Anti-tyrosinase, antioxidant, and antibacterial activities of novel 5-hydroxy-4-acetyl-2,3-dihydronaphtho[1,2-b]furans

Discovery of novel 1,2,4-triazole tethered β-hydroxy sulfides as bacterial tyrosinase inhibitors: synthesis and biophysical evaluation through in vitro and in silico approaches

In this study, a series of 1,2,4-triazole-tethered β-hydroxy sulfide scaffolds 11a-h was synthesized in good to remarkable yields (69-90%) through the thiolysis of oxiranes by the thiols in aqueous basic catalytic conditions. The synthesized 1,2,4-triazole-tethered β-hydroxy sulfides were screened against bacterial tyrosinase enzyme, and Gram-positive and Gram-negative bacterial cultures i.e., (S. aureus) Staphylococcus aureus & (E. coli) Escherichia coli. Among the synthesized derivatives, the molecules 11a (IC50 = 7.67 ± 1.00 μM), 11c (IC50 = 4.52 ± 0.09 μM), 11d (IC50 = 6.60 ± 1.25 μM), and 11f (IC50 = 5.93 ± 0.50 μM) displayed the better tyrosinase inhibitory activity in comparison to reference drugs ascorbic acid (IC50 = 11.5 ± 1.00 μM) and kojic acid (IC50 = 30.34 ± 0.75 μM). The molecule benzofuran-triazol-propan-2-ol 11c proved to be the most potent bacterial tyrosinase inhibitory agent with a minimum IC50 of 4.52 ± 0.09 μM, as compared to other synthesized counterparts and both standards (kojic acid and ascorbic acid). The compound diphenyl-triazol-propan-2-ol 11a and benzofuran-triazole-propan-2-ol 11c showed comparable anti-bacterial chemotherapeutic efficacy with minimum inhibitory concentrations (MIC = 2.0 ± 2.25 mg mL-1 and 2.5 ± 0.00 mg mL-1, respectively) against S. aureus bacterial strain in comparison with standard antibiotic penicillin (MIC = 2.2 ± 1.15 mg mL-1). Furthermore, among the synthesized derivatives, only compound 11c demonstrated better anti-bacterial activity (MIC = 10 ± 0.40 mg mL-1) against E. coli, which was slightly less than the standard antibiotic i.e., penicillin (MIC = 2.4 ± 1.00 mg mL-1). The compound 11c demonstrated a better binding score (-7.08 kcal mol-1) than ascorbic acid (-5.59 kcal mol-1) and kojic acid (-5.78 kcal mol-1). Molecular docking studies also validate the in vitro anti-tyrosinase assay results; therefore, the molecule 11c can be the lead bacterial tyrosinase inhibitor as well as the antibacterial agent against both types of bacterial strains after suitable structural modifications.

Synthesis of a New Series of Anthraquinone-Linked Cyclopentanone Derivatives: Investigating the Antioxidant, Antibacterial, Cytotoxic and Tyrosinase Inhibitory Activities of the Mushroom Tyrosinase Enzyme Using Molecular Docking

Purpose

New bioactive anthraquinone derivatives are investigated for antibacterial, tyrosinase inhibitory, antioxidant cytotoxic activity, and molecular docking.

Methods

The compounds were produced using the grindstone method, yielding 69 to 89%. These compounds were analyzed using IR, 1H, and 13C NMR and elemental and mass spectral methods. Additionally, the antibacterial, antioxidant, and tyrosinase inhibitory activities of all the synthesised compounds were evaluated.

Results

Compound 2 showed remarkable tyrosinase inhibition activity, with an (IC50: 13.45 µg/mL), compared to kojic acid (IC50: 19.40 µg/mL). It also exhibited moderate antioxidant and antibacterial activities with respect to the references BHT and ampicillin, respectively. Kinetic analysis revealed that the tyrosinase inhibitory activity of compound 2 was non-competitive and competitive, whereas that of compound 1 was low. All compounds (1-8) were significantly less active than doxorubicin (LC50: 0.74±0.01μg/mL). However, compound 2 affinity for the 2Y9X protein was lower than kojic acid, with a lower docking score (-8.6 kcal/mol compared to (-4.7 kcal/mol), making it more effective.

Conclusion

All synthesized compounds displayed remarkable antibacterial, tyrosinase inhibitory, antioxidant, and cytotoxic activities, with compound 2 showing exceptional potency as a multitarget agent. Anthraquinone substituent groups may offer the potential for the development of treatments. The derivatives were synthesized using the grindstone method, and their antibacterial, antioxidant, tyrosinase inhibitory, and cytotoxic activities were inspected. Molecular docking and molecular dynamics simulations were performed using compound 2 and kojic acid to validate the results and confirm the stability of the compounds.

Gaafar AR, Gurusamy R, Akbar I. Synthesis of anthraquinone-connected coumarin derivatives via grindstone method and their evaluation of antibacterial, antioxidant, tyrosinase inhibitory activities with molecular docking, and DFT calculation studies

Anthraquinones and coumarins have excellent pharmacological activities and are an important class of natural plant metabolites with various biological activities. In this study, anthraquinone-9,10-dione and coumarin derivatives were combined to develop a novel anthraquinone-connected coumarin-derivative sequence. The synthesised novel anthraquinone-connected coumarin derivatives (1a-t) were screened for in vitro antibacterial, antioxidant, and tyrosinase inhibitory activities. The antibacterial activities of the synthesised compounds (1a-t) were tested against both gram-positive and gram-negative bacteria. Specifically, compound 1t was more active against E. aerogenes than ciprofloxacin. With regard to antioxidant activity, compound 1o (50.68 % at 100 μg/mL) was highly active compared to the other compounds, whereas it was less active than the standard BHT (76.74 % at 100 μg/mL). In terms of compound 1r (9.31 ± 0.45 μg/mL) was highly active against tyrosinase inhibitory activity compared with kojic acid (10.42 ± 0.98 μg/mL). In the molecular docking study, compound 1r had a higher docking score (-8.8 kcal mol-1) than kojic acid (-1.7 kcal mol-1). DFT calculations were performed to determine the energy gap of highly active compound 1r (ΔE = 0.11) and weakly active compound 1a (ΔE = 0.12). In this study, we found that every molecule displayed significant antibacterial, antioxidant, and tyrosinase inhibitory properties. Based on these reports, compounds 1r and 1t may act as multi-target agents.

Synthesis, In Silico Studies, and Antioxidant and Tyrosinase Inhibitory Potential of 2-(Substituted Phenyl) Thiazolidine-4-Carboxamide Derivatives

Heterocyclic nuclei have shown a wide variety of biological activities, highlighting their importance in drug discovery. Derivatives of 2,4-subsituted thiazolidine have a structural similarity with the substrates of tyrosinase enzymes. Hence, they can be used as an inhibitor to compete against tyrosine in the biosynthesis of melanin. This study is focused on design, synthesis, biological activities, and in silico studies of thiazolidine derivatives substituted at positions 2 and 4. The synthesized compounds were evaluated to determine the antioxidant activity and tyrosine inhibitory potential using mushroom tyrosinase. The most potent tyrosinase enzyme inhibitor was compound 3c having IC₅₀ value 16.5 ± 0.37 µM, whereas compound 3d showed maximum antioxidant activity in a DPPH free radical scavenging assay (IC₅₀ = 18.17 µg/mL). Molecular docking studies were conducted using mushroom tyrosinase (PDB ID: 2Y9X) to analyze binding affinities and binding interactions of the protein-ligand complex. Docking results indicated that hydrogen bonds and hydrophobic interactions were mainly involved in the ligand and protein complex. The highest binding affinity was found to be -8.4 Kcal/mol. These results suggest that thiazolidine-4-carboxamide derivatives could serve as lead molecules for development of novel potential tyrosinase inhibitors.

One-Pot Synthesis, E-/Z-Equilibrium in Solution of 3-Hetarylaminomethylidenefuran-2(3H)-ones and the Way to Selective Synthesis of the E-Enamines

We describe a method to synthesize a new class of hetarylaminomethylidene derivatives of furan-2(3H)-ones. The method uses 5-(4-chlorophenyl)furan-2(3H)-one, triethyl orthoformate, and heterocyclic amines with different ring sizes and heteroatoms under refluxing in absolute isopropyl alcohol. The obtained enamines exist in an equilibrium of E- and Z-isomers, whose configurations relative to the double exocyclic C=C bond were confirmed with a set of NMR spectroscopy data. The E-/Z-equilibrium of the synthesized compounds is affected by the configuration of the intermediate, the volume of its substituents, the site of enolate attack, the presence of intramolecular interactions of amino components, the time of the transformation, the order of mixing of the initial reagents, and the use of polar solvents in the NMR experiment. The advantages of the method are that the reaction time is short, the product yield is high, and product purification is easy.

Preparation of Dihydronaphthofurans from α-Hydroxyl Ketones via a One-Pot Multicomponent Reaction Based on Heyns Rearrangement

Polysubstituted 1,2-dihydronaphthofurans were efficiently obtained in high yields and good diastereoselectivities with readily available substrates. The reaction proceeds smoothly via a series of tandem reactions, including Heyns rearrangement, oxidation, Friedel-Crafts reaction, and cyclization. The high stereoselectivity of the reaction is ascribed to the activation of the imine via an intramolecular hydrogen bond. Air is directly used as the oxidation medium, which makes the reaction safe and easy to perform. Moreover, the reaction features multiple components, which ensures the diversity of products.

[3 + 2] Coupling of Quinone Monoacetals with Vinyl Ethers Effected by Tetrabutylammonium Triflate: Regiocontrolled Synthesis of 2-Oxygenated Dihydrobenzofurans

The synthesis of 2-oxygenated dihydrobenzofurans involving the [3 + 2] coupling of quinone monoacetals with vinyl ethers has been realized by tetrabutylammonium triflate catalysis. The reaction involves a new activation method of the acetal moiety in quinone monoacetals under acid-free conditions affording the highly oxygenated dihydrobenzofurans. This new activation mode was achieved by using the triflate anion catalyst for stabilization of the highly reactive cationic intermediate.

Metal-Free Intramolecular [3+2] Cycloaddition of γ-Hydroxy Acetylenic Ketones with Alkynes for the Synthesis of Naphtho[1,2-c]furan-5-ones and Its Derivatization via a Selective C(sp2)-H Deuteration Reaction

A metal-free intramolecular [3+2] cycloaddtion has been achieved by treating benzene-linked propynol-ynes with AcOH/H₂O in a one-pot manner. The reaction provides greener, 100% atom-economic, highly regioselective, and more practical access to functionalized naphtho[1,2-c]furan-5-ones with valuable and versatile applications. The regioselective α-deuteration of naphtho[1,2-c]furan-5-ones has been also presented with excellent deuterium incorporation and chemical yields. Moreover, the fluorescent properties of naphtho[1,2-c]furan-5-one products have been investigated in solution.

Dopamine-Mediated Vanillin Multicomponent Derivative Synthesis via Grindstone Method: Application of Antioxidant, Anti-Tyrosinase, and Cytotoxic Activities

Purpose

This study aimed to determine the extent of contribution of dopamine to antioxidant and anti-tyrosinase activities, by dopamine addition to vanillin. This study achieved the synthesis of dopamine-associated vanillin Mannich base derivatives prepared via a one-step reaction involving a green chemistry approach, and investigation of antioxidant and anti-tyrosinase activities.

Methods

Novel one-pot synthesis of Mannich base dopamine-connected vanillin (1a-l) derivatives can be achieved via green chemistry without using a catalyst. Newly-prepared compounds were characterised with FTIR and NMR (¹H and ¹³C) spectra, mass spectra, and elemental analyses. In total, 12 compounds (1a-l) were synthesised and their antioxidant and anti-tyrosinase activities evaluated. Antioxidant activities of 2,2-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide (NO), hydrogen peroxide (H₂O₂), and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and diammonium assays, ABTS^•+ radical scavenging, and linoleic acid peroxidation were used to screen all synthesised compounds (1a-l) for anti-tyrosinase activities and cytotoxicity against MCF-7 and Vero cell lines;.

Results

The compound 1k inhibited (IC₅₀:11.02µg/mL) the DPPH-scavenging activity to a greater extent than the standard BHT (IC₅₀:25.17µg/mL), and showed high activity in H₂O₂ and NO scavenging assays. Compound 1e was more potent (96.21%) against ABTS and compound 1k was more potent (95.28%) against 2,2ʹ-azobis(2-amidinopropane)dihydrochloride antioxidant than the standard trolox. All synthesised compounds were screened for anti-tyrosinase inhibitory activity. Compound 1e had higher activity against tyrosinase (IC₅₀=10.63 µg/mL), than kojic acid (IC₅₀=21.52µg/mL), and was more cytotoxic (GI₅₀ 0.01µM) against MCF-7 cell line than the doxorubicin standard and other tested compounds.

Conclusion

In this study, all compounds were found to possess significant antioxidant and anti-tyrosinase activities. Compounds 1e and 1k performed well, compared with other compounds, in all assays. In addition, this study successfully identified several promising molecules that exhibited antioxidant and anti-tyrosinase activities.

Tel-Cu-NPs Catalyst: Synthesis of Naphtho[2,3-g]phthalazine Derivatives as Potential Inhibiters of Tyrosinase Enzymes and Their Investigation in Kinetic, Molecular Docking, and Cytotoxicity Studies

Novel one-pot synthesis naphtho[2,3-g]phthalazine (1a–1k) of Mannich base derivatives can be achieved via grindstone chemistry using a Tel-Cu-NPs (telmisartan-copper nanoparticles) catalyst. This method offers efficient mild reaction conditions and high yields. Tyrosinase inhibitory activity was evaluated for all synthesized compounds, along with analysis of kinetic behavior and molecular docking studies. The synthesized compound, 1c was (IC50 = 11.5 µM) more active than kojic acid (IC50 = 78.0 µM). Lineweaver Burk plots were used to analyze the kinetic behavior of the most active compound 1c, it was reversible and competitive behavior. Compound 1c and kojic acid occurred in the presence of 2-hydroxyketone, which has the same inhibitory mechanism. The molecular docking of compound 1c and the control kojic acid were docked against 2Y9X protein via the Schrodinger Suite. The compound 1c showed a respectable dock score (−5.6 kcal/mol) compared to kojic acid with a dock score of (−5.2 kcal/mol) in the 2Y9X protein. Cytotoxicity activity was also evaluated by using HepG2 (liver), MCF-7 (breast), and HeLa (cervical) cancer cell lines, and high activity for 1c (GI50 = 0.01, 0.03, and 0.04 µM, respectively) against all cell lines was found compared to standard and other compounds. Therefore, this study succeeded in testing a few promising molecules as potential antityrosinase agents.

Electroreductive Coupling of Phthalic Anhydrides with α,β-Unsaturated Carbonyl Compounds: Synthesis of 1,4-Dihydroxynaphthalenes

Electroreductive coupling of phthalic anhydrides with α,β-unsaturated carbonyl compounds in the presence of TMSCl and subsequent treatment with 1 M HCl gave 1,4-dihydroxynaphthalenes and 2-methyl-2,3-dihydronaphthalene-1,4-diones.

Dihydronaphthofurans: synthetic strategies and applications

Dihydronaphthofurans (DHNs) are an important class of arene ring-fused furans which are widely found in many natural and non-natural products and drug candidates with relevant biological and pharmacological activities. Furthermore, vinylidene-naphthofurans exhibit photochromic properties when exposed to UV or sun light at room temperature. For these reasons, a vast array of synthetic procedures for the preparation of dihydronaphthofurans including annulation of naphthols with various reagents, cycloaddition reactions ([3 + 2], [4 + 1] and Diels-Alder), intramolecular transannulation, Friedel-Crafts, Wittig, Claisen rearrangement, neophyl rearrangement and other reactions under various conditions have been developed over the past decades. This review aims to describe the different strategies developed so far for the synthesis of dihydronaphthofurans and their applications. After a brief introduction to the types of dihydronaphthofurans and their biological activities, the different synthetic approaches such as chemical, photochemical, and electrochemical, methods are described and organized on the basis of the catalysts and the other reagents employed in the syntheses. The subsequent section focuses on biological and pharmacological applications and photochromic properties of the target compounds.

Antibacterial and antioxidant activities for natural and synthetic dual-active compounds

Antimicrobial resistance is widely recognized as a grave threat to global health in the 21st century, since the past decades have seen a dramatic increase in human-pathogenic bacteria that are resistant to one or multiple antibiotics. New antimicrobial agents are urgently required, particularly in the treatment of chronic infections such as cystic fibrosis, often associated with persistent colonization by drug-resistant pathogens and epithelial damage by pulmonary oxidative stress. In such events, it would be favourable to find agents that could have antioxidant and antibacterial activities combined in one molecule. The discovery of compounds that can show a dual-target activity considerably increased in the last years, reflecting the growing confidence that this new approach could lead to better therapeutic solutions for complex multigenic diseases. The aim of this review is to report those natural and synthetic compounds displaying significant antioxidant and antibacterial activities. In recent years there has been a growing attention on plant-derived antimicrobials as an alternative to antibiotics, for their efficacy and low tendency in developing bacterial resistance. Moreover, it was found that some natural products could enhance the activity of common antibiotics displaying a synergistic effect. We then report some selected synthetic compounds with an in-built capacity to act on two targets or with the combination in a single structure of two pharmacophores with antioxidant and antibacterial activities. Recent literature instances were screened and the most promising examples of dual-active antibacterial-antioxidant molecules were highlighted.

Biochemical fingerprint and pharmacological applications of Barleria noctiflora L.f. leaves

Background Antioxidant and antihistamine agents from Barleria noctiflora L.f. as natural source due to the existing modern medicine give various adverse effects to overcome these problems with natural products. MethodsB. noctiflora leaves extract was fractionated with column chromatography; the homogenized fractions were monitored with thin layer chromatography (TLC) and characterized by using UV-visible, FT-IR, 1H NMR, 13C NMR and mass spectrometry spectral studies. The volatile phytoconstituents of B. noctiflora extract were analysed by gas chromatography-mass spectrometry. Phytoconstituents from B. noctiflora leaves extract were screened for their antioxidant and antihistamine potential in vitro (2,2-diphenyl-1-picrylhydrazyl radical scavenging activity, 2,2'-azinobis-3-ethylbenzothiozoline-6-sulfonic acid radical decolouration assay, nitric oxide radical scavenging activity, superoxide radical scavenging activity and hydrogen peroxide radical scavenging activity) and in silico (molecular docking), respectively. Results Antioxidant and antihistamine barlerinoside has been isolated and characterized from the leaves of B. noctiflora L.f. Barlerinoside revealed their free-radical scavenging ability on OH-, OH•, NO-, O2- and H2O2 radicals and found high percentage inhibition against OH- radical at the IC50 value of 50.45±2.52  µg. The methanol (MeOH) extract of B. noctiflora leaves contains cyclotene; N,N-dimethylglycine; tetrahydrocyclopenta [1,3] dioxin-4-one; phenol, 2-methoxy-; benzofuran, 2-methyl-; 1,4:3,6-dianhydro-α-d-glucopyranose; 2-methoxy-4-vinylphenol; 1,3;2,5-dimethylene-l-rhamnitol; levoglucosan and bicyclo[2.2.2]oct-7-ene-2,5-dione as being the major compounds. Among phytoconstituents present in the extract, the hexestrol; 1,2-benzenedicarboxylic acid, bis(2-methylpropyl) ester; 1-(3,6,6-trimethyl-1,6,7,7a-tetrahydrocyclopenta[c]pyran-1-yl) ethanone; megastigmatrienone; furan interacted with histamine H1 receptor and bind at GLU-177 and ASP-178 with high binding energy score -13.95, -13.41, -12.56, -12.03, and -11.72 kcal/mol, respectively, and the expected hydrolysed products of compound-1a and compound-1b from barlerinoside showed -8.91 and -8.68 kcal/mol binding energy against the histamine H1 receptor. This showed that the active ligands exactly bind with active binding site of the protein. ConclusionsWe can conclude that isolated barlerinoside from B. noctflora L.f. has potent antioxidant activity against synthetic free radicals and antihistamine activity against histamine H1 receptor.

Improved TLC Bioautographic Assay for Qualitative and Quantitative Estimation of Tyrosinase Inhibitors in Natural Products

INTRODUCTION

TLC bioautography for tyrosinase inhibitors has made recent progress; however, an assay with a relative low consumption of enzyme and quantitative capability would greatly advance the efficacy of related TLC bioautographic assays.

OBJECTIVE

An improved TLC bioautographic assay for detecting tyrosinase inhibitors was developed and validated in this study.

METHODS

L-DOPA (better water-solubility than L-tyrosine) was used as the substrate instead of reported L-tyrosine. The effects of enzyme and substrate concentrations, reaction temperatures and times, and pH values of the reaction system as well as different plate types on the TLC bioautographic assay were optimised. The quantitative analysis was conducted by densitometric scanning of spot areas, and expressed as the relative tyrosinase inhibitory capacity (RTIC) using a positive control (kojic acid) equivalent.

RESULTS

The limit of detection (LOD) of this assay was 1.0 ng for kojic acid. This assay has acceptable accuracy (101.73-102.90%), intra- and inter-day, and intra- and inter-plate precisions [relative standard deviation (RSD), less than 7.0%], and ruggedness (RSD, less than 3.5%). The consumption of enzyme (75 U/mL) is relatively low. Two tyrosinase inhibitory compounds including naringenin and 1-O-β-D-glucopyranosyl-4-allylbenzene have been isolated from Rhodiola sacra guided by this TLC bioautographic assay.

CONCLUSION

Our improved assay is a relatively low-cost, sensitive, and quantitative method compared to the reported TLC bioautographic assays. Copyright © 2016 John Wiley & Sons, Ltd.

Luminescent closed shell nickel(ii) pyridyl-azo-oximates and the open shell anion radical congener: molecular and electronic structure, ligand redox behaviour and biological activity

Luminescent nickel(ii) complexes have been synthesized using redox-active azo-oximes. The superior π-acidity of the organic backbone is a key to the isolation of Ni(ii) anion radicals.

Molecular docking studies and biological evaluation of 1,3,4-thiadiazole derivatives bearing Schiff base moieties as tyrosinase inhibitors

1,3,4-Thiadiazole derivatives bearing Schiff base moieties were designed, synthesized, and their tyrosinase inhibitory activities were evaluated. Some compounds displayed potent tyrosinase inhibitory activities, especially, 4-(((5-mercapto-1,3,4-thiadiazol-2-yl)-imino)methyl)-2-methoxy-phenol (14) exhibited superior inhibitory effect to the other compounds with an IC₅₀ value of 0.036μM. The structure-activity relationships (SARs) were preliminarily discussed and docking studies showed compound 14 had strong binding affinity to mushroom tyrosinase. Hydroxy might be the active groups. The inhibition kinetics study revealed that compounds (13 and 14) inhibited tyrosinase by acting as uncompetitive inhibitors. The LD₅₀ value of the compound 14 was 5000mg/kg.

Transition-metal free thiocyanooxygenation of functionalized alkenes: facile routes to SCN-containing dihydrofurans and lactones

An efficient transition-metal free tandem cyclization of functionalized alkenes with thiocyanate salts has been developed under mild conditions. This protocol offers a simple, easy-to-handle, and atom-economical method for the synthesis of SCN-containing dihydrofurans and lactones with good to excellent yields.

Re2O7-catalyzed formal [3 + 2] cycloaddition for diverse naphtho[1,2-b]furan-3-carboxamides and their biological evaluation

Diverse naphtho[1,2-b]furan-3-carboxamide derivatives 12a-12q were synthesized in high yield via the novel Re2O7-catalyzed formal [3 + 2] cycloaddition of 1,4-naphthoquinones with β-ketoamides as the key step. This methodology offers several advantages, such as environmentally benign character, the use of a mild catalyst, high yields, and ease of handling. The synthesized compounds were screened for their tyrosinase inhibitory, antioxidant, and antibacterial activities. The results showed that compound 12c exhibited excellent tyrosinase inhibitory activity with an IC50 of 13.48 μg/mL, which is comparable to that of kojic acid (IC50 = 19.45 μg/mL). Compounds 12a, 12b, and 12i displayed moderate antioxidant activities in a DPPH assay. Compound 12m showed good activity against S. aureus (MIC = 16 μg/mL), and compound 12p was found to be active against E. coli (MIC = 16 μg/mL).