Joyce Benzaquem Ribeiro

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.

Improving the Toolbox of Bioreductions by the Use of Continuous Flow Systems

Packed bed reactors can be used as an interesting alternative on the bioreduction of β-ketoesteres mediated by immobilized microorganisms. Here in, we report our results on the bioreduction of ethyl 3-oxohexanoate by immobilized Kluyveromyces marxianus cells and tert-butyl 3-oxobutanoate by immobilized Rhodotorula rubra cells under continuous flow conditions leading the desired β-hydroxy esters corresponding in high yields and enantiomeric excess.

Whole Cells in Enantioselective Reduction of tert-Butyl Acetoacetate

Abstract The β-ketoester tert-butyl acetoacetate was enantioselectively reduced to tert-butyl (S)-3-hydroxybutanoate by seven microorganism strains. The best result using free cells was obtained with the yeast R. rubra, which furnished 97.6% ee and higher than 99% of conversion within 24 h. After immobilization in calcium alginate spheres, R. rubra furnished 96% ee and higher than 99% ee within 24 h, even if substrate concentration was 58 mM. Immobilized cells were reused three times without loss of enantioselectivity. GRAPHICAL ABSTRACT

Whole cells in enantioselective reduction of benzyl acetoacetate.

The β-ketoester benzyl acetoacetate was enantioselectively reduced to benzyl (S)-3-hydroxybutanoate by seven microorganism species. The best result using free cells was obtained with the yeast Hansenula sp., which furnished 97% ee and 85% of conversion within 24 h. After immobilization in calcium alginate spheres, K.marxianus showed to be more stable after 2 cycles of reaction.

Hydroxylation of 1,8-cineole by Mucor ramannianus and Aspergillus niger

The monoterpenoid 1,8-cineole is obtained from the leaves of Eucalyptus globulus and it has important biological activities. It is a cheap natural substrate because it is a by-product of the Eucalyptus cultivation for wood and pulp production. In this study, it was evaluated the potential of three filamentous fungi in the biotransformation of 1,8-cineole. The study was divided in two steps: first, reactions were carried out with 1,8-cineole at 1 g/L for 24 h; afterwards, reactions were carried out with substrate at 5 g/L for 5 days. The substrate was hydroxylated into 2-exo-hydroxy-1,8-cineole and 3-exo-hydroxy-1,8-cineole by fungi Mucor ramannianus and Aspergillus niger with high stereoselectivity. Trichoderma harzianum was also tested but no transformation was detected. M. ramannianus led to higher than 99% of conversion within 24 h with a starting high substrate concentration (1 g/L). When substrate was added at 5 g/L, only M. ramannianus was able to catalyze the reaction, but the conversion level was 21.7% after 5 days. Both products have defined stereochemistry and could be used as chiral synthons. Furthermore, biological activity has been described for 3-exo-hydroxy-1,8-cineol. To the best of our knowledge, this is the first report on the use of M. ramannianus in this reaction.