Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, 20892, USA.
Angew Chem Int Ed Engl. 2019 Oct 21;58(43):15309-15312. doi: 10.1002/anie.201908416. Epub 2019 Sep 17.
In aqueous solution, many biochemical reaction pathways involve reaction of an aldehyde with an amine, which progresses through generally unstable, hydrated and dehydrated, Schiff base intermediates that often are unobservable by conventional NMR. There are 4 states in the relevant equilibrium: 1) gem-diol, 2) aldehyde, 3) hemiaminal, and 4) Schiff base. For the reaction between protein amino groups and DOPAL, a highly toxic metabolite of dopamine, the H resonances of both the hemiaminal and the dehydrated Schiff base can be observed by CEST NMR, even when their populations fall below 0.1 %. CEST NMR reveals the quantitative exchange kinetics between reactants and Schiff base intermediates, explaining why the Schiff base NMR signals are rarely observed. The reactivity of DOPAL with N -amino groups is greater than with lysine N -amines and, in the presence of O , both types of Schiff base DOPAL-peptide intermediates rapidly react with free DOPAL to irreversibly form dicatechol pyrrole adducts.
在水溶液中，许多生化反应途径涉及醛与胺的反应，该反应通过通常不稳定的、水合的和脱水的希夫碱中间体进行，这些中间体通常通过常规 NMR 无法观察到。在相关平衡中有 4 种状态：1）偕二醇，2）醛，3）半亚胺，4）希夫碱。对于蛋白质氨基与多巴胺的高度毒性代谢物 DOPAL 之间的反应，通过 CEST NMR 甚至可以观察到半亚胺和脱水希夫碱的 H 共振，即使它们的丰度低于 0.1%。CEST NMR 揭示了反应物和希夫碱中间体之间的定量交换动力学，解释了为什么很少观察到希夫碱 NMR 信号。DOPAL 与 N-氨基的反应性大于与赖氨酸 N-胺的反应性，并且在 O 的存在下，这两种类型的希夫碱 DOPAL-肽中间体与游离 DOPAL 快速反应，不可逆地形成二邻苯醌吡咯加合物。
