Bioactive Naphtho-α-Pyranones from Two Endophytic Fungi of the Genus Polyphilus
Jan‐Peer Wennrich, Ellen Sepanian, Sherif S. Ebada, Natalia A. Llanos‐López, Samad Ashrafi, Wolfgang Maier, Tibor Kurtán, Marc Stadler
Abstract
In the course of our survey to study the metabolic potential of two species of a new helotialean genus Polyphilus, namely P. frankenii and P. sieberi, their crude extracts were obtained using different cultivation techniques, which led to the isolation and characterization of two new naphtho-α-pyranone derivatives recognized as a monomer (1) and its 6,6′-homodimer (2) together with two known diketopiperazine congeners, outovirin B (3) and (3S,6S)-3,6-dibenzylpiperazine-2,5-dione (4). The structures of isolated compounds were determined based on extensive 1D and 2D NMR and HRESIMS. The absolute configuration of new naphtho-α-pyranones was determined using a comparison of their experimental ECD spectra with those of related structural analogues. 6,6′-binaphtho-α-pyranone talaroderxine C (2) exhibited potent cytotoxic activity against different mammalian cell lines with IC50 values in the low micromolar to nanomolar range. In addition, talaroderxine C unveiled stronger antimicrobial activity against Bacillus subtilis rather than Staphylococcus aureus with MIC values of 0.52 µg mL−1 (0.83 µM) compared to 66.6 µg mL−1 (105.70 µM), respectively.