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

Discovery of (E)-3-(4-chlorophenyl)-N-(5-hydroxypentyl)acrylamide among N-substituted cinnamamide derivatives as a novel cosmetic ingredient for hyperpigmentation

Hyperpigmentation disorders may result from inappropriate melanin deposition and/or excessive melanin synthesis. They are classified mainly as aesthetic problems, but they can significantly affect human health by decreasing self-esteem. There are available only limited treatment options for hyperpigmentation disorder, among others, cosmetic products applied topically. Depigmenting ingredients were found to be ineffective and characterized by various side effects. As a result, many efforts are made to discover novel, potent, and safe melanogenesis inhibitors for possible use in topical cosmetic depigmenting formulations. Cinnamic acid derivatives constitute a widely tested group for that purpose. This article reports research in the group of N-alkyl cinnamamide derivatives (un)substituted in phenyl ring. Among tested series, (E)-3-(4-chlorophenyl)-N-(5-hydroxypentyl)acrylamide (compound 21) showed the most promising inhibitory properties in mushroom tyrosinase assay (IC50 = 36.98 ± 1.07 µM for monophenolase activity, IC50 = 146.71 ± 16.82 µM for diphenolase activity) and melanin production inhibition in B16F10 mouse melanoma cell line at concentration 6.25 µM resulting probably from decreasing of Tyr, Mitf, Tyrp-1, and Tyrp-2 genes expression. This compound also showed melanin production inhibitory properties in pigmented reconstructed human epidermis when used in 1 % and 2 % solutions in 50 % PEG400. In vitro evaluation of its safety profile showed no cytotoxicity to human keratinocytes HaCaT, human skin fibroblasts BJ, and human primary epidermal melanocytes HEMa, no mutagenicity in the Ames test, no genotoxicity in micronucleus test, no phototoxicity, as well as no skin irritation potential tested in PEG400 solution. This compound was also shown to penetrate across the epidermis to reach the possible site of action. The performed research led to classify (E)-3-(4-chlorophenyl)-N-(5-hydroxypentyl)acrylamide as a novel potential depigmenting cosmetic ingredient.

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.

GC-MS screening of the phytochemical composition of Ziziphus honey: ADME properties and in vitro/in silico study of its antimicrobial activity

A revival interest has been given to natural products as sources of phytocompounds to be used as alternative treatment against infectious diseases. In this context, we aimed to investigate the antimicrobial potential of Ziziphus honey (ZH) against twelve clinical bacterial strains and several yeasts and molds using in vitro and computational approaches. The well-diffusion assay revealed that ZH was able to induce growth inhibition of most Gram-positive and Gram-negative bacteria. The high mean growth inhibition zone (mGIZ) was recorded in E. coli (Clinical strain, 217), S. aureus followed by E. coli ATCC 10536 (mGIZ values: 41.00 ± 1 mm, 40.67 ± 0.57 mm, and 34.67 ± 0.57 mm, respectively). The minimal bactericidal concentrations (MBCs) and minimal fungicidal concentration values (MFCs) from approximately 266.33 mg/mL to over 532.65 mg/mL. Molecular docking results revealed that the identified compounds maltose, 2-furoic acid, isopropyl ester, 2,4-imidazolidinedione, 5-(2-methylpropyl)-(S)- and 3,4,5-trihydroxytoluene, S-Methyl-L-Cysteine, 2-Furancarboxylic acid, L-Valine-N-ethoxycarbonyl, Hexanoic acid, 3,5,5-trimethyl-, Methyl-beta-D-thiogalactoside, gamma-Sitosterol, d-Mannose, 4-O-Methylmannose, 2,4-Imidazolidinedione, 5-(2-methylpropyl)- (S) were found to have good affinity for targeted receptor, respectively. Through a 100-ns dynamic simulation research, binding interactions and stability between promising phytochemicals and the active residues of the studied enzymes were confirmed. The ADMET profiling of all identified compounds revealed that most of them could be qualified as biologically active with good absorption and permeation. Overall, the results highlighted the efficiency of ZH against the tested clinical pathogenic strains. The antimicrobial potential and the potency displayed by the identified compounds could imply their further pharmacological applications.Communicated by Ramaswamy H. Sarma.

DNA protection, molecular docking, antioxidant, antibacterial, enzyme inhibition, and enzyme kinetic studies for parietin, isolated from Xanthoria parietina (L.) Th. Fr

Parietin was isolated from Xanthoria parietina (L.) Th. Fr.' (methanol:chloroform) extract, using a silica column. 13 C NMR and 1H NMR were used to confirm the structure of the isolated parietin. For the first time, parietin was investigated for its antioxidant, antibacterial and DNA protective activities. Molecular docking was carried out to determine the binding affinity and interactions between the enzymes and our molecule. Inhibition and kinetic mechanism studies for the action of the enzymes were performed too. Parietin exhibited high metal chelating activity. The MIC values of parietin were sufficient to inhibit different bacterial strains; E. coli, P. aeruginosa, K. pneumoniae and S. aureus. Molecular docking applications exhibited that acetylcholinesterase (AChE), butyrylcholinesterase (BChE), lipase, and tyrosinase have high potential for binding with the parietin. Especially, the parietin's highest binding affinity was recorded with AChE and tyrosinase. These results were confirmed by the inhibition and kinetics results, where, parietin observed a potent inhibition with an IC50 values between 0.013-0.003 µM. Moreover, parietin acts' as a non-competitive inhibitor against AChE, BChE, and lipase, and as a competitive inhibitor against tyrosinase with a high rate of inhibition stability. The promising biological properties of parietin revealed its effectiveness in terms of suitability in the food and pharmaceutical industries.Communicated by Ramaswamy H. Sarma.

Design and synthesis of 2-amino-4,6-diarylpyrimidine derivatives as potent α-glucosidase and α-amylase inhibitors: structure-activity relationship, in vitro, QSAR, molecular docking, MD simulations and drug-likeness studies

In the present study, a series of 2-amino-4,6-diarylpyrimidine derivatives was designed, synthesized, characterized and evaluated for their in vitro α-glucosidase and α-amylase enzyme inhibition assays. The outcomes proved that this class of compounds exhibit considerable inhibitory activity against both enzymes. Among the target compounds, compounds 4p and 6p demonstrated the most potent dual inhibition with IC50 = 0.087 ± 0.01 μM for α-glucosidase; 0.189 ± 0.02 μM for α-amylase and IC50 = 0.095 ± 0.03 μM for α-glucosidase; 0.214 ± 0.03 μM for α-amylase, respectively as compared to the standard rutin (IC50 = 0.192 ± 0.02 μM for α-glucosidase and 0.224 ± 0.02 μM for α-amylase). Remarkably, the enzyme inhibition results indicate that test compounds have stronger inhibitory effect on the target enzymes than the positive control, with a significantly lower IC50 value. Moreover, these series of compounds were found to inhibit α-glucosidase activity in a reversible mixed-type manner with IC50 between 0.087 ± 0.01 μM to 1.952 ± 0.26 μM. Furthermore, molecular docking studies were performed to affirm the binding interactions of this scaffold to the active sites of α-glucosidase and α-amylase enzymes. The quantitative structure-activity relationship (QSAR) investigations showed a strong association between 1p-15p structures and their inhibitory actions (IC50) with a correlation value (R2) of 0.999916. Finally, molecular dynamic (MD) simulations were carried out to assess the dynamic behavior, stability of the protein-ligand complex, and binding affinity of the most active inhibitor 4p. The experimental and theoretical results therefore exposed a very good compatibility. Additionally, the drug-likeness assay revealed that some compounds exhibit a linear association with Lipinski's rule of five, indicating good drug-likeness and bioactivity scores for pharmacological targets.Communicated by Ramaswamy H. Sarma.

Investigation of photophysical and electronic properties of aurone derivatives: Insights from spectroscopic techniques and density functional theory calculations

This paper reports on a study of the photophysical properties, density functional theory (DFT) calculations, infrared (IR), ultraviolet (UV) and nuclear magnetic resonance (NMR) spectroscopic techniques of a series of aurone compounds. The photophysical properties were investigated using UV absorption and fluorescence spectroscopy in a dimethyl sulfoxide (DMSO) solution. Furthermore, the fluorescence quantum yields of the target compounds (1-24) were also investigated. Remarkably, these compounds revealed high quantum yields (Φ = 0.001-0.729) as compared to the already existing aurones in literature. The DFT calculations were performed to elucidate the electronic structure, energy levels and draw a comparison between experimental and theoretical findings. The simulated properties such as molecular frontier orbitals, the density of states, reactivity descriptors (GCRD), electrostatic potential distribution, transition density matrix, electron localization function (ELF) and localized orbital locator (LOL) have been calculated using DFT. The DFT calculations provided insight into the electronic structure and energy levels of the aurone compounds, while the IR and UV spectroscopy results shed light on their functional groups and electronic transitions, respectively. The results of this study contribute to a better understanding of the photophysical properties of aurone compounds and suggest their potential use in technological applications.

Potent inhibition of human tyrosinase inhibitor by verproside from the whole plant of Pseudolysimachion rotundum var. subintegrum

Affinity-based ultrafiltration-mass spectrometry coupled with ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry was utilised for the structural identification of direct tyrosinase ligands from a crude Pseudolysimachion rotundum var. subintegrum extract. False positives were recognised by introducing time-dependent inhibition in the control for comparison. The P. rotundum extract contained nine main metabolites in the UPLC-QTOF-MS chromatogram. However, four metabolites were reduced after incubation with tyrosinase, indicating that these metabolites were bound to tyrosinase. The IC50 values of verproside (1) were 31.2 µM and 197.3 µM for mTyr and hTyr, respectively. Verproside showed 5.6-fold higher efficacy than that of its positive control (kojic acid in hTyr). The most potent tyrosinase inhibitor, verproside, features a 3,4-dihydroxybenzoic acid moiety on the iridoid glycoside and inhibits tyrosinase in a time-dependent and competitive manner. Among these three compounds, verproside is bound to the active site pocket with a docking energy of -6.9 kcal/mol and four hydrogen bonding interactions with HIS61 and HIS85.

Antioxidant activity, anti-tyrosinase activity, molecular docking studies, and molecular dynamic simulation of active compounds found in nipa palm vinegar

Tyrosinase is a key enzyme in melanogenesis and its inhibitors have become increasingly because of their potential activity as hypopigmenting agents which have less side effects. Nipa palm vinegar is an aqueous product that is normally used as a food supplement. The aim of this study was to study the determination of antioxidant activity and tyrosinase inhibitory activities of aqueous extract of original nipa palm vinegar (AE O-NPV), nipa palm vinegar powder (NPV-P) and aqueous extract of nipa palm vinegar powder (AE NPV-P) were examined. Nipa palm vinegars were evaluated the phenolic and flavonoid content, and the active compounds which were submitted to molecular docking and molecular dynamic simulation, chemoinformatics, rule of five, skin absorption and toxicity. The highest phenolic and flavonoid contents in the AE O-NPV were 2.36 ± 0.23 mg gallic acid equivalents/g extract and 5.11 ± 0.59 mg quercetin equivalents/g, and the highest ABTS radical cation scavenging activity was also found. The AE O-NPV, NPV-P and AE NPV-P showed anti-mushroom tyrosinase activity. The HPLC analysis showed that there were vanillic acid and three flavonoids (catechin, rutin and quercetin). The molecular docking study revealed that the binding of the vanillic acid and three flavonoids occurred in the active site residues (histidine and other amino acids). Moreover, the number of hydrogen bond acceptors/donors, solubility, polar surface area and bioavailability score of the vanillic acid and three flavonoids were acceptable compared to Lipinski's Rule of Five. The molecular dynamic simulation showed that vanillic acid interacts with HIS284 through π-π stacking hydrophobic interactions and forms a metal-acceptor interaction with the copper molecule at the tyrosinase active site. All compounds revealed good skin permeability and nontoxicity. Nipa palm vinegar could be a promising source of a new ingredient for tyrosinase inhibition for cosmetics or pharmaceutical products.

Computational methods to analyze and predict the binding mode of inhibitors targeting both human and mushroom tyrosinase

Tyrosinase, a copper-containing enzyme critical in melanin biosynthesis, is a key drug target for hyperpigmentation and melanoma in humans. Testing the inhibitory effects of compounds using tyrosinase from Agaricus bisporus (AbTYR) has been a common practice to identify potential therapeutics from synthetic and natural sources. However, structural diversity among human tyrosinase (hTYR) and AbTYR presents a challenge in developing drugs that are therapeutically effective. In this study, we combined retrospective and computational analyses with experimental data to provide insights into the development of new inhibitors targeting both hTYR and AbTYR. We observed contrasting effects of Thiamidol™ and our 4-(4-hydroxyphenyl)piperazin-1-yl-derivative (6) on both enzymes; based on this finding, we aimed to investigate their binding modes in hTYR and AbTYR to identify residues that significantly improve affinity. All the information led to the discovery of compound [4-(4-hydroxyphenyl)piperazin-1-yl](2-methoxyphenyl)methanone (MehT-3, 7), which showed comparable activity on AbTYR (IC50 = 3.52 μM) and hTYR (IC50 = 5.4 μM). Based on these achievements we propose the exploitation of our computational results to provide relevant structural information for the development of newer dual-targeting molecules, which could be preliminarily tested on AbTYR as a rapid and inexpensive screening procedure before being tested on hTYR.

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.