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Graphical abstract: <br>Display Omitted<br>Highlights: ► <b>Ligularia achyrotricha</b> is a traditional Tibetan medicine. ► Ligulachyroine A, a new alkaloid was isolated from the roots of <b>L. achyrotricha</b>. ► Eleven known compounds were also isolated from this species. ► Ligulachyroine A exhibited moderate activity against HL-60 and SMMC-7721 cells.<br><b>Ligularia achyrotricha</b> (Diels) Ling has been used as a traditional Tibetan herbal medicine. Ligulachyroine A (<b>1</b>), a new twelve-membered macrocyclic pyrrolizidine alkaloid with a ketonic group located at C-3 and an hydroxy group linked at C-8, was isolated from the roots of <b>L</b>. <b>achyrotricha</b>. It is particularly noteworthy that the structure of <b>1</b> rarely appears in any other naturally occurring twelve-membered macrocyclic pyrrolizidine alkaloid reported to date. Three known lignans (<b>2</b>-<b>4</b>) and eight known coniferyl and sinapyl alcohol derivatives (<b>5</b>-<b>12</b>) were also obtained in this species. Their structures were elucidated through a careful analysis of their IR, MS, and NMR spectra. Compound <b>1</b> exhibited moderate activity against HL-60 and SMMC-7721 cells.
In a search for naturally occurring antibacterial compounds in medicinal plants, six hitherto unknown thiophene acetylenes, named 10,11-threo-xanthopappin D, 10,11-erythro-xanthopappin D, 10,11-cis-xanthopappin B, 5-(but-4-chloro-3-hydroxy-1-ynyl)-2-(Z)-pent-3-ene-1-ynylthiophene, 5-(but-4-chloro-3-hydroxy-1-ynyl)-2-(E)-pent-3-ene-1-ynylthiophene, 5-(but-3,4-dihydroxy-1-ynyl)-2-(Z)-pent-3-ene-1-ynylthiophene and two furanosesquiterpenes, as well as fifteen known compounds, were isolated from Xanthopappus subacaulis, which has been used as a traditional Tibetan medicine in China. A biosynthetic pathway to thiophene acetylenes was proposed and, the isolated compounds were tested for their antibacterial activity against five bacteria. Within the series of thiophene acetylenes tested, 10,11-threo-xanthopappin D with a threo configuration exhibited strong activity against Bacillus subtilis, with a minimum inhibitory concentration (MIC) of 7.25μg/mL, whereas 10,11-erythro-xanthopappin D with erythro configuration possessed broad-spectrum antibacterial activity against Escherichia coli, Bacillus cereus, Staphylococcus aureus and Erwinia carotovora, with MICs of 12.5, 15.5, 7.25 and 7.25μg/mL, respectively. Meanwhile, the compounds 10,11-cis-xanthopappin B, xanthopappin B, 5-(but-4-chloro-3-hydroxy-1-ynyl)-2-(Z)-pent-3-ene-1-ynylthiophene and 5-(but-4-chloro-3-hydroxy-1-ynyl)-2-(E)-pent-3-ene-1-ynylthiophene substituted with a Cl atom at C-14 showed moderate inhibitory activity against E. coli, B. cereus, S. aureus, E. carotovora and B. subtilis, with MICs ranging from 31.25 to 62.5μg/mL. The structures of these compounds were elucidated through the comprehensive analysis of spectroscopic data, including UV, IR, MS and NMR.