Bioactive Naphtho-α-Pyranones from Two Endophytic Fungi of the Genus Polyphilus

Abstract

In the course of our survey to study the metabolic potential of two species of a new helotialean genus <i>Polyphilus</i>, namely <i>P. frankenii</i> and <i>P. sieberi</i>, their crude extracts were obtained using different cultivation techniques, which led to the isolation and characterization of two new naphtho-<i>α</i>-pyranone derivatives recognized as a monomer (<b>1</b>) and its 6,6'-homodimer (<b>2</b>) together with two known diketopiperazine congeners, outovirin B (<b>3</b>) and (3<i>S</i>,6<i>S</i>)-3,6-dibenzylpiperazine-2,5-dione (<b>4</b>). The structures of isolated compounds were determined based on extensive 1D and 2D NMR and HRESIMS. The absolute configuration of new naphtho-<i>α</i>-pyranones was determined using a comparison of their experimental ECD spectra with those of related structural analogues. 6,6'-binaphtho-<i>α</i>-pyranone talaroderxine C (<b>2</b>) 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 <i>Bacillus subtilis</i> rather than <i>Staphylococcus aureus</i> with MIC values of 0.52 µg mL^-1 (0.83 µM) compared to 66.6 µg mL^-1 (105.70 µM), respectively.