Mild method for preparation of 4,4-dimethyloxazoline derivatives of polyunsaturated fatty acids for GC-MS.

A mild and convenient method has been developed for preparing 4,4-dimethyloxazoline (DMOX) derivatives of fatty acids for GC-MS analysis. First, fatty acid methyl esters are converted to corresponding amides by incubation overnight at room temperature with 2-amino-2-methyl-1-propanol and a catalytic amount of sodium methoxide. The resulting 2-(methylpropanol) amides were isolated by partition between hexane-diethyl ether and water, and then converted to 4,4-dimethyloxazoline derivatives by treatment with trifluoroacetic anhydride under mild conditions (50 °C for 45 min). Structures of 2-methylpropanol amide and a DMOX derivative of oleic acid were confirmed by GC-MS. This method was applied to different FAME prepared from animal, plant or microbial lipids. The suggested method is most suitable for structure analysis of polyunsaturated fatty acids (PUFA) and for acids with double bonds in close to terminal positions. Application of the method is illustrated with spectra of the DMOX derivatives of 16:1(n-13), 24:5(n-6) and 24:6(n-3) acids.