title: Characterization of in vitro metabolites of the antipsychotic drug tiospirone by mass spectrometry.
abstract: Metabolism of the antipsychotic drug tiospirone was studied in vitro with phenobarbital-induced rat liver microsomes. Metabolites were isolated and purified to homogeneity by high-performance liquid chromatography. It was possible to characterize the metabolites as trimethylsilyl (TMS) derivatives by gas chromatography/electron impact mass specrometry (GC/EIMS) so long as the sulfur was present in the reduced form. However, sulfoxide and sulfone analogs of tiospirone underwent reductive decomposition on the GC column. In addition, no molecular ions were observed in the EI spectra of these analogs. Desorption chemical ionization/mass spectrometry (DCI/MS) in the positive ion mode with methane as reagent gas successfully distinguished sulfoxides and sulfones from their parent sulfides. Protonated molecular ions were observed together with structurally significant fragment ions. Five microsomal metabolites of tiospirone were characterized by a combination of GC/EIMS and DCI/MS. From the structures of the metabolites three major pathways of metabolism were identified: N-dealkylation of the butyl side chain at the piperazinyl nitrogen, hydroxylation alpha to the glutarimidyl carbonyl at C-6 on the azaspirodecanedione ring, and sulfoxide formation on the benzisothiazole moiety.
authors.affiliation: Department of Chemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
authors.forename: H K
authors.initials: HK
authors.lastname: Jajoo
authors.forename: I A
authors.initials: IA
authors.lastname: Blair
authors.forename: L J
authors.initials: LJ
authors.lastname: Klunk
authors.forename: R F
authors.initials: RF
authors.lastname: Mayol
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D008401:Gas Chromatography-Mass Spectrometry; D066298:In Vitro Techniques; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D011619:Psychotropic Drugs / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013141:Spiro Compounds / Q000378:metabolism*
chemical_list: D011619:Psychotropic Drugs; D013141:Spiro Compounds; C042709:tiospirone