Unexpected adduct ion formation under chemical ionization conditions

Abstract

As part of our efforts to characterize the in vivo metabolic fate of the antihypertensive agent alpha-methyldopa, we have examined the urine of alpha-methyldopa-treated rats with the aid of a direct insertion probe chemical ionization mass spectral assay. The mass spectrum of the sample obtained by chromatographic purification followed by treatment with ethanolic hydrochloric acid and pentafluoropropionic anhydride displayed an intense ion at m/z 812, consistent with the beta-ethoxy-N,O,O,O-tetrakispentafluoropropionyl derivative of 6-hydroxy-alpha-methyl-norepinephrine, a potential aromatic hydroxylation product of the known alpha-methyldopa metabolite alpha-methyl-norepinephrine. Comparison of this spectrum with the spectrum obtained with the corresponding synthetic 6-hydroxy-alpha-methylnorepinephrine, however, ruled out this possibility. A more thorough examination of the mass spectral data established that the ion at m/z 812 observed with the metabolic species was due to the formation of an unexpected adduct ion between a known metabolite of alpha-methyldopa and an impurity ion formed from a common constituent of urine. This paper summarizes the characterization of this adduct ion.

In vivo and in vitro metabolism of 3,4-(methylenedioxy)methamphetamine in the rat: identification of metabolites using an ion trap detector

“…The ketone was then demethylated by using boron tribromide in dichloromethane, according to the method of McOmie et al (41). The reaction was quenched by addition of methanol (42); subsequent evaporation yielded a dark oil. Purification of (3,4-dihydroxyphenyl)acetone was by silica gel chromatography; the elution solvent was toluene/dichloromethane/ethyl acetate (2:5:1).…”