Quassinoids are a class of highly oxygenated degraded triterpenoids exclusively discovered from plants of the Simaroubaceae family. In this study, eight new (1−8) and 15 known quassinoids (9−23) were isolated from an extract of the stems of Picrasma quassioides. The structures were elucidated by spectroscopic analysis and electronic circular dichroism spectra combined with quantum chemical calculations. Compounds 4 and 5 represent the first examples of 18-nor-quassinoids from P. quassioides. All isolates were screened for their neuroprotective activities toward H 2 O 2 -induced cell damage in SH-SY5Y cells. Further study revealed that the potential protective activities of these compounds appeared to occur via the suppression of cell apoptosis and downregulation of caspase-3 activation.

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Four pairs of β-carboline enantiomers (1a/1b–4a/4b), 2 β-carboline derivatives (5 – 6) with a single enantiomeric configuration, together with 2 known achiral congeners (7 – 8) were isolated from the stems of Picrasma quassioides. Their structures were elucidated on the basis of extensive spectroscopic analyses and quantum mechanical calculations. Compound 5 possesses a 4,5-seco β-carboline framework and represents the first example of this type of β-carboline alkaloids from nature. A possible biosynthetic pathway is proposed to generate the racemate 4 and the enantiomerically pure compounds 5 and 6. All isolates were screened for their cytotoxicity against hepatocellular carcinoma Hep3B and HepG2 cells, which revealed that enantiomeric compounds 4a and 4b had distinctive effects in HepG2 cells. Further investigation showed that 4b could induce apoptosis in HepG2 cells.

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