Lithocarpins A–D: four tenellone-macrolide conjugated [4 + 2] hetero-adducts from the deep-sea derived fungus Phomopsis lithocarpus FS508

Lithocarpins A–D ( 1–4 ), the first examples of highly oxygenated tenellone-macrolide conjugated dimers, were isolated from the deep-sea derived fungus Phomopsis lithocarpus FS508. Their structures were elucidated by extensive spectroscopic analyses and X-ray diffraction techniques. Their plausible biogenetic pathways suggested a very intriguing and unusual [4 + 2] cycloaddition with an isobenzofuran as an electron-donating diene. Lithocarpins C and D exhibited a moderate inhibitory effect against three tumor cell lines with IC 50 values ranging from 17.0 to 21.6 μM.