Three New Meroterpenoids With Antimicrobial Activity Characterized From the Cold‐seep‐derived <i>Alternaria alstroemeriae</i> CS‐745

Three new meroterpenoids, tricycloalternarenes P and Z (1 and 2), and didehydrotricycloalternarene Z (3), together with nine known congeners (4-12), were obtained from the culture of Alternaria alstroemeriae, a fungus isolated from the sunken logs collected from the cold seep environment in the South China Sea. Their structures were determined by detailed interpretation of nuclear magnetic resonance (NMR) spectroscopy spectroscopic and mass spectrometric data. The relative configurations of compounds 1-3 were assigned by nuclear Overhauser effect spectroscopy correlations combined with gauge-independent atomic orbital NMR shift calculations and DP4+ probability analysis, while their absolute configurations were assigned by time-dependent density functional theory electronic circular dichroism calculations. The biological analysis results revealed that compounds 1-4, 7, and 9-11 showed antibacterial activities against Klebsiella pneumonia and methicillin-resistant Staphylococcus aureus with minimum inhibitory concentrations of 22.2-100 µM.