Synthesis and evaluation of lactam and maleimide derivatives of 16-hydroxycleroda-3, 13 (14) Z-dien-15, 16-olide from Polyalthia longifolia as potential anticancer agents.

Diterpenes are plant secondary metabolites with diverse bioactivities, yet their anticancer potential remains underexplored. Here, we report the design and synthesis of thirty-nine novel derivatives of clerodane diterpene 1, isolated from Polyalthia longifolia, including twenty lactam and nineteen maleimide analogs. All compounds were screened at 10 μM against colon (DLD-1, HCT116, HT-29) and breast (MCF-7, MDA-MB-231, 4T1) cancer cell lines. Compound 5o emerged as the lead, demonstrating significant growth inhibition (>70 %) in colon cancer cells. Subsequent IC determinations across seven cancer types (colon, breast, lung, hepatic, ovarian, cervical, prostate) revealed highest selectivity for the 5-fluorouracil-resistant DLD-1 cell line. Mechanistic studies showed that 5o induces caspase-dependent apoptosis, triggers reactive oxygen species (ROS) generation, and causes DNA damage, leading to cell-cycle arrest. Importantly, 5o exhibited minimal cytotoxicity toward normal human cell lines (HEK293, MCF10A) and effectively suppressed colony formation and migration in both 2D and 3D colon cancer models. Metabolic stability assays in simulated gastric, intestinal, and plasma fluids confirmed that >80 % of 5o remains intact over 4 h, and pharmacokinetic profiling in mice showed a half-life of ∼3.0 h with favorable oral bioavailability. In a Balb/c colon cancer xenograft model, oral dosing of 5o produced significant tumor growth inhibition without observable toxicity. Together, these data establish 5o as a promising lead for the development of new oral therapies targeting colon cancer.