The electron capture negative ion chemical ionization mass spectra of 2-(4′,6′-bistrifluoromethyl-2′-pyrimidinyl)-tetrahydroisoquinoline and 4-substituted analogues

Abstract

Reaction of debrisoquine and 4-hydroxydebrisoquine with hexafluoroacetylacetone to form pyrimidinyltetrahydroisoquinolines is used as the basis for a gas chromatographic mass spectrometric assay for these two compounds. The electron impact, positive ion chemical ionization and electron capture negative ion chemical ionization mass spectra of these pyrimidinyltetrahydroisoquinolines are described and compared. The latter were found to give an intense response under electron capture negative ion chemical ionization conditions, thus allowing the development of a much more sensitive assay for debrisoquine and 4-hydroxydebrisoquine. Derivatives of the hydroxyl group in 2-(4′,6′-bistrifluoromethyl-2′-pyrimidinyl)-4-hydroxytetrahydroisoquinoline were synthesized with a view to further improving the electron capture negative ion chemical ionization response. The resulting mass spectra showed extensive fragmentation for perfluoroacyl esters and halogenated silyl ethers. Only dimethylsilyl and trimethylsilyl ethers gave similar spectral responses to the parent compound.