Stereospecific analysis of triacylglycerols rich in long-chain polyunsaturated fatty acids.
Six oils of marine, algal, and microbial origin were analyzed for stereospecific distribution of component fatty acids. The general procedure involved preparation of sn-1,2-(2,3)-diacylglycerols by partial deacylation with ethylmagnesium bromide or pancreatic lipase, separation of X-1,3- and sn-1,2(2,3)-diacylglycerols by borate thin-layer chromatography, resolution of the sn-1,2- and sn-2,3-enantiomers by chiral phase high-performance liquid chromatography following preparation of dinitrophenylurethane derivatives, and determination of the fatty acid composition by gas chromatography. Unexpected complications arose during a stereospecific analysis of triacylglycerols containing over 33% of either 20:4 or 22:6 fatty acids. The sn-1,2(2,3)-diacylglycerols made up of two long-chain polyunsaturated acids migrated with the X-1,3-diacylglycerols and required separate chiral phase resolution. Furthermore, the enzymatic method yielded sn-1,2(2,3)-diacylglycerols, overrepresenting the polyenoic species due to their relative resistance to lipolysis, but prolonged digestion yielded correct composition for the 2-monoacylglycerols. The final positional distribution of the fatty acids was established by pooling and normalizing the data from subfractions obtained by normal- and chiral-phase separation of diacylglycerols. The molecular species of X-1,3-, sn-1,2- and sn-2,3-diacylglycerol dinitrophenylurethanes were identified by chiral-phase liquid chromatography/mass spectrometry with electrospray ionization, which demonstrated a preferential association of the paired long-chain acids with the sn-1,2- and sn-2,3-diacylglycerol isomers.
Myher
J J
JJ
Banting and Best Department of Medical Research, University of Toronto, Canada.
Kuksis
A
A
Geher
K
K
Park
P W
PW
Diersen-Schade
D A
DA
D002849:Chromatography, Gas; D002851:Chromatography, High Pressure Liquid; D004075:Diglycerides / Q000032:analysis; D056890:Eukaryota; D005231:Fatty Acids, Unsaturated / Q000032:analysis*; D005395:Fish Oils / Q000032:analysis; D005989:Glycerides / Q000032:analysis; D013058:Mass Spectrometry; D009821:Oils / Q000032:analysis*; D013237:Stereoisomerism; D014280:Triglycerides / Q000032:analysis*
C011439:1,2-diacylglycerol; D004075:Diglycerides; D005231:Fatty Acids, Unsaturated; D005395:Fish Oils; D005989:Glycerides; D009821:Oils; D014280:Triglycerides