Abstract: This study deals with the design and synthesis of a series of novel 4-methoxy-substituted and 5-methyl-substituted (3'S ,4'S )-(-)-cis -khellactones. The newly synthesized compounds were characterized by ¹H nuclear magnetic resonance (NMR), ¹³C-NMR, mass spectrometry, and elemental analysis. All the derivatives were subjected to in vitro cytotoxicity screening against HEPG-2 (human liver carcinoma), SGC-7901 (human gastric carcinoma), and LS174T (human colon carcinoma), by using the MTT assay. The results revealed that several of the 4-methoxy-substituted compounds exhibited potent cytotoxicity. Among these, compound 12e showed the highest activity against cancer cells which 50% inhibitory concentration (IC₅₀) values were in the range of 6.1–9.2 µM with low toxicity on normal human hepatocyte. Preliminary investigation of possible mechanisms of action of compound 12e against HEPG-2 cells indicated possible induction of apoptosis, as determined by morphological observations and Annexin V/propidium iodide (PI) double staining, in addition to apparent dissipation of mitochondrial membrane potential (MMP), as measured by 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-imidacarbocyanine iodide (JC-1) staining in combination with the activation of caspase-9 and caspase-3 by Western blot analysis. Overall, the data suggest that compound 12e may be a promising potential anticancer agent that could act primarily by inducing apoptosis through the mitochondria-mediated intrinsic pathway in human hepatoma cells.
Keywords: 4-methoxy-substituted and 5-methyl-substituted (3'S ,4'S )-(-)-cis -khellactones, synthesis, cytotoxic activity, apoptosis