- Lipases aided esterification of (2,2-dimethyl-1,3-dioxolan-4-yl)methanol
-
Racemic solketal (2,2-Dimethyl-1,3-dioxolan-4-yl)methanol 1, was treated with carboxylic acids of varying chain length or their vinyl esters in the presence of different lipases. The esterification reaction was carried out in n-hexane or diisopropyl ether as a solvent. The yield of the solketal esters and their enantiopurity were satisfactory, as indicated by gas chromatography using chiral column. Lipases from Rhizopus oryzae and Pseudomonas fluorescence gave the best enantiomeric excess (ee) when the solketal was treated with vinyl butyrate in a solution of diisopropyl ether at room temperature.
- Zniszczol, Aurelia,Walczak, Krzysztof Z.
-
-
- Enhanced enantioselectivity of Bacillus coagulans in the hydrolysis of 1,2-O-isopropylidene glycerol esters by thermal knock-out of undesired enzymes
-
The enantioselective hydrolysis of different (RS)-1,2-O-isopropylidene glycerol esters has been achieved with whole cells of Bacillus coagulans NCIMB 9365 furnishing the (S)-alcohol as the major enantiomer. The reaction is catalysed by a thermostable cell-bound carboxylesterase and improvement of the enantioselectivity has been achieved by heat treatment of the whole cells, which causes the knock-outs a non-enantioselective competing enzyme. Thermally-treated cells hydrolysed (RS)-1,2-O-isopropylidene glycerol esters with high enantioselectivity, the highest enantiomeric ratio (80-100) being observed for the benzoate. The biocatalyst displayed good stability and could be re-used after filtration for 12 cycles before showing significant loss of activity; repeated biotransformation batches allowed the recovery of 9.55 g/L of enantiomerically pure (S)-isopropylideneglycerol benzoate starting from 24.0 g/L of the racemic mixture.
- Romano, Diego,Falcioni, Francesco,Mora, Diego,Molinari, Francesco,Buthe, Andreas,Ansorge-Schumacher, Marion
-
p. 841 - 845
(2007/10/03)
-
- Lipase-mediated desymmetrization of glycerol with aromatic and aliphatic anhydrides
-
Chirazyme L-2 (Candida antarctica) catalyzed esterification of glycerol with aromatic and aliphatic anhydrides in 1,4-dioxane is described. All the aromatic monoacylglycerols (MAGs) were produced as (R)-enantiomers, while aliphatic MAGs were obtained either as racemic mixtures or the (S)-enantiomers. The influence of substituted aromatic rings, chain length, and presence of a conjugated double bond in the acyl donor moiety on the enantiotopic selectivity as well as the efficiency of the enzyme was studied.
- Batovska, Daniela I.,Tsubota, Shuichirou,Kato, Yasuo,Asano, Yasuhisa,Ubukata, Makoto
-
p. 3551 - 3559
(2007/10/03)
-
- Method of manufacture of 1,3-oxathiolane nucleosides
-
Processes for the preparation of 1,3-oxathiolane nucleosides are provided that include efficient methods for the preparation of the 1,3-oxathiolane ring and subsequent condensation of the 1,3-oxathiolane with a pyrimidine or purine base. Using the processes described herein, the compounds can be provided as isolated enantiomers.
- -
-
-
- Quantitative screening of hydrolase libraries using pH indicators: Identifying active and enantioselective hydrolases
-
The slowest step in finding a selective hydrolase for synthesis is often the screening step. Researchers must run small test reactions and measure the amounts of stereoisomers formed by HPLC, GC, or NMR. We have developed a colorimetric method to speed up this screening. We quantitatively detect ester hydrolysis using a pH indicator, 4-nitrophenol. We estimate the selectivity by measuring the initial rates of hydrolysis for pure stereoisomers separately. To demonstrate the utility of this method, we screened seventy-two commercial enzymes for enantioselective hydrolysis of racemic solketal butyrate, an important chiral building block. First, we eliminated the twenty hydrolases that did not catalyze hydrolysis of either enantiomer. Next, we measured initial rates of hydrolysis of the pure enantiomers of solketal butyrate. For horse-liver esterase, these initial rates differed by a factor of twelve. Subsequent GC experiments confirmed an enantiomeric ratio of fifteen for this hydrolase. Although this enantioselectivity is moderate, it is the highest enantioselectivity reported for a hydrolysis of solketal esters.
- Janes, Lana E.,Loewendahl, A. Christina,Kazlauskas, Romas J.
-
p. 2324 - 2331
(2007/10/03)
-
- Enzymatic resolution of 2,2-disubstituted-1,3-dioxolane-4-methanol carboxylic esters
-
The enantioselectivity of enzymatic hydrolysis of carboxylic esters of various 1,2-ketals of glycerol has been investigated. The influence of the ketal group has been studied. A number of lipases and proteinases have been tested and the best enantioselectivity was obtained with proteinase from Aspergillus oryzae which gave an E-value of 9 with 2,2-dimethyl-1,3-dioxolane-4-methanol butanoate. Variations in the acyl part revealed that butanoyl was optimal. All hydrolysis products have been synthesised in homochiral forms from homochiral starting materials.
- Partali,Melbye,Alvik,Anthonsen
-
-