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.
Two new guaianolides, named chinensiolides D (5) and E (6), were isolated from Ixeris chinensis Nakai, and their structures were determined to be 10alpha-hydroxy-3-oxoguaia-11(13)-eno-12,6alpha-lactone (5) and 10alpha-hydroxy-3beta-O-[2,6-di(p-hydroxyphenylacetyl)-beta-glucopylanosyl]guaia-4(15),11(13)-dieno-12,6alpha-lactone (6). The first isolation of (11S)-10alpha-hydroxy-3-oxoguaia-4-eno-12,6alpha-lactone (4) from natural sources and its characterization are also reported. Chinenciolide E (6) showed significant growth inhibitory activity toward VA-13 malignant lung tumor cells (IC50 = 0.72 microM).
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