Isolation and NMR-based Structural Characterization of the Major Saponins from a Chilean Landrace of Phaseolus vulgaris.

The common bean (Phaseolus vulgaris L.) is an important dietary legume and a source of triterpenoid saponins, compounds associated with both nutritional and biological activities. Despite numerous reports describing bean saponin profiles by mass spectrometry, the isolation and full structural characterization of individual saponins remain limited, particularly for landrace varieties. In this study, the major saponins present in a Chilean P. vulgaris landrace ('Azufrado') were isolated and structurally characterized. A secondary metabolite-enriched extract was prepared from bean seeds and fractionated using Sephadex LH-20 gel permeation followed by HPLC with DAD and ELSD detection for peak assignment and DAD-guided fraction collection. Six saponins were obtained and analyzed by mass spectrometry and extensive one- and two-dimensional NMR spectroscopy. Two monodesmosidic soyasaponins were identified as soyasaponin V (Ba) and soyasaponin I (Bb), both based on a soyasapogenol B aglycone. Two additional fractions contained minor DDMP-conjugated derivatives of these saponins, supported by diagnostic NMR signals and accurate mass measurements. In addition, two bidesmosidic saponins were identified as phaseoside I and sophoraflavoside I based on exact mass, fragmentation patterns, and comparison with reported data. This work provides structural confirmation of major common bean saponins and expands the chemical characterization of P. vulgaris landraces, supporting future studies on their stability, metabolism, and bioactivity.