Isobenzofuranones and Isochromenones from the Deep-Sea Derived Fungus Leptosphaeria sp SCSIO 41005

Four new isobenzofuranones, leptosphaerins J-M (1-4), including an unusual naturally-occurring centrosymmetric dimer skeleton (1), and two new isochromenones, clearanols I-J (9-10), were obtained from a culture of a deep-sea sediment-derived fungus Leptosphaeria sp. SCSIO 41005, together with four known isobenzofuranones (5-8) and six known isochromenones (11-16). These structures were elucidated by extensive spectroscopic analyses, and absolute configurations were assigned on the basis of electronic circular dichroism and optical rotations data comparison. Additionally, the absolute configurations of the new compounds 1 and 9, together with the known one 7 with stereochemistry undetermined, were further confirmed by single crystal X-ray diffraction experiments. A plausible biosynthetic pathway of these isobenzofuranones and isochromenones was also proposed.