Production of bioactive spirodioxynaphthalenes from Hermatomyces reticulatus (Pleosporales)

Species of the genus Hermatomyces (Pleosporales) are saprotrophic fungi associated with decaying wood and plant litter in tropical ecosystems. Although these species have been extensively studied in the previous decade, their secondary metabolite profiles remain uninvestigated. During preliminary screening, cultures of several Hermatomyces species exhibited antifungal activity, indicating the presence of bioactive secondary metabolites and motivating further study. In this study, ethyl acetate extracts obtained from eight Hermatomyces species were screened for antimicrobial activity. Based on the observed activity, the ethyl acetate extract of H. reticulatus was selected for further chemical analysis and fractionated using preparative high-performance liquid chromatography. Structural elucidation of the isolated compounds was performed using nuclear magnetic resonance spectroscopy and X-ray crystallography. From the extract containing a complex mixture of metabolites, two known spiroketal compounds with documented antimicrobial activity, palmaromycins C2 and C12, were successfully identified. These compounds, previously reported from other fungal taxa, may contribute to the antifungal activity observed in Hermatomyces and suggest a potential ecological role of secondary metabolites in competitive interactions with other microorganisms. In addition, we provide a curated database of known palmarumycins and related compounds, compiled from published peer-reviewed structures, to facilitate future metabolite identification.