Four new chlorinated cyclopentene derivatives, rhytidhyesters A - D (1: - 4: ), were isolated from Rhytidhysteron sp. BZM-9, an endophytic fungus from Leptospermum brachyandrum. The planar structures of compounds 1: - 4: were mainly elucidated by 1D, 2D NMR, and HRESIMS data. Their absolute configurations were established by X-ray crystallographic analysis, quantum chemical 13C NMR, and electronic circular dichroism calculations. Compounds 1: and 2: are a pair of epimers. Moreover, all the isolated compounds were evaluated for cytotoxic activities against 3 human colon cancer cell lines (SW620, HT29, SW480) and antimicrobial activity against Staphylococcus aureus. All compounds exhibited weak to moderate antiproliferative activities with IC50 values ranging from 15.4 to 37.7 µM but were inactive against S. aureus.
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