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

Design, synthesis and biological evaluation of novel kojic acid triazole hybrids as tyrosinase inhibitors and antibrowning agents

In this study, two series of kojic acid triazole hybrids, namely 6a-6p and 13a-13t, were designed and synthesized. Subsequently, their biological activities including anti-tyrosinase, antioxidant, and as anti-browning effects were investigated. The results showed that most of compounds demonstrated excellent inhibitory effect against mushroom tyrosinase compared with standard reference drug (kojic acid, IC50 = 26.090 µM). Of particular note, 13t proved to be the most potent tyrosinase inhibitor with an IC50 value as low as 1.363 µM. Further kinetic inhibition studies suggested that 13t presented such powerful anti-tyrosinase efficacy by functioning as a mixed-type inhibitor (Ki = 0.3647 µM, Kis = 0.8492 µM). Moreover, the results from molecular docking and fluorescence quenching studies revealed that 13t's inhibitory effect on tyrosinase stemmed from its ability to directly bind to the active site of mushroom tyrosinase. Besides, the antioxidant activity, anti-browning effect, and cytotoxicity of 13t were accordingly investigated, all yielding highly satisfactory results. Collectively, these findings position 13t as a highly promising candidate, providing a valuable molecular framework for the development of novel, efficient, and safe tyrosinase inhibitors endowed with potent antioxidant and anti-browning capabilities.

Recent Studies on Heterocyclic Cholinesterase Inhibitors Against Alzheimer's Disease

Alzheimer's disease is a progressive and neurodegenerative disease characterized by impairment in emotion, language, memory, and cognitive judgment. There are many factors related to Alzheimer's disease, such as amyloid beta plaques (Aβ) due to impaired metabolism of amyloid precursor protein (APP), tau hyperphosphorylation, and accumulation of neurofibrillary tangles, and disruption of the cholinergic system. Disruption of the cholinergic system responsible for cognitive function and memory processes is one of the important causes of Alzheimer's disease. Therefore, cholinesterase (acetylcholinesterase and butyrylcholinesterase) inhibitors that maintain choline (acetylcholine and butyrylcholine) levels in the synaptic gap play an important role in the symptomatic treatment of Alzheimer's disease. Numerous studies have been carried out against Alzheimer's disease involving acetylcholinesterase and butyrylcholinesterase inhibitors. However, there are very few drugs (tacrine, rivastigmine, galantamine, and donepezil) approved as cholinesterase inhibitors. Therefore, cholinesterase inhibitors are needed against Alzheimer's disease. This review is focused on using heterocyclic rings that show remarkable cholinesterase inhibitory activity for Alzheimer's disease. In this review, chemical structures and structure-activity relationships of recently reported cholinesterase inhibitors are emphasized. This review will give important ideas to medicinal chemists in the discovery and development of potent cholinesterase inhibitors in their future studies.

Sulfinate-Promoted Defluorinative Cyclization of Polyfluoroalkyl Tetralones Enabled by Photocatalysis

A Ru-catalyzed defluorinative cyclization of polyfluoroalkyl tetralones has been developed under visible-light irradiation for the precise assembly of γ-pyrones featuring α-perfluoroalkyl and β-fluorine substituents. Selective functionalization of five C(sp3)-F bonds at three carbon sites on the perfluoroalkyl chain provides a new mode for utilizing polyfluorides as versatile synthons to access difficult-to-obtain heterocyclic scaffolds. Moreover, the sulfinate salt serves dual roles as an oxygen source for creating the carbonyl group and as a defluorinating promoter.

Novel anti-neuroinflammatory pyranone-carbamate derivatives as selective butyrylcholinesterase inhibitors for treating Alzheimer's disease

Butyrylcholinesterase (BuChE) and neuroinflammation have recently emerged as promising therapeutic directions for Alzheimer's disease (AD). Herein, we synthesised 19 novel pyranone-carbamate derivatives and evaluated their activities against cholinesterases and neuroinflammation. The optimal compound 7p exhibited balanced BuChE inhibitory activity (eqBuChE IC50 = 4.68 nM; huBuChE IC50 = 9.12 nM) and anti-neuroinflammatory activity (NO inhibition = 28.82% at 10 μM, comparable to hydrocortisone). Enzyme kinetic and docking studies confirmed compound 7p was a mix-type BuChE inhibitor. Additionally, compound 7p displayed favourable drug-likeness properties in silico prediction, and exhibited high BBB permeability in the PAMPA-BBB assay. Compound 7p had good safety in vivo as verified by an acute toxicity assay (LD50 > 1000 mg/kg). Most importantly, compound 7p effectively mitigated cognitive and memory impairments in the scopolamine-induced mouse model, showing comparable effects to Rivastigmine. Therefore, we envisioned that compound 7p could serve as a promising lead compound for treating AD.

Inhibition of polyphenol oxidase for preventing browning in edible mushrooms: A review

Edible mushrooms are rich in nutrients and bioactive compounds, but their browning affects their quality and commercial value. This article reviews various methods to inhibit polyphenol oxidase (PPO)-induced browning in mushrooms. Physical methods such as heat treatment, low temperatures, irradiation, and ultrasound effectively reduce PPO activity but may affect mushroom texture and flavor. Chemical inhibitors, including synthetic chemicals and natural plant extracts, provide effective PPO inhibition but require careful monitoring of their content. Biological methods, including gene editing and microbial fermentation, show promise in targeting PPO genes and enhancing antioxidant production. Combining these methods offers a comprehensive strategy for preserving mushroom quality, extending shelf life, and maintaining nutritional value. PRACTICAL APPLICATION: These approaches can be applied in the food industry to improve post-harvest mushroom preservation, enhance product quality, and reduce waste, benefiting both producers and consumers. Further research and innovation are needed to optimize the practical application of these methods in large-scale processing and storage conditions.

Design, synthesis, in silico ADME, DFT, molecular dynamics simulation, anti-tyrosinase, and antioxidant activity of some of the 3-hydroxypyridin-4-one hybrids in combination with acylhydrazone derivatives

Tyrosinase is the rate-limiting enzyme in synthesizing melanin. Melanin is responsible for changing the color of fruits and vegetables and protecting against skin photo-carcinogenesis. Herein, some of the hybrids of 3-hydroxypyridine-4-one and acylhydrazones were designed and synthesized to study the anti-tyrosinase and antioxidant activities. The diphenolase activity of mushroom tyrosinase using L-DOPA assayed the inhibitory effects, and the antioxidant activity was assessed using DPPH free radical. The synthesized derivatives were confirmed using 1H-NMR, 13C-NMR, IR, and Mass spectroscopy. Among analogs, compound 5h bearing furan ring with IC50=8.94 μM was more potent than kojic acid (IC50=16.68 μM). The pharmacokinetic profile of the compounds showed that the tested compounds had suitable oral bioavailability and drug-likeness properties. The molecular docking studies showed that compound 5h was located in the tyrosinase-binding site. Also, the molecular dynamics simulation was performed on compound 5h, proving the obtained molecular docking results. At the B3LYP/6-31 + G** level of theory, the reactivity descriptors for 5 g and 5h were investigated using DFT calculations. Also, IR frequency was calculated to verify DFT results with experimental data. The electrostatic potential energy of the surface and the HOMO and LUMO molecular orbitals were also studied. It agrees with experimental results that the 5h is a soft molecule and ready for chemical reaction with other interacting molecules.Communicated by Ramaswamy H. Sarma.

Mechanistic Analysis of 5-Hydroxy γ-Pyrones as Michael Acceptor Prodrugs

Substituted 5-hydroxy γ-pyrones have shown promise as covalent inhibitor leads against cysteine proteases and transcription factors, but their hydrolytic instability has hindered optimization efforts. Previous mechanistic proposals have suggested that these molecules function as Michael acceptor prodrugs, releasing a leaving group to generate an o-quinone methide-like structure. Addition to this electrophile of either water or an active site cysteine was purported to lead to inhibitor hydrolysis or enzyme inhibition, respectively. Through the use of kinetic nuclear magnetic resonance experiments, Hammett analysis, kinetic isotope effect studies, and density functional theory calculations, our findings suggest that enzyme inhibition and hydrolysis proceed by distinct pathways and are differentially influenced by substituent electronics. This mechanistic revision helps enable a more rational optimization for this class of promising compounds.

Synthesis, biological evaluation, molecular docking, MD simulation and DFT analysis of new 3-hydroxypyridine-4-one derivatives as anti-tyrosinase and antioxidant agents

In the present study, ten new substituted 3-hydroxypyridine-4-one derivatives were synthesized in a four-step method, and their chemical structures were confirmed using various spectroscopic techniques. Subsequently, the inhibitory activities of these derivatives against tyrosinase enzyme and their antioxidant activities were evaluated. Amongest the synthesized compounds, 6b bearing a 4-OH-3-OCH3 substitution was found to be a promising tyrosinase inhibitor with an IC50 value of 25.82 μM, which is comparable to the activity of kojic acid as control drug. Kinetic study indicated that compound 6b is a competitive inhibitor of tyrosinase enzyme, which was confirmed by molecular docking results. The molecular docking study and MD simulation showed that compound 6b was properly placed within the tyrosinase binding pocket and interacted with key residues, which is consistent with its biological activity. The DFT analysis demonstrated that compound 6b is kinetically more stable than the other compounds. In addition, compounds 6a and 6b exhibited the best antioxidant activities. The findings indicate that compound 6b could be a promising lead for further studies.

New 3-Hydroxypyridine-4-one Analogues: Their Synthesis, Antimicrobial Evaluation, Molecular Docking, and In Silico ADME Prediction

INTRODUCTION

Drug resistance to existing antimicrobial drugs has become a serious threat to human health, which highlights the need to develop new antimicrobial agents.

METHODS

In this study, a new set of 3-hydroxypyridine-4-one derivatives (6a-j) was synthesized, and the antimicrobial effects of these derivatives were evaluated against a variety of microorganisms using the microdilution method. The antimicrobial evaluation indicated that compound 6c, with an electron-donating group -OCH3 at the meta position of the phenyl ring, was the most active compound against S. aureus and E. coli species with an MIC value of 32 μg/mL. Compound 6c was more potent than ampicillin as a reference drug.

RESULTS

The in vitro antifungal results showed that the studied derivatives had moderate effects (MIC = 128-512 μg/mL) against C. albicans and A. niger species. The molecular modeling studies revealed the possible mechanism and suitable interactions of these derivatives with the target protein.

CONCLUSION

The obtained biological results offer valuable insights into the design of more effective antimicrobial agents.

Novel kojic acid-1,2,4-triazine hybrids as anti-tyrosinase agents: Synthesis, biological evaluation, mode of action, and anti-browning studies

A class of new kojic acid hybrids (7a-7o) bearing a 1,2,4-triazine moiety were prepared, and their inhibitory activities and mechanism on tyrosinase were investigated. All derivatives showed good to excellent anti-tyrosinase activity with IC₅₀ values ranging from 0.34 ± 0.06 μM to 8.44 ± 0.73 μM. In kinetic study, compound 7m was a mixed-type inhibitor with K_i and K_is of 0.73 and 1.27 μM, respectively. The interaction mechanism toward tyrosinase of compound 7m was further elaborated in combination with molecular docking and various spectral techniques. The results showed that compound 7m could change the secondary structure of tyrosinase to reduce its catalytic activity. Anti-browning assays demonstrated that 7m inhibited the browning of bananas effectively during storage. What's more, 7m was found to have low cytotoxicity in vitro. In conclusion, compound 7m has the potential to be applied as an anti-browning agent.

Oxidative Ring-Opening Transformation of 5-Acyl-4-pyrones as an Approach for the Tunable Synthesis of Hydroxylated Pyrones and Furans

A selective and tunable approach for oxidation of 4-pyrones has been developed via ring-opening transformations leading to various hydroxylated oxaheterocycles. The first step of the strategy includes the base-catalyzed epoxidation of 5-acyl-4-pyrones in the presence of hydrogen peroxide for the effective synthesis of pyrone epoxides in high yields. The epoxides bearing the CO2Et group are reactive molecules that can undergo both pyrone and oxirane ring-opening via deformylation to produce hydroxylated 2-pyrones or 4-pyrones. The acid-promoted transformation led to 3-hydroxy-4-pyrones (24-76% yields), whereas the K2CO3-catalyzed ring-opening process of 2-carbethoxy-4-pyrone epoxides proceeded as an attack of alcohol at the C-3 position bearing the CO2Et group to give functionalized 6-acyl-5-hydroxy-2-pyrones (27-87% yields). The base-catalyzed reaction of 2-aryl-4-pyrone epoxides was followed by ring contraction and the dearoylation process to produce 3-hydroxyfuran-2-carbaldehydes in 42-80% yields. The transformation of 3-aroylchromone epoxides led to flavonols and 3-hydroxybenzofuran-2-carbaldehyde in the acidic and basic conditions, respectively. The prepared hydroxylated heterocycles demonstrated high reactivity for further transformations and low cytotoxicity and are promising fluorophores or UV filters.

Synthesis and biological evaluation of new kojic acid-1,3,4-oxadiazole hybrids as tyrosinase inhibitors and their application in the anti-browning of fresh-cut mushrooms

In the food industry, inhibition of tyrosinase activity is considered as one of the main means to prevent browning. Therefore, fourteen kojic acid-1,3,4-oxadiazole hybrids (5a-5n) were prepared and tested for their tyrosinase inhibitory effects. Among them, 5f (IC₅₀ = 5.32 ± 0.58 μM) has the best anti-tyrosinase activity and was 9 times higher than that of kojic acid (IC₅₀ = 49.77 ± 1.19 μM). Additionally, the inhibitory mechanism was studied by copper-chelating assay, ultraviolet spectrophotometry, fluorescence quenching, molecular docking, etc. The results had shown that 5f could not only bind to the copper ion in the active region of tyrosinase but also change the secondary structure of tyrosinase. Combined with the outstanding anti-browning effect and low cytotoxicity of 5f, it is concluded that these title derivatives could be used as the leading molecules in the development of new anti-browning agents.

Anti-browning and antibacterial dual functions of novel hydroxypyranone-thiosemicarbazone derivatives as shrimp preservative agents: Synthesis, bio-evaluation, mechanism, and application

To develop new shrimp preservative agents with dual functions of anti-browning and antibacterial, thirteen hydroxypyranone-thiosemicarbazone derivatives were prepared according to molecular hybridization. Thereinto, compound 7j (IC₅₀ = 1.99 ± 0.19 μM) shown the strongest anti-tyrosinase activity and was about twenty-three folds stronger than kojic acid (45.73 ± 4.03 μM). The anti-tyrosinase mechanism of 7j was illustrated through enzyme kinetic, copper ion chelating ability, fluorescence quenching, ultraviolet spectrum, AFM analysis, and molecular docking study. On the other hand, antibacterial assay and time-kill kinetics analysis confirmed that 7j also had good antibacterial activity against V. parahaemolyticus (MIC = 0.13 mM). PI uptake test, SDS-PAGE, and fluorescence spectrometry analysis proved that 7j can affect the bacterial cell membrane. Finally, the shrimp preservation and safety study indicated that 7j has dual effects of inhibiting bacterial growth and preventing enzyme browning, and can be applied to the preservation of fresh shrimp.

Novel neuroprotective pyromeconic acid derivatives with concurrent anti-Aβ deposition, anti-inflammatory, and anti-oxidation properties for treatment of Alzheimer's disease

We synthesized a series of novel pyromeconic acid-styrene hybrid compounds and measured their activities in inhibiting Aβ_1-42 self-aggregation and promoting disaggregation, and their anti-inflammatory and antioxidant properties. The most potent compound, compound 30, had IC₅₀ values of 11.15 μM and 6.87 μM for inhibition of fibril aggregation and promotion of fibril disaggregation, respectively. Because of its redox metal chelating property, 30 also inhibited Cu²⁺-induced Aβ_1-42 fibril aggregation and promoted fibril disaggregation with IC₅₀ of 3.69 μM and 3.35 μM, respectively. Molecular docking demonstrated that 30 interacted with key amino acids of Aβ_1-42, and the reliability of the complex was confirmed by molecular dynamics. In addition, 30 displayed excellent antioxidative activity (oxygen radical absorbance capacity = 2.65 Trolox equivalents) and moderate anti-inflammatory activity and neuroprotection in cell culture assays. Compound 30 was safe in acute toxicity test in mice, and it exhibited favorable pharmacokinetic properties, particularly, accumulation in the hippocampus (maximum ratio of hippocampus to plasma = 7.12). Compound 30 alleviated cognitive deficits in scopolamine-induced amnesia mice; this property may have been attributed to reducing neuroinflammation by inhibiting ionized calcium binding adapter molecule 1 and glial fibrillary acidic protein expression and reducing oxidative stress by activating the Nrf2/HO-1 signaling pathway. In view of its many properties, we envision that 30 is a promising lead for the treatment of Alzheimer's disease.

The Construction of Polycyclic Pyridones via Ring-Opening Transformations of 3-hydroxy-3,4-dihydropyrido[2,1-c][1,4]oxazine-1,8-diones

This work describes the synthesis of 3-hydroxy-3,4-dihydropyrido[2,1-c][1,4]oxazine-1,8-diones, their tautomerism, and reactivity towards binucleophiles. These molecules are novel and convenient building-blocks for the direct construction of biologically important polycyclic pyridones via an oxazinone ring-opening transformation promoted with ammonium acetate or acetic acid. In the case of o-phenylenediamine, partial aromatization of the obtained heterocycles proceeded to form polycyclic benzimidazole-fused pyridones (33-91%).

Tyrosinase inhibitory mechanism and anti-browning properties of novel kojic acid derivatives bearing aromatic aldehyde moiety

Kojic acid-aromatic aldehydes 6a-6m were synthesized and screened for their anti-tyrosinase activities. These compounds showed potently anti-tyrosinase activity with IC₅₀ values in the range of 5.32 ± 0.23 to 77.89 ± 3.36 μM compared with kojic acid (IC₅₀ = 48.05 ± 3.28 μM). Thereinto, compound 6j with 3-fluorine and 4-aldehyde substitutions showed the most potent anti-tyrosinase activity (IC₅₀ = 5.32 ± 0.23 μM). Enzyme kinetic study revealed that 6j is a noncompetitive tyrosinase inhibitor (Ki = 2.73 μM). The action mechanism of 6j was evaluated by fluorescence spectrum quenching, molecular docking, ¹H NMR titration, etc. The anti-browning assay showed that 6j could delay the enzymatic browning of fresh-cut apples. Besides, the cell viability assay proved that 6j had a good safety profile as an anti-browning agent. Hence, these results identify a new class of anti-tyrosinase and anti-browning agents for further investigation in the food industry.

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

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

Kojic Acid Showed Consistent Inhibitory Activity on Tyrosinase from Mushroom and in Cultured B16F10 Cells Compared with Arbutins

Kojic acid, β-arbutin, α-arbutin, and deoxyarbutin have been reported as tyrosinase inhibitors in many articles, but some contradictions exist in their differing results. In order to provide some explanations for these contradictions and to find the most suitable compound as a positive control for screening potential tyrosinase inhibitors, the activity and inhibition type of the aforementioned compounds on monophenolase and diphenolase of mushroom tyrosinase (MTYR) were studied. Their effects on B16F10 cells melanin content, tyrosinase (BTYR) activity, and cell viability were also exposed. Results indicated that α-arbutin competitively inhibited monophenolase activity, whereas they uncompetitively activated diphenolase activity of MTYR. β-arbutin noncompetitively and competitively inhibited monophenolase activity at high molarity (4000 µM) and moderate molarity (250–1000 µM) respectively, whereas it activated the diphenolase activity of MTYR. Deoxyarbutin competitively inhibited diphenolase activity, but could not inhibit monophenolase activity and only extended the lag time. Kojic acid competitively inhibited monophenolase activity and competitive–noncompetitive mixed-type inhibited diphenolase activity of MTYR. In a cellular experiment, deoxyarbutin effectively inhibited BTYR activity and reduced melanin content, but it also potently decreased cell viability. α-arbutin and β-arbutin dose-dependently inhibited BTYR activity, reduced melanin content, and increased cell viability. Kojic acid did not affect cell viability at 43.8–700 µM, but inhibited BTYR activity and reduced melanin content in a dose-dependent manner. Therefore, kojic acid was considered as the most suitable positive control among these four compounds, because it could inhibit both monophenolase and diphenolase activity of MTYR and reduce intercellular melanin content by inhibiting BTYR activity without cytotoxicity. Some explanations for the contradictions in the reported articles were provided.