C-13-NMR ANALYSIS OF THE POSITIONAL DISTRIBUTION OF FATTY-ACIDS IN PLANT GLYCOLIPIDS

High-resolution, natural abundance C-13-NMR spectroscopy was used to analyze the positional distribution of fatty acids in the predominant plant glycoglycerolipids. Fatty acid profiles attributed spectroscopically to the sn-l and sn-2 positions were in very good agreement with the enzymatically measured distribution using a lipase from Rhizopus arrhizus. The C-13-NMR spectroscopy analysis makes use of small shift differences of the acyl carbonyl carbons. As in other lipids, in glycolipids sw-l-bound acyl carbonyls art: also shifted further downfield than the sn-2-bound carbonyls. Furthermore, in both positions the carbonyl shift depends on the distance to the nearest double bond resulting in identical series of incremental sequence shifts to higher fields from saturated to Delta 9, Delta 7 and Delta 6 double bonds, respectively. These deductions were enabled by analysis of galactolipids isolated from plants belonging to the Apiaceae and Boraginaceae, which contain high proportions of all-cis-Delta 7,10,13-hexadecatrienoic and all-cis Delta 6,9,12,15-octadecatetraenoic acid, respectively, in the sn-2 position.