HPLC determination and NMR structural elucidation of sesquiterpene lactones in Inula helenium

A high performance liquid chromatography (HPLC) method was developed for the simultaneous quantification of three bioactive sesquiterpene lactones in Inula helenium L., namely igalane (1), isoalantolactone (2) and alantolactone (3). The HPLC separation was performed on an Agilent Zorbax XDB-C18 column (250 mm × 4.6 mm, 5 μm) with a mobile phase consisting of 55% acetonitrile and 45% water, at a flow rate of 1.0 ml/min, and detected at 210 nm. All three regression equations indicated good linear relationships (r2 ≥ 0.9994) between the peak area of each compound and its respective concentration. The HPLC assay was reproducible with overall intra- and inter-day variation of less than 2.85%. The recoveries, measured at three concentrations, varied from 96.60 to 104.43%. This assay was successfully applied to the determination of three bioactive sesquiterpene lactones in eleven samples. The results demonstrated that the assay developed herein was rapid, accurate, reliable and could be readily utilized as a quality control method for I. helenium. In addition, two minor isomers in I. helenium were isolated by semi-preparative HPLC. Their structures were elucidated on the basis of NMR analysis.