Imino-2H-Chromene Based Derivatives as Potential Anti-Alzheimer's Agents: Design, Synthesis, Biological Evaluation and in Silico Study.

A new series of imino-2H-chromene derivatives were rationally designed and synthesized as novel multifunctional agents against Alzheimer's disease. A set of phenylimino-2H-chromenes as well as the newly synthesized iminochromene derivatives were evaluated as BACE1, acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE) inhibitors. The results indicated that among the iminochromene set, 10c bearing fluorobenzyl moiety was the most potent BACE1 inhibitor with an IC50 value 6.31 µM. In vitro anti-cholinergic activities demonstrated that compound 10a bearing benzyl pendant was the best inhibitor of AChE (% inhibition at 30 µM=24.4) and BuChE (IC50 =3.3 µM). Kinetic analysis of compound 10a against BuChE was also performed and showed a mixed-type inhibition pattern. The neuroprotective assessment revealed that compound 11b, a phenylimino-2H-chromene derivative with hydroxyethyl moiety, provided 32.3 % protection at 25 µM against Aß-induced PC12 neuronal cell damage. In addition, docking and simulation studies of the most potent compounds against BACE1 and BuChE confirmed the experimental results.

Interplay between perivascular and perineuronal extracellular matrix remodelling in neurological and psychiatric diseases.

Vascular damage, central nervous system (CNS) injury, seizure or even psychological stress may trigger activation of microglia and infiltration of other immune cells, accompanied by high levels of expression and activity of extracellular proteases, such as matrix metalloproteinases (MMPs), and degradation/remodelling of the perivascular and perineuronal extracellular matrix (ECM). This acute response is followed by the recovery/chronic phase, during which the activation of astrocytes leads to the upregulated synthesis of ECM molecules, which, in combination with elevated expression of tissue inhibitor of metalloproteinases (TIMP) proteins, increases the aggregation of ECM molecules. This biphasic dysregulation of local balance between extracellular proteases and the ECM activates multiple temporally overlapping signalling cascades, involving receptor-type protein tyrosine phosphatases, integrins, Toll-like receptors, cell adhesion molecules, and ion channels, resulting in impaired synaptic plasticity and cognition. An additional level of complexity is related to the leakage of blood plasma proteins, such as fibrinogen, and the diffusion of perivascularly overproduced MMPs, TIMPs and ECM molecules into the CNS parenchyma, leading to diverse effects on neurons and incorporation of these molecules into the interstitial neural ECM. This review aims to outline these complex common mechanisms in stroke, CNS injury, depression, epilepsy, multiple sclerosis and cerebral small vessel disease and to discuss translational strategies to advance the development of new therapies for these neurological and psychiatric diseases.

The natural-based optimization of kojic acid conjugated to different thio-quinazolinones as potential anti-melanogenesis agents with tyrosinase inhibitory activity.

Melanin pigment and melanogenesis are a two-edged sword. Melanin has a radioprotection role while melanogenesis has undesirable effects. Targeting the melanogenesis pathway, a series of kojyl thioether conjugated to different quinazolinone derivatives were designed, synthesized, and evaluated for their inhibitory activity against mushroom tyrosinase. All the synthesized compounds were screened for their anti-tyrosinase activity and all derivatives displayed better potency than kojic acid as the positive control. In this regard, 5j and 5h as the most active compounds showed an IC50 value of 0.46 and 0.50 µM, respectively. In kinetic evaluation against tyrosinase, 5j depicted an uncompetitive inhibition pattern. Designed compounds also exhibited mild antioxidant capacity. Moreover, 5j and 5h achieved good potency against the B16F10 cell line to reduce the melanin content, whilst showing limited toxicity against malignant cells. The proposed binding mode of new inhibitors evaluated through molecular docking was consistent with the results of structure-activity relationship analysis.

4H-benzochromene derivatives as novel tyrosinase inhibitors and radical scavengers: synthesis, biological evaluation, and molecular docking analysis.

A series of ethyl 2-amino-4H-benzo[h]chromene-3-carboxylate derivatives, having phenyl ring with diverse substituents at C4 position of 4H-benzochromene nucleus, were synthesized via one-pot three-component reaction between various aromatic aldehydes, α-naphthol, and ethyl cyanoacetate. The synthesized compounds were screened for their antityrosinase activity. Compound 4i, bearing 4-dimethylamino substitution on C4-phenyl ring, was the most potent tyrosinase inhibitor (IC50 = 34.12 µM). The inhibition kinetic analysis of 4i indicated that the compound was a competitive tyrosinase inhibitor. Compounds 4a, 4g, 4i and 4j were the effective radical scavengers with EC50s in the range of 0.144-0.943 mM. According to the in silico drug-like and ADME predictions, 4i can be considered as a suitable candidate. Molecular docking results confirmed that the derivative was well accommodated within the mushroom tyrosinase binding site. Therefore, 4i can be introduced as a novel tyrosinase inhibitor that might be a promising lead in medicine, cosmetics, and food industry.

Design, synthesis, in vitro and in silico studies of novel Schiff base derivatives of 2-hydroxy-4-methoxybenzamide as tyrosinase inhibitors.

Due to the fact that tyrosinase is responsible for biosynthesis and regulation of melanins and browning food products, tyrosinase inhibitors can be favorable agents in cosmetics and medicinal industries. A series of novel 2-hydroxy-4-methoxybenzohydrazide were designed, synthesized, and their new application as tyrosinase inhibitors was also disclosed. Based on in vitro tyrosinase inhibitory assay, 4d as the strongest inhibitor of tyrosinase with an IC50 value of 7.57 µM showed approximately 2.5-fold better inhibition than kojic acid as positive control followed by two compounds 4b (IC50  = 8.19 ± 0.25 µM) and 4j (IC50  = 8.92 ± 0.016) which displayed preferable tyrosinase inhibitory activity. Detailed investigations on the mechanism of action of the 4d reported mix type of inhibition. More importantly, molecular modeling assessments proposed the ability of 4d for potential interaction with Cu (metal)-His (residue) within tyrosinase active site. Overall, 4d is a promising candidate for the development of anti-tyrosinase agents.

Oxytocinergic system mediates the proconvulsant effects of sildenafil: The role of calcineurin.

Sildenafil is a phosphodiesterase type 5 inhibitor used to treat male erectile dysfunction and pulmonary hypertension. A potential side effect of sildenafil is a noticeable decrease in seizure threshold. Oxytocin (OXT) secretion and the subsequent cAMP-responsive element-binding (CREB) phosphorylation are involved in proconvulsant effects of sildenafil in experimental models. The aim of the present study was to investigate the potential role of OXT receptors and their downstream calcineurin (CN)/inducible nitric oxide synthase (iNOS) pathways in proconvulsant effects of sildenafil. The pentylenetetrazole (PTZ)-induced seizure was used as a standard convulsion model in this study. Cortical CN activity, hippocampal nitrite levels, and proinflammatory cytokine content were measured. Our results indicated that following PTZ administration, sildenafil significantly increased CN activity at 40 mg/kg, respectively, in the control group. The combination of sildenafil and OXT receptor antagonist, atosiban (10 µg/kg, i.c.v) 30 min before sildenafil administration significantly reduced the CN activity. Also, the subeffective dose of CN inhibitor cyclosporine (5 mg/kg) 30 min before the administration of effective dose of sildenafil (40 mg/kg) reversed proconvulsant actions of sildenafil. This effect was iNOS-dependent because pretreatment of a low dose of aminoguanidine (20 mg/kg) 15 min before the administration of a low dose of cyclosporine (1 mg/kg) reversed the proconvulsant action of sildenafil (40 mg/kg). Finally, sildenafil induced the elevation of tumor necrosis factor alpha (TNF-α) and the nitrite level was blocked by the administration of cyclosporine in PTZ-treated mice. Collectively, our data provide insights into the role of OXT receptor/CN/iNOS pathway in the proconvulsant aspect of sildenafil.

One-pot synthesis of thioxo-tetrahydropyrimidine derivatives as potent ß-glucuronidase inhibitor, biological evaluation, molecular docking and molecular dynamics studies.

A series of N,N-diethyl phenyl thioxo-tetrahydropyrimidine carboxamide have been synthesized and investigated for their ß-glucuronidase inhibitory activities. All molecules exhibited excellent inhibition with IC50 values ranging from 0.35 to 42.05 µM and found to be even more potent than the standard d-saccharic acid. Structure-activity relationship analysis indicated that the meta-aryl-substituted derivatives significantly influenced ß-glucuronidase inhibitory activities while the para-substitution counterpart outperforming moderate potency. The most potent compound in this series was 4g bearing thiophene motif with IC50 of 0.35 ± 0.09 µM. To verify the SAR, molecular docking and molecular dynamics studies were also performed.

Novel small molecule therapeutic agents for Alzheimer disease: Focusing on BACE1 and multi-target directed ligands.

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder that effects 50 million people worldwide. In this review, AD pathology and the development of novel therapeutic agents targeting AD were fully discussed. In particular, common approaches to prevent Aß production and/or accumulation in the brain including α-secretase activators, specific γ-secretase modulators and small molecules BACE1 inhibitors were reviewed. Additionally, natural-origin bioactive compounds that provide AD therapeutic advances have been introduced. Considering AD is a multifactorial disease, the therapeutic potential of diverse multi target-directed ligands (MTDLs) that combine the efficacy of cholinesterase (ChE) inhibitors, MAO (monoamine oxidase) inhibitors, BACE1 inhibitors, phosphodiesterase 4D (PDE4D) inhibitors, for the treatment of AD are also reviewed. This article also highlights descriptions on the regulator of serotonin receptor (5-HT), metal chelators, anti-aggregants, antioxidants and neuroprotective agents targeting AD. Finally, current computational methods for evaluating the structure-activity relationships (SAR) and virtual screening (VS) of AD drugs are discussed and evaluated.

A Series of Benzylidenes Linked to Hydrazine-1-carbothioamide as Tyrosinase Inhibitors: Synthesis, Biological Evaluation and Structure-Activity Relationship.

Tyrosinase is a type 3 copper enzyme responsible for skin pigmentation disorders, skin cancer, and enzymatic browning of vegetables and fruits. In the present article, 12 small molecules of 2-benzylidenehydrazine-1-carbothioamide were designed, synthesized and evaluated for their anti-tyrosinase activities followed by molecular docking and pharmacophore-based screening. Among synthesized thiosemicarbazone derivatives, one compound, (2E)-2-[(4-nitrophenyl)methylidene]hydrazine-1-carbothioamide, is the strongest inhibitor of mushroom tyrosinase with IC50 of 0.05 µM which demonstrated a 128-fold increase in potency compared to the positive control. Kinetic studies also revealed mix type inhibition by this compound. Docking studies confirmed the complete fitting of the synthesized compounds into the tyrosinase active site. The results underline the potential of 2-benzylidenehydrazine-1-carbothioamides as potent pharmacophore to extend the tyrosinase inhibition in drug discovery.

1,2,3-Triazole-linked 5-benzylidene (thio)barbiturates as novel tyrosinase inhibitors and free-radical scavengers.

In this study, benzyl-1,2,3-triazole-linked 5-benzylidene (thio)barbiturate derivatives 7a-d and 8a-h were designed as potential tyrosinase inhibitors and free-radical scavengers. The twelve derivatives were synthesized via the [3+2] cycloaddition reaction of the corresponding benzyl azide as a dipole and the corresponding alkyne as a dipolarophile in the presence of copper(I) species, generated in situ from copper(II)/ascorbate. The thiobarbiturate derivative 8h and the barbiturate derivative 8b bearing 4-fluoro and 4-bromo groups on the benzyl-triazole moiety were found to be the most potent tyrosinase inhibitors with IC50 values of 24.6 ± 0.9 and 26.8 ± 0.8 µM, respectively. Almost all the compounds showed a good radical scavenging activity with EC50 values in the range of 29.9-324.9 µM. Derivatives 7a, 8f, and 8h were the most potent free-radical scavengers with EC50 values of 29.9 ± 0.8, 36.8 ± 0.9, and 39.2 ± 1.1 µM, respectively. The kinetic analysis revealed that compound 8h was a mixed-type tyrosinase inhibitor. The molecular docking analysis indicated that 8b and 8h were well accommodated in the active site of the tyrosinase enzyme and possessed the most negative binding energy values of -8.55 and -8.81 kcal/mol, respectively. Moreover, it was found that the two residues, Asn81 and Glu322, played a significant role in forming stable enzyme-inhibitor complexes.

Veratric acid derivatives containing benzylidene-hydrazine moieties as promising tyrosinase inhibitors and free radical scavengers.

Tyrosinase enzyme plays a crucial role in melanin biosynthesis and enzymatic browning process of vegetables and fruits. A series of veratric acid derivatives containing benzylidene-hydrazine moieties with different substitutions were synthesized and their inhibitory effect on mushroom tyrosinase and free radical scavenging activity were evaluated. The results indicated that N'-(4-chlorobenzylidene)-3,4-dimethoxybenzohydrazide (D5) and N'-(2,3-dihydroxybenzylidene)-3,4-dimethoxybenzohydrazide (D12) showed the highest tyrosinase inhibitory activity with IC50 values of 19.72 ±â€¯1.84 and 20.63 ±â€¯0.79 µM, respectively, that were comparable with the IC50 value of kojic acid (19.08 ±â€¯1.21 µM). D12 was also a potent radical scavenger with EC50 value of 0.0097 ±â€¯0.0011 mM. The free radical scavenging activity of D12 was comparable with the standard quercetin. The inhibition kinetic analyzed by Lineweaver-Burk plots revealed that compound D5 was a competitive tyrosinase inhibitor. Molecular docking study was carried out for the derivatives demonstrating tyrosinase inhibitory activity. D5 and D12 possessed the most negative estimated free energies of binding in mushroom tyrosinase active site. Therefore, D5 and D12 could be introduced as potent tyrosinase inhibitors that might be promising leads in medicine, cosmetics and food industry.

1,2,3-Triazole-based kojic acid analogs as potent tyrosinase inhibitors: Design, synthesis and biological evaluation.

A series of kojic acid-derived compounds 6a-p bearing aryloxymethyl-1H-1,2,3-triazol-1-yl moiety were designed by modifying primary alcoholic group of kojic acid as tyrosinase inhibitors. The target compounds 6a-p were synthesized via click reaction. All compounds showed very potent anti-tyrosinase activity (IC50s = 0.06-6.80 µM), being superior to reference drug, kojic acid. In particular, the naphthyloxy analogs 6o and 6p were found to be 31-155 times more potent than kojic acid. The metal-binding study of selected compound 6o revealed that the prototype compound possesses metal-chelating ability, particularly with Cu2+ ions. The promising compounds 6o and 6p had acceptable safety profile as demonstrated by cytotoxicity assay against melanoma (B16) cell line and Human Foreskin Fibroblast (HFF) cells.

Synthesis of New Benzimidazole-1,2,3-triazole Hybrids as Tyrosinase Inhibitors.

A novel series of benzimidazole-1,2,3-triazole hybrids containing substituted benzyl moieties were designed, synthesized and evaluated for their inhibitory activity against mushroom tyrosinase. The results indicated that 2-(4-{[1-(3,4-dichlorobenzyl)-1H-1,2,3-triazol-4-yl]methoxy}phenyl)-1H-benzimidazole (6g) and 2-(4-{[1-(4-bromobenzyl)-1H-1,2,3-triazol-4-yl]methoxy}phenyl)-1H-benzimidazole (6h) exhibited effective inhibitory activity with IC50 values of 9.42 and 10.34 µm, respectively, comparable to that of kojic acid as the reference drug (IC50 = 9.28 µm). Kinetic study of compound 6g confirmed mixed-type inhibitory activity towards tyrosinase indicating that it can bind to free enzyme as well as enzyme-substrate complex. Also, molecular docking analysis was performed to determine the binding mode of the most potent compounds (6g and 6h) in the active site of tyrosinase. Consequently, 6g and 6h derivatives might serve as promising candidates in cosmetics, medicine or food industry, and development of such compounds may be of an interest.

Structure-based design, synthesis, molecular docking study and biological evaluation of 1,2,4-triazine derivatives acting as COX/15-LOX inhibitors with anti-oxidant activities.

A set of 1,2,4-triazine derivatives were designed as cyclooxygenase-2 (COX-2) inhibitors. These compounds were synthesized and screened for inhibition of cyclooxygenases (COX-1 and COX-2) based on a cellular assay using human whole blood (HWB) and lipoxygenase (LOX-15) that are key enzymes in inflammation. The results showed that 3-(2-(benzo[d][1,3]dioxol-5-ylmethylene)hydrazinyl)-5,6-bis(4-methoxyphenyl)-1,2,4-triazine (G11) was identified as the most potent COX-2 inhibitor (78%) relative to COX-1 (50%). Ferric reducing anti-oxidant power (FRAP) assay revealed that compound G10 possesses the highest anti-oxidant activity. The compound G3 with IC50 value of 124 µM was the most potent compound in LOX inhibitory assay. Molecular docking was performed and a good agreement was observed between computational and experimental results.

Verapamil, a Calcium-Channel Blocker, Improves the Wound Healing Process in Rats with Excisional Full-Thickness Skin Wounds Based on Stereological Parameters.

OBJECTIVE: Calcium can play noticeable roles in the wound-healing process, such as its effects on organization of F-actinin collagen bundles by fibroblasts at the injury site. In addition, calcium-channel blockers such as verapamil have antioxidant activity by increasing nitric oxide production that promotes angiogenesis, proliferation of fibroblasts, and endothelial cells in the skin-regeneration process. Therefore, in this study, the authors' objective was to investigate the effects of verapamil on the process of wound healing in rat models according to stereological parameters. MATERIALS AND METHODS: In this experimental study, 36 male Wistar rats were randomly divided into 3 groups (n = 12): the control group that received no treatment, gel-base-treated group, and the 5% verapamil gel-treated group. Treatments were done every 24 hours for 15 days. Wound closure rate, volume densities of the collagen bundles and the vessels, vessel's length density and mean diameter, and fibroblast populations were estimated using stereological methods and were analyzed by the Kruskal-Wallis and Mann-Whitney U tests; P < .05 was considered statistically significant. RESULTS: The verapamil-treated group showed a faster wound closure rate in comparison with control and gel-base groups (P = .007 and P = .011). The numerical density of fibroblasts, volume density of collagen bundles, mean diameter, and volume densities of the vessels in the verapamil group were significantly higher than those in the control and the base groups (P < .005). CONCLUSIONS: The authors showed that verapamil has the ability to improve wound healing by enhancing fibroblast proliferation, collagen bundle synthesis, and revascularization in skin injuries.

A COX/5-LOX Inhibitor Licofelone Revealed Anticonvulsant Properties Through iNOS Diminution in Mice.

Licofelone is a COX/5-LOX inhibitor, which recently was approved as an effective treatment for osteoarthritis. Beside its analgesic and anti-inflammatory effects, some reports show neuro-protective properties for this agent in central nervous system. Several lines of evidence declare the involvement of COX or LOX isoenzymes in epileptic disorders. To set the foundation for future research into the neurobiology of licofelone as a potential therapeutic agent, we studied the effect of licofelone in an animal model of epilepsy. Although different neurotransmitters and neuro-modulators like nitric oxide were introduced as suggested targets of licofelone, the underlying mechanisms of central effects of this drug are not still fully understood. We have utilized pentylenetetrazole-induced clonic seizure model to investigate the behavioral consequences of licofelone administration and its possible mechanisms in seizure susceptibility. Licofelone revealed anticonvulsant properties at the dose of 10 mg/kg (i.p) or higher in mice. Pre-treatment with NO (nitric oxide) donor, L-arginine, reversed this anticonvulsant effects dose dependently. L-NAME, as a non-selective nitric oxide synthase (NOS) inhibitor, potentiated the anticonvulsant effects of licofelone. A neuronal NOS inhibitor, 7-NI did not affect seizure threshold alone or in combination with licofelone. Using non-effective doses of selective inhibitors of inducible NOS, aminoguanidine or 1400W, significantly increased the seizure threshold when were accompanied by licofelone in low doses. These data support the involvement of NO as an important role player in the central neuro-protective properties of licofelone. Furthermore, it implies that down regulation of iNOS seems crucial for anticonvulsant properties of this COX/5-LOX inhibitor in seizure susceptibility.

Synthesis and cytotoxic activity of novel poly-substituted imidazo[2,1-c][1,2,4]triazin-6-amines.

A novel series of 3,4-diphenyl-7-(hetero)arylimidazo[2,1-c][1,2,4]triazin-6-amine derivatives were synthesized via three-component reaction of 5,6-diphenyl-1,2,4-triazin-3-amine, various aromatic aldehydes, and cyclohexyl isocyanide. All synthesized compounds were tested against HL60 (human promyelocytic leukemia), MOLT-4 (human T lymphoblastic leukemia), and MCF-7 (human breast adenocarcinoma) cell lines, as cytotoxic agents. The structure-activity relationships study revealed that the introduction of hydroxyl and methoxy groups on the 7-phenyl ring can modulate the cytotoxic activity of these compounds. Among the 7-aryl derivatives, 3-hydroxyphenyl and 3-hydroxy-4-methoxyphenyl derivatives (6h and 6o) were the most potent compounds against HL60 and MCF-7 cells (IC(50s) = 9.8 - 20.4 µM). However, the replacement of the 7-aryl moiety with pyridyl or furan-2-yl resulted in compounds 6p or 6r with more promising cytotoxicity against MOLT-4 cell line (IC50 values 12.1 and 13.0 µM, respectively). Also, the acridine orange/ethidium bromide staining assay in MCF-7 cells suggested that the cytotoxic activity of compound 6r occurs via apoptosis.

Microvascular damage, neuroinflammation and extracellular matrix remodeling in Col18a1 knockout mice as a model for early cerebral small vessel disease.

Collagen type XVIII (COL18) is an abundant heparan sulfate proteoglycan in vascular basement membranes. Here, we asked (i) if the loss of COL18 would result in blood-brain barrier (BBB) breakdown, pathological alterations of small arteries and capillaries and neuroinflammation as found in cerebral small vessel disease (CSVD) and (ii) if such changes may be associated with remodeling of synapses and neural extracellular matrix (ECM). We found that 5-month-old Col18a1-/- mice had elevated BBB permeability for mouse IgG in the deep gray matter, and intravascular erythrocyte accumulations were observed brain-wide in capillaries and arterioles. BBB permeability increased with age and affected cortical regions and the hippocampus in 12-month-old Col18a1-/- mice. None of the Col18a1-/- mice displayed hallmarks of advanced CSVD, such as hemorrhages, and did not show perivascular space enlargement. Col18a1 deficiency-induced BBB leakage was accompanied by activation of microglia and astrocytes, a loss of aggrecan in the ECM of perineuronal nets associated with fast-spiking inhibitory interneurons and accumulation of the perisynaptic ECM proteoglycan brevican and the microglial complement protein C1q at excitatory synapses. As the pathway underlying these regulations, we found increased signaling through the TGF-ß1/Smad3/TIMP-3 cascade. We verified the pivotal role of COL18 for small vessel wall structure in CSVD by demonstrating the protein's involvement in vascular remodeling in autopsy brains from patients with cerebral hypertensive arteriopathy. Our study highlights an association between the alterations of perivascular ECM, extracellular proteolysis, and perineuronal/perisynaptic ECM, as a possible substrate of synaptic and cognitive alterations in CSVD.

Benzylidene-6-hydroxy-3,4-dihydronaphthalenone chalconoids as potent tyrosinase inhibitors.

BACKGROUND AND PURPOSE: Tyrosinase enzyme has a key role in melanin biosynthesis by converting tyrosine into dopaquinone. It also participates in the enzymatic browning of vegetables by polyphenol oxidation. Therefore, tyrosinase inhibitors are useful in the fields of medicine, cosmetics, and agriculture. Many tyrosinase inhibitors having drawbacks have been reported to date; so, finding new inhibitors is a great need. EXPERIMENTAL APPROACH: A variety of 6-hydroxy-3,4-dihydronaphthalenone chalcone-like analogs (C1-C10) have been synthesized by aldol condensation of 6-hydroxy tetralone and differently substituted benzaldehydes. The compounds were evaluated for their inhibitory effect on mushroom tyrosinase by a spectrophotometric method. Moreover, the inhibition manner of the most active compound was determined by Lineweaver-Burk plots. Docking study was done using AutoDock 4.2. The drug-likeness scores and ADME features of the active derivatives were also predicted. RESULTS/FINDINGS: Most of the compounds showed remarkable inhibitory activity against the tyrosinase enzyme. 6-Hydroxy-2-(3,4,5-trimethoxybenzylidene)-3,4-dihydronaphthalen-1(2H)-one (C2) was the most potent derivative amongst the series with an IC50 value of 8.8 µM which was slightly more favorable to that of the reference kojic acid (IC50 = 9.7 µM). Inhibitory kinetic studies revealed that C2 behaves as a competitive inhibitor. According to the docking results, compound C2 formed the most stable enzyme-inhibitor complex, mainly via establishing interactions with the two copper ions in the active site. In silico drug-likeness and pharmacokinetics predictions for the proposed tyrosinase inhibitors revealed that most of the compounds including C2 have proper drug-likeness scores and pharmacokinetic properties. CONCLUSION AND IMPLICATIONS: Therefore, C2 could be suggested as a promising tyrosinase inhibitor that might be a good lead compound in medicine, cosmetics, and the food industry, and further drug development of this compound might be of great interest.

Structure-Based Design, Synthesis, Biological Evaluation and Molecular Docking Study of 4-Hydroxy-N'-methylenebenzohydrazide Derivatives Acting as Tyrosinase Inhibitors with Potentiate Anti-Melanogenesis Activities.

BACKGROUND: Melanogenesis is a process of melanin synthesis, which is a primary response for the pigmentation of human skin. Tyrosinase is a key enzyme, which catalyzes a ratelimiting step of the melanin formation. Natural products have shown potent inhibitors, but some of these possess toxicity. Numerous synthetic inhibitors have been developed in recent years may lead to the potent anti- tyrosinase agents. OBJECTIVE: A number of 4-hydroxy-N'-methylenebenzohydrazide analogues with related structure to chalcone and tyrosine were constructed with various substituents at the benzyl ring of the molecule and evaluate as a tyrosinase inhibitor. In addition, computational analysis and metal chelating potential have been evaluated. METHODS: Design and synthesized compounds were evaluated for activity against mushroom tyrosinase. The metal chelating capacity of the potent compound was examined using the mole ratio method. Molecular docking of the synthesized compounds was carried out into the tyrosine active site. RESULTS: Novel 4-hydroxy-N'-methylenebenzohydrazide derivatives were synthesized. The two compounds 4c and 4g showed an IC50 near the positive control, led to a drastic inhibition of tyrosinase. Confirming in vitro results were performed via the molecular docking analysis demonstrating hydrogen bound interactions of potent compounds with histatidine-Cu+2 residues with in the active site. Kinetic study of compound 4g showed competitive inhibition towards tyrosinase. Metal chelating assay indicates the mole fraction of 1:2 stoichiometry of the 4g-Cu2+ complex. CONCLUSION: The findings in the present study demonstrate that 4-Hydroxy-N'- methylenebenzohydrazide scaffold could be regarded as a bioactive core inhibitor of tyrosinase and can be used as an inspiration for further studies in this area.