Stable Isotope-labeling Studies on the Oxidative Coupling of Caffeic Acid via o-Quinone
作者:Hiroyuki TAZAKI、Daisuke TAGUCHI、Takaomi HAYASHIDA、Kensuke NABETA
DOI:10.1271/bbb.65.2613
日期:2001.1
The formation of ortho-quinone from ortho-diphenol is a key step in its dimerization. An NMR analysis of the oxidation of 3,4-dihydroxycinnamic acid (caffein acid) by NaIO4 revealed the formation of 3-(3',4'-dioxo-1',5'-cyclohexadienyl) propenoic acid (o-quinone) prior to the formation of furofuran-type lignan 4,8-exo-bis(3,4-dihydroxyphenyl)-3,7-dioxabicyclo[3.3.0]octane-2,6-dione. Both electrolytic and enzymatic oxidation of caffeic acid also generated o-quinone. The yields of o-quinone from caffeic acid were quantified by NMR and HPLC analyses. A stable isotope-labeling study of the formation of lignans directly proved the random radical coupling of semiquinone radicals formed from a set of caffeic acid and o-quinone.
由邻二酚形成邻醌是其二聚化的关键步骤。对 NaIO4 氧化 3,4-二羟基肉桂酸(咖啡酸)的核磁共振分析表明,在形成呋喃类木脂素 4,8-外-双(3,4-二羟基苯基)-3,7-二氧双环[3.3.0]辛烷-2,6-二酮之前,会形成 3-(3',4'-二氧代-1',5'-环己二烯基)丙烯酸(邻奎宁酮)。电解和酶法氧化咖啡酸也能生成邻醌。通过核磁共振和高效液相色谱分析,对咖啡酸产生的邻醌进行了定量。对木质素形成的稳定同位素标记研究直接证明了咖啡酸和邻醌所形成的半醌自由基的随机自由基偶联。