Melanogenesis-Inhibitory and Cytotoxic Activities of Triterpene Glycoside Constituents from the Bark of Albizia procera

Five oleanane-type triterpene glycosides including three new ones, proceraosides E–G (1–3), were isolated from a MeOH-soluble extract of Albizia procera bark. The structures of 1–3 were determined by use of NMR spectra, HRESIMS, and chemical methods. Compounds 1–5 exhibited inhibitory activities against the proliferation of the A549, SKBR3, AZ521, and HL60 human cancer cell lines (IC₅₀ 0.28–1.8 μM). Additionally, the apoptosis-inducing activity of compound 2 was evaluated by Hoechst 33342 staining and flow cytometry, while the effects of 2 on the activation of caspases-9, -8, and -3 in HL60 cells were revealed by Western blot analysis.