al-Kazwini A T, O'Neill P, Adams G E, Cundall R B, Maignan J, Junino A
MRC Radiobiology Unit, Chilton, Didcot, UK.
Melanoma Res. 1994 Dec;4(6):343-50. doi: 10.1097/00008390-199412000-00001.
One-electron oxidation of a series of C(2)- and C(3)-methyl substituted analogues of 5,6-dihydroxyindole (DHI), in the pH range 5-9, was studied using the technique of pulse radiolysis with spectrophotometric detection. This investigation was undertaken to further our understanding of the involvement of free radical species in the polymerization processes leading to melanin formation. The optical absorption spectra of the protonated indole semiquinone radicals resulting from the one-electron oxidation of C(2)- and C(3)-methyl substituted indoles were similar to those of their corresponding hydroxylated indoles. From this similarity, it is inferred that methylation at C(2) and C(3) of DHI has little or no effect upon the initial radicals. The semiquinone radicals of these analogues subsequently decay to yield the corresponding quinone methide/imine. However, methyl substitution at C(2) and C(3) of the quinone methide derived from these analogues results in their stabilization. This stabilization contracts with the reactivity of the corresponding quinone methide from DHI. Further, these stabilized quinone methides do not interact with the azide ion (N3-), in contrast to the reaction of N3- with the quinone methide of DHI. It is concluded that methylation at C(2) and C(3) of DHI will modify the pathways so that the polymerization processes are less effective than those with DHI.
利用脉冲辐解技术和分光光度检测法，研究了一系列5,6 - 二羟基吲哚（DHI）的C(2)-和C(3)-甲基取代类似物在pH值5 - 9范围内的单电子氧化过程。进行这项研究是为了进一步了解自由基物种在导致黑色素形成的聚合过程中的作用。由C(2)-和C(3)-甲基取代吲哚的单电子氧化产生的质子化吲哚半醌自由基的光吸收光谱与其相应的羟基化吲哚的光谱相似。由此相似性推断，DHI的C(2)和C(3)位甲基化对初始自由基几乎没有影响。这些类似物的半醌自由基随后衰变生成相应的醌甲基化物/亚胺。然而，这些类似物衍生的醌甲基化物在C(2)和C(3)位的甲基取代导致其稳定。这种稳定性与DHI相应醌甲基化物的反应性不同。此外，与N3-与DHI的醌甲基化物的反应相反，这些稳定的醌甲基化物不与叠氮离子（N3-）相互作用。得出的结论是，DHI的C(2)和C(3)位甲基化将改变反应途径，从而使聚合过程比DHI的聚合过程效率更低。
