Madecassic acid analogues with a five-membered A-ring and their cytotoxic activity.

The structural modification of madecassic acid focused on the contraction of the six-membered A-ring to a five-membered ring, combined with the dehydration of 6-OH to form a new double bond and formation of the esterification or amidation at C-28. The synthesised structures were identified based on the analysis of their NMR and EIS-MS data. Eighteen new madecassic acid analogues were tested in vitro for their cytotoxicity against three cancer cell lines, including human mouth carcinoma (KB), human hepatocellular carcinoma (HepG2), and human lung carcinoma (A549) using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. Among them, compounds 5 and 12 exhibited potent and selective cytotoxic activity in KB and HepG2 cell lines, with IC₅₀ values ranging from 3.57 to 6.32 µM. The results also indicated that analogues with a 5-membered A-ring containing an α,β-unsaturated aldehyde esterified at C-23 showed a decrease in their cytotoxic activity compared to precursors in the tested cancer cells.