Two novel isosteroid alkaloids from Fritillaria monatha

Two new isosteroid alkaloids, N-methyl-22,26-imino-13,22-oxido-5α,20α-jervine-3β-ol-6-one, pengbeimine B (1) and N-methyl-22,26-imino-13,22-oxido-5α,20β-jervine-3β-ol-6-one, pengbeimine D (2) were isolated from the fresh bulbs of Fritillaria monatha Migo. Their structures were determined by spectral methods, and were proved by X-ray diffraction.