As basic studies to clarify the role of glycosphigolipids and to produce new medicines from marine natural products, we have been conducting isolation, structure elucidation and synthesis of biologically active starfish glycosphigolipids. In this time, we wish to report the usefulness of FAB MS/MS (Tandem MS) spectrometry to structure elucidation of starfish glycosphingolipids. The sphingosine-type glucocerebrosides S-1-3〜5, which were isolated from the starfish Stellaster equestris, were characterized as described in Chart 1 on the basis of chemical and spectral evidences. Especially, the position of conjugated double bond in the side chain was determined from the characteristic fragments observed in the negative ion FAB MS/MS spectrum (Fig. 1) of diol derived from the native glucocerebroside. The ganglioside molecular species LG-2, which was obtained from the starfish Astropecten latespinosus, was completely methylated followed by separated with reversed phase HPLC to give a methylated major component LG-2M-5 in a pure state. The CAD spectrum originated from ceramide ion (m/z 680) in the positive ion FAB MS/MS spectrum of LG-2M-5 reveals characteristic peaks indicating the composition of ceramide moiety (Fig.2). Thus the structure of the major component in LG-2 was elucidated as shown in Chart 2. The above mentioned fragmentation due to the ceramide ion was verified from the measurements of positive ion FAB MS/MS spectra of cerebroside permethylates prepared from four known starfish cerebrosides.
