2-Methylimidazole (2MI), as well as imidazole, has been though to undergo cupro-ascorbate (Cu-VC)-catalyzed oxidative transformation in vitro to become a reactive species capable of combining with aldehydes intrinsic to connective-tissue proteins. We attempted to seize the essence of the above reaction through obtaining the structural information of an aldehyde-bonding species. As major products from 2MI in the in vitro Cu-VC system, 2-hydroxymethylimidazole (2(OH)MI) and 2-methyl-4-(5H)(or 5(4H))-imidazolone (2MIone) were identified by mass-spectral and chromatographic comparison with the corresponding authentic standards synthesized. The in situ addition of acetaldehyde or propionaldehyde as a simple protein-aldehyde model to the system resulted in the deducible formation of an aldol condensate, 2-methyl-4(or 5)-ethylidene-4(5H)(or 5(4H))-imidazolone (2MEIone) or its possible analogue with a propylidene moiety, respectively. The authentic compound of 2MIone directly reacted with acetaldehyde and easily afforded the products assignable to the isomers of 2MEIone through the ethylidfene moiety at physiological pH and temperature, whereas neither 2MI or 2(OH)MI reacted at all. These results suggest that a 4(5H)(or 5(4H))-imidazolone product, although simply a monooxygenated form, is sufficiently reactive to give aldol condensation-typed covalent adducts with aldehydes, even under physiological conditions, probably having an activated methylene moiety in the ring strucuture. Based on the present results, we discussed the mechanism of the retention of imidazole-containing drugs in connective tissue.
2-甲基咪唑(2MI)和
咪唑一样,在体外通过
铜-
抗坏血酸盐(Cu-
VC)催化氧化反应,成为能与结缔组织蛋白固有的醛结合的反应性物质。我们试图通过获得醛结合物质的结构信息来抓住上述反应的本质。作为2MI在体外Cu-
VC系统中的主要产物,2-羟甲基
咪唑(2(OH)MI)和2-甲基-4-(5H)(或5(4H))-
咪唑酮(2MIone)通过与相应合成标准品的质量谱和色谱比较来鉴定。将
乙醛或
丙醛作为简单的蛋白质-醛模型原位添加到系统中,可分别推断出醛缩合物的形成,即2-甲基-4(或5)-亚乙基-4(5H)(或5(4H))-
咪唑酮(2MEIone)或其可能的类似物,带有丙亚基。2MIone的正宗化合物与
乙醛直接反应,在生理pH值和温度下,通过乙亚基部分很容易得到可归因于2MEIone异构体的产物,而2MI或2(OH)MI则完全没有反应。这些结果表明,4(5H)(或5(4H))-
咪唑酮产物虽然只是单加氧形式,但具有足够的反应性,即使在生理条件下,也能与醛发生醛缩合