Advances in structural determination of saponins and terpenoid glycosides

Saponins and triterpenoid glycosides are polar constituents of plants many of which exhibit a broad spectrum of biological activities. They often occu r as intricate mixtures difficult to separate by conventional procedures. I mprovements in liquid chromatographic techniques and availability of new ma trices have improved the possibility of purifying even the isomeric saponin s. The application of newer isolation and purification processes are illust rated in the present review with examples both from the literature and from the reviewers laboratories. Advances in mass spectrometry, for example tan dem mass spectrometry, offer considerable advantages in structure determina tion of complex saponins, and their use has been illustrated. The major str uctural information however comes from NMR spectra. Due to the complex stru ctures, interpretation of NMR spectra recorded even with high field instrum ents is not easy. The present review summarizes the available 2D NMR techni ques particularly HMBC, NOESY and HOHAHA for simplifying spectral interpret ation with suitable examples. In special cases, use of molecular mechanics and molecular dynamics studies of structure leads to valuable information o n conformation of molecules. Their application was found to be of considera ble advantage for saponins possessing polysubstituted monosaccharides.