title: Contribution of artifacts to N-methylated piperazine cyanide adduct formation in vitro from N-alkyl piperazine analogs.
abstract: In the liver microsome cyanide (CN)-trapping assays, piperazine-containing compounds formed significant N-methyl piperazine CN adducts. Two pathways for the N-methyl piperazine CN adduct formation were proposed: 1) The α-carbon in the N-methyl piperazine is oxidized to form a reactive iminium ion that can react with cyanide ion; 2) N-dealkylation occurs followed by condensation with formaldehyde and dehydration to produce N-methylenepiperazine iminium ion, which then reacts with cyanide ion to form the N-methyl CN adduct. The CN adduct from the second pathway was believed to be an artifact or metabonate. In the present study, a group of 4'-N-alkyl piperazines and 4'-N-[¹³C]methyl-labeled piperazines were used to determine which pathway was predominant. Following microsomal incubations in the presence of cyanide ions, a significant percentage of 4'-N-[¹³C]methyl group in the CN adduct was replaced by an unlabeled natural methyl group, suggesting that the second pathway was predominant. For 4'-N-alkyl piperazine, the level of 4'-N-methyl piperazine CN adduct formation was limited by the extent of prior 4'-N-dealkylation. In a separate study, when 4'-NH-piperaziens were incubated with potassium cyanide and [¹³C]-labeled formaldehyde, 4'-N-[¹³C]methyl piperazine CN-adduct was formed without NADPH or liver microsome suggesting a direct Mannich reaction is involved. However, when [¹³C]-labeled methanol or potassium carbonate was used as the one-carbon donor, 4'-N-[¹³C]methyl piperazine CN adduct was not detected without liver microsome or NADPH present. The biologic and toxicological implications of bioactivation via the second pathway necessitate further investigation because these one-carbon donors for the formation of reactive iminium ions could be endogenous and readily available in vivo.
authors: Drug Metabolism and Pharmacokinetics, AstraZeneca Pharmaceuticals, 35 Gatehouse Dr., Waltham, MA 02451, USA. minli.zhang@AstraZeneca.com
authors: Minli
authors: M
authors: Zhang
authors: Christina M
authors: CM
authors: Resuello
authors: Jian
authors: J
authors: Guo
authors: Mark E
authors: ME
authors: Powell
authors: Charles S
authors: CS
authors: Elmore
authors: Jun
authors: J
authors: Hu
authors: Karthick
authors: K
authors: Vishwanathan
mesh_terms: D000478:Alkylation; D016477:Artifacts; D002853:Chromatography, Liquid; D003486:Cyanides / Q000737:chemistry* / Q000378:metabolism; D013058:Mass Spectrometry; D008861:Microsomes / Q000378:metabolism; D000077489:Piperazine; D010879:Piperazines / Q000737:chemistry* / Q000378:metabolism
chemical_list: D003486:Cyanides; D010879:Piperazines; D000077489:Piperazine