From Natural Limonoids to a Rationally Designed Derivative: Facilitating the Study of Anti-Adenocarcinoma Potential and Mechanisms Through Solubility Enhancement.

Natural limonoids, exemplified by limonin from lemon seeds, exhibit promising antitumor activity but are hindered by poor aqueous solubility, which critically limits their bioavailability and cellular engagement. To address this, a rational structure-based design was employed, focusing on the under-explored C-7 position. Methoxyamination of limonin yielded a novel derivative, limonin-7-methoxime. Comprehensive ¹H and ¹³C NMR spectroscopy confirmed its structure, and the modification markedly improved aqueous solubility. Cytotoxicity assessment across three human adenocarcinoma cell lines (MCF-7, HT-29, LNCaP) showed that both limonin-7-methoxime and the natural analog obakunone exerted measurable, albeit moderate, activity. They exhibited the strongest effect against LNCaP prostate cancer cells, with IC50 values of 249.35 and 236.15 μM, respectively. Mechanistic studies indicated that both compounds were associated with cell cycle arrest and the activation of caspase-3-mediated apoptosis in LNCaP cells. Collectively, this work validates C-7 functionalization as an effective strategy to enhance the drug-like properties of limonoids. It delivers a structurally optimized lead compound and provides a foundation for further development aimed at improving its antitumor potency.