Maria da Conceição Klaus V. Ramos

Microbiological enantioselective reduction of ethyl acetoacetate

Abstract Different microorganisms (MOs) were used to carry out the enantioselective reduction of ethyl acetoacetate to (S)-(+)-3-hydroxybutanoate or (R)-(−)-3-hydroxybutanoate. Surprisingly, the commercially available Saccaromyces cerevisiae led to only 58% ee of (S)-(+)-3-hydroxybutanoate. Other MOs such as Hansenula sp. and Dekera sp. furnished the same enantiomer with greater ees, 81 and 73%, respectively. Aspergilus niger and Kluyveromyces marxianus although leading to lower ees, 30 and 18%, yielded the opposite enantiomer. All reactions proceeded to greater than 85% conversion. This is the first report on the use of Hansenula sp. and Dekera sp. in reductions of β-ketoesters.

Chiral separation of γ-butyrolactone derivatives by gas chromatography on 2,3-di-O-methyl-6-O-tert.-butyldimethylsilyl-β-cyclodextrin

Abstract The chiral GC separation of 2-alkyl-2-keto-γ-butyrolactone derivatives and their alcohol analogs using 2,3-di- O -methyl-6- O - tert .-butyldimethylsilyl-β-cyclodextrin (DIMETBCD) as chiral selector was discussed. The results, supported by the ketone preliminary molecular modelling calculations, suggest that the chiral recognition for DIMETBCD depends more on the geometry than on the polarity of the alkyl substituents on the butyrolactones. Hydrogen bonds and alkyl group steric effects should be an important function of the alcohol chiral recognition for DIMETBCD. Comparison of the retention times of the alcohol derivatives, in achiral and chiral stationary phases, suggests a specific structural effect for the cyclodextrin selector.

STUDIES ON THE DIASTEREO- SELECTIVE REDUCTION OF 2-ACETYL-2-ALKYL- γ-BUTYROLACTONES WITH BORON HYDRIDES1*

ABSTRACT Reduction of 2-acetyl-2-alkyl-γ-butyrolactone derivatives with boron hydrides in the presence and absence of several chelating agents were studied. This process is influenced more by steric than chelation factors, yielding the isomeric alcohols syn (13–23) and anti (14–24) in good diastereomeric excess. *This paper is the contribution #53 from LASSbio.

Improvement of enantioselective syntheses and chiral high resolution gas chromatographic analyses of (+)-2-allyl-2-carboethoxy-cyclopentanol.

The improvement of the biocatalytic reduction of 2-allyl-carboethoxy-cyclopentanone (2) to the corresponding cyclopentanol derivative (+)-(1R,2R)-(1) was accomplished employing bakers yeast in organic media. This chiral cyclopentanol derivative (1), analyzed by high resolution gas chromatography performed over beta-cyclodextrin stationary phase, was obtained in 38% yield (> 99% e.e.).

Distribution of indoor air pollutants in downtown Rio de Janeiro, Brazil

Indoor air quality (IAQ) has been a matter of public concern in Brazil. However, few studies have been performed in the whole country. This work presents an IAQ survey conducted in different kinds of indoor environments in Rio de Janeiro City. Air samples were analyzed to determine individual and total volatile organic compounds (TVOCs), aldehydes, total particulate matter (TPM) and fungi. TVOC concentrations ranged from 101 to 12823 µg m-3 with an average of 1594 µg m-3, exceeding the suggested limit from ANVISA7 (500 µg m-3). Indoor/outdoor ratios for most of the parameters were higher than unit, indicating indoor sources of pollution. On the other hand, low levels of airborne fungi were detected (14-314 cfu m-3) being below than the ANVISA standard7 (750 cfu m-3). Overall, the environments did not present good air quality for the occupants due to chemical pollutants.

Asymmetric bioreduction of β-ketoesters derivatives by Kluyveromyces marxianus: influence of molecular structure on the conversion and enantiomeric excess

This study presents the bioreduction of six β-ketoesters by whole cells of Kluyveromyces marxianus and molecular investigation of a series of 13 β-ketoesters by hologram quantitative structure-activity relationship (HQSAR) in order to relate with conversion and enantiomeric excess of β-stereogenic-hydroxyesters obtained by the same methodology. Four of these were obtained as (R)-configuration and two (S)-configuration, among them four compounds exhibited >99% enantiomeric excess. The β-ketoesters series LUMO maps showed that the β-carbon of the ketoester scaffold are exposed to undergo nucleophilic attack, suggesting a more favorable β-carbon side to enzymatic reduction based on adopted molecular conformation at the reaction moment. The HQSAR method was performed on the β-ketoesters derivatives separating them into those provided predominantly (R)- or (S)-β-hydroxyesters. The HQSAR models for both (R)- and (S)-configuration showed high predictive capacity. The HQSAR contribution maps suggest the importance of β-ketoesters scaffold as well as the substituents attached therein to asymmetric reduction, showing a possible influence of the ester group carbonyl position on the molecular conformation in the enzyme catalytic site, exposing a β-carbon side to the bioconversion to (S)- and (R)-enantiomers.

Glicerol como solvente verde em eficiente obtenção de beta-hidroxiésteres

In this work, we report a new method for obtaining racemic β-hydroxyesters by reduction of β-ketoesters. The use of glycerol as a reactional medium in selective reduction of β-ketoesters into the corresponding alcohols was shown to be a viable and more efficient alternative compared with the conventional methodology, taking into account green chemistry prerogatives.