Sugumaran M, Tan S, Sun H L
Department of Biology, University of Massachusetts at Boston 02125, USA.
Arch Biochem Biophys. 1996 May 15;329(2):175-80. doi: 10.1006/abbi.1996.0206.
The oxidation chemistry of dopa in relation to melanin biosynthesis has been extensively studied. However, the oxidation of its lower homolog viz., 3,4-dihydroxyphenylglycine has not been described. Using 3,4-dimethoxybenzaldehyde as the starting material, the chemical synthesis of 3,4-dihydroxyphenylglycine was accomplished by Strecker's synthesis and demethylation reactions. Tyrosinase readily oxidized this unusual amino acid to the expected quinone. The glycyl-o-benzoquinone thus formed was highly unstable like its higher analog, dopaquinone. However, unlike its counterpart, it failed to exhibit intramolecular cyclization reaction. Rather, glycyl-o-benzoquinone exhibited facile transformation(s) to ultimately generate 3,4-dihydroxybenzaldehyde as an isolatable product. A probable mechanism involving intermediary formation of unstable quinone methide and carbinolamine intermediates is proposed to account for the novel transformation of glycyl-o-benzoquinone to 3,4-dihydroxybenzaldehyde.
多巴在黑色素生物合成方面的氧化化学已得到广泛研究。然而，其低级同系物即3,4 - 二羟基苯甘氨酸的氧化情况尚未见报道。以3,4 - 二甲氧基苯甲醛为起始原料，通过施特雷克合成法和脱甲基反应完成了3,4 - 二羟基苯甘氨酸的化学合成。酪氨酸酶能轻易地将这种特殊氨基酸氧化为预期的醌。如此形成的甘氨酰 - 邻苯醌与它的高级类似物多巴醌一样高度不稳定。然而，与多巴醌不同的是，它未能发生分子内环化反应。相反，甘氨酰 - 邻苯醌表现出易于转化，最终生成可分离产物3,4 - 二羟基苯甲醛。本文提出了一种可能的机制，涉及不稳定的醌甲基化物和甲醇胺中间体的中间形成，以解释甘氨酰 - 邻苯醌向3,4 - 二羟基苯甲醛的新型转化。
