Isolation, structure elucidation and bioactivity of schischkiniin, a unique indole alkaloid from the seeds of Centaurea schischkinii

Reversed-phase HPLC analysis of the methanol extract of the seeds of Centaurea schischkinii afforded a novel indole alkaloid, named schischkiniin (), together with four lignans, arctiin (), matairesinoside (), matairesinol (), and arctigenin (), and three flavonoids, astragalin (), afzelin () and apigenin (). While the structure of schiskiniin () was established unequivocally by UV, HRFABMS and a series of 1D and 2D NMR analyses, all known compounds were readily identified by comparison of their spectroscopic data with literature data. The free radical scavenging properties of these compounds were assessed using the DPPH assay, and their general toxicity and cytotoxicity were evaluated, respectively, by brine shrimp lethality and MTT cytotoxicity assays with CaCo-2 colon cancer cell lines. Arctigenin () exhibited promising in vitro anticancer activity (IC50=7 μM) while with schischkiniin () the activity was of moderate level (IC50=76 μM).