Pyridine and pyrimidine analogs of acetaminophen as inhibitors of lipid peroxidation and cyclooxygenase and lipoxygenase catalysis
作者:Tae-gyu Nam、Susheel J. Nara、Irène Zagol-Ikapitte、Thomas Cooper、Luca Valgimigli、John A. Oates、Ned A. Porter、Olivier Boutaud、Derek A. Pratt
DOI:10.1039/b912528k
日期:——
Herein we report an investigation of the efficacy of pyridine and pyrimidine analogs of acetaminophen (ApAP) as peroxyl radical-trapping antioxidants and inhibitors of enzyme-catalyzed lipid peroxidation by cyclooxygenases (COX) and lipoxygenases (LOX). In inhibited autoxidations we find that ApAP, the common analgesic and antipyretic agent, is a very good antioxidant with a rate constant for reaction with peroxyl radicals (kinh = 5 × 105 M−1 s−1) that is higher than many widely-used phenolic antioxidants, such as the ubiquitous butylated hydroxytoluene (BHT). This reactivity is reduced substantially upon incorporation of nitrogen into the phenolic ring, owing to an increase in the O–H bond dissociation enthalpy of pyridinols and pyrimidinols with respect to phenols. Incorporation of nitrogen into the phenolic ring of ApAP was also found to decrease its efficacy as an inhibitor of prostaglandin biosynthesis by ovine COX-1 (oCOX-1). This is explained on the basis of an increase in its oxidation potential and its reduced reactivity as a reducing co-substrate of the peroxidase protoporphyrin. In contrast, the efficacy of ApAP as an inhibitor of lipid hydroperoxide biosynthesis by soybean LOX-1 (sLOX-1) increased upon incorporation of nitrogen into the ring, suggesting a different mechanism of inhibition dependent on the acidity of the phenolic O–H which may involve chelation of the catalytic non-heme iron atom. The greater stability of the 3-pyridinols and 5-pyrimidinols to air oxidation as compared to phenols allowed us to evaluate some electron-rich pyridinols and pyrimidinols as inhibitors of oCOX-1 and sLOX-1. While the pyridinols had the best combination of activities as antioxidants and inhibitors of oCOX-1 and sLOX-1, they were found to be more toxic than ApAP in preliminary assays in human hepatocellular carcinoma (HepG2) cell culture. The pyrimidinols, however, were up to 17-fold more reactive to peroxyl radicals and up to 25-fold better inhibitors of prostaglandin biosynthesis than ApAP, with similar cytotoxicities to HepG2 cells at high levels of exposure.
在此,我们报告了对吡啶和嘧啶类对乙酰氨基酚(ApAP)作为过氧自由基捕获抗氧化剂以及环氧合酶(COX)和脂氧合酶(LOX)催化的脂质过氧化反应抑制剂的有效性研究。在抑制的自氧化反应中,我们发现,作为常用的镇痛和退烧药物的ApAP,是一种非常好的抗氧化剂,其与过氧自由基的反应速率常数(kinh = 5 × 10^5 M−1 s−1)高于许多广泛使用的酚类抗氧化剂,如普遍存在的丁基羟基甲苯(BHT)。由于吡啶醇和嘧啶醇的O–H键解离焓相比于酚类有所增加,导致将氮引入酚环后,其反应性大幅降低。ApAP酚环中氮的引入也发现减少了其作为羔羊COX-1(oCOX-1)前列腺素生物合成抑制剂的有效性。这可以通过其氧化电位的增加以及其作为过氧化氢酶原卟啉还原共底物的反应性降低来解释。相较之下,ApAP作为大豆LOX-1(sLOX-1)对脂质过氧化氢生物合成的抑制剂的有效性在引入氮元素后有所提高,这表明其抑制机制可能依赖于酚类O–H的酸度,可能涉及对催化性非血红素铁原子的螯合。相比于酚类,3-吡啶醇和5-嘧啶醇对空气氧化的稳定性更高,使我们能够评估一些富电子的吡啶醇和嘧啶醇作为oCOX-1和sLOX-1的抑制剂。尽管吡啶醇在抗氧化剂和oCOX-1、sLOX-1抑制剂的活性方面表现最佳,但在对人类肝细胞癌(HepG2)细胞培养的初步实验中发现其毒性明显高于ApAP。然而,嘧啶醇对过氧自由基的反应性高达ApAP的17倍,对前列腺素生物合成的抑制效果好达ApAP的25倍,在高浓度暴露下,其对HepG2细胞的细胞毒性相似。