糖与氨基酸反应中自由基中间产物的EPR、NMR研究Ⅰ.自由基产物的结构和反应机理的研究

糖与氨基酸反应涉及一种新的自由基的生成。这种自由基EPR谱特征的超精细结构是由一组两个等性的氮核、三组等性的质子所贡献。谱的超精细特征和谱线分裂的数目主要取决于氨基酸的结构。从¹³C NMR谱和反应过程的分析,我们提出如下设想:这种新自由基产物应该是1,2-4,5四取代的哌嗪双自由基。用实验中测得的波谱参数在ASPECT-2000型计算机上进行了EPR谱的模拟,模拟的理论谱与实验谱很好地重合,进一步支持了上述的设想。本文还提出了反应中自由基形成的可能机理。

EPR AND 13C NMR STUDIES OF THE FREE RADICAL PRODUCTS FORMED BY THE REACTIONS OF SUGAR WITH AMINO ACIDS. I. INVESTIGATIONS ON THE STRUCTURE OF THE FREE RADICAL PRODUCTS AND THE MECHANISM OF FREE RADICAL FORMATION

EPR and ¹³C-NMR techniques were used to study systematically tbe new free radical products formed by the reaction cf D-gluoose with amino acids. The hyperfine structure and splitting line numbers of EPR spectra of the free radical products depended mainly upon the structure of amino compounds, and could be assigned to the contributions of one set with two equivalent nitrogens and of three sets of equivalent protons. The chemical shifts of ¹³C-NMR spectra of the free radical products showed that ihe principal structure would be:According to the analyses of EPR,¹³C-NMR spectra and the reaction processes,, We propose the assumption of theidentity of the radical product as 1,2-1, 5 tetrasubstituted piperazine biradical. The assumed structure and EPR spectral analyses mechanism were strongly supported by the close agreement between, the observedSpectra and those simulated on aspect 2000 computer. The proposed mechanism of the free radical formation in the reaction of sugar withamino acids is presented in this paper.