Sesquiterpenoids and tirucallane triterpenoids from the roots of Scorzonera divaricata

Abstract

A sulfated guaiane sesquiterpene lactone, an unusual pyridinium alkaloid with a sulfated guaiane sesquiterpene lactone nucleus, an amino conjugate of a sulfated guaiane sesquiterpene lactone, a bisabolane sesquiterpene, three tirucallane triterpenes, and six known compounds, were isolated from roots of Scorzonera divaricata. Their structures and absolute configurations were established based on chemical and spectroscopic methods, X-ray single crystal crystallography, and also by comparison with experimental and calculated ECD spectra. One of the tirucallane triterpenes exhibited significant cytotoxic activities against four human cancer cell lines (HL60, HeLa, HepG2, and SMMC-7721) in vitro. Two of sulfated guaiane sesquiterpenoids also exhibited antioxidant activities by scavenging ABTS cation free radicals. Tirucallane-type and dammarane-type triterpenes were not previously known in the genus Scorzonera. The study suggests that sulfated guaiane-type sesquiterpenoids are a valuable marker for systematic chemical studies in the Lactuceae tribe of the Asteraceae.

Keywords: ABTS radical scavenging capacity; Asteraceae; Circular dichroism; Cytotoxicity; Scorzonera divaricata; Sesquiterpenoid; Structure elucidation; Triterpenoids; X-ray single crystal diffraction.