Lesetja J. Legoabe

Inhibition of monoamine oxidase by selected C6-substituted chromone derivatives.

Chromone has been reported to be a useful scaffold for the design of monoamine oxidase (MAO) inhibitors. In an attempt to discover highly potent MAO inhibitors and to contribute to the known structure-activity relationships (SAR) of MAO inhibition by chromones, in the present study, we have synthesized a series of chromone derivatives substituted at C6 with a variety of alkyloxy substituents, and evaluated the resulting compounds as inhibitors of recombinant human MAO-A and -B. The results document that the C6-substituted chromones are potent reversible MAO-B inhibitors with IC(50) values in the low nM range (2-76 nM). The chromones were also found to bind reversibly to MAO-A, but with lower affinities compared to MAO-B. It may therefore be concluded that C6-substituted chromones are highly potent MAO-B selective inhibitors and promising lead compounds for the development of therapy for neurodegenerative disorders such as Parkinsons disease. The results of this study are discussed with reference to possible binding orientations of a selected C6-substituted chromone in the active site cavities of MAO-A and -B.

Selected C7-substituted chromone derivatives as monoamine oxidase inhibitors.

A series of C7-substituted chromone (1-benzopyran-4-one) derivatives were synthesized and evaluated as inhibitors of recombinant human monoamine oxidase (MAO) A and B. The chromones are structurally related to a series of C7-functionalized coumarin (1-benzopyran-2-one) derivatives which has been reported to act as potent MAO inhibitors. The results of the current study document that the chromones are highly potent reversible inhibitors of MAO-B with IC(50) values ranging from 0.008 to 0.370 μM. While the chromone derivatives also exhibit affinities for MAO-A, with IC(50) values ranging from 0.495 to 8.03 μM, they are selective for the MAO-B isoform. Structure-activity relationships (SAR) show that 7-benzyloxy substitution of chromone is suitable for MAO-B inhibition with tolerance for a variety of substituents and substitution patterns on the benzyloxy ring. It may be concluded that 7-benzyloxychromones are appropriate lead compounds for the design of reversible and selective MAO-B inhibitors. With the aid of modeling studies, potential binding orientations and interactions of selected chromone derivatives in the MAO-A and -B active sites are examined.

Selected chromone derivatives as inhibitors of monoamine oxidase

A previous study has shown that a series of C6-benzyloxy substituted chromones exhibit high binding affinities for human monoamine oxidase (MAO) B. In an attempt to discover additional chromones with potent and selective MAO-B inhibitory potencies and to further examine the structure-activity relationships of MAO-B inhibition by chromones, the series was expanded with homologues containing polar functional groups on C3 of the chromone ring. The results demonstrate that 6-[(3-bromobenzyl)oxy]chromones containing acidic and aldehydic functional groups on C3 act as potent reversible MAO-B inhibitors with IC(50) values of 2.8 and 3.7 nM, respectively. Interestingly, a 2-hydroxy-2,3-dihydro-1-benzopyran-4-one derivative as well as open-ring 2-acetylphenol analogues of the chromones also were potent MAO-B inhibitors with IC(50) values ranging from 4 to 11 nM. Chromone derivatives containing the benzyloxy substituent on C5 of the chromone ring, however, exhibit MAO-B inhibition potencies that are several orders of magnitude weaker. High potency inhibitors of MAO-B may find application in the therapy of neurodegenerative disorders such as Parkinsons disease.

α-Tetralone derivatives as inhibitors of monoamine oxidase

In the present study, a series of fifteen α-tetralone (3,4-dihydro-2H-naphthalen-1-one) derivatives were synthesised and evaluated as inhibitors of recombinant human monoamine oxidase (MAO) A and B. The α-tetralone derivatives examined are structurally related to a series of chromone (1-benzopyran-4-one) derivatives which has previously been shown to act as MAO-B inhibitors. The results document that the α-tetralones are highly potent MAO-B inhibitors with all compounds exhibiting IC50 values in the nanomolar range (<78nM). Although most compounds are selective inhibitors of MAO-B, the α-tetralones are also potent MAO-A inhibitors with ten compounds exhibiting IC50 values in the nanomolar range (<792nM). The most potent MAO-B inhibitor, 6-(3-iodobenzyloxy)-3,4-dihydro-2H-naphthalen-1-one, exhibits an IC50 value of 4.5nM with a 287-fold selectivity for MAO-B over the MAO-A isoform, while the most potent MAO-A inhibitor, 6-(3-cyanobenzyloxy)-3,4-dihydro-2H-naphthalen-1-one, exhibits an IC50 value of 24nM with a 3.25-fold selectivity for MAO-A. Analyses of the structure-activity relationships for MAO inhibition show that substitution on the C6 position of the α-tetralone moiety is a requirement for MAO-A and MAO-B inhibition, and that a benzyloxy substituent on this position is more favourable for MAO-A inhibition than phenylethoxy and phenylpropoxy substitution. For MAO-B inhibition, alkyl and halogen substituents on the meta and para positions of the benzyloxy ring enhance inhibitory potency. It may be concluded that α-tetralone derivatives are promising leads for design of therapies for Parkinsons disease and depression.

Monoamine oxidase inhibition by selected anilide derivatives

A series of anilide derivatives were synthesized and evaluated as inhibitors of recombinant human monoamine oxidase (MAO) A and B. The most potent inhibitors among the derivatives that were initially evaluated were (2E)-N-(3-chlorophenyl)-3-phenylprop-2-enamide (2c) and (2E)-N-(3-bromophenyl)-3-phenylprop-2-enamide (2d) with IC(50) values of 0.53 μM and 0.45 μM, respectively. These derivatives exhibited reversible and selective inhibition of MAO-B with binding affinities 37 fold higher for MAO-B than for MAO-A. Analysis of the possible binding interactions of these inhibitors with active site models of human MAO-A and -B led to the design of phenolic and benzonitrile derivatives of 2c and 2d. Among these were (2E)-N-(3-chlorophenyl)-3-(4-hydroxyphenyl)prop-2-enamide (7c) and (2E)-N-(3-bromophenyl)-3-(4-hydroxyphenyl)prop-2-enamide (7d) which inhibited MAO-B selectively and reversibly with IC(50) values of 0.032 μM and 0.026 μM, respectively. These inhibitors were at least 14 fold more potent than 2c and 2d. This study concludes that N,3-diphenylprop-2-enamide is a suitable scaffold for the design of selective MAO-B inhibitors and structural modifications to enhance the binding affinities of the inhibitors for the MAO-B active site include substitution with halogens on the N-phenyl ring and substitution with hydroxyl and nitrile functional groups on the para and meta positions, respectively, of the C3 phenyl ring. Possible binding modes of these structures within the MAO-B active site are proposed with the emphasis on the interactions of the inhibitor halogens and the hydroxyl and nitrile functional groups with active site residues and water molecules.

In‐vitro transdermal penetration of cytarabine and its N4‐alkylamide derivatives

Objectives The aim of this study was to synthesise and determine the transdermal penetration of cytarabine alkylamide derivatives and assess the correlation of flux with physicochemical properties.

The Synthesis and Evaluation of C7-Substituted α-Tetralone Derivatives as Inhibitors of Monoamine Oxidase.

Based on a previous report that α‐tetralone (3,4‐dihydro‐2H‐naphthalen‐1‐one) is a promising scaffold for the design of highly potent inhibitors of the enzyme, monoamine oxidase, the present study investigates the monoamine oxidase inhibitory properties of a synthetic series of fifteen C7‐substituted α‐tetralone derivatives. Arylalkyloxy substitution on C7 of the α‐tetralone moiety yielded compounds with high inhibition potencies toward the human monoamine oxidase‐B isoform with all compounds possessing IC50 values in the submicromolar range (0.00089–0.047 μm). The C7‐substituted α‐tetralones also were highly potent monoamine oxidase‐A inhibitors with thirteen (of fifteen) compounds possessing IC50 values in the submicromolar range (0.010–0.741 μm). The α‐tetralones were, however, in each instance selective for monoamine oxidase‐B over the monoamine oxidase‐A isoform. Dialyses of enzyme–inhibitor mixtures show that, while a representative inhibitor acts as a reversible monoamine oxidase‐A inhibitor, inhibition of monoamine oxidase‐B is not readily reversed by dialysis. Using a molecular modeling approach, possible binding orientations and interactions of selected α‐tetralones with the active sites of the monoamine oxidases are also proposed. This study suggests that C7‐substituted α‐tetralones are promising monoamine oxidase inhibitors and may represent lead compounds for the development of therapies for Parkinsons disease and depression.

2-Heteroarylidene-1-indanone derivatives as inhibitors of monoamine oxidase.

In the present study a series of fifteen 2-heteroarylidene-1-indanone derivatives were synthesised and evaluated as inhibitors of recombinant human monoamine oxidase (MAO) A and B. These compounds are structurally related to series of heterocyclic chalcone derivatives which have previously been shown to act as MAO-B specific inhibitors. The results document that the 2-heteroarylidene-1-indanones are in vitro inhibitors of MAO-B, displaying IC50 values of 0.0044-1.53μM. Although with lower potencies, the derivatives also inhibit the MAO-A isoform with IC50 values as low as 0.061μM. An analysis of the structure-activity relationships for MAO-B inhibition indicates that substitution with the methoxy group on the A-ring leads to a significant enhancement in MAO-B inhibition compared to the unsubstituted homologues while the effect of the heteroaromatic substituent on activity, in decreasing order is: 5-bromo-2-furan>5-methyl-2-furan>2-pyridine≈2-thiophene>cyclohexyl>3-pyridine≈2-furan. It may therefore be concluded that 2-heteroarylidene-1-indanone derivatives are promising leads for the design of MAO inhibitors for the treatment of Parkinsons disease and possibly other neurodegenerative disorders.

3-Coumaranone derivatives as inhibitors of monoamine oxidase.

The present study examines the monoamine oxidase (MAO) inhibitory properties of a series of 20 3-coumaranone [benzofuran-3(2H)-one] derivatives. The 3-coumaranone derivatives are structurally related to series of α-tetralone and 1-indanone derivatives, which have recently been shown to potently inhibit MAO, with selectivity for MAO-B (in preference to the MAO-A isoform). 3-Coumaranones are similarly found to selectively inhibit human MAO-B with half-maximal inhibitory concentration (IC50) values of 0.004–1.05 µM. Nine compounds exhibited IC50<0.05 µM for the inhibition of MAO-B. For the inhibition of human MAO-A, IC50 values ranged from 0.586 to >100 µM, with only one compound possessing an IC50<1 µM. For selected 3-coumaranone derivatives, it is established that MAO-A and MAO-B inhibition are reversible since dialysis of enzyme–inhibitor mixtures almost completely restores enzyme activity. On the basis of the selectivity profiles and potent action, it may be concluded that the 3-coumaranone derivatives are suitable leads for the development of selective MAO-B inhibitors as potential treatment for disorders such as Parkinson’s disease and Alzheimer’s disease.

2-acetylphenol analogs as potent reversible monoamine oxidase inhibitors

Based on a previous report that substituted 2-acetylphenols may be promising leads for the design of novel monoamine oxidase (MAO) inhibitors, a series of C5-substituted 2-acetylphenol analogs (15) and related compounds (two) were synthesized and evaluated as inhibitors of human MAO-A and MAO-B. Generally, the study compounds exhibited inhibitory activities against both MAO-A and MAO-B, with selectivity for the B isoform. Among the compounds evaluated, seven compounds exhibited IC50 values <0.01 µM for MAO-B inhibition, with the most selective compound being 17,000-fold selective for MAO-B over the MAO-A isoform. Analyses of the structure–activity relationships for MAO inhibition show that substitution on the C5 position of the 2-acetylphenol moiety is a requirement for MAO-B inhibition, and the benzyloxy substituent is particularly favorable in this regard. This study concludes that C5-substituted 2-acetylphenol analogs are potent and selective MAO-B inhibitors, appropriate for the design of therapies for neurodegenerative disorders such as Parkinson’s disease.