New taxonomically significant sesquiterpenoids from Leontodon autumnalis

The methanolic extract of subaerial parts of Leontodon autumnalis afforded four new and two known sesquiterpenoids of the guaiane type. The known compounds were identified by means of (1)H and (13)C NMR spectroscopy as crepidiaside A (1) and B (2). The structures of the new compounds were determined by extensive 1D and 2D NMR experiments as 15-glucopyranosyloxy-2-oxo-guaia-3,11(13)-dien-1alp ha,5alpha, 6beta,7alpha,10alphaH-12,6-olide (3); 15-glucopyranosyloxy-2-oxo-guai-3-en-1alpha,5alpha+ ++,6beta,7alpha, 10alpha,11betaH-12,6-olide (4); 15-hydroxy-2-oxo-guai-3-en-1alpha, 5alpha,6beta,7alpha,10alpha,11betaH-12,6-+ ++olide (5); and 15-glucopyranosyloxy-2-oxo-guaia-3,11(13)-dien-1bet a,5alpha,6beta, 7alpha,10alphaH-12,6-olide (6), respectively. HPLC-DAD and HPLC-MS analyses of crude extracts of subaerial parts of 25 different taxa of the genus Leontodon revealed that compounds 1 and 2 occur in all investigated members of the section Oporinia (L. autumnalis, L. croceus, L. helveticus, L. montaniformis, L. montanus, L. pyrenaicus, and L. rilaensis) and in L. duboisii from the section Kalbfussia. Compounds 1-6 are detectable neither in other investigated taxa of Kalbfussia (L. cichoraceus, L. muelleri, and L. palisae) nor in any members of the subgenus Leontodon. Compounds 3-5 occur in high amounts only in L. croceus and L. pyrenaicus and in samples of L. autumnalis from northwestern Europe. In other members of the section Oporinia, in L. duboisii as well as in samples of L. autumnalis from the Pyrenees, the Alps, the Carpathians, and southern Central Europe, these substances occur only in trace amounts; in L. montanus and its closest relatives, compounds 3-5 are not detectable at all. Compound 6 is only detectable in samples of L. autumnalis, L. helveticus, L. pyrenaicus, L. rilaensis, and L. duboisii.