Isochromenones, isobenzofuranone, and tetrahydronaphthalenes produced by Paraphoma radicina, a fungus isolated from a freshwater habitat

Six isochromenones (1–6), clearanols F (5) and G (6), one isobenzofuranone (7), and two tetrahydronaphthalene derivatives (8 and radinaphthalenone (9)), were isolated and identified from a culture of the fungus Paraphoma radicina, which was isolated from submerged wood in a freshwater lake. Compounds 5, 6 and 9 were previously unknown. The structures were elucidated using a set of spectroscopic and spectrometric techniques; the absolute configurations of compounds 5 and 6 were determined by comparison of their experimental ECD measurements with values predicted by TDDFT calculations. Compounds 1–9 were evaluated for antimicrobial activity against an array of bacteria and fungi. The inhibitory activity of compound 4 against Staphylococcus aureus biofilm formation was evaluated.Abbreviations: BLAST, basic local alignment search tool; CHCl3, chloroform; CH3CN, acetonitrile; COSMO, conductor-like screening model; DFT, density functional theory; ECD, electronic circular dichroism; HPLC, high performance liquid chromatography; HRESIMS, high-resolution electrospray ionization mass spectrometry; ITS, internal transcribed spacer; LS, large scale; LSU, large subunit; MeOH, methanol; MICs, minimal inhibitory concentrations; NMR, nuclear magnetic resonance; nrDNA, nuclear ribosomal deoxyribonucleic acid; PDA, potato dextrose agar; rRNA, ribosomal ribonucleic acid; SCRF, self-consistent reaction field; TDDFT, time-dependent density functional theory; UPLC, ultra-performance liquid chromatography; UV, ultraviolet; UV–Vis, ultraviolet/visibl