Structure⁻Activity Relationship of the Tyrosinase Inhibitors Kuwanon G, Mulberrofuran G, and Albanol B from Morus Species: A Kinetics and Molecular Docking Study

Anilino-1,4-naphthoquinones as potent mushroom tyrosinase inhibitors: in vitro and in silico studies

Tyrosinase, a pivotal enzyme in melanin synthesis, is a primary target for the development of depigmenting agents. In this work, in vitro and in silico techniques were employed to identify novel tyrosinase inhibitors from a set of 12 anilino-1,4-naphthoquinone derivatives. Results from the mushroom tyrosinase activity assay indicated that, among the 12 derivatives, three compounds (1, 5, and 10) demonstrated the most significant inhibitory activity against mushroom tyrosinase, surpassing the effectiveness of the kojic acid. Molecular docking revealed that all studied derivatives interacted with copper ions and amino acid residues at the enzyme active site. Molecular dynamics simulations provided insights into the stability of enzyme-inhibitor complexes, in which compounds 1, 5, and particularly 10 displayed greater stability, atomic contacts, and structural compactness than kojic acid. Drug likeness prediction further strengthens the potential of anilino-1,4-naphthoquinones as promising candidates for the development of novel tyrosinase inhibitors for the treatment of hyperpigmentation disorders.

Chemistry, bioactivities, structure-activity relationship, biosynthesis and metabolism of prenylated flavonoids in Moraceae plants

Plants from Moraceae are globally popular as they represent a valuable resource with wide applications in food, health-care products, and other fields. Prenylated flavonoids are important active components in Moraceae. These compounds share a flavonoid skeleton with prenylated side chain, mostly in the form of single or multiple isoprenyl substituents and benzodimethylfuran structures. So far, nearly 400 prenylated flavonoids have been found in Moraceae, especially a large number of Diels-Alder adducts, which are characteristic components of this family. Due to their distinctive structures, diverse pharmacological properties and interesting synthesis processes, these compounds have attracted considerable attention from scientists. Herein, we review the advances in the structural characteristics, bioactivities, structure-activity relationships, biosynthesis strategies and in vivo metabolism of prenylated flavonoids in Moraceae plants, aiming at strengthening research efforts and utilization toward the great untapped potential of these unique constituents in human health.

Structurally Diverse Stilbenoids as Potent α-Glucosidase Inhibitors with Antidiabetic Effect from Morus alba

Fifteen stilbenoid derivatives, including five previously undescribed ones (albaphenols A-E, 1-5) with diverse scaffolds, were obtained from the well-known agricultural economic tree Morus alba. Their structures, including absolute stereochemistries, were fully characterized by detailed interpretation of spectroscopic data and quantum chemical computational analyses of nuclear magnetic resonance (NMR) and electric circular dichroism (ECD). Albaphenol A (1) features an unprecedented rearranged carbon skeleton incorporating a novel 2-oxaspiro[bicyclo[3.2.1]octane-6,3'-furan] motif; albaphenol C (3) is likely derived from a cometabolite through an interesting intramolecular transesterification reaction; and albaphenol E (5) bears a cleavage-reconnection scaffold via a dioxane ring. All of the compounds exhibited significant inhibition against the diabetic target α-glucosidase, with low to submicromole IC50 values (0.70-8.27 μM), and the binding modes of selected molecules with the enzyme were further investigated by fluorescence quenching, kinetics, and molecular docking experiments. The antidiabetic effect of the most active and abundant mulberrofuran G (6) was further assessed in vivo in diabetic mice, revealing potent antihyperglycemic activity and comparable antidiabetic efficacy to the clinical drug acarbose.

Comprehensive overview of different medicinal parts from Morus alba L.: chemical compositions and pharmacological activities

Morus alba L., a common traditional Chinese medicine (TCM) with a centuries-old medicinal history, owned various medicinal parts like Mori folium, Mori ramulus, Mori cortex and Mori fructus. Different medical parts exhibit distinct modern pharmacological effects. Mori folium exhibited analgesic, anti-inflammatory, hypoglycemic action and lipid-regulation effects. Mori ramulus owned anti-bacterial, anti-asthmatic and diuretic activities. Mori cortex showed counteraction action of pain, inflammatory, bacterial, and platelet aggregation. Mori fructus could decompose fat, lower blood lipids and prevent vascular sclerosis. The main chemical components in Morus alba L. covered flavonoids, phenolic compounds, alkaloids, and amino acids. This article comprehensively analyzed the recent literature related to chemical components and pharmacological actions of M. alba L., summarizing 198 of ingredients and described the modern activities of different extracts and the bioactive constituents in the four parts from M. alba L. These results fully demonstrated the medicinal value of M. alba L., provided valuable references for further comprehensive development, and layed the foundation for the utilization of M. alba L.

The Protective Effect of Sanggenol L Against DMBA-induced Hamster Buccal Pouch Carcinogenesis Induces Apoptosis and Inhibits Cell Proliferative Signalling Pathway

BACKGROUND

Oral squamous cell carcinoma (OSCC) has a poor prognosis when treated with surgery and chemotherapy. Therefore, a new therapy and preventative strategy for OSCC and its underlying mechanisms are desperately needed. The purpose of this study was to examine the chemopreventive effects of sanggenol L on oral squamous cell carcinoma (OSCC). The research focused on molecular signalling pathways in 7,12-dimethylbenz(a)anthracene (DMBA)-induced hamster buccal pouch (HBP) carcinogenesis.

AIM

The purpose of this study was to look at the biochemical and chemopreventive effects of sanggenol L on 7,12-dimethylbenz(a)anthracene (DMBA)-induced HBP (hamster buccal pouch) carcinogenesis via cell proliferation and the apoptotic pathway.

METHODS

After developing squamous cell carcinoma, oral tumours continued to progress leftward into the pouch 3 times per week for 10 weeks while being exposed to 0.5 % reactive DMBA three times per week. Tumour growth was caused by biochemical abnormalities that induced inflammation, increased cell proliferation, and decreased apoptosis.

RESULTS

Oral sanggenol L (10 mg/kg bw) supplementation with cancer-induced model DMBApainted hamsters prevented tumour occurrences, improved biochemistry, inhibited inflammatory markers, decreased cell proliferation marker expression of tumour necrosis factor-alpha (TNF- α), nuclear factor (NF-κB), cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and induced apoptosis.

CONCLUSION

Sanggenol L could be developed into a new medicine for the treatment of oral carcinogenesis.

Anti-Browning Effect of 2-Mercaptobenzo[d]imidazole Analogs with Antioxidant Activity on Freshly-Cut Apple Slices and Their Highly Potent Tyrosinase Inhibitory Activity

Ten 2-mercaptobenzimidazole (2-MBI) analogs were synthesized as potential tyrosinase inhibitors because mercapto-containing compounds can bind to copper ions at the active site of tyrosinase to inhibit enzyme activity. Nine 2-MBI analogs showed sub-micromolar IC50 values for mushroom tyrosinase monophenolase activity; analog 4 was 280-fold more potent than kojic acid, and in diphenolase activity, 6 was 970-fold more potent than kojic acid. The inhibition mode of the 2-MBI analogs was investigated using kinetic studies supported by docking simulations. Benzimidazoles without the 2-mercapto substituent of the 2-MBI analogs lost their tyrosinase inhibitory activity, implying that the 2-mercapto substituent plays an important role in tyrosinase inhibition. The 2-MBI analogs exerted potent antioxidant effects against 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and reactive oxygen species (ROS). The results obtained from apple slices and human embryonic kidney cells (HEK-293) suggest that most 2-MBI analogs are sufficiently safe candidates to delay the browning of apple slices effectively. Thus, these results support the potential use of 2-MBI analogs as anti-browning agents in foods such as mushrooms, vegetables, and fruits.

Naturally-Occurring Tyrosinase Inhibitors Classified by Enzyme Kinetics and Copper Chelation

Currently, there are three major assaying methods used to validate in vitro whitening activity from natural products: methods using mushroom tyrosinase, human tyrosinase, and dopachrome tautomerase (or tyrosinase-related protein-2, TRP-2). Whitening agent development consists of two ways, melanin synthesis inhibition in melanocytes and downregulation of melanocyte stimulation. For melanin levels, the melanocyte cell line has been used to examine melanin synthesis with the expression levels of TRP-1 and TRP-2. The proliferation of epidermal surfaced cells and melanocytes is stimulated by cellular signaling receptors, factors, or mediators including endothelin-1, α-melanocyte-stimulating hormone, nitric oxide, histamine, paired box 3, microphthalmia-associated transcription factor, pyrimidine dimer, ceramide, stem cell factors, melanocortin-1 receptor, and cAMP. In addition, the promoter region of melanin synthetic genes including tyrosinase is upregulated by melanocyte-specific transcription factors. Thus, the inhibition of growth and melanin synthesis in gene expression levels represents a whitening research method that serves as an alternative to tyrosinase inhibition. Many researchers have recently presented the bioactivity-guided fractionation, discovery, purification, and identification of whitening agents. Melanogenesis inhibition can be obtained using three different methods: tyrosinase inhibition, copper chelation, and melanin-related protein downregulation. There are currently four different types of inhibitors characterized based on their enzyme inhibition mechanisms: competitive, uncompetitive, competitive/uncompetitive mixed-type, and noncompetitive inhibitors. Reversible inhibitor types act as suicide substrates, where traditional inhibitors are classified as inactivators and reversible inhibitors based on the molecule-recognizing properties of the enzyme. In a minor role, transcription factors can also be downregulated by inhibitors. Currently, the active site copper iron-binding inhibitors such as kojic acid and chalcone exhibit tyrosinase inhibitory activity. Because the tyrosinase catalysis site structure is important for the mechanism determination of tyrosinase inhibitors, understanding the enzyme recognition and inhibitory mechanism of inhibitors is essential for the new development of tyrosinase inhibitors. The present review intends to classify current natural products identified by means of enzyme kinetics and copper chelation to exhibit tyrosinase enzyme inhibition.

An Arylbenzofuran, Stilbene Dimers, and Prenylated Diels–Alder Adducts as Potent Diabetic Inhibitors from Morus bombycis Leaves

Morus bombycis has a long history of usage as a treatment for metabolic diseases, especially, diabetes mellitus (DM). Thus, we aimed to isolate and evaluate bioactive constituents derived from M. bombycis leaves for the treatment of DM. According to bioassay-guided isolation by column chromatography, eight compounds were obtained from M. bombycis leaves: two phenolic compounds, p-coumaric acid (1) and chlorogenic acid methyl ester (2), one stilbene, oxyresveratrol (3), two stilbene dimers, macrourin B (4) and austrafuran C (6), one 2-arylbenzofuran, moracin M (5), and two Diels–Alder type adducts, mulberrofuran F (7) and chalcomoracin (8). Among the eight isolated compounds, the anti-DM activity of 3–8 (which possess chemotaxonomic significance in Morus species) was evaluated by inhibition of α-glucosidase, protein tyrosine phosphatase 1B (PTP1B), human recombinant aldose reductase (HRAR), and advanced glycation end-product (AGE) formation as well as by scavenging peroxynitrite (ONOO−), which are crucial therapeutic targets of DM and its complications. Compounds 4 and 6–8 significantly inhibited α-glucosidase, PTP1B, and HRAR enzymes with mixed-type and non-competitive-type inhibition modes. Furthermore, the four compounds had low negative binding energies in both enzymes according to molecular docking simulation, and compounds 3–8 exhibited strong antioxidant capacity by inhibiting AGE formation and ONOO− scavenging. Overall results suggested that the most active stilbene-dimer-type compounds (4 and 6) along with Diels–Alder type adducts (7 and 8) could be promising therapeutic and preventive resources against DM and have the potential to be used as antioxidants, anti-diabetic agents, and anti-diabetic complication agents.

Structure-Based Virtual Screening of Furan-1,3,4-Oxadiazole Tethered N-phenylacetamide Derivatives as Novel Class of hTYR and hTYRP1 Inhibitors

Human tyrosinase (hTYR) is a key and rate-limiting enzyme along with human tyrosinase-related protein-1 (hTYRP1), which are among the most prominent targets of inhibiting hyper pigmentation and melanoma skin cancer. In the current in-silico computer-aided drug design (CADD) study, the structure-based screening of sixteen furan-1,3,4-oxadiazole tethered N-phenylacetamide structural motifs BF1-BF16 was carried out to assess their potential as hTYR and hTYRP1 inhibitors. The results revealed that the structural motifs BF1-BF16 showed higher binding affinities towards hTYR and hTYRP1 than the standard inhibitor kojic acid. The most bioactive lead furan-1,3,4-oxadiazoles BF4 and BF5 displayed stronger binding in affinities (-11.50 kcal/mol and -13.30 kcal/mol) than the standard drug kojic acid against hTYRP1 and hTYR enzymes, respectively. These were further confirmed by MM-GBSA and MM-PBSA binding energy computations. The stability studies involving the molecular dynamics simulations also provided stability insights into the binding of these compounds with the target enzymes, wherein it was found that they remain stable in the active sites during the 100 ns virtual simulation time. Moreover, the ADMET, as well as the medicinal properties of these novel furan-1,3,4-oxadiazole tethered N-phenylacetamide structural hybrids, also showed a good prospect. The excellent in-silico profiling of furan-1,3,4--oxadiazole structural motifs BF4 and BF5 provide a hypothetical gateway to use these compounds as potential hTYRP1 and hTYR inhibitors against melanogenesis.

Mulberrofuran G, a Mulberry Component, Prevents SARS-CoV-2 Infection by Blocking the Interaction between SARS-CoV-2 Spike Protein S1 Receptor-Binding Domain and Human Angiotensin-Converting Enzyme 2 Receptor

Despite the recent development of RNA replication-targeted COVID-19 drugs by global pharmaceutical companies, their prescription in clinical practice is limited by certain factors, including drug interaction, reproductive toxicity, and drug resistance. COVID-19 drugs with multiple targets for the SARS-CoV-2 life cycle may lead to a successful reduction in drug resistance as well as enhanced therapeutic efficacy, and natural products are a potential source of molecules with therapeutic effects against COVID-19. In this study, we investigated the inhibitory efficacy of mulberrofuran G (MG), a component of Morus alba L., also known as mulberry, which has been used as food and traditional medicine, on the binding of the spike S1 receptor-binding domain (RBD) protein to the angiotensin-converting enzyme 2 (ACE2) receptor, which is the initial stage of the SARS-CoV-2 infection. In competitive enzyme-linked immunosorbent assays, MG effectively blocked the spike S1 RBD: ACE2 receptor molecular binding, and investigations using the BLItz system and in silico modeling revealed that MG has high affinity for both proteins. Finally, we confirmed that MG inhibits the entry of SARS-CoV-2 spike pseudotyped virus and a clinical isolate of SARS-CoV-2 into cells, suggesting that MG might be a promising therapeutic candidate for preventing SARS-CoV-2 binding to the cell surface during early infection.

Mulberry Diels-Alder-type adducts: isolation, structure, bioactivity, and synthesis

Mulberry Diels-Alder-type adducts (MDAAs) are unique phenolic natural products biosynthetically derived from the intermolecular [4 + 2]-cycloaddition of dienophiles (mainly chalcones) and dehydroprenylphenol dienes, which are exclusively distributed in moraceous plants. A total of 166 MDAAs with diverse skeletons have been isolated and identified since 1980. Structurally, the classic MDAAs characterized by the chalcone-skeleton dienophiles can be divided into eight groups (Types A - H), while others with non-chalcone dienophiles or some variations of classic MDAAs are non-classic MDAAs (Type I). These compounds have attracted significant attention of natural products and synthetic chemists due to their complex architectures, remarkable biological activities, and synthetic challenges. The present review provides a comprehensive summary of the structural properties, bioactivities, and syntheses of MDAAs. Cited references were collected between 1980 and 2021 from the SciFinder, Web of Science, and China National Knowledge Internet (CNKI).

Discovery of Novel Tyrosinase Inhibitors From Marine Cyanobacteria

Tyrosinase, an important oxidase involved in the primary immune response in humans, can sometimes become problematic as it can catalyze undesirable oxidation reactions. Therefore, for decades there has been a strong pharmaceutical interest in the discovery of novel inhibitors of this enzyme. Recent studies have also indicated that tyrosinase inhibitors can potentially be used in the treatment of melanoma cancer. Over the years, many new tyrosinase inhibitors have been discovered from various natural sources; however, marine natural products (MNPs) have contributed only a small number of promising candidates. Therefore, in this study we focused on the discovery of new MNP tyrosinase inhibitors of marine cyanobacterial and algal origins. A colorimetric tyrosinase inhibitory assay was used to screen over 4,500 marine extracts against mushroom tyrosinase (A. bisporus). Our results revealed that scytonemin monomer (ScyM), a pure compound from our compound library and also the monomeric last-step precursor in the biosynthesis of the well-known cyanobacterial sunscreen pigment “scytonemin,” consistently showed the highest tyrosinase inhibitory score. Determination of the half maximal inhibitory concentration (IC₅₀) further indicated that ScyM is more potent than the commonly used commercial inhibitor standard “kojic acid” (KA; IC₅₀ of ScyM: 4.90 μM vs. IC₅₀ of KA: 11.31 μM). After a scaled-up chemical synthesis of ScyM as well as its O-methyl analog (ScyM-OMe), we conducted a series of follow-up studies on their structures, inhibitory properties, and mode of inhibition. Our results supported ScyM as the second case ever of a novel tyrosinase inhibitory compound based on a marine cyanobacterial natural product. The excellent in vitro performance of ScyM makes it a promising candidate for applications such as a skin-whitening agent or an adjuvant therapy for melanoma cancer treatment.

Tyrosinase Inhibitory Activity of Soybeans Fermented with Bacillus subtilis Capable of Producing a Phenolic Glycoside, Arbutin

The production of arbutin, an effective tyrosinase inhibitor as well as an outstanding antioxidant, by 691 Bacillus strains isolated from soybean-based foods was tested to enhance the tyrosinase inhibitory activity of soybeans via fermentation with the strains. Among the strains tested, the 5 strains capable of significantly producing arbutin were identified as B. subtilis via 16S rRNA sequencing. When soybeans were fermented with each of the selected strains, the arbutin content was highest on day 1 of fermentation and decreased thereafter. However, the tyrosinase inhibitory activity of the fermented soybeans continuously increased as fermentation progressed, whereas the activity of non-inoculated soybeans was consistently low. The results indicate that arbutin enhances the tyrosinase inhibitory activity of soybeans in the early period of fermentation, while other substances besides arbutin contribute to the activity in the later period. Consequently, soybeans fermented with arbutin-producing B. subtilis strains could be considered as a natural source of cosmeceuticals and nutricosmetics used in skin lightening and may be of interest in the food industry because they contain well-known and powerful antioxidants such as arbutin and other substances.

Folium nelumbinis (Lotus leaf) volatile-rich fraction and its mechanisms of action against melanogenesis in B16 cells

This study was aimed at determining the influence of Folium nelumbinis (Lotus leaf) extracts on melanogenesis in vitro models of melanoma cell line. The anticancer activity of four fractions, including petroleum ether (PEE), n-hexane (HE), ethanol (EE), and ethyl acetate (EAE) from F. nelumbinis on B16 cell lines (C57BL/6J melanoma cell), were evaluated after 24 and 48 h treatment. Results showed that PEE as well as volatile-rich fractions of linolenic acid and linolenic acid ethyl ester significantly (p < 0.05) reduced tyrosinase activity and melanin content in B16 melanoma cells model. Meanwhile, PEE and its primarily contained compound triggered apoptosis of B16 cells in a dose-dependent way. These results demonstrated that PEE possessed effective activities against melanin and tyrosinase generations through the induction of apoptosis. Moreover, a relation between the volatile-rich fractions of F. nelumbinis and the anticancer effects was demonstrated as well.

Advances on Antiviral Activity of Morus spp. Plant Extracts: Human Coronavirus and Virus-Related Respiratory Tract Infections in the Spotlight

(1) Background: Viral respiratory infections cause life-threatening diseases in millions of people worldwide every year. Human coronavirus and several picornaviruses are responsible for worldwide epidemic outbreaks, thus representing a heavy burden to their hosts. In the absence of specific treatments for human viral infections, natural products offer an alternative in terms of innovative drug therapies. (2) Methods: We analyzed the antiviral properties of the leaves and stem bark of the mulberry tree (Morus spp.). We compared the antiviral activity of Morus spp. on enveloped and nonenveloped viral pathogens, such as human coronavirus (HCoV 229E) and different members of the Picornaviridae family-human poliovirus 1, human parechovirus 1 and 3, and human echovirus 11. The antiviral activity of 12 water and water-alcohol plant extracts of the leaves and stem bark of three different species of mulberry-Morus alba var. alba, Morus alba var. rosa, and Morus rubra-were evaluated. We also evaluated the antiviral activities of kuwanon G against HCoV-229E. (3) Results: Our results showed that several extracts reduced the viral titer and cytopathogenic effects (CPE). Leaves' water-alcohol extracts exhibited maximum antiviral activity on human coronavirus, while stem bark and leaves' water and water-alcohol extracts were the most effective on picornaviruses. (4) Conclusions: The analysis of the antiviral activities of Morus spp. offer promising applications in antiviral strategies.

Screening for tyrosinase inhibitors from actinomycetes; identification of trichostatin derivatives from Streptomyces sp. CA-129531 and scale up production in bioreactor

In the course of a primary screening of 614 microbial actinomycete extracts for the discovery of tyrosinase inhibitors, the EtOAc extract of the fermentation broth of the strain Streptomyces sp. CA-129531 isolated from a Martinique sample, exhibited in cell free and cell-based assays the most promising activity (IC₅₀ value of 63 μg/mL). Scaled-up production in a bioreactor led to the isolation of one new trichostatic acid analogue, namely trichostatic acid B (1), along with six known trichostatin derivatives (2-7), four diketopiperazines (8-11), two butyrolactones (12-13) and one hydroxamic acid siderophore (14). Among them, trichostatin A (4) showed a Ki value of 6.1 μM and six times stronger anti-tyrosinase activity (IC₅₀ 2.18 μΜ) than kojic acid (IC₅₀ 14.07 μΜ) used as a positive control. Deoxytrichostatin A (6) displayed also strong inhibitory activity against tyrosinase (IC₅₀ 19.18 μΜ). Trichostatin A production in bioreactor started together with the exponential phase of growth (day 4) and the maximum concentration was reached at day 9 (2.67 ± 0.13 μg/mL). Despite the cytotoxicity of some individual components, the EtOAc extract showed no cytotoxic effect on HepG2, A2058, A549, MCF-7 and MIA PaCa-2 cell lines, (IC₅₀ >2.84 mg/mL) and against BG fibroblasts at the concentrations where the whitening effect was exerted, reassuring its safety and great tyrosinase inhibitory potential.

The structure-activity relationship review of the main bioactive constituents of Morus genus plants

Abstract

Morus genus plants are mainly distributed in the temperate to tropical areas over the world and include 17 species and two subspecies. Due to their excellent pharmacological activity, security in food additives and high value in the national economy, Morus genus plants have drawn more and more attention in recent years. In the light of the references published over the last few decades, flavonoids, benzofurans, stilbenes, and Diels–Alder adducts have been reported to be the main bioactive constituents of Morus genus plants. This review summarizes the compounds with excellent bioactivities isolated from Morus genus plants as well as their structure–activity relationships (SARs), which might be useful for the further research and development of Morus genus plants.

Graphic abstract

The aromatic heterocycles with excellent bioactivities isolated from Morus genus plants as well as their structure–activity relationships (SARs) were summarized.

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.

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.

A Potent Tyrosinase Inhibitor, (E)-3-(2,4-Dihydroxyphenyl)-1-(thiophen-2-yl)prop-2-en-1-one, with Anti-Melanogenesis Properties in α-MSH and IBMX-Induced B16F10 Melanoma Cells

In this study, we designed and synthesized eight thiophene chalcone derivatives (1a–h) as tyrosinase inhibitors and evaluated their mushroom tyrosinase inhibitory activities. Of these eight compounds, (E)-3-(2,4-dihydroxyphenyl)-1-(thiophen-2-yl)prop-2-en-1-one (1c) showed strong competitive inhibition activity against mushroom tyrosinase with IC₅₀ values of 0.013 μM for tyrosine hydroxylase and 0.93 μM for dopa oxidase. In addition, we used enzyme kinetics study and docking program to further evaluate the inhibitory mechanism of 1c toward tyrosinase. As an underlying mechanism of 1c mediated anti-melanogenic effect, we investigated the inhibitory activity against melanin contents and cellular tyrosinase in B16F10 melanoma cells. As the results, the enzyme kinetics and docking results supports that 1c highly interacts with tyrosinase residues in the tyrosinase active site and it can directly inhibit tyrosinase as competitive inhibitor. In addition, 1c exhibited dose-dependent inhibitory effects in melanin contents and intracellular tyrosinase on α-MSH and IBMX-induced B16F10 cells. Overall, our results suggested that 1c might be considered potent tyrosinase inhibitor for use in the development of therapeutic agents for diseases associated with hyperpigment disorders.