Hydroxylated Coumarin-Based Thiosemicarbazones as Dual Antityrosinase and Antioxidant Agents

Novel Aminocoumarin-Based Schiff Bases: High Antifungal Activity in Agriculture

Structural modification is an effective way to improve the antifungal activity of natural products and has been widely used in the development of novel fungicides. In this work, a series of aminocoumarin-based Schiff bases were synthesized and characterized by 1H-NMR, 13C NMR and HR-MS spectra. The in vitro inhibition activity of all compounds was tested against four phytopathogenic fungi (Alternaria solani, Fusarium oxysporum, Botrytis cinerea, and Alternaria alternata) using the mycelial growth rate method. The results showed that most of the target compounds exhibited significant antifungal activities. In particular, compounds 5b, 5c, 5d, 5h, 5n, 7c, 7n, and 7p exhibited more effective antifungal activity than commercially available fungicides, chlorothalonil and azoxystrobin. The structure-activity relationship revealed that the electron-withdrawing groups with more electronegativity introduced at the C-3 position were effective in improving the inhibitory activity and that halogenated benzaldehydes would be necessary in the preparation of Schiff bases. The compound 5n against Fusarium oxysporum (EC50=8.73 μg/mL) and the compound 7p against Alternaria alternata (EC50=26.25 μg/mL) were much better than the positive controls (chlorothalonil and azoxystrobin). Therefore, compounds 5n and 7p could serve as promising lead compounds for the development of novel broad-spectrum fungicides, which could be useful for applications in the agriculture.

Design, Synthesis, Structural Insights, Tyrosinase Inhibition, and Sun Protection Factor of New Thiosemicarbazone Derivatives

Tyrosinase, a key protein in the biosynthesis of melanin pigments, is crucial in determining skin pigmentation. Inhibiting tyrosinase activity is a promising approach for treating conditions related to excessive pigmentation. For the synthesis of more potent tyrosinase inhibitors, we combined two approaches, para-substitution and lipophilicity, to enhance the inhibitory properties of (E)-2-(4-hydroxybenzylidene)hydrazine-1-carbotiamide, whose enzyme inhibitory properties have been previously demonstrated. The newly synthesized compounds showed potent inhibition activity against tyrosinase in the micromolar concentration range. The synthesised compounds were up to 41 times more effective than kojic acid. In addition to this biological activity, all molecules were evaluated for their sun protection factor to determine their photoprotective effects. All the compounds showed higher efficacy than reference compounds, used as sunscreens in photoprotective preparations. All compounds were noncytotoxic at the concentration required to inhibit tyrosinase activity. With the aim of defining the potential binding modes and the kind of interactions between the studied molecules and the catalytic site of mushroom tyrosinase, molecular docking simulations were also performed.

Coumarin: A natural solution for alleviating inflammatory disorders

Coumarin, a naturally occurring compound found in various plants, has a rich history of use in traditional medicine. Recent research has highlighted its anti-inflammatory properties, positioning it as a promising candidate for treating inflammatory disorders such as rheumatoid arthritis, asthma, and inflammatory bowel disease. This narrative review aims to comprehensively summarize the current knowledge regarding coumarin's pharmacological effects in alleviating inflammatory conditions by analyzing preclinical and clinical studies. The review focuses on elucidating the mechanisms through which coumarin exerts its anti-inflammatory effects, including its antioxidant activity, inhibiting pro-inflammatory cytokine production, and modulation of immune cell functions. Additionally, the paper addresses potential limitations of using coumarin, such as concerns about toxicity at high doses or with prolonged use. Before widespread clinical application, further investigation is needed to fully understand coumarin's potential benefits and risks.

Computational studies of tyrosinase inhibitors

Computational studies have significantly advanced the understanding of tyrosinase (TYR) function, mechanism, and inhibition, accelerating the development of more effective and selective inhibitors. This chapter provides an overview of in silico studies on TYR inhibitors, emphasizing key inhibitory chemotypes and the main residues involved in ligand-target interactions. The chapter discusses tools applied in the context of TYR inhibitor development, e.g., structure-based virtual screening, molecular docking, artificial intelligence, and machine learning algorithms.

Design, synthesis, and in vitro and in silico study of 1-benzyl-indole hybrid thiosemicarbazones as competitive tyrosinase inhibitors

Developing new anti-tyrosinase drugs seems crucial for the medical and industrial fields since irregular melanin synthesis is linked to the resurgence of several skin conditions, including melanoma, and the browning of fruits and vegetables. A novel series of N-1 and C-3 substituted indole-based thiosemicarbazones 5(a-r) are synthesized and further analyzed for their inhibition potential against tyrosinase enzyme through in vitro assays. The synthesized compounds displayed very good to moderate inhibition with half maximal inhibitory concentration in the range of 12.40 ± 0.26 μM to 47.24 ± 1.27 μM. Among all the derivatives 5k displayed the highest inhibitory activity. According to SAR analysis, the derivatives with 4-substitution at the benzyl or phenyl ring of the thiosemicarbazones exhibited better inhibitory potential against tyrosinase. In silico analysis (including ADMET prediction and molecular docking) was conducted and compared with the standard drug (kojic acid). These findings may help the hunt for new melanogenesis inhibitors that the food and cosmetics industries may find valuable.

Organoruthenium metallocycle induced mutation in gld-1 tumor suppression gene in JK1466 strain and appreciable lifespan expansion

Four Ru(II) complexes (A2-A5) were synthesized from the reaction of coumarin Schiff base ligands (7da2-tsc, 7da3-mtsc, 7da4-etsc and 7da5-ptsc) with [RuHCl(CO)(PPh3)3]. The compounds were characterized by FT-IR, UV-Vis, 1H, 13C and 31P NMR, mass spectrometry and crystallographic analysis. Calf Thymus DNA (CT-DNA) binding studies revealed the intercalative mode of binding of the complexes with DNA. The results of Bovine serum albumin (BSA) binding studies established the interaction between BSA followed static quenching mechanism. The cytotoxic effects of the complexes and the ligands were evaluated against breast (MCF-7 and MDA-MB-231) and lung carcinoma cell lines (A549 and NCI-H460) using MTT assay. Complex A4 demonstrated potent cytotoxic effects on both breast and lung cancer cells. Furthermore, morphological observations and FACS analysis showed the decrease in cell density by complex A4 by induced morphological changes and apoptotic body formation and cell death in both breast and lung cancer cells. Moreover, the invertebrate model Caenorhabditis elegans was employed to assess the in vivo anticancer activity of compound A4. The findings indicated that the treatment with A4 reduced tumor development and significantly extended organismal lifespan by 64 % in the tumoral strain JK1466 without adversely affecting essential physiological functions of the worm. Additionally, A4 demonstrated an upregulation of two crucial antioxidant defense genes. Overall, these results suggested that the compound A4 can be a potential candidate with novel chemotherapeutic applications.

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.

Heterocyclic Compounds as Synthetic Tyrosinase Inhibitors: Recent Advances

Tyrosinase is a copper-containing enzyme which is widely distributed in nature (e.g., bacteria, mammals, fungi) and involved in two consecutive steps of melanin biosynthesis. In humans, an excessive production of melanin can determine hyperpigmentation disorders as well as neurodegenerative processes in Parkinson's disease. The development of molecules able to inhibit the high activity of the enzyme remain a current topic in medicinal chemistry, because the inhibitors reported so far present several side effects. Heterocycle-bearing molecules are largely diffuse in this sense. Due to their importance as biologically active compounds, we decided to report a comprehensive review of synthetic tyrosinase inhibitors possessing heterocyclic moieties reported within the last five years. For the reader's convenience, we classified them as inhibitors of mushroom tyrosinase (Agaricus bisporus) and human tyrosinase.

Antioxidant Activity of Coumarins and Their Metal Complexes

Ubiquitously present in plant life, coumarins, as a class of phenolic compounds, have multiple applications-in everyday life, in organic synthesis, in medicine and many others. Coumarins are well known for their broad spectrum of physiological effects. The specific structure of the coumarin scaffold involves a conjugated system with excellent charge and electron transport properties. The antioxidant activity of natural coumarins has been a subject of intense study for at least two decades. Significant research into the antioxidant behavior of natural/semi-synthetic coumarins and their complexes has been carried out and published in scientific literature. The authors of this review have noted that, during the past five years, research efforts seem to have been focused on the synthesis and examination of synthetic coumarin derivatives with the aim to produce potential drugs with enhanced, modified or entirely novel effects. As many pathologies are associated with oxidative stress, coumarin-based compounds could be excellent candidates for novel medicinal molecules. The present review aims to inform the reader on some prominent results from investigations into the antioxidant properties of novel coumarin compounds over the past five years.