In our ongoing investigation into bioactive compounds from the genus Ligularia (Compositae) plants [1][2][3][4][5][6][7] we have studied the roots of Ligularia tongolensis (FRANCH) HAND-MAZZ collected in mountainous areas (altitude: 3600 m) in southwestern China. Ligularia tongolensis is used as a traditional folk medicine in China and its roots can reduce phlegm, relieve coughing and cure pulmonary tuberculosis, urinary track blockages, common cold, and pharyngitis.
8)However, the chemical constituents of this plant have not been reported up until now. In this paper, we report the isolation and structural elucidation of four new compounds (1, 2, 7, 8) and nine known compounds 3, 9) 4, 10) 5, 11) 6, 6) 9, 12) 10, 13) 11, 14) 12 15) and 13 14) from its roots. In addition, the cytotoxic activity in vitro of compounds 1, 2, 3, 7 and 8 were tested against human hepatoma (SMMC-7721), human embryo liver (L-02) and human leukemia (HL-60) cell lines with 10-hydroxycamptothecine as a standard.
Results and DiscussionCompound 1 , and the other 15 carbon signals suggested that 1 was an eremophilenolide-type sesquiterpene and its NMR data were similar to those of the known compound, 3b-angeloyloxy-8bH-eremophil-7(11)-ene-12,8a (14,6a)-diolide, 3) except for the presence of a 2-methylbutanoyloxy group in 1 instead of an angeloyloxy group in the known compound. The localization of the 2-methylbutanoyloxy group moiety at C-3 was deduced from the heteronuclear multiple bond correlation (HMBC) spectrum, in which H-3 (d H 5.47) gave a long-range coupling with C-1Ј (d C 175.5). Stereochemically, Me-14 and Me-15 are biogenetically b-orientated.16) The positive nuclear Overhauser effect spectrometry (NOEs) between Me-15 and H-10 (5.30%) showed a cis-fused eremophilane. The coupling pattern observed for H-3 (d H 5.47 q, 3.0 Hz) implied that H-3 was an equatorial proton and should be a-orientated.17,18) H-6 and H-8 were identified as b-orientated from the evidence of positive NOEs between H-6 and H-15 (7.73%), between H-6 and H-8 (4.35%). Therefore, compound 1 was assigned as 3b -(2Ј-methylbutanoyloxy)-8b H-eremophil-7(11)-ene-12,8a (14,6a)-diolide.The molecular formula of compound 2, C 15 H 16 O 4 , was determined by the HR-SI-MS, 13 C-NMR and DEPT (distortionless enhancement by polarization transfer) data. The NMR and IR data were similar to those of compound 1 except for the presence of a double bond at C-3 in 2 instead of the 2-methylbutanoyloxy group in 1. The signals of H-3 and C-3 as well as the adjacent C-4 were shifted downfield [H-3 at d H 6.85, C-3 at d C 136.9 and C-4 at d C 129.6], which indicated that a double bond was between C-3 and C-4. In combination with the other NMR data (Tables 1, 2) and HMBC spectrum, compound 2 was confirmed as 8bH-eremophil-3,7(11)-dien-12,8a (14,6a)-diolide. The molecular formula C 29 H 48 O 3 for compound 7 was determined by the high resolution electrospray ionization mass spectrometry (HR-ESI-MS) and the data of 13 C-NMR and DEPT. Its IR spectrum showed strong hydroxyl bands at * To whom cor...
