Undescribed sesquiterpenoids from Leontodon × grassiorum (Cichorieae, Asteraceae) including UHPLC-HRMS data of additional hybrid compounds

Abstract

Abstract

A phytochemical investigation of the acetone extract of the subaerial part of Leontodon × grassiorum [ L. hochstetteri × L. hispidus ] yielded 14-hydroxyhypocretenolide-β- d -glucopyranoside-6′- O - p -hydroxyphenylacetic acid ester and the dimeric sesquiterpenoid 14-hydroxyhypocretenolide-β- d -glucopyranoside-4′-14″-hydroxyhypocretenoate-6′- O - p -hydroxyphenylacetic acid ester, for which we suggest the name leograssiolide A. These previously undescribed natural products seemed to be hybrid compounds that display features of both parental species of Leontodon × grassiorum . The paternal parent L. hispidus contains 14-hydroxyhypocretenolides and a dimeric 14-hydroxyhypocretenolide. These are the core moieties of the compounds reported here. The maternal parent L. hochstetteri , an endemic species of the Azores, on the other hand, is the source of 1,10-epoxy-14-hydroxy-hypocretenolides, that are unique for the Leontodon species from the Azorean archipelago. Compounds found in L. hochstetteri can also be substituted with a p -hydroxyphenylacetyl moiety, a feature that had never been reported in L. hispidus sesquiterpene lactones, but is also present in the newly discovered compounds. A comparison of extracts from Leontodon hispidus and Leontodon × grassiorum both growing in our botanical garden proofed the occurrence of the previously unreported dimeric compound also in L. hispidus , albeit to a much lesser extent. The structures of 14-hydroxyhypocretenolide-β- d -glucopyranoside-6′- O - p -hydroxyphenylacetic acid ester and 14-hydroxyhypocretenolide-β- d -glucopyranoside-4′-14″-hydroxyhypocretenoate-6′- O - p -hydroxyphenylacetic acid ester were established by 1D and 2D NMR experiments and by high-resolution mass spectrometry. Additionally, feature-based molecular network analysis and comparison of the MS/MS spectra revealed evidence of four hybrid natural products that were only occurring in the hybrid species. Based on their fragmentation, these compounds seem to be composed of sesquiterpenoids that show features known from both parental species.