Hypomiltin, a novel azaphilone from Hypoxylon hypomiltum, and chemotypes in Hypoxylon sect. Hypoxylon as inferred from analytical HPLC profiling

A novel azaphilone named hypomiltin was isolated by preparative reversed phase HPLC from the stromatal extract of the xylariaceous ascomycete Hypoxylon hypomiltum. Its chemical structure was determined by mass spectrometry and 2D nuclear magnetic resonance spectroscopy. Analytical HPLC profiling of stromatal crude extracts, using UV/visual (diode array) and mass spectrometric detection based on electrospray ionisation, revealed the presence of hypomiltin also in Hypoxylon intermedium, H. perforatum, H. trugodes, and Pulveria porrecta. In contrast, this compound was found neither in type material of H. hypomiltum var. lavandulocinereum nor in several further Hypoxylon species. Despite being chemically related to mitorubrin, hypomiltin never co-occurred with the latter compound and its derivatives. Characteristic secondary metabolite profiles of several further Hypoxylon species are correlated with the colours of their taxonomically significant KOH-extractable pigments. These species are divided into chemotypes, based on analytical HPLC data. The results point toward an extraordinary diversity of secondary metabolites in Hypoxylon.