Stereochemical structures of synthesized and natural plasmalogalactosylceramides from equine brain

Modified galactosylceramide with a long-chain cy- clic acetal at the sugar moiety, plasmalogalactosylceramide, was isolated from equine brain. To identify the isomeric ste- reostructure of the natural product, the plasmalo derivative was chemically synthesized from galactosylceramide through acetalization. The presence of cyclic acetal linkage, the linked position and length of the acetal chain of the synthe- sized and natural products were determined by proton nuclear magnetic resonance spectroscopy and fast-atom bombardment-mass spectrometry, as well as gas chroma- tography-mass spectrometry and gas-liquid chromatogra- phy. The orientation of the acetal chain linked to galacto- side was characterized by connectivity between the cyclic acetal proton and ring proton(s) on the sugar moiety using the homonuclear Overhauser effect. This revealed that, of the two positional isomers of the acetal linkage with 4,6- O - acetal and 3,4- O -acetal derivatives obtained from the acetal- ization reaction, the former positional isomer, separated into two spots, was identified to 'endo'- and 'exo'-type acetal chains. In comparison to the NMR data of the synthesized derivative, equine brain acetalized lipid was found to be an 'endo'-type 4,6- O -acetal derivative.— Yachida, Y., M. Kashi- wagi, T. Mikami, K. Tsuchihashi, T. Daino, T. Akino, and S. Gasa. Stereochemical structures of synthesized and natural plasmalogalactosylceramides from equine brain. J. Lipid Res. 1998. 39: 1039-1045.