Interconvertible Pyridone Alkaloids from the Marine-Derived Fungus QDU1.

Eleven new pyridone alkaloids, penicipyridones A-K (-), and three new tetramic acids, tolypocladenols D-F (-), were isolated from rice media cultures of the marine-derived fungus QDU1. Their structures, including absolute configurations, were determined by comprehensive analyses of spectroscopic data, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction data. Interestingly, several of the penicipyridones undergo interconversions between hydroxy and methoxy groups at C-4 in acidic MeOH solution. Furthermore, in an acidic aqueous solution, OH-4 could be replaced by diverse substituent groups. Compounds , , , , , , and exhibited moderate inhibitory effects on NO production in the LPS-induced RAW264.7 macrophages, with IC values ranging from 9.2 to 19 μM.