Síntese multicomponente de derivados de quinolinas e suas aplicações como fungicida

Abstract

The increase in agricultural losses caused by phytopathogenic fungi, associated with the intensive use of synthetic fungicides and the emergence of microbial resistance, has encouraged the search for new molecules with antifungal potential. In this context, nitrogen-containing heterocyclic compounds, such as quinolines and hexahydroquinolines, stand out due to their structural versatility and the wide range of biological activities reported in the literature. Therefore, this study aimed to synthesize, characterize, and evaluate the antifungal activity of hexahydroquinoline and quinoline-4-carboxylic acid derivatives against phytopathogenic fungi. The hexahydroquinoline derivatives were obtained through a Hantzsch-type multicomponent reaction using aromatic aldehydes, ethyl acetoacetate, cyclohexane-1,3-dione, and ammonium acetate. The quinoline-4- carboxylic acid derivatives were synthesized through an adaptation of the Doebner reaction, using substituted anilines, aromatic aldehydes, and sodium pyruvate. The obtained compounds were characterized by Fourier-transform infrared spectroscopy, differential scanning calorimetry, and 1H and 13C nuclear magnetic resonance, allowing confirmation of the proposed structures. Antifungal activity was evaluated by the poisoned food method in PDA medium against Fusarium graminearum and Alternaria alternata. The hexahydroquinoline derivatives showed low inhibitory efficiency against the evaluated fungi, with the fluorinated derivative showing a relatively better performance against F. graminearum. In contrast, the quinoline-4-carboxylic acid derivatives showed greater potential against A. alternata with EC50 values of approximately 160 and 240 ppm. Overall, the results indicate that the quinoline-4- carboxylic acid core showed greater antifungal potential than the hexahydroquinoline core under the evaluated conditions.