Journal of Molecular Catalysis B: Enzymatic 109 (2014) 47–52 Contents lists available at ScienceDirect Journal of Molecular Catalysis B: Enzymatic j ourna l ho me pa ge: www.elsevier.com/locate/molcatb Enantioselective reduction of flavanone and oxidation of cis- and trans-flavan-4-ol by selected yeast cultures Tomasz Janeczko ∗ , Monika Dymarska, Monika Siepka, Radosław Gniłka, Agnieszka Le´ sniak, Jarosław Popło ´ nski, Edyta Kostrzewa-Susłow Department of Chemistry, Wroclaw University of Environmental and Life Sciences, Norwida 25, 50-375 Wroclaw, Poland a r t i c l e i n f o Article history: Received 26 March 2014 Received in revised form 8 August 2014 Accepted 11 August 2014 Available online 20 August 2014 Keywords: Flavanone Flavan-4-ol Biotransformation Yeast Enantioselective oxidation a b s t r a c t This research investigated stereochemistry of reduction of racemic flavanone and a concurrent com- petitive process of oxidation, taking place in cultures of live yeast strains. The results obtained gave us information about capability of tested biocatalysts for enantioselective (with respect to both substrate and product) reduction of flavanone and for enantioselective oxidation of the resulting cis- and trans- flavan-4-ols. As a result of our experiments we obtained (2S,4S)-cis-flavan-4-ol with 43% of conversion and 96% of enantiomeric excess, and (2R,4S)-trans-flavan-4-ol with 41% of conversion and ee > 99% in the culture of Rhodotorula rubra; (2S,4S)-cis-flavan-4-ol (43%, ee = 96%) along with (2R,4R)-cis-flavan- 4-ol (44%, ee = 61%) in the culture of Zygosaccharomyces bailii KCh 907. Additionally, some of the tested strains demonstrated an excellent capability for enantioselective oxidation of (±)-cis-flavan-4-ol and (±)- trans-flavan-4-ol, obtained by chemical synthesis. A one-day biotransformation in the culture of Candida parapsilosis KCh 909 afforded (S)-flavanone (ee = 93%) as 49% of the reaction mixture and 49% of unreacted (2R,4R)-cis-flavan-4-ol with ee = 97%. Racemic trans-flavan-4-ol was effectively oxidized in the culture of Yarrowia lipolytica KCh 71 – after a three-day biotransformation the reaction mixture contained 52% of (R)-flavanone (ee = 85%) and 48% of (2R,4S)-trans-flavan-4-ol with a high enantiomeric excess (ee = 93%). © 2014 Elsevier B.V. All rights reserved. 1. Introduction Flavonoids are natural compounds widely present in the plant kingdom, which are biosynthesized by plants from phenylala- nine [1,2]. They are naturally found in fruits, vegetables, seeds and plant products, therefore they are an integral part of human diet. Flavonoids proved to be safe for human organism and their daily intake has been estimated to be about 1 g per day [3–5]. Natural flavan-4-ones are homochiral and show levorotation. In isolated from plants flavanones: pinocembrin, pinostrobin, hes- peretin and naringenin at the C-2 stereogenic centre there has been (S)-configuration assigned [6–9]. Natural flavan-4-ols have also S- configuration at C-2, whereas the hydroxyl group at C-4 is situated trans to the phenyl group [10,11]. Such an orientation of the sub- stituents at C-2 and C-4, which has been described in literature for luteoforol, apiforol [12,13] and glycosides: abacopterin I, Triphyllin ∗ Corresponding author. Tel.: +48 71 320 52 52; fax: +48 71 3284124. E-mail addresses: janeczko13@interia.pl, tomasz.janeczko@up.wroc.pl (T. Janeczko). A, and Eruberin B [14,15], means that the hydroxyl group is in a pseudo axial position, and the established absolute configuration at C-4 is R [12,15,16]. It has been reported in literature that racemic flavanone (4) can be enantiospecifically reduced to (2R,4R)-cis-flavan-4-ol (5) with the help of chiral ruthenium complexes [17]. Except for the respective flavan-4-ol (5) this method afforded also unre- acted (S)-flavanone (4) with a high enantiomeric excess [17]. (S)-flavanone (4) and (2S,4S)-cis-flavan-4-ol (5) were also obtained by means of an enantioselective Ru/NHC-catalyzed hydrogena- tion of flavone [18]. (S)-flavanone (4) was prepared in six steps, starting from commercially available 3,5-dimethoxyphenol and (+)-ethyl (R)-3-hydroxy-3-phenylpropanoate [19]. Optically active (R)- and (S)-flavanone (4) were prepared by the enantioselective enzymatic hydrolysis of (±)-flavanone O-acyl oxime using lipase [20]. Optically active cis-flavan-4-ols (5) were obtained in two ways: by enzymatic esterification of respective alcohols [21], and by enantioselective hydrolysis of respective esters [22]. Incubation of (±)-flavanone (4) in the culture of bakers’ yeast gave (+)-(2S,4S)- cis-4-hydroxyflavan (5) in 32% yield (83% ee) and optically active (+)-(R)-flavanone (4) in 51% yield (20% ee) [22]. http://dx.doi.org/10.1016/j.molcatb.2014.08.006 1381-1177/© 2014 Elsevier B.V. All rights reserved.