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Facile preparation of leukotrienes C(4), D(4) and E(4) containing carbon-13 and nitrogen-15 for quantification of cysteinyl leukotrienes by mass spectrometry.

With the recent ability to use combined liquid chromatography/electrospray tandem mass spectrometry to analyze for several eicosanoids in biological samples in a single and rapid experiment, heavy isotope-labeled eicosanoids are needed as internal standards in order to quantify eicosanoid analytes. The present study describes a practical preparation of cysteinyl leukotrienes (leukotriene C(4), D(4) and E(4)) with three (13)C atoms and one (15)N atom in the cysteinyl residue. The method involves solid-phase peptide synthesis to make glutathione with heavy isotopes in the cysteinyl residue and reaction of this tripeptide with commercially available leukotriene A(4) methyl ester to give labeled leukotriene C(4) methyl ester, which is hydrolyzed to labeled leukotriene C(4). Labeled leukotriene E(4) is prepared in the same way with the use of labeled cysteine. Labeled leukotriene D(4) is prepared by treatment of labeled leukotriene C(4) with commercially available γ-glutamyl transpeptidase.