Inhibitory Potential of New Phenolic Hydrazide-Hydrazones with a Decoy Substrate Fragment towards Laccase from a Phytopathogenic Fungus: SAR and Molecular Docking Studies

Laccase from pathogenic fungi participates in both the delignification and neutralization of phytoantibiotics. Furthermore, it interferes with the hormone signaling in plants and catalyzes melanization. Infections of these pathogens contribute to loss in forestry, agriculture, and horticulture. As there is still a need to expand knowledge on efficient defense strategies against phytopathogenic fungi, the present study aimed to reveal more information on the molecular mechanisms of laccase inhibition with natural and natural-like carboxylic acid semi-synthetic derivatives. A set of hydrazide-hydrazones derived from carboxylic acids, generally including electron-rich arene units that serve as a decoy substrate, was synthesized and tested with laccase from Trametes versicolor. The classic synthesis of the title inhibitors proceeded with good to almost quantitative yield. Ninety percent of the tested molecules were active in the range of K_I = 8–233 µM and showed different types of action. Such magnitude of inhibition constants qualified the hydrazide-hydrazones as strong laccase inhibitors. Molecular docking studies supporting the experimental data explained the selected derivatives’ interactions with the enzyme. The results are promising in developing new potential antifungal agents mitigating the damage scale in the plant cultivation, gardening, and horticulture sectors.

Synthesis of new hydrazone derivatives and evaluation of their monoamine oxidase inhibitory activity

A novel series of hydrazone derivatives were designed and synthesized. Their structures were characterized by IR, ¹H NMR, ¹³C NMR and HR-MS spectroscopic methods. The newly synthesized compounds were evaluated for their inhibitory activity against monoamine oxidase enzymes (MAO-A and MAO-B). Compounds 2a, 2k, 4a and 4i showed significant inhibitory activity against MAO-A, with IC₅₀ value in the range of 0.084-0.207 µM compared to reference drug moclobemide (IC₅₀ value = 6.061 µM). These compounds (2a, 2k, 4a and 4i) were exposed to cytotoxicity tests to establish their preliminary toxicological profiles and were found to be non-cytotoxic. Moreover, the most effective compound 4i was evaluated using enzyme kinetics and docking studies to elucidate the plausible mechanisms of inhibition of MAO-A. According to enzyme kinetic studies, compound 4i was a reversible and competitive inhibitor with similar inhibition features as the substrates. Also, it was seen that this compound was settled down very properly at the active site of MAO-A enzyme by doing important interactions owing to the docking studies. Finally, ADME predictions were applied to estimate pharmacokinetic profiles of synthesized compounds. According to calculated ADME predictions, all parameters of the compounds were within the standard ranges in terms of "Rule of Five" and "Rule of Three" and it was detected that the synthesized compounds (2a-4i) have good and promising pharmacokinetic profiles.