Total synthesis of 17,17,18,18-d4-iPF2α-VI and quantification of iPF2α-VI in human urine by gas chromatography mass spectrometry

Isoprostanes are a new class of natural products formed in humans as a result of free-radical-catalyzed lipid peroxidation of polyunsaturated fatty acids. These endogenous compounds are isomeric with biologically active prostaglandins and have great promise as markers of oxidant stress in vivo. iPF(2 alpha)-III (previously 8-iso-PGF(2 alpha)), an isoprostane from Class III (previously known. as Class TV), has been used as an index of free-radical-induced oxidative stress. This isoprostane is also produced by the cyclooxygenase enzymes COX1 and COX2. We are proposing a new reliable index of oxidative stress based on iPF(2 alpha)-VI (previously IPF2 alpha-I), a new Class VI isoprostane we recently discovered. The advantages of iPF(2 alpha)-VI are that it is several fold more abundant in urine than iPF(2 alpha)-III, hence allowing more accurate determinations. Equally, the proximity of the C-5 OH function to the carboxylic acid allows the formation of the lactone 35 which is easier to purify from other iPs which cannot form such lactones. We have performed the first total synthesis of d(4)-iPF(2 alpha)-VI by using two synthons, (3,3,4,4-d(4))-hexylphosphonium bromide 23 prepared from 5-hexynol and syn-anti-syn lactone 25 synthesized from D-glucose. We have developed two variants of a sensitive GC/MS assay using the synthetic d(4)-iPF(2 alpha)-VI as an internal standard to determine the levels of endogenous iPF(2 alpha)-VI in biological fluids. Quantification of iPF(2 alpha)-VI formed in vivo may be a more reliable index to assess oxidant stress in humans. (C) 1998 Academic Press.