Syntheses and pKa determination of 1-(o-hydroxyphenyl)imidazole carboxylic esters
作者:James P. Collman、Zhong Wang、Min Zhong、Li Zeng
DOI:10.1039/b000119h
日期:——
All three isomers of 1-(o-hydroxyphenyl)imidazole carboxylic esters (1–3) have been synthesized regioselectively via their methyl ether precursors. Methyl 1-(o-methoxyphenyl)imidazole-2-carboxylate (6) and the corresponding 1,4-isomer (11) were synthesized via Cu-catalyzed coupling of 2-iodoanisole with imidazole followed by methoxycarbonylation, and by direct coupling of 2-iodoanisole with methyl imidazole-4-carboxylate (7), respectively. The 1,5-isomer (15) was prepared by annulation of an N-aryl glycine ester derivative (13). The boron tribromide mediated cleavage of methyl ethers gave the hydroxyphenyl compounds (1–3) in good to excellent yields. These compounds can serve as building blocks for synthesizing a new generation of active-site model compounds of cytochrome c oxidase (CcO). The pKa values have been determined by spectrophotometric measurements in order to provide a basis for the understanding of the proton transfer processes in CcO.
通过其甲醚前体,选择性合成了1-(邻羟基苯基)咪唑羧酸酯的全部三种异构体(1–3)。甲基1-(邻甲氧基苯基)咪唑-2-羧酸酯(6)及其对应的1,4-异构体(11)分别通过铜催化的2-碘苯甲醚与咪唑的偶联反应后进行甲氧羰基化,以及直接将2-碘苯甲醚与甲基咪唑-4-羧酸酯(7)偶联来合成。1,5-异构体(15)通过N-芳基甘氨酸酯衍生物(13)的环合反应制备。通过三溴化硼介导的甲醚断裂反应,以良好至优良的收率得到了羟基苯基化合物(1–3)。这些化合物可作为合成新一代细胞色素c氧化酶(CcO)活性部位模型化合物的构建模块。为了为理解CcO中的质子转移过程提供基础,通过分光光度法测量确定了pKa值。