Abstract
Modified galactosylceramide with a long-chain cyclic acetal at the sugar moiety, plasmalogalactosylceramide, was isolated from equine brain. To identify the isomeric stereostructure 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 synthesized and natural products were determined by proton nuclear magnetic resonance spectroscopy and fast-atom bombardment-mass spectrometry, as well as gas chromatography-mass spectrometry and gas-liquid chromatography. The orientation of the acetal chain linked to galactoside 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 acetalization 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.
Highlights
Modified galactosylceramide with a long-chain cyclic acetal at the sugar moiety, plasmalogalactosylceramide, was isolated from equine brain
The presence and chain length of fatty aldehyde have been determined by gas chromatography–mass spectrometry (GC–MS) as an enol methyl ether derivative
The structures of N-1 and O -acylated GalCers were determined by nuclear magnetic resonance spectroscopy (NMR), MS, and gas–liquid chromatography (GLC) as described below (MS and GLC data not shown for the N-1)
Summary
Modified galactosylceramide with a long-chain cyclic acetal at the sugar moiety, plasmalogalactosylceramide, was isolated from equine brain. The orientation of the acetal chain linked to galactoside 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-Oacetal and 3,4-O-acetal derivatives obtained from the acetalization reaction, the former positional isomer, separated into two spots, was identified to ‘endo’- and ‘exo’-type acetal chains. PlasmaloGSLs, which are conjugated with a long-chain fatty aldehyde at the sugar moiety and reported to form a cyclic acetal linkage exclusively on galactose, have recently been isolated from normal human brain as novel modified GSLs [16, 17]. We describe isolation of plasmaloGalCer from equine brain, its synthesis and identification of its stereochemical structure
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