A New Labdane-Type Diterpenoid from the Branches and Leaves of Aphanamixis polystachya

• • A new labdane-type diterpenoid (1) was isolated from Aphanamixis polystachya with a yield of 0.002% (w/w), requiring 50 kg of dried plant material to obtain 1 g of pure compound; this low abundance directly impacts scalability for preclinical studies. • • Compound 1 exhibited moderate cytotoxicity against HepG2, A549, and MCF-7 cell lines with IC50 values of 18.7, 24.3, and 32.4 μM, respectively, compared to doxorubicin (IC50 0.8–2.1 μM), indicating a 10–40-fold lower potency that limits immediate therapeutic translation. • • The structure was unequivocally determined by HR-ESI-MS (m/z 317.2115 [M+H]+, calcd 317.2111) and 2D NMR, with the absolute configuration established via ECD calculations; this rigorous characterization prevents misassignment of stereochemistry, which is critical for reproducible bioactivity. • • The 1,4-dien-3-one moiety in the labdane skeleton is a rare feature in Meliaceae, suggesting a unique biosynthetic pathway; this chemotaxonomic marker could guide targeted isolation of analogues with improved potency from related species.