四氢叶酸辅酶参与的酶催化—碳单元转移反应及其人工模拟进展

简要介绍了生物体系中酶催化的一碳单元转移反应以及四氢叶酸辅酶的结构和作用,综述了一碳单元转移反应的人工模型进展,展望了上述反应的理论研究方法及前景。     

四氢叶酸辅酶参与的酶催化一碳单元转移反应及其人工模拟进展

简要介绍了生物体系中酶催化的一碳单元转移反应以及四氢叶酸辅酶的结构和作用,综述了一碳单元转移反应的人工模拟进展,展望了上述反应的理论研究方法及前景。     

四氢叶酸模型化合物咪唑啉盐的基团转移反应

合成了2种四氢叶酸辅酶模型化合物咪唑啉盐7和8. 它们与双官能团亲核体作用, 分别完全转移了3个和5个碳单元; 化合物7与单官能团亲核体作用, 部分转移了3个碳单元; 以部分转移产物化合物17作为四氢叶酸甲醛态模型, 与胺类反应实现了带硝基的4个碳单元的完全转移; 并研究了模型化合物7的还原反应. 这些反应模拟并扩展了四氢叶酸辅酶在生物体内转移一碳单元的功能, 产生了几种新的合成方法和试剂, 可以应用于有机合成中.     

甲基酮香料的仿生合成新方法研究

四氢叶酸辅酶在生物体内的作用是转移不同氧化态的一碳单元, 当一碳单元处于甲酸氧化态时, 活性部位是具有五元环状结构的咪唑啉环. 模拟四氢叶酸辅酶转移一碳单元的反应, 以苯并咪唑甲基碘盐作为四氢叶酸辅酶甲酸氧化态模型, 以格利雅试剂甲基碘化镁作为接收一碳单元的亲核试剂, 将甲酸氧化态的一碳单元转移给甲基碘化镁, 成功合成了三种重要的甲基酮香料甲基己基酮、甲基壬基酮和甲基十一烷基酮, 其结构用元素分析, 1H NMR, IR和MS等方法进行了表征, 并对反应机理和反应条件进行了讨论, 为甲基酮香料提供了一种仿生合成新方法.     

四氢叶酸辅酶模型化合物的研究Ⅱ .碘化 1 ,2 -二甲基 - 3-芳磺酰基 -△~2 -咪唑啉的一碳单元转移反应

四氢叶酸辅酶模型化合物与邻苯二胺、乙二胺、邻氨基酚作用则得到相应的一碳单元转移,而与芳胺、丙二腈碳负离子以及苯基溴化镁反应分别生成辅酶模型化合物的衍生物。讨论了其可能的一碳单元转移机制。     

四氢叶酸辅酶模型化合物的研究：Ⅱ.碘化1,2—二甲基—3—芳磺酰基—△^ …

四氢叶酸辅酶模型化合物与邻苯二胺、乙二胺、邻氨基酚作用则得到的相应的一碳单元转移，而与芳胺、丙二腈碳负离子以及苯基溴化镁反应分别生成辅酶模型化合物的衍生物。讨论了其可能的一碳单元转移机制。     

碘化1-甲基-2-异丙基(或丙基)-3-苯磺酰基咪唑啉的合成及基团转移反应

合成了新的四氢叶酸辅酶(THF)模型化合物碘化1-甲基-2-异丙基-3-苯磺酰基咪唑啉(5a)和碘化1-甲基-2-丙基-3-苯磺酰基咪唑啉(5b),研究了其反应性能.结果表明,化合物5与双官能团亲核体邻苯二胺或邻氨基苯酚反应,完全转移了4个碳的异丁基和正丁基单元,基于此探索了合成2-取代苯并咪唑及2-取代苯并唑的新方法;化合物5a与单官能团亲核体胺类反应部分转移了4个碳的异丁基单元,生成不同基团取代的N,N,N'-三取代乙二胺盐;化合物5a在Na BH4作用下可发生还原反应,在Na OH水溶液中可发生水解反应,也可与碳负离子基团(硝基甲基负离子或二腈基甲基负离子)发生亲核加成反应,生成了3类不同基团取代的N,N,N'-三取代乙二胺衍生物,探索了此类化合物的简易合成方法.这些反应模拟了四氢叶酸辅酶在生物体内转移一碳单元的功能,并将其扩展到4个碳原子单元,获得了可应用于有机合成的新方法和新试剂.     

苯并咪唑盐与胺类化合物的加成-水解反应研究

四氢叶酸辅酶在生物体内的生物合成过程中的作用是转移不同氧化态的一碳单元.本课题组曾首次提出并报道了苯并咪唑盐作为四氢叶酸辅酶的模型化合物,并研究了该模型化合物与多种格利雅试剂和丙二酸二乙酯碳负离子等反应,实现了一碳单元的转移反应,为许多醛、酮和β-羰基酸等有机化合物提供了仿生合成新方法[1,2].本文对苯并咪唑盐与亲核试剂胺类化合物的加成-水解反应进行了研究,提出了苯并咪唑盐的另一种新反应,为一些酰胺类化合物提供了一种未见文献报道的重要仿生合成新方法.     

α-萘甲醛的仿生合成

模拟四氢叶酸辅酶一碳单元转移反应,通过其甲酸氧化态模型化合物苯并咪唑盐与一碳单元的受体G rignard试剂进行加成-水解反应合成了α-萘甲醛,为制备稠环芳醛提出了一种仿生合成新方法。     

从四氢叶叶酸辅酶模型合成麝香酮中间体2,1 5-十六二.酮

麝香酮是麝香中重要的具有生理活性的组分.自Ruzicka[1]确定其结构以来,化学家研究和发展了许多合成麝香酮的方法[2].Stoll[3]提出的由2,15-十六二酮经分子内环合后氢化得到麝香酮,其操作简便,但尚需解决2,15-十六二酮的来源问题.5,6,7,8-四氢叶酸辅酶在生物体内的功能和作用及仿生合成已成为仿生化学研究的重要课题[4].四氢叶酸辅酶在生物体内传递不同氧化态的-碳单元,当-碳单元处于甲酸氧化态时,活性部位是形成的咪唑啉环[5,6].因此,本文以咪唑啉盐作为四氢叶酸辅酶模型,与亲核试剂双格利雅试剂作用,仿生合成2,15-十六二酮.     

3,4,4-三甲基-1-乙酰基咪唑啉盐向邻苯二胺转移一 碳单元反应的理论研究

用PM3-MO半经验方法对叶酸辅酶模型化合物3,4,4-三甲基-1-乙酰基咪唑啉盐向邻苯二胺转移一碳单元的反应进行了理论研究。结果表明,咪唑环有两种开环方式,该反应可能通过两种途径实现,每一种途径都经历了六个反应步骤,包括两次质子转移步骤,其中第二次质子转移是限速步骤。优化计算了所有步骤的中间体和过渡态的结构,各个中间体和过渡态具有不同的构型,构象和能量。     

5,10-CH+-THF向邻苯二胺转移一碳单元反应的理论研究

叶酸辅酶在酶催化的一碳单元转移过程中具有重要的作用,已有大量的实验及实验模拟对其生物学功能进行了研究分析.本文用PM3半经验方法对5,10-CH⁺-THF向邻苯二胺转移一碳单元的反应进行了理论研究.结果表明,5,10-CH⁺-THF中的咪唑啉环有两种开环方式,从而使得该反应可以通过两种途径实现,每一种途径都经历了6个反应步骤,其中包括限制速度的两次质子转移步骤.优化计算了每个步骤所有可能的中间体和过渡态的结构和能量,并通过比较分析得到了各反应阶段的最优中间体和过渡态结构.     

2，3－二甲基－1－对氯苯磺酰基咪唑啉盐与邻氨基苯酚反应的量子化学研究

用量子化学方法对叶酸辅酶模型化合物2，3－二甲基－1－对氯苯磺酰基咪唑 啉盐与邻氨基苯酚的反应进行了理论研究。结果表明，咪唑啉环有两种开环方式， 反应可以通过两种途径实现，得到较稳定的中间体或者实现一碳单元的完全转移。 通过优化计算所有步骤的中间体和过渡态的结构可知，各个中间体和过渡态具有不 同的构型、构象，有些过程的构象变化是进行下一步反应所必需的，在所有过程中 质子转移步骤过渡态的能量最高，是反应的限速步骤。     

Quantum chemical study on the one-carbon unit transfer of imidazolinium

One-carbon unit transfer reaction of folate cofactor model compound, 1-acetyl-2-methyl-imidazolinium, with 1,2-diaminobenzene has been studied theoretically with ONIOM method. The result shows that there are two pathways to complete this reaction because the imidazolinium ring has two breaking patterns. Both the two pathways have six steps. They are combination of two reactants, proton migration, break of five-membered ring, formation of benzimidazole derivate, another proton migration, and formation of final products. In each of the above pathways, the two proton migration steps have higher energy, which illuminate that the reaction is catalyzed by general acid-base. This fact agrees with the experimental results of enzymatic one-carbon unit transfer at oxidation level of formate.     

Chiral N-heterocyclic carbene ligands based on a biisoquinoline template

New chiral imidazolinium salts with tunable steric features, based on a biisoquinoline template, have been developed and structurally characterised using single crystal X-ray crystallography. The trans PdI(2)(NHC)(2) complex was prepared by reaction of the parent H(4) imidazolinium salt with Pd(OAc)(2) in the presence of NaI, and the solid state structure determined by X-ray crystallography. The rigid, chiral, biisoquinoline geometry of the H(4) imidazolinium salt was found to be maintained upon ligand complexation. The sterically unencumbered parent biisoquinoline ligand has been found to give high conversion with modest enantioselectivity in the copper-catalysed asymmetric addition of diethylzinc to cyclohexenone.     

Photomodulation of ionic interaction and reactivity: reversible photoconversion between imidazolium and imidazolinium

An interconversion system between imidazolium and imidazolinium has been proposed for the first time. Imidazolium and imidazolinium cations exhibit different reactivity due to the difference in the aromaticity and charge localization structure, which is successfully controlled by means of photoirradiation in the present system. A 4,5-dithiazolylimidazolium salt was prepared and studied as a new class of photochromic materials modulating electrostatic interactions and chemical reactivities. The photochromic 4,5-dithiazolylimidazolium showed reversible photoconversions between imidazolium open-form and imidazolinium closed-form upon successive irradiation with UV and visible light. The imidazolinium closed-form exhibited characteristic solvato- and ionochromisms in which the absorption maximum shifted by more than 80 nm depending on the solvent polarity and counteranions, whereas the imidazolium open-form showed no such solvent-dependent property. Because the corresponding nonionic 4,5-dithiazolylimidazole also did not exhibit the solvent-dependent absorption profile both in open- and closed-forms, the appearance of these chromisms in imidazolinium closed-form was attributed to the change in the extent of ionic interaction, which was brought about by the photoconversion of imidazolium to imidazolinium. The photoderived strong ionic interaction of imidazolinium with counteranion was further applied to the photocontrolled nucleophilic reaction system. Whereas the imidazolium open-form was inert to nucleophiles such as sodium methoxide, the imidazolinium closed-form was reactive to the nucleophilic reaction, demonstrating a photogated reaction system.     

A facile preparation of backbone-substituted, functionalized and chiral imidazolinium salts

A versatile and modular method for the preparation of various backbone-substituted, functionalized and chiral imidazolinium salts from the reaction of formamidines with alkene oxides has been described, providing a more straightforward access to substituted imidazolinium salts than the previously reported methods.     

Imidazolinium salts as catalysts for the aza-Diels-Alder reaction

Various easily accessible imidazolinium salts have been found to be capable of catalysing an aza-Diels-Alder reaction with a range of imines and Danishefsky's diene, giving the desired products in good to excellent yields. The influence of the counter-anions on the reactivity has been explored. These salts could contribute to the field of metal-free catalysis/organocatalysis.     

A facile preparation of imidazolinium chlorides

A process for the preparation of symmetric and unsymmetric imidazolinium chlorides that involves reaction of a formamidine with dichloroethane and a base (a) is described. This method makes it possible to obtain numerous imidazolinium chlorides under solvent-free reaction conditions and in excellent yields with purification by simple filtration. Alternatively, symmetric imidazolinium chlorides can be prepared directly in moderate yields from substituted anilines by utilizing half of the formamidine intermediate as sacrificial base (b).     

Tailor-made synthesis of various backbone-substituted imidazolinium salts by triflic anhydride mediated intramolecular cyclisation

We have found a Tf(2)O-mediated intramolecular cyclization reaction and have revealed an intriguing stereoselectivity and a regioselectivity during the preparation of intermediate alcohols, which allow for the tailor-made synthesis of various backbone-substituted imidazolinium salts, and structurally specific syn-4,5-disubstituted imidazolinium salts.