Benzofurans nor-sesquiterpenoids from Petasites hybridus rhizomes and absolute configuration by circular dichroism

Abstract

Petasites hybridus (L.) G.Gaertn., B.Mey. & Scherb. has been used as a medicine for different illnesses. A phytochemical study on hexane extract has been carried out using normal phase silica gel column and RP-HPLC chromatography. Five sesquiterpenoids were isolated, purified, and identified from hexane extract. The structures were elucidated by applying extensive 1D and 2D NMR and HRESI-TOFMS spectroscopy. In addition, circular dichroism (CD) spectra were applied to determine absolute configurations of constituents. Two never described benzofuran nor-sesquiterpenes (2S,3S)-5'-acetyl-(Z)-3-(acetoxymethyl) but-2-enoate tremetone) (4) and (2R,3R)-5'-acetyl-(Z)-3-(acetoxymethyl) but-2-enoate-7-hydroxytremetone (5) as well as euparin (1), (2S,3R)-3,6-dihydroxytremetone (2), and (2S,3S)-3,6-dihydroxytremetone (3) were isolated from the rhizome of Petasites hybridus, a species in Flora of Iran. Also, the euparin content of the MeOH extracts of seven populations of Iran was measured by HPLC-PDA. Notably, isolated euparin was the main constituent of Iranian P. hybridus varying between 2.7 and 9.7 µg/mg among samples.