Two New Isoindole Alkaloids from Aspergillus fumigatus as Potential Activators for Tobacco Powdery Mildew

To further explore powdery mildew (caused by Golovinomyces cichoracearum) natural products, an extract from the fermentation of endophytic Aspergillus fumigatus was investigated. As a result, six isoindole alkaloid derivatives (1–6) were isolated. Among them, two compounds (1 and 2) were newly discovered and the activity evaluation of the purified compounds 1–6 against G. cichoracearum was studied. The results revealed that compounds 1–6 demonstrated obvious anti-G. cichoracearum activities for cigar tobacco in the range of 40.6% ± 5.4 to 66.5% ± 4.9 at a concentration of 250 μg/mL, respectively. However, these rates are lower than that of positive control. By isolating and structurally identifying the above isoindole alkaloids, new materials conducive to improving the utilization of N. tabacum-derived fungi could be developed for screening anti-powdery mildew drugs.