Unusual sesquiterpene lactones with a new carbon skeleton and new acetylenes from Ajania przewalskii

Four new compounds, a noreudesmanolide (1), a guaianolide (4), and acetylenes (7–8), together with 16 other known compounds, were isolated from Ajania przewalskii. The novel sesquiterpenolide (1) possesses a rare carbon skeleton. Acetylation of 1 gave 1a. New compounds were elucidated as 1β-hydroxyl-2-noreudesm-4(15)-en-5α,6β,7α,11αH-12,6-olide (1), 1β-acetoxyoxyl-2-noreudesm-4(15)-en-5α,6β,7α,11αH-12,6-olide (1a), 8α-angeloyloxyl-3α,4α-dihydroxyguaia-1,9,11(13)-trien-6,12-olide (4), (E)-3β,4α-dihydroxyl-2-(2′,4′-hexadiynylidene)-1,6-dioxaspiro[4,5]decane (7) and 2-hydroxyl-2-[(E)-1α,2β,3-trihydroxyl-3-nonaene-5,7-diyne]-4H-pyran (8), by chemical and spectroscopic methods, including HRESIMS, 1D and 2D NMR. Cytotoxicity of nine compounds was assessed by their effects on selected cancer cell lines, K562, K562/ADM, BGC-823, and Hep-G2 cells. Phenolic acid 12 exhibited strong activity against K562 and K562/ADM cells and sesquiterpenolide 3 strong activity against K562/ADM cells. Radical-scavenging activities of 12 compounds, the mixed solvent extract (petrol ether–ether–methanol = 1:1:1), and the n-butanol extract were determined by ABTS and DPPH radical-scavenging assays. Phenols and coumarins (11–16), MSE, and n-BE displayed significant antioxidation (IC50 < 20 μg/ml).