Cynasibirolide A, One New Humulanolide Sesquiterpene from Cynanchum acutum subsp. sibiricum

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.