Guo Q, Zhao B, Shen S, Hou J, Hu J, Xin W
Institute of Biophysics, Academia Sinica, 15 Datun Road, Beijing 100101, People's Republic of China.
Biochim Biophys Acta. 1999 Mar 14;1427(1):13-23. doi: 10.1016/s0304-4165(98)00168-8.
The purpose of this study is to examine the relationship between the free radical scavenging activities and the chemical structures of tea catechins ((-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC) and (-)-epicatechin (EC)) and their corresponding epimers ((-)-gallocatechin gallate (GCG), (-)-gallocatechin (GC) and (+)-catechin ((+)-C)). With electron spin resonance (ESR) we investigated their scavenging effects on superoxide anions (O-.2) generated in the irradiated riboflavin system, singlet oxygen(1O2) generated in the photoradiation-hemoporphyrin system, the free radicals generated from 2,2'-azobis(2-amidinopropane)hydrochloride (AAPH) and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical. The results showed that the scavenging effects of galloylated catechins (EGCG and GCG) on the four free radicals were stronger than those of nongalloylated catechins (EGC, GC, EC, (+)-C), and the scavenging effects of EGC and GC were stronger than those of EC and (+)-C. Thus, it is suggested that the presence of the gallate group at the 3 position plays the most important role in their free radical-scavenging abilities and an additional insertion of the hydroxyl group at the 5' position in the B ring also contributes to their scavenging activities. Moreover, the corresponding phenoxyl radicals formed after the reaction with O-.2 were trapped by DMPO and the ESR spectra of DMPO/phenoxyl radical adducts were observed (aN=15.6 G and aHbeta=21.5 G). No significant differences were found between the scavenging effects of the catechins and their epimers when their concentrations were high. However, significant differences were observed at relatively low concentrations, and the lower their concentrations, the higher the differences. The scavenging abilities of GCG, GC and (+)-C were stronger than those of their corresponding epimers (EGCG, EGC and EC). The differences between their sterical structures played a more important role in their abilities to scavenge large free radicals, such as the free radicals generated from AAPH and the DPPH radical, than to scavenge small free radicals, such as O-.2 and 1O2, especially in the case with EGCG and GCG with more bulky steric hindrance.
本研究的目的是考察茶儿茶素（（-）-表没食子儿茶素没食子酸酯（EGCG）、（-）-表没食子儿茶素（EGC）和（-）-表儿茶素（EC））及其相应的差向异构体（（-）-没食子儿茶素没食子酸酯（GCG）、（-）-没食子儿茶素（GC）和（+）-儿茶素（（+）-C））的自由基清除活性与化学结构之间的关系。我们利用电子自旋共振（ESR）研究了它们对核黄素照射体系中产生的超氧阴离子（O₂⁻）、光辐射-血卟啉体系中产生的单线态氧（¹O₂）、2,2'-偶氮二（2-脒基丙烷）盐酸盐（AAPH）产生的自由基以及1,1-二苯基-2-苦基肼（DPPH）自由基的清除作用。结果表明，没食子酰化儿茶素（EGCG和GCG）对这四种自由基的清除作用强于非没食子酰化儿茶素（EGC、GC、EC、（+）-C），且EGC和GC的清除作用强于EC和（+）-C。因此，提示3位没食子酸基团的存在对其自由基清除能力起最重要作用，B环5'位额外插入羟基也有助于其清除活性。此外，与O₂⁻反应后形成的相应苯氧自由基被DMPO捕获，并观察到DMPO/苯氧自由基加合物的ESR谱（aN = 15.6 G，aHβ = 21.5 G）。当儿茶素及其差向异构体浓度较高时，它们的清除作用无显著差异。然而，在相对较低浓度时观察到显著差异，且浓度越低，差异越大。GCG、GC和（+）-C的清除能力强于其相应的差向异构体（EGCG、EGC和EC）。它们空间结构的差异在清除大自由基（如AAPH产生的自由基和DPPH自由基）的能力方面比清除小自由基（如O₂⁻和¹O₂）的能力方面起更重要的作用，尤其是在空间位阻较大的EGCG和GCG的情况下。
