Lipase-Catalyzed Ring-Opening Polymerizations of 4-Substituted ε-Caprolactones: Mechanistic Considerations
摘要:
Lipase-catalyzed ring-opening polymerizations of 4-substituted epsilon-caprolactones employing Novozym 435 as the biocatalyst demonstrate dramatic differences in polymerization rates and selectivity depending on the size of the substituent. Quantification of the reaction rates shows that the polymerization rate decreases by a factor of 2 upon the introduction of a Me substituent at the 4-position. Moreover, 4-EtCL polymerizes 5 times slower than 4-MeCl and 4-PrCL is even 70 times slower. The decrease in polymerization rate is accompanied by a strong decrease in enantioselectivity: while the E-ratio of 4-MeCL polymerization is 16.9, the E-ratios of 4-EtCL and 4-PrCL are 7.1 and 2.0, respectively. Interestingly, Novozym 435 displays S-selectivity for 4-MeCL and 4-EtCL in the polymerization reaction, but the enantioselectivity is changed to the (R)-enantiomer in the case of the 4-PrCL. The nature of these differences was investigated by hydrolyzing all monomers in water/diisopropyl ether mixtures employing Novozym 435 as the catalyst. In the hydrolysis reactions, the rates are only moderately affected upon increasing the substituent size, and the enantioselectivity is S in all cases, also for 4-PrCL. Again, a steady decrease of the E-ratio was observed upon increasing the substituent size, but this was less pronounced than in the polymerization reactions: the E-ratios were 17.6, 12.4, and 4.6, going from 4-MeCL to 4-PrCL. For 4-substituted epsilon-caprolactones, the results obtained are a clear indication that the chirality of the propagating alcohol chain end is important in the catalytic cycle and that-in contrast to unsubstituted lactones-the rate-determining step is not necessarily the formation of the acyl-enzyme intermediate but more likely the deacylation of the acyl-enzyme intermediate by the propagating alcohol chain end.
Functional divergence between closely related Baeyer-Villiger monooxygenases from Aspergillus flavus
作者:F.M. Ferroni、M.S. Smit、D.J. Opperman
DOI:10.1016/j.molcatb.2014.05.015
日期:2014.9
well-characterized BVMOs including cyclohexanone, phenylacetone and 4-hydroxyacetophenone monooxygenase. Building on the Grogan classification/clustering of BVMOs, we have designated this new group of BVMOs, Group VI. Group VI BVMOs show an early divergence from the cyclopentanone monooxygenase (CPMO) type BVMOs (Group I). Substrate profiling using cyclic, bicyclic, aliphatic and aryl ketones show a clear divergence
Assessing the Substrate Selectivities and Enantioselectivities of Eight Novel Baeyer−Villiger Monooxygenases toward Alkyl-Substituted Cyclohexanones
作者:Brian G. Kyte、Pierre Rouvière、Qiong Cheng、Jon D. Stewart
DOI:10.1021/jo030253l
日期:2004.1.1
4-alkyl-substituted cyclohexanones tested, enzymes were discovered that afforded each of the corresponding (S)-lactones in ≥98% ee. This was also true for the 2-alkyl-substituted cyclohexanones examined. The situation was more complex for 3-akyl-substituted cyclohexanones. In a few cases, single Baeyer−Villiger monooxygenases possessed both high regio- and enantioselectivities toward these compounds
Selective Nickel-Catalyzed Conversion of Model and Lignin-Derived Phenolic Compounds to Cyclohexanone-Based Polymer Building Blocks
作者:Wouter Schutyser、Sander Van den Bosch、Jan Dijkmans、Stuart Turner、Maria Meledina、Gustaaf Van Tendeloo、Damien P. Debecker、Bert F. Sels
DOI:10.1002/cssc.201403375
日期:2015.5.22
Valorization of lignin is essential for the economics of future lignocellulosic biorefineries. Lignin is converted into novel polymerbuildingblocks through four steps: catalytic hydroprocessing of softwood to form 4‐alkylguaiacols, their conversion into 4‐alkylcyclohexanols, followed by dehydrogenation to form cyclohexanones, and Baeyer–Villiger oxidation to give caprolactones. The formation of alkylated
木质素的增价对于未来木质纤维素生物精炼厂的经济性至关重要。木质素通过以下四个步骤转化为新型的聚合物结构单元:针叶木的催化加氢处理形成4-烷基愈创木酚,将其转化为4-烷基环己醇,然后脱氢形成环己酮,以及Baeyer-Villiger氧化生成己内酯。烷基化环己醇的形成是该系列中最困难的步骤之一。在CeO 2或ZrO 2上存在镍的液相过程本文证明了催化剂可产生最高的环己醇收率。与4-烷基愈创木酚的催化反应遵循两条平行的途径,且速率相近:1)环加氢形成相应的烷基化2-甲氧基环己醇,以及2)脱甲氧基化形成4-烷基苯酚。尽管随后的苯酚向环己醇的转化速度很快,但从2-甲氧基环己醇中除去甲氧基的速率受到限制。总的来说,这最后一个反应是限速步骤,需要足够的温度(> 250°C)才能克服能垒。Ni / CeO 2的底物反应性(相对于烷基链的类型)和反应速率的催化剂特性(镍负载量和镍粒度)的细节已详细报道。催化剂。最好的Ni
Exceptional activity of gallium(<scp>iii</scp>) chloride and chlorogallate(<scp>iii</scp>) ionic liquids for Baeyer–Villiger oxidation
作者:Magdalena Markiton、Anna Chrobok、Karolina Matuszek、Kenneth R. Seddon、Małgorzata Swadźba-Kwaśny
DOI:10.1039/c6ra03435g
日期:——
a range of metal chlorides in different solvents, and in neat chlorogallate(III) ionic liquids. The extremely high activity of GaCl3 in promoting oxidation with H2O2, irrespective of solvent, was reported for the first time. The activity of all other metal chlorides was strongly solvent-dependent. In particular, AlCl3 was very active in a protic solvent (ethanol), and tin chlorides, SnCl4 and SnCl2
使用H 2 O 2作为氧化剂,使用一系列金属氯化物在不同溶剂中和纯净的氯镓酸盐(III)离子液体中,系统研究了Bayerer-Villiger对环酮的氧化。首次报道了GaCl 3在促进H 2 O 2氧化方面的极高活性,而与溶剂无关。所有其他金属氯化物的活性都高度依赖溶剂。特别是,AlCl 3在质子溶剂(乙醇)中非常活泼,氯化锡,SnCl 4和SnCl 2,在非质子传递溶剂(甲苯和二恶烷)中具有活性。为了消除对挥发性有机溶剂的需求,使用路易斯酸性氯镓酸盐(III)离子液体代替GaCl 3,在环境条件下,其在1-120分钟内通常可产生89-94%的内酯收率。Raman和71 Ga NMR光谱研究表明,在GaCl 3和galgallate(III)离子液体系统中的活性物质均为chlorohydroxygallate(III)阴离子[GaCl 3 OH] -,它们是GaCl 3部分水解的产物。和氯
A robust chemo-enzymatic lactone synthesis using acyltransferase from Mycobacterium smegmatis
isolated from Mycobacterium smegmatis for the chemo-enzymatic Baeyer-Villiger oxidation of cyclic ketones to lactones was demonstrated. Acyltransferase exhibited high activity, and high stability under harsh reaction conditions, like oxidation with 60% aq. H2O2 at 45 °C. This paves the way to a novel robust chemo-enzymatic method for lactone synthesis with high yields.
证明了从耻垢分枝杆菌分离的酰基转移酶在环酮化学酶Baeyer-Villiger氧化为内酯的新应用。酰基转移酶在苛刻的反应条件下表现出高活性和高稳定性,例如在60%aq。在45°C下为H 2 O 2。这为新型高产内酯合成的鲁棒化学酶法铺平了道路。