Altering the Acidity and Solution Properties of Bilirubin. Methoxy and Methylthio Substituents
作者:Stefan E. Boiadjiev、David A. Lightner
DOI:10.1021/jo980740e
日期:1998.9.1
Substitution of electron-withdrawing groups at the alpha-position of an aliphatic carboxylic acid can be expected to increase the acidity of the acid. Methoxy and methylthio groups are especially effective; they increase the acidity of acetic acid by approximately 1.1 pK(a) units. Bilirubin, the water-insoluble pigment of jaundice, has two propionic acids, and an alpha-methoxy or alpha-methylthio substituent
可以预期,在脂肪族羧酸的α位上取代吸电子基团会增加酸的酸度。甲氧基和甲硫基特别有效;它们使乙酸的酸度增加了约1.1 pK(a)单位。黄胆素的水不溶性颜料胆红素具有两种丙酸,每个丙酸中的一个α-甲氧基或一个α-甲硫基取代基可以类似地降低pK(a),从而改变其溶解性。(先前合成的类似物,α,α'-二氟红宝石(4)可溶于水。)胆红素的两个新类似物,α,α'-二甲氧基红宝石(1)和α,α'-双(甲硫基)红宝石(2 ),已经合成,分离为非对映异构体,并进行了分析。NMR显示该异构体采用分子内氢键合的脊-瓦状构象。像胆红素一样,1和2都不溶于水。与胆红素不同,1可溶于稀碳酸氢盐水溶液,而2不溶于水,这不能由1和2具有相同的pK(a)来预测。数据暗示相对于OCH(3),SCH(3)的空间更大。