RT Journal Article SR Electronic T1 Reaction of Homopiperazine with Endogenous Formaldehyde: A Carbon Hydrogen Addition Metabolite/Product Identified in Rat Urine and Blood JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 1478 OP 1486 DO 10.1124/dmd.112.044917 VO 40 IS 8 A1 Scott Martin A1 Eva M. Lenz A1 Dave Temesi A1 Martin Wild A1 Malcolm R. Clench YR 2012 UL http://dmd.aspetjournals.org/content/40/8/1478.abstract AB Drug reactivity and bioactivation are of major concern to the development of potential drug candidates in the pharmaceutical industry (Chem Res Toxicol 17:3–16, 2004; Chem Res Toxicol 19:889–893, 2006). Identifying potentially problematic compounds as soon as possible in the discovery process is of great importance, so often early in vitro screening is used to speed up attrition. Identification of reactive moieties is relatively straightforward with appropriate in vitro trapping experiments; however, on occasion unexpected reactive intermediates can be found later during more detailed in vivo studies. Here, we present one such example involving a series of compounds from an early drug discovery campaign. These compounds were found to react with endogenous formaldehyde from a rat in vivo study, resulting in the formation of novel +13-Da bridged homopiperazine products (equivalent to the addition of one carbon and one hydrogen atom), which were detected in urine and blood. The identification of these +13-Da products and their origin and mechanism of formation are described in detail through analyses of a representative homopiperazine compound [N-(3-(3-fluorophenyl)-1,2,4-thiadiazol-5-yl)-4-(4-isopropyl-1,4-diaze-pane-2-carbonyl)piperazine-1-carboxamide (AZX)] by liquid chromatography-UV-mass spectrometry, 1H NMR, and chemical tests.