Structure-activity relationships for Saponins from Allium hirtifolium and Allium elburzense and their antispasmodic activity

A phytochemical study of Allium hirtifolium Boiss flowers has led to the isolation of high amounts of six new furostanol and spirostanol saponins, named hirtifoliosides A1/A2 (1a/1b), B(2), C1/C2 (3a/3b), and D (4) along with three known spirostanol saponins, alliogenin 3-O-beta-D-glucopyranoside, gitogenin 3-O-beta-D-glucopyranosyl-(1 -> 4)-O-beta-D-glucopyranoside, and agapanthagenin 3-O-beta-D-glucopyranoside. High concentrations of the following known flavonol glycosides have been isolated from both flowers and bulbs: kaempferol 3-O-beta-D-rhamnopyranosyl-(1 -> 2)-glucopyranoside, kaempferol 3-O-beta-D-glucopyranosyl-(1 -> 4)-glucopyranoside, kaempferol 3-O-glucopyranoside, kaempferol 7-O-glucopyranoside. The isolated saponins along with the four saponins elburzensosides A1/A2 and C1/C2 and the sapogenin agapanthagenin, previously described from A. elburzense, have been subjected to biological assays for evaluating possible antispasmodic activity in the guinea-pig isolated ileum. The obtained results served as a basis for the establishment of structure-activity relationships within this class of antispasmodic agents. They highlight the positive effects of a hydroxyl group at position 5 and of a glucose unit at position 26 and demonstrate the detrimental effects of both a hydroxyl group at position 6 and of a glucose unit at position 3. Among the tested compounds, elburzensosides C1/C2 and agapanthagenin showed the highest activity in reducing induced contractions as measured by the reduction of histamine release by about 50%. The observed effect therefore contributes to the explanation of the traditional use of onion and garlic in the treatment of disturbances of the gastrointestinal tract.