Antifungal activity of prenylated flavonoids isolated from Tephrosia apollinea L. against four phytopathogenic fungi

Abstract

Four prenylated flavonoids, isoglabratephrin, (+)-glabratephrin, tephroapollin-F and lanceolatin-A were isolated from Tephrosia apollinea L. growing in Egypt. The structures of compounds have been elucidated using physical and spectroscopic methods including (UV, IR, 1H NMR, 13C NMR, DEPT, 2D 1H–1H COSY, HSQC, HMBC and NOESY). The isolated flavonoids showed considerable antifungal activity against four phytopathogenic fungi, namely Alternaria alternata, Helminthosporium sp., Colletotrichum acutatum and Pestalotiopsis sp. in a dose-dependent manner using the agar well-diffusion bioassay. They differ significantly in their activity with tephroapollin-F was the most effective. In a test using a concentration of 4 mg/ml of tephroapollin-F, strong fungicidal activities (32.8–58.3%) were produced against the test fungi, where C. acutatum, Helminthosporium sp. and Pestalotiopsis sp. showed greater susceptibility, while A. alternata was the least susceptible. Using the same concentration, the two flavonoids isoglabratephrin and (+)-glabratephrin showed moderate activities with % inhibition of fungal growth were ranged between (16.1–37.8) against A. alternata, Helminthosporium sp. and Pestalotiopsis sp., while showed a strong antifungal activity against C. acutatum (% growth inhibition were 46.4 and 42.9, respectively). In all treatments, the flavonoid lanceolatin-A exhibited weak to moderate activities. Using lower concentrations of the test flavonoids (2 and 1 mg/ml), weak to moderate antifungal activities were observed against all of the test fungal strains. In all cases and regardless of the flavonoid tested, C. acutatum was the most susceptible, while A. alternata was the least. The study recommends the use of the test compounds as rational fungicides of natural origin.