Discovery of new mitorubrin derivatives from Hypoxylon fulvo-sulphureum sp nov (Ascomycota, Xylariales)

A specimen of the Hypoxylon rubiginosum complex featuring unusual bicoloured stromata was collected in northern Thailand and examined by means of classical morphological methodology, complemented by studies of its secondary metabolites using high performance liquid chromatography coupled with diode array and electrospray mass spectrometric detection (HPLC-DAD/MS), and molecular phylogenetic analysis of its ITS and partial beta-tubulin DNA sequences. In addition, the ultrastructure of its ascospores was examined by SEM. The chemotaxonomic studies revealed the presence of two putatively unknown, apparently specific azaphilone pigments in the stromata. These metabolites were consequently isolated to purity by preparative HPLC and identified by means of nuclear magnetic resonance spectroscopy and high resolution mass spectrometry as the novel natural products, (+)-6 ''-hydroxymitorubrinol acetate (1) and (+)-6 ''-hydroxymitorubrinol (3).