Phomopsols A and B from the Mangrove Endophytic Fungus Phomopsis sp. xy21: Structures, Neuroprotective Effects, and Biogenetic Relationships

A polyketide-derived alkaloid featuring a unique 3,4-dihydro-2H-indeno­[1,2-b]­pyridine 1-oxide motif, named phomopsol A (1), and a highly oxidized polyketide containing a new 3,5-dihydro-2H-2,5-methanobenzo­[e]­[1,4]­dioxepine moiety, named phomopsol B (2), were isolated from the Thai mangrove endophytic fungus Phomopsis sp. xy21, together with the related biosynthetic polyketide 3. The structures of 1–3 were unambiguously established by single-crystal X-ray diffraction analysis (Cu Kα), and their neuroprotective effects in PC12 cells were evaluated. The biosynthetic origins of 1–3 are proposed.