Targeting high-performance liquid chromatography–high-resolution mass spectrometry–solid-phase extraction–nuclear magnetic resonance analysis with high-resolution radical scavenging profiles—Bioactive secondary metabolites from the endophytic fungus Penicillium namyslowskii

The high-resolution radical scavenging profile of an extract of the endophytic fungus Penicillium namyslowskii was used to target analysis by high-performance liquid chromatography–high-resolution mass spectrometry–solid-phase extraction–nuclear magnetic resonance spectroscopy, i.e., HPLC–HRMS–SPE–NMR, for identification of anti-oxidative secondary metabolites. This revealed the two chromatographic peaks with the highest relative response in the radical scavenging profile to be griseophenone C and peniprequinolone. The HPLC–HRMS–SPE–NMR analysis was performed in the tube-transfer mode using a cryogenically cooled NMR probe designed for 1.7 mm NMR tubes. To further explore the potential of the above HPLC–HRMS–SPE–NMR platform for analysis of endophytic extracts, six peaks displaying no radical scavenging activity were also analyzed. This allowed unambiguous identification of six metabolites, i.e., dechlorogriseofulvin, dechlorodehydrogriseofulvin, griseofulvin, dehydrogriseofulvin, mevastatin acid, and mevastatin. The high mass sensitivity of the 1.7 mm cryogenically cooled NMR probe allowed for the first time acquisition of direct detected 13C NMR spectra of fungal metabolites, i.e., dechlorogriseofulvin and griseofulvin, directly from crude extract via HPLC–HRMS–SPE–NMR. Dechlorodehydrogriseofulvin was reported for the first time from nature.