Three new oplopane sesquiterpenes, knorringianalarins D - F (1 - 3, respectively), and five known analogues (4 - 8, respectively), were isolated from the roots and rhizomes of Ligularia knorringiana. The structures of three new compounds were identified as 4-acetoxy-11α,12-epoxy-2β-hydroxy-3β-(2-methylbutyryloxy)-9α-(4-methylsenecioyloxy)oplop-10(14)-ene (1), 3β,4-diacetoxy-9α-(4-acetoxy-4-methylsenecioyloxy)-11α,12-epoxy-8α-(2-methylbutyryloxy)oplop-10(14)-ene (2), and (1R,5R,6R,7R,9R)-5,9,11-trihydroxy-4,15-dinoroplop-10(14)-en-3-one (3) based on spectroscopic methods including 1D- and 2D-NMR, mass spectrometry, and CD spectroscopy techniques. All compounds were evaluated for their anti-complementary activity on the classical pathway of the complement system in vitro. Among which, three oplopane sesquiterpenes (3, 7, and 8) exhibited better anti-complementary effects with CH values ranging from 0.33 to 0.89 mm, which are plausible candidates for developing potent anti-complementary agents.

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A new eremophilanolide sesquiterpene, 1α,6β,10β-trihydroxyeremophila-7(11),8-dien-12,8-olide (macrophyllalarin A, 1), and along with 5 known eremophilanolide sesquiterpenes, 6α,10β-dihydroxyeremophila-7(11)-en-12,8-olide (2), 8β-hydroxyeremophila-7(11)-en-12,8α(15,6α)-diolide (3), 6α,15β-epoxy-8β-hydroxyeremophila-7(11)-en-8α,12-olide (4), 6β,10α-dihydroxy-1-oxo-eremophila-7(11),8-dien-8,12-olide (5), and 1β,10-epoxy-6β,8β-dihydroxyeremophila-7(11)-en-8α,12-olide (6), were isolated from the roots and rhizomes of Ligularia macrophylla. The structure of the new compound was identified by comprehensive spectral analysis.