Structural evolution of quinine derivatives for enhanced antifungal potency: key modifications and quantitative structure-activity relationship (QSAR) analysis.

Abstract

Background: The escalating resistance of phytopathogenic fungi to conventional fungicides, combined with increasing environmental concerns, necessitates the development of novel bioactive agents.

Results: In this study, utilizing the natural product quinine as a lead scaffold, a series of novel 2-aminoquinine derivatives were designed and synthesized via PyBroP-mediated amination. The antifungal activities of these compounds against seven plant pathogens, including Rhizoctonia solani (R. solani), Cytospora chrysosperma (C. chrysosperma), Fusarium oxysporum (F. oxysporum), Magnaporthe oryzae (M. oryzae), Fusarium graminearum (F. graminearum), Sphaeropsis sapinea (S. sapinea), and Botrytis cinerea (B. cinerea), were evaluated using the mycelial growth rate method. Among the synthesized derivatives, compound Qed-3 exhibited broad-spectrum efficacy, particularly against S. sapinea with a half-maximal effective concentration (EC₅₀) value of 0.46 μg mL^-1. In vivo assays further confirmed its superior curative potential against pine shoot blight compared to the commercial fungicide boscalid. Mechanistic investigations, utilizing scanning electron microscopy (SEM) and transmission electron microscopy (TEM), revealed that compound Qed-3 disrupts the integrity of hyphal cell walls and membranes, leading to electrolyte leakage and the accumulation of reactive oxygen species (ROS).

Conclusions: Molecular docking and quantitative structure-activity relationship (QSAR) analyses provided insights into the binding modes and structural determinants essential for antifungal potency. These findings highlight the potential of 2-arylaminoquinine as a promising and eco-friendly candidate for novel fungicide development. © 2026 Society of Chemical Industry.