Cryptococcus laurentii as a new biocatalyst for the asymmetric reduction of substituted acetophenones

Taguchi analysis and asymmetric keto-reduction of acetophenone and its derivatives by soil filamentous fungal isolate: Penicillium rubens VIT SS1

Microbial asymmetric reduction of ketone is an efficient tool for the synthesis of chiral alcohols. This research focuses on exploring the soil fungal isolates for their ability toward the keto reduction of acetophenone and its derivatives to their corresponding chiral alcohols using growing cells. Bioreduction of acetophenone, 4-fluoro acetophenone, 4-methyl acetophenone, and 3-hydroxy acetophenone was carried out using different fungal cultures isolated from soil. Among the fungal isolates, Penicillium sp. and Aspergillus sp. showed significant bioconversion with varying enantio-selectivity. However, the Penicillium sp. has shown the maximum ability of bioreduction. The potential isolate was characterized using the internal transcribed spacer (ITS) region and found to be Penicillium rubens VIT SS1 (Genbank accession number: MK063869.1), which showed higher conversion and selectivity > 90%. The biocatalyst production and the reaction conditions were optimized using Taguchi analysis. The process conditions such as pH, temperature, media components, cosolvent, and substrate dosing were evaluated for the bioreduction of 3-hydroxy acetophenone, which is a key chiral intermediate of Phenylephrine and Rivastigmine using P. rubens VIT SS1. This study concludes about the potential of fungal cultures for sustainable synthesis of key chiral intermediates of Phenylephrine and Rivastigmine, similarly many aromatic chiral alcohols in simpler, novel, and cost-effective manner.

Production of chiral compounds using immobilized cells as a source of biocatalysts

The importance of chiral compounds in all fields of technology and life sciences is shown. Small chiral molecules are mainly used as building blocks in the synthesis of more complex and functionalized compounds. Nature creates and imposes stereoselectivity by means of enzymes, which are highly efficient biocatalysts. The use of whole cells as a biocatalyst source is a promising strategy for avoiding some drawbacks associated with the use of pure enzymes, especially their high cost. The use of free cells is also challenging, since cell lysis can also occur under the reaction conditions. However, cell immobilization has been employed to increase the catalytic potential of enzymes by extending their lifetimes in organic solvents and non-natural environments. Besides, immobilized cells maintain their biocatalytic performance for several reaction cycles. Considering the above-mentioned arguments, several authors have synthesized different classes of chiral compounds such as alcohols, amines, carboxylic acids, amides, sulfides and lactones by means of immobilized cells. Our aim was to discuss the main aspects of the production of chiral compounds using immobilized cells as a source of biocatalysts, except under fermentation conditions.