Conversion of N-hydroxyamphetamine to phenylacetone oxime by rat liver microsomes

A Chemical Perspective of Pharmacology and Toxicology

“…Further experiments by Gerald Miwa, who was then at Merck, and by our laboratory showed that whereas NOHP indeed uncouples the CYP system with the resulting superoxide available for further oxidation, NOHAmp forms an inhibitory complex and blocks further enzymatic activity. Richard Matsumoto then demonstrated that NOHAmp is converted to OxAmp by a non-CYP enzyme (19). Collectively, we concluded that the presence of the additional alpha methyl group in phentermine sterically prevented formation of the MI complex and uncoupled the system, an unexpected specificity for what was considered to be a nonselective enzyme (21).…”

“…John Duncan, a postdoc from the UCLA biochemistry department who began protein purification procedures in the laboratory, subsequently showed that this reaction involves cytochrome P450 (CYP) (16,17). NOHP was found to undergo further oxidation to the corresponding nitro compound (NO 2 P) (18) and N-hydroxyamphetamine (NOHAmp) to phenylacetone oxime (OxAmp) (19) as determined respectively by Michael Maynard and Richard Matsumoto, who were graduate students in the lab.…”

“…Richard Matsumoto, whose graduate work mostly entailed in vitro metabolic studies (19,21), suggested that our group needed to devote more effort to relationships between these metabolic studies and PD in intact animals. He suggested that we investigate the relationship between Amp PD/PK using our bioanalytical skills.…”

N‐Oxidative Transformations ofCNGroups as Means of Toxification and Detoxification

“…Indeed, 28 was identified in rat and rabbit liver microsomal incubates of N-hydroxyamphetamine 33,35,121 . Oxime formation was NADPH/O 2 -dependent, but did not appear to involve H 2 O 2 or superoxide 35,121 . The R N-hydroxy enantiomer was converted at a faster rate than the S C form 33 .…”

“…However, the quantitative difference in conversion between the N-hydroxyamphetamine enantiomers as well as the inability of boiled enzyme to produce substantial amounts of oxime have been advocated to prove the enzymatic nature of the process 33 . The latter has been shown to be a P-450-independent reaction, since oxime formation from the hydroxylamine precursor was insensitive to the presence of CO, SKF 525A or DPEA and was unaffected by pretreatment of the animals with phenobarbital 35,121 . This finding is in accord with the observation that highly purified FMO can catalyze oxidation of primary alkylhydroxylamines to oximes 123 Oximes have been isolated along with primary hydroxylamines from incubation mixtures containing arylalkylamines 22,33,87,126 and related compounds 23 .…”