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.

Modulation of the lipophilicity and molecular size of thiosemicarbazone inhibitors to regulate tyrosinase activity

A group of 5-methylsalicylaldehyde thiosemicarbazone derivatives (HMTs) bearing different lipophilic and steric substituents attached at the 3-position of cresol ring were synthesized and investigated as mushroom tyrosinase (TYR) inhibitors. The ability of HMTs to inhibit the diphenolase activity of TYR was evaluated with L-DOPA as substrate by determining IC₅₀ values in relation to their structure modifications. HMTs displayed distinct inhibitory competencies towards TYR activity with IC₅₀ values in the range of 1.02-143.56 μM. A close correlation between their inhibition potency and both lipophilicity and molecular size was observed. The inhibitory effect of the hydroxyethyl-containing derivatives was much higher than the hydroxyethyl-free ones overall. Among them, HMT-NBO exhibited the most potent effect with IC₅₀ of 5.85 μM, which was nearly 25-fold and 3.8-fold lower than its parent HMT-NBE and the control kojic acid, respectively. The hydroxyethyl clearly benefited the improvement of the inhibitory competences and acted as a regulating group of lipophilicity of the inhibitors. The kinetic analyses showed that HMTs were reversible and mixed type inhibitors against mushroom TYR. The inhibition mechanism was studied by means of fluorescence spectroscopy, FT-IR, ESI-MS and molecular docking analysis. The results indicated that the observed inhibitory effect of HMTs was accomplished by acting on the amino acid residues rather than by chelating the centre copper ions of TYR. Each of HMTs can insert the hydrophobic pocket and interact with the residues of TYR through Van der Waals forces and hydrogen bonds, with additional electrostatic interactions for HMT-NEE and HMT-NEO further strengthening the affinity. Meanwhile, the inhibitors were observed to bind with L-DOPA or/and L-DOPAquinone forming 1:1 stoichiometric complexes, probably exerting indirect inhibition against TYR activity.

Copper-thiosemicarbazone complexes conjugated-cellulose fibers: Biodegradable materials with antibacterial capacity

Personal protective equipment (PPE) is vital in battling bacteria crisis, but conventional PPE materials lack antimicrobial activities and environmental friendliness. Our work focused on developing biodegradable and antibacterial fibers as promising bioprotective materials. Here, we grafted highly effective antibacterial copper-thiosemicarbazone complexes (CT1-4) on cellulose fibers via covalent linkages. Multiple methods were used to characterize the chemical composition or morphology of CT1-4 conjugated-fibers. Conjugation of CT1-4 maintains the mechanical properties (Breaking strength: 2.35-2.45 cN/dtex, Breaking elongation: 7.19 %-7.42 %) and thermal stability of fibers. CT1 can endow cellulose fibers with the excellent growth inhibition towards Escherichia coli (E. coli) (GIR: 61.5 % ± 1.28 %), Staphylococcus aureus (S. aureus) (GIR: 85.7 % ± 1.93 %), and Bacillus subtilis (B. subtilis) (GIR: 87.6 % ± 1.44 %). We believe that the application of CT1 conjugated-cellulose fibers is not limited to the high-performance PPE, and also can be extended to various types of protective equipment for food and medicine safety.

Synthesis and Biological Activity Evaluation of 2-Cyanopyrrole Derivatives as Potential Tyrosinase Inhibitors

In order to find potential inhibitors of tyrosinase, two series of pyrrole derivatives A (1–17) and B (1–8) were synthesized and screened for their inhibitory activities on tyrosinase. Most of the 2-cyanopyrrole derivatives exhibited effective inhibitory activities. In particular, A12 exhibited the strongest inhibitory activities, with the IC₅₀ values of 0.97 μM, which is ∼30 times stronger than the reference inhibitor kojic acid (IC₅₀: 28.72 μM). The inhibitory mechanism analysis results revealed that A12 was a reversible and mixed-type inhibitor. Molecular docking experiments clarified the interaction between A12 with tyrosinase. Furthermore, A12 (100 μM) presented effective inhibitory effect on tyrosinase in B16 melanoma cells with inhibition of 33.48%, which was equivalent to that of Kojic acid (39.81%). Accordingly, compound A12 may serve as the lead structure for the further design of potent tyrosinase inhibitors. Molecular docking studies confirmed the interaction between the compound and tyrosinase.

A novel fluorescent off–on probe based on 4-methylumbelliferone for highly sensitive determination of tyrosinase

A novel fluorescent probe for high-sensitivity determination of tyrosinase, with 4-methylumbelliferone as the fluorophore and 3-hydroxybenzyl as the recognition group.

5-Substituted isatin thiosemicarbazones as inhibitors of tyrosinase: Insights of substituent effects

Seven isatin-thiosemicarbazone analogues bearing different substituents (R) attached at C-5 of the indoline ring, TSC-ISA-R (R = -H, -CH₃, -OCH₃, -OCF₃, -F, -Cl and -NO₂), were synthesized and evaluated as inhibitors of mushroom tyrosinase (TYR). The inhibitory behaviour and performance of TSC-ISA-R were investigated spectroscopically in relation to the substituent modifications through examining their inhibition against the diphenolase activity of TYR using L-DOPA as a substrate. The IC₅₀ values of TSC-ISA-R were determined to be in the range of 81-209 μM. The kinetic analysis showed that TSC-ISA-R were reversible and mixed type inhibitors. Three potential non-covalent interactions rather than complexation including the binding of TSC-ISA-R with free TYR, TYR-L-DOPA complex, and with substrate L-DOPA were found to be involved in the inhibition. The substituent modifications affected these interactions by varying the characters of the resulting TSC-ISA-R in different degrees. The thiosemicarbazido moiety of each TSC-ISA-R contributed predominantly to the inhibition, and the isatin moiety seemed to play a regulatory role in the binding of TSC-ISA-R to the target molecules. The results of theoretical calculations using density functional theory method indicated a different effect of -R on the electron distribution in HOMO of TSC-ISA-R. The LUMO-HOMO energy gap of TSC-ISA-R almost accords with the trend of their experimental inhibition potency.

Guedes da Silva MF, Marzano C. Synthesis, Characterization and Biological Activity of Novel Cu(II) Complexes of 6-Methyl-2-Oxo-1,2-Dihydroquinoline-3-Carbaldehyde-4n-Substituted Thiosemicarbazones

Three new 6-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-thiosemicarbazones-N-4-substituted pro-ligands and their Cu(II) complexes (1, -NH2; 2, -NHMe; 3, -NHEt) have been prepared and characterized. In both the X-ray structures of 1 and 3, two crystallographically independent complex molecules were found that differ either in the nature of weakly metal-binding species (water in 1a and nitrate in 1b) or in the co-ligand (water in 3a and methanol in 3b). Electron Paramagnetic Resonance (EPR) measurements carried out on complexes 1 and 3 confirmed the presence of such different species in the solution. The electrochemical behavior of the pro-ligands and of the complexes was investigated, as well as their biological activity. Complexes 2 and 3 exhibited a high cytotoxicity against human tumor cells and 3D spheroids derived from solid tumors, related to the high cellular uptake. Complexes 2 and 3 also showed a high selectivity towards cancerous cell lines with respect to non-cancerous cell lines and were able to circumvent cisplatin resistance. Via the Transmission Electron Microscopy (TEM) imaging technique, preliminary insights into the biological activity of copper complexes were obtained.

Antioxidant Properties of Camphene-Based Thiosemicarbazones: Experimental and Theoretical Evaluation

The thiosemicarbazone derivatives have a wide range of biological activities, such as antioxidant activity. In this study, the antiradical activities of six camphene-based thiosemicarbazones (TSC-1~6) were investigated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and peroxyl radical scavenging capacity (PSC) assays, respectively, and the results reveal that TSC1~6 exhibited good abilities for scavenging free radicals in a dose-dependent way. Compound TSC-2 exhibited the best effect of scavenging DPPH radical, with the lowest EC₅₀ (0.208 ± 0.004 mol/mol DPPH) as well as the highest bimolecular rate constant K_b (4218 M^-1 s^-1), which is 1.18-fold higher than that of Trolox. Meanwhile, TSC-2 also obtained the lowest EC₅₀ (1.27 µmol of Trolox equiv/µmol) of scavenging peroxyl radical. Furthermore, the density functional theory (DFT) calculation was carried out to further explain the experimental results by calculating several molecular descriptors associated with radical scavenging activity. These theoretical data suggested that the electron-donating effect of the diethylamino group in TSC-2 leads to the enhancement of the scavenging activities and the studied compounds may prefer to undergo the hydrogen atom transfer process.