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Bioassay-guided fractionation of the ethanolic extract of the stem bark of Albizia julibrissin led to the isolation of ten new oleanane-type triterpenoid saponins, julibrosides J 37 –J 46 ( 1 – 10 ), along with six known analogues ( 11 – 16 ). In addition, 11 prosapogenins ( 17 – 27 ) were prepared by mild or strong alkaline hydrolysis of the total saponin. The structures of 1 − 27 were determined by spectroscopic and chemical means, and their cytotoxicities against four human cancer cell lines, BGC-823, A549, HCT-116, and HepG2 were evaluated. Compounds 5 – 16 exhibited significant inhibitory activity with IC 50 values ranging from 2.59 to 9.30 μM, and 8 turned out to be the most active compound with all IC 50 values < 5 μM. A preliminary structure-activity relationship of these saponins clearly indicated that the outer monoterpenoid moiety (MT′) is a crucial substituent for cytotoxicity, and the linkage sites of the MT′ unit greatly influenced the activity. It could also be inferred that the existence of 16-OH of the aglycone almost has no effect on cytotoxicity and the N -acetyl-glucosamine moiety at C-3 seems to enhance activity. [ABSTRACT FROM AUTHOR]

Three new minor oleanane triterpenoid saponins acetylated with monoterpenoid acid, julibroside J32, julibroside J35 and julibroside J36, along with one new natural product, prosapogenin 9, were isolated from the stem bark of Albizia julibrissin. Their structures were elucidated on the basis of the chemical and spectroscopic evidences. [Copyright &y& Elsevier]