Monoamine oxidase inhibition by selected anilide derivatives

Amidation of Enones via Beckmann Rearrangement

The Beckmann reaction is one of the most atom-economical methods for the preparation of amides from ketones. Unlike ketones, the multiple competing reactivities of enones as well as the requirement of demanding reaction conditions for in situ generation of oximes have severely impacted the application of this reaction for the preparation of α,β-unsaturated amides. Herein, we describe the first chemoselective method for the direct conversion of enones to the corresponding α,β-unsaturated amides using N-Boc-O-tosylhydroxylamine.

Monoamine oxidase B inhibitors based on natural privileged scaffolds: A review of systematically structural modification

Monoamine oxidase is a flavin enzyme that catalyzes the oxidation of monoamine neurotransmitters in the brain. Various toxic by-products, aldehydes and hydrogen peroxide produced during the catalytic process, can cause oxidative stress and neuronal cell death. Overexpression of MAO-B and insufficient dopamine concentration are recognized as pathological factors in neurodegenerative diseases (NDs) including Parkinson's disease (PD) and Alzheimer's disease (AD). Therefore, the inhibition of MAO-B is an attractive target for the treatment of NDs. Despite significant efforts, few selective and reversible MAO-B inhibitors have been clinically approved. Natural products have emerged as valuable sources of lead compounds in drug discovery. Compounds such as chromone, coumarin, chalcone, caffeine, and aurone, present in natural structures, are considered as privileged scaffolds in the synthesis of MAO-B inhibitors. In this review, we summarized the structure-activity relationship (SAR) of MAO-B inhibitors based on the naturally privileged scaffolds over the past 20 years. Additionally, we proposed a balanced discussion on the advantages and limitations of natural scaffold-based MAO-B inhibitors with providing a future perspective in drug development.

Domino Michael/Michael reaction catalyzed by switchable modularly designed organocatalysts

The domino Michael/Michael reaction between (E)-7-aryl-7-oxohept-5-enals and trans-cinnamaldehydes was investigated by using modularly designed organocatalysts (MDOs). It was found that both the enamine and iminium catalytic modes of the MDOs are switchable and can be individually switched on and off by using appropriate combinations of the precatalyst modules and the reaction conditions. When both the enamine and iminium catalysis modes of the MDOs are switched on, the desired domino reaction products can be obtained in good yields and stereoselectivities under optimized conditions.

Selected Class of Enamides Bearing Nitro Functionality as Dual-Acting with Highly Selective Monoamine Oxidase-B and BACE1 Inhibitors

A small series of nitro group-bearing enamides was designed, synthesized (NEA1–NEA5), and evaluated for their inhibitory profiles of monoamine oxidases (MAOs) and β-site amyloid precursor protein cleaving enzyme 1 (β-secretase, BACE1). Compounds NEA3 and NEA1 exhibited a more potent MAO-B inhibition (IC₅₀ value = 0.0092 and 0.016 µM, respectively) than the standards (IC₅₀ value = 0.11 and 0.14 µM, respectively, for lazabemide and pargyline). Moreover, NEA3 and NEA1 showed greater selectivity index (SI) values toward MAO-B over MAO-A (SI of >1652.2 and >2500.0, respectively). The inhibition and kinetics studies suggested that NEA3 and NEA1 are reversible and competitive inhibitors with K_i values of 0.013 ± 0.005 and 0.0049 ± 0.0002 µM, respectively, for MAO-B. In addition, both NEA3 and NEA1 showed efficient BACE1 inhibitions with IC₅₀ values of 8.02 ± 0.13 and 8.21 ± 0.03 µM better than the standard quercetin value (13.40 ± 0.04 µM). The parallel artificial membrane permeability assay (PAMPA) method demonstrated that all the synthesized derivatives can cross the blood–brain barrier (BBB) successfully. Docking analyses were performed by employing an induced-fit docking approach in the GLIDE module of Schrodinger, and the results were in agreement with their in vitro inhibitory activities. The present study resulted in the discovery of potent dual inhibitors toward MAO-B and BACE1, and these lead compounds can be fruitfully explored for the generation of newer, clinically active agents for the treatment of neurodegenerative disorders.

Manganese(I) Catalyzed α-Alkenylation of Amides Using Alcohols with Liberation of Hydrogen and Water

Herein, unprecedented manganese-catalyzed direct α-alkenylation of amides using alcohols is reported. Aryl amides are reacted with diverse primary alcohols, which provided the α,β-unsaturated amides in moderate to good yields with excellent selectivity. Mechanistic studies indicate that Mn(I) catalyst oxidizes the alcohols to their corresponding aldehydes and also plays an important role in efficient C═C bond formation through aldol condensation. This selective olefination is facilitated by metal-ligand cooperation by the aromatization-dearomatization process operating in the catalytic system. Biorenewable alcohols are used as alkenylation reagents for the challenging α-alkenylation of amides with the highly abundant base metal manganese as a catalyst, which results in water and dihydrogen as the only byproduct, making this catalytic transformation attractive, sustainable, and environmentally benign.

A review on ferulic acid and analogs based scaffolds for the management of Alzheimer's disease

Alzheimer's disease (AD) is an age-related multifactorial neurodegenerative disorder characterized by severe central cholinergic neuronal loss, gradually contributing to cognitive dysfunction and impaired motor activity, resulting in the brain's cell death at the later stages of AD. Although the etiology of AD is not well understood, however, several factors such as oxidative stress, deposition of amyloid-β (Aβ) peptides to form Aβ plaques, intraneuronal accumulation of hyperphosphorylated tau protein, and low level of acetylcholine are thought to play a major role in the pathogenesis of AD. There is practically no drug for AD treatment that can address the basic factors responsible for the neurodegeneration and slow down the disease progression. The currently available therapies for AD in the market focus on providing only symptomatic relief without addressing the aforesaid basic factors responsible for the neurodegeneration. Ferulic acid (FA) is a phenol derivative from natural sources and serves as a potential pharmacophore that exerts multiple pharmacological properties such as antioxidant, neuroprotection, Aβ aggregation modulation, and anti-inflammatory. Several FA based hybrid analogs are under investigation as a multi-target directed ligand (MTDLs) to develop novel hybrid compounds for the treatment of AD. In the present review article, we are focused on the critical pathogenic factors responsible for the onset of AD followed by the developments of FA pharmacophore-based hybrids compounds as a novel multifunctional therapeutic agent to address the limitations associated with available treatment for AD. The rationale behind the development of these compounds and their pharmacological activities in particular to their ChE inhibition (ChEI), neuroprotection, antioxidant property, Aβ aggregation modulation, and metal chelation ability, are discussed in detail. We have also discussed the discovery of caffeic and cinnamic acids based MTDLs for AD. This review paper provides an in-depth insight into the research progress and current status of these novel therapeutics in AD and prospects for developing a druggable molecule with desired pharmacological affinity and reduced toxicity for the management of AD.

(Hetero-)(arylidene)arylhydrazides as Multitarget-Directed Monoamine Oxidase Inhibitors

Fourteen (hetero-)(arylidene)arylhydrazide derivatives (ABH1-ABH14) were synthesized, and their inhibitory activities against monoamine oxidases (MAOs) and acetylcholinesterase (AChE) were evaluated. Compound ABH5 most potently inhibited MAO-B with an IC₅₀ value of 0.025 ± 0.0019 μM; ABH2 and ABH3 exhibited high IC₅₀ values as well. Most of the compounds weakly inhibited MAO-A, except ABH5 (IC₅₀ = 3.31 ± 0.41 μM). Among the active compounds, ABH2 showed the highest selectivity index (SI) of 174 for MAO-B, followed by ABH5 (SI = 132). ABH3 and ABH5 effectively inhibited AChE with IC₅₀ values of 15.7 ± 6.52 and 16.5 ± 7.29 μM, respectively, whereas the other compounds were weak inhibitors of AChE. ABH5 was shown to be a reversible competitive inhibitor for MAO-A and MAO-B with K_i values of 0.96 ± 0.19 and 0.024 ± 0.0077 μM, respectively, suggesting that this molecule can be considered as an interesting candidate for further development as a multitarget inhibitor relating to neurodegenerative disorders.

Synthesis, in vitro enzyme activity and molecular docking studies of new benzylamine-sulfonamide derivatives as selective MAO-B inhibitors

Many studies have been conducted on the selective inhibition of human monoamine oxidase B (hMAO-B) enzyme using benzylamine-sulphonamide derivatives. Using various chemical modifications on BB-4h, which was reported previously by our team and showed a significant level of MAO-B inhibition, novel benzylamine-sulphonamide derivatives were designed, synthesised, and their MAO inhibition potentials were evaluated. Among the tested derivatives, compounds 4i and 4t achieved IC₅₀ values of 0.041 ± 0.001 µM and 0.065 ± 0.002 µM, respectively. The mechanism of hMAO-B inhibition by compounds 4i and 4t was studied using Lineweaver–Burk plot. The nature of inhibition was also determined to be non-competitive. Cytotoxicity tests were conducted and compounds 4i and 4t were found to be non-toxic. Molecular docking studies were also carried out for compound 4i, which was found as the most potent agent, within hMAO-B catalytic site.

Evaluation of nitrocatechol chalcone and pyrazoline derivatives as inhibitors of catechol-O-methyltransferase and monoamine oxidase

Literature reports that chalcones inhibit the monoamine oxidase (MAO) enzymes, mostly with specificity for the MAO-B isoform, while nitrocatechol compounds are established inhibitors of catechol-O-methyltransferase (COMT). Based on this, nitrocatechol derivatives of chalcone have been proposed to represent dual-target-directed compounds that may inhibit both MAO-B and COMT. Both these enzymes play key roles in the metabolism of dopamine and levodopa, and inhibitors are thus relevant to the treatment of Parkinson's disease. The present study expands on the discovery of dual MAO-B/COMT inhibitors by synthesising additional nitrocatechol derivatives of chalcones which include heterocyclic derivatives, and converting them to the corresponding pyrazoline derivatives. The newly synthesised chalcone and pyrazoline compounds were evaluated as inhibitors of human MAO and rat COMT, and the inhibition potencies were expressed as IC₅₀ values. A pyrazoline derivative, compound 8b, was the most potent COMT inhibitor with an IC₅₀ value of 0.048 μM. This is more potent than the reference COMT inhibitor, entacapone, which has an IC₅₀ value of 0.23 μM. The results indicated that the pyrazoline derivatives (IC₅₀ = 0.048-0.21 µM) are more potent COMT inhibitors than the chalcones (IC₅₀ = 0.14-0.29 µM). Unfortunately, the chalcone and pyrazoline derivatives were weak MAO inhibitors with IC₅₀ values > 41.4 µM. This study concludes that the nitrocatechol derivatives investigated here are promising COMT inhibitors, while not being suitable as MAO inhibitors. Using molecular docking, potential binding modes and interactions of selected inhibitors with COMT are proposed.

Design of enamides as new selective monoamine oxidase-B inhibitors

OBJECTIVES

To develop of new class of selective and reversible MAO-B inhibitors from enamides.

METHODS

Syntheses of the titled derivatives (AD1-AD11) were achieved by reacting cinnamoyl chloride and various primary and secondary amines in basic medium. All eleven compounds were investigated for in vitro inhibitory activities against recombinant human MAO-A and MAO-B. The reversibilities of lead compound inhibitions were analysed by dialysis. MTT assays of lead compounds were performed using normal VERO cell lines.

KEY FINDINGS

Compounds AD3 and AD9 exhibited the greatest inhibitory activity against MAO-B with IC₅₀ values of 0.11 and 0.10 µm, respectively, and were followed by AD2 and AD1 (0.51 and 0.71 µm, respectively). Most of the compounds weakly inhibited MAO-A, with the exceptions AD9 and AD7, which had IC₅₀ values of 4.21 and 5.95 µm, respectively. AD3 had the highest selectivity index (SI) value for MAO-B (>363.6) and was followed by AD9 (SI 42.1). AD3 and AD9 were found to be competitive inhibitors of MAO-B with K_i values of 0.044 ± 0.0036 and 0.039 ± 0.0047 µm, respectively. Reversibility experiments showed AD3 and AD9 were reversible inhibitors of MAO-B; dialysis restored the activity of MAO-B to the reference level. MTT assays revealed AD3 and AD9 were non-toxic to normal VERO cell lines with IC₅₀ values of 153.96 and 194.04 µg/ml, respectively. Computational studies provided hypothetical binding modes for AD3 and AD9 in the binding cavities of MAO-A and MAO-B.

CONCLUSIONS

These results encourage further studies on the enamide scaffold as potential drug candidates for the treatment of Alzheimer's and Parkinson's diseases.

Monoamine oxidase-B inhibitors as potential neurotherapeutic agents: An overview and update

Monoamine oxidase (MAO) inhibitors have made significant contributions and remain an indispensable approach of molecular and mechanistic diversity for the discovery of antineurodegenerative drugs. However, their usage has been hampered by nonselective and/or irreversible action which resulted in drawbacks like liver toxicity, cheese effect, and so forth. Hence, the search for selective MAO inhibitors (MAOIs) has become a substantial focus in current drug discovery. This review summarizes our current understanding on MAO-A/MAO-B including their structure, catalytic mechanism, and biological functions with emphases on the role of MAO-B as a potential therapeutic target for the development of medications treating neurodegenerative disorders. It also highlights the recent developments in the discovery of potential MAO-B inhibitors (MAO-BIs) belonging to diverse chemical scaffolds, arising from intensive chemical-mechanistic and computational studies documented during past 3 years (2015-2018), with emphases on their potency and selectivity. Importantly, readers will gain knowledge of various newly established MAO-BI scaffolds and their development potentials. The comprehensive information provided herein will hopefully accelerate ideas for designing novel selective MAO-BIs with superior activity profiles and critical discussions will inflict more caution in the decision-making process in the MAOIs discovery.

Selected aryl thiosemicarbazones as a new class of multi-targeted monoamine oxidase inhibitors

A series of 13 phenyl substituted thiosemicarbazones (SB1-SB13) were synthesized and evaluated for their inhibitory potential towards human recombinant monoamine oxidase A and B (MAO-A and MAO-B, respectively) and acetylcholinesterase. The solid state structure of SB4 was ascertained by the single X-ray diffraction technique. Compounds SB5 and SB11 were potent for MAO-A (IC50 1.82 ± 0.14) and MAO-B (IC50 0.27 ± 0.015 μM), respectively. Furthermore, SB11 showed a high selectivity index (SI > 37.0) for MAO-B. The effects of fluorine orientation revealed that SB11 (m-fluorine) showed 28.2 times higher inhibitory activity than SB12 (o-fluorine) against MAO-B. Furthermore, inhibitions by SB5 and SB11 against MAO-A and MAO-B, respectively, were recovered to near reference levels in reversibility experiments. Both SB5 and SB11 showed competitive inhibition modes, with K i values of 0.97 ± 0.042 and 0.12 ± 0.006 μM, respectively. These results indicate that SB5 and SB11 are selective, reversible and competitive inhibitors of MAO-A and MAO-B, respectively. Compounds SB5, SB7 and SB11 showed moderate inhibition against acetylcholinesterase with IC50 values of 35.35 ± 0.47, 15.61 ± 0.057 and 26.61 ± 0.338 μM, respectively. Blood-brain barrier (BBB) permeation was studied using the parallel artificial membrane permeation assay (PAMPA) method. Molecular docking studies were carried out using AutoDock 4.2.

Synthesis of Amide and Ester Derivatives of Cinnamic Acid and Its Analogs: Evaluation of Their Free Radical Scavenging and Monoamine Oxidase and Cholinesterase Inhibitory Activities

A series of cinnamic acid derivatives, amides (1-12) and esters (13-22), were synthesized, and structure-activity relationships for antioxidant activity, and monoamine oxidases (MAO) A and B, acetylcholinesterase, and butyrylcholinesterase (BChE) inhibitory activities were analyzed. Among the synthesized compounds, compounds 1-10, 12-18, and rosmarinic acid (23), which contained catechol, o-methoxyphenol or 5-hydroxyindole moieties, showed potent 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity. Compounds 9-11, 15, 17-22 showed potent and selective MAO-B inhibitory activity. Compound 20 was the most potent inhibitor of MAO-B. Compounds 18 and 21 showed moderate BChE inhibitory activity. In addition, compound 18 showed potent antioxidant activity and MAO-B inhibitory activity. In a comparison of the cinnamic acid amides and esters, the amides exhibited more potent DPPH free radical scavenging activity, while the esters showed stronger inhibitory activities against MAO-B and BChE. These results suggested that cinnamic acid derivatives such as compound 18, p-coumaric acid 3,4-dihydroxyphenethyl ester, and compound 20, p-coumaric acid phenethyl ester, may serve as lead compounds for the development of novel MAO-B inhibitors and candidate lead compounds for the prevention or treatment of Alzheimer's disease.

Identification of Indole-Based Chalcones: Discovery of a Potent, Selective, and Reversible Class of MAO-B Inhibitors

A series of 11 indole-based chalcones (IC1-11) with various electron donating and withdrawing groups at the para position of the phenyl ring B were synthesized. All the compounds were tested for their human monoamine oxidase (hMAO)-A and hMAO-B inhibitory potencies. Most of the synthesized candidates proved to be potent and selective inhibitors of MAO-B rather than MAO-A, with a reversible and competitive mode. Among them, compound IC9 was found to be a potent inhibitor of hMAO-B with Ki  = 0.01 ± 0.005 μM and a selectivity index of 120. It was found to be better than the standard drug, selegiline (hMAO-B with Ki  = 0.20 ± 0.020 μM) with a selectivity index of 30.55. PAMPA assays were carried out for all the compounds in order to evaluate the capacity of the compounds to cross the blood-brain barrier. Moreover, the most potent MAO-B inhibitor, IC9, was nontoxic at 5 and 25 μM, with 95.20 and 69.17% viable cells, respectively. The lead compound IC9 has an antioxidant property of 1.18 Trolox equivalents by ABTS assay. Molecular modeling studies were performed against hMAO-B to observe binding site interactions of the lead compound.

Synthesis, Biochemistry, and Computational Studies of Brominated Thienyl Chalcones: A New Class of Reversible MAO-B Inhibitors

A series of (2E)-1-(5-bromothiophen-2-yl)-3-(para-substituted phenyl)prop-2-en-1-ones (TB1-TB11) was synthesized and tested for inhibitory activity toward human monoamine oxidase (hMAO). All compounds were found to be competitive, selective, and reversible toward hMAO-B except (2E)-1-(5-bromothiophen-2-yl)-3-(4-nitrophenyl)prop-2-en-1-one (TB7) and (2E)-1-(5-bromothiophen-2-yl)-3-(4-chlorophenyl)prop-2-en-1-one (TB8), which were selective inhibitors of hMAO-A. The most potent compound, (2E)-1-(5-bromothiophen-2-yl)-3-[4-(dimethylamino)phenyl]prop-2-en-1-one (TB5), showed the best inhibitory activity and higher selectivity toward hMAO-B, with Ki and SI values of 0.11±0.01 μm and 13.18, respectively. PAMPA assays for all compounds were carried out in order to evaluate the capacity of the compounds to cross the blood-brain barrier. Moreover, the most potent MAO-B inhibitor, TB5, was found to be nontoxic at 5 and 25 μm, with 95.75 and 84.59 % viability among cells, respectively. Molecular docking simulations were carried out to understand the crucial interactions responsible for selectivity and potency.

Recent developments on the structure–activity relationship studies of MAO inhibitors and their role in different neurological disorders

Development of MAO inhibitors as effective drug candidates for the management and/or treatment of different neurological disorders.

Lessons from black pepper: piperine and derivatives thereof

INTRODUCTION

Piperine is a simple and pungent alkaloid found in the seeds of black pepper (Piper nigrum). Following its isolation and full characterization, the biological properties of piperine have been extensively studied, and piperine-like derivatives have shown an interesting range of pharmacological activities. In this context, significant advances have been made in the discovery of new chemical entities based on the piperine scaffold endowed with therapeutic potential.

AREAS COVERED

The aim of this review is to provide a thorough inquiry on the therapeutic potential of piperine and related derivatives. It provides an overview of recent developments in patented processes and applications thereof between 2000 and 2015.

EXPERT OPINION

Cumulative evidence shows that piperine is currently paving its way to become a privileged scaffold for the development of bioactive compounds with therapeutic application in multiple human diseases. In particular, piperine derivatives were shown to modulate the activity of several targets related to neurological disorders, including epilepsy, Parkinson's disease, depression and pain related disorders. Moreover, the efflux pump inhibitory ability of piperine and its analogues tackles important drug resistance mechanisms and may improve the clinical efficacy of antibiotic and anticancer drugs. Although the use of piperine as a scaffold for bioactive compounds is still in its early stages, the continuous exploration of this structure may lead to remarkable advances in drug discovery programs.

Development of fluorinated methoxylated chalcones as selective monoamine oxidase-B inhibitors: Synthesis, biochemistry and molecular docking studies

A series of methoxylated chalcones with fluoro and trifluoromethyl derivatives were synthesized and investigated for their ability to inhibit human monoamine oxidase A and B. The chemical structures of the compounds have been characterized by means of their (1)H NMR, (13)C NMR, Mass spectroscopic datas and elemental analysis. The results demonstrate that these compounds are reversible and selective MAO-B inhibitors with a competitive mode of inhibition. The most potent compound (2E)-1-(4-methoxyphenyl)-3-[4-(trifluoromethyl)phenyl] prop-2-en-1-one showed the best activity and higher selectivity towards hMAO-B with Ki and SI values of 0.22±0.01μM and 0.05 comparable to that standard drug, Selegiline Ki and SI values were found as 0.33±0.03μM and 0.04, respectively. Molecular docking studies were carried out to further explain the in vitro results of the new compounds, and to identify the hypothetical binding mode for the compounds inside the inhibitor binding cavity of hMAO-B.

New Frontiers in Selective Human MAO-B Inhibitors

Accumulating evidence shows a relationship between the human MAO-B (hMAO-B) enzyme and neuropsychiatric/degenerative disorder, personality traits, type II alcoholism, borderline personality disorders, aggressiveness and violence in crime, obsessive-compulsive disorder, depression, suicide, schizophrenia, anorexia nervosa, migraine, dementia, and PD. Thus, MAO-B represents an attractive target for the treatment of a number of human diseases. The discovery, development, and therapeutic use of drugs that inhibit MAO-B are major challenges for future therapy. Various compounds and drugs that selectively target this isoform have been discovered recently. These agents are synthetic compounds or natural products and their analogues, including chalcones, pyrazoles, chromones, coumarins, xanthines, isatin derivatives, thiazolidindiones, (thiazol-2-yl)hydrazones, and analogues of marketed drugs. Despite considerable efforts in understanding the binding interaction with specific substrates or inhibitors, structural information available for the rational design of new hMAO-B inhibitors remains unsatisfactory. Therefore, the quest for novel, potent, and selective hMAO-B inhibitors remains of high interest.

Anxiolytic-like effect of danshensu [(3-(3,4-dihydroxyphenyl)-lactic acid)] in mice

AIMS

Danshensu [3-(3,4-dihydroxyphenyl)-lactic acid], a phenylpropanoid compound isolated from Prunella vulgaris var. lilacina, is a well-known antioxidant. Although its antioxidant activity and cardioprotective effect have been reported, the pharmacological properties of danshensu in the central nervous system remain unclear. We investigated whether danshensu exerts anxiolytic-like activity in mice.

MAIN METHODS

We conducted monoamine oxidase A (MAO-A) inhibition assay on danshensu in vitro, and behavioral tests including the elevated plus-maze test (EPM), the hole-board test, the rotarod test and the open field test were employed.

KEY FINDINGS

We found that danshensu significantly inhibited the activity of MAO-A in vitro. The administration of danshensu (3 or 10mg/kg) produced a significant anxiolytic-like effect in the EPM and hole-board test. In addition, no changes in the spontaneous locomotor activity and no myorelaxant effects were observed compared to the control group; these effects were confirmed with the open field test and the rotarod test. Moreover, the anxiolytic-like properties of danshensu were antagonized by a dopamine D1 receptor antagonist (SCH 23390) but not by a 5-HT1A receptor antagonist (WAY 100635) or an α1-adrenergic receptor antagonist (prazosin).

SIGNIFICANCE

These results indicate that danshensu exerts its anxiolytic-like properties, in part, through dopaminergic neurotransmitter signaling.

Inhibition of monoamine oxidase by selected phenylalkylcaffeine analogues

Objectives

Caffeine represents a useful scaffold for the design of monoamine oxidase (MAO) type B inhibitors. Specifically, substitution on the C8 position yields structures which are high-potency MAO-B inhibitors. To explore the structure–activity relationships of MAO-B inhibition by caffeine-derived compounds, this study examines the MAO inhibitory properties of a series of phenylalkylcaffeine analogues.

Methods

Employing the recombinant human enzymes, the potencies (IC50 values) by which the caffeine analogues inhibit MAO-A and MAO-B were measured. The reversibility of inhibition of a selected inhibitor was determined by measuring the recovery of enzyme activity after dilution and dialysis of enzyme-inhibitor mixtures.

Key findings

The results document that the phenylalkylcaffeine analogues are reversible and selective MAO-B inhibitors with a competitive mode of inhibition. The most potent analogue, 8-(7-phenylheptyl)caffeine, exhibits IC50 values for the inhibition of MAO-A and MAO-B of 3.01 μm and 0.086 μm, respectively. Increasing the length of the alkyl side chain leads to enhanced MAO-A and MAO-B inhibitory potency while introduction of a carbonyl group reduces MAO-B inhibitory potency.

Conclusions

Phenylalkylcaffeines represent a new class of high-potency MAO-B inhibitors with the longer alkyl side chains yielding enhanced inhibitory activity. Such compounds may represent useful leads for the development of anti-parkinsonian therapies.