Picolinic Acid Derivatives and Biosynthetic Pathway from <i>Epicoccum sorghinum</i> SDU-F549

Two new picolinic acid derivatives, ethylfusaric acid A (<b>1</b>) and ethylfusaric acid B (<b>2</b>), along with two known picolinic acid derivatives (<b>3</b>-<b>4</b>), were isolated from the culture of <i>Rehmannia glutinosa</i> endophytic fungus <i>Epicoccum sorghinum</i> SDU-F549. The chemical structures of the compounds were elucidated by the combination of 1D and 2D nuclear magnetic resonance spectroscopy and electronic circular dichroism calculations. Compounds <b>1</b>-<b>4</b> exhibited antibacterial activity against a panel of <i>Staphylococcus aureus</i> strains, with MIC values ranging from 16 to 32 <i>μ</i>g/mL. In contrast, they showed no significant cytotoxic activity against a range of human tumor cell lines at 10 <i>μ</i>M. Furthermore, bioinformatic analysis revealed that the <i>bty</i> biosynthetic gene cluster in <i>E. sorghinum</i> SDU-F549 is responsible for assembling the picolinic acid derivatives, enabling us to propose the biosynthetic pathways of compounds <b>1</b>-<b>4</b>.