A new cytotoxic 12-membered macrolactone from the endophytic fungus Exserohilum rostratum LPC-001

A new oxacyclododecindione-type macrolactone, (13R,14S,15R)-13-hydroxy-14-deoxyoxacyclododecindione (1), has been obtained from the solid cultures of the fungus Exserohilum rostratum, a fungal strain endophytic in Gymnadenia conopsea. Its structure, including the absolute configuration, was extensively established by 1D and 2D NMR data, the modified Mosher method, and a combination of experimental and theoretically calculated electronic circular dichroism (ECD) spectra. Compound 1 showed weak selective cytotoxicity against the A549 lung cell line with an IC₅₀ value of 9.2 µM.