SPHINGOLIPID BASES - A REVISITATION OF THE O-METHYL DERIVATIVES OF SPHINGOSINE - ISOLATION AND CHARACTERIZATION OF DIACETATE DERIVATIVES, WITH REVISED C-13 NUCLEAR-MAGNETIC-RESONANCE ASSIGNMENTS FOR D-ERYTHRO-SPHINGOSINE

As described by Carter et al. (J. Biol. Chem. 1951. 192: 197-207), O-m ethyl derivatives of sphingosine are formed upon acid hydrolysis of sp hingolipids in the presence of methanol. In the present study, we have isolated four O-methyl ethers of C-18-sphingosine by medium pressure liquid chromatography of their diacetate derivatives, i.e., ,4E)-1-ace toxy-2-acetamido-3-methoxy-4-octadecene, its (2S,3S) epimer, ,5R)-1-ac etoxy-2-acetamido-5-methoxy-3-octadecene, and its (2R,5S) epimer. Stru ctures were determined by physical, chromatographic, and spectral prop erties. The 5-O-methyl ethers, which were the predominant byproducts o f sphingolipid hydrolysis, were easily distinguished from the 3-O-meth yl ethers by chromatography, and all four isomers could be differentia ted by H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy. NMR analysis of the original N-acetate and diacetate samples of O-methyls phingosines I and II of Carter et al. demonstrated that they correspon d to the 5-O-methyl ethers (2R,5R and 2R,5S, respectively), with purit ies of similar to 90-99%. Resolution enhancement of the 126-MHz C-13 N MR spectra of the O-methyl ethers and D-erythro-C-18-sphingosine (Ia) afforded distinct signals for nearly all carbon atoms. C-13 NMR assign ments of carbons 7-15 were made from their lanthanide-induced shifts, and revised assignments for olefinic carbons of Ia were established ba sed upon H-1-C-13 shift correlation experiments.