A New Labdane-Type Diterpenoid from the Branches and Leaves of Aphanamixis polystachya
Phytochemical investigation of the branches and leaves of Aphanamixis polystachya (Meliaceae) yielded a previously undescribed labdane-type diterpenoid, designated as compound 1, together with known analogues. The structure of the new metabolite was established through comprehensive spectroscopic analysis, including HR-ESI-MS, 1D and 2D NMR (HSQC, HMBC, NOESY), and comparison with literature data. The absolute configuration was assigned by electronic circular dichroism (ECD) calculations. Compound 1 features a 1,4-dien-3-one moiety within a labdane skeleton, a structural motif rarely encountered in the Meliaceae family. All isolates were evaluated for their cytotoxic activities against a panel of human cancer cell lines (HepG2, A549, and MCF-7) using the MTT assay. Compound 1 exhibited moderate inhibitory effects with IC50 values ranging from 18.7 to 32.4 μM, while the positive control doxorubicin showed IC50 values of 0.8–2.1 μM. The discovery of this new diterpenoid expands the chemical diversity of A. polystachya and provides a potential scaffold for further anticancer drug development. However, the moderate potency and low yield (0.002% w/w) highlight the need for semisynthetic or biotechnological production strategies to enable preclinical evaluation.