(±)-Rhytidhymarins A and B, two pairs of new isocoumarin derivatives from endophytic fungus Rhytidhysteron sp. BZM-9

Two pairs of isocoumarin derivatives, (±)-rhytidhymarins A and B ( 1–2 ), one aromatic ester, rhytidhyster A (3), together with three known compounds ( 4–6 ) were isolated from fungus Rhytidhysteron sp. BZM-9. Compounds 1 and 2 are presented as racemates and resolved into optically pure enantiomers (+)- 1 /(−)- 1 and (+)- 2 /(−)- 2 by chiral column separation, respectively. Their planar structures were elucidated by HRESIMS, 1D and 2D NMR data and their absolute configurations were determined by X-ray crystallographic analysis and electronic circular dichroism (ECD) calculation. Compound 5 showed significant cytotoxic activity against SMMC7721 cells with an IC 50 value of 0.338 μM and exhibited moderate antimicrobial activity to MRSA with a MIC value of 6.25 μg mL −1 ; compound 3 showed cytotoxicity against HepG2 cells with an IC 50 value of 11.46 μM.