Re-characterization of three conjugated linolenic acid isomers by GC-MS and NMR

Conjugated linolenic acids (CLN) refer to a group of octadecatrienoic acids with three conjugated double bonds. Minor positional and geometrical differences among CLN isomers make their separation and identification difficult. We have used GC-MS and NMR to study three common CLN isomers namely alpha-eleostearic acid, beta-eleostearic acid and punicic acid, finding that some signals of olefinic carbon atoms in NMR spectra were mistakenly assigned in the literature. The present study was therefore undertaken to re-characterize the location of C=C double bonds and assign the chemical signals of proton and carbon atoms using H-1 NMR, C-13 NMR, H-1-H-1 two-dimensional correlation spectra (H-1-H-1 COSY) and C-13-H-1 two-dimensional correlation spectra (C-13-H-1 COSY). The geometrical structure of double bonds in these three CLN isomers was identified using homonuclear decoupling technique. (c) 2006 Elsevier Ireland Ltd. All rights reserved.