Abstract
Three new guaianolides, 10alpha-hydroxy-3-oxoguaia-4(15),11(13)-dieno-12,6alpha-lactone (1), 10alpha-hydroxy-3-oxo-4betaH-guaia-11(13)-eno-12,6alpha-lactone (2), and 10alpha-hydroxy-3-oxoguaia-4,11(13)-dieno-12,6alpha-lactone (3), named chinensiolides A, B, and C were isolated from the whole plant of Siyekucai (Ixeris chinensis). The structures were determined by HREIMS, UV, IR, and one- and two-dimensional NMR techniques ((1)H and (13)C NMR, COSY, HMQC, HMBC, and NOE difference and NOESY experiments). Compounds 1 and 2 were indicated to be a mixture of flexible conformers by analyses of their 1D NOE and NOESY spectra as well as the temperature dependence of their (1)H and (13)C NMR spectra. Chinensiolide B (2) was transformed to chinensiolide C (3) in a three-step conversion.
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