Fast-atom-bombardment chemistry of sulfatide (3-sulfogalactosylceramide)

F.a.b.-m.s. of sulfatide (3-sulfogalactosylceramide, 1) in the negative-ion mode reveals the molecular weight and the presence of the sulfate ester without ambiguity. The size of the long-chain base is represented as the (M - H)- ion of the corresponding lyso-form (deacylated molecule) only when the fatty acid is alpha-hydroxylated. The spectrum in the positive-ion mode indicates the molecular weight by a pair of sodium adduct ions separated by 102 a.m.u. However, the desulfated fragment ion is not shown in the B/E-constant linked-scanning mode. If the long-chain base ion [CH2C(NH2) = CHR]+ is present, B/E-constant linked scanning confirms that the double bond is located at C-4. B/E-Constant linked scanning of the (M - H)- ions in the negative-ion mode indicates the location of a double bond in the fatty acid moiety at C-15 for the most abundant molecular species c24:1.