Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239, Cracow, Poland.
Chemistry. 2013 Jan 7;19(2):771-81. doi: 10.1002/chem.201202825. Epub 2012 Nov 13.
The mechanism of oxidative epoxidation catalyzed by HppE, which is the ultimate step in the biosynthesis of fosfomycin, was studied by using hybrid DFT quantum chemistry methods. An active site model used in the computations was based on the available crystal structure for the HppE-Fe(II)-(S)-HPP complex and it comprised first-shell ligands of iron as well as second-shell polar groups interacting with the substrates. The reaction energy profiles were constructed for three a priori plausible mechanisms proposed in the literature, and it was found that the most likely scenario for the native substrate, that is, (S)-HPP, involves generation of the reactive Fe(III)-O·/Fe(IV)=O species, which is responsible for the C-H bond-cleavage. At the subsequent reaction stage, the OH-rebound, which would lead to a hydroxylated product, is prevented by a fast protonation of the OH ligand and, as a result, ring closure is the energetically preferred step. For the R enantiomer of the substrate ((R)-HPP), which is oxidized to a keto product, comparable barrier heights were found for the C-H bond activation by both the Fe(III)-O(2)· and Fe(IV)=O species.
采用杂化 DFT 量子化学方法研究了 HppE 催化氧化环氧化反应的机制，该酶是 fosfomycin 生物合成的最后一步。计算中使用的活性位点模型基于 HppE-Fe(II)-(S)-HPP 复合物的现有晶体结构，其中包含铁的第一壳层配体以及与底物相互作用的第二壳层极性基团。为文献中提出的三种先验合理的机制构建了反应能量曲线，结果发现，对于天然底物 (S)-HPP，最可能的情况是生成负责 C-H 键断裂的反应性 Fe(III)-O·/Fe(IV)=O 物种。在随后的反应阶段，通过 OH 配体的快速质子化阻止了 OH 基团的回折，因此，闭环是能量上优先的步骤。对于底物的 R 对映异构体 ((R)-HPP)，其被氧化为酮产物，对于 Fe(III)-O(2)·和 Fe(IV)=O 物种的 C-H 键活化，发现可比的势垒高度。
