New isosteroidal alkaloids with tracheal relaxant effect from the bulbs of Fritillaria pallidiflora Schrenk.

Four new isosteroidal alkaloids, yibeinones A-D (1-4), along with four known ones, imperialine-3β-d-glucoside (5), imperialine (6), imperialine β-N-oxide (7), and dongbeinine (8), were isolated from the bulbs of Fritillaria pallidiflora. Their structures were confirmed on the basis of extensive spectroscopic analysis or comparison with the data in the literatures (known compounds). Compounds 2, 3, 4, and 6 showed an apparent concentration-dependant relaxation of isolated tracheal preparation, amongst 3 and 6 exhibited significant effects with pA2 values of 6.19 ± 0.02 and 8.41 ± 0.10, and EC50 values of 0.65 ± 0.02 μmol L(-1) and 4.40 ± 0.90 nmol L(-1), respectively.