Antioxidant and tyrosinase docking studies of heterocyclic sulfide derivatives containing a thymol moiety

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

Tyrosinase enzyme plays an essential role in melanin biosynthesis and enzymatic browning of fruits and vegetables. To discover potent tyrosinase inhibitors, the present studies were undertaken. In this context, synthetic aurone derivatives 26-50 were designed, synthesized, and structurally elucidated by various spectroscopic techniques including IR, UV, 1H- & 13C-NMR and mass spectrometry. The target compounds 26-50 were screened for their anti-tyrosinase inhibitory potential, and thus kinetic mechanism was analyzed by Lineweaver-Burk plots. All target compounds exhibited good to excellent IC50 values in the range of 7.12 ± 0.32 μM to 66.82 ± 2.44 μM. These synthesized aurone derivatives were found as potent tyrosinase inhibitors relative to the standard kojic acid (IC50 = 16.69 ± 2.81 μM) and the compound 39 inhibited tyrosinase non-competitively (Ki = 11.8 μM) by forming an enzyme-inhibitor complex. The binding modes of these molecules were ascribed through molecular docking studies against tyrosinase protein (PDB ID: 2Y9X). The quantitative structure-activity relationship studies displayed a good correlation between 26-50 structures and their anti-tyrosinase activity (IC50) with a correlation coefficient (R2) of 0.9926. The computational studies were coherent with experimental results and these ligands exhibited good binding values against tyrosinase and interacted with core residues of target protein. Moreover, the drug-likeness analysis also showed that some compounds have a linear correlation with Lipinski's rule of five, indicating good drug-likeness and bioactivity scores for pharmacological targets.Communicated by Ramaswamy H. Sarma.

Antioxidant Activity and Cytotoxicity of Aromatic Oligosulfides

Natural or synthetic antioxidants with biomimetic fragments protect the functional and structural integrity of biological molecules at a minimum concentration, and may be used as potential chemotherapeutic agents. This paper is devoted to in silico and in vitro evaluation of the antioxidant and cytotoxic properties of synthetic analogues of natural compounds—aromatic oligosulfides. The antiradical and SOD-protective activity of oligosulfides was demonstrated in the reaction with O₂^–• generated in enzymatic and non-enzymatic systems. It was found that phenol-containing disulfides significantly reduced the accumulation level of hydroperoxides and secondary carbonyl thiobarbituric acid reactive substances, which are primary products of oleic acid peroxidation. The antioxidant efficiency of bis(3,5-di-tert-butyl-4-hydroxyphenyl) disulfide increased over time due to the synergistic action of the 2,6-di-tert-butylphenol fragment and the disulfide linker. The highest cytotoxicity on the A-549 and HCT-116 cell lines was found for bis(3,4-dimethoxyphenyl) disulfide. Significant induction of apoptosis in HCT-116 cells in the presence of bis(3,4-dimethoxyphenyl) disulfide indicates the prospect of its use as an antitumor agent. The significant and moderate dependences revealed between various types of activities of the studied aromatic oligosulfides can be used in the development of a strategy for the synthesis and study of target-oriented compounds with predictable biological activity.

Design, Synthesis, and Structural Characterization of Thioflavones and Thioflavonols as Potential Tyrosinase Inhibitors: In Vitro and In Silico Studies

To find new potential tyrosinase inhibitors, a diverse range of 2-arylchromone-4-thione derivatives (2a-2p) were designed and synthesized by employing a multistep strategy, and the newly synthesized compounds, for the first time, were screened in vitro for their tyrosinase inhibitory activity. In this context, the newly synthesized compounds (2a-2p) were characterized using a combination of several spectroscopic techniques including Fourier transform infrared, UV-vis, ¹H NMR, and ¹³C NMR spectroscopies and electron ionization-mass spectrometry. All the target compounds were potent against tyrosinase as compared to the standard inhibitor kojic acid (half-maximal inhibitory concentration (IC₅₀) = 12.6 ± 0.6 μM). The compounds (2a-2p) produced IC₅₀ values in the range from 1.12 ± 0.04 to 5.68 ± 0.13 μM. Among the synthesized 4-thioflavones and 4-thioflavonols, the compound 2n exhibited excellent tyrosinase inhibitory activity with the lowest IC₅₀ of 1.12 ± 0.04 μM that could be recommended as potential lead candidates to cure tyrosinase-mediated hyperpigmentation in the future. A kinetic study of compound 2n revealed that compound 2n inhibited tyrosinase in a competitive mode. Furthermore, the nontoxic performance of the most beneficial compounds ranging from 1 to 25 g/mL was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test method for A375 human melanoma cells for the highly efficient target compounds (2m, 2n, 2o, and 2p). Moreover, a molecular modeling study was performed against tyrosinase enzyme (2Y9X) to check the binding interactions of the synthesized compounds (2a-2p) against the target protein. Furthermore, quantitative structure-activity relationship studies were conducted based on an antityrosinase assay. The value of the correlation coefficient (R ²) 0.9997 shows that there was a good correlation between (2a-2p) structures and selected properties. The geometry optimization of all complexes was performed by using Gaussian 09. Additionally, a drug-likeness research was used to establish the potent analogues' positive action as a new antityrosinase agent (2n, 2o, and 2p).

Tailored Functionalization of Natural Phenols to Improve Biological Activity

Phenols are widespread in nature, being the major components of several plants and essential oils. Natural phenols' anti-microbial, anti-bacterial, anti-oxidant, pharmacological and nutritional properties are, nowadays, well established. Hence, given their peculiar biological role, numerous studies are currently ongoing to overcome their limitations, as well as to enhance their activity. In this review, the functionalization of selected natural phenols is critically examined, mainly highlighting their improved bioactivity after the proper chemical transformations. In particular, functionalization of the most abundant naturally occurring monophenols, diphenols, lipidic phenols, phenolic acids, polyphenols and curcumin derivatives is explored.

The recent development of thymol derivative as a promising pharmacological scaffold

Thymol (a phenol ring bearing active phytoconstituent) is a privileged scaffold, which is diversified in natural sources. This scaffold acts as an obligatory template for scheming and arriving at designing some newer drug-molecules with potential biological activities. In the pharmacological perspective, the promising active sites of the scaffold are the positions C-1, C-4, and C-6 of thymol that would be accountable for developing potent drug candidates. This review aims to explore the various synthetic routes and the structural-activity relationship of thymol scaffold with suitable active pharmacophore sites.

Mechanically induced solvent-free esterification method at room temperature

Herein, we describe two novel strategies for the synthesis of esters, as achieved under high-speed ball-milling (HSBM) conditions at room temperature. In the presence of I2 and KH2PO2, the reactions afford the desired esterification derivatives in 45% to 91% yields within 20 min of grinding. Meanwhile, using KI and P(OEt)3, esterification products can be obtained in 24% to 85% yields after 60 min of grinding. In addition, the I2/KH2PO2 protocol was successfully extended to the late-stage diversification of natural products showing the robustness of this useful approach. Further application of this method in the synthesis of inositol nicotinate was also discussed.