Novel marine flagellate fatty acid: structural elucidation by GC-MS analysis of DMOX derivatives and DMDS adducts.

Abstract

In situ biodegradation experiments of marine particles were performed in deep Atlantic waters. Lipid changes were associated with the colonization of the decaying detritus by marine flagellates smaller than 10 microm in size. Fatty acid methyl esters (FAMEs) of these flagellates showed high proportion of a FAME with a molecular weight (MW) of 320. Its structure could not be unambiguously resolved by retention times on gas chromatography runs using polar and nonpolar columns, nor by routine gas chromatography coupled to mass spectrometry (GC-MS). Complementary GC-MS analysis of two types of derivatives was performed to fully elucidate the structure of this novel acid. GC-MS analysis of 4,4-dimethyloxazoline (DMOX) derivative of the compound enabled localization of a double bond in position Delta17, whereas other double bond locations could not be unambiguously located by spectrum interpretation. DMDS addition on the flagellate biomarker produced monocyclic triadducts. Fragment suites corresponding to gradual losses of thiomethyl substituents indicated the presence of a five-membered thioether cycle, located on the methyl side of the derivative. Fragment suites produced by cleavage of C linked to sulfured substituents revealed various possible structures. However, interpretation of the spectra in relation with the fragmentation of the DMOX derivative yielded a convergent identification of the flagellate biomarker, as a non-methylene-interrupted C20:3Delta7,13,17 FAME.