Benzazepine metabolism revisited. Evidence for the formation of novel amine conjugates.

Three novel metabolites of the benzazepine SK&F 86466 (6-chloro-2,3,4,5-tetrahydro-3-methyl-1H-3-benzazepine) have been isolated from dog urine and characterized by tandem mass spectrometry, using fast atom bombardment and thermospray ionization, and 1H and 13C NMR spectroscopy. The parent drug undergoes oxidation to yield an N-oxide or N-demethylation to yield the primary metabolite SK&F 101055 (6-chloro-2,3,4,5-tetrahydro-1H-3-benzazepine). This desmethyl metabolite then undergoes N-sulfoconjugation to yield 6-chloro-2,3,4,5-tetrahydro-1H-3-benzazepine-3-N-sulfonate. Two glucuronide conjugates derived from the desmethyl metabolite were also isolated and characterized. One glucuronide is formed from an intermediate carbamic acid, formally derived from the addition of CO2 to the desmethyl benzazepine. A second glucuronide is derived from an intermediate hydroxylamine metabolite. Methodology for characterizing the carbamyl glucuronide was developed, using an ethanolysis reaction to give a stable ethyl carbamate derivative that can then be characterized by GC-MS. This methodology should prove useful in establishing whether such carbamylation reactions occur with other amines.