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

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-d-glucuronopyranosyl 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.