Cynasibirolide A (1), one new humulanolide sesquiterpene, together with four known analogs, asteriscanolide (2), (1S,8S)‐8‐hydroxyhumula‐2Z,6E,9E‐trien‐1,12‐olide (3), (1S,7R)‐8‐oxohumula‐2Z,9E‐dien‐1,12‐olide (4), and (+)‐6,7,9,10‐tetrahydroasteriscunolide (5) were isolated from the roots and rhizomes of Cynanchum acutum subsp. sibiricum. Their structures and configurations were elucidated by spectroscopic methods, including 2D‐NMR techniques, and the structure of 1 was confirmed by single‐crystal X‐ray diffraction. All compounds were evaluated for their anti‐complementary activity in vitro, and compound 3 exhibited anti‐complement effect with CH50 value of 0.45 mM.
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Luo et al. (2023) studied this question.