A new procedure for synthesis of 3-keto derivatives of sphingolipids and its application for study of fatty acid composition of brain ceramides and cerebrosides containing dihydrosphingosine of sphingosine

3-Keto derivatives were prepared in good yield by the oxidative procedure with 2,3-dichloro-5,6-dicyanobenzoquinone from N-acetyl sphingosine, N-palmitoyl sphingosine, N-lignoceroyl sphingosine, and N-lignoceroyl psychosine. None of these 3-keto derivatives, except the one from N-acetyl sphingosine, have been previously reported. Ceramides were isolated from a calf brain and reacted with 2,3-dichloro-5, 6-dicyanobenzoquinone. Ceramides containing sphingosine (4-sphingenine) were converted to 3-keto derivative, while those containing dihydrosphingosine (sphinganine) remained intact under these conditions. The 3-keto ceramides were then separated from the ceramides containing dihydrosphingosine by preparative thin layer chromatography. Similarly cerebrosides from the same calf brain were oxidized and fractionated to 3-ketocerebrosides (from cerebrosides containing sphingosine) and unreacted cerebrosides (cerebrosides containing dihydrosphingosine). The fatty acid composition of these four sphingolipids were determined. Both the ceramides and the cerebrosides containing sphingosine had more unsaturated fatty acids than the corresponding dihydrosphingosine-containing compounds. The ratio of C₁₆-C₂₀ fatty acids to C₂₂-C₂₆ acids was higher in the ceramides containing sphingosine than in ceramides containing dihydrosphingosine, while the ratio was reversed in cerebrosides. The possible precursor-product relationship among these lipids is discussed.