Key fragments for identification of positional isomer pair in glucuronidesfrom the hydroxylated metabolites of RT-3003 (Vintoperol) by liquid chromatography/electrospray ionization mass spectrometry

The mass spectral properties of glucuronides of the 9- and 10-hydroxylated metabolites of RT-3003 (Vintoperol; (-)-1 beta-ethyl-1 alpha-hydroxymethyl- 1,2,3,4,6,7,12b alpha-octahydroindolo[2,3-a]quinolizine), which were fracti onated by high-performance liquid chromatography with fluorescence detectio n, were investigated using: the positive ion electrospray ionization mode. These glucuronides showed predominantly the protonated molecular ion ([M H](+) ion), and the [M + H](+) ion provided a characteristic product ion sp ectrum in which abundant ions were obtained at m/z 301, 160 and 142, The fi rst ion, corresponding to the [aglycone + H](+) ion, was produced by neutra l loss of the glucuronic acid moiety from the [M + H](+) ion. The product i on spectrum of the [M + H](+) ion of hydroxy-RT-3003 revealed a number of i ons common to the glucuronide spectra, suggesting that other two ions obser ved most likely represent fragmentation of hydroxy-RT-3003, In turn, these glucuronides were positional isomers with respect to the binding site of gl ucuronic acid. The structures of the isomer pairs were discriminated by the presence of the ion of m/z 318 or 336 in the product ion spectrum. These i ons were produced by fission of the C-ring, the same as for the formation o f the ions of m/z 160 and 142, as were observed in the product ion spectrum from the [M + H](+) ion of hydroxy-RT-3003. For the formation of these ion s, an unusual fragmentation process was proposed, and these ion structures were supported by evidence from the accurate mass measurement data. Additio nally, in the sulfates of hydroxylated metabolites, a similar product ion c orresponding to the ion of m/z 336 found in the phenolic glucuronides was o bserved, and was applied for identification of the sulfate metabolites. Cop yright (C) 1999 John Wiley & Sons, Ltd.