Lithocarols A-F, six tenellone derivatives from the deep-sea derived fungus Phomopsis lithocarpus FS508

Lithocarols A-F (1-6) possessing novel highly-oxygenated isobenzofuran core, together with a related known compound isoprenylisobenzofuran A (7) were isolated from the marine-derived fungus Phomopsis lithocarpus FS508. Among them, lithocarols A-E (1-5) represent the first examples of poly-ketal derivatives in tenellone family. The structures for all these compounds were fully elucidated by spectroscopic analysis, X-ray diffraction, and electronic circular dichroism calculations. Their cytotoxic assay disclosed that compounds 1-4 displayed moderate growth inhibitory effect against four human tumor cell lines with the IC50 values ranging from 10.5 to 38.7 mu M.