Picolinic Acid Derivatives and Biosynthetic Pathway from Epicoccum sorghinum SDU-F549

Two new picolinic acid derivatives, ethylfusaric acid A (1) and ethylfusaric acid B (2), along with two known picolinic acid derivatives (3-4), were isolated from the culture of Rehmannia glutinosa endophytic fungus Epicoccum sorghinum 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 1-4 exhibited antibacterial activity against a panel of Staphylococcus aureus strains, with MIC values ranging from 16 to 32 μg/mL. In contrast, they showed no significant cytotoxic activity against a range of human tumor cell lines at 10 μM. Furthermore, bioinformatic analysis revealed that the bty biosynthetic gene cluster in E. sorghinum SDU-F549 is responsible for assembling the picolinic acid derivatives, enabling us to propose the biosynthetic pathways of compounds 1-4.