Potent, selective and reversible hMAO-B inhibition by benzalphthalides: Synthesis, enzymatic and cellular evaluations and virtual docking and predictive studies.

Monoaminooxidases (MAOs) are important targets for drugs used in the treatment of neurological and psychiatric disorders and particularly on Parkinson's Disease (PD). Compounds containing a trans-stilbenoid skeleton have demonstrated good selective and reversible MAO-B inhibition. Here, twenty-two (Z)-3-benzylidenephthalides (benzalphthalides, BPHs) displaying a trans-stilbenoid skeleton have been synthesised and evaluated as inhibitors of the MAO-A and MAO-B isoforms. Some BPHs have selectively inhibited MAO-B, with IC50 values ranging from sub-nM to µM. The most potent compound with IC50 = 0.6 nM was the 3',4'-dichloro-BPH 16, which showed highly selective and reversible MAO-B inhibitory activity. Furthermore, the most selective BPHs displayed a significant protection against the apoptosis, and mitochondrial toxic effects induced by 6-hydroxydopamine (6OHDA) on SH-SY5Y cells, used as a cellular model of PD. The results of virtual binding studies on the most potent compounds docked in MAO-B and MAO-A were in agreement with the potencies and selectivity indexes found experimentally. Additionally, related to toxicity risks, drug-likeness and ADME properties, the predictions found for the most relevant BPHs in this research were within those ranges established for drug candidates.

Phytochemical Analysis and Antiproliferative Activity of Ulex gallii Planch. (Fabaceae), a Medicinal Plant from Galicia (Spain).

The genus Ulex comprises thirteen accepted species of perennial shrubs in the family Fabaceae. In Galicia (Spain) many of these are considered spontaneous colonizing species, which are easy to establish and maintain. Among them, Ulex gallii Planch. is used in traditional medicine for the same anti-infective, hypotensive and diuretic purposes as Ulex europaeus L., which is the most studied species. Likewise, some studies have described the antitumoral properties of several species. However, there are few scientific studies that justify the use of Ulex gallii Planch. and nothing has been reported about its composition to date. In our study, the entire plant was extracted with methanol and the crude extract was subjected to liquid phase extraction with distinct solvents, yielding three fractions: hexane (H), dichloromethane (D) and methanol (M), which were subsequently fractionated. The dichloromethane (D5, D7 and D8) and methanol (M4) sub-fractions showed antiproliferative activity on A549 (lung cancer) and AGS (stomach cancer) cell lines, and caspase 3/7 activity assessment and DNA quantification were also performed. Targeted analysis via UHPLC-QToF, in combination with untargeted analysis via MS-Dial, MS-Finder and Global Natural Products Social Molecular Networking (GNPS), allowed us to tentatively identify different metabolites in these sub-fractions, mostly flavonoids, that might be involved in their antiproliferative activity.

Curcumin-Coumarin Hybrid Analogues as Multitarget Agents in Neurodegenerative Disorders.

Neurodegenerative diseases have a complex nature which highlights the need for multitarget ligands to address the complementary pathways involved in these diseases. Over the last decade, many innovative curcumin-based compounds have been designed and synthesized, searching for new derivatives having anti-amyloidogenic, inhibitory of tau formation, as well as anti-neuroinflammation, antioxidative, and AChE inhibitory activities. Regarding our experience studying 3-substituted coumarins with interesting properties for neurodegenerative diseases, our aim was to synthesize a new series of curcumin-coumarin hybrid analogues and evaluate their activity. Most of the 3-(7-phenyl-3,5-dioxohepta-1,6-dien-1-yl)coumarin derivatives 11-18 resulted in moderated inhibitors of hMAO isoforms and AChE and BuChE activity. Some of them are also capable of scavenger the free radical DPPH. Furthermore, compounds 14 and 16 showed neuroprotective activity against H2O2 in SH-SY5Y cell line. Nanoparticles formulation of these derivatives improved this property increasing the neuroprotective activity to the nanomolar range. Results suggest that by modulating the substitution pattern on both coumarin moiety and phenyl ring, ChE and MAO-targeted derivatives or derivatives with activity in cell-based phenotypic assays can be obtained.

GC/MSn analysis of the crude reaction mixtures from Friedel-Crafts acylation: Unambiguous identification and differentiation of 3-aroylbenzofurans from their 4- and 6-regioisomers.

RATIONALE: 3-Aroylbenzofurans and their 2-nitrophenyl derivatives constitute fundamental intermediates for the synthesis of target compounds with pharmaceutical properties. However, their preparation via the Friedel-Crafts acylation of 2-phenylbenzofurans, using Lewis acid as catalyst, often leads to mixtures of regioisomeric aroylbenzofurans that can be challenging to distinguish, thus preventing the reaction characterization. METHOD: We report a method for the unambiguous identification and differentiation of the desired 3-benzoyl isomers from their 4- and 6-regioisomers in a crude reaction mixture using gas chromatography coupled to multiple-stage mass spectrometric (GC/MSn ) analysis performed in collision-induced dissociation (CID) mode. RESULTS: Upon electron ionization, each set of isomers displayed nearly identical mass spectra. MSn revealed fragmentation patterns that varied in the location of the benzoyl group on the benzofuran scaffold: CID experiments performed on the molecular ion allowed the distinction of the 3-acyl isomers from the 4- and 6-regioisomers; CID experiments on the [M - Ar]+ ion allowed the distinction of the 4-benzoyl from the 6-benzoyl regioisomer, when the nitro group is located on the 2-phenyl ring. Moreover, the unusual loss of OH• radical allowed ascertaining the position of the nitro group in 3-acyl regioisomers bearing the NO2 group. The origin of the diagnostic OH• loss was investigated through MSn experiments using 18 O-labelled 3-benzoyl derivatives. CONCLUSIONS: The method allows the rapid characterization of crude reaction mixtures of benzoylbenzofurans using solely GC/MSn analysis, simplifying the workflow of extensive isolation and purification for structure elucidation.

Novel coumarin-pyridazine hybrids as selective MAO-B inhibitors for the Parkinson's disease therapy.

The 3-pyridazinylcoumarin scaffold was previously reported as an efficient core for the discovery of reversible and selective inhibitors of MAO-B, a validated drug target for PD therapy which also plays an important role in the AD progress. Looking for its structural optimization, novel compounds of hybrid structure coumarin-pyridazine, differing in polarizability and lipophilicity properties, were synthesized and tested against the two MAO isoforms, MAO-A and MAO-B (compounds 17a-f and 18a-f). All the designed compounds selectively inhibited the MAO-B isoenzyme, exhibiting many of them IC50 values ranging from sub-micromolar to nanomolar grade and lacking neuronal toxicity. The 7-bromo-3-(6-bromopyridazin-3-yl)coumarin (18c), the most potent compound of these series (IC50 = 60 nM), was subjected to further in vivo studies in a reserpine-induced mouse PD model. The obtained results suggest a promising potential for 18c as antiparkinsonian agent. Molecular modeling studies also provided valuable information about the enzyme-drug interactions and the potential pharmacokinetic profile of the novel compounds.

Redox-Active Phenolic Compounds Mediate the Cytotoxic and Antioxidant Effects of Carpodesmia tamariscifolia (=Cystoseira tamariscifolia).

Carpodesmia tamariscifolia is a brown alga rich in (poly)phenols with important cytotoxic and antioxidant effects. However, the relationship between its chemical composition and its effects is unknown. The aim of this study is to identify the potential compounds and mechanisms responsible for its main effects. The alga was extracted consecutively with hexane, dichloromethane and methanol and further fractionated using Sephadex LH-20 and silica gel columns when appropriate. The fractions were subjected to thin-layer chromatography and liquid chromatography-mass spectrometry analysis and evaluated for their total phenolic content (Folin-Ciocalteu assay), radical scavenging activity (DPPH assay), cytotoxic activity (MTT assay on the SH-SY5Y cell line), and ability to generate H2 O2 (Amplex Red assay). Chromatographic and phenolic analyses of the fractions indicate that abundant redox-active phenols are present in all the fractions and that a high amount of prenylated hydroquinone derivatives is present in the apolar ones. In the hexane and dichloromethane fractions, the cytotoxic and antioxidant activities are closely related to their phenolic content, whereas in the methanol fractions, the cytotoxicity is negatively related to the phenolic content and the antioxidant activity is positively related to it. In the same tests, hydroquinone behaves as both strong cytotoxic and antioxidant agent. H2 O2 assay shows that C. tamariscifolia fractions and hydroquinone can autoxidize and generate H2 O2 . Our results suggest that redox-active phenols produce the pharmacological effects described for C. tamariscifolia and that the hydroquinone moiety of prenylated hydroquinone derivatives is responsible for both cytotoxic (through a pro-oxidant mechanism secondary to its autoxidation) and antioxidant effects of the apolar fractions.

Discovery of new phthalazinones as vasodilator agents and novel pharmacological tools to study calcium channels.

Aim: Hydralazine has led to the synthesis of phthalazinone derivatives which induce vasorelaxation. Methods: A new series of 2-(aminoalkyl)-4-benzyl-2H-phthalazin-1-one derivatives has been synthesized to study their vasorelaxant activity. Results: At the highest-studied concentration, most of the new compounds relaxed the denuded aortic rings precontracted with phenylephrine by 72.9-85.7%. Compound 25 (C25) suppressed almost totally the contractile effects of phenylephrine, high KCl concentration, ionomycin and caffeine related to the activation of Ca2+ channels, whereas its inhibitory effect was reversed with high CaCl2 concentrations. Conclusion: Vasodilator effects of C25 appear to be due exclusively to the reversible blockage of different calcium channels. As broad range calcium channel blocker, C25 seems to be suitable as a pharmacological tool for calcium channel research.

Computational Drug Target Screening through Protein Interaction Profiles.

The development of computational methods to discover novel drug-target interactions on a large scale is of great interest. We propose a new method for virtual screening based on protein interaction profile similarity to discover new targets for molecules, including existing drugs. We calculated Target Interaction Profile Fingerprints (TIPFs) based on ChEMBL database to evaluate drug similarity and generated new putative compound-target candidates from the non-intersecting targets in each pair of compounds. A set of drugs was further studied in monoamine oxidase B (MAO-B) and cyclooxygenase-1 (COX-1) enzyme through molecular docking and experimental assays. The drug ethoxzolamide and the natural compound piperlongumine, present in Piper longum L, showed hMAO-B activity with IC50 values of 25 and 65 µM respectively. Five candidates, including lapatinib, SB-202190, RO-316233, GW786460X and indirubin-3'-monoxime were tested against human COX-1. Compounds SB-202190 and RO-316233 showed a IC50 in hCOX-1 of 24 and 25 µM respectively (similar range as potent inhibitors such as diclofenac and indomethacin in the same experimental conditions). Lapatinib and indirubin-3'-monoxime showed moderate hCOX-1 activity (19.5% and 28% of enzyme inhibition at 25 µM respectively). Our modeling constitutes a multi-target predictor for large scale virtual screening with potential in lead discovery, repositioning and drug safety.

Synthesis, biological evaluation and structure-activity relationships of new phthalazinedione derivatives with vasorelaxant activity.

Five series of 1,4-phthalazinedione derivatives were synthesized in good yields. Vasorelaxant activity of these new derivatives was measured on either intact or endothelium-denuded isolated rat thoracic aortic rings pre-contracted with phenylephrine. Most of studied compounds, substituted in both nitrogen atoms, attained practically the total relaxation of the organ at low micromolar concentrations. The presence of functional endothelium significantly reduced the EC50 values for most of studied compounds. Some structure-activity relationships were established and compounds 2d and 5d can be considered as new leads for further modifications.

Monoamine oxidase (MAO) inhibitory activity: 3-phenylcoumarins versus 4-hydroxy-3-phenylcoumarins.

Monoamine oxidase (MAO) is a useful target in the treatment of neurodegenerative diseases and depressive disorders. Both isoforms, MAO-A and MAO-B, are known to play critical roles in disease progression, and as such, the identification of novel, potent and selective inhibitors is an important research goal. Here, two series of 3-phenylcoumarin derivatives were synthesized and evaluated against MAO-A and MAO-B. Most of the compounds tested acted preferentially on MAO-B, with IC50 values in the micromolar to nanomolar range. Only 6-chloro-4-hydroxy-3-(2'-hydroxyphenyl)coumarin exhibited activity against the MAO-A isoform, while still retaining good selectivity for MAO-B. 6-Chloro-3-phenylcoumarins unsubstituted at the 4 position were found to be more active as MAO-B inhibitors than the corresponding 4-hydroxylated coumarins. For 4-unsubstituted coumarins, meta and para positions on the 3-phenyl ring seem to be the most favorable for substitution. Molecular docking simulations were used to explain the observed hMAO-B structure-activity relationships for this type of compound. 6-Chloro-3-(3'-methoxyphenyl)coumarin was the most active compound identified (IC50=0.001 µM) and is several times more potent and selective than the reference compound, R-(-)-deprenyl hydrochloride. This compound represents a novel tool for the further investigation of the therapeutic potential of MAO-B inhibitors.

MAO inhibitory activity of 2-arylbenzofurans versus 3-arylcoumarins: synthesis, in vitro study, and docking calculations.

Monoamine oxidase (MAO) is an important drug target for the treatment of neurological disorders. Several 3-arylcoumarin derivatives were previously described as interesting selective MAO-B inhibitors. Preserving the trans-stilbene structure, a series of 2-arylbenzofuran and corresponding 3-arylcoumarin derivatives were synthesized and evaluated as inhibitors of both MAO isoforms, MAO-A and MAO-B. In general, both types of derivatives were found to be selective MAO-B inhibitors, with IC50 values in the nano- to micromolar range. 5-Nitro-2-(4-methoxyphenyl)benzofuran (8) is the most active compound of the benzofuran series, presenting MAO-B selectivity and reversible inhibition (IC50 =140 nM). 3-(4'-Methoxyphenyl)-6-nitrocoumarin (15), with the same substitution pattern as that of compound 8, was found to be the most active MAO-B inhibitor of the coumarin series (IC50 =3 nM). However, 3-phenylcoumarin 14 showed activity in the same range (IC50 =6 nM), is reversible, and also severalfold more selective than compound 15. Docking experiments for the most active compounds into the MAO-B and MAO-A binding pockets highlighted different interactions between the derivative classes (2-arylbenzofurans and 3-arylcoumarins), and provided new information about the enzyme-inhibitor interaction and the potential therapeutic application of these scaffolds.

Synthesis and NMR studies of novel chromone-2-carboxamide derivatives.

Chromones are heterocyclic compounds of natural or synthetic origin that possess relevant pharmacological activities. Versatile functionalization of the chromone nucleus allows attaining of a chemical diversity suitable to perform structure-activity relationships in drug discovery and development programs. Accordingly, the synthesis and identification of novel chromone carboxamide derivatives with electron-donating and electron-withdrawing substituents in different positions of the exocyclic ring are reported in this work. Their complete structural characterization was performed using one-dimensional and two-dimensional resonance techniques. The data acquired are useful for a prompt analysis of related compounds that encompass our integrated medicinal chemistry sketch.

Predicting monoamine oxidase inhibitory activity through ligand-based models.

The evolution of bio- and cheminformatics associated with the development of specialized software and increasing computer power has produced a great interest in theoretical in silico methods applied in drug rational design. These techniques apply the concept that "similar molecules have similar biological properties" that has been exploited in Medicinal Chemistry for years to design new molecules with desirable pharmacological profiles. Ligand-based methods are not dependent on receptor structural data and take into account two and three-dimensional molecular properties to assess similarity of new compounds in regards to the set of molecules with the biological property under study. Depending on the complexity of the calculation, there are different types of ligand-based methods, such as QSAR (Quantitative Structure- Activity Relationship) with 2D and 3D descriptors, CoMFA (Comparative Molecular Field Analysis) or pharmacophoric approaches. This work provides a description of a series of ligand-based models applied in the prediction of the inhibitory activity of monoamine oxidase (MAO) enzymes. The controlled regulation of the enzymes' function through the use of MAO inhibitors is used as a treatment in many psychiatric and neurological disorders, such as depression, anxiety, Alzheimer's and Parkinson's disease. For this reason, multiple scaffolds, such as substituted coumarins, indolylmethylamine or pyridazine derivatives were synthesized and assayed toward MAO-A and MAO-B inhibition. Our intention is to focus on the description of ligand-based models to provide new insights in the relationship between the MAO inhibitory activity and the molecular structure of the different inhibitors, and further study enzyme selectivity and possible mechanisms of action.

A novel tetrahydrobenzoangelicin with dark and photo biological activity.

The synthesis of 8,9,10,11-tetrahydro-5-(3-dimethylaminopropoxy)-4-methylbenzofuro[2,3-h]coumarin (5) is described. The new compound showed the ability to inhibit cell growth both upon UVA irradiation and in the dark. The investigation on the mechanism of action highlighted the capacity of 5 to covalently photoadd to thymine, as demonstrated by the isolation and characterization of the 4',5'-monoadduct. Furthermore, in the ground state 5 interferes with the topoisomerase II relaxation activity, suggesting that this enzyme could constitute a molecular target responsible for the dark antiproliferative effect.

Synthesis, human monoamine oxidase inhibitory activity and molecular docking studies of 3-heteroarylcoumarin derivatives.

Monoamine oxidase (MAO) is an important drug target for the treatment of neurological disorders. Series of 3-indolyl and 3-thiophenylcoumarins were synthesized and evaluated as inhibitors of the two human MAO isoforms, hMAO-A and hMAO-B. In general, the derivatives were found to be selective hMAO-B inhibitors with IC(50) values in the nanoMolar (nM) to microMolar (µM) range. Docking experiments were carried out in order to compare the theoretical and experimental affinity of these compounds to the hMAO-B protein. According to our results, docking experiments could be an interesting approach to try to predict the activity of this class of coumarins against MAO-B receptors.

Synthesis and vasorelaxant and platelet antiaggregatory activities of a new series of 6-halo-3-phenylcoumarins.

A series of 6-halo-3-hydroxyphenylcoumarins (resveratrol-coumarins hybrid derivatives) was synthesized in good yields by a Perkin reaction followed by hydrolysis. The new compounds were evaluated for their vasorelaxant activity in intact rat aorta rings pre-contracted with phenylephrine (PE), as well as for their inhibitory effects on platelet aggregation induced by thrombin in washed human platelets. These compounds concentration-dependently relaxed vascular smooth muscle and some of them showed a platelet antiaggregatory activity that was up to thirty times higher than that shown by trans-resveratrol and some other previously synthesized derivatives.

Tyrosinase inhibitor activity of coumarin-resveratrol hybrids.

In the present work we report on the contribution of the coumarin moiety to tyrosinase inhibition. Coumarin-resveratrol hybrids 1-8 have been resynthesized to investigate the structure-activity relationships and the IC(50) values of these compounds were measured. The results showed that these compounds exhibited tyrosinase inhibitory activity. Compound 3-(3',4',5'-trihydroxyphenyl)-6,8-dihydroxycoumarin (8)is the most potentcompound (0.27 mM), more so than umbelliferone (0.42 mM), used as reference compound. The kinetic studies revealed that compound 8 caused non-competitive tyrosinase inhibition.

A new series of 3-phenylcoumarins as potent and selective MAO-B inhibitors.

6-Methyl-3-phenylcoumarins 3-6 were designed, synthesized and evaluated as monoamine oxidase A and B (MAO-A and MAO-B) inhibitors. The synthesis of these new compounds (resveratrol-coumarin hybrids) was carried out with good yield by a Perkin reaction, from the 5-methylsalicylaldehyde and the corresponding phenylacetic acid. They show high selectivity to the MAO-B isoenzyme, with IC(50) values in the nanomolar range. Compound 5 is the most active compound and is several times more potent and selective than the reference compound, R-(-)-deprenyl.

New insights into the antioxidant activity of hydroxycinnamic acids: Synthesis and physicochemical characterization of novel halogenated derivatives.

An interdisciplinary research project was developed combining the synthesis of a series of hydroxycinnamic acid derivatives and the evaluation of their physicochemical parameters (namely redox potentials and partition coefficients), along with the corresponding antioxidant activity. A structure-property-activity relationship (SPAR) approach was then applied aiming at establishing a putative relation between the physicochemical parameters of the compounds under study and their antioxidant activity. The results gathered allow concluding that the redox potentials could contribute to the understanding of the antioxidant activity and that the presence of an electron withdrawing group (EWG) of halogen type, namely a bromo atom, in an ortho position to a phenolic group of the cinnamic scaffold does not influence the antioxidant activity. On the other hand after the introduction of this type of substituent a significant increase on the lipophilicity of cinnamic derivatives was observed, which is a feature of extreme importance in the development of novel lipophilic antioxidants. The SPAR results revealed a relation between the redox potentials and the antioxidant activity of hydroxycinnamic acids and derivatives. The data obtained operate as a positive reinforce of the tendency to use redox properties as a guideline of the rational design of this type of compounds.

Quantitative structure-activity relationship and complex network approach to monoamine oxidase A and B inhibitors.

The work provides a new model for the prediction of the MAO-A and -B inhibitor activity by the use of combined complex networks and QSAR methodologies. On the basis of the obtained model, we prepared and assayed 33 coumarin derivatives, and the theoretical prediction was compared with the experimental activity data. The model correctly predicted 27 compounds, and most of the active derivatives showed IC 50 values in the muM-nM range against both the MAO-A and MAO-B isoforms. Compound 14 shows the same MAO-A inhibitory activity (IC 50 = 7.2 nM), as clorgyline used as a reference inhibitor and has the highest MAO-A specificity (1000-fold higher compared to MAO-B). On the other hand, compounds 24 (IC 50 = 1.2 nM) and 28 (IC 50 = 1.5 nM) show higher activity than selegiline (IC 50 = 19.6 nM) and high MAO-B selectivity with 100-fold and 1600-fold inhibition levels, with respect to the MAO-A isoform.