Isolation and structural elucidation of steroid oligoglycosides from the starfish Asterias rubens by means of direct online LC-NMR-MS hyphenation andone- and two-dimensional NMR investigations

LC-NMR-MS hyphenation has been applied in the screening of an asterosaponin subfraction obtained from the starfish Asterias rubens for unknown compoun ds. The suitability of this technique for characterizing compounds in the m olecular weight range of 1200 to 1400 a.m.u, has been demonstrated. The add itional information concerning the number of exchangeable protons provided by the LC-NMR-MS experiment proved to be particularly valuable for the stru ctural elucidation. The LC-NMR-MS screening indicated the presence of hithe rto unknown asterosaponins in the sample. Based on this information, four n ew compounds (ruberosides A-D; 2-4 and 6) have been isolated and their stru ctures have been elucidated using one- and two-dimensional NMR techniques. A minor component has tentatively been assigned the structure 5.