Synthesis, computational molecular docking analysis and effectiveness on tyrosinase inhibition of kojic acid derivatives

Novel Tripeptides as Tyrosinase Inhibitors: In Silico and In Vitro Approaches

Tyrosinase is a key enzyme responsible for the formation of melanin (a natural skin pigment with ultraviolet-protection properties). However, some people experience melanin overproduction, so new, safe, and biocompatible enzyme inhibitors are sought. New tripeptide tyrosinase inhibitors were developed using molecular modeling. A combinatorial library of tripeptides was prepared and docked to the mushroom tyrosinase crystal structure and investigated with molecular dynamics. Based on the results of calculations and expert knowledge, the three potentially most active peptides (CSF, CSN, CVL) were selected. Their in vitro properties were examined, and they achieved half-maximal inhibitory concentration (IC50) values of 136.04, 177.74, and 261.79 µM, respectively. These compounds attach to the binding pocket of tyrosinase mainly through hydrogen bonds and salt bridges. Molecular dynamics simulations demonstrated the stability of the peptid-tyrosinase complexes and highlighted the persistence of key interactions throughout the simulation period. The ability of these peptides to complex copper ions was also confirmed. The CSF peptide showed the highest chelating activity with copper. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay confirmed that none of the test tripeptides showed cytotoxicity toward the reconstructed human epidermis. Our results indicated that the developed tripeptides were non-toxic and effective tyrosinase inhibitors. They could be applied as raw materials in skin-brightening or anti-aging cosmetic products.

Computational studies of tyrosinase inhibitors

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

Discovery of novel 1,2,4-triazole tethered β-hydroxy sulfides as bacterial tyrosinase inhibitors: synthesis and biophysical evaluation through in vitro and in silico approaches

In this study, a series of 1,2,4-triazole-tethered β-hydroxy sulfide scaffolds 11a-h was synthesized in good to remarkable yields (69-90%) through the thiolysis of oxiranes by the thiols in aqueous basic catalytic conditions. The synthesized 1,2,4-triazole-tethered β-hydroxy sulfides were screened against bacterial tyrosinase enzyme, and Gram-positive and Gram-negative bacterial cultures i.e., (S. aureus) Staphylococcus aureus & (E. coli) Escherichia coli. Among the synthesized derivatives, the molecules 11a (IC50 = 7.67 ± 1.00 μM), 11c (IC50 = 4.52 ± 0.09 μM), 11d (IC50 = 6.60 ± 1.25 μM), and 11f (IC50 = 5.93 ± 0.50 μM) displayed the better tyrosinase inhibitory activity in comparison to reference drugs ascorbic acid (IC50 = 11.5 ± 1.00 μM) and kojic acid (IC50 = 30.34 ± 0.75 μM). The molecule benzofuran-triazol-propan-2-ol 11c proved to be the most potent bacterial tyrosinase inhibitory agent with a minimum IC50 of 4.52 ± 0.09 μM, as compared to other synthesized counterparts and both standards (kojic acid and ascorbic acid). The compound diphenyl-triazol-propan-2-ol 11a and benzofuran-triazole-propan-2-ol 11c showed comparable anti-bacterial chemotherapeutic efficacy with minimum inhibitory concentrations (MIC = 2.0 ± 2.25 mg mL-1 and 2.5 ± 0.00 mg mL-1, respectively) against S. aureus bacterial strain in comparison with standard antibiotic penicillin (MIC = 2.2 ± 1.15 mg mL-1). Furthermore, among the synthesized derivatives, only compound 11c demonstrated better anti-bacterial activity (MIC = 10 ± 0.40 mg mL-1) against E. coli, which was slightly less than the standard antibiotic i.e., penicillin (MIC = 2.4 ± 1.00 mg mL-1). The compound 11c demonstrated a better binding score (-7.08 kcal mol-1) than ascorbic acid (-5.59 kcal mol-1) and kojic acid (-5.78 kcal mol-1). Molecular docking studies also validate the in vitro anti-tyrosinase assay results; therefore, the molecule 11c can be the lead bacterial tyrosinase inhibitor as well as the antibacterial agent against both types of bacterial strains after suitable structural modifications.

Real-Time Monitoring of Tyrosine Hydroxylase Activity with a Ratiometric Fluorescent Probe

Parkinson's disease (PD) represents the second most widespread neurodegenerative disease, and early monitoring and diagnosis are urgent at present. Tyrosine hydroxylase (TH) is a key enzyme for producing dopamine, the levels of which can serve as an indicator for assessing the severity and progression of PD. This renders the specific detection and visualization of TH a strategically vital way to meet the above demands. However, a fluorescent probe for TH monitoring is still missing. Herein, three rationally designed wash-free ratiometric fluorescent probes were proposed. Among them, TH-1 exhibited ideal photophysical properties and specific dual-channel bioimaging of TH activity in SH-SY5Y nerve cells. Moreover, the probe allowed for in vivo imaging of TH activity in zebrafish brain and living striatal slices of mice. Overall, the ratiometric fluorescent probe TH-1 could serve as a potential tool for real-time monitoring of PD in complex biosystems.

Artificial Intelligence-Assisted Optimization of Antipigmentation Tyrosinase Inhibitors: De Novo Molecular Generation Based on a Low Activity Lead Compound

Artificial intelligence (AI) de novo molecular generation is a highly promising strategy in the drug discovery, with deep reinforcement learning (RL) models emerging as powerful tools. This study introduces a fragment-by-fragment growth RL forward molecular generation and optimization strategy based on a low activity lead compound. This process integrates fragment growth-based reaction templates, while target docking and drug-likeness prediction were simultaneously performed. This comprehensive approach considers molecular similarity, internal diversity, synthesizability, and effectiveness, thereby enhancing the quality and efficiency of molecular generation. Finally, a series of tyrosinase inhibitors were generated and synthesized. Most compounds exhibited more improved activity than lead, with an optimal candidate compound surpassing the effects of kojic acid and demonstrating significant antipigmentation activity in a zebrafish model. Furthermore, metabolic stability studies indicated susceptibility to hepatic metabolism. The proposed AI structural optimization strategies will play a promising role in accelerating the drug discovery and improving traditional efficiency.

Isolation, Characterization, Genome Annotation, and Evaluation of Tyrosinase Inhibitory Activity in Secondary Metabolites of Paenibacillus sp. JNUCC32: A Comprehensive Analysis through Molecular Docking and Molecular Dynamics Simulation

A potential strain, Paenibacillus sp. JNUCC32, was isolated and subjected to whole-genome sequencing. Genome functional annotation revealed its active metabolic capabilities. This study aimed to investigate the pivotal secondary metabolites in the biological system. Fermentation and extraction were performed, resulting in the isolation of seven known compounds: tryptophol (1), 3-(4-hydroxyphenyl)propionic acid (2), ferulic acid (3), maculosin (4), brevianamide F (5), indole-3-acetic acid (6), and butyric acid (7). Tryptophol exhibited favorable pharmacokinetic properties and demonstrated certain tyrosinase inhibitory activity (IC50 = 999 μM). For further analysis of its inhibition mechanism through molecular docking and molecular dynamics (MD) simulation, tryptophol formed three hydrogen bonds and a pro-Michaelis complex with tyrosinase (binding energy = -5.3 kcal/mol). The MD simulation indicated favorable stability for the tryptophol-mushroom tyrosinase complex, primarily governed by hydrogen bond interactions. The crucial residues VAL-283 and HIS-263 in the docking were also validated. This study suggests tryptophol as a potential candidate for antibrowning agents and dermatological research.

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.

Optimization of a Novel Tyrosinase Inhibitory Peptide from Atrina pectinata Mantle and Its Molecular Inhibitory Mechanism

In order to realize the multi-level utilization of marine shellfish resources and to develop the potential biological activity of processing by-products of Atrina pectinata, gelatin was extracted from the mantle and the potential whitening effect of its enzymatic peptides was explored. Taking tyrosinase inhibitory activity as the evaluation index, the enzyme hydrolysate process was optimized by response-surface methodology, and the optimal enzyme hydrolysate conditions were as follows: pH 5.82, 238 min enzyme hydrolysate time, and temperature of 54.5 °C. Under these conditions, the tyrosinase inhibition activity of Atrina pectinata mantle gelatin peptide (APGP) was 88.6% (IC50 of 3.268 ± 0.048 mg/mL). The peptides obtained from the identification were separated by ultrafiltration and LC-MS/MS, and then four new peptides were screened by molecular docking, among which the peptide Tyr-Tyr-Pro (YYP) had the strongest inhibitory effect on tyrosinase with an IC50 value of 1.764 ± 0.025 mM. The molecular-docking results indicated that hydrogen bonding is the main driving force for the interaction of the peptide YYP with tyrosinase. From the Lineweaver-Burk analysis, it could be concluded that YYP is inhibitory to tyrosinase and exhibits a mixed mechanism of inhibition. These results suggest that YYP could be widely used as a tyrosinase inhibitor in whitening foods and pharmaceuticals.

Synthesis and biological evaluation of substituted aurone derivatives as potential tyrosinase inhibitors: in vitro, kinetic, QSAR, docking and drug-likeness studies

Tyrosinase enzyme plays an essential role in melanin biosynthesis and enzymatic browning of fruits and vegetables. To discover potent tyrosinase inhibitors, the present studies were undertaken. In this context, synthetic aurone derivatives 26-50 were designed, synthesized, and structurally elucidated by various spectroscopic techniques including IR, UV, 1H- & 13C-NMR and mass spectrometry. The target compounds 26-50 were screened for their anti-tyrosinase inhibitory potential, and thus kinetic mechanism was analyzed by Lineweaver-Burk plots. All target compounds exhibited good to excellent IC50 values in the range of 7.12 ± 0.32 μM to 66.82 ± 2.44 μM. These synthesized aurone derivatives were found as potent tyrosinase inhibitors relative to the standard kojic acid (IC50 = 16.69 ± 2.81 μM) and the compound 39 inhibited tyrosinase non-competitively (Ki = 11.8 μM) by forming an enzyme-inhibitor complex. The binding modes of these molecules were ascribed through molecular docking studies against tyrosinase protein (PDB ID: 2Y9X). The quantitative structure-activity relationship studies displayed a good correlation between 26-50 structures and their anti-tyrosinase activity (IC50) with a correlation coefficient (R2) of 0.9926. The computational studies were coherent with experimental results and these ligands exhibited good binding values against tyrosinase and interacted with core residues of target protein. Moreover, the drug-likeness analysis also showed that some compounds have a linear correlation with Lipinski's rule of five, indicating good drug-likeness and bioactivity scores for pharmacological targets.Communicated by Ramaswamy H. Sarma.

Harnessing the Bioactive Potential of Limonium spathulatum (Desf.) Kuntze: Insights into Enzyme Inhibition and Phytochemical Profile

This study assessed the halophyte species Limonium spathulatum (Desf.) as a possible source of natural ingredients with the capacity to inhibit enzymes related to relevant human health disorders and food browning. Extracts using food-grade solvents such as water and ethanol were prepared by maceration from dried L. spathulatum leaves. They were evaluated for in vitro inhibition activity of enzymes such as acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), α-glucosidase, tyrosinase and lipase, related to Alzheimer's disease, type-2-diabetes mellitus, skin hyperpigmentation, and obesity, respectively. These extracts were also appraised for in vitro acute toxicity on tumoral and non-tumoral cell lines and their chemical composition by high-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS/MS). The extracts were more effective towards BChE than AChE. The best results were obtained with the hydroethanolic and water extracts, with IC50 values of 0.03 mg/mL and 0.06 mg/mL, respectively. The hydroethanolic extract had the highest capacity to inhibit α-glucosidase (IC50: 0.04 mg/mL), higher than the positive control used (acarbose, IC50 = 3.14 mg/mL). The ethanol extract displayed the best inhibitory activity against tyrosinase (IC50 = 0.34 mg/mL). The tested samples did not inhibit lipase and exhibited low to moderate cytotoxic activity against the tested cell lines. The hydroethanolic extract had a higher diversity of compounds, followed by the ethanol and water samples. Similar molecules were identified in all the extracts and were mainly hydroxybenzoic acids, hydroxycinnamic acids, and flavonoids. Taken together, these results suggest that L. spathulatum should be further explored as a source of bioactive ingredients for the food, cosmetic, and pharmaceutical industries.

Treatments of heating and ultrasound improve the inhibition of gallocatechin gallate on tyrosinase

BACKGROUND

Gallocatechin gallate (GCG), a catechin of tea polyphenols, possesses inhibitory ability against tyrosinase, but few studies have reported how common processing methods affect it. In this research, the influence of heating and ultrasound treatments on the inhibition of GCG against tyrosinase was explored by ultraviolet-visible absorption, fluorescence spectroscopy, high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry.

RESULTS

Both heating and ultrasound treatments of GCG alone improved GCG's inhibitory ability against tyrosinase compared with the untreated, and a combination of heating and ultrasound treatment (100 °C, 20 min + 630 W, 20 min) further decreased the relative tyrosinase activity to 26.8%. The treated GCG exhibited a stronger fluorescence quenching effect on tyrosinase, but did not have any influence on the static quenching mechanism. Compared to the untreated GCG, the binding constants of treated GCG by heating, ultrasound and their combination with tyrosinase significantly increased, but the number of binding sites was still approximately one and the main driving force of the treated GCG was still hydrophobic interaction. After treatments of heating, ultrasound and their combination, the composition of GCG solutions was changed.

CONCLUSION

The enhanced inhibition of treated GCG on tyrosinase may be due to partial conversion of GCG into epigallocatechin-3-gallate (EGCG) and gallic acid (GA), which may cooperate with GCG to better inhibit the enzyme activity. This study has provided some valuable information for the application of catechins against tyrosinase in food processing and cosmetic industry. © 2022 Society of Chemical Industry.

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.

Click linker: efficient and high yielding synthesis of a new family of kojic acid congeners as cytotoxic agents

Highly efficient methodology was developed for the construction of functionalized Kojic acid involving Click linker via 1,3-dipolar cycloaddition and their cytotoxicity against MCF-7, MIAPaCa-2 and DU145 mammalian cell lines were evaluated. Preliminary studies on structure-activity-relationship (SAR) revealed that substitution at C-2 of kojic acid as well as C-5 of 1,2,3-triazole motif played a major role in the activity profile. Kojic acid 1,2,3-triazole analogue 3 b containing an alkyl chain (n = 6) exhibited two fold potent activity than the parent compound, kojic acid against MCF-7 and MIA PaCa-2 cell lines. It induced apoptosis in these cell lines via ID1/PARP1 mediated pathway. The structures of the new analogues of kojic acid 1,2,3-triazole were confirmed by the detailed spectroscopic data analysis.

New Insights into the Inhibition of Hesperetin on Polyphenol Oxidase: Inhibitory Kinetics, Binding Characteristics, Conformational Change and Computational Simulation

The inhibitory activity of hesperetin on polyphenol oxidase (PPO) and their interaction characteristics were investigated using multiple spectroscopic methods and computational simulation. Hesperetin, a mixed inhibitor, reversibly inhibited PPO activity, and its half-maximum inhibitory concentration (IC₅₀) values on monophenolase and diphenolase were 80.8 ± 1.4 μM and 776.0 ± 15.5 μM, respectively. Multivariate curve resolution-alternate least squares (MCR-ALS) analysis suggested PPO interacted with hesperetin and formed PPO-hesperetin complex. Hesperetin statically quenched PPO's endogenous fluorescence, and hydrophobic interactions mainly drove their binding. Hesperetin affected the polarity of the microenvironment around the Trp residues in PPO, but had no effect on that around Tyr residues. Circular dichroism (CD) results showed that hesperetin increased α-helix content and decreased β-fold and random coil contents, thus tightening PPO's structure. Molecular docking showed that hesperetin entered the hydrophobic cavity of PPO, bound near the dinuclear copper active center, interacted with Val283, Phe264, His85, Asn260, Val248, and His263 via hydrophobic interactions, formed hydrogen bonds with Met280, His89, and His259 residues and also interacted with Phe292, His61, Phe90, Glu256, His244, Asn260, Phe264, and Gly281 via van der Waals forces. The molecular dynamics simulation results also demonstrated that the addition of hesperetin reduced the stability and hydrophobicity of PPO and increased PPO's structural denseness. Thus, the inhibition of hesperetin on PPO may be because hesperetin bound near the active center of PPO, interacted with the surrounding residues, occupied the binding site for substrate, and induced the changes in PPO's secondary structure, thus inhibiting the catalytic activity of PPO. This study may provide novel views for the inhibition of hesperetin on PPO and theoretical guidance for developing flavonoids as new and efficient PPO inhibitors.

Biological activities and safety data of kojic acid and its derivatives - a review

Kojic acid presents a variety of applications for human use, especially as a depigmenting agent. Its derivatives are also proposed in order to prevent chemical degradation, prevent adverse effects and improve efficacy. The aim of this study was to peer review the current scientific literature concerning the biological activities and safety data of kojic acid or its derivatives, aiming at human use, and trying to elucidate the action mechanisms. Three different databases were assessed and the word "kojic" was crossed with "toxicity", "adverse effect", "efficacy", "effect", "activity" and "safety". Articles were selected according to pre-defined criteria. Besides the depigmenting activity, kojic acid and derivatives can act as antioxidant, antimicrobial, anti-inflammatory, radioprotector, anticonvulsant and obesity management agents, and present potential as antitumor substances. Depigmenting activity is due to the molecules, after penetrating the cell, binding to tyrosinase active site, regulating melanogenesis factors, leucocytes modulation and free radical scavenging activity. Hence, polarity, size and ligands are also important factors for activity. Kojic acid and derivatives present cytotoxicity to some cancerous cell lines, including melanoma, hepatocellular carcinoma, ovarian cancer, breast cancer and colon cancer. Regarding safety, kojic acid or its derivatives are safe molecules for human use in the concentrations tested. Kojic acid and its derivatives have great potential for cosmetic, pharmaceutical and medical applications.

Discovery of Novel Tyrosinase Inhibitors From Marine Cyanobacteria

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

Phytochemicals and anti-tyrosinase activities of Paeonia ostii leaves and roots

Tree peony (sect. Moutan) is a kind of Traditional Chinese Medicine and ornamental plant, which has been widely cultivated and utilized for thousands of years. To further study the active components of Paeonia ostii (Moutan, Fengdan), six fractions (soluble free (F), soluble esterification, soluble glycosylation, insoluble bound, insoluble esterification and insoluble glycosylation) were extracted from the leaves and roots by alkaline and acid treatment for the first time. Twenty-one typical compounds were identified and quantified by HPLC-MS. The results showed that total phenolic content (TPC) in peony roots (PR) and peony leaves (PL) were as high as 125.48 and 280.38 mg GAE·g^-1 dw, which maximizes the extraction efficiency of phenolic compounds, especially leaves, compared with the conventional method. PR-F and PL-F had the highest TPC, antioxidant and anti-tyrosinase activities. Paeoniflorin was the main compounds in PL and PR. It and pentagalloylglucose (PGG) almost reached the anti-tyrosinase level of kojic acid, but they showed different inhibitory mechanisms by molecular docking. On the whole, PR-F, PL-F, PGG and paeoniflorin might be potential for skin whitening products.

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.

Sonochemistry in an organocatalytic domino reaction: an expedient multicomponent access to structurally functionalized dihydropyrano[3,2-b]pyrans, spiro-pyrano[3,2-b]pyrans, and spiro-indenoquinoxaline-pyranopyrans under ambient conditions

A highly convenient and sustainable one-pot approach for the diversely-oriented synthesis of a variety of medicinally privileged amino-substituted 4,8-dihydropyrano[3,2-b]pyran-3-carbonitriles, and spiro[indoline-3,4'-pyrano[3,2-b]pyran]-3-carbonitrile/carboxylate derivatives on the basis of a domino three-component reaction of readily available carbonyl compounds including aryl aldehydes or isatins, active methylene compounds, and kojic acid as a Michael donor using secondary amine catalyst l-proline under ultrasound irradiation in aqueous ethanolic solution at ambient temperature has been developed. This methodology can involve the assembly of C-C, C[double bond, length as m-dash]C, C-O, C-N bonds via a one-pot operation, and following this protocol, a series of novel amino-substituted spiro[indeno[1,2-b]quinoxaline-11,4-pyrano[3,2-b]pyran]-3-carbonitrile/carboxylates have been synthesized. The practical utility of this method was found to be very efficient for scale-up reaction and other useful transformations. The methodology provides significant advantages including mild reaction conditions, energy-efficiency, short reaction time, fast reaction, simple work-up procedure, broad functional group tolerances, utilization of reusable catalyst, green solvent system, being metal-free, ligand-free, waste-free, inexpensive, etc. Excellent chemical yields have been achieved without using column chromatography. To address the issues of green and more sustainable chemistry, several metrics including Atom Economy (AE), Reaction Mass Efficiency (RME), Atom efficiency, E-factor, Process Mass Intensity (PMI), and Carbon Efficiency (CE) have been quantified for the present methodology that indicates the greenness of the present protocol.

Theoretical Studies of Cyanophycin Dipeptides as Inhibitors of Tyrosinases

The three-dimensional structure of tyrosinase has been crystallized from many species but not from Homo sapiens. Tyrosinase is a key enzyme in melanin biosynthesis, being an important target for melanoma and skin-whitening cosmetics. Several studies employed the structure of tyrosinase from Agaricus bisporus as a model enzyme. Recently, 98% of human genome proteins were elucidated by AlphaFold. Herein, the AlphaFold structure of human tyrosinase and the previous model were compared. Moreover, tyrosinase-related proteins 1 and 2 were included, along with inhibition studies employing kojic and cinnamic acids. Peptides are widely studied for their inhibitory activity of skin-related enzymes. Cyanophycin is an amino acid polymer produced by cyanobacteria and is built of aspartic acid and arginine; arginine can be also replaced by other amino acids. A new set of cyanophycin-derived dipeptides was evaluated as potential inhibitors. Aspartate–glutamate showed the strongest interaction and was chosen as a leading compound for future studies.

Tyrosinase inhibition by novel benzimidazole-thione Schiff base derivatives

Background:

Tyrosinase is the enzyme responsible for the conversion of tyrosine to dopaquinone, which is related to melanoma, neurodegenerative disorders, freckles, pigmented acne and age spots. Controlling the tyrosinase activity could be an important way for treating overproduction of melanin.

Objective:

The development of safe and specific tyrosinase inhibitors could be used to treat hypermelanosis.

Methods:

5-nitro-1H-benzo[d]imidazole-2(3H)-thione was synthesized from 4-nitro-o-phenylenediamine and carbon disulfide. The nitro group of 5-nitro-1H- S-1 ESI-HRMS benzo[d]imidazole-2(3H)-thione was reduced with iron powder. The 5-amino-1H-benzo[d]imidazole- 2(3H)-thione Schiff base derivatives were obtained by the reaction of 5-amino-1H-benzo[d]imidazole-2(3H)-thione with substituted benzaldehyde. The tyrosinase inhibitory activities were investigated. The studies of kinetic analysis, metal-chelating properties, docking and cytotoxicity were also performed.

Results:

All of the compounds showed strong tyrosinase inhibitory activities with 5-((4-nitrobenzylidene) amino)-1H-benzo [d]imidazole-2(3H)-thione (S-4) as the best tyrosinase inhibitor with an IC50 value of 4.8 ± 1.4 nM. Compound S-4 exhibited mixed type inhibition of mushroom tyrosinase, with Ki 15 nM and Kis 42 nM. Copper binding to S-4 was detected spectrophotometrically and 1-100 ìÌ S-4 displayed negligible cytotoxicity to murine B16 melanoma cells.

Conclusion:

Our results demonstrated that these benzimidazolethione Schiff base derivatives might be promising candidates as tyrosinase inhibitors.

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.

Natural and synthetic flavonoid derivatives as new potential tyrosinase inhibitors: a systematic review

Tyrosinase is a multifunctional glycosylated and copper-containing oxidase that is highly prevalent in plants and animals and plays a pivotal role in catalyzing the two key steps of melanogenesis: tyrosine's hydroxylation to dihydroxyphenylalanine (DOPA), and oxidation of the latter species to dopaquinone. Melanin guards against the destructive effects of ultraviolet radiation which is known to produce considerable pathological disorders such as skin cancer, among others. Moreover, the overproduction of melanin can create aesthetic problems along with serious disorders linked to hyperpigmented spots or patches on skin. Several skin-whitening products which reduce melanogenesis activity and alleviate hyperpigmentation are commercially available. A few of them, particularly those obtained from natural sources and that incorporate a phenolic scaffold, have been exploited in the cosmetic industry. In this context, synthetic tyrosinase inhibitors (TIs) with elevated efficacy and fewer side effects are direly needed in the pharmaceutical and cosmetic industries owing to their protective effect against pigmentation and dermatological disorders. Furthermore, the biological significance of the chromone skeleton and its associated medicinal and bioactive properties has drawn immense interest and inspired many researchers to design and develop novel anti-tyrosinase agents based on the flavonoid core (2-arylchromone). This review article is oriented to provide an insight and a deeper understanding of the tyrosinase inhibitory activity of an array of natural and bioinspired phenolic compounds with special emphasis on flavonoids to demonstrate how the position of ring substituents and their interaction with tyrosinase could be correlated with their effectiveness or lack thereof against inhibiting the enzyme.

The Role of Anthocyanins, Deoxyanthocyanins and Pyranoanthocyanins on the Modulation of Tyrosinase Activity: An In Vitro and In Silico Approach

Tyrosinase is the central enzyme involved in the highly complex process of melanin formation, catalyzing the rate-limiting steps of this biosynthetic pathway. Due to such a preponderant role, it has become a major target in the treatment of undesired skin pigmentation conditions and also in the prevention of enzymatic food browning. Numerous phenolic-based structures from natural sources have been pointed out as potential tyrosinase inhibitors, including anthocyanins. The aim of the present study was to individually assess the tyrosinase inhibitory activity of eight purified compounds with a variable degree of structural complexity: native anthocyanins, deoxyanthocyanins, and pyranoanthocyanins. The latter two, the groups of anthocyanin-related compounds with enhanced stability, were tested for the first time. Compounds 1 to 4 (luteolinidin, deoxymalvidin, cyanidin-, and malvidin-3-O-glucoside) revealed to be the most effective inhibitors, and further kinetic studies suggested their inhibition mechanism to be of a competitive nature. Structure–activity relationships were proposed based on molecular docking studies conducted with mushroom tyrosinase (mTYR) and human tyrosinase-related protein 1 (hTYRP1) crystal structures, providing information about the binding affinity and the different types of interactions established with the enzyme’s active center which corroborated the findings of the inhibition and kinetic studies. Overall, these results support the applicability of these compounds as pigmentation modulators.

Piperazine skeleton in the structural modification of natural products: a review

Piperazine moiety is a cyclic molecule containing two nitrogen atoms in positions 1 and 4, as well as four carbon atoms. Piperazine is one of the most sought heterocyclics for the development of new drug candidates with a wide range of applications. Over 100 molecules with a broad range of bioactivities, including antitumor, antibacterial, anti-inflammatory, antioxidant, and other activities, were reviewed. This article reviewed investigations regarding piperazine groups for the modification of natural product derivatives in the last decade, highlighting parameters that affect their biological activity.

An overview of hydroxypyranone and hydroxypyridinone as privileged scaffolds for novel drug discovery

Hydroxypyranone and hydroxypyridinone are important oxygen-containing or nitrogen-containing heterocyclic nucleus and attracted increasing attention in medicinal chemistry and drug discovery over the past decade. Previous literature reports revealed that hydroxypyranone and hydroxypyridinone derivatives exhibit a wide range of pharmacological activities such as antibacterial, antifungal, antiviral, anticancer, anti-inflammatory, antioxidant, anticonvulsant, and anti-diabetic activities. In this review, we systematically summarized the literature reported biological activities of hydroxypyranone and hydroxypyridinone derivatives. In particular, we focus on their biological activity, structure-activity relationship (SAR), mechanism of action, and interaction mechanisms with the target. The collected information is expected to provide rational guidance for the development of clinically useful agents from these pharmacophores.

Gonçalves Vianez JL, Santana da Costa K, de Molfetta FA, Nahum Alves C. Analysis of Kojic Acid Derivatives as Competitive Inhibitors of Tyrosinase: A Molecular Modeling Approach

Tyrosinases belong to the functional copper-containing proteins family, and their structure contains two copper atoms, in the active site, which are coordinated by three histidine residues. The biosynthesis of melanin in melanocytes has two stages depending on the actions of the natural substrates L-DOPA and L-tyrosine. The dysregulation of tyrosinase is involved in skin cancer initiation. In the present study, using molecular modeling tools, we analyzed the inhibition activity of tyrosinase activity using kojic acid (KA) derivatives designed from aromatic aldehydes and malononitrile. All derivatives showed conformational affinity to the enzyme active site, and a favorable distance to chelate the copper ion, which is essential for enzyme function. Molecular dynamics simulations revealed that the derivatives formed promising complexes, presenting stable conformations with deviations between 0.2 and 0.35 Å. In addition, the investigated KA derivatives showed favorable binding free energies. The most stable KA derivatives showed the following binding free energies: -17.65 kcal mol-1 (D6), -18.07 kcal mol-1 (D2), -18.13 (D5) kcal mol-1, and -10.31 kcal mol-1 (D4). Our results suggest that these derivatives could be potent competitive inhibitors of the natural substrates of L-DOPA (-12.84 kcal mol-1) and L-tyrosine (-9.04 kcal mol-1) in melanogenesis.

Design, synthesis and evaluation of cholinesterase hybrid inhibitors using a natural steroidal alkaloid as precursor

To date, Alzheimer's disease is the most alarming neurodegenerative disorder worldwide. This illness is multifactorial in nature and cholinesterase inhibitors have been the ones used in clinical treatments. In this context, many of these drugs selectively inhibit the acetylcholinesterase enzyme interacting in both the active site and the peripheric anionic site. Besides, some agents have exhibited extensive benefits being able to co-inhibit butyrylcholinesterase. In this contribution, a strategy previously explored by numerous authors is reported; the synthesis of hybrid cholinesterase inhibitors. This strategy uses a molecule of recognized high inhibitory activity (tacrine) together with a steroidal alkaloid of natural origin using different connectors. The biological assays demonstrated the improvement in the inhibitory activity compared to the alkaloidal precursor, together with the reinforcement of the interactions in multiple sites of the enzymatic cavity. This strategy should be explored and exploited in this area. Docking and molecular dynamic studies were performed to explain enzyme-ligand interactions, assisting a structure-activity relationship analysis.

Dopamine-Mediated Vanillin Multicomponent Derivative Synthesis via Grindstone Method: Application of Antioxidant, Anti-Tyrosinase, and Cytotoxic Activities

Purpose

This study aimed to determine the extent of contribution of dopamine to antioxidant and anti-tyrosinase activities, by dopamine addition to vanillin. This study achieved the synthesis of dopamine-associated vanillin Mannich base derivatives prepared via a one-step reaction involving a green chemistry approach, and investigation of antioxidant and anti-tyrosinase activities.

Methods

Novel one-pot synthesis of Mannich base dopamine-connected vanillin (1a-l) derivatives can be achieved via green chemistry without using a catalyst. Newly-prepared compounds were characterised with FTIR and NMR (¹H and ¹³C) spectra, mass spectra, and elemental analyses. In total, 12 compounds (1a-l) were synthesised and their antioxidant and anti-tyrosinase activities evaluated. Antioxidant activities of 2,2-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide (NO), hydrogen peroxide (H₂O₂), and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and diammonium assays, ABTS^•+ radical scavenging, and linoleic acid peroxidation were used to screen all synthesised compounds (1a-l) for anti-tyrosinase activities and cytotoxicity against MCF-7 and Vero cell lines;.

Results

The compound 1k inhibited (IC₅₀:11.02µg/mL) the DPPH-scavenging activity to a greater extent than the standard BHT (IC₅₀:25.17µg/mL), and showed high activity in H₂O₂ and NO scavenging assays. Compound 1e was more potent (96.21%) against ABTS and compound 1k was more potent (95.28%) against 2,2ʹ-azobis(2-amidinopropane)dihydrochloride antioxidant than the standard trolox. All synthesised compounds were screened for anti-tyrosinase inhibitory activity. Compound 1e had higher activity against tyrosinase (IC₅₀=10.63 µg/mL), than kojic acid (IC₅₀=21.52µg/mL), and was more cytotoxic (GI₅₀ 0.01µM) against MCF-7 cell line than the doxorubicin standard and other tested compounds.

Conclusion

In this study, all compounds were found to possess significant antioxidant and anti-tyrosinase activities. Compounds 1e and 1k performed well, compared with other compounds, in all assays. In addition, this study successfully identified several promising molecules that exhibited antioxidant and anti-tyrosinase activities.

Cylindromicin from Arctic-Derived Fungus Tolypocladium sp. SCSIO 40433

The fungus strain SCSIO 40433 was isolated from an Arctic-derived glacier sediment sample and characterized as Tolypocladium cylindrosporum. A new compound, cylindromicin (1), and seven known secondary metabolites (2–8) were isolated from this strain. The chemical structures of these compounds were elucidated by comprehensive spectroscopic analyses. Cylindromicin (1) featured a 3,4-dihydro-2H-pyran skeleton. The absolute configuration of compound 1 was assigned via interpretation of key Nuclear Overhauser Effect Spectroscopy (NOESY) correlations and Electronic Circular Dichroism (ECD) calculation. Cylindromicin (1) exhibited significant tyrosinase inhibition activity. This study highlights Polar fungi as a potential resource for new bioactive natural products.

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.

Comparing the inhibitory abilities of epigallocatechin-3-gallate and gallocatechin gallate against tyrosinase and their combined effects with kojic acid

Inhibition of tyrosinase activity contributes to the control of food browning and skin pigmentation diseases. Herein, the inhibitory mechanism of epigallocatechin-3-gallate (EGCG) and gallocatechin gallate (GCG) on tyrosinase were investigated. Both EGCG and GCG inhibited tyrosinase in a mixed manner with the IC₅₀ values of 39.4 ± 0.54 μM and 36.8 ± 0.21 μM, and showed a synergism with their combination, while EGCG and GCG combined with kojic acid (IC₅₀ = 19.2 ± 0.26 μM) exhibited antagonism and additive effect, respectively. EGCG and GCG interacted with tyrosinase mainly by hydrogen bonding and hydrophobic interactions and induced a looser conformation of tyrosinase. Molecular docking indicated that EGCG and GCG bound to the active center of tyrosinase and interacted with copper ions and key amino acid residues. Molecular dynamics simulation further characterized the structure and property of EGCG/GCG-tyrosinase complex. This study provides novel insights into the mechanism of catechins as tyrosinase inhibitors.

A systematic review of synthetic tyrosinase inhibitors and their structure-activity relationship

Tyrosinase is a copper-containing oxidation enzyme, which is responsible for the production of melanin. This enzyme is widely distributed in microorganisms, animals and plants, and plays an essential role in undesirable browning of fruits and vegetables, antibiotic resistance, skin pigment formation, sclerotization of cuticle, neurodegeneration, etc. Hence, it has been recognized as a therapeutic target for the development of antibrowning agents, antibacterial agents, skin-whitening agents, insecticides, and other therapeutic agents. With great potential application in food, agricultural, cosmetic and pharmaceutical industries, a large number of synthetic tyrosinase inhibitors have been widely reported in recent years. In this review, we systematically summarized the advances of synthetic tyrosinase inhibitors in the literatures, including their inhibitory activity, cytotoxicity, structure-activity relationship (SAR), inhibition kinetics, and interaction mechanisms with the enzyme. The collected information is expected to provide a rational guidance and effective strategy to develop novel, potent and safe tyrosinase inhibitors for better practical applications in the future.

An allomaltol derivative triggers distinct death pathways in luminal a and triple-negative breast cancer subtypes

Breast cancer is the most common cancer in women that shows a predisposition to metastasize to the distant organs. Kojic acid is a natural fungal metabolite exhibiting various biological activities. Compounds derived from kojic acid have been extensively studied and proved to demonstrate anti-neoplastic features on different cancer types. In the present study, allomaltol-structural analog of kojic acid and its seven derivatives including four novel compounds, have been synthesized, characterized and their possible impact on breast cancer cell viability was investigated. It was discovered that compound 5, bearing 3,4-dichlorobenzyl piperazine moiety, could decrease the viability of both MCF-7 and MDA-MB-231 cell lines distinctively. To ascertain the death mechanism, cells were subjected to different tests following the application of IC₅₀ concentration of compound 5. Data obtained from lactate dehydrogenase activity and gene expression assays pointed out that necrosis had taken place predominantly in MDA-MB-231. On the other hand, in MCF-7 cells, the p53 apoptotic pathway was activated by overexpression of the pro-apoptotic TP53 and Bax genes and suppression of the anti-apoptotic Mdm-2 and Bcl-2 genes. Furthermore, Bax/Blc-2 ratio was escalated by 3.5 fold in the study group compared to the control. Compound 5 did not provoke drug resistance in MCF-7 cells since the Mdr-1 gene expression, drug efflux, and H₂O₂ content remained unaltered. As for MDA-MB-231 cells, only a 1.4 fold increase in the Mdr-1 gene expression was detected. These results indicate the advantage of the allomaltol derivative over the chemotherapeutic agents conventionally used for breast cancer treatment that can be highly toxic and mostly lead to drug resistance. Thus, this specific allomaltol derivative offers an alternative therapeutic approach for breast cancer which needs further investigation.

Design, synthesis, and anticancer activity of novel 4-thiazolidinone-phenylaminopyrimidine hybrids

4-Thiazolidinones and phenylaminopyrimidines are known as anticancer agents. Imatinib is the pioneer phenylaminopyrimidine derivative kinase inhibitor, which is used for the treatment of chronic myeloid leukemia. With a hybrid approach, a novel series of 5-benzylidene-2-arylimino-4-thiazolidinone derivatives containing phenylaminopyrimidine core were designed, synthesized, and tested for their anticancer activity on K562 (chronic myeloid leukemia), PC3 (prostat cancer), and SHSY-5Y (neuroblastoma) cells. Since superior anticancer activity was observed on K562 cells, further biological studies of selected compounds (8, 15, and 34) were performed on K562 cells. For the synthesis of designed compounds, thiourea compounds were converted to 2-imino-1,3-thiazolidin-4-ones with α-chloroacetic acid in the presence of sodium acetate. 5-Benzylidene-2-imino-1,3-thiazolidin-4-one derivatives were obtained by Knoevenagel condensation of 2-imino-1,3-thiazolidin-4-ones with related aldehydes. Compounds 8, 15, and 34 were evaluated for cell viability, apoptosis studies, cell cycle experiments, and DNA damage assays. IC₅₀ values of compounds 8, 15, and 34 were found as 5.26 ± 1.03, 3.52 ± 0.91, and 8.16 ± 1.27 μM, respectively, in K562 cells. Preferably, these compounds showed less toxicity towards L929 cells compared to imatinib. Furthermore, compounds 8 and 15 significantly induced early and late apoptosis in a time-dependent manner. Compounds 15 and 34 induced cell cycle arrest at G0/G1 phase and compound 8 caused cell cycle arrest at G2/M phase. Based on DNA damage assay, compounds 8 and 15 were found to be more genotoxic than imatinib towards K562 cells. To put more molecular insight, possible Abl inhibition mechanisms of most active compounds were predicted by molecular docking studies. In conclusion, a novel series of 5-benzylidene-2-arylimino-4-thiazolidinone derivatives and their promising anticancer activities were reported herein.

Synthesis, molecular docking, dynamic simulations, kinetic mechanism, cytotoxicity evaluation of N-(substituted-phenyl)-4-{(4-[(E)-3-phenyl-2-propenyl]-1-piperazinyl} butanamides as tyrosinase and melanin inhibitors: In vitro, in vivo and in silico approaches

In the current research work, different N-(substituted-phenyl)-4-{(4-[(E)-3-phenyl-2-propenyl]-1-piperazinyl}butanamides have been synthesized according to the protocol described in scheme 1. The synthesis was initiated by reacting various substituted anilines (1a-e) with 4-chlorobutanoyl chloride (2) in aqueous basic medium to give various electrophiles, 4-chloro-N-(substituted-phenyl)butanamides (3a-e). These electrophiles were then coupled with 1-[(E)-3-phenyl-2-propenyl]piperazine (4) in polar aprotic medium to attain the targeted N-(substituted-phenyl)-4-{(4-[(E)-3-phenyl-2-propenyl]-1-piperazinyl}butanamides (5a-e). The structures of all derivatives were identified and characterized by proton-nuclear magnetic resonance (¹H NMR), carbon-nuclear magnetic resonance (¹³C NMR) and Infra-Red (IR) spectral data along with CHN analysis. The in vitro inhibitory potential of these butanamides was evaluated against Mushroom tyrosinase, whereby all compounds were found to be biologically active. Among them, 5b exhibited highest inhibitory potential with IC₅₀ value of 0.013 ± 0.001 µM. The same compound 5b was also assayed through in vivo approach, and it was explored that it significantly reduced the pigments in zebrafish. The in silico studies were also in agreement with aforesaid results. Moreover, these molecules were profiled for their cytotoxicity through hemolytic activity, and it was found that except 5e, all other compounds showed minimal toxicity. The compound 5a also exhibited comparable results. Hence, some of these compounds might be worthy candidates for the formulation and development of depigmentation drugs with minimum side effects.