Specialized metabolites from the aerial parts of Centaurea polyclada DC

The genus Centaurea L. (Asteraceae) is represented by 200 taxa in the flora of Turkey and several Centaurea species are used as herbal remedies against different conditions. Previous phytochemical investigations on this genus generally revealed the isolation of sesquiterpene lactones and flavonoid derivatives. In our continuous search on Centaurea genus, a phytochemical study was performed on Centaurea polyclada DC., an endemic of West Anatolia. Previously undescribed two sesquiterpene-amino acid conjugates, an elemane and an eudesmane derivative were isolated from the aerial parts of Centaurea polyclada, together with eight known compounds; two elemane derivatives, three flavonoids, a lignan, a phenolic glucoside and a phenylpropanoid glucoside. Structural elucidation of the compounds was based on spectroscopic evidence, including 1D and 2D NMR and high-resolution mass spectrometry, chemical degradation results and reference data comparison. Sesquiterpene-amino acid conjugates are representatives of an unusual group of sesquiterpenes, and elemane-amino acid conjugates are herein reported for the first time in nature. Five previously undescribed sesquiterpene-type compounds, including rare amino acid-sesquiterpene conjugates, were isolated from the aerial parts of Centaurea polyclada DC. (Asteraceae), together with seven known compounds. [Display omitted] •Five previously undescribed sesquiterpenes were isolated from Centaura polyclada DC.•Elemane sesquiterpene-aminoacid conjugates were reported for the first time in the genus Centaurea.•The structures of the isolated compounds were established by spectroscopic and chemical methods.