Cycloartane and Oleanane Saponins from Astragalus sp

Astragalus spp. (Leguminosae) represent a valid rural crop of ecological importance in many countries, and some species serve as foodstuffs and pharmaceutical emulsifiers. Astragalus species are used in Chinese traditional medicine as antiperspirant, antihypertensive, antidiabetic, diuretic and tonic. The pharmacologically active constituents of theseAstragalus are of two different types, polysaccharides and saponins, and the most interesting pharmacological properties are hepatoprotective, immunostimulant and antiviral. Astragalus species are a source of cycloartane type saponins, derived from cycloartenol by oxidation at C-6, C-16, C-20, C-23, C-24, followed by possible ring closures with the formation of a 20,24-epoxide (cycloastragenol or cyclogalegenin) or a 20,25-epoxide, or a 16,24-20,24- diepoxide (cycloalpigenin), or a 16,23-16,24-diepoxide (cycloorbigenin B). Approximatively 100 saponins mainly derivatives of the 20(R),24(S) form of cycloastragenol [3β,6α,25-tetrahydroxy-20(R),24(S)-epoxy-9,19-cyclolanostane], (astragalosides or astraversianins), and more rarely of the 20(S), 24(R) form (cyclogalegenin), have been isolated. Some species also contain trihydroxyolean-12-ene saponins. Details on the isolation, purification and structural elucidation, along with recent results on the pharmacological properties of Astragalus cycloartane and oleanane saponins, will be discussed.