MODEL COMPOUNDS FOR PLASMALOGLYCOLIPIDS - PREPARATION OF LONG-CHAIN CYCLIC ACETALS OF METHYL BETA-D-GALACTOPYRANOSIDE AND DETERMINATION OF THEIR REGIOCHEMISTRY AND STEREOCHEMISTRY BY PROTON NMR

Plasmalopsychosines and plasmalocerebrosides comprise a novel class of human brain glycosphingolipids consisting of long chain fatty aldehyd es conjugated to the galactose moiety of psychosine or cerebroside via cyclic acetal linkages. In order to clarify questions concerning the detailed stereochemistry of the acetal linkages in the natural lipids, model compounds having a simplified aglycone were synthesized. Methyl beta-D-galactopyranoside was condensed with 1,1-dimethoxyhexadecane i n the presence of p-TsOH to give a mixture of stereoisomeric cyclic ac etals. After acetylation, the mixture of acetals was separated by HPLC and the structure of each isomer was established by 1-D NOE experimen ts. By comparison of NMR data from the model compounds with spectra of synthetic plasmalopsychosines it was possible to determine the stereo chemistry of the acetal chains in the latter, and, by extension, their stereochemistry in the natural lipids.