Stereoselective oxidation of aliphatic diols and reduction of hydroxy-ketones with galactitol dehydrogenase from Rhodobacter sphaeroides D.
From the Rhodobacter sphaeroides mutant D a galactitol dehydrogenase (GDH) was isolated and characterized in an earlier investigation (1). The enzyme expressed activity with a wide spread substrate spectrum, like sugars, sugar alcohols, secondary alcohols or the corresponding ketones and it can be used for the production of the rare sugar L-tagatose by regioselective oxidation of galactitol (2). This study focuses on the preparation of optically pure aliphatic diols by oxidation of one enantiomer or stereospecific reduction of keto-alcohols and diketones. The oxidation of 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol and 1,2-hexanediol occurred highly specific with the S-enantiomer leaving the R-enantiomer of the diols in the reaction vessel. Also (S)-1,2,6-hexanetriol was oxidized by GDH to 1,6-dihydroxy-2-hexanone. The Km values of these reactions decreased with increasing length of the carbon chain. Reduction of hydroxyacetone or 1-hydroxy-2-butanone resulted in an excess of 93% (S)-1,2-propanediol and more than 98% of (S)-1,2-butanediol, respectively. The diketone 2,3-hexanedione was only reduced to (2R,3S)-2,3-hexanediol, one of the possible four configurations. The wide substrate spectrum on one hand and the selectivity in the reaction on the other hand make GDH a very interesting enzyme for the production of optically pure building blocks in the chemical synthesis of bioactive compounds.
Institute for Applied Microbiology, Saarland University, Im Stadtwald, D-66123 Saarbruecken, Germany. gkohring@mx.uni-saarland.de
G W
GW
Kohring
P
P
Wiehr
M
M
Jeworski
F
F
Giffhorn
D004101:Dihydroxydihydrobenzopyrenes / Q000493:pharmacokinetics; D007659:Ketones / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D012242:Rhodobacter sphaeroides / Q000201:enzymology* / Q000254:growth & development; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013379:Substrate Specificity; D013401:Sugar Alcohol Dehydrogenases / Q000378:metabolism*
D004101:Dihydroxydihydrobenzopyrenes; D007659:Ketones; D013401:Sugar Alcohol Dehydrogenases; C095946:galactitol 2-dehydrogenase