Abstract
A novel GM3 O-acetylated at C-4 and at C-9 of N-glycolylneuraminic acid (4,9-di- O-Ac GM3), together with a second GM3 O-acetylated at O-4 of the neuraminic acid and O-6 of d-galactose (4,6′-di- O-Ac GM3) were isolated from equine erythrocytes as a mixture in approximate 1:1 ratio. These two major species were chromatographically inseparable. Their structures, especially the positions of the acetoxy group(s), were determined by means of 1D- and 2D- 1H NMR and fast atom bombardment-MS as well as by gas chromatography-MS of partially O-methylated O-trimethylsilylated monosaccharides derived from the di- O-Ac GM3s. In addition, 4- O-Ac GM3 was chemically mono- O-acetylated with trimethyl orthoacetate under acidic conditions, giving exclusively 4,9-di- O-Ac GM3, the NMR and mass spectra of which were used as references to confirm the 4,9-di- O-acetylated structure of the naturally-occurring GM3.
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