Isolation and Structural Determination of Triterpenoid Glycosides from the Aerial Parts of Alsike Clover (Trifolium hybridum L.)

Abstract

Five azukisapogenol glycosides (1−5) have been isolated from the aerial parts of alsike clover (Trifolium hybridum L.), and their structures were elucidated by combined spectroscopic, spectrometric (1D and 2D NMR; HRESIMS, ESI−MS/MS), and chemical methods. Three of them are new compounds and were identified as 3-O-[-α-L-arabinopyranosyl(1→2)]-β-Dglucuronopyranosyl azukisapogenol (1), 3-O-[-β-D-glucuronopyranosyl(1→2)-β-D-glucuronopyranosyl]-29-O-β-D-glucopyranosyl azukisapogenol (2), and 3-O-[-α-L-arabinopyranosyl(1→2)-β-D-glucuronopyranosyl]-29-O-β-D-glucopyranosyl azukisapogenol (3). The remaining two (4, 5) are known compounds but have not been previously described as saponins constituents of the genus Trifolium. Also, azukisapogenol is reported here as a triterpenoid aglycone for the first time in this genus. Finally, the main chemotaxonomic features that may be recognized as specific of Trifolium species were discussed.