Two new steroidal saponins from Allium macrostemon

: Two new steroidal saponins, macrostemonoside A and D, were isolated from the bulbs of Allium macrostemon Bung (Chinese name as Xie bai), a Traditional Chinese Medicine used for the treatment of myocardial infarction. Their structures were established as tigogenin-3-O-beta-D-glucopyranosyl(1-->2) [beta-D-glucopyranosyl(1-->3)1]-beta-D-glucopyranosyl(1-->4)-beta-D- galactopyranoside (1) and tigogenin-3-O-beta-D-glucopyranosyl(1-->2)[beta-D-glucopyranosyl (1-->3)(6-O-acetyl-beta-D-glucopyranosyl)] (1-->4)-beta-D-galactopyranoside (2) by spectral and chemical evidences. 1 showed remarkable inhibitory effect on rabbit platelet aggregation induced by ADP in vitro (IC50 = 0.065 mmol).