The biomimetic oxidative coupling of the ethyl ester of N-acetyl-3,5-diiodotyrosine (1) to yield the ethyl ester of N-acetylthyroxine (2) has been investigated. A putative mechanism involving phenolic coupling to yield an intermediate aryloxydienone (7) followed by an E2 elimination for loss of the side chain has been proposed. Oxidative couplings with analogous 4-substituted 3,5-diiodophenols indicate that a number of mechanisms are possible; these include quinone methide intermediates and SN2 substitutions in the intermediate aryloxydienones. Rearomatization of the intermediate aryloxydienones is a strong driving force for the loss of the side chains. The results indicate that 3,5-diiodo-4-aryloxydienones are good leaving groups in E2 and SN2 mechanisms. The synthetic method provides a facile synthesis of thyroxine analogues from readily available 4-substituted 3,5-diiodophenols. Keywords: diiodotyrosine, phenolic coupling, phenoxyl radicals, thyroxine.
已研究了生物仿生氧化偶联N-乙酰-3,5-二碘酪氨酸乙酯(1)生成N-乙酰甲状腺素乙酯(2)的过程。提出了一个假设机制,涉及酚偶联生成中间芳基氧二烯酮(7),随后进行E2消除以失去侧链。与类似的4-取代3,5-二碘酚进行氧化偶联表明可能存在多种机制;其中包括醌亚甲基中间体和中间芳基氧二烯酮中的SN2取代。中间芳基氧二烯酮的重芳构是失去侧链的强大推动力。结果表明,3,5-二碘-4-芳基氧二烯酮在E2和SN2机制中是良好的脱离基团。这种合成方法提供了一种便捷的方法,可以从易得的4-取代3,5-二碘酚合成甲状腺素类似物。关键词:二碘酪氨酸,酚偶联,酚氧基自由基,甲状腺素。