Marinoacrebols A–D, New Peptaibol-like Peptides Isolated from a Marine-Derived Fungus, Acremonium persicinum ACE-015

Four new peptaibol-like peptides, marinoacrebols A–D (1–4), were isolated from the marine-derived fungus Acremonium persicinum ACE-015. Their planar structures were elucidated through comprehensive spectroscopic analyses, including 1D and 2D nuclear magnetic resonance (NMR) experiments, together with high-resolution mass spectrometry. Detailed analysis of COSY and HMBC correlations, supported by electrospray ionization tandem mass spectrometry (ESI-MS/MS) fragmentation data, enabled the determination of their amino acid sequences. Marinoacrebols A–C (1–3) were identified as 19-residue peptides, whereas marinoacrebol D (4) was identified as an 18-residue peptide. The absolute configurations of the chiral amino acid residues were determined using advanced Marfey’s analysis, while electronic circular dichroism (ECD) analysis supported a right-handed helical conformation. Compounds 1–4 exhibited selective antibacterial activity against Gram-positive bacteria, with minimum inhibitory concentration (MIC) values ranging from 8–64 μg/mL. Notably, compound 2 showed the strongest antibacterial activity against Kocuria rhizophila KCTC 1915, with an MIC value of 8 μg/mL.