Biocatalytical production of (5S)-hydroxy-2-hexanone

Abstract

Biocatalytical approaches have been investigated in order to improve accessibility of the bifunctional chiral building block (5S)-hydroxy-2-hexanone ((S)-2). As a result, a new synthetic route starting from 2,5-hexanedione (1) was developed for (S)-2, which is produced with high enantioselectivity (ee >99%). Since (S)-2 can be reduced further to furnish (2S,5S)-hexanediol ((2S,5S)-3), chemoselectivity is a major issue. Among the tested biocatalysts the whole-cell system S. cerevisiae L13 surpasses the bacterial dehydrogenase ADH-T in terms of chemoselectivity. The use of whole-cells of S. cerevisiae L13 affords (S)-2 from prochiral 1 with 85% yield, which is 21% more than the value obtained with ADH-T. This is due to the different reaction rates of monoreduction (1-->2) and consecutive reduction (2-->3) of the respective biocatalysts. In order to optimise the performance of the whole-cell-bioreduction 1 2 with S. cerevisiae, the system was studied in detail, revealing interactions between cell-physiology and xenobiotic substrate and by-products, respectively. This study compares the whole-cell biocatalytic route with the enzymatic route to enantiopure (S)-2 and investigates factors determining performance and outcome of the bioreductions.

Application of Material and Energy Flow Analysis in the Early Stages of Biotechnical Process Development – A Case Study

“…The biocatalytic process developed utilizes the dehydrogenase ADH-T, which has been found to catalyze the reduction of 2,5-hexanedione giving (2S,5S)-hexanediol in > 99 % ee and de [38,39]. This enzyme uses the co-factor NADPH instead of molecular hydrogen as the ultimate hydrogen donor of the reduction reaction.…”

Promiscuous Substrate Binding Explains the Enzymatic Stereo‐ and Regiocontrolled Synthesis of Enantiopure Hydroxy Ketones and Diols

“…The bioreduction of diketones has not been extensively studied, [19][20][21][22][23][24][25][26] and in several cases microorganisms or plants [27][28][29][30][31][32] were used for this purpose. Thus, the obtained results in terms of regioand stereoselectivity usually remained unclear.…”

“…[9][10][11][12][13][14][15][16][17][18] In the particular case of the synthesis of enantiopure hydroxy ketones and/or diols starting from the corresponding diketones employing isolated ADHs, there are few examples available in the literature. [19][20][21][22][23][24][25][26] In other cases plants or microorganisms are employed, [27][28][29][30][31][32] frequently affording a mixture of stereo-and regioisomers due to the action of several enzymes with different and/or opposite selectivities. These derivatives are important building blocks of many natural compounds, [33,34] such as pheromones [35,36] or antitumor agents like discodermolide.…”

High-level production of (5S)-hydroxyhexane-2-one by two thermostable oxidoreductases in a whole-cell catalytic approach

“…They used L. kefir for the monoreduction of 2,5-hexanedione in a plug flow reactor and achieved a STY of 87 g/L/d. The reduction to (5S)-hydroxyhexane-2-one was performed by Katzberg et al [22] with whole-cells of S. cerevisiae L13 in a batch mode. However, like in all other published batch reactions [15,17,21], only rather low substrate concentrations of 20-110 mM 2,5-hexanedione were applied, resulting in only low final product concentrations.…”