Trichosterol A, a unique 6/6/6/5/6-fused steroid–alkaloid hybrid with bioherbicidal activity from <i>Trichoderma koningiopsis</i>

Naturally occurring steroids constitute a class of pharmacologically privileged scaffolds, owing to their rigid tetracyclic frameworks and well-defined stereochemistry, which have served as the basis for numerous clinically important drugs. In this study, four steroidal derivatives (1-4) were isolated from the endophytic fungus <i>Trichoderma koningiopsis</i>, which was obtained from the gut of a centipede collected in our Tongji campus. Remarkably, trichosterol A (1) represents the first naturally occurring steroid-alkaloid hybrid featuring a rare 6/6/6/5/6-fused pentacyclic skeleton incorporating an unusual 1,2-oxazine moiety. The structure of compound 1 was unambiguously determined by detailed NMR spectroscopic analysis and single-crystal X-ray diffraction. A plausible biosynthetic pathway for compound 1 is proposed. Furthermore, compound 1 exhibited notable herbicidal activity against <i>Medicago sativa</i> (alfalfa), suggesting its potential as a promising lead compound for the development of natural bioherbicides.