Complete NMR assignments of undegraded asterosaponins from Asterias amurensis

Four asterosaponins, thornasteroside A (1), versicoside A (2), anasteroside B (3), and asteronylpentaglycoside sulfate (4), were isolated from the predatory starfish Asterias amurensis Lutken. Unlike previous studies focusing on structure elucidation by degradation of the complex saponin molecules, complete nuclear magnetic resonance (NMR) assignment for the intact molecules was accomplished using 600 MHz high magnetic field NMR. The complete set of NMR assignments can help in the structure elucidation of asterosaponins isolated in low yields without resorting to chemical degradation. Furthermore, this approach can be extended to other complex steroidal saponins, which may accelerate the discovery of bioactive secondary metabolites from this invasive starfish species.