Omnipolyphilins A and B: Chlorinated Cyclotetrapeptides and Naphtho-α-pyranones from the Plant Nematode-Derived Fungus Polyphilus sieberi .

Chemical exploration for two isolates of the recently described ascomycete species Polyphilus sieberi , derived from the eggs of the plant parasitic nematode Heterodera filipjevi , afforded the identification of many compounds that belong to various metabolite families: two previously undescribed chlorinated cyclotetrapeptides, omnipolyphilins A ( 1 ) and B ( 2 ), one new pyranonaphthoquinone, ventiloquinone P ( 3 ), a 6,6'-binaphto-α-pyranone dimer, talaroderxine D ( 4 ) in addition to nine known metabolites ( 5 - 13 ) were isolated from this biocontrol candidate. All isolated compounds were characterized by comprehensive 1D, 2D NMR, and HR-ESI-MS analyses. The absolute configurations of the cyclotetrapeptides were determined by a combination of advanced Marfey's method, ROE correlation aided by conformational analysis, and TDDFT-ECD calculations, while ECD calculations, Mosher's method, and experimental ECD spectra were used for ventiloquinone P ( 3 ) and talaroderxine D ( 4 ). Among the isolated compounds, talaroderxine D ( 4 ) showed potent antimicrobial activities against Bacillus subtilis and Staphylococcus aureus with MIC values of 2.1 and 8.3 μg mL -1 , respectively. Additionally, promising inhibitory effects on talaroderxine D ( 4 ) against the formation of S. aureus biofilms were observed up to a concentration of 0.25 μg mL -1 . Moreover, ophiocordylongiiside A ( 10 ) showed activity against the free-living nematode Caenorhabditis elegans .