Species differences in the metabolism of acetylenic compounds commonly used in the formulation of pharmaceuticals and pesticides have not been investigated. To better understand the in vivo reactivity of this bond, the metabolism of propargyl alcohol (PA), 2-propyn-1-ol, was examined in rats and mice. An earlier study (Banijamali, A. R.; Xu, Y.; Strunk, R. J.; Gay, M. H.; Ellis, M. C.; Putterman, G. J. J. Agric. Food Chem. 1999, 47, 1717-1729) in rats revealed that PA undergoes extensive metabolism primarily via glutathione conjugation. The current research describes the metabolism of PA in CD-1 mice and compares results for the mice to those obtained for rats. [1,2,3-(13)C;2,3-(14)C]PA was administered orally to the mice. Approximately 60% of the dose was excreted in urine by 96 h. Metabolites were identified, directly, in whole urine by 1- and 2-D (13)C NMR and HPLC/MS and by comparison with the available reference compounds. The proposed metabolic pathway involves glucuronide conjugation of PA to form 2-propyn-1-ol-glucuronide as well as oxidation of PA to the proposed intermediate 2-propynal. The aldehyde undergoes conjugation with glutathione followed by further metabolism to yield as final products 3,3-bis[(2-acetylamino-2-carboxyethyl)thio]-1-propanol, 3-[(2-acetylamino-2-carboxyethyl)thio]-3-[(2-amino-2-carboxyethyl)thi o]-1-propanol, 3,3-bis[(2-amino-2-carboxyethyl)thio]-1-propanol, 3-[(2-amino-2-carboxyethyl)thio]-2-propenoic acid, and 3-[(2-formylamino-2-carboxyethyl)thio]-2-propenoic acid. A small portion of 2-propynal is also oxidized to result in the excretion of 2-propynoic acid. On the basis of urinary metabolite data, qualitative and quantitative differences are noted between rats and mice in the formation of the glucuronide conjugate of PA and in the formation of 2-propynoic acid and metabolites derived from glutathione. These metabolites represent further variation on glutathione metabolism following its addition to the carbon-carbon triple bond compared to those described for the rat.

Our earlier research clearly revealed glutathione (GSH) conjugation as a major pathway for the metabolism of propargyl alcohol (2-propyn-1-ol) in rats and in mice. The identification of the metabolite 3,3-bis[(2-acetylamino-2-carboxyethyl)thio]-1-propanol (I) and its congeners represented the first example of multi-glutathione addition to a triple bond, and invoked further research to determine the mechanism for bis-conjugation. To determine whether GSH conjugated directly with propargyl alcohol or after oxidation of the latter to 2-propynal, urinary metabolites from rats administered deuterium-labeled propargyl alcohol were characterized. Following TLC separation and HPLC purification, mass spectrometry was used to show a single mass unit increase for metabolite I over that of the chemically synthesized standard. This result indicates that conjugation of propargyl alcohol with GSH to form the bis-conjugates occurred after initial oxidation to 2-propynal, a reaction that is analogous to a Michael addition.