Monoepoxy octadecadienoates and monoepoxy octadecatrienoates 2: mass spectral characterization

Methyl esters of C18 polyunsaturated fatty acids, including γ-linolenic acid, α-linolenic acid and stearidonic acid, were epoxidised using m-chloroperbenzoic acid. Nine monoepoxides were obtained by normal-phase HPLC, identified using LC–MS and NMR, and characterized by NMR spectroscopy and mass spectrometry. This study is focused on structural characterization using LC–MS and LC/APCI/MS/MS. The elution profiles of these monoepoxides in RP-HPLC are determined as 12,13- > 9,10- > 6,7-epoxy, 9,10- > 15,16- > 12,13-epoxy and 15,16- > 12,13- > 9,10-epoxy derivatives of γ-linolenic, α-linolenic and stearidonic acid methyl esters, respectively. The major diagnostic fragmentations in MS/MS identified are postulated to be induced by cleavages of the epoxide ring and α-bond cleavage to the epoxy group from [M+H]+ and/or [M+H–MeOH]+.