Protoilludane-Type and Related Nor-Sesquiterpenes from <i>Phellinus hartigii</i> and Their Anti-Hypertrophic Activities in Rat Cardiomyocytes

Three nor-sesquiterpenes, phellinharts A–C (1–3), isolated from Phellinus hartigii, exhibited unprecedented protoilludane and cerapicane-type structures. The structures of compounds 1–3 were elucidated via spectroscopic analysis, quantum chemical calculations, and X-ray diffraction. Potential biogenic pathways involving demethylation, ring cleavage, and rearrangement were proposed. Compounds 1–3 displayed potent anti-hypertrophic activities with low cytotoxicity (CC50 > 50 μM) in rat cardiomyocytes, underscoring their therapeutic potential.