IDENTIFICATION OF 11-DEHYDRO-2,3-DINORTHROMBOXANE B-3 IN HUMAN URINE BASED ON THE MASS-SPECTRAL PROPERTIES OF 11-DEHYDROTHROMBOXANE B-3 ANDRELATED-COMPOUNDS

11-Dehydro-2,3-dinorthrombaxane B-3 (an enzymatic metabolite of TXB(3) ) was identified, Urine from a healthy male adult who had received dai ly administration of 1.8 g (0.6 g three times) of eicosapentaenoic aci d (EPA) ethyl ester was collected, A urine sample was extracted with a n affinity column of anti-11-dehydro-TXB(2) monoclonal antibody. Conve rsion of 11-dehydro-2,3-dinor-TXB(3) in the urine extract into the met hyl ester (ME)-11-n-propylamide (PA)-9, 12, 15-dimethylisopropylsilyl (DMIPS) ether derivative was followed by gas chromatography with selec ted-ion monitoring (GC/SIM) (resolution: 8000) and GC/mass spectrometr y (MS), High-resolution SIM result revealed that a major component cor responded to the [M - C3H7](+) (m/z 668.4198) ion, which may be specif ic for the structural integrity by analogy with the corresponding 11-d ehydro-TXB(3) derivative, Conventional GC/MS analysis confirmed that t he peak of the interest was the title compound, The mass spectrum of t he 11-dehydro-2,3-dinor-TXB(3) ME-PA-DMIPS ether derivative was domina ted by the ions of [M - CH3](+) (m/z 696) and [M - C3H7](+) (m/z 668, base peak) and ions containing a protected 11-carboxylic acid moiety t ogether with the unidentified additional ions which were considered to derive from urinary endogenous substances, However, the quality was s ufficient for use for mass spectral identification of 11-dehydro-2,3-d inor-TXB(3), the beta-oxidation product of 11-dehydro-TXB(3). Characte ristic fragment ions of [M - C5H9-(dimethylisopropylsilanol)(8)](+) (m /z 524 and 406) yielding information about the position of the incorpo rated double bond were prominent, the same as the corresponding ions f ound in the mass spectrum of the 11-dehydro-TXB(3) derivative. Consequ ently, the fragmentation products were closely related to those of the 11-dehydro-TXB(3) derivative, except for an obvious shift produced by the lack of C-2/C-3 hydrocarbon units. The results demonstrate the en dogenous formation of TXA(3) in humans after administration of EPA eth yl ester and excretion of 11-dehydro-2,3-dinor-TXB(3) into urine as on e of the enzymatic metabolites of TXB(3), together with the previously reported 11-dehydro-TXB(3).