Fast atom bombardment tandem mass spectrometry of the anti‐parasitic agent pentamidine and its oxygenated metabolites

Abstract

Although pentamidine (1,5bis(4'-amidinophenoxy)pentane) is currently in use for the treatment of a variety of parasitic infections, including acquired immune deficiency syndrome-related Pneumocystis carinii pneumonia, its metabolism is still under investigation. Positive-ion fast atom bombardment mass spectrometry was used with highenergy collision-activated dissociation (CAD) and linked scanning at constant B/E to obtain tandem mass spectra of protonated molecules of pentamidine and seven synthetic oxygenated derivatives, which are known metabolites of pentamidine. Charge-initiated fragmentation produced abundant fragment ions of m/z 120 and 137 and loss of neutral ammonia from the protonated analyte that characterized the amidinophenoxy group. The structures of isomeric Zhydroxypentamidine, 3-hydroxypentamidine and N-hydroxypentamidine could be distinguished based on charge-remote fragmentation that produced a series of fragment ions of the pentyl chain and permitted the exact location of the hydroxyl group in each molecule to be determined. Next, tandem mass spectra were obtained and the charge-initiated and charge-remote fragmentation discussed for four other metabolites of pentamidine, including N,N-dihydroxypentamidine, 5-(4'-amidinophenoxy)pentanoic acid, 5-(4'-amidinophenoxy) pentan-1-01, and p-hydroxybenzamidine. Finally, tandem mass spectrometry was used to identify pentamidine and three pentamidine metabolites contained in high-performance liquid chromatographic (HPLC) fractions from rat liver perfusate and rat urine following treatment with pentamidine. Pentamidine metabolites identified in rat urine and liver perfusate using mass spectrometry and HPLC retention times included Zhydroxypentamidine,

Anti- Pneumocystis Activities of Aromatic Diamidoxime Prodrugs

“…1A confirm previous observations that rat liver homogenates reduce the diamidoxime (compound 1) of pentamidine, forming the monoamidine-monoamidoxime (compound 9) and smaller quantities of the diamidine, pentamidine (compound 2). The metabolites have previously been identified by mass spectrometry (16,52) and were confirmed in the present study by coelution with authentic standards.…”

“…Although synthetic standards were not available for the monoamidine-monoamidoxime derivatives of compounds 3, 5, and 7, the relative retention times of the chromatographic peaks are entirely consistent with those predicted for the monoamidoxime derivatives. Most monoamidine-monoamidoxime derivatives have been difficult to synthesize and to analyze by mass spectrometric methods developed to characterize pentamidine metabolites (7,16,52). Positive identification of these putative metabolites must await successful development of new synthetic and analytical approaches.…”

Applications and mechanisms of charge-remote fragmentation

“…Furthermore, they also proposed a mechanism for its function in the biosynthesis of abierixin and nigericin. Van Breemen et al (1995) employed FAB-MS/MS to determine the structures of the anti-parasitic pentamidine and its metabolites. Because the amidino groups have high proton af®nities, the [M H] ion of pentamidine was produced, and CA of this ion causes charge-remote fragmentation along the alkyl chain (Fig.…”