Fast atom bombardment mass spectrometry of N-acetylated neoglycolipids of the 1-deoxy-1-phosphatidylethanolamino-lactitol-type.

N-Acetylated neoglycolipids (neoGL) of the 1-deoxy-1-phosphatidylethanolamino-lactitol-type (Lac-PtdEtn) carrying lactose, sialyllactose, disialyllactose, II3sialylgangliotetraose, II3,IV3disialylgangliotetraose, lacto-N-tetraose, IV6sialyllacto-N-tetraose, lacto-N-triaose, and bloodgroup A determinant as carbohydrate moieties were synthesized either chemically or enzymatically by glycosylation or deglycosylation of the parent compounds. The neoGL were then analyzed by fast atom bombardment mass spectrometry (FAB MS) with positive (FAB(+)) and negative ion (FAB(-)) detection. The resulting spectra showed intense pseudomolecular ions and characteristic fragmentations. FAB(-) spectra of the N-acetylated Lac-PtdEtn-type neoGL showed pseudomolecular ions (M-H)- of one magnitude higher intensity compared to those from the corresponding non-acetylated compounds. The main fragment ions were obtained from successive cleavage of the sugar units, thereby indicating the monosaccharide sequence. In FAB(+) spectra of the title compounds clearly detectable pseudomolecular ions were observed. The most prominent peaks, however, were obtained from cleavage of phosphatidic acid. The N-acetyl-ethyleneamine moieties of the corresponding glycosyl-Etn-fragments most probably formed five membered rings and thereby mesomery-stabilized cations. Secondary ions resulting from loss of the respective terminal sugars demonstrated the monosaccharide sequence.

1-Deoxy-1-phosphatidylethanolamino-lactitol-type neoglycolipids serve as acceptors for sialyltransferases from rat liver golgi vesicles.

1-Deoxy-1-phosphatidylethanolamino-lactitols (LacPtdEtns), 1-deoxy-1-phosphatidylethanolamino-sialyllactitols (NeuAcLacPtdEtns) and their corresponding N-acetylated derivatives were synthesized and characterized by fast-atom-bombardment mass spectrometry (FAB MS). The neoglycolipids were used as acceptors for sialyltransferases from rat liver Golgi vesicles. Sialylation rates were as good as or even better than those obtained with the corresponding authentic acceptors lactosylceramide (LacCer) and ganglioside GM3. The sialylation of LacPtdEtns and NeuAcLacPtdEtns yielded sialyl and disialyl compounds, respectively, as shown by FAB MS analysis of the reaction products. The results of competition experiments indicate that the neoglycolipids and the authentic acceptors are sialylated by the same sialyltransferases.