Seaweeds as Source of Bioactive Pigments with Neuroprotective and/or Anti-Neurodegenerative Activities: Astaxanthin and Fucoxanthin.

The marine kingdom is an important source of a huge variety of scaffolds inspiring the design of new drugs. The complex molecules found in the oceans present a great challenge to organic and medicinal chemists. However, the wide variety of biological activities they can display is worth the effort. In this article, we present an overview of different seaweeds as potential sources of bioactive pigments with activity against neurodegenerative diseases, especially due to their neuroprotective effects. Along with a broad introduction to seaweed as a source of bioactive pigments, this review is especially focused on astaxanthin and fucoxanthin as potential neuroprotective and/or anti-neurodegenerative agents. PubMed and SciFinder were used as the main sources to search and select the most relevant scientific articles within the field.

2H-chromene and 7H-furo-chromene derivatives selectively inhibit tumour associated human carbonic anhydrase IX and XII isoforms.

Tumour associated carbonic anhydrases (CAs) IX and XII have been recognised as potential targets for the treatment of hypoxic tumours. Therefore, considering the high pharmacological potential of the chromene scaffold as selective ligand of the IX and XII isoforms, two libraries of compounds, namely 2H-chromene and 7H-furo-chromene derivatives, with diverse substitution patterns were designed and synthesised. The structure of the newly synthesised compounds was characterised and their inhibitory potency and selectivity towards human CA off target isoforms I, II and cancer-associated CA isoforms IX and XII were evaluated. Most of the compounds inhibit CA isoforms IX and XII with no activity against the I and II isozymes. Thus, while the potency was influenced by the substitution pattern along the chromene scaffold, the selectivity was conserved along the series, confirming the high potential of both 2H-chromene and 7H-furo-chromene scaffolds for the design of isozyme selective inhibitors.

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.

Thiocoumarins: From the Synthesis to the Biological Applications.

Coumarin is a privilege scaffold in medicinal chemistry. Coumarin derivatives are still an emerging class of highly potent pharmaceutical drugs, best known in the field of antimicrobials and anticoagulants. Thiocoumarins are a particular class of coumarins in which one or two of the oxygen atoms are replaced by a sulfur. They are chemically subdivided in three groups: Thiocoumarins, 2-thioxocoumarins, and dithiocoumarins. This review emphasizes the rationale behind the synthesis and biological applications of the most relevant publications related to this family of compounds. Particular attention has been given to their potential as drug candidates, with particular emphasis in the last 5 years. This article is based on the most relevant information collected from multiple electronic databases, including SciFinder, Pubmed, Espacenet, and Mendeley.

Hydroxy-3-Phenylcoumarins as Multitarget Compounds for Skin Aging Diseases: Synthesis, Molecular Docking and Tyrosinase, Elastase, Collagenase and Hyaluronidase Inhibition, and Sun Protection Factor.

Skin aging is a progressive biological process of the human body, and it is not only time-dependent. Differently substituted 3-phenylcoumarins proved to efficiently inhibit tyrosinase. In the current work, new substitution patterns have been explored, and the biological studies were extended to other important enzymes involved in the processes of skin aging, as elastase, collagenase and hyaluronidase. From the studied series, five compounds presented inhibitory activity against tyrosinase, one compound against elastase, eight compounds against collagenase and two compounds against hyaluronidase, being five compounds dual inhibitors. The 3-(4'-Bromophenyl)-5,7-dihydroxycoumarin (1) and 3-(3'-bromophenyl)-5,7-dihydroxycoumarin (2) presented the best profiles against tyrosinase (IC50 = 1.05 µM and 7.03 µM) and collagenase (IC50 = 123.4 µM and 110.4 µM); the 3-(4'-bromophenyl)-6,7-dihydroxycoumarin (4) presented a good inhibition against tyrosinase and hyaluronidase; the 3-(3'-bromophenyl)-6,7-dihydroxycoumarin (5) showed an effective tyrosinase and elastase inhibition; and 6,7-dihydroxy-3-(3'-hydroxyphenyl)coumarin (11) presented a dual profile inhibition against collagenase and hyaluronidase. Furthermore, considering the overall activities tested, compounds 1 and 2 proved to be the most promising anti-aging compounds. These compounds also showed to have a photo-protective effect, without being cytotoxic to human skin keratinocyte cells. To predict the binding site with the target enzymes, computational studies were also carried out.

Coumarin-Resveratrol-Inspired Hybrids as Monoamine Oxidase B Inhibitors: 3-Phenylcoumarin versus trans-6-Styrylcoumarin.

Monoamine oxidases (MAOs) are attractive targets in drug design. The inhibition of one of the isoforms (A or B) is responsible for modulating the levels of different neurotransmitters in the central nervous system, as well as the production of reactive oxygen species. Molecules that act selectively on one of the MAO isoforms have been studied deeply, and coumarin has been described as a promising scaffold. In the current manuscript we describe a comparative study between 3-phenylcoumarin (endo coumarin-resveratrol-inspired hybrid) and trans-6-styrylcoumarin (exo coumarin-resveratrol-inspired hybrid). Crystallographic structures of both compounds were obtained and analyzed. 3D-QSAR models, in particular CoMFA and CoMSIA, docking simulations and molecular dynamics simulations have been performed to support and better understand the interaction of these molecules with both MAO isoforms. Both molecules proved to inhibit MAO-B, with trans-6-styrylcoumarin being 107 times more active than 3-phenylcoumarin, and 267 times more active than trans-resveratrol.

Combined 3D-QSAR and docking analysis for the design and synthesis of chalcones as potent and selective monoamine oxidase B inhibitors.

Monoamine oxidases (MAOs) are important targets in medicinal chemistry, as their inhibition may change the levels of different neurotransmitters in the brain, and also the production of oxidative stress species. New chemical entities able to interact selectively with one of the MAO isoforms are being extensively studied, and chalcones proved to be promising molecules. In the current work, we focused our attention on the understanding of theoretical models that may predict the MAO-B activity and selectivity of new chalcones. 3D-QSAR models, in particular CoMFA and CoMSIA, and docking simulations analysis have been carried out, and their successful implementation was corroborated by studying twenty-three synthetized chalcones (151-173) based on the generated information. All the synthetized molecules proved to inhibit MAO-B, being ten out of them MAO-B potent and selective inhibitors, with IC50 against this isoform in the nanomolar range, being (E)-3-(4-hydroxyphenyl)-1-(2,2-dimethylchroman-6-yl)prop-2-en-1-one (152) the best MAO-B inhibitor (IC50 of 170 nM). Docking simulations on both MAO-A and MAO-B binding pockets, using compound 152, were carried out. Calculated affinity energy for the MAO-A was +2.3 Kcal/mol, and for the MAO-B was -10.3 Kcal/mol, justifying the MAO-B high selectivity of these compounds. Both theoretical and experimental structure-activity relationship studies were performed, and substitution patterns were established to increase MAO-B selectivity and inhibitory efficacy. Therefore, we proved that both 3D-QSAR models and molecular docking approaches enhance the probability of finding new potent and selective MAO-B inhibitors, avoiding time-consuming and costly synthesis and biological evaluations.

New benzimidazolequinones as trypanosomicidal agents.

Herein, the design and synthesis of new 2-phenyl(pyridinyl)benzimidazolequinones and their 5-phenoxy derivatives as potential anti-Trypanosoma cruzi agents are described. The compounds were evaluated in vitro against the epimastigotes and trypomastigote forms of Trypanosoma cruzi. The replacing of a benzene moiety in the naphthoquinone system by an imidazole enhanced the trypanosomicidal activity against Trypanosoma cruzi. Three of the tested compounds (11a-c) showed potent trypanosomicidal activity and compound 11a, with IC50 of 0.65 µM on the trypomastigote form of T. cruzi, proved to be 15 times more active than nifurtimox. Additionally, molecular docking studies indicate that the quinone derivatives 11a-c could have a multitarget profile interacting preferentially with trypanothione reductase and Old Yellow Enzyme.

3-Phenylcoumarins as a Privileged Scaffold in Medicinal Chemistry: The Landmarks of the Past Decade.

3-Phenylcoumarins are a family of heterocyclic molecules that are widely used in both organic and medicinal chemistry. In this overview, research on this scaffold, since 2010, is included and discussed, focusing on aspects related to its natural origin, synthetic procedures and pharmacological applications. This review paper is based on the most relevant literature related to the role of 3-phenylcoumarins in the design of new drug candidates. The references presented in this review have been collected from multiple electronic databases, including SciFinder, Pubmed and Mendeley.

Trending Topics on Coumarin and Its Derivatives in 2020.

Coumarins are naturally occurring molecules with a versatile range of activities. Their structural and physicochemical characteristics make them a privileged scaffold in medicinal chemistry and chemical biology. Many research articles and reviews compile information on this important family of compounds. In this overview, the most recent research papers and reviews from 2020 are organized and analyzed, and a discussion on these data is included. Multiple electronic databases were scanned, including SciFinder, Mendeley, and PubMed, the latter being the main source of information. Particular attention was paid to the potential of coumarins as an important scaffold in drug design, as well as fluorescent probes for decaging of prodrugs, metal detection, and diagnostic purposes. Herein we do an analysis of the trending topics related to coumarin and its derivatives in the broad field of drug discovery.

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.

3-Arylcoumarins as highly potent and selective monoamine oxidase B inhibitors: Which chemical features matter?

Monoamine oxidase B inhibitory activity is closely regulated by the interaction of the small molecules with the enzyme. It is therefore desirable to use theoretical approaches to design rational methods to develop new molecules to modulate specific interactions with the protein. Here, we report such methods, and we illustrate their successful implementation by studying six synthetized 3-arylcoumarins (71-76) based on them. Monoamine oxidase B inhibition is essential to maintain the balance of dopamine, and one of its major functions is to combat dopamine degradation, a phenomenon linked to Parkinson's disease. In this work, we study small-molecule inhibitors based on the 3-arylcoumarin scaffold and their monoamine oxidase B selective inhibition. We show that 3D-QSAR models, in particular CoMFA and CoMSIA, and molecular docking approaches, enhance the probability to find new interesting inhibitors, avoiding very costly and time-consuming synthesis and biological evaluations.

Discovery and optimization of 3-thiophenylcoumarins as novel agents against Parkinson's disease: Synthesis, in vitro and in vivo studies.

Monoamine oxidase B (MAO-B) inhibitors are still receiving great attention as promising therapeutic agents for central nervous system disorders. This study explores, for the first time, the potential of 3-thiophenylcoumarins as in vitro and in vivo agents against Parkinsons disease. Twelve compounds were synthesized via Perkin-Oglialoro reaction, and in vitro evaluation of six hydroxylated molecules was performed. MAO-A and MAO-B inhibition, DPPH scavenging and inhibition of ROS formation, neurotoxicity on motor cortex neurons and neuroprotection against H2O2, were studied. In vivo effect on locomotor activity using the open field test was also evaluated for the best candidate [3-(4'-bromothiophen-2'-yl)-7-hydroxycoumarin, 5], a potent, selective and reversible MAO-B inhibitor (IC50 = 140 nM). This compound proved to have a slightly better in vivo profile than selegiline, one of the currently treatments for Parkinson's disease, in reserpinized mice pretreated with levodopa and benserazide. Results suggested that, comparing positions 7 and 8, substitution at position 7 of the coumarin scaffold is better for the enzymatic inhibition. However, the presence of a catechol at positions 7 and 8 exponentially increases the antioxidant potential and the neuroprotective properties. Finally, all the molecules present good theoretical physicochemical properties that make them excellent candidates for the optimization of a lead compound.

Exploring the Multi-Target Performance of Mitochondriotropic Antioxidants against the Pivotal Alzheimer's Disease Pathophysiological Hallmarks.

Alzheimer disease (AD) is the most common neurodegenerative disease featuring progressive and degenerative neurological impairments resulting in memory loss and cognitive decline. The specific mechanisms underlying AD are still poorly understood, but it is suggested that a deficiency in the brain neurotransmitter acetylcholine, the deposition of insoluble aggregates of fibrillar ß-amyloid 1-42 (Aß42), and iron and glutamate accumulation play an important role in the disease progress. Despite the existence of approved cholinergic drugs, none of them demonstrated effectiveness in modifying disease progression. Accordingly, the development of new chemical entities acting on more than one target is attracting progressively more attention as they can tackle intricate network targets and modulate their effects. Within this endeavor, a series of mitochondriotropic antioxidants inspired on hydroxycinnamic (HCA's) scaffold were synthesized, screened toward cholinesterases and evaluated as neuroprotectors in a differentiated human SH-SY5Y cell line. From the series, compounds 7 and 11 with a 10-carbon chain can be viewed as multi-target leads for the treatment of AD, as they act as dual and bifunctional cholinesterase inhibitors and prevent the neuronal damage caused by diverse aggressors related to protein misfolding and aggregation, iron accumulation and excitotoxicity.

Adenosine Receptor Ligands: Coumarin-Chalcone Hybrids as Modulating Agents on the Activity of hARs.

Adenosine receptors (ARs) play an important role in neurological and psychiatric disorders such as Alzheimer's disease, Parkinson's disease, epilepsy and schizophrenia. The different subtypes of ARs and the knowledge on their densities and status are important for understanding the mechanisms underlying the pathogenesis of diseases and for developing new therapeutics. Looking for new scaffolds for selective AR ligands, coumarin-chalcone hybrids were synthesized (compounds 1-8) and screened in radioligand binding (hA1, hA2A and hA3) and adenylyl cyclase (hA2B) assays in order to evaluate their affinity for the four human AR subtypes (hARs). Coumarin-chalcone hybrid has been established as a new scaffold suitable for the development of potent and selective ligands for hA1 or hA3 subtypes. In general, hydroxy-substituted hybrids showed some affinity for the hA1, while the methoxy counterparts were selective for the hA3. The most potent hA1 ligand was compound 7 (Ki = 17.7 µM), whereas compound 4 was the most potent ligand for hA3 (Ki = 2.49 µM). In addition, docking studies with hA1 and hA3 homology models were established to analyze the structure-function relationships. Results showed that the different residues located on the protein binding pocket could play an important role in ligand selectivity.

Quercetin and Related Chromenone Derivatives as Monoamine Oxidase Inhibitors: Targeting Neurological and Mental Disorders.

Monoamine oxidase inhibitions are considered as important targets for the treatment of depression, anxiety, and neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. This has encouraged many medicinal chemistry research groups for the development of most promising selective monoamine oxidase (MAO) inhibitors. A large number of plant isolates also reported for significant MAO inhibition potential in recent years. Differently substituted flavonoids have been prepared and investigated as MAO-A and MAO-B inhibitors. Flavonoid scaffold showed notable antidepressant and neuroprotective properties as revealed by various and established preclinical trials. The current review made an attempt to summarizing and critically evaluating the new findings on the quercetin and related flavonoid derivatives functions as potent MAO isoform inhibitors.

Hesperidin as a Neuroprotective Agent: A Review of Animal and Clinical Evidence.

Neuroprotection is the preservation of function and networks of neural tissues from damages caused by various agents, as well as neurodegenerative diseases such as Parkinson's, Alzheimer's, Huntington's diseases, and multiple sclerosis. Hesperidin, a flavanone glycoside, is a natural phenolic compound with a wide range of biological effects. Mounting evidence has demonstrated that hesperidin possesses inhibitory effect against development of neurodegenerative diseases. Our review discusses neuropharmacological mechanisms for preventive and therapeutic effects of hesperidin in neurodegenerative diseases. In addition, the review examines clinical evidence confirming its neuroprotective function. Various cellular and animal models specific to neurodegenerative diseases have been conducted to evaluate the underlying neuropharmacological mechanisms of hesperidin. Neuroprotective potential of this flavonoid is mediated by improvement of neural growth factors and endogenous antioxidant defense functions, diminishing neuro-inflammatory and apoptotic pathways. Despite the various preclinical studies on the role of hesperidin in the neurodegenerative diseases, less is known about its definite effect on humans. A limited number of clinical trials showed that hesperidin-enriched dietary supplements can significantly improve cerebral blood flow, cognition, and memory performance. Further clinical trials are also required for confirming neuroprotective efficacy of this natural flavonoid and evaluating its safety profile.

Potent in Vitro α-Glucosidase Inhibition of Secondary Metabolites Derived from Dryopteris cycadina.

α-glucosidase is responsible for the hydrolysis of complex carbohydrates into simple absorbable glucose and causes postprandial hyperglycemia. α-glucosidase inhibition is thus the ideal target to prevent postprandial hyperglycemia. The present study was therefore designed to analyze the effects of various compounds isolated from Dryopteris cycadina against α-glucosidase including ß-Sitosterol 1, ß-Sitosterol3-O-ß-d-glucopyranoside 2, 3, 5, 7-trihydroxy-2-(p-tolyl) chorman-4-one 3, Quercetin-3-0-ß-d-glucopyranoside (3/→0-3///)- ß-d- Quercetin -3-0- ß â»d-galactopyranoside 4 and 5, 7, 4/-Trihydroxyflavon-3-glucopyranoid 5. The in vitro spectrophotometric method was used for the analysis of test compounds against possible inhibition. Similarly, molecular docking studies were performed using the MOE software. These compounds showed concentration-dependent inhibition on α-glucosidase, and compounds 1 (IC50: 143 ± 0.47 µM), 3 (IC50:133 ± 6.90 µM) and 5 (IC50: 146 ± 1.93 µM) were more potent than the standard drug, acarbose (IC50: 290 ± 0.54 µM). Computational studies of these compounds strongly supported the in vitro studies and showed strong binding receptor sensitivity. In short, the secondary metabolites isolated from D. cycadina demonstrated potent α-glucosidase inhibition that were supported by molecular docking with a high docking score.

Insights into the Discovery of Novel Neuroprotective Agents: A Comparative Study between Sulfanylcinnamic Acid Derivatives and Related Phenolic Analogues.

Exogenous antioxidants may be beneficial therapeutic tools to tackle the oxidative damage in neurodegenerative diseases by regulation of the redox state that is critical for cell viability and organ function. Inspired by natural plant polyphenols, a series of cinnamic acid-based thiophenolic and phenolic compounds were synthesized and their antioxidant and neuroprotective properties were studied. In general, our results showed that the replacement of the hydroxyl group (OH) by a sulfhydryl group (SH) increased the radical scavenging activity and enhanced the reaction rate with 1,1-diphenyl-2-picrylhydrazyl radical (DPPH•) and galvinoxyl radical (GO•). These results correlated well with the lower oxidation potential (Ep) values of thiophenols. However, a lower peroxyl radical (ROO•) scavenging activity was observed for thiophenols in oxygen radical absorbance capacity (ORAC-FL) assay. Furthermore, the introduction of 5-methoxy and 5-phenyl groups in the aromatic ring of 4-thioferulic acid (TFA) 2 and ferulic acid (FA) 1 did not significantly improve their antioxidant activity, despite the slight decrease of Ep observed for compounds 5, 6, and 9. Concerning cinnamic acid amides, the antioxidant profile was similar to the parent compounds. None of the compounds under study presented significant cytotoxic effects in human differentiated neuroblastoma cells. Thiophenolic amide 3 stands out as the most promising thiophenol-based antioxidant, showing cellular neuroprotective effects against oxidative stress inducers (hydrogen peroxide and iron).

Antibacterial Activity and Molecular Docking Studies of a Selected Series of Hydroxy-3-arylcoumarins.

Antibiotic resistance is one of the main public health concerns of this century. This resistance is also associated with oxidative stress, which could contribute to the selection of resistant bacterial strains. Bearing this in mind, and considering that flavonoid compounds are well known for displaying both activities, we investigated a series of hydroxy-3-arylcoumarins with structural features of flavonoids for their antibacterial activity against different bacterial strains. Active compounds showed selectivity against the studied Gram-positive bacteria compared to Gram-negative bacteria. 5,7-Dihydroxy-3-phenylcoumarin (compound 8) displayed the best antibacterial activity against Staphylococcus aureus and Bacillus cereus with minimum inhibitory concentrations (MICs) of 11 g/mL, followed by Staphylococcus aureus (MRSA strain) and Listeria monocytogenes with MICs of 22 and 44 g/mL, respectively. Moreover, molecular docking studies performed on the most active compounds against Staphylococcus aureus tyrosyl-tRNA synthetase and topoisomerase II DNA gyrase revealed the potential binding mode of the ligands to the site of the appropriate targets. Preliminary structure-activity relationship studies showed that the antibacterial activity can be modulated by the presence of the 3-phenyl ring and by the position of the hydroxyl groups at the coumarin scaffold.