Kojic acid-natural product conjugates as mushroom tyrosinase inhibitors

Tyrosinase inhibition by natural stilbenoid glycosides: Critical role of the vinyl moiety in piceid for melanogenesis suppression

Skin hyperpigmentation due to UV-induced tyrosinase activation and melanin overproduction is an ongoing challenge in cosmetic and dermatological applications. While resveratrol analogues show anti-melanogenic potential, the structure-activity relationships of their glycosylated derivatives remain underexplored. Here, we investigate how the vinyl moiety in the food-derived stilbenoid glycoside piceid (resveratrol-3-O-β-glucoside) affects tyrosinase inhibition. We reduced the vinyl moiety to yield dihydropiceid by catalytic hydrogenation and systematically assessed both compounds for anti-melanogenic effects. As results, piceid exhibited superior monophenolase inhibition over dihydropiceid in enzyme kinetics, while both compounds showed comparable diphenolase inhibition. Cellular assays revealed that piceid reduced melanin production by 59.2 % at 25 μM in α-MSH-stimulated B16F10 melanoma cells, whereas dihydropiceid showed weaker activity (<25 % reduction). MolgpKa analysis indicated that the vinyl moiety lowered the 4'-OH pKa (9.7 vs. 9.9), while UV-vis spectroscopy validated that the vinyl moiety enhanced the copper chelation capacity of piceid (ΔOD: 0.459) over dihydropiceid (ΔOD: 0.233). Molecular docking revealed that 4'-OH in piceid closely coordinated the tyrosinase binuclear copper center, whereas molecular dynamics simulation validated that hydrogen bonding supports the binding of both compounds to tyrosinase. Collectively, this study establishes the vinyl moiety in dietary stilbenoids as a critical pharmacophore for tyrosinase inhibition and thereby provides a molecular basis for developing natural anti-hyperpigmentation functional foods or cosmeceuticals.

Detection of Tyrosinase Activity and Inhibitor Validation Based on N-GQDs Fluorescence Sensor

Tyrosinase inhibitors have the ability to resist melanin formation and can be used for clinical and cosmetic, so it is becoming extremely crucial to search a rapid and effective method for detecting t the activity of tyrosinase. In this study, a sensing probe based on Nitrogen-doped graphene quantum dots (N-GQDs) were prepared with carbamide and citric acid. Tyrosinase can oxidize dopamine to dopamine quinone, which can quench the fluorescence of N-GQDs based on the principle of fluorescence resonance energy transfer (FRET) process, and then the detection of tyrosinase activity can be achieved. The result demonstrated that the fluorescence intensity of N-GQDs was a linear correlation with the activity of tyrosinase. Wide detection linear ranges between 0.05 and 5 U/mL and high selectivity. The detection range of tyrosinase was 0.05 to 5 U/mL and LOD of 0.005 U/mL. According to the above, the fluorescence method established in this work could be successfully used for the trace analysis of tyrosinase and it was verified that KA is an inhibitor of tyrosinase.

Advancing the accuracy of tyrosinase inhibitory peptides prediction via a multiview feature fusion strategy

Tyrosinase plays a crucial role as an enzyme in the production of melanin, which is the pigment accountable for determining the color of the hair, eyes, and skin. Tyrosinase inhibitory peptides (TIPs), mainly designed to regulate the activity of the enzyme tyrosinase, are of interest in various domains, including cosmetics, dermatology, and pharmaceuticals, due to their potential applications in controlling skin pigmentation. To date, a few machine learning-based models have been proposed for predicting TIPs, but their predictive performance remains unsatisfactory. In this study, we propose an innovative computational approach, named TIPred-MVFF, to accurately predict TIPs using only sequence information. Firstly, we established an up-to-date and high-quality dataset by collecting samples from various sources. Secondly, we applied a multi-view feature fusion (MVFF) strategy to extract and explore probability and category information embedded in TIPs, employing several machine learning (ML) algorithms coupled with different commonly used sequence-based feature encodings. Then, we employed resampling approaches to address the class imbalance issue. Finally, to maximize the utility of each feature, we fused probability-based and sequence-based features, generating more informative feature that were used to develop the final prediction model. Based on the independent test, experimental results showed that TIPred-MVFF outperformed several conventional ML classifiers and existing methods in terms of prediction accuracy and robustness, achieving an accuracy of 0.937 and a Matthew's correlation coefficient of 0.847. This new computational approach is anticipated to aid community-wide efforts in rapidly and cost-effectively discovering novel peptides with strong tyrosinase inhibitory activities.

Small-Molecule Tyrosinase Inhibitors for Treatment of Hyperpigmentation

Increasing attention is being focused on skin health currently, especially the excessive deposition of melanin in the skin. Tyrosinase, the rate-limiting enzyme in melanin biosynthesis, is a crucial enzyme in melanin synthesis. However, existing tyrosinase inhibitors pose some degree of toxicity to humans. Therefore, the development of more efficient and low-toxicity tyrosinase inhibitors is urgently needed. This review briefly depicts the melanin biosynthesis process and the crystal structure and catalytic mechanism of tyrosinase. The latest research progress regarding small-molecule tyrosinase inhibitors is also reviewed. Moreover, the structure-function relationships are analyzed and summarized. This is expected to provide new and more scientific insights to enable researchers to explore safer and more potent tyrosinase inhibitors.

Preservative effects and mechanism of condensed tannins from Cercis chinensis Bunge leaves on fresh-cut lotus root

This study aimed to investigate the potential of condensed tannins isolated from Cercis chinensis Bunge leaves as natural preservatives for fruits and vegetables. The research demonstrated that C. chinensis leaves condensed tannins (CLCT) significantly delay the browning process and reduce nutritional loss in fresh-cut lotus roots. Prodelphinidins were identified as the primary component of CLCT through electrospray ionization mass spectrometry and high-performance liquid chromatography analyses, with minor proportions of procyanidins and high levels of galloylation. The structural units predominantly consisted of (epi)gallocatechin. CLCT exhibited substantial inhibitory activity against tyrosinase, which may involve interactions with copper ions at the enzyme's active site and alterations in enzyme conformation, resulting in reversible inhibition. Additionally, CLCT displayed remarkable antioxidant and antibacterial properties, effectively scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'- azinobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) radicals and significantly inhibiting the growth of Pseudomonas aeruginosa and Staphylococcus aureus. Overall, the potential of CLCT as a natural preservative and tyrosinase inhibitor underscores its promising application in preserving fruits and vegetables.

7-(Diethylamino) coumarin-3-carboxylic acid as a novel antibrowning agent: Activity and mechanism

Browning caused by polyphenol oxidase (PPO) and microorganisms significantly impacts the nutritional quality of fruits and vegetables. This study identified 7-(Diethylamino) coumarin-3-carboxylic acid (7-DCCA) as an effective inhibitor of both PPO and bacteria. Enzyme assays revealed that 7-DCCA competitively inhibits PPO activity with an IC50 value of 0.275 ± 0.002 mM. Fluorescence and molecular simulation methods demonstrated that 7-DCCA forms a complex with PPO through hydrogen bonding and hydrophobic interactions, altering the enzyme's structure and reducing its activity. Thermogravimetric and differential scanning calorimetry (DSC) assays showed that 7-DCCA stabilizes PPO, delaying its thermal decomposition. Antibacterial tests proved that 7-DCCA inhibits Staphylococcus aureus and Escherichia coli by disrupting cell membranes. Additionally, 7-DCCA suppressed PPO and peroxidase activities, delaying phenolic oxidation and preventing browning in fruits and vegetables. Cytotoxicity assays confirmed its safety, with over 85 % cell viability at concentrations up to 0.1 mM. Stability experiments verified that 7-DCCA had greatly light and thermal stability. This study highlighted 7-DCCA as a promising antibrowning agent with potential application in food preservation.

Kinetic studies, molecular docking, and antioxidant activity of novel 1,3-diphenyl pyrazole-thiosemicarbazone with anti-tyrosinase and anti-melanogenesis properties

This study reports the Design Hypothesis of a novel series of 1,3-diphenyl pyrazole-thiosemicarbazone as novel tyrosinase inhibitors (TYRI). The designed compounds were prepared and their TYRI activity and mechanisms were studied. The results showed that the selected compounds exhibited potent tyrosinase inhibitory activities greater than that of kojic acid (KA). Lead candidates, denoted as 6g and 6n, with a para-hydroxyphenyl group attached to the 3-position of the pyrazole ring demonstrated IC50 values of 2.09 and 3.18 µM, respectively. The potency of these compounds was approximately 5-8 times higher than that of KA. The in vitro melanin content of 6g or 6n-treated melanoma cells resulted in significant efficacy in melanin reduction. The DPPH assay result revealed that the tyrosinase inhibition mechanism for these derivatives was independent of a redox effect and corresponded to the interaction with tyrosinase. According to the Lineweaver-Burk plot, the most potent compounds, 6g and 6n, exhibit a mixed type of inhibition, primarily noncompetitive inhibition. In silico molecular docking studies were employed to determine the binding mode and explore the Design Hypothesis in detail. The results suggested that these compounds could be considered promising leads for the further development of novel inhibitors to treat disorders related to tyrosinase.

Multi-functional tyrosinase inhibitors derived from kojic acid and hydroquinone-like diphenols for treatment of hyperpigmentation: Synthesis and in vitro biological evaluation

A series of multi-functional tyrosinase inhibitors derived from kojic acid (KA) and hydroquinone-like diphenols were designed and synthesized using click chemistry. The in vitro enzymatic assay revealed that all compounds containing a free enolic structure showed excellent activity against tyrosinase (IC50 = 0.14-3.7 µM), being significantly more potent than KA. The most active compounds were catechol (6c) and α-naphthol (6i) analogs with 138- and 96-fold higher potency than KA. On the other hand, all free phenolic compounds (6a-c and 6g-j) derived from aromatic diols showed outstanding free radical scavenging activities superior to KA. Certainly, the α-naphthol derivative 6i with IC50 = 10.1 µM was the most active anti-oxidant, being as potent as quercetin. The SAR analysis indicated that the enolic head of the conjugate molecules mainly contributes to the anti-tyrosinase activity, and the free phenolic part of the molecules can offer anti-oxidant potency. The anti-melanogenic assay of the most promising derivative, 6i, against melanoma (B16F10) cells demonstrated that the prototype compound 6i can significantly reduce the melanin content, more effectively than KA. By using a conjugation strategy, we have improved the tyrosinase inhibitory and radical scavenging activity in the multi-functional agents such as 6i over the parent compound KA, being potentially useful in the treatment of hyperpigmentation and other skin disorders.

Discovery of anti-melanogenic components in persimmon (Diospyros kaki) leaf using LC-MS/MS-MN, AlphaFold2-enabled virtual screening and biological validation

Persimmon (Diospyros kaki) leaf is widely used as a tea substitute in East Asia, offering potential health benefits. Although studies have highlighted their effects on hyperpigmentation disorders, the active components remain unidentified. This study introduces a novel approach combining LC-MS/MS-based molecular networking with AlphaFold2-enabled virtual screening to expedite the identification of bioactive components in persimmon leaf. A total of 105 compounds were identified by MS/MS analysis. Further, virtual screening identified five flavonoids with potential anti-melanogenic properties. Bioassays confirmed myricetin, quercetin, and kaempferol inhibited melanogenesis in human melanocytes in a dose-dependent manner. Biolayer interferometry assays revealed strong binding affinity between these flavonols and hsTYR, with KD values of 23.26 ± 11.77 for myricetin, 12.43 ± 0.37 for quercetin, and 14.99 ± 3.80 μM for kaempferol. Molecular dynamics simulations provided insights into the binding interactions of these flavonols with hsTYR, particularly highlighting the essential role of the 3-OH group on the C-ring. This study elucidates the bioactive components responsible for the anti-melanogenic effects of persimmon leaf, supporting their use in product development.

Skin healthcare protection with antioxidant and anti-melanogenesis activity of polysaccharide purification from Bletilla striata

In this study, we investigated the structural characterization and biological activities of Bletilla striata polysaccharides (BSPs) for their role as antioxidants and anti-melanogenesis agents in skin healthcare protection. Three neutral polysaccharides (BSP-1, BSP-2, and BSP-3) with molecular weights of 269.121 kDa, 57.389 kDa, and 28.153 kDa were extracted and purified. Their structural characteristics were analyzed by ion chromatography, GC-MS, and 1D/2D NMR. The results showed that BSP-1, which constitutes the major part of BSPs, was composed of α-D-Glcp, β-D-Glcp, β-D-Manp, and 2-O-acetyl-β-D-Manp, with the branched-chain accompanied by β-D-Galp and α-D-Glcp. BSP-1, BSP-2, and BSP-3 can enhance the total antioxidant capacity of skin fibroblasts with non-toxicity. Meanwhile, BSP-1, BSP-2, and BSP-3 could significantly inhibit the proliferative activity of melanoma cells. Among them, BSP-1 and BSP-2 showed more significance in anti-melanogenesis, tyrosinase inhibition activity, and cell migration inhibition. BSPs have effective antioxidant capacity and anti-melanogenesis effects, which should be further emphasized and developed as skin protection components.

In vitro and in vivo anti-pigmentation effects of 2-mercaptobenzimidazoles as nanomolar tyrosinase inhibitors on mammalian cells and zebrafish embryos: Preparation of pigment-free zebrafish embryos

Recently, 10 2-mercaptobenzo[d]imidazole (2-MBI) compounds (1-10) were synthesized. Although all 2-MBI compounds are tyrosinase inhibitors that inhibit mushroom tyrosinase at extremely low concentrations (IC50 values: 20-740 nM) and effectively inhibit the browning of apples, to our knowledge, no studies have determined whether 2-MBI compounds inhibit mammalian tyrosinase. Mammalian tyrosinase is different from mushroom tyrosinase in its distribution within the cell and has structural characteristics that are different from mushroom tyrosinase in amino acid sequence and in the presence of a quaternary structure. Thus, the effect of the 10 2-MBI compounds on mammalian tyrosinase activity was investigated in B16F10 cells. Six compounds (1-6) exhibited stronger intracellular tyrosinase inhibition than that of kojic acid and phenylthiourea (PTU), which are known to be the most potent tyrosinase inhibitors; their strong tyrosinase inhibitory activity robustly inhibited intracellular melanin production in B16F10 cells. None of the tested 2-MBI compounds exhibited appreciable cytotoxicity in HaCaT and B16F10 cells. To confirm the anti-melanogenic efficacy of the 2-MBI compounds in vivo, a zebrafish embryo model was used. At concentrations 100 times lower than kojic acid, most 2-MBI compounds demonstrated much stronger depigmentation efficacy than that of kojic acid, and three 2-MBI compounds (2-4) showed depigmentation activity similar to or more potent than that of PTU, resulting in nearly pigment-free zebrafish embryos. These results suggest that 2-MBI compounds may be potential therapeutic agents for hyperpigmentation-related disorders.

Mushroom tyrosinase enzyme catalysis: synthesis of larvicidal active geranylacetone derivatives against Culex quinquesfasciatus and molecular docking studies

The grindstone process, which uses tyrosinase as a catalyst, was used to create analogues of geranylacetone. Tyrosinase was used to prepare the Mannich base under favourable reaction conditions, resulting in a high yield. All synthesized compounds were characterized using FTIR, Nuclear magnetic resonance, and mass spectral analyses. The active geranylacetone derivatives (1a-l) were investigated for larvicidal activity against Culex quinquefasciatus; compound 1b (LD50:20.7 μg/mL) was noticeably more effective than geranylacetone (LD50: >100 μg/mL) and permethrin (LD50: 24.4 μg/mL) lead compounds because of their ability to kill larvae and use them as pesticides. All compounds (1a-1l) were found to be low toxic, whereas compounds 1b, 1d, and 1k were screened for antifeedant screening of non -aquatic target for the toxicity measurement against marine fish Oreochromis mossambicus at 100 μg/mL caused 0% mortality in within 24 h. Molecular docking studies of synthesised compound 1b and permethrin docked with 3OGN, compound 1b demonstrated a greater binding affinity (-9.6 kcal/mol) compared to permethrin (-10.5 kcal/mol). According to these results, the newly synthesised geranylacetone derivatives can serve as lead molecules of larvicides agents.

Exploring the effect of a series of flavonoids on tyrosinase using integrated enzyme kinetics, multispectroscopic, and molecular modelling analyses

The control of food browning can be achieved by inhibiting tyrosinase (TY) activity, but current studies on the interaction of flavonoids as potent inhibitors with TY are inadequate. Herein, the effect of a library of flavonoids on TY was investigated using enzyme kinetics, multispectroscopic methods, and molecular modelling. Some flavonoids including 4, 8, 10, 17, 18, 28, 30, 33, and 34 exhibited potent TY inhibitory activity, with compound 10 demonstrating reversible inhibition in a mixed-competitive manner. Ultraviolet-visible spectral changes confirmed the formation of flavonoid-TY complexes. Fluorescence quenching analysis suggested effective intrinsic fluorescence quenching by flavonoids through static quenching with the ground-state complex formation. Synchronous fluorescence spectra showed the microenvironment change around the fluorophores induced by flavonoids. ANS-binding fluorescence assay indicated TY's surface hydrophobicity change by flavonoids and highlighted the change in secondary structure conformation, which was further confirmed by Fourier-transform infrared spectra. Molecular modelling results helped visualize the preferred binding conformation at the active site of TY, and demonstrated the important role of hydrophobic interaction and hydrogen bonding in stabilizing the flavonoid-TY complexes. These findings prove that diverse flavonoid structures distinctly impact their binding behavior on TY and contribute to understanding flavonoids' potential as TY inhibitors in controlling food browning.

Synthesis of flurbiprofen thiadiazole urea derivatives and assessment of biological activities and molecular docking studies

Totally 15 novel flurbiprofen urea derivatives were synthesized bearing the thiadiazole ring. Their inhibition effects on tyrosinase were determined. 3c was found to be the strongest inhibitor with the IC50 value of 68.0 μM against tyrosinase. The enzyme inhibition types of the synthesized compounds were determined by examining the kinetic parameters. The inhibition type of 3c was determined as uncompetitive and the Ki value was calculated as 36.3 μM. Moreover, their cytotoxic effects on hepatocellular carcinoma (HepG2), colorectal carcinoma (HT-29), and melanoma (B16F10) cell lines were evaluated. According to the cytotoxicity results, 3l (IC50  = 14.11 μM) showed the highest cytotoxicity on the HT-29 cells, while 3o (IC50  = 4.22 μM) exhibited the strongest cytotoxic effect on HepG2 cell lines. Also, 3j (IC50  = 7.55 μM strongly affected B16F10. The effects of synthesized compounds on the healthy cell line were evaluated on the CCD-986Sk cell line. Molecular modelling studies have indicated the potential binding interactions of the uncompetitive inhibitor 3c with the enzyme-substrate complex.

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.

Catechol-mimicking transition-state analogues as non-oxidizable inhibitors of tyrosinases

Tyrosinases are copper-containing metalloenzymes involved in several processes in both mammals, insects, bacteria, fungi and plants. Their phenol oxidation properties are especially responsible for human melanogenesis, potentially leading to abnormal pigmentation, and for postharvest vegetable tissue browning. Thus, targeting tyrosinases attracts interest for applications both in dermocosmetic and agrofood fields. However, a large part of the literature about tyrosinase inhibitors is dedicated to the report of copper-interacting phenolic compounds, that are more likely alternative substrates leading to undesirable toxic quinones production. To circumvent this issue, the use of catechol-mimicking copper-chelating groups that are analogues of the tyrosinase oxidation transition state appears as a valuable strategy. Relying on several non-oxidizable pyridinone, pyrone or tropolone moieties, innovative inhibitors were developed, especially within the past decade, and the best reported analogues reached IC50 values in the nanomolar range. Herein, we review the design, the activity against several tyrosinases, and the proposed binding modes of reported catechol-mimicking, non-oxidizable molecules, in light of recent structural data.

Design, synthesis, in vitro, and in silico evaluations of kojic acid derivatives linked to amino pyridine moiety as potent tyrosinase inhibitors

In the present study, novel series of kojic acid derivatives conjugated to amino pyridine moiety were designed and synthesized to explore their inhibitory activity against tyrosinase. To this end, the structure of all derivatives was characterized by 1H NMR, 13C NMR, FT-IR, and elemental analysis. Next, all derivatives were evaluated against tyrosinase compared to the kojic acid as positive control and exhibited different inhibitory potencies. Furthermore, the antioxidant potential of all derivatives was determined. The kinetic analysis of the most active agent revealed that 3-hydroxy-6-(hydroxymethyl)-2-((3-nitrophenyl)(pyridin-2-ylamino)methyl)-4H-pyran-4-one (4h) binds to the enzyme in the uncompetitive mode of action. The docking analysis and molecular dynamic simulations showed considerable binding affinity and significant interactions with tyrosinase enzyme to target the melanogenesis pathway, proposing them as potent candidates to control hyperpigmentation in the future.

Synthesis, Anti-Tyrosinase Activity, and Spectroscopic Inhibition Mechanism of Cinnamic Acid-Eugenol Esters

Tyrosinase plays crucial roles in mediating the production of melanin pigment; thus, its inhibitors could be useful in preventing melanin-related diseases. To find potential tyrosinase inhibitors, a series of cinnamic acid-eugenol esters (c1~c29) was synthesized and their chemical structures were confirmed by 1H NMR, 13C NMR, HRMS, and FT-IR, respectively. The biological evaluation results showed that all compounds c1~c29 exhibited definite tyrosinase inhibitory activity; especially, compound c27 was the strongest tyrosinase inhibitor (IC50: 3.07 ± 0.26 μM), being ~4.6-fold stronger than the positive control, kojic acid (IC50: 14.15 ± 0.46 μM). Inhibition kinetic studies validated compound c27 as a reversible mixed-type inhibitor against tyrosinase. Three-dimensional fluorescence and circular dichroism (CD) spectra results indicated that compound c27 could change the conformation and secondary structure of tyrosinase. Fluorescence-quenching results showed that compound c27 quenched tyrosinase fluorescence in the static manner with one binding site. Molecular docking results also revealed the binding interactions between compound c27 and tyrosinase. Therefore, cinnamic acid-eugenol esters, especially c27, could be used as lead compounds to find potential tyrosinase inhibitors.

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.

Advances of bioorthogonal coupling reactions in drug development

Currently, bioorthogonal coupling reactions have garnered considerable interest due to their high substrate selectivity and less restrictive reaction conditions. During recent decades, bioorthogonal coupling reactions have emerged as powerful tools in drug development. This review describes the current applications of bioorthogonal coupling reactions in compound library building mediated by the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction and in situ click chemistry or conjunction with other techniques; druggability optimization with 1,2,3-triazole groups; and intracellular self-assembly platforms with ring tension reactions, which are presented from the viewpoint of drug development. There is a reasonable prospect that bioorthogonal coupling reactions will accelerate the screening of lead compounds, the designing strategies of small molecules and expand the variety of designed compounds, which will be a new trend in drug development in the future.

Fungal production of kojic acid and its industrial applications

Kojic acid has gained its importance after it was known worldwide that the substance functions primarily as skin-lightening agent. Kojic acid plays a vital role in skin care products, as it enhances the ability to prevent exposure to UV radiation. It inhibits the tyrosinase formation which suppresses hyperpigmentation in human skin. Besides cosmetics, kojic acid is also greatly used in food, agriculture, and pharmaceuticals industries. Conversely, according to Global Industry Analysts, the Middle East, Asia, and in Africa especially, the demand of whitening cream is very high, and probably the market will reach to $31.2 billion by 2024 from $17.9 billion of 2017. The important kojic acid-producing strains were mainly belongs to the genus Aspergillus and Penicillium. Due to its commercial potential, it continues to attract the attention for its green synthesis, and the studies are still widely conducted to improve kojic acid production. Thus, the present review is focused on the current production processes, gene regulation, and limitation of its commercial production, probable reasons, and possible solutions. For the first time, detailed information on the metabolic pathway and the genes involved in kojic acid production, along with illustrations of genes, are highlighted in the present review. Demand and market applications of kojic acid and its regulatory approvals for its safer use are also discussed. KEY POINTS: • Kojic acid is an organic acid that is primarily produced by Aspergillus species. • It is mainly used in the field of health care and cosmetic industries. • Kojic acid and its derivatives seem to be safe molecules for human use.

Design, Synthesis, and Biological Evaluation of Novel Hybrids Containing Dihydrochalcone as Tyrosinase Inhibitors to Treat Skin Hyperpigmentation

Excessive melanin deposition may lead to a series of skin disorders. The production of melanin is carried out by melanocytes, in which the enzyme tyrosinase performs a key role. In this work, we identified a series of novel tyrosinase inhibitor hybrids with a dihydrochalcone skeleton and resorcinol structure, which can inhibit tyrosinase activity and reduce the melanin content in the skin. Compound 11c possessed the most potent activity against tyrosinase, showing IC₅₀ values at nanomolar concentration ranges, along with significant antioxidant activity and low cytotoxicity. Furthermore, in vitro permeation tests, supported by HPLC analysis and 3D OrbiSIMS imaging visualization, revealed the excellent permeation of 11c. More importantly, compound 11c reduced the melanin content on UV-induced skin pigmentation in a guinea pig model in vivo. These results suggest that compound 11c may serve as a promising potent tyrosinase inhibitor for the development of a potential therapy to treat skin hyperpigmentation.

Spectroscopic analysis, kinetic mechanism, computational docking, and molecular dynamics of active metabolites from the aerial parts of Astragalus membranaceusBunge as tyrosinase inhibitors

A new isoflavane derivative (2), a new natural isoflavane (6), four new oleanane-type triterpenoid saponins (23, 25, 28, and 29), and twenty three known secondary metabolites (1, 3-5, 7-22, 24, 26, and 27) were isolated from the aerial parts of Astragalus membranaceus Bunge. The chemical structures of these compounds were elucidated through spectroscopic analysis and compared with those identified in previous studies. Tyrosinase inhibition ability of isolated compounds (1-29) was evaluated. Of these, compounds 3, 4, 6, and 14 exhibited inhibitory effects, with IC₅₀ values ranging from 24.6 to 59.2 μM. According to kinetic analysis, compounds 3 and 4 were non-competitive inhibitors of tyrosinase, whereas compounds 6 and 14 inhibited tyrosinase in uncompetitive and competitive modes, respectively. Molecular docking analysis identified that compounds 3, 4, and 6 could bind to allosteric sites and compound 14 could bind to the catalytic site of tyrosinase, which is consistent with the results of kinetic studies. Molecular dynamics behaviors of the active compounds in complex with tyrosinase were investigated via 60 ns simulation which demonstrated their high stability. These findings indicate that the aerial parts of A. membranaceus are a potential source of natural tyrosinase inhibitors.

Biomolecular interactions and binding dynamics of inhibitor arachidonic acid, with tyrosinase enzyme

Hyperpigmentation is a disorder caused by increased melanin deposition and changes in skin pigmentation. Inhibition of tyrosinase activity contributes to the control of food browning and skin pigmentation diseases. The effects of arachidonic acid (AA) on tyrosinase activity were examined using different spectroscopy methods including UV-VIS spectrophotometry, fluorescence spectroscopy, circular dichroism (CD) differential scanning calorimetry, and molecular dynamics (MD) simulations. Based on the kinetic results, arachidonic acid showed mixed-type of inhibition with Ki = 4.7 µM. Fluorescence and CD studies showed changes of secondary and tertiary structures of enzyme and a reduction of α-helix* amino acids after its incubation with different concentrations of AA, which is also confirmed by DSSP analysis. In addition, differential scanning calorimetry (DSC) studies showed a decrease in thermodynamic stability of enzyme from Tm = 338.65k for sole enzyme after incubation with AA in comparison with complex enzyme with Tm= 334.26k, ΔH =7.52 kJ/mol, and ΔS = 0.15 kJ/mol k. Based on the theoretical methods, it was found that the interaction between enzyme and AA follows an electrostatic manner with ΔG = -8.314 kJ/mol and ΔH = -12.9 kJ/mol. The MD results showed the lowest flexibility in the complex amino acids and minimal fluctuations in AA interaction with tyrosinase in Residue 240 to 260 and 66 to 80. Thus, AA inhibitory and structural and thermodynamic instability of tyrosinase supported advantages of this fatty acid for prevention of medical hyperpigmentation. Therefore, it is a good candidate for cosmetic applications. Communicated by Ramaswamy H. Sarma.

Exploring the Co-Crystallization of Kojic Acid with Silver(I), Copper(II), Zinc(II), and Gallium(III) for Potential Antibacterial Applications

Co-crystallization of kojic acid (HKA) with silver(I), copper(II), zinc(II), or gallium(III) salts yielded three 1D coordination polymers and one 0D complex in which kojic acid was present as a neutral or anionic terminal or bridging ligand. All reactions were conducted mechanochemically via ball milling and manual grinding, or via slurry. All solids were fully characterized via single-crystal and/or powder X-ray diffraction. As kojic acid is a mild antimicrobial compound that is widely used in cosmetics, and the metal cations possess antibacterial properties, their combinations were tested for potential antibacterial applications. The minimal inhibition concentrations (MICs) and minimal biocidal concentrations (MBCs) for all compounds were measured against standard strains of the bacteria P. aeruginosa, S. aureus, and E. coli. All compounds exerted appreciable antimicrobial activity in the order of silver, zinc, copper, and gallium complexes.

Ugi Bis-Amide Derivatives as Tyrosinase Inhibitor; Synthesis, Biology Assessment, and in Silico Analysis

Herein, a straightforward synthetic strategy mediated by Ugi reaction was developed to synthesize novel series of compounds as tyrosinase inhibitors. The structures of all compounds were confirmed by FT-IR, ¹ H-NMR, ¹³ C-NMR, and CHNOS techniques. The tyrosinase inhibitory activities of all synthesized derivatives 5a-m were determined against mushroom tyrosinase and it was found that derivative 5c possesses the best inhibition with an IC₅₀  value of 69.53±0.042 μM compared to the rest of the synthesized derivatives. Structure-activity relationships (SARs) showed that the presence of 4-MeO or 4-NO₂ at the R² position plays a key role in tyrosinase inhibitory activities. The enzyme kinetics studies showed that compound 5c is an noncompetitive inhibitor. For in silico study, the allosteric site detection was first applied to find the appropriate binding site and then molecular docking and molecular dynamic studies were performed to reveal the position and interactions of 5c as the most potent inhibitor within the tyrosinase active site. The results showed that 5c bind well with the proposed binding site and formed a stable complex with the target protein.

Inhibition of Aflatoxin Production by Citrinin and Non-Enzymatic Formation of a Novel Citrinin-Kojic Acid Adduct

Screening for microorganisms that inhibit aflatoxin production from environments showed that Penicillium citrinum inhibited aflatoxin production by Aspergillus parasiticus. The inhibitory substance in the culture medium of P. citrinum was confirmed to be citrinin (CTN). RT-PCR analyses showed that CTN did not inhibit expressions of aflatoxin biosynthetic genes (aflR, pksL1, and fas-1) of A. parasiticus, whereas feeding experiments using A. parasiticus showed that CTN inhibited the in vivo conversion of dihydrosterigmatocystin to AFB₂·AFG₂. These results suggest that CTN inhibits a certain post-transcriptional step in aflatoxin biosynthesis. CTN in the culture medium of A. parasiticus was found to be decreased or lost with time, suggesting that a certain metabolite produced by A. parasiticus is the cause of the CTN decrease; we then purified, characterized, and then analyzed the substance. Physico-chemical analyses confirmed that the metabolite causing a decrease in CTN fluorescence was kojic acid (KA) and the resulting product was identified as a novel substance: (1R,3S,4R)-3,4-dihydro-6,8-dihydroxy-1-(3-hydroxy-6-(hydroxymethyl)-4-oxo-4H-pyran-2-yl)-3,4,5-trimethyl-1H-isochromene-7-carboxylic acid, which was named "CTN-KA adduct". Our examination of the metabolites' toxicities revealed that unlike CTN, the CTN-KA adduct did not inhibit aflatoxin production by A. parasiticus. These results indicate that CTN's toxicity was alleviated with KA by converting CTN to the CTN-KA adduct.

Green preparation, characterization, evaluation of anti-melanogenesis effect and in vitro/in vivo safety profile of kojic acid hydrogel as skin lightener formulation

The local treatment of kojic acid (KA) as a tyrosinase inhibitor results in inadequate skin absorption and a number of side effects. The current study aims to maximize KA skin delivery. To produce KA-hydrogel, 1% KA was injected into a Chitosan/alginate hydrogel. The impacts of biopolymer proportion on the KA-hydrogel preparations were investigated. Swelling analysis, weight loss analysis, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), UV absorption spectroscopy, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy were used to evaluate the KA-hydrogel. The swelling percentages of KA-hydrogel increased significantly after 4 h. After two weeks, up to 60% of the primary mass of the KA- hydrogel has been removed. By alternation in biopolymer proportion, the drug release profile of KA-hydrogel demonstrated a sustained pattern. According to the skin absorption experiment, KA-hydrogel had higher skin deposition (25.630 ± 3.350%) than KA-plain gel (5.170 ± 0.340%). Moreover, an in vitro cytotoxicity analysis for the modified KA-hydrogel preparations revealed no cytotoxic effects on HFF cell line (90%). Moreover, KA hydrogel had inhibitory effect on melanin synthesis and are comparable with KA. Furthermore, KA-hydrogel had higher inhibitory effect on L-dopa auto oxidation (94.84 ± 2.41%) in comparison KA solution (73.95 ± 3.28%). Also, the dermal irritation study on Wistar rat revealed that the hydrogel constituent used did not irritate the skin. These results revealed that the KA-hydrogel might be employed as KA local administration, thus opening up new prospects for the therapies of hyperpigmentation problems.

Design, synthesis, in silico studies, and antiproliferative evaluations of novel indolin-2-one derivatives containing 3-hydroxy-4-pyridinone fragment

Keeping in view the pharmacological properties of indolinones as promising scaffold as kinase inhibitors, herein, a novel series of 3-hydrazonoindolin-2-one derivatives bearing 3-hydroxy-4-pyridinone moiety were synthesized, studied by molecular docking, and fully characterized by spectroscopic techniques. All the prepared compounds were evaluated for their cytotoxicity attributes against a panel of tumor cell lines, including non-small cell lung cancer (A549), breast carcinoma (MCF-7), acute myeloid leukemia (AML), and chronic myeloid leukemia (CML). They displayed moderate to promising antiproliferative effects toward A549 and MCF-7 cells but remarkable results against AML and CML. Especially, compound 10k was found to be more potent against AML (EC₅₀ = 0.69 μM) compare to the other halogen-substituted derivatives. FMS-like tyrosine kinase 3 (FLT3) is known to be expressed in AML cancer cells. The molecular docking studies demonstrated that our prepared compounds were potentially bound to AML active site through essential H-bond and other vital interactions with critical binding residues.

Vegetable-derived indole enhances the melanoma-treating efficacy of chemotherapeutics

Food-drug interaction is an important but overlooked issue. For example, little is known concerning whether or not the chemotherapy of cancers is affected by the well-defined dietary chemicals such as 2-(indol-3-ylmethyl)-3,3'-diindolylmethane (LTr1) derived from daily consumed cruciferous vegetables. This work, inspired by the described melanogenesis reduction by certain indoles, presents that LTr1 mitigates the melanogenesis and thus potentiates the in vitro and in vivo anti-melanoma effectiveness of different chemotherapeutic agents including dacarbazine, vemurafenib, and sorafenib. In B16 melanoma cells, LTr1 was shown to inhibit the melanogenesis by acting towards the regulatory (R) subunit of protein kinase A (PRKAR1a) associated with the phosphorylation of cAMP-response element binding protein (CREB). This allows LTr1 to reduce the expression of melanogenesis-related enzymes such as tyrosinase (TYR), tyrosinase-related protein 1 (TYRP1), and tyrosinase-related protein 2 (TYRP2). Furthermore, LTr1 was addressed to bind to the aryl hydrocarbon receptor (AhR) and up-regulate the expression of CYP1A1 encoding cytochrome P450 1A1, leading to the escalation of reactive oxygen species (ROS) level. The increased ROS generation promotes the cysteine-to-cystine transformation to inhibit the pheomelanogenesis in melanomas. Collectively, the work identifies LTr1 as a new melanogenesis inhibitor that modulates the PKA/CREB/MITF and AhR/CYP1A1/ROS pathways, thereby providing a new option for (re)sensitizing melanomas to chemotherapeutics.

Azole inhibitors of mushroom and human tyrosinases: Current advances and prospects of drug development for melanogenic dermatological disorders

Azoles are a famous and promising class of drugs for treatment of a range of ailments especially fungal infections. A wide variety of azole derivatives are also known to exhibit tyrosinase inhibition, some of which possess promising activity with potential for treatment of dermatological disorders such as post-inflammatory hyperpigmentation, nevus, flecks, melasma, and melanoma. Recently, thiazolyl-resorcinol derivatives have demonstrated potent human tyrosinase inhibition with a safe and effective therapeutic profile for treatment of skin hyperpigmentation in humans, which are currently under clinical trials. If approved these derivatives would be the first azole drugs to be used for treatment of skin hyperpigmentation. Although the scientific literature has been witnessing general reviews on tyrosinase inhibitors to date, there is none that specifically and comprehensively discusses azole inhibitors of tyrosinase. Appreciating such potential of azoles, this focused review highlights a wide range of their derivatives with promising mushroom and human tyrosinase inhibitory activities and clinical potential for treatment of melanogenic dermatological disorders. Presently, these disorders have been treated with kojic acid, hydroquinone and other drugs, the design and development of which are based on their ability to inhibit mushroom tyrosinase. The active sites of mushroom and human tyrosinases carry structural differences which affect substrate or inhibitor binding. For this reason, kojic acid and other drugs pose efficacy and safety issues since they were originally developed using mushroom tyrosinase and have been clinically used on human tyrosinase. Design and development of tyrosinase inhibitors should be based on human tyrosinase, however, there are challenges in obtaining the human enzyme and understanding its structure and function. The review discusses these challenges that encompass structural and functional differences between mushroom and human tyrosinases and the manner in which they are inhibited. The review also gauges promising azole derivatives with potential for development of drugs against skin hyperpigmentation by analyzing and comparing their tyrosinase inhibitory activities against mushroom and human tyrosinases, computational data, and clinical profile where available. It aims to lay groundwork for development of new azole drugs for treatment of skin hyperpigmentation, melanoma, and related dermatological disorders.

Rational Design, Synthesis, in Vitro, and in Silico Studies of Chlorophenylquinazolin-4(3H)-One Containing Different Aryl Acetohydrazides as Tyrosinase Inhibitors

Tyrosinase plays a pivotal role in the hyperpigmentation and enzymatic browning of fruit and vegetable. Therefore, tyrosinase inhibitors can be of interest in industries as depigmentation compounds as well as anti-browning agents. In the present study, a series of chlorophenylquinazolin-4(3H)-one derivative were rationally designed and synthesized. The formation of target compounds was confirmed by spectral characterization techniques such as IR, ¹ H-NMR, ¹³ C-NMR, and elemental analysis. Among the synthesized derivatives, compound 8l was proved to be the most potent inhibitor with an IC₅₀ value of 25.48±1.19 μM. Furthermore, the results of the molecular docking study showed that this compound fitted well in the active site of tyrosinase with the binding score of -10.72.

The Hypopigmentation Mechanism of Tyrosinase Inhibitory Peptides Derived from Food Proteins: An Overview

Skin hyperpigmentation resulting from excessive tyrosinase expression has long been a problem for beauty lovers, which has not yet been completely solved. Although researchers are working on finding effective tyrosinase inhibitors, most of them are restricted, due to cell mutation and cytotoxicity. Therefore, functional foods are developing rapidly for their good biocompatibility. Food-derived peptides have been proven to display excellent anti-tyrosinase activity, and the mechanisms involved mainly include inhibition of oxidation, occupation of tyrosinase’s bioactive site and regulation of related gene expression. For anti-oxidation, peptides can interrupt the oxidative reactions catalyzed by tyrosinase or activate an enzyme system, including SOD, CAT, and GSH-Px to scavenge free radicals that stimulate tyrosinase. In addition, researchers predict that peptides probably occupy the site of the substrate by chelating with copper ions or combining with surrounding amino acid residues, ultimately inhibiting the catalytic activity of tyrosinase. More importantly, peptides reduce the tyrosinase expression content, primarily through the cAMP/PKA/CREB pathway, with PI3K/AKT/GSK3β, MEK/ERK/MITF and p38 MAPK/CREB/MITF as side pathways. The objective of this overview is to recap three main mechanisms for peptides to inhibit tyrosinase and the emerging bioinformatic technologies used in developing new inhibitors.

Molecular Docking, Tyrosinase, Collagenase, and Elastase Inhibition Activities of Argan By-Products

The argan tree (Argania spinosa (L.) Skeels) is one of the most important floristic resources in Morocco. This Moroccan endemic tree is known for its numerous therapeutic and medicinal uses. In addition to some medicinal and cosmetic uses, argan fruit pulp and press cake are traditionally used by the Berber population for heating and feeding livestock. Molecular docking is an in silico approach that predicts the interaction between a ligand and a protein. This approach is mainly used in chemistry and pharmacology of natural products as a prediction tool with the purpose of selecting plant extracts or fractions for in vitro tests. The aim of this research is to study the evaluation of potential tyrosinase, collagenase, and elastase inhibitory activities of argan fruit press-cake and pulp extracts. Extracts were evaluated for their total phenolic content (TPC), and the major polyphenols of both press-cake and pulp extracts were submitted to molecular docking in order to determine the mechanisms of action of these compounds. Obtained results revealed that fruit pulp had the strongest dermocosmetic activities, as well as the highest TPC, with values above 55 mg gallic-acid equivalent per gram of dry matter (mgeq AG/gDM). Moreover, those results were positively correlated with the docking findings, suggesting that the pulp lead compounds have higher affinity with tyrosinase, collagenase, and elastase action sites. The results here presented are very promising and open new perspectives for the exploitation of argan-tree by-products as cosmetic agents towards the development of new anti-aging products.

Three New Isoprenylated Flavones from Artocarpus chama Stem and Their Bioactivities

Phytochemical investigation of Artocarpus chama stem was performed by chromatographic techniques, resulting from the isolation and structure elucidation of three new compounds, namely 3′-farnesyl-apigenin (1), 3-(hydroxyprenyl) isoetin (2), and 3-prenyl-5,7,2′,5′-tetrahydroxy-4′-methoxyflavone (3), and five known compounds, namely homoeriodictyol (4), isocycloartobilo-xanthone (5), artocarpanone (6), naringenin (7), and artocarpin (8). From the screening result, A. chama extract showed a potent tyrosinase inhibitory effect. Ihe isolated compounds 1, 4 and 6 also exhibited tyrosinase inhibition with IC50 of 135.70, 52.18, and 38.78 µg/mL, respectively. Moreover, compounds 3, 4, 5, 6, and 8 showed strong activity against Staphylococcus epidermidis, S. aureus, methicillin-resistant S. aureus, and Cutibacterium acnes. This study is the first report on phytochemical investigation with new compounds and biological activities of A. chama. Skin infection can cause dark spots or hyperpigmentation. The isolated compounds that showed both anityrosinase and antimicrobial activities will be further studied in in vivo and clinical trials in order to develop treatment for hyperpigmentation, which is caused by infectious diseases by microorganisms.

Inhibitory Effect of Chlorogenic Acid Analogues Comprising Pyridine and Pyrimidine on α-MSH-Stimulated Melanogenesis and Stability of Acyl Analogues in Methanol

In continuation of studies for α-MSH stimulated melanogenesis inhibitors, we have evaluated the design, synthesis, and activity of a new series of chlorogenic acid (CGA) analogues comprising pyridine, pyrimidine, and diacyl derivatives. Among nineteen synthesized compounds, most of them (fifteen) exhibited better inhibitions of melanin formation in B16 melanoma cells. The results illustrated that a pyridine analogue 6f and a diacyl derivative 13a of CGA showed superior inhibition profiles (IC50: 2.5 ± 0.7 μM and 1.1 ± 0.1 μM, respectively) of α-MSH activities than positive controls, kojic acid and arbutin (IC50: 54 ± 1.5 μM and 380 ± 9.5 μM, respectively). The SAR studies showed that both -CF3 and -Cl groups exhibited better inhibition at the meta position on benzylamine than their ortho and para positions. In addition, the stability of diacyl analogues of CGA in methanol monitored by HPLC for 28 days indicated the steric bulkiness of acyl substituents as a key factor in their stability.

Synthesis and Some Properties of New 5-Hydroxy-2-[(hetarylthio)methyl]-4H-pyran-4-ones

Abstract

The reaction of 2-thioxoazines with chlorokojic acid in the presence of KOH in DMF led to the formation of new hybrid molecules containing fragments of kojic acid and azaheterocycle linked by the SCH2 spacer. In silico prediction of bioavailability parameters was carried out, possible protein targets were predicted by the protein ligand docking method.

Spectrophotometric Assays for Sensing Tyrosinase Activity and Their Applications

Tyrosinase (TYR, E.C. 1.14.18.1), a critical enzyme participating in melanogenesis, catalyzes the first two steps in melanin biosynthesis including the ortho-hydroxylation of L-tyrosine and the oxidation of L-DOPA. Previous pharmacological investigations have revealed that an abnormal level of TYR is tightly associated with various dermatoses, including albinism, age spots, and malignant melanoma. TYR inhibitors can partially block the formation of pigment, which are always used for improving skin tone and treating dermatoses. The practical and reliable assays for monitoring TYR activity levels are very useful for both disease diagnosis and drug discovery. This review comprehensively summarizes structural and enzymatic characteristics, catalytic mechanism and substrate preference of TYR, as well as the recent advances in biochemical assays for sensing TYR activity and their biomedical applications. The design strategies of various TYR substrates, alongside with several lists of all reported biochemical assays for sensing TYR including analytical conditions and kinetic parameters, are presented for the first time. Additionally, the biomedical applications and future perspectives of these optical assays are also highlighted. The information and knowledge presented in this review offer a group of practical and reliable assays and imaging tools for sensing TYR activities in complex biological systems, which strongly facilitates high-throughput screening TYR inhibitors and further investigations on the relevance of TYR to human diseases.

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.

New Benzimidazothiazolone Derivatives as Tyrosinase Inhibitors with Potential Anti-Melanogenesis and Reactive Oxygen Species Scavenging Activities

Thirteen (Z)-2-(substituted benzylidene)benzimidazothiazolone analogs were synthesized and evaluated for their inhibitory activity against mushroom tyrosinase. Among the compounds synthesized, compounds 1–3 showed greater inhibitory activity than kojic acid (IC₅₀ = 18.27 ± 0.89 μM); IC₅₀ = 3.70 ± 0.51 μM for 1; IC₅₀ = 3.05 ± 0.95 μM for 2; and IC₅₀ = 5.00 ± 0.38 μM for 3, and found to be competitive tyrosinase inhibitors. In silico molecular docking simulations demonstrated that compounds 1–3 could bind to the catalytic sites of tyrosinase. Compounds 1–3 inhibited melanin production and cellular tyrosinase activity in a concentration-dependent manner. Notably, compound 2 dose-dependently scavenged ROS in B16F10 cells. Furthermore, compound 2 downregulated the protein kinase A (PKA)/cAMP response element-binding protein (CREB) and mitogen-activated protein kinase (MAPK) signaling pathways, which led to a reduction in microphthalmia-associated transcription factor (MITF) expression, and decreased tyrosinase, tyrosinase related protein 1 (TRP1), and TRP2 expression, resulting in anti-melanogenesis activity. Hence, compound 2 may serve as an anti-melanogenic agent against hyperpigmentation diseases.

Anti-melanogenesis and anti-tyrosinase properties of aryl-substituted acetamides of phenoxy methyl triazole conjugated with thiosemicarbazide: Design, synthesis and biological evaluations

A series of aryl phenoxy methyl triazole conjugated with thiosemicarbazides were designed, synthesized, and evaluated for their tyrosinase inhibitory activities in the presence of l-dopa and l-tyrosine as substrates. All the compounds showed tyrosinase inhibition in the sub-micromolar concentration. Among the derivatives, compound 9j bearing benzyl displayed exceptionally high potency against tyrosinase with IC₅₀ value of 0.11 μM and 0.17 μM in the presence of l-tyrosine and l-dopa as substrates which is significantly lower than that of kojic acid as the positive control with an IC₅₀ value of 9.28 μM for l-tyrosine and 9.30 μM for l-dopa. According to Lineweaver-Burk plot, 9j demonstrated an uncompetitive type of inhibition in the kinetic assay. Also, in vitro antioxidant activities determined by DPPH assay recorded an IC₅₀ value of 68.43 μM for 9i. The melanin content of 9j was determined on B16F10 melanoma human cells which demonstrated a significant reduction of the melanin content. Moreover, the binding energies corresponding to the same ligand as well as computer-aided drug-likeness and pharmacokinetic studies were also carried out. Compound 9j also possessed metal chelation potential correlated to its high anti-TYR activity.

SAR and QSAR research on tyrosinase inhibitors using machine learning methods

Tyrosinase is a key rate-limiting enzyme in the process of melanin synthesis, which is closely related to human pigmentation disorders. Tyrosinase inhibitors can down-regulate tyrosinase to effectively reduce melanin synthesis. In this work, we conducted structure-activity relationship (SAR) study on 1097 diverse mushroom tyrosinase inhibitors. We applied five kinds of machine learning methods to develop 15 classification models. Model 5B built by fully connected neural networks and ECFP4 fingerprints achieved the highest prediction accuracy of 91.36% and Matthews correlation coefficient (MCC) of 0.81 on the test set. The applicability domains (AD) of classification models were defined by d S T D - P R O method. Moreover, we clustered the 1097 inhibitors into eight subsets by K-Means to figure out inhibitors' structural features. In addition, 10 quantitative structure-activity relationship (QSAR) models were constructed by four machine learning methods based on 813 inhibitors. Model 6 J, the best QSAR model, was developed by fully connected neural networks with 50 RDKit descriptors. It resulted in a coefficient of determination (r ²) of 0.770 and a root mean squared error (RMSE) of 0.482 on the test set. The AD of Model 6 J was visualized by Williams plot. The models built in this study can be obtained from the authors.

Trending Topics on Coumarin and Its Derivatives in 2020

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