Two oleanane triterpenoids with a C-4 methyl substitution from Camellia oleifera Abel and their anti-inflammatory activities

Two previously undescribed oleanane-type triterpenoids, 16α,22α,23,28-tetrahydroxyolean-12-en-3-one (1) and 4α-methyl-16α,21β,22α, 27-tetrahydroxyolean-12-en-3-one (2), together with three known analogues (3–5), were isolated from the seed cake of Camellia oleifera Abel. Their molecular structures were determined by NMR, HRMS and X-ray crystallography. Compound 2 features a rare C-4 monomethyl substitution. The anti-inflammatory activity of all compounds was evaluated in LPS-induced RAW264.7 macrophages. They dose-dependently inhibited the production of IL-6, NO, PGE2, and TNF-α without obvious cytotoxicity. Compound 4 exhibited the most potent broad-spectrum inhibition, while compounds 2 and 3 showed selective suppression of IL-6 and TNF-α, respectively. These findings expand the chemical diversity of triterpenoids from C. oleifera seed cake and highlight its potential as a source of anti-inflammatory lead compounds. The rare C-4 methylated skeleton of compound 2 provides new insights into structure–activity relationships among oleanane-type triterpenoids.