- The Ru-catalyzed enantioselective preparation of chiral halohydrins and their application in the synthesis of (R)-clorprenaline and (S)-sotalol
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The asymmetric transfer hydrogenation of a series of halo-substituted aryl methyl ketones, including those substituted in both α-methyl and aryl rings, was studied for the preparation of chiral halohydrins. Up to 99.7% ee was obtained with 2-chloro-1-(2-chlorophenyl)ethanone as the substrate and Ru-CsDPEN as the catalyst in an HCOONa/H2O system. (R)-Clorprenaline, a drug used in the treatment of respiratory disorders, such as bronchitis and asthma, and (S)-sotalol, a class-III antiarrhythmic compound, were prepared with these chiral halohydrins.
- Lu, Chuanjun,Luo, Zonghua,Huang, Ling,Li, Xingshu
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- Chiral guanidine catalyzed acylative kinetic resolution of racemic 2-bromo-1-arylethanols
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In this study, chiral guanidine catalyzed acylative kinetic resolution of racemic 2-bromo-1-arylethanols was achieved with high selectivity. Irrespective of the electronic nature and the substitution patterns on the aromatic rings, a variety of substrates were suitable for this reaction. The branched acyl component was considered to be optimal for obtaining high s-values. The transition state of the reaction was proposed based on the absolute configuration of the obtained product.
- Sawada, Erika,Nakata, Kenya
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p. 371 - 373
(2021/03/16)
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- Lipase mediated enzymatic kinetic resolution of phenylethyl halohydrins acetates: A case of study and rationalization
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Racemic phenylethyl halohydrins acetates containing several groups attached to the aromatic ring were resolved via hydrolysis reaction in the presence of lipase B from Candida antarctica (Novozym 435). In all cases, the kinetic resolution was highly selective (E > 200) leading to the corresponding (S)-β-halohydrin with ee > 99 %. However, the time required for an ideal 50 % conversion ranged from 15 min for 2,4-dichlorophenyl chlorohydrin acetate to 216 h for 2-chlorophenyl bromohydrin acetate. Six chlorohydrins and five bromohydrins were evaluated, the latter being less reactive. For the β-brominated substrates, steric hindrance on the aromatic ring played a crucial role, which was not observed for the β-chlorinated derivatives. To shed light on the different reaction rates, docking studies were carried out with all the substrates using MD simulations. The computational data obtained for the β-brominated substrates, based on the parameters analysed such as NAC (near attack conformation), distance between Ser-O and carbonyl-C and oxyanion site stabilization were in agreement with the experimental results. On the other hand, the data obtained for β-chlorinated substrates suggested that physical aspects such as high hydrophobicity or induced change in the conformation of the enzymatic active site are more relevant aspects when compared to steric hindrance effects.
- Fonseca, Thiago de Sousa,Vega, Kimberly Benedetti,da Silva, Marcos Reinaldo,de Oliveira, Maria da Concei??o Ferreira,de Lemos, Telma Leda Gomes,Contente, Martina Letizia,Molinari, Francesco,Cespugli, Marco,Fortuna, Sara,Gardossi, Lucia,de Mattos, Marcos Carlos
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