on the enzyme inhibition-kinetics analysis with varying concentrations of acacetin 7-methyl ether and the substrate (kynuramine) suggested a competitive mechanism of inhibition of MAO-B by acacetin 7-methyl ether with Ki value of 45 nM. The docking scores and binding-free energies of acacetin 7-methyl ether to the X-ray crystal structures of MAO-A and MAO-B confirmed the selectivity of binding of this molecule to MAO-B over MAO-A. In addition, molecular dynamics results also revealed that acacetin 7-methyl ether formed a stable and strong complex with MAO-B. The selective inhibition of MAO-B suggests further investigations on acacetin 7-methyl as a potential new drug lead for the treatment of neurodegenerative disorders, including Parkinson’s disease.

Computationally aided stereochemical assignment of undescribed bisabolenes from Calea urticifolia

Calea urticifolia (Mill.) DC. (Compositae) is a medicinal plant found in El Salvador. Calea is used in folkloric medicine as a psychoactive principle with calming effect, as well as in the treatment of diarrhea and fever. Three undescribed bisabolenes, named caleanolenes A-C, as well as, three known sesquiterpene lactones 2,3-epoxyjuanislamin, calealactone B, calein C, and the flavonoid acacetin, were isolated from the chloroform extract of the leaves of C. urticifolia. The chemical structures of the isolated compounds were determined on the basis of HRMS, IR, CD, and from 1D and 2D NMR spectroscopic studies. The absolute configurations of the caleanolenes have been partly established using GIAO NMR and ECD calculations. The isolated compounds were evaluated for cytotoxicity against the CA46 and Raji lymphoma, and the MCF7 breast cancer cell lines, with 2,3-epoxyjuanislamin showing the best activity in all cell lines (IC₅₀ value range 2.9-12.3 μM).

3D-QSAR and in-silico Studies of Natural Products and Related Derivatives as Monoamine Oxidase Inhibitors

BACKGROUND

The computational development of human monoamine oxidase (MAO) inhibitors led to advancement in drug design and the treatment of many neurodegenerative diseases and neuropsychiatric disorders. The computational development of human monoamine oxidase (MAO) inhibitors led to advancement in drug design and the treatment of many neurodegenerative diseases and neuropsychiatric disorders. Different natural heterocyclic structures are reported to display selective MAO inhibitory activity by preclinical and in-silico modeling.

OBJECTIVE

Currently, the major interest is devoted to the study of natural based therapeutic agents from the different categories. Therefore, we presenting the review to critically discuss and outline the recent advances in our knowledge on the importance of natural and natural based ligand-MAO insilico methods for novel MAO inhibitors.

DISCUSSION

Several natural and related synthetic heterocyclic compounds such as coumarins, β- carboline, piperine, naphthoquinone, morpholine, caffeine, amphetamine moreover flavonoids, chalcones, xanthones, curcumin are discussed for their MAO inhibitory profile along with molecular docking and quantitative structure-activity relationship studies.

CONCLUSION

It is clear that, by this computational drug design approach, more particular, reversible and potent compounds can be proposed as MAO inhibitors by exact changes on the fundamental framework.

Dinghupeptins A-D, Chymotrypsin Inhibitory Cyclodepsipeptides Produced by a Soil-Derived Streptomyces

Four new cyclodepsipeptides, dinghupeptins A-D (1-4), possessing a rare N⁵-(2-hydroxylethyl)glutamine moiety, were isolated from cultures of the soil-derived Streptomyces sp. SC0581. Their structures were elucidated by spectroscopic and advanced Marfey's amino acid analysis, and their 3D structures were established by theoretical conformational analysis. Compounds 1 and 2, containing a 3-amino-6-hydroxypiperidone unit, displayed selective inhibition of chymotrypsin with IC₅₀ values of 2.1 and 1.1 μM, respectively. Enzyme kinetic analysis and molecular docking experiments revealed they are competitive inhibitors binding to the active site of chymotrypsin.

Interactions of endocannabinoid virodhamine and related analogs with human monoamine oxidase-A and -B

The endocannabinoid system plays an important role in the pathophysiology of various neurological disorders, such as anxiety, depression, neurodegenerative diseases, and schizophrenia; however, little information is available on the coupling of the endocannabinoid system with the monoaminergic systems in the brain. In the present study, we tested four endocannabinoids and two anandamide analogs for inhibition of recombinant human MAO-A and -B (monoamine oxidase). Virodhamine inhibited both MAO-A and -B (IC50 values of 38.70 and 0.71 μM, respectively) with ∼55-fold greater inhibition of MAO-B. Two other endocannabinoids (noladin ether and anandamide) also showed good inhibition of MAO-B with IC50 values of 18.18 and 39.98 μM, respectively. Virodhamine was further evaluated for kinetic characteristics and mechanism of inhibition of human MAO-B. Virodhamine inhibited MAO-B (Ki value of 0.258 ± 0.037 μM) through a mixed mechanism/irreversible binding and showed a time-dependent irreversible mechanism. Treatment of Neuroscreen-1 (NS-1) cells with virodhamine produced significant inhibition of MAO activity. This observation confirms potential uptake of virodhamine by neuronal cells. A molecular modeling study of virodhamine with MAO-B and its cofactor flavin adenine dinucleotide (FAD) predicted virodhamine's terminal -NH2 group to be positioned near the N5 position of FAD, but for docking to MAO-A, virodhamine's terminal -NH2 group was far away (∼6.52 Å) from the N5 position of FAD, and encountered bad contacts with nearby water molecules. This difference could explain virodhamine's higher potency and preference for MAO-B. The binding free energies for the computationally-predicted poses also showed that virodhamine was selective for MAO-B. These findings suggest potential therapeutic applications of virodhamine for the treatment of neurological disorders.

Isoform selectivity of harmine-conjugated 1,2,3-triazoles against human monoamine oxidase

AIM

There is little information available on the monoamine oxidase isoform selectivity of N-alkyl harmine analogs, which exhibit a myriad of activities including MAO-A, DYRK1A and cytotoxicity to several select cancer cell lines.

RESULTS

Compounds 3e and 4c exhibited an IC₅₀ of 0.83 ± 0.03 and 0.43 ± 0.002 μM against MAO-A and an IC₅₀ of 0.26 ± 0.04 and 0.36 ± 0.001 μM against MAO-B, respectively. Molecular docking studies revealed π-π interactions between the synthesized molecules and aromatic amino acid residues. Conclusion & future perspective: The current study delineates the structural requirements for MAO-A selectivity and such information may be helpful in designing selective analogs for kinase, DYRK1A and harmine-based cytotoxics without apparent MAO enzyme inhibition.

Inhibition of human monoamine oxidase A and B by flavonoids isolated from two Algerian medicinal plants

BACKGROUND

Monoamine oxidases (MAOs) are outer mitochondrial membrane flavoenzymes. They catalyze the oxidative deamination of a variety of neurotransmitters. MAO-A and MAO-B may be considered as targets for inhibitors to treat neurodegenerative diseases and depression and for managing symptoms associated with Parkinson's and Alzheimer's diseases.

PURPOSE

The objective was to evaluate the inhibitory effect of Hypericum afrum and Cytisus villosus against MAO-A and B and to isolate the compounds responsible for the MAO-inhibitory activity.

METHODS

The inhibitory effect of extracts and purified constituents of H. afrum and C. villosus were investigated in vitro using recombinant human MAO-A and B, and through bioassay-guided fractionation of ethyl acetate fractions of areal parts of the two plants collected in northeastern Algeria. In addition, computational protein-ligand docking and molecular dynamics simulations were carried out to explain the MAO binding at the molecular level.

RESULTS

The ethyl acetate (EtOAc) fractions of H. afrum and C. villosus showed the highest MAO inhibition activity against MAO A and B with IC50 values of 3.37 µg/ml and 13.50 µg/ml as well as 5.62 and 1.87 µg/ml, respectively. Bioassay-guided fractionation of the EtOAc fractions resulted in the purification and identification of the known flavonoids quercetin, myricetin, genistein and chrysin as the principal MAO-inhibitory constituents. Their structures were established by extensive 1 and 2D NMR studies and mass spectrometry. Quercetin, myricetin and chrysin showed potent inhibitory activity towards MAO-A with IC50 values of 1.52, 9.93 and 0.25 µM, respectively, while genistein more efficiently inhibited MAO-B (IC50 value: 0.65 µM). The kinetics of the inhibition and the study of dialysis dissociation of the complex of quercetin and myricetin and the isoenzyme MAO-A showed competitive and mixed inhibition, respectively. Both compounds showed reversible binding. Molecular docking experiments and molecular dynamics simulations allowed to estimate the binding poses and to identify the most important residues involved in the selective recognition of molecules in the MAOs enzymatic clefts.

CONCLUSION

Quercetin and myricetin isolated from H. afrum together with genistein and chrysin isolated from C. villosus have been identified as potent MAO-A and -B inhibitors. H. afrum and C. villosus have properties indicative of potential neuroprotective ability and may be new candidates for selective MAO-A and B inhibitors.

Isolation and Biological Evaluation of Prenylated Flavonoids from Maclura pomifera

Phytochemical analysis of the ethanolic extract of Maclura pomifera fruits yielded four new compounds (I-IV) along with eleven known compounds (V-XV). The crude extract exhibited significant activity towards cannabinoid receptors (CB1: 103.4% displacement; CB2: 68.8% displacement) and possibly allosteric interaction with δ and μ opioid receptors (-49.7 and -53.8% displacement, resp.). Compound I was found to be possibly allosteric for κ and μ opioid receptors (-88.4 and -27.2% displacement, resp.) and showed moderate activity (60.5% displacement) towards CB1 receptor. Compound II exhibited moderate activity towards cannabinoid receptors CB1 and CB2 (47.9 and 42.3% displacement, resp.). The known compounds (V-VIII) exhibited prominent activity towards cannabinoid receptors: pomiferin (V) (IC50 of 2.110 and 1.318 μM for CB1 and CB2, resp.), auriculasin (VI) (IC50 of 8.923 μM for CB1), warangalone (VII) (IC50 of 1.670 and 4.438 μM for CB1 and CB2, resp.), and osajin (VIII) (IC50 of 3.859 and 7.646 μM for CB1 and CB2, resp.). The isolated compounds were also tested for inhibition of human monoamine oxidase-A and monoamine oxidase-B enzymes activities, where all the tested compounds showed fewer inhibitory effects on MAO-A compared to MAO-B activities: auriculasin (VI) (IC50 of 1.91 and 45.98 μM for MAO-B and MAO-A, resp.).

Interactions of Desmethoxyyangonin, a Secondary Metabolite from Renealmia alpinia, with Human Monoamine Oxidase-A and Oxidase-B

Renealmia alpinia (Zingiberaceae), a medicinal plant of tropical rainforests, is used to treat snakebites and other injuries and also as a febrifuge, analgesic, antiemetic, antiulcer, and anticonvulsant. The dichloromethane extract of R. alpinia leaves showed potent inhibition of human monoamine oxidases- (MAOs-) A and B. Phytochemical studies yielded six known compounds, including pinostrobin 1, 4′-methyl ether sakuranetin 2, sakuranetin 3, pinostrobin chalcone 4, yashabushidiol A 5, and desmethoxyyangonin 6. Compound 6 displayed about 30-fold higher affinity for MAO-B than MAO-A, with Ki values of 31 and 922 nM, respectively. Kinetic analysis of inhibition and equilibrium-dialysis dissociation assay of the enzyme-inhibitor complex showed reversible binding of desmethoxyyangonin 6 with MAO-A and MAO-B. The binding interactions of compound 6 in the active site of the MAO-A and MAO-B isoenzymes, investigated through molecular modeling algorithms, confirmed preferential binding of desmethoxyyangonin 6 with MAO-B compared to MAO-A. Selective reversible inhibitors of MAO-B, like desmethoxyyangonin 6, may have important therapeutic significance for the treatment of neurodegenerative disorders, such as Parkinson's disease and Alzheimer's disease.