Prenylated flavonoids isolated from the twigs of Artocarpus champeden as potential activators for tobacco powdery mildew and their mode of actions

Abstract

Abstract Background Golovinomyces cichoracearum (DC.) is the main pathogen for tobacco powdery mildew fungus disease. Its outbreaks often result in severe harvest losses for the yield and quality of tobacco. Artocarpus champeden is rich in prenylated flavonoids, which are important for the plant’s defensive strategies. With the aim of continuously exploring bioactive natural metabolites for agricultural chemicals, the chemical investigations on the twigs of A. champeden were carried out. Results Six new (1–6) and five known (7–11) prenylated flavonoids were isolated. Compound 1 is the first example of flavone whose prenylated side-chain is converted into an unusual 1H-pyrrol-2-yl functional group. Compounds 2 and 3 are rare flavones bearing a 4-methylfuran-2-yl moiety. The frameworks of the above three flavones are reported in natural products for the first time. Interestingly, compound 1 showed high anti-G. cichoracearum activity with an inhibition rate of 88.3% ± 6.2. This rate is higher than that of the positive control (with an inhibition rate of 81.5% ± 6.3) compared to the negative control, compounds 2–11 also showed potential activities with inhibition rates in the range of 50.9%–72.0%. In addition, the mechanistic studies on 1 revealed that it has a potent direct effect on conidiospores of G. cichoracearum and induces systemic acquired resistance for tobacco plants, which may be the reasons for its significant effects against G. cichoracearum. Conclusions Powdery mildew is a fungal disease harmful to tobacco. Flavonoids have been identified as the sources of promising antifungal agents. For prenylated flavonoids, the combination of a flavonoid skeleton with prenylated side-chain can give the resultant more potential for biological activities. The successful isolation and structure identification of the above prenylated flavonoids provide new materials for the screening of powdery mildew inhibitors, and also contribute to the improved utilization of A. champeden. Graphical Abstract