Mirilactams C–E, novel polycyclic macrolactams isolated from combined-culture of actinosynnema mirum NBRC 14064 and mycolic acid-containing bacterium

Mycolic acid-containing bacteria (MACB) are known to activate cryptic natural product biosynthesis in co-cultures with actinobacteria. We cultured Actinosynnema mirum NBRC 14064, a producer of the mono-cyclic polyene macrolactam mirilactam A (6), with the MACB Tsukamurella pulmonis TP-B0596. As a result, three novel compounds (mirilactams C–E, 1–3) were produced in the co-culture conditions. Compounds 1–3 were likely derived from 6 by epoxidation and subsequent spontaneous cyclization. The chemical structures and stereochemistries of 1–3 were determined by spectroscopic analyses (NMR and MS), conformational searches in the optimized potentials for liquid simulations-3 (OPLS3) force field, and calculations of electronic circular dichroism (ECD).