LAUSR

BACKGROUND Phytopathogenic bacteria, such as Xanthomonas oryzae pv. oryzae (Xoo) and Ralstonia solanacearum (Rs), seriously threaten crop production and cause enormous yield losses. Endophytic fungi are abundant sources of the bioactive metabolites, which can be potential candidates in the development of new agrochemicals. This work emphasized the discovery of bioactive polyketides from endophytic Alternaria alternata ZHJG5 and reported their structural elucidation, and antibacterial activities in detail. RESULTS Five novel polyketide derivatives, isotalaroflavone (2), (±)-5'-dehydroxytalaroflavone (3a/3b), (+)-talaroflavone (4b), and bialternacin G (7), along with five known compounds (1, 4a, 5, 6, and 8), were obtained from the Cercis chinensis-derived fungus Alternaria alternata ZHJG5. The compound structures were characterized by spectroscopic methods and X-ray diffraction. Chiral HPLC was used to separate the racemates 3 and 4, whose absolute configurations were unambiguously confirmed by comparing their experimental and calculated ECD data. All isolated compounds were tested for antibacterial activities against the phytopathogenic bacteria Xoo, Xanthomonas oryzae pv. oryzicola (Xoc) and Rs. Compounds 1, 2 and 8 showed pronounced antibacterial activities against all tested bacteria, with MIC values ranging from 0.5 μg/mL to 64 μg/mL; in addition, compound 1 showed a potent protective effect against rice bacterial leaf blight caused by Xoo with the protective efficacy of 75.1% at a concentration of 200 μg/mL. CONCLUSION These findings highlight the practical potential of the antibacterial compounds as candidates for the novel bactericide discovery. This article is protected by copyright. All rights reserved.