Potencialidad antifúngica y caracterización fitoquímica preliminar de hojas de la especie vegetal Tibouchina grossa (Melastomataceae)

Abstract

Tibouchina grossa is an endemic species of Colombian territory, present as a shrub, extensively distributed in the Andes mountain range and traditionally known as "siete cueros rojo" (seven red skins). This study aimed to evaluate the antifungal activity of the extract and fractions from leaves against the phytopathogen Fusarium oxysporum, which is widely recognized in the agro-industrial sector for its negative impact on crops such as banana, onion, potato, Cape gooseberry, among others. Additionally, a preliminary phytochemical study of the fraction showing the highest activity was conducted. From the plant material collected in the páramo de Guacheneque and identified in the National Herbarium of Colombia under collection number COL 626926, extraction was carried out using the cold maceration technique with 96% ethanol, yielding 90.5 g (16.01% w/w) of total extract E.EtOH.TgH. From this, fractionation was performed using the continuous liquid-liquid extraction technique with solvents of increasing polarity, obtaining the hexane (Fx.Hex.TgH (8.48%)), dichloromethane (Fx.DCM.TgH (4.37%)), and ethyl acetate (Fx.AcOEt.TgH (21.47%)) fractions. The latter was the fraction with the highest bioactivity, showing an inhibition percentage of 27.87% at a concentration of 1000 μg/mL. According to preliminary phytochemical results, the presence of metabolites such as terpenes, quinones, alkaloids, and flavonoids was identified in the ethanolic extract. Tentatively, gallic acid, quercetin, and rutin were determined in the ethanolic extract by HPLC-DAD, and in the fraction showing the highest bioactivity (Fx.AcOEt.TgH), it was evidenced that the metabolites in higher concentration corresponded to glycosylated flavonoids, with a lower concentration in aglycone form. Finally, LC-HRMS tentatively recognized glycosylated flavonoids such as isorhamnetin-3,4’-diglucoside, isoquercitrin, or 3,5-O-di-β-glucoside peonidin, which are authentic markers in the Tibouchina genus.