Mass spectrometry of fatty acids with methylene-interrupted ene-yne systems

When crepenynic acid and octadec-14-yn-17-enoic acid were converted to 4,4-dimethyloxazoline (DMOX) derivatives by the usual procedure. considerable isomerization occurred. The former was converted in part to 7-(5-pentyl-cyclohexadienyl)-heptadecanoate, as was confirmed by mass spectrometry, including preparation of a Diels-Alder adduct with 4-methyl-1,2,4-triazoline-3,5-dione. A mild procedure for preparation of dimethyloxazoline derivatives was therefore developed that did not cause such artefact formation. The mass spectra of the dimethyloxazoline and picolinyl ester derivatives of the two acids are described. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.