63261-45-0Relevant articles and documents
Microstructure Analysis of Poly(cyclopentene carbonate)s at the Diad Level
Liu, Ye,Li, Rong-Rong,Lu, Xiao-Bing
, p. 6941 - 6947 (2015)
The spectroscopic assignment of poly(cyclopentene carbonate)s at the diad level was performed by using two kinds of model compounds: isotactic and syndiotactic dimers of cyclopentene carbonate unit. By comparing the signals in the carbonyl region, we concluded that the signals at 153.85 and 153.78 ppm in the 13C NMR spectrum of poly(cyclopentene carbonate) were attributed to m-diad and r-diad, respectively. The signals at 82.61 and 82.53 ppm in the 13C NMR spectrum were assigned to m-diad and r-diad peak of methine resonance, respectively. It was found that the carbonate carbon signals were sensitive toward the stereocenters on adjacent epoxide ring-opening units. The syndiotactic and isotactic diads matched well with the microstructures of the stereoregular poly(cyclopentene carbonate)s that were prepared by using chiral dinuclear Co(III) complex catalysts.
Structural and Computational Insight into the Catalytic Mechanism of Limonene Epoxide Hydrolase Mutants in Stereoselective Transformations
Sun, Zhoutong,Wu, Lian,Bocola, Marco,Chan, H. C. Stephen,Lonsdale, Richard,Kong, Xu-Dong,Yuan, Shuguang,Zhou, Jiahai,Reetz, Manfred T.
supporting information, p. 310 - 318 (2018/01/17)
Directed evolution of limonene epoxide hydrolase (LEH), which catalyzes the hydrolytic desymmetrization reactions of cyclopentene oxide and cyclohexene oxide, results in (R,R)- and (S,S)-selective mutants. Their crystal structures combined with extensive theoretical computations shed light on the mechanistic intricacies of this widely used enzyme. From the computed activation energies of various pathways, we discover the underlying stereochemistry for favorable reactions. Surprisingly, some of the most enantioselective mutants that rapidly convert cyclohexene oxide do not catalyze the analogous transformation of the structurally similar cyclopentene oxide, as shown by additional X-ray structures of the variants harboring this slightly smaller substrate. We explain this puzzling observation on the basis of computational calculations which reveal a disrupted alignment between nucleophilic water and cyclopentene oxide due to the pronounced flexibility of the binding pocket. In contrast, in the stereoselective reactions of cyclohexene oxide, reactive conformations are easily reached. The unique combination of structural and computational data allows insight into mechanistic details of this epoxide hydrolase and provides guidance for future protein engineering in reactions of structurally different substrates.
Chiral-Substituted Poly-N-vinylpyrrolidinones and Bimetallic Nanoclusters in Catalytic Asymmetric Oxidation Reactions
Hao, Bo,Gunaratna, Medha J.,Zhang, Man,Weerasekara, Sahani,Seiwald, Sarah N.,Nguyen, Vu T.,Meier, Alex,Hua, Duy H.
supporting information, p. 16839 - 16848 (2017/01/10)
A new class of poly-N-vinylpyrrolidinones containing an asymmetric center at C5 of the pyrrolidinone ring were synthesized from l-amino acids. The polymers, particularly 17, were used to stabilize nanoclusters such as Pd/Au for the catalytic asymmetric oxidations of 1,3- and 1,2-cycloalkanediols and alkenes, and Cu/Au was used for C-H oxidation of cycloalkanes. It was found that the bulkier the C5 substituent in the pyrrolidinone ring, the greater the optical yields produced. Both oxidative kinetic resolution of (±)-1,3- and 1,2-trans-cycloalkanediols and desymmetrization of meso cis-diols took place with 0.15 mol % Pd/Au (3:1)-17 under oxygen atmosphere in water to give excellent chemical and optical yields of (S)-hydroxy ketones. Various alkenes were oxidized with 0.5 mol % Pd/Au (3:1)-17 under 30 psi of oxygen in water to give the dihydroxylated products in >93% ee. Oxidation of (R)-limonene at 25 °C occurred at the C-1,2-cyclic alkene function yielding (1S,2R,4R)-dihydroxylimonene 49 in 92% yield. Importantly, cycloalkanes were oxidized with 1 mol % Cu/Au (3:1)-17 and 30% H2O2 in acetonitrile to afford chiral ketones in very good to excellent chemical and optical yields. Alkene function was not oxidized under the reaction conditions. Mechanisms were proposed for the oxidation reactions, and observed stereo- and regio-chemistry were summarized.
