Guaianolides from Tanacetopsis karataviensis (Kovalevsk.) Kovalevsk
In continuation of our phytochemical study on the aerial part of Tanacetopsis karataviensis (Kovalevsk.) Kovalevsk, three new guaiane-type sesquiterpene lactones were isolated namely karatanolide (1), 11,13β-dihydrokaratanolide (2) and 11,13α-dihydrokaratanolide (3), in addition to the two known sesquiterpene lactones 1β,10α-dihydroxyarglabin (4) and artefin (5). The structures of the isolated sesquiterpene lactones were elucidated by IR and NMR spectroscopy. Single crystal X-ray diffraction allowed to unambiguously confirm the structure of the isolated sesquiterpene lactones. Quantum chemical calculations of the guaianolides 1–3 suggested the existence of two conformations for the seven-membered cycle. All sesquiterpene lactones from Tanacetopsis karataviensis were isolated for the first time.