Eremophilane Derivatives with a Novel Carbon Skeleton from Ligularia veitchiana

Phytochemical Investigation and Cytotoxic Evaluation of the Components of the Medicinal Plant Ligularia atroviolacea

“…The localization of the (angeloyl)oxy moiety at C(3) was deduced from the HMBC spectrum of 2 in which HÀC(3) (d(H) 5.58 (q, J ¼ 3.0)) showed a diagnostic long-range coupling with C(1') (d(C) 174.2). The coupling pattern observed for HÀC(3) (a triple doublet with J(3a,2a) ¼ J(3a,2b) ¼ J(3a,4a) ¼ 3.0 Hz) implied that HÀC(3) was an equatorial H-atom and should be a-orientated [13]. In addition, a homoallylic coupling (J ¼ 1.2 Hz) between the olefinic Me group HÀC (13) and H a ÀC(6), typically attributable to an eremophil-7(11)-en-12,8b-olide derivative [14], was evident in the 1 H-NMR spectrum of 2.…”

“…The coupling pattern observed for HÀC(3) (a triple doublet with J(3a,2a) ¼ J(3a,2b) ¼ J(3a,4a) ¼ 3.0 Hz) implied that HÀC(3) was an equatorial H-atom and should be a-orientated [13]. In addition, a homoallylic coupling (J ¼ 1.2 Hz) between the olefinic Me group HÀC (13) and H a ÀC(6), typically attributable to an eremophil-7(11)-en-12,8b-olide derivative [14], was evident in the 1 H-NMR spectrum of 2. Consequently, compound 2 was elucidated as 3b-[(2-methylbut-2-enoyl)oxy]eremophil-7(11)-en-12,8b-olid-14-oic acid.…”

“…Except for the isobutyroxy moiety, the 13 C-NMR and DEPT spectra exhibited 15 C-atom signals ascribed to six C-atoms, and four CH, two CH 2 , and three Me groups ( Table 2). Based on the above-mentioned data, as well as biogenetic considerations, compound 3 was suggested to be a furoeremophilane, similar to 6b-(angeloyloxy)-1a,10b-dihydroxy-9-oxofuroeremophilane [15].…”

“…more, the 13 C-NMR spectrum of 6 contained only 15 signals including those of two Me, three CH 2 , and three CH groups, as well as of seven quaternary C-atoms according to a DEPT spectrum (Table 3). Therefore, compound 6 should be made up of two identical sesquiterpenolide units [18], the two units being linked to each other through a CÀC bond containing a C 2 -axis.…”

“…The signals of a conjugated olefinic H-atom at d(H) 7.10 (dt, J ¼ 12.8, 6.4, HÀC(3), HÀC(3')) and at d(C) 138.9, 134.4, and of a C¼O group at d(C) 169.6 were also visible in the downfield part of 7. Moreover, a single olefinic C-atom signal at d(C) 129.7 (C(13)/C(13')) in the 13 C-NMR spectrum suggested that the two units were linked to each other with a C¼C bond. Additionally, the 1 H, 1 H-COSY spectrum of 7 showed correlations of HÀC(2) with HÀC(1) and HÀC(3), and of HÀC (7) with HÀC(9).…”