Soyasaponins and Related Glycosides of Desmodium canadense and Desmodium illinoense

Abstract

Seed extracts of Desmodium canadense (L.) DC., a native Canadian legume, were examined by HPLC and electrospray ionization mass spectrometry (LC/MS) for the presence of triterpenoid saponins of the oleanene type. An aqueous methanol extract, fractionated by use of a Diaion™ HP-20 macroporous resin, was found to possess soyasaponin III (soyasaponin Bb´) and the 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one conjugate of soyasaponin III (DDMP S-III) as major saponin components. Minor components were identified by LC/MS as C-24 aldehyde (sandosapogenol) derivatives, S-III al and DDMP S-III al. Soyasaponin I (soyasaponin Bb), soyasaponin VI (soyasaponin  g) and dehydro- soyasaponin I (soyasaponin Be) were also found as minor components. These components were also detected in extracts obtained by Soxhlet extraction with water followed by partitioning into n-butanol. Extracts from foliage of greenhouse and field origins were essentially free of these saponins. Soyasaponin VI was the main seed saponin of Desmodium illi- noense A. Gray whereas soyasaponin III and DDMP S-III were found as minor components. Components corresponding in molecular mass to C-22 glycosides of soyasaponin I and soyasaponin III were also detected in saponin-enriched ex- tracts. Neither species was a good source of alkaloids.