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

Small-Molecule Tyrosinase Inhibitors for Treatment of Hyperpigmentation

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

Discovery of new benzothiazole-1,2,3-triazole hybrid-based hydrazone/thiosemicarbazone derivatives as potent EGFR inhibitors with cytotoxicity against cancer

Considering the widespread availability of certain medicines, there is still a critical need for potent anti-cancer agents. It is owing to numerous negative impacts and non-functionality of current drugs, particularly during the late stages of illness. To accomplish this, the new array of 1,2,3-triazole-benzothiazole molecular conjugates tethering hydrazone/thiosemicarbazone linkage 8a-l have been successfully synthesized via the efficient copper-catalyzed 1,3-dipolar cycloaddition of the appropriate un/substituted benzothiazole azides 4a-c with several O-propargylated benzylidene derivatives 7a-d. The newly established 1,2,3-triazole structural hybrids were thoroughly characterized using appropriate spectroscopic techniques (IR, 1H, 13C-NMR & CHN analysis). The cytotoxic features of the investigated triazole hybrids were assessed against three human cancer cell lines, A549, T47-D, and HCT-116 cancer cells, using the MTT assay. Based on the findings, the breast cancer cell line T47D displayed promising results with IC50 values of 13, 17, and 19 μM for the synthesized molecules 8a-c, respectively. Furthermore, the safety assessment of these compounds on normal cell lines revealed a relatively low risk to normal cells, as indicated by their IC50 values exceeding 500 μM, suggesting a reasonable safety margin. Interestingly, the most relevant derivatives 8a, 8b, and 8c, exhibited IC50 values of 0.69, 1.16, and 4.82 μM, respectively, causing inhibition of 98.5%, 96.8%, and 92.3%, compared to Erlotinib (IC50 = 1.3 μM, 98.2% inhibition). Molecular docking results exhibited a good binding affinity of compounds 8a and 8b towards the EGFR active site. Accordingly, these compounds can be further developed as target-oriented EGFR chemotherapeutics against cancer.

Synthesis, biological evaluations, and in silico assessments of phenylamino quinazolinones as tyrosinase inhibitors

A series of novel phenylamino quinazolinone derivatives were designed and synthesized as potential tyrosinase inhibitors. Among these compounds, 9r emerged as the most potent derivative, exhibiting IC50 values of 17.02 ± 1.66 µM, compared to kojic acid as the positive control with an IC50 value of 27.56 ± 1.27 µM. Antioxidant assessment of 9r compounds showed 24.67% inhibition at 100 µM. Molecular docking studies of these derivatives were conducted, revealing their proper fitting within the enzyme's active site. Additionally, density functional theory analysis was performed on the potent derivatives, indicating their stability and reactivity. Notably, the highest values of the energy gap were observed in 9r and 9s derivatives, underscoring their potential efficacy. Further kinetic studies of compound 9r, identified as the most potent derivative, demonstrated a competitive mode of inhibition with a Ki value of 14.87 µM. Molecular dynamics simulations of the 9r-tyrosinase complex revealed stability over time, with a reduction in critical residual fluctuation during the simulation. Overall, these findings contribute to a deeper understanding of the potential therapeutic value of these derivatives as tyrosinase inhibitors.

Naphthyl-functionalized acetamide derivatives: Promising agents for cholinesterase inhibition and antioxidant therapy in Alzheimer's disease

This study presents the synthesis and characterization of a series of 13 novel acetamides. These were subjected to Ellman's assay to determine the efficacy of the AChE and BChE inhibitors. Finally, we report their antioxidant activity as an alternative approach for the search for drugs to treat AD. These studies revealed that compounds 1a-1k and 2l-2m were obtained in moderate yield. Four amides (1h, 1j, 1k, and 2l) were selective for one of the enzymes (BChE); thus, those that inhibited BChE were more active than the positive control (galantamine) and showed better IC50 values (3.30-5.03 µM). The theoretical free binding energies calculated by MM-GBSA indicated that all inhibitors were more stable than rivastigmine, and the inhibition mechanisms involved the entire active site: peripheral anionic site, oxyanion hole, acyl-binding pockets, and catalytic site. We examined the cytotoxicity of compounds 1h, 1j, 1k, and 2l in human dermal cells and found that they did not exhibit any toxic effects under the tested conditions. Additionally, these compounds, which also inhibited BChE, displayed mixed inhibition and did not exhibit hemolytic effects on human erythrocytes. Furthermore, the ABTS and DPPH assays indicated that, although none of the compounds showed activity in the DPPH assay, the EC50 values for radical trapping by the ABTS method showed that compounds 1a, 1d, 1e, and 1g had EC50 values lower than 10 µg/mL, indicating their strong radical scavenging capacity. We also report the crystal structures of compounds 1c, 1d, 1f, and 1g, which are found in monoclinic crystal systems.

Muti-target rationale design of novel substituted N-phenyl-2-((6-phenylpyridazin-3-yl)thio)acetamide candidates as telomerase/JAK1/STAT3/TLR4 inhibitors: In vitro and in vivo investigations

In this work, additional effort was applied to design new BIBR1532-based analogues with potential inhibitory activity against telomerase and acting as multitarget antitumor candidates to overcome the resistance problem. Therefore, novel substituted N-phenyl-2-((6-phenylpyridazin-3-yl)thio)acetamide candidates (4a-n) were synthesized. Applying the lead optimization strategy of the previously designed compound 8e; compound 4l showed an improved telomerase inhibition of 64.95 % and a superior growth inhibition of 79 % suggesting its potential use as a successful "multitarget-directed drug" for cancer therapy. Accordingly, compound 4l was further selected to evaluate its additional JAK1/STAT3/TLR4 inhibitory potentials. Compound 4l represented a very promising JAK1 inhibitory potential with a 0.46-fold change, compared to that of pacritinib reference standard (0.33-fold change). Besides, it showed a superior STAT3-inhibitory potential with a 0.22-fold change compared to sorafenib (0.33-fold change). Additionally, compound 4l downregulated TLR4 protein expression by 0.81-fold change compared to that of resatorvid (0.29-fold change). Also, molecular docking was performed to investigate the binding mode and affinity of the superior candidate 4l towards the four target receptors (telomerase, JAK1, STAT3, and TLR4). Furthermore, the therapeutic potential of compound 4l as an antitumor agent was additionally explored through in vivo studies involving female mice implanted with Solid Ehrlich Carcinoma (SEC). Remarkably, compound 4l led to prominent reductions in tumor size and mass. Concurrent enhancements in biochemical, hematologic, histopathologic, and immunohistochemical parameters further confirmed the suppression of angiogenesis and inflammation, elucidating additional mechanisms by which compound 4l exerts its anticancer effects.

Design, Synthesis, Structural Insights, Tyrosinase Inhibition, and Sun Protection Factor of New Thiosemicarbazone Derivatives

Tyrosinase, a key protein in the biosynthesis of melanin pigments, is crucial in determining skin pigmentation. Inhibiting tyrosinase activity is a promising approach for treating conditions related to excessive pigmentation. For the synthesis of more potent tyrosinase inhibitors, we combined two approaches, para-substitution and lipophilicity, to enhance the inhibitory properties of (E)-2-(4-hydroxybenzylidene)hydrazine-1-carbotiamide, whose enzyme inhibitory properties have been previously demonstrated. The newly synthesized compounds showed potent inhibition activity against tyrosinase in the micromolar concentration range. The synthesised compounds were up to 41 times more effective than kojic acid. In addition to this biological activity, all molecules were evaluated for their sun protection factor to determine their photoprotective effects. All the compounds showed higher efficacy than reference compounds, used as sunscreens in photoprotective preparations. All compounds were noncytotoxic at the concentration required to inhibit tyrosinase activity. With the aim of defining the potential binding modes and the kind of interactions between the studied molecules and the catalytic site of mushroom tyrosinase, molecular docking simulations were also performed.

Design, synthesis and evaluation of benzothiazole-derived phenyl thioacetamides as dual inhibitors of monoamine oxidases and cholinesterases

A series of rationally designed benzothiazole-derived thioacetamides was synthesized and investigated for monoamine oxidases (MAO-A and MAO-B) and cholinesterases (AChE and BChE) inhibition properties. The tested compounds 18-31 inhibited MAO-A and MAO-B in the micromolar to nanomolar range and AChE in the submicromolar range. Compound 28 was identified as the most potent MAO-A inhibitor with an IC50 = 0.030 ± 0.008 µM, whereas compound 30 showed the highest potency towards MAO-B and AChE with IC50 values of 0.015 ± 0.007 µM and 0.114 ± 0.003 µM, respectively. Further, compound 30 inhibited BChE at an IC50 value of 4.125 ± 0.143 µM. Among all screened molecules, compound 30 emerged as the lead dual MAO-B and AChE inhibitor that blocked these enzymes in a competitive-reversible and mixed-reversible mode, respectively. Selected compounds have displayed iron-chelation and antioxidant properties. Further, computational assessment of ligand binding affinity and pharmacokinetic parameters of all new compounds and molecular dynamic simulation of compound 30 with MAO-B and AChE were carried out to understand ligand efficiency, pharmacokinetic, and virtual molecular interaction profile, respectively. The in silico ADMET prediction studies revealed a few undesired pharmacokinetic attributes of our compounds. The attempted virtual lead-based library synthesis and subsequent biological investigation produced a new benzothiazole-bearing dual MAO-B and AChE inhibitor as a prospective MTDL candidate for treating neurological disorders.

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

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

Synthesis and biological assessment of novel 4H-chromene-3-carbonitrile derivatives as tyrosinase inhibitors

Excessive activity of the tyrosinase enzyme during melanogenesis results in hyperpigmentation in the skin. To address this issue, there is a need to develop effective tyrosinase inhibitors as a treatment for hyperpigmentation. In this study, we synthesized some novel 4H-chromene-3-carbonitrile compounds (6a-o) and assessed their inhibitory activities against tyrosinase, comparing them with kojic acid, which is known as a positive control. Compound 6f emerged as the most effective inhibitor, with an IC50 of 35.38 ± 2.12 µM. Kinetic studies of 6f exhibited competitive inhibition, with Ki = 16.15 µM. Molecular docking studies highlighted the importance of π-π stacking and hydrogen bonding interactions within the binding site. Molecular dynamics simulations showed that the R-enantiomer 6f exhibited superior binding stability compared to the S-enantiomer, with a lower standard deviation of RMSD and more persistent interactions with the key active site residues. These findings underscore the potential of the R-enantiomer of compound 6f as a potent tyrosinase inhibitor and provide insights for developing effective treatments for hyperpigmentation and related skin conditions.

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.

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.

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.

Design, synthesis, and molecular dynamics simulation studies of some novel kojic acid fused 2-amino-3-cyano-4H-pyran derivatives as tyrosinase inhibitors

A novel series of kojic acid fused 2-amino-3-cyano-4H-pyran derivatives were synthesized via a multicomponent reaction involving kojic acid, benzyloxy benzaldehyde, and malonitrile as tyrosinase inhibitors. Subsequently, the structures of the compounds were characterized using FT-IR, 1H-, and 13C-NMR spectroscopic analyses. The designed compounds fall into three series: (1) 4-benzyloxy-phenyl kojopyran 6a-e, (2) 3-benzyloxy- phenyl kojopyran derivatives 6f-j, and (3) 4-benzyloxy-3-methoxy-phenyl kojopyran derivative 6 k-o. The assessment of tyrosinase inhibition activity was conducted using L-Dopa as the substrate. Among synthesized compounds, 2-amino-4-(4-((4-fluorobenzyl)oxy)phenyl)-6-(hydroxymethyl)-8-oxo-4,8-dihydropyrano[3,2-b]pyran-3-carbonitrile (6b) demonstrated the highest antityrosinase activity with a competitive inhibition pattern (IC50 = 7.69 ± 1.99 μM) as compared to the control agent kojic acid (IC50 = 23.64 ± 2.56 µM). Since compound 6b was synthesized as a racemic mixture, in silico studies were performed for both R and S enantiomers. The R- enantiomer showed critical interactions compared with the S-enantiomer. Specifically, it established hydrogen bonds and hydrophobic interactions with crucial and highly conserved amino acids within the enzyme's binding site in the target protein. Moreover, the molecular dynamics simulations revealed that compound 6b demonstrated significant interactions with essential residues of the binding site, resulting in a stable complex throughout the entire simulation run. The drug-like and ADMET properties predictions showed an acceptable profile for compound 6b. Thus, it can serve as a drug candidate to develop more potent antityrosinase agents due to its low toxicity and its high inhibition activity.

Structure-based development of 3,5-dihydroxybenzoyl-hydrazineylidene as tyrosinase inhibitor; in vitro and in silico study

A series of new analogs of 3,5-dihydroxybenzoyl-hydrazineylidene conjugated to different methoxyphenyl triazole (11a-n) synthesized using click reaction. The structures of all synthesized compounds were characterized by FTIR, 1H, 13C-NMR spectroscopy, and CHO analysis. The tyrosinase inhibitory potential of the synthesized compounds was studied. The newly synthesized scaffolds were found to illustrate the variable degree of the inhibitory profile, and the most potent analog of this series was that one bearing 4-methoxyphenyl moiety, and exhibited an IC50 value of 55.39 ± 4.93 µM. The kinetic study of the most potent derivative reveals a competitive mode of inhibition. Next, molecular docking studies were performed to understand the potent inhibitor's binding mode within the enzyme's binding site. Molecular dynamics simulations were accomplished to further investigate the orientation and binding interaction over time and the stability of the 11m-tyrosinase complex.

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

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

Recent advances in triazoles as tyrosinase inhibitors

The tyrosinase enzyme, which is widely found in microorganisms, animals and plants, has a significant position in melanogenesis, plays an important role in undesirable browning of fruits and vegetables, antibiotic resistance, skin pigment formation, sclerotization of cuticle, neurodegeneration, etc. Therefore, with the wide potential application fields of tyrosinase in food, agriculture, cosmetics and pharmaceutical industries, which has become the target enzyme for the development of therapeutic agents such as antibrowning, anticancer, antibacterial, skin whitening, insecticides, etc., a large number of synthetic tyrosinase inhibitors have been widely reported in recent years. The triazole ring, which has a broad spectrum of biological action, is of increasing interest in the synthesis of new tyrosinase inhibitors. In this review, tyrosinase inhibition effects, structure-activity relationships, enzyme inhibition kinetics and mechanisms of action of 1,2,3- or 1,2,4-triazole derivatives were investigated. The data gathered is anticipated to supply rational guidance and an influential strategy for the development of novel, potent and safe tyrosinase inhibitors for better practical application in the future.

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

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

Microwave-assisted solvent-free synthesis of some novel thiazole-substituted thiosemicarbazone analogues: antimicrobial and anticancer studies

The increased resistance to antibiotics has compelled researchers to devise novel active compounds targeting multidrug-resistant pathogenic microorganisms. A series of thiosemicarbazone derivatives was synthesized by reacting thiosemicarbazide with 2-aryl-4-formylthiazole, 2-aryl-5-formyl-4-methylthiazole, and/or 5-acetyl-2-aryl-4-methylthiazole compounds. These thiosemicarbazone-based thiazole adducts were evaluated for their inhibitory activities against tuberculosis H37Ra and Bovis BCG mycobacteria. Their cytotoxicity was assessed against two cancer cell lines: colonic carcinoma (HCT-116) and cervical cancer (HeLa). Notably, these thiosemicarbazones exhibited minimal cytotoxic effects on these cell lines even at their highest concentrations. Furthermore, the prepared thiosemicarbazone derivatives demonstrated significant antimicrobial efficacy against Bacillus subtilis and Staphylococcus aureus (Gram-positive bacterial pathogens) as well as Escherichia coli and Pseudomonas fluorescens (Gram-negative bacterial pathogens). While most of the prepared thiosemicarbazone derivatives exhibited moderate activity against Candida albicans (a fungal strain), their performance was notable. The thiosemicarbazone-based thiazole adducts were also successfully synthesized using a solvent-free approach under microwave irradiation. Compared with conventional reflux methods, the microwave-assisted technique yielded high thiazole yields within just 5 min, obviating the need for catalysis. This study signifies significant strides toward the rational design of more potent antimycobacterial agents.

Synthesis and tyrosinase inhibitory activities of novel isopropylquinazolinones

To find new anti-browning and whitening agents in this study, new series of isopropylquinazolinone derivatives were designed and synthesized. All derivatives were evaluated as possible tyrosinase inhibitors and compound 9q bearing 4-fluorobenzyl moieties at the R position exhibited the best potencies with an IC₅₀ value of 34.67 ± 3.68 µM. The kinetic evaluations of 9q as the most potent derivatives recorded mix-type inhibition. Compounds 9o and 9q also exhibited potent antioxidant capacity with IC₅₀ values of 38.81 and 40.73 µM, respectively confirming their antioxidant potential. Molecular docking studies of 9q as the most potent derivative were exacuated and it was shown that quinazolinone and acetamide moieties of compound 9q participated in interaction with critical His residues of the binding site. The obtained results demonstrated that the 9q can be considered a suitable pharmacophore to develop potent tyrosinase inhibitors.

Heterocyclic Compounds as Synthetic Tyrosinase Inhibitors: Recent Advances

Tyrosinase is a copper-containing enzyme which is widely distributed in nature (e.g., bacteria, mammals, fungi) and involved in two consecutive steps of melanin biosynthesis. In humans, an excessive production of melanin can determine hyperpigmentation disorders as well as neurodegenerative processes in Parkinson's disease. The development of molecules able to inhibit the high activity of the enzyme remain a current topic in medicinal chemistry, because the inhibitors reported so far present several side effects. Heterocycle-bearing molecules are largely diffuse in this sense. Due to their importance as biologically active compounds, we decided to report a comprehensive review of synthetic tyrosinase inhibitors possessing heterocyclic moieties reported within the last five years. For the reader's convenience, we classified them as inhibitors of mushroom tyrosinase (Agaricus bisporus) and human tyrosinase.

Bis-triazole linked organosilane based sensing platform for Cu2+ ions and insilico tyrosinase inhibitor activity

The development of a ligand for their selective and sensitive detection is required due to the widespread use of Cu²⁺ in many industrial processes and the potential threat to human health. Herein, we report a bis-triazole linked organosilane (5) derived from the Cu(I) catalyzed azide-alkyne cycloaddition reaction. The synthesized compound 5 was characterized by (¹H and ¹³C) NMR spectroscopic and mass spectrometry techniques. The UV-Visible and Fluorescence experiments of the designed compound 5 were performed with various metal ions, revealing its high selectivity and sensitivity to Cu²⁺ ions in MeOH: H₂O (8:2, v/v, pH = 7.0, PBS buffer) solution. The selective fluorescence quenching upon addition of Cu²⁺ to the compound 5 is due to Photo-induced electron transfer process (PET). The limit of detection of compound 5 to Cu²⁺ was calculated as 2.56 × 10^-6 M and 4.36 × 10^-7 M through UV-Visible and Fluorescence titration data, respectively. The possible mechanism of 1:1 binding of 5 with Cu²⁺ could be affirmed by the density functional theory (DFT). Further, it was found that compound 5 showed a reversible behavior towards Cu²⁺ ions by the accumulation of sodium salt of CH₃COO^- which can be used in the construction of molecular logic gate where Cu²⁺ and CH₃COO^- are considered as inputs and the absorbance at 260 nm as output. Moreover, the molecular docking studies provide useful information about compound 5's interaction with the tyrosinase enzyme (PDB ID- 2Y9X).

Thioquinoline derivatives conjugated to thiosemicarbazide as potent tyrosinase inhibitors with anti-melanogenesis properties

In the present study, a series of aryl-substituted thioqunoline conjugated to thiosemicarbazide were rationally designed and synthesized. The formation of target compounds was confirmed by spectral characterization techniques such as IR, ¹H-NMR, ¹³C-NMR, ESI-MS, and elemental analysis. Among the synthesized derivatives, compound 10g bearing para-chlorophenyl moiety was proved to be the most potent tyrosinase inhibitor with an IC₅₀ value of 25.75 ± 0.19 µM. Compound 10g as the most potent derivative exhibited a noncompetitive inhibition pattern against tyrosinase in the kinetic study. Furthermore, the in silico cavity detection, as well as the molecular docking assessments, were performed to follow the behavior of 10g within the proposed binding site. Besides, the toxicity of 10g and its potency to reduce the melanin content on A375 cell lines were also measured. Consequently, aryl-substituted thioqunolines conjugated to thiosemicarbazide might be a promising candidate in the cosmetics, medicine, and food industry as tyrosinase inhibitors.

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

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

Design, synthesis, spectroscopic characterization, in vitro tyrosinase inhibition, antioxidant evaluation, in silico and kinetic studies of substituted indole-carbohydrazides

In the current study, twenty-five indole-carbohydrazide derivatives linked to different aryl substitutions were rationally designed and synthesized. The structures of all derivatives were confirmed using different spectroscopic techniques including ¹H NMR, ¹³C NMR, Mass spectrometry, and elemental analysis. The tyrosinase inhibitory activities of all synthetic compounds exhibited IC₅₀ values in the range of 0.070 to > 100 μM. Structure-activity relationships showed that compounds 4f (R = 4-OH, IC₅₀ = 0.070 μM), 8f (R = 4-OH, IC₅₀ = 0.072 μM), and 19e (IC₅₀ = 0.19 μM) with para-OH substituent at the R position was found to be the most active members of all three tested series. Kinetic studies exhibited that compounds 4f, 8f, and 19e are mixed-type inhibitors. Furthermore, toxicity and cell-based anti-melanogenesis assessments were performed on the most potent derivatives and it was shown that 4f, 8f, and 19e had no toxicity at 8 µM and reduced the percent of melanin content to 68.43, 72.61, 73.47 at 8 μM, respectively. In silico analyses of absorption, distribution, metabolism, and excretion (ADME) profile of synthesized compounds showed that these molecules followed drug-likeness rules and acceptable predictive ADMET features. Results of the docking study were almost in line with biological results with ChemPLP values of 53.56 to 79.33. Also, the docking study showed the critical interactions of potent inhibitors with the active site of the enzyme which affects the potency of the synthesized hybrids. Based on molecular dynamic simulations, compound 4f exhibited pronounced interaction with the critical residues of the tyrosinase active site so that the indole ring participated in H-bond interaction with Gly281 and 4-hydroxy benzylidene recorded another H-bond interaction with Asp289 plus hydrophobic interactions with Phe292. Hydrazide linker also exhibited three H-bond interactions with His263 and Gly281.

Design, synthesis, and molecular docking studies of diphenylquinoxaline-6-carbohydrazide hybrids as potent α-glucosidase inhibitors

A novel series of diphenylquinoxaline-6-carbohydrazide hybrids 7a-o were rationally designed and synthesized as anti-diabetic agents. All synthesized compounds 7a-o were screened as possible α-glucosidase inhibitors and exhibited good inhibitory activity with IC50 values in the range of 110.6 ± 6.0 to 453.0 ± 4.7 µM in comparison with acarbose as the positive control (750.0 ± 10.5 µM). An exception in this trend came back to a compound 7k with IC50 value > 750 µM. Furthermore, the most potent derivative 7e bearing 3-fluorophenyl moiety was further explored by kinetic studies and showed the competitive type of inhibition. Additionally, the molecular docking of all derivatives was performed to get an insight into the binding mode of these derivatives within the active site of the enzyme. In silico assessments exhibited that 7e was well occupied in the binding pocket of the enzyme through favorable interactions with residues, correlating to the experimental results.

Modern metal-catalyzed and organocatalytic methods for synthesis of coumarin derivatives: a review

Coumarin is an important pharmaceutical structural motif, abundantly found in numerous commonly used drugs. Compounds containing this core show a broad spectrum of medicinal properties and biological activities. The increasing importance and wide usages of coumarin derivatives have drawn attention to its synthetic methods, among which metal-catalyzed and organocatalytic methods have proved the most effective. Several metal-catalyzed and/or organocatalytic synthetic strategies for coumarin have been investigated and reported in recent decades. This review focuses on more recent reports on catalysis methods for synthesizing coumarin and coumarin-like structures (including light-mediated methods and nano-catalysts), exploring the mechanistic aspects, simplicity, efficiency, repeatability, and other advantages and disadvantages of these methods.

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

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

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

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

Synthesis and biological evaluation of benzimidazoles/1,3,5-triazine-2,4-diamine hybrid compounds: a new class of multifunctional alzheimer targeting agents

Twelve novel benzimidazole/1,3,5-triazine-2,4-diamine hybrids were synthesized and biologically studied as multifunctional Alzheimer-controlling agents.

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

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