Design, synthesis and bioevaluation of novel umbelliferone analogues as potential mushroom tyrosinase inhibitors

Recent advances in triazoles as tyrosinase inhibitors

The tyrosinase enzyme, which is widely found in microorganisms, animals and plants, has a significant position in melanogenesis, plays an important role in undesirable browning of fruits and vegetables, antibiotic resistance, skin pigment formation, sclerotization of cuticle, neurodegeneration, etc. Therefore, with the wide potential application fields of tyrosinase in food, agriculture, cosmetics and pharmaceutical industries, which has become the target enzyme for the development of therapeutic agents such as antibrowning, anticancer, antibacterial, skin whitening, insecticides, etc., a large number of synthetic tyrosinase inhibitors have been widely reported in recent years. The triazole ring, which has a broad spectrum of biological action, is of increasing interest in the synthesis of new tyrosinase inhibitors. In this review, tyrosinase inhibition effects, structure-activity relationships, enzyme inhibition kinetics and mechanisms of action of 1,2,3- or 1,2,4-triazole derivatives were investigated. The data gathered is anticipated to supply rational guidance and an influential strategy for the development of novel, potent and safe tyrosinase inhibitors for better practical application in the future.

Tyrosinase Inhibitors Naturally Present in Plants and Synthetic Modifications of These Natural Products as Anti-Melanogenic Agents: A Review

Tyrosinase is a key enzyme target to design new chemical ligands against melanogenesis. In the current review, different chemical derivatives are explored which have been used as anti-melanogenic compounds. These are different chemical compounds naturally present in plants and semi-synthetic and synthetic compounds inspired by these natural products, such as kojic acid produced by several species of fungi; arbutin-a glycosylated hydroquinone extracted from the bearberry plant; vanillin-a phenolic aldehyde extracted from the vanilla bean, etc. After enzyme inhibition screening, various chemical compounds showed different therapeutic effects as tyrosinase inhibitors with different values of the inhibition constant and IC₅₀. We show how appropriately designed scaffolds inspired by the structures of natural compounds are used to develop novel synthetic inhibitors. We review the results of numerous studies, which could lead to the development of effective anti-tyrosinase agents with increased efficiency and safety in the near future, with many applications in the food, pharmaceutical and cosmetics industries.

Identification of two novel thiazolidin-2-imines as tyrosinase inhibitors: synthesis, crystal structure, molecular docking and DFT studies

Various N- and S-containing 5-membered heterocycles such as imidazole-2-thiones, thiazolidinones and thiazolidin-2-imines are among the most eminent biologically active organic heterocycles and are present in many marketed drugs. In view of their synthetic and biological significance, an efficient synthesis of two novel thiazolidine-2-imines (4a-b) utilizing a three-component one-pot approach starting from an aldimine, an alkyne and isothiocyanates has been developed. The reaction proceeded via a 5-exo digonal (5-exo dig) cyclization of a propargyl thiourea, formed in situ in the presence of Zn^(II)-catalyst. The structures of the resulting products are elucidated by spectroscopic methods and X-ray crystallography. A DFT study explored the structural, thermodynamic and molecular electrostatic potential parameters for the compounds. The newly synthesized compounds (4a & 4b) were evaluated for the inhibition of tyrosinase both in vitro and in silico. The in vitro results revealed that the synthesized thiazolidine-2-imines (4a-b) showed good inhibition activity towards mushroom tyrosinase (IC₅₀ = 1.151 ± 1.25 and 2.079 ± 0.87 μM respectively) in comparison to the kojic acid standard (IC₅₀ = 16.031 ± 1.27 μM) a commonly used anti-pigment agent in plant and animal tissues. The experimental inhibition was further assessed by molecular docking studies between synthesized ligands and the human tyrosinase protein complex to investigate the intermolecular interactions responsible for tyrosinase inhibition activity.

Paving the way towards effective plant-based inhibitors of hyaluronidase and tyrosinase: a critical review on a structure-activity relationship

Human has used plants to treat many civilisation diseases for thousands of years. Examples include reserpine (hypertension therapy), digoxin (myocardial diseases), vinblastine and vincristine (cancers), and opioids (palliative treatment). Plants are a rich source of natural metabolites with multiple biological activities, and the use of modern approaches and tools allowed finally for more effective bioprospecting. The new phytochemicals are hyaluronidase (Hyal) inhibitors, which could serve as anti-cancer drugs, male contraceptives, and an antidote against venoms. In turn, tyrosinase inhibitors can be used in cosmetics/pharmaceuticals as whitening agents and to treat skin pigmentation disorders. However, the activity of these inhibitors is stricte dependent on their structure and the presence of the chemical groups, e.g. carbonyl or hydroxyl. This review aims to provide comprehensive and in-depth evidence related to the anti-tyrosinase and anti-Hyal activity of phytochemicals as well as confirming their efficiency and future perspectives.

Molecular Docking, Synthesis, and Tyrosinase Inhibition Activity of Acetophenone Amide: Potential Inhibitor of Melanogenesis

Tyrosinase and its related proteins are responsible for pigmentation disorders, and inhibiting tyrosinase is an established strategy to treat hyperpigmentation. The carbonyl scaffolds can be effective inhibitors of tyrosinase activity, and the fact that both benzoic and cinnamic acids are safe natural substances with such a scaffolded structure, it was speculated that hydroxyl-substituted benzoic and cinnamic acid derivatives may exhibit potent tyrosinase inhibitory activity. These moieties were incorporated into new chemotypes that displayed in vitro inhibitory effect against mushroom tyrosinase with a view to explore antimelanogenic ingredients. The most active compound, 2-((3-acetylphenyl)amino)-2-oxoethyl(E)-3-(2,4-dihydroxyphenyl)acrylate (5c), inhibited mushroom tyrosinase with an IC50 of $0.0020\pm 0.0002\mu \text{M}$ , while 2-((3-acetylphenyl)amino)-2-oxoethyl 2,4-dihydroxybenzoate (3c) had an IC50 of $27.35\pm 3.6\mu \text{M}$ in comparison to the positive control arbutin and kojic acid with a tyrosinase inhibitory activity of IC50 of $191.17\pm 5.5\mu \text{M}$ and IC50 of $16.69\pm 2.8\mu \text{M}$ , respectively. Analysis of enzyme kinetics revealed that 5c is a competitive and reversible inhibitor with dissociation constant (Ki) value 0.0072 μM. In silico docking studies with mushroom tyrosinase (PDB ID 2Y9X) predicted possible binding modes in the enzymatic pocket for these compounds. The orthohydroxyl of the cinnamic acid moiety of 5c is predicted to form hydrogen bond with the active site side chain carbonyl of Asn 260 (2.16 Å) closer to the catalytic site Cu ions. The acetyl carbonyl is picking up another hydrogen bond with Asn 81 (1.90 Å). The inhibitor 5c passed the panassay interference (PAINS) alerts. This study presents the potential of hydroxyl-substituted benzoic and cinnamic acids and could be beneficial for various cosmetic formulations.

Recent advances in the design and discovery of synthetic tyrosinase inhibitors

Tyrosinase is a copper-containing metalloenzyme that is responsible for the rate-limiting catalytic step in the melanin biosynthesis and enzymatic browning. As a promising target, tyrosinase inhibitors can be used as skin whitening agents and food preservatives, thus having broad potential in the fields of food, cosmetics, agriculture and medicine. From 2015 to 2020, numerous synthetic inhibitors of tyrosinase have been developed to overcome the challenges of low efficacy and side effects. This review summarizes the enzyme structure and biological functions of tyrosinase and demonstrates the recent advances of synthetic tyrosinase inhibitors from the perspective of medicinal chemistry, providing a better understanding of the catalytic mechanisms and more effective tyrosinase inhibitors.

Kojic acid-natural product conjugates as mushroom tyrosinase inhibitors

As part of our effort to develop potential tyrosinase inhibitors, we have conjugated the well-known tyrosinase inhibitor kojic acid (KA) with several phenolic natural products such as umbelliferone, sesamol, thymol, carvacrol, eugenol, isoeugenol, vanillin, isovanillin, and apocynin that some reports have shown their activity on tyrosinase enzyme. The designed compounds were synthesized using click reaction and 1,2,3-triazole formation. All compound showed potent anti-tyrosinase activity significantly higher than KA. The best activities were observed with apocynin and 4-coumarinol analogs (10c and 16c) displaying IC₅₀ values of 0.03 and 0.02 μM, respectively. The potency of 16c was >460-times more than that of KA. Cell-based assays against B16F10 and HFF cells revealed that the representative compounds can efficiently suppress the melanogenesis without significant toxicity on cells.

Phaeosphaones: Tyrosinase Inhibitory Thiodiketopiperazines from an Endophytic Phaeosphaeria fuckelii

Phaeosphaeria fuckelii, an endophytic fungus associated with the herbal medicine Phlomis umbrosa, produced four new thiodiketopiperazine alkaloids, phaeosphaones A-D (1-4), featuring an unusual β-(oxy)thiotryptophan motif, along with four known analogues, phaeosphaone E (5), chetoseminudin B (6), polanrazine B (7), and leptosin D (8). Their structures were elucidated by extensive spectroscopic data analysis, and their absolute configurations were determined by single-crystal X-ray diffraction and ECD calculations. Compounds 4, 6, and 8 were found to display mushroom tyrosinase inhibitory activity with IC₅₀ values of 33.2 ± 0.2, 31.7 ± 0.2, and 28.4 ± 0.2 μM, respectively, more potent than that of the positive control, kojic acid (IC₅₀ = 40.4 ± 0.1 μM). A molecular-docking study disclosed the π-π stacking interaction between the indole moiety of 8 and the His243 residue of tyrosinase.

Synthesis of pyrano[2,3-f]chromen-2-ones vs. pyrano[3,2-g]chromen-2-ones through site controlled gold-catalyzed annulations

Regioselective access to 10-substituted-2H,8H-pyrano[2,3-f]chromen-2-ones through the gold-catalyzed intramolecular hydroarylation of readily available 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one derivatives at their C-8 congested position was investigated by tuning the electronic and steric properties of the ligand on the gold complex. On the other hand, the combination of the JohnPhosAu(MeCN)SbF6 catalyzed intramolecular hydroarylation of 8-iodo-7-(prop-2-yn-1-yloxy)-2H-chromen-2-one derivatives followed by selective palladium/formate C-I reduction allows for the exclusive formation of 2H,8H-pyrano[3,2-g]chromen-2-one regioisomers. The development of these two protocols provides versatile synthetic tools required for exploring the biological activities of these new pyranocoumarin derivatives.

Synthesis, computational studies, tyrosinase inhibitory kinetics and antimelanogenic activity of hydroxy substituted 2-[(4-acetylphenyl)amino]-2-oxoethyl derivatives

The over expression of melanogenic enzymes like tyrosinase caused many hyperpigmentaion disorders. The present work describes the synthesis of hydroxy substituted 2-[(4-acetylphenyl)amino]-2-oxoethyl derivatives 3a-e and 5a-e as antimelanogenic agents. The tyrosinase inhibitory activity of synthesized derivatives 3a-e and 5a-e was determined and it was found that derivative 5c possesses excellent activity with IC50 = 0.0089 µM compared to standard kojic acid (IC50 = 16.69 µM). The presence of hydroxyl groups at the ortho and the para position of cinnamic acid phenyl ring in compound 5c plays a vital role in tyrosinase inhibitory activity. The compound 5d also exhibited good activity (IC50 = 8.26 µM) compared to standard kojic acid. The enzyme inhibitory kinetics results showed that compound 5c is a competitive inhibitor while 5d is a mixed-type inhibitor. The mode of binding for compounds 5c and 5d with tyrosinase enzyme was also assessed and it was found that both derivatives irreversibly bind with target enzyme. The molecular docking and molecular dynamic simulation studies were also performed to find the position of attachment of synthesized compounds at tyrosinase enzyme (PDB ID 2Y9X). The results showed that all of the synthesized compounds bind well with the active binding sites and most potent derivative 5c formed stable complex with target protein. The cytotoxicity results showed that compound 5c is safe at a dose of 12 µg/mL against murine melanoma (B16F10) cells. The same dose of 5c was selected to determine antimelanogenic activity; the results showed that it produced antimelenogenic effects in murine melanoma (B16F10) cells. Based on our investigations, it was proposed that compound 5c may serve as a lead structure to design more potent antimelanogenic agents.

A comprehensive review on tyrosinase inhibitors

Tyrosinase is a multi-copper enzyme which is widely distributed in different organisms and plays an important role in the melanogenesis and enzymatic browning. Therefore, its inhibitors can be attractive in cosmetics and medicinal industries as depigmentation agents and also in food and agriculture industries as antibrowning compounds. For this purpose, many natural, semi-synthetic and synthetic inhibitors have been developed by different screening methods to date. This review has focused on the tyrosinase inhibitors discovered from all sources and biochemically characterised in the last four decades.

Hydroxyl substituted benzoic acid/cinnamic acid derivatives: Tyrosinase inhibitory kinetics, anti-melanogenic activity and molecular docking studies

The inhibition of tyrosinase is an established strategy for treating hyperpigmentation. Our previous findings demonstrated that cinnamic acid and benzoic acid scaffolds can be effective tyrosinase inhibitors with low toxicity. The hydroxyl substituted benzoic and cinnamic acid moieties of these precursors were incorporated into new chemotypes that displayed in vitro inhibitory effect against mushroom tyrosinase. The most active compound, (2-(3-methoxyphenoxy)-2-oxoethyl (E)-3-(4-hydroxyphenyl) acrylate) 6c, inhibited tyrosinase with an IC₅₀ of 5.7 µM, while (2-(3-methoxyphenoxy)-2-oxoethyl 2, 4-dihydroxybenzoate) 4d had an IC₅₀ of 23.8 µM. In comparison, the positive control, kojic acid showed tyrosinase inhibition with an IC₅₀ = 16.7 µM. Analysis of enzyme kinetics revealed that 6c and 4d displayed noncompetitive reversible inhibition of the second tyrosinase enzymatic reaction with K_i values of 11 µM and 130 µM respectively. In silico docking studies with mushroom tyrosinase (PDB ID 2Y9X) predicted possible binding modes in the catalytic site for these active compounds. The phenolic para-hydroxy group of the most active compound 6c is predicted to interact with the catalytic site Cu⁺⁺ ion. The methoxy part of this compound is predicted to form a hydrogen bond with Arg 268. Compound 6c had no observable toxic effects on cell morphology or cell viability at the highest tested concentration of 91.4 µM. When dosed at 91.4 µM onto B16F10 melanoma cells in vitro6c showed anti-melanogenic effects equivalent to kojic acid at 880 µM. 6c displayed no PAINS (pan-assay interference compounds) alerts. Our results show that compound 6c is a more potent tyrosinase inhibitor than kojic acid and is a candidate for further development. Our exposition of the details of the interactions between 6c and the catalytic pocket of tyrosinase provides a basis for rational design of additional potent inhibitors of tyrosinase, built on the cinnamic acid scaffold.

Natural and Bioinspired Phenolic Compounds as Tyrosinase Inhibitors for the Treatment of Skin Hyperpigmentation: Recent Advances

One of the most common approaches for control of skin pigmentation involves the inhibition of tyrosinase, a copper-containing enzyme which catalyzes the key steps of melanogenesis. This review focuses on the tyrosinase inhibition properties of a series of natural and synthetic, bioinspired phenolic compounds that have appeared in the literature in the last five years. Both mushroom and human tyrosinase inhibitors have been considered. Among the first class, flavonoids, in particular chalcones, occupy a prominent role as natural inhibitors, followed by hydroxystilbenes (mainly resveratrol derivatives). A series of more complex phenolic compounds from a variety of sources, first of all belonging to the Moraceae family, have also been described as potent tyrosinase inhibitors. As to the synthetic compounds, hydroxycinnamic acids and chalcones again appear as the most exploited scaffolds. Several inhibition mechanisms have been reported for the described inhibitors, pointing to copper chelating and/or hydrophobic moieties as key structural requirements to achieve good inhibition properties. Emerging trends in the search for novel skin depigmenting agents, including the development of assays that could distinguish between inhibitors and potentially toxic substrates of the enzyme as well as of formulations aimed at improving the bioavailability and hence the effectiveness of well-known inhibitors, have also been addressed.

Characterizing Tyrosinase Modulators from the Roots of Angelica keiskei Using Tyrosinase Inhibition Assay and UPLC-MS/MS as the Combinatorial Novel Approach

In this study, an in vitro tyrosinase inhibition assay in combination with ultra performance liquid chromatography-orbitrap mass spectrometry (UPLC-orbitrap-MS) was developed for the rapid screening and identification of tyrosinase modulators from roots of Angelica keiskei. Of the 15 candidates considered, nine chalcones, xanthoangelols (1), B (2), D (3), E (4), G (5), H (6), 4-hydroxyderricin (7), xanthokeismin B (8) and (2E)-1-[4-hydroxy-2-(2-hydroxy-2-propanyl)-2,3-dihydro-1-benzofuran-7-yl]-3-(4-hydroxyphenyl)-2-propen-1-one (9), five coumarins, umbelliferone (10), selinidin (11), isopimpinellin (12), phellopterin (13) and xanthyletin (14), and one other compound, ashitabaol A (15), were distinguished between the test samples and the controls with statistical significance, and the structure of each compound was determined by comparing with in-house standards and the literature. Among these, six compounds, xanthoangelol (1), xanthoangelol D (3), xanthoangelol H (6), 4-hydroxyderricin (7), laserpitin (16) and isolaserpitin (17), were isolated from roots of A. keiskei. Of the compounds isolated, compounds 1, 7 and 16 were subjected to tyrosinase inhibitory assay, and the IC₅₀ values were 15.87 ± 1.21, 60.14 ± 2.29 and >100 μM, respectively. The present study indicated that the combination of in vitro tyrosinase inhibition assay coupled with UPLC-MS/MS could be widely applied to the rapid screening of active substances from various natural resources.

Natural options for management of melasma, a review

A blemish free, even-toned skin is universally associated with healthy skin. This reasoning makes people desire to have a flawless skin. Melanin is a naturally occurring pigment in humans. This pigment is responsible for skin, hair, and eye color, therefore determines our race and phenotypic appearance. On darker skin types, it is common that melanin production processes malfunctions. These malfunctions often lead to overproduction and secretion of melanin. As a result, unwanted pigmentary problems such melasma occur. Due to unknown etiology and its recurrence in nature, melasma is challenging to treat. The current available melasma treatment options often produce undesired side effects and suboptimum results. First-line topical treatments usually involve hydroquinone or topical steroids. Apart from the irritant reactions, this treatment mode is not suitable for all skin types. Skin care specialists are in search of an effective long-term cosmetics and cosmeceuticals to address hypermelanosis problems. Understanding of naturally occurring depigmenting agents provides an opportunity for more effective ways to manage melasma in all skin types. This review considers the benefits of naturally occurring ingredients which could help address skin pigmentation problems and broaden the choice for skin-lightening treatments.

Skin whitening agents: medicinal chemistry perspective of tyrosinase inhibitors

Melanogenesis is a process to synthesize melanin, which is a primary responsible for the pigmentation of human skin, eye and hair. Although numerous enzymatic catalyzed and chemical reactions are involved in melanogenesis process, the enzymes such as tyrosinase and tyrosinase-related protein-1 (TRP-1) and TRP-2 played a major role in melanin synthesis. Specifically, tyrosinase is a key enzyme, which catalyzes a rate-limiting step of the melanin synthesis, and the downregulation of tyrosinase is the most prominent approach for the development of melanogenesis inhibitors. Therefore, numerous inhibitors that target tyrosinase have been developed in recent years. The review focuses on the recent discovery of tyrosinase inhibitors that are directly involved in the inhibition of tyrosinase catalytic activity and functionality from all sources, including laboratory synthetic methods, natural products, virtual screening and structure-based molecular docking studies.

Potent anti-melanogenic activity and favorable toxicity profile of selected 4-phenyl hydroxycoumarins in the zebrafish model and the computational molecular modeling studies

7-Hydroxy-4-phenylcoumarin (7C) and 5,7-dihydroxy-4-phenylcoumarin (5,7C) have been evaluated as potential anti-melanogenic agents in the zebrafish (Danio rerio) model in comparison to commercially utilized depigmenting agents hydroquinone and kojic acid. 7C and 5,7C decreased the body pigmentation at 5 µg/mL, while did not affect the embryos development and survival at doses ≤50 µg/mL and ≤25 µg/mL. Unlike hydroquinone and kojic acid, 4-phenyl hydroxycoumarins were no melanocytotoxic, showed no cardiotoxic side effects, neither caused neutropenia in zebrafish embryos, suggesting these compounds may present novel skin-whitening agents with improved pharmacological properties. Inhibition of tyrosinase was identified as the possible mode of anti-melanogenic action. Molecular docking studies using the homology model of human tyrosinase as well as adenylate cyclase revealed excellent correlation with experimentally obtained results.

Development of highly potent melanogenesis inhibitor by in vitro, in vivo and computational studies

The present work describes the synthesis of few hydroxylated amide derivatives as melanogenesis inhibitors. In vitro, in vivo and computational studies proved that compound 6d is a highly potent melanogenesis inhibitor compared to standard kojic acid. The title amides 4a–e and 6a–e were synthesized following simple reaction routes with excellent yields. Most of the synthesized compounds exhibited good mushroom tyrosinase inhibitory activity, but compound 6d showed excellent activity (IC₅₀ 0.15 µM) compared to standard kojic acid (IC₅₀ 16.69 µM). Lineweaver–Burk plots were used for the determination of kinetic mechanism, and it was found that compounds 4c and 6d showed non-competitive inhibition while 6a and 6b showed mixed-type inhibition. The kinetic mechanism further revealed that compound 6d formed irreversible complex with the target enzyme tyrosinase. The Ki values determined for compounds 4c, 6a, 6b and 6d are 0.188, 0.84, 2.20 and 0.217 µM respectively. Results of human tyrosinase inhibitory activity in A375 human melanoma cells showed that compound 6d exhibited 91.9% inhibi-tory activity at a concentration of 50 µg/mL. In vivo cytotoxicity evaluation of compound 6d in zebrafish embryos showed that it is non-toxic to zebrafish. Melanin depigmentation assay performed in zebrafish indicated that compound 6d possessed greater potential in decreasing melanin contents compared to kojic acid at the same concentration. Computational studies also supported the wet lab findings as compound 6d showed a highest binding affinity with the target protein (PDBID: 2Y9X) with a binding energy value of −7.90 kcal/mol. Molecular dynamic simulation studies also proved that amide 6d formed the most stable complex with tyrosinase. Based upon our in vitro, in vivo and computational studies, we propose that compound 6d is a promising candidate for the development of safe cosmetic agent.

Carvacrol derivatives as mushroom tyrosinase inhibitors; synthesis, kinetics mechanism and molecular docking studies

The present work describesthe development of highly potent mushroom tyrosinase inhibitor better than the standard kojic acid. Carvacrol derivatives 4a-f and 6a-d having substituted benzoic acid and cinnamic acidresidues were synthesized with the aim to possess potent tyrosinase inhibitory activity.The structures of the synthesized compounds were ascertained by their spectroscopic data (FTIR, ¹HNMR, ¹³CNMR and Mass Spectroscopy).Mushroom tyrosinase inhibitory activity of synthesized compounds was determined and it was found that one of the derivative 6c possess higher activity (IC₅₀ 0.0167μM) than standard kojic acid (IC₅₀ 16.69μM). The derivatives 4c and 6b also showed good tyrosinase inhibitory activity with (IC₅₀ 16.69μM) and (IC₅₀ 16.69μM) respectively.Lineweaver—Burk and Dixon plots were used for the determination of kinetic mechanism of the compounds 4c and 6b and 6c. The kinetic analysis revealed that compounds 4c and 6b showed mixed-type inhibition while 6c is a non-competitive inhibitor having Ki values19 μM, 10 μM, and 0.05 μMrespectively. The enzyme inhibitory kinetics further showed thatcompounds 6b and 6c formed irreversible enzyme inhibitor complex while 4c bind reversibly with mushroom tyrosinase.The docking studies showed that compound 6c have maximum binding affinity against mushroom tyrosinase (PDBID: 2Y9X) with binding energy value (-7.90 kcal/mol) as compared to others.The 2-hydroxy group in compound 6c interacts with amino acid HIS85 which is present in active binding site. The wet lab results are in good agreement with the dry lab findings.Based upon our investigation we may propose that the compound 6c is promising candidate for the development of safe cosmetic agent.

Antifungal activity of umbelliferone derivatives: Synthesis and structure-activity relationships

Umbelliferone was an important allelochemical with a wide spectrum bioactivity. In our previous study, C7 hydroxy in the backbone of umbelliferone was identified to be responsible for its phytotoxicity and the targeted modification of the above site could lead to the phytotoxicity loss. In view of this, a series of hydroxycoumarins and C7 O-substituted umbelliferone derivatives were efficiently synthesized to evaluate their antifungal activity against four phytopathogenic fungi. Most of them, as we predicted, exhibited improved fungicidal activity. The phytotoxicity of effective compounds was also assayed by Lactuca sativa to investigate their side effects on plant growth. Compounds 9 and 17 were identified to show strong antifungal activity with low phytotoxicity. A brief investigation on structure-activity relationships revealed that the modification at the C7 hydroxy of umbelliferone could be a promising way to enhance the antifungal activity with decreasing the phytotoxicity.

Synthesis of chiral pyrazolo[4,3-e][1,2,4]triazine sulfonamides with tyrosinase and urease inhibitory activity

A new series of sulfonamide derivatives of pyrazolo[4,3-e][1,2,4]triazine with chiral amino group has been synthesized and characterized. The compounds were tested for their tyrosinase and urease inhibitory activity. Evaluation of prepared derivatives demonstrated that compounds (8b) and (8j) are most potent mushroom tyrosinase inhibitors whereas all of the obtained compounds showed higher urease inhibitory activity than the standard thiourea. The compounds (8a), (8f) and (8i) exhibited excellent enzyme inhibitory activity with IC₅₀ 0.037, 0.044 and 0.042 μM, respectively, while IC₅₀ of thiourea is 20.9 μM.