Fusarielins Q-Y: fusarielin polyketides from Fusarium asiaticum QA-6 inhabiting the roots of the cultivated Artemisia argyi and their antibacterial activity against aquatic pathogens.

Artemisia argyi Levl. et Van. var. argyi cv. Qiai is a commercially important medicinal plant specifically cultivated in Qichun County, Hubei Province of Central China. Investigation of the antibacterial functional constituents of the endophytic Fusarium asiaticum QA-6, which is derived from Qiai, resulted in the characterization of nine previously undescribed polyketides fusarielins Q-Y (compounds 1-9) and two known congeners fusarielins M (compound 10) and F (compound 11). Structurally, compounds 1-9 possess a highly functionalized decalin moiety, whereas compounds 1-3 feature shorter polyene side chains compared to other fusarielins. The shortened chain in 2 and 3 likely results from a missed S-adenosyl-l-methionine (SAM)-dependent methylation, with 3 being an oxidation product of 2. Conversely, the truncation in 1 may stem from a missed acetyl-CoA addition. The isolated compounds were assayed for antibacterial activity against aquatic bacterial pathogens, among which, compounds 1, 5, 10, and 11 exhibited activity against specific Gram-negative strains, with compound 1 inhibited Aeromonas hydrophilia (MIC = 2.92 μM) and Vibrio alginolyticus (MIC = 5.84 μM), compound 5 targeted the aquatic pathogen Edwardsiella ictarda (MIC = 2.39 μM), compound 10 acted against E. ictarda, Vibrio harveyi, and V. parahaemolyticus (each with an MIC value of 2.60 μM), and compound 11 inhibited V. alginolyticus (MIC = 4.80 μM). All these antibacterial activities were equivalent to or superior to those of the positive control, chloramphenicol (MICs = 1.55 to 6.19 μM). In the preliminary screening against HeLa cells, none of the isolated compounds exhibited significant cytotoxic activity at the concentration 20 μM.