Investigation of the chemical basis of nitroalkane toxicity: tautomerism and decomposition of propane 1- and 2-nitronate under physiological conditions.
Unlike primary nitroalkanes, such as 1-nitropropane, the secondary nitroalkane 2-nitropropane is geno- and hepatotoxic. Nitroalkanes exist in equilibrium with alkane nitronates. In order to investigate the relationship between nitroalkane toxicity and generation and stability of nitronates, propane 1- or 2-nitronate (4-6 mM) were incubated in buffer (pH 3.8 -7.4) in the absence or presence of cysteine. Equilibrium formation and degradation were studied by 1H-NMR spectroscopy and ion pair HPLC chromatography. Propane 1-nitronate generated 1-nitropropane rapidly and almost quantitatively. In the case of propane 2-nitronate equilibrium at pH 7.4 was reached within 8 h, when 48% of initial nitronate had tautomerised to 2-nitropropane. The pKa of the reaction 2-nitropropane less than--greater than propane 2-nitronate measured by HPLC was 7.63. Equilibrium formation, hydrolysis and reduction of nitronates were pH-dependent and, in the case of propane 2-nitronate, yielded mainly acetone, nitrite and acetone oxime, apart from 2-nitropropane. Hydrolysis of propane 2-nitronate (4 mM) to nitrite was modulated by cysteine (4 mM) and p-methoxyphenol (0.4 mM). At pH 7.4 they increased nitrite generation by 300 and 28%, respectively, at pH 4.8 they decreased nitrite formation by 91 and 82%, respectively, probably by scavenging radical intermediates. Differences between nitroalkanes in terms of content of nitronate tautomer at equilibrium are probably an important chemical determinant of their toxic potential.
Linhart
I
I
Department of Pharmaceutical Sciences, Aston University, Birmingham, U.K.
Gescher
A
A
Goodwin
B
B
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D006868:Hydrolysis; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008862:Microsomes, Liver / Q000187:drug effects; D009595:Nitroparaffins / Q000737:chemistry / Q000633:toxicity*; D011407:Propane / Q000031:analogs & derivatives* / Q000737:chemistry / Q000633:toxicity
D009595:Nitroparaffins; C035314:1-nitropropane; C016617:2-nitropropane; D011407:Propane