In Situ Mass Spectrometry Monitoring of Fungal Cultures Led to the Identification of Four Peptaibols with a Rare Threonine Residue

Peptaibols are an intriguing class of fungal metabolites due both to their wide range of reported bioactivities and to the structural variability that can be generated by the exchange of variable amino acid building blocks. In an effort to streamline the discovery of structurally diverse peptaibols, a mass spectrometry surface sampling technique was applied to screen the chemistry of fungal cultures in situ. Four previously undescribed peptaibols, all containing a rare threonine residue, were identified from a fungal culture (MSX53554), which was identified as Nectriopsis Maire (Bionectriaceae, Hypocreales, Ascomycota). These compounds not only increased the known threonine-containing peptaibols by nearly 20%, but also, the threonine residue was situated in a unique place compared to the other reported threonine-containing peptaibols. After the initial in situ detection and characterization, a large-scale solid fermentation culture was grown. The four peptaibols were isolated and characterized by mass spectrometry. In addition, one of the peptaibols was fully characterized by NMR and amino acid analysis using Marfey's reagent and exhibited moderate in vitro anticancer activity