Oleanane- and Noroleanane-Type Triterpenoid Saponins from the Seeds of Camellia japonica

Twelve new triterpenoid saponins, tsubakisaponins A–L (1–12), together with four known triterpenoid saponins (13–16), were isolated from the defatted seed residue of Camellia japonica. Their structures were elucidated by extensive spectroscopic analyses, including one-dimensional (1D) and 2D-NMR experiments, high-resolution electrospray ionization MS, and acid hydrolysis. These compounds were characterized as olean-12-ene- or 28-norolean-12-ene-type triterpenoid saponins bearing a common tetrasaccharide chain and are distinguished by acylation of the hydroxy groups at C-16, C-22, or C-28 with tigloyl, 2-methylbutanoyl, isovaleryl, or acetyl moieties. Compound 12 is the first saponin isolated from the genus Camellia to possess a 28-noroleanane-type aglycone bearing a C-23 aldehyde moiety. These findings expand the structural diversity of saponins from C. japonica and provide NMR-based criteria for determining the positions of acyl substituents in related triterpenoids.