Identification and quantification of lignans and sesquilignans in the fruits of Cnicus benedictus L.: Quantitative chromatographic and spectroscopic approaches

Identification, quantification and isolation of lignans (Lig-s: arctiin, arctigenin and matairesinol) and sesquilignans (SLig-s: lappaol A, isolappaol A, lappaol C and isolappaol C), in Cnicus benedictus L. fruit (CBfr) were performed for the first time. Identity of Lig-s and SLig-s was confirmed by gas chromatography-mass spectrometry (GC-MS) and by high performance liquid chromatography-time-of-flight (HPLC-TOF) MS, while their detailed structures were defined by nuclear magnetic resonance (NMR) spectroscopy. As a novelty to the field, fruit part-specific accumulation of Lig-s and SLig-s under germination and their transformation during acidic and enzymatic hydrolyses were followed in a quantitative manner by HPLC-UV. It was shown that during germination, the spontaneous separation of Lig-s and SLig-s occurs: the fruit wall part accumulates SLig-s, while the embryo accumulates the Lig arctiin. It was confirmed that under optimized mild acidic conditions (50 °C, 2 M trifluoroacetic acid, TFA), lappaol C and isolappaol C can be transformed into lappaol A and isolappaol A, quantitatively. Analytical performance characteristics (reliability and reproducibility), in the HPLC-UV quantifications of Lig-s and SLig-s were defined by the relative standard deviation percentages (RSD%-s) of analyses (averages of RSD%-s ≤ 3.7). Due to our new harmonized analysis system, CBfr proved to be a new and rich source of SLig-s: levels as high as 5.8 mmol/100 g were determined compared to the highest level (0.72 mmol/100 g) reported so far.