Enantiomeric Dibenzo-α-Pyrone Derivatives from <i>Alternaria alternata</i> ZHJG5 and Their Potential as Agrochemicals
Shuangshuang Zhao, Kailin Tian, Yu Li, Wenxia Ji, Fang Liu, Babar Khan, Wei Yan, Yonghao Ye
Abstract
Three pairs of enantiomeric dibenzo-α-pyrone derivatives (1–3) including two pairs of new racemates (±)-alternaone A (1) and (±)-alternaone B (2) and one new enantiomer (−)-alternatiol (3), together with five known compounds (4–8) were isolated from the fungus Alternaria alternata ZHJG5. Their structures were confirmed by spectroscopic data and single-crystal X-ray diffraction analysis. All enantiomers were separated via chiral high-performance liquid chromatography, with their configurations determined by electronic circular dichroism calculation. Biogenetically, a key epoxy-rearrangement step was proposed for the formation of skeletons in 1–3; (+) 1, (−)-1, and 5 presented moderate antibacterial inhibition on phytopathogenic bacteria Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola. In the antifungal test, compounds 7 and 8 showed a moderate protective effect against Botrytis cinerea in vivo.