Characterization of three saponins from a fraction using 1D DOSY as a solvent signal suppression tool. Agabrittonosides E–F. Furostane Saponins from <i>Agave brittoniana</i> Trel. spp. <i>Brachypus</i>

Abstract

A careful NMR analysis, especially by 1D TOCSY and 1D ROESY, of a refined saponin fraction allowed us to determine the structure of three saponins from a polar extract of Agave brittoniana Trel. spp. Brachypus leaves. The use of 1D DOSY for the suppression of the solvent signal was useful to obtain the chemical shifts of anomeric signals. A full assignment of the (1)H and (13)C spectral data for the new saponins, agabrittonosides E-F (1-2) and the well-known Karatavioside C (3) and their methoxyl derivatives, is reported. The structures were established using a combination of 1D and 2D ((1)H, (1)H-COSY, TOCSY, ROESY, g-HSQC, g-HMBC and g-HSQC-TOCSY) NMR techniques and ESI-MS. In addition, the methoxylation of these furostane saponins in the presence of MeOH was studied.