Characterization of novel mono-O-acetylated GM3s containing 9-O-acetyl sialic acid and 6-O-acetyl galactose in equine erythrocytes.

Novel mono-O-acetylated GM3s, one containing 9-O-acetyl N-glycolyl neuraminic acid and another containing 6'-O-acetyl galactose, were isolated as a mixture from equine erythrocytes, and the structures were characterized by one- and two-dimensional proton nuclear magnetic resonance (NMR) and fast atom bombardment-mass spectrometry (FAB-MS). The position of the O-acetyl residue was identified by the downfield shift of the methylene protons at C-9 of N-glycolyl neuraminic acid (9-O-Ac GM3) and C-6 of galactose (6'-O-Ac GM3) in the NMR spectrum, in comparison to the respective non-acetylated counterparts. To confirm the presence of 6'-O-Ac GM3, the O-acetylated GM3 mixture was desialylated with Arthrobacter neuraminidase, giving 6-O-acetyl galactosyl glucosylceramide, the structure of which was estimated by NMR and FAB-MS, together with non-acetylated lactosylceramide with a ratio of 1:1.