New Polyketide Congeners with Antibacterial Activities from an Endophytic Fungus Stemphylium globuliferum 17035 (China General Microbiological Culture Collection Center No. 40666)

Abstract

Four new polyketides, heterocornol Y (1), stemphyindan (2), pestalospirane C (3), and stemphyspyrane (4), along with five known ones (5–9) were isolated from the endophytic fungus Stemphylium globuliferum 17035 (SG17035) based on the One Strain Many Compounds (OSMAC) strategy allied with an LC-MS approach. These structures were elucidated through extensive spectroscopic analyses, single-crystal X-ray diffraction, and 13C NMR-DP4 analysis. Pestalospirane C (3) and stemphyspyrane (4) featured unprecedented spiroketal skeletons. In addition, the putative biosynthetic logic for compounds 1–4 was proposed. Antibacterial and cytotoxic activities of compounds 1–9 were evaluated. Stemphyspyrane (4) displayed promising antibacterial activity against different pathogens, especially against Staphylococcus aureus, Porphyromonas gingivalis, and methicillin-resistant Staphylococcus aureus (MRSA) with MIC values of 3.125 μM, 6.25 μM, and 12.5 μM, respectively. It is promising as an antibacterial agent for further optimization.