*2.3. Key Diagnostic Sugar Residues in the Sea Cucumber Saponins*

Characterization of common key fragments expedited the structure elucidation of new and reported saponins. Tandem mass spectrometry analysis of saponins showed the presence of several diagnostic key fragments corresponding to certain common structural element of saponins as summarized in Table 1. Here we report a new diagnostic key fragment at *m/z* 643 corresponding to the sodiated hydrated sugar residue MeGlc-Glc-Xyl-Xyl.


**Table 1.** Key diagnostic ions in the MS<sup>2</sup> of the holothurians saponins. It has been adapted from [12] and modified.

The structures of sugar components of saponins were established by the identification of these diagnostic ions produced by tandem mass spectrometry. Observing these oligosaccharide moieties (*m/z* 493 and/or 507 and/or 511 (493 + H2O) and/or 523 and/or 643 and/or 657) simplified the characterization of the saponin structure.
