Recent advances in triazoles as tyrosinase inhibitors

Study on the synthesis and biological activity of kojic acid triazol thiosemicarbazide Schiff base derivatives

A series of kojic acid triazol thiosemicarbazide Schiff base derivatives were designed and synthesised. Evaluation on the inhibition of tyrosinase activity showed that these compounds possessed potent inhibit tyrosinase activity, and the compound 6w (IC50 = 0.94 μM) exhibited the best inhibitory effect. Preliminary structure-activity relationships indicate that steric hindrance, halogen atom radius, and electron donating ability of functional groups have some impact on the inhibition of tyrosinase activity. Inhibition mechanism showed that compound 6w is a non-competitive mixed inhibitor, and this result was further confirmed by molecular docking. The fluorescence quenching mode of compound 6w is dynamic quenching, and interacts with tyrosinase by changing the amide structure of tyrosinase. Compound 6w has some anti-browning effect. Compound 6p had the strongest DPPH radical scavenging activity (IC50 = 10.53 ± 0.014 μM), and compound 6w showed the best ABTS scavenging activity (IC50 = 3.03 ± 0.009 μM).

Design and Synthesis of Heptadecane-Linked 1,2,4-Triazoles as Antimicrobial Agents

Superbugs, as bacterial resistance species, resist known antibiotics. In this study, 20 novel 1,2,4-triazole-functionalized piperazine-stearic acid derivatives 6a-p were designed, synthesized, and characterized via spectroscopic analyses, evaluating their antimicrobial potential against clinically relevant bacterial and fungal strains. Notably, five derivatives (6a, 6c, 6m, 6n, and 6o) demonstrated superior antimicrobial efficacy compared to the gentamicin standard, with compound 6n showing the most potent activity (minimal inhibitory concentration = 3.125 µg/mL against Staphylococcus aureus). Molecular docking simulations further revealed strong binding affinities of these compounds to microbial target proteins (ΔG = -8.2 to -9.7 kcal/mol). These findings present promising antimicrobial candidates of 1,2,4-triazole-appended piperazine-stearic moiety derivatives.

Design, synthesis, and evaluation of carboxylic acid-substituted celecoxib isosteres as potential anti-inflammatory agents

A library comprising twenty-four isosteric derivatives of celecoxib substituted with carboxylic acid (labeled as 5a-5x), was synthesized and characterized through 1H NMR, 13C NMR, HRMS, and elemental analysis. Molecular docking studies revealed that all compounds successfully docked into the binding pocket of COX-2, and the introduction of carboxyl group enhances the interaction between the derivatives and COX-2. The compounds were further evaluated for cell toxicity, and in vitro anti-inflammatory activity. Notably, compound 5l exhibited significant inhibition of both COX-2 and NO release in vitro in comparison to the standard compound, displaying the highest selectivity towards the COX-2 enzyme (SI = 295.9) in comparison to celecoxib (SI = 261.3). 5l also exhibited the most potent anti-inflammatory activity and safety (ulcer index = 5.2) in vivo comparable to celecoxib at the same concentration. Through the molecular modeling and dynamics analysis, it was observed that compound 5l effectively stabilized within the active binding site of COX-2 through strong hydrogen bond interactions, and through the ADMET studies investigated the physiochemical properties and drug-likeliness behavior of compound 5l. In conclusion, compound 5l demonstrated to be a potential selective COX-2 anti-inflammatory candidate with reduced gastrointestinal risks.

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.

Investigation of the Inhibitory Activity of β-Arbutin and its Analogues on Tyrosinase Based on Molecular Docking and Enzyme Inhibition Kinetics

β-Arbutin, a natural glucoside hydroquinone derivative known for its skin-whitening properties through tyrosinase inhibition in melanin synthesis, may pose potential risks of allergy and carcinogenicity due to the release of hydroquinone during use. This study explores the inhibitory effects of phenyl-β-D-pyranoglucoside (compound 1), 4-methoxyphenyl-β-D-pyranoglucoside (compound 2), 4-hydroxymethylphenyl-β-D-pyranoglucoside (compound 3), and β-arbutin (compound 4) on tyrosinase using enzyme kinetics, molecular docking, and molecular dynamics simulations. Results show compounds 1, 3, and 4 exhibit competitive inhibition, while compound 2 shows mixed inhibition. Docking analysis reveals phenyl rings of all compounds interact with the enzyme's active site, with compound 3 forming a metal bond with copper ions. MD simulations indicate high stability for compounds 2, 3, and 4, with compound 3 showing the lowest RMSD and compact Rg, suggesting stronger binding. Compound 1 is less stable and less inhibitory. These insights are valuable for designing effective tyrosinase inhibitors.

Development of novel pyrazole-1,2,4-triazole derivatives as tyrosinase inhibitors: Design, preparation, mechanism of action and anti-browning application

Tyrosinase (Polyphenol oxidase), a key enzyme in enzymatic browning, is an attractive target for developing new anti-browning agents in the food industry. In this work, twenty pyrazole-1,2,4-triazole derivatives (3a-3n, 4a-4f) were synthesized and tested in vitro, most of compounds showed potent anti-tyrosinase activity. Of these, 3c (IC50 = 1.02 ± 0.08 μM) was found to be 14 folds stronger than kojic acid (IC50 = 14.74 ± 1.23 μM) and behaved as a mixed type inhibitor. Besides, the disappeared peak of dopaquinone in the HPLC assay intuitively validated the inhibitory effect of 3c. Copper ions chelating, fluorescence quenching and molecular docking assays showed that coordination with copper is the key to play a role. Furthermore, 3c exhibited excellent anti-browning ability for the Rosa roxburghii Tratt, the non-enzymatic browning experiment showed that 3c could prevent browning in non-enzymatic ways. It is suggested that these derivatives could serve as the leading compounds to find more efficient anti-browning agents in the future.

Enhanced skin benefits of EGCG loaded in nonapeptide-1-conjugated mesoporous silica nanoparticles to reverse skin photoaging

Epigallocatechin-3-gallate (EGCG), a catechin present in green tea, has been studied extensively for its potential as a cosmetic ingredient due to its various biological properties. However, the low stability and bioavailability of EGCG have hindered its effective utilization in cosmetic applications. This study, to improve the stability and bioavailability of EGCG for reversing skin photo-aging, nonapeptide-1-conjugated mesoporous silica nanoparticles (EGCG@NP-MSN) were fabricated to load EGCG. MSNs can regulate the EGCG release and provide ultraviolet light (UV) protection to possess excellent photostability. Nonapeptide-1 exhibits melanin transfer interference properties and reduces the melanin content in treated skin areas. In vitro and in vivo results confirmed that the EGCG-loaded MSNs retained antioxidant properties, effectively scavenged the melanin and significantly reduced the deoxyribonucleic acid (DNA) damage in skin cells exposed to UV irradiation. The melanin inhibition rate is 5.22 times and the tyrosinase inhibition rate is 1.57 times that of free EGCG. The utilization of this innovative platform offers the potential for enhanced stability, controlled release, and targeted action of EGCG, thereby providing significant advantages for skin application.This delivery system combines the advantages of antioxidant, anti-aging, and anti-UV radiation properties, paving the way for the cosmetics development with improved efficacy and better performance in promoting skin health and appearance.

Metabolites Obtained from Boraginaceae Plants as Potential Cosmetic Ingredients-A Review

One of the challenges of the pharmaceutical and cosmetic industries is to deliver biochemical compounds that can be advantageous for the skin. Research on Boraginaceae taxa has confirmed their use in traditional medicine and proved the potential biological importance of various molecules in cosmetology. The main classes of valuable compounds associated with Boraginaceae taxa are fatty acids, including γ-linolenic acid, essential oils, phenolic acids (e.g., rosmarinic acid), flavonoids, anthocyanins, tannins, and saponins. Highly specific are naphthoquinone pigments (including shikonin) and allantoin. Another distinguishing feature is the accumulation of silica (silicon dioxide) in trichomes. Some taxa produce mucilages. However, pyrrolizidine alkaloids (PAs) with toxic properties are also found (mainly in Symphytum spp.); therefore, their applications should be avoided. Extracts or individual compounds of Boraginaceae plants are characterized by antioxidant, anti-inflammatory, antiseptic, anti-irritant, antiaging, and photoprotective activities. Boraginaceae products are widespread in the cosmetic industry as ingredients of creams, balms, lotions, gels, shampoos, lipsticks, perfumes, and deodorants. The most valuable for the cosmetic industry are raw materials obtained from the genera Alcanna Anchusa, Arnebia, Borago, Buglossoides, Cerinthe, Cordia, Echium, Ehretia, Eriodictyon, Glendora, Lappula, Lithospermum, Lycopsis, Macrotomia, Maharanga, Mertensia, Messerschmidia, Myosotis, Omphalodes, Onosma, Pulmonaria, Rindera, Symphytum, Trachystemon, and Trigonotis. Further research should focus on the search for active substances in other plants of the family.

Tokishakuyakusan alleviates ultraviolet-induced skin pigmentation by decreasing the expression of melanogenesis-related enzymes

ETHNOPHARMACOLOGICAL RELEVANCE

Tokishakuyakusan (TSS), a traditional Kampo medicine, can effectively alleviate symptoms unique to women, such as menstrual pain and menopausal symptoms, and this effect is believed to be related to its ability to increase the secretion of female hormones. TSS is also believed to be effective against skin pigmentation. However, no studies have examined the effect of TSS on pigmentation.

AIM OF THE STUDY

In this study, we conducted basic research to determine the effects of TSS on pigmentation.

MATERIALS AND METHODS

Female HRM-2 mice were given free access to a normal diet or a TSS-containing diet for 7 weeks. For 3 weeks starting from the 4th week of treatment, the back of the skin was irradiated with ultraviolet (UV) light, and the melanin level was measured. The expression levels of melanogenesis-related genes and inflammatory markers in the skin were analyzed.

RESULTS

The melanin level in the skin of the mice exposed to UV radiation was approximately three times greater than that in the skin of the mice in the non-UV-irradiated group, confirming pigmentation due to UV irradiation. The protein expression levels of tyrosinase (Tyr), tyrosinase-related protein-1 (Tyrp1), and dopachrome tautomerase (Dct), which are important for melanin production, were significantly greater in the UV irradiation group than in the non-UV irradiation group. In contrast, the amount of skin melanin in the mice treated with TSS was significantly lower than that in the UV-irradiated group, and the expression levels of melanogenesis-related enzymes were also lower. Furthermore, TSS significantly decreased the expression of microphthalmia transcription factor (Mitf), a transcription factor for melanogenesis-related enzymes, and the inflammatory cytokines interleukin-1β and interleukin-6.

CONCLUSIONS

TSS inhibits melanin production in melanocytes by suppressing the increase in the expression of melanogenesis-related enzymes caused by UV irradiation. These findings suggested that this effect of TSS is exerted through the combined regulation of MITF expression and anti-inflammatory responses.

Synthesis, Characterization and Assessment of Antioxidant and Melanogenic Inhibitory Properties of Edaravone Derivatives

A series of edaravone derivatives and the corresponding Cu(II) complexes were synthesized and characterized using spectroscopic and analytical techniques such as IR, UV, NMR and elemental analysis. Antioxidant activities of all compounds were examined using free radical scavenging methods such as hydrogen peroxide scavenging activity (HPSA), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2-2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) assays. All of the tested compounds exhibited good antioxidant activity. Further, the frontier orbital energy levels, as well as various chemical properties, were determined using the density functional theory (DFT) calculations. The MEP maps of all of the derivatives were plotted to identify the nucleophilic and electrophilic reactive sites. Further, binding energies of all of the organic compounds with the protein tyrosinase was investigated to determine their potential anti-melanogenic applications. The selected ligand, L6 was subjected to molecular dynamics simulation analysis to determine the stability of the ligand-protein complex. The MD simulation was performed (150 ns) to estimate the stability of the tyrosinase-L6 complex. Other key parameters, such as, RMSD, RMSF, Rg, hydrogen bonds, SASA and MMPBSA were also analyzed to understand the interaction of L6 with the tyrosinase protein.

A new strategy for the treatment of Parkinson's disease: Discovery and bio-evaluation of the first central-targeting tyrosinase inhibitor

The high level of tyrosinase leads to the generation of neuromelanin, further causing the abnormality of redox-related protein level and mediating the occurrence and development of Parkinson's disease (PD). However, the existing tyrosinase inhibitors are mostly natural product extracts or polyphenolic derivatives, which hindered them from penetrating the blood-brain barrier (BBB). Herein, we obtained a novel tyrosinase inhibitor, 2-06 (tyrosinase: monophenolase IC50 = 70.44 ± 22.69 μM, diphenolase IC50 = 1.89 ± 0.64 μM), through the structure-based screening method. The compound 2-06 presented good in vitro and in vivo safety, and can inhibit the tyrosinase and melanogenesis in B16F10. Moreover, this compound showed neuroprotective effects and Parkinsonism behavior improving function. 2-06 was proved to penetrate the BBB and enter the central nervous system (CNS). The exploration of the binding mode between 2-06 and tyrosinase provided the foundation for the subsequent structural optimization. This is the first research to develop a central-targeting tyrosinase inhibitor, which is crucial for in-depth study on the new strategy for utilizing tyrosinase inhibitors to treat PD.

Inhibitory Effects, Fluorescence Studies, and Molecular Docking Analysis of Some Novel Pyridine-Based Compounds on Mushroom Tyrosinase

Melanin biosynthesis in different organisms is performed by a tyrosinase action. Excessive enzyme activity and pigment accumulation result in different diseases and disorders including skin cancers, blemishes, and darkening. In fruits and vegetables, it causes unwanted browning of these products and reduces their appearance quality and economic value. Inhibiting enzyme activity and finding novel powerful and safe inhibitors are highly important in agriculture, food, medical, and pharmaceutical industries. In this regard, in the present study, some novel synthetic pyridine-based compounds including 2,6-bis (tosyloxymethyl) pyridine (compound 3), 2,6-bis (butylthiomethyl) pyridine (compound 4), and 2,6-bis (phenylthiomethyl) pyridine (compound 5) were synthesized for the first time, and their inhibitory potencies were assessed on mushroom tyrosinase diphenolase activity. The results showed that while all tested compounds significantly decreased the enzyme activity, compounds 4 and 5 had the highest inhibitory effects (respectively, 80 and 89% inhibition with the IC50 values of 17.0 and 9.0 μmol L-1), and the inhibition mechanism was mixed-type for both compounds. Ligand-binding studies were carried out by fluorescence quenching and molecular docking methods to investigate the enzyme-compound interactions. Fluorescence quenching results revealed that the compounds can form nonfluorescent complexes with the enzyme and result in quenching of its intrinsic emission by the static process. Molecular docking analyses predicted the binding positions and the amino acid residues involved in the interactions. These compounds appear to be suitable candidates for more studies on tyrosinase inhibition.

Rubus urticifolius Compounds with Antioxidant Activity, and Inhibition Potential against Tyrosinase, Melanin, Hyaluronidase, Elastase, and Collagenase

In our study, using chromatographic techniques, we isolated three bioactive compounds, which were structurally elucidated as (E)-2-(3-(3,4-dimethoxyphenyl)acrylamido)-N-methylbenzamide (1), 4-Hydroxyquinoline-2-carboxylic acid (2), and (E)-2-Cyano-3-(4-hydroxyphenyl)acrylic acid (3), using spectroscopic methods. The anti-melanogenic, anti-inflammatory, antioxidant, and anti-aging properties were evaluated in vitro by measuring the activity of pharmacological targets including tyrosinase, melanin, NF-κB, hyaluronidase, elastase, collagenase, and Nrf2. Our results show that compound 1 is the most active with IC50 values of 14.19 μM (tyrosinase inhibition), 22.24 μM (melanin inhibition), 9.82-12.72 μM (NF-κB inhibition), 79.71 μM (hyaluronidase inhibition), 80.13 μM (elastase inhibition), 76.59 μM (collagenase inhibition), and 116-385 nM (Nrf2 activation) in the THP-1, HEK001, WS1, and HMCB cells. These findings underscore the promising profiles of the aqueous extract of R. urticifolius at safe cytotoxic concentrations. Additionally, we report, for the first time, the isolation and characterisation of these nitrogenous compounds in the R. urticifolius species. Finally, compound 1, isolated from R. urticifolius, is a promising candidate for the development of more effective and safer compounds for diseases related to skin pigmentation, protection against inflammation, and oxidative stress.

Elucidating bis-pyrimidines as new and efficient mushroom tyrosinase inhibitors: synthesis, SAR, kinetics and computational studies

In this study, a series of novel bis-pyrimidine derivatives (1P-8P) were designed, synthesized, characterized, and investigated for their in vitro inhibitory activity against mushroom tyrosinase, an enzyme critical in melanin biosynthesis and implicated in various hyperpigmentation disorders. To the best of our knowledge, the bispyrimidine scaffold has been evaluated for the first time for its tyrosinase inhibitory activity. Their inhibitory activities were assessed, revealing inhibition with IC50 values in the micromolar range. Additionally, this series of compounds were found to inhibit tyrosinase activity in a mixed-type manner, with IC50 values ranging from 12.36 ± 1.24 to 86.67 ± 3.08 μM. To further elucidate the binding interactions, molecular docking simulations were performed, identifying key residues in the active site responsible for binding affinity. Furthermore, molecular dynamics (MD) simulations were conducted to assess the dynamic behavior, stability, and binding affinity of the most potent inhibitor, compound 6P. Quantitative Structure-Activity Relationship (QSAR) models were developed to correlate the structural features of the bis-pyrimidines with their inhibitory activity, providing insights into the structure-activity relationships (SAR) that govern their potency. The experimental and theoretical findings demonstrated excellent agreement. These findings pave the way for the development of novel bis-pyrimidine-based therapeutic agents for treating hyperpigmentation and related conditions.

Investigation of the Efficacy of Benzylidene-3-methyl-2-thioxothiazolidin-4-one Analogs with Antioxidant Activities on the Inhibition of Mushroom and Mammal Tyrosinases

Based on the fact that substances with a β-phenyl-α,β-unsaturated carbonyl (PUSC) motif confer strong tyrosinase inhibitory activity, benzylidene-3-methyl-2-thioxothiazolidin-4-one (BMTTZD) analogs 1-8 were prepared as potential tyrosinase inhibitors. Four analogs (1-3 and 5) inhibited mushroom tyrosinase strongly. Especially, analog 3 showed an inhibitory effect that was 220 and 22 times more powerful than kojic acid in the presence of l-tyrosine and l-dopa, respectively. A kinetic study utilizing mushroom tyrosinase showed that analogs 1 and 3 competitively inhibited tyrosinase, whereas analogs 2 and 5 inhibited tyrosinase in a mixed manner. A docking simulation study indicated that analogs 2 and 5 could bind to both the tyrosinase active and allosteric sites with high binding affinities. In cell-based experiments using B16F10 cells, analogs 1, 3, and 5 effectively inhibited melanin production; their anti-melanogenic effects were attributed to their ability to inhibit intracellular tyrosinase activity. Moreover, analogs 1, 3, and 5 inhibited in situ B16F10 cellular tyrosinase activity. In three antioxidant experiments, analogs 2 and 3 exhibited strong antioxidant efficacy, similar to that of the positive controls. These results suggest that the BMTTZD analogs are promising tyrosinase inhibitors for the treatment of hyperpigmentation-related disorders.

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.

Variation of the essential oil components of Citrus aurantium leaves upon using different distillation techniques and evaluation of their antioxidant, antidiabetic, and neuroprotective effect against Alzheimer's disease

Citrus fruit essential oil is considered one of the widely studied essential oils while its leaves attract less attention although being rich in nearly the same composition as the peel and flowers. The leaves of bitter orange or sour orange (Citrus aurantium L.) were extracted using three different techniques namely; hydrodistillation (HD), steam distillation (SD), and microwave-assisted distillation (MV) to compare their chemical composition. The three essential oil samples were analyzed through GC/FID and GC/MS analyses. The samples were tested in vitro using different antioxidant techniques (DPPH, ABTS, CUPRAC, FRAP, PBD, and MCA), neuroprotective enzyme inhibitory activities (acetylcholine and butyl choline enzymes), and antidiabetic activities (α-amylase and α-glucosidase). The results showed that thirty-five volatile ingredients were detected and quantified. Monoterpenes represented the most abundant class in the three essential oils followed by sesquiterpenes. C. aurantium essential oil carried potential antioxidant activity where SD exhibited the highest antioxidant activity, with values arranged in the following order: FRAP (200.43 mg TE/g), CUPRAC (138.69 mg TE/g), ABTS (129.49 mg TE/g), and DPPH (51.67 mg TE/g). SD essential oil also presented the most potent α-amylase (0.32) inhibition while the MV essential oil showed the highest α-glucosidase inhibition (2.73 mmol ACAE/g), followed by HD (2.53 mmol ACAE/g), and SD (2.46 mmol ACAE/g). The SD essential oil exhibited the highest BChE and AChE inhibitory activities (3.73 and 2.06 mg GALAE/g), respectively). Thus, bitter orange essential oil can act as a potential source of potent antioxidant, antidiabetic, and neuroprotective activities for future drug leads.

Novel Benzotriazole-β-lactam Derivatives as Antimalarial Agents: Design, Synthesis, Biological Evaluation and Molecular Docking Studies

Many people around the world suffer from malaria, especially in tropical or subtropical regions. While malaria medications have shown success in treating malaria, there is still a problem with resistance to these drugs. Herein, we designed and synthesized some structurally novel benzotriazole-β-lactams using 2-(1H-benzo[d][1,2,3]triazol-1-yl)acetic acid as a key intermediate. To synthesize the target molecules, the ketene-imine cycloaddition reaction was employed. First, The reaction of 1H-benzo[d][1,2,3]triazole with 2-bromoacetic acid in aqueous sodium hydroxide yielded 2-(1H-benzo[d][1,2,3]triazol-1-yl)acetic acid. Then, the treatment of 2-(1H-benzo[d][1,2,3]triazol-1-yl)acetic acid with tosyl chloride, triethyl amine, and Schiff base provided new β-lactams in good to moderate yields.The formation of all cycloadducts was confirmed by elemental analysis, FT-IR, NMR and mass spectral data. Moreover, X-ray crystallography was used to determine the relative stereochemistry of 4a compound. The in vitro antimalarial activity test was conducted for each compound against P. falciparum K1. The IC50 values ranged from 5.56 to 25.65 μM. A cytotoxicity profile of the compounds at 200 μM final concentration revealed suitable selectivity of the compounds for malaria treatment. Furthermore, the docking study was carried out for each compound into the P. falciparum dihydrofolate reductase enzyme (PfDHFR) binding site to analyze their possible binding orientation in the active site.

Biochemical and In Silico Studies on Triazole Derivatives as Tyrosinase Inhibitors: Potential Treatment of Hyperpigmentation Related Skin Disorders

INTRODUCTION

Tyrosinase is a versatile, glycosylated copper-containing oxidase enzyme that mainly catalyzes the biosynthesis of melanin in mammals. Its overexpression leads to the formation of excess melanin, resulting in hyperpigmentary skin disorders, such as dark spots, melasma, freckles, etc. Therefore, inhibition of tyrosinase is a therapeutic approach for the treatment of hyperpigmentation.

METHODS

The current study focused on evaluating tyrosinase inhibitory activities of triazole derivatives 1-20, bearing different substituents on the phenyl ring. 17 derivatives have shown a potent tyrosinase inhibition with IC50 values between 1.6 to 13 μM, as compared to the standard drug, i.e., kojic acid (IC50 = 24.1 ± 0.5 μM). Particularly, compounds 11 and 15 displayed 12 times more potent inhibitory effects than the kojic acid.

RESULTS

The structure-activity relationship revealed that substituting halogens at the C-4 position of the benzene ring renders remarkable anti-tyrosinase activities. Compounds 1-3 and 8 showed a competitive type of inhibition, while compounds 5, 11, and 15 showed a non-competitive mode of inhibition. Next, we performed molecular docking analyses to study the binding modes and interactions between the ligands (inhibitors) and the active site of the tyrosinase enzyme (receptor). Besides this, we have assessed the toxicity profile of inhibitors on the BJ human fibroblast cell line.

CONCLUSION

The majority of the newly identified tyrosinase inhibitors were found to be noncytotoxic. The results presented herein form the basis of further studies on triazole derivatives as potential drug leads against tyrosinase-related diseases.

Investigation on the inhibition mechanism and binding behavior of paeonol to tyrosinase and its anti-browning property by multi-spectroscopic and molecular docking methods

Paeonol, as one effective tyrosinase inhibitor, had been used as food preservative and clinical medication for skin disorders. In this study, the inhibition mechanism and binding behavior of paeonol to tyrosinase and its anti-browning property were investigated using multi-spectroscopic and molecular docking methods. Activity assay and kinetic results confirmed paeonol as a reversible mixed-type tyrosinase inhibitor. Results of the mechanistic studies were clarified using fluorescence quenching, synchronous fluorescence, CD spectra and 3D fluorescence, and showed that the binding of paeonol to tyrosinase might change the chromophore microenvironment and conformation of tyrosinase to inhibit enzyme catalytic activity. Molecular docking results revealed the detailed binding between paeonol and tyrosinase. Moreover, paeonol could prevent the browning of fresh-cut apples, as well as inhibiting PPO and POD activities and increasing APX activity. All above findings established a reliable basis for the inhibitory mechanism of paeonol against tyrosinase and therefore contributed to its application in anti-browning.

In Vitro and In Vivo Biological Evaluation of Indole-thiazolidine-2,4-dione Derivatives as Tyrosinase Inhibitors

Tyrosinase is an important rate-limiting enzyme in melanin biosynthesis. To find potential tyrosinase inhibitors with anti-melanogenic activity, a series of indole-thiazolidine-2,4-dione derivatives 5a~5z were synthesized by incorporating indole with thiazolidine-2,4-dione into one compound and assayed for their biological activities. All compounds displayed tyrosinase inhibitory activities and 5w had the highest anti-tyrosinase inhibitory activity with an IC50 value of 11.2 μM. Inhibition kinetics revealed 5w as a mixed-type tyrosinase inhibitor. Fluorescence quenching results indicated that 5w quenched tyrosinase fluorescence in a static process. CD spectra and 3D fluorescence spectra results suggested that the binding of 5w with tyrosinase could change the conformation and microenvironment of tyrosinase. Molecular docking also represented the binding between 5w and tyrosinase. Moreover, 5w could inhibit tyrosinase activity and melanogenesis both in B16F10 cells and the zebrafish model. Therefore, compound 5w could serve as a tyrosinase inhibitor with anti-melanogenic activity.

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.