FAST-ATOM-BOMBARDMENT TANDEM MASS-SPECTROMETRY OF THE ANTIPARASITIC AGENT PENTAMIDINE AND ITS OXYGENATED METABOLITES

Although pentamidine (1,5-bis(4'-amidinophenoxy)pentane) is currently in use for the treatment of a variety of parasitic infections, includi ng acquired immune deficiency syndrome-related Pneumocystis carinii pn eumonia, its metabolism is still under investigation. Positive-ion fas t atom bombardment mass spectrometry was used with high-energy collisi on-activated dissociation (CAD) and linked scanning at constant BIE to obtain tandem mass spectra of protonated molecules of pentamidine and seven synthetic oxygenated derivatives, which are known metabolites o f pentamidine. Charge-initiated fragmentation produced abundant fragme nt ions of m/z 120 and 137 and loss of neutral ammonia from the proton ated analyte that characterized the amidinophenoxy group. The structur es of isomeric 2-hydroxypentamidine, 3-hydroxypentamidine and N-hydrox ypeotamidine could be distinguished based on charge-remote fragmentati on that produced a series of fragment ions of the pentyl chain and per mitted the exact location of the hydroxyl group in each molecule to be determined Next, tandem mass spectra were obtained and the charge-ini tiated and charge-remote fragmentation discussed for four other metabo lites of pentamidine, including N,N'-dihydroxypentamidine, 5-(4'-amidi nophenoxy)pentanoic acid, 5-(4'-amidinophenoxy) pentan-1-ol, and p-hyd roxybenzamidine. Finally, tandem mass spectrometry was used to identif y pentamidine and three pentamidine metabolites contained in high-perf ormance liquid chromatographic (HPLC) fractions from rat Liver perfusa te and rat urine following treatment with pentamidine. Pentamidine met abolites identified in rat urine sad liver perfusate using mass spectr ometry and HPLC retention times included 2-hydroxypentamidine, 3-hydro xypentamidine and 5-(4'-amidinophenoxy)pentanoic acid.