Highly Efficient Synthesis of Optically Pure (S)-1-phenyl-1,2-ethanediol by a Self-Sufficient Whole Cell Biocatalyst

One-pot enantioselective synthesis of chiral phenyllactic acids by combining stereocomplementary d- and l-lactate dehydrogenases with multi-enzyme expression fine-tuning

Chiral phenyllactic acid (PLA) is a new type of antiseptic agent and a valuable precursor for active ingredients in pharmaceuticals and agrochemicals. In this study, we designed a multi-enzyme cascade that combined stereocomplementary d- and l-lactate dehydrogenases with threonine aldolase, phenylserine dehydratase, and formate dehydrogenase for the one-pot conversion of achiral glycine and benzaldehyde to synthesize d-PLA and l-PLA. To overcome the imbalance of multi-enzymes in a single cell, two enzyme modules, overexpressing four enzymes, were assembled in Escherichia coli cells to construct whole-cell catalysis systems (WCCSs). Furthermore, by optimizing reaction conditions and components, recombinant E. coli (WCCS 26) was able to produce 100 mM d-PLA with >99 % ee using a fed-batch strategy, while E. coli (WCCS 60) produced 47.2 mM l-PLA with >99 % ee. This study presents a sustainable and efficient method for synthesizing chiral PLAs from food-grade achiral starting materials.

Synthesis of α-hydroxy ketones and vicinal diols with the Bacillus licheniformis DSM 13T butane-2,3-diol dehydrogenase

The enantioselective synthesis of α-hydroxy ketones and vicinal diols is an intriguing field because of the broad applicability of these molecules. Although, butandiol dehydrogenases are known to play a key role in the production of 2,3-butandiol, their potential as biocatalysts is still not well studied. Here, we investigate the biocatalytic properties of the meso-butanediol dehydrogenase from Bacillus licheniformis DSM 13^T (BlBDH). The encoding gene was cloned with an N-terminal StrepII-tag and recombinantly overexpressed in E. coli. BlBDH is highly active towards several non-physiological diketones and α-hydroxyketones with varying aliphatic chain lengths or even containing phenyl moieties. By adjusting the reaction parameters in biotransformations the formation of either the α-hydroxyketone intermediate or the diol can be controlled.

Synthesis of α-hydroxy ketones and vicinal (R,R)-diols by Bacillus clausii DSM 8716T butanediol dehydrogenase

α-hydroxy ketones (HK) and 1,2-diols are important building blocks for fine chemical synthesis. Here, we describe the R-selective 2,3-butanediol dehydrogenase from B. clausii DSM 8716^T (BcBDH) that belongs to the metal-dependent medium chain dehydrogenases/reductases family (MDR) and catalyzes the selective asymmetric reduction of prochiral 1,2-diketones to the corresponding HK and, in some cases, the reduction of the same to the corresponding 1,2-diols. Aliphatic diketones, like 2,3-pentanedione, 2,3-hexanedione, 5-methyl-2,3-hexanedione, 3,4-hexanedione and 2,3-heptanedione are well transformed. In addition, surprisingly alkyl phenyl dicarbonyls, like 2-hydroxy-1-phenylpropan-1-one and phenylglyoxal are accepted, whereas their derivatives with two phenyl groups are not substrates. Supplementation of Mn²⁺ (1 mM) increases BcBDH's activity in biotransformations. Furthermore, the biocatalytic reduction of 5-methyl-2,3-hexanedione to mainly 5-methyl-3-hydroxy-2-hexanone with only small amounts of 5-methyl-2-hydroxy-3-hexanone within an enzyme membrane reactor is demonstrated.

Reduction of symmetric or asymmetric vicinal diketones with BcBDH leads to the synthesis of either α-hydroxyketones or vicinal diols.

Halogenated Compounds from Directed Fermentation of Penicillium concentricum, an Endophytic Fungus of the Liverwort Trichocolea tomentella

One new chlorinated xanthone, 6-chloro-3,8-dihydroxy-1-methylxanthone (1), a new 2-bromo-gentisyl alcohol (2), and a mixture of 6-epimers of 6-dehydroxy-6-bromogabosine C (3a and 3b), together with 19 previously identified compounds, epoxydon (4), norlichexanthone (5), 2-chlorogentisyl alcohol (6), hydroxychlorogentisyl quinone (7), 6-dehydroxy-6α-chlorogabosine C (8a), 6-dehydroxy-6β-chlorogabosine C (8b), gentisyl alcohol (9), gentisyl quinone (10), (R,S)-1-phenyl-1,2-ethanediol (11), dehydrodechlorogriseofulvin (12), dechlorogriseofulvin (13), dehydrogriseofulvin (14), griseofulvin (15), ethylene glycol benzoate (16), alternariol (17), griseoxanthone C (18), drimiopsin H (19), griseophenone C (20), and griseophenone B (21), were isolated from cultures of Penicillium concentricum, a fungal endophyte of the liverwort Trichocolea tomentella. The structures of the new compounds (1, 2, 3a, and 3b) were elucidated by interpretation of spectroscopic data including one- and two-dimensional NMR techniques. Among these, compounds 2-4 displayed modest cytotoxicity to the MCF-7 hormone-dependent breast cancer cell line with IC₅₀ values of 8.4, 9.7, and 5.7 μM, respectively, whereas compound 9 exhibited selective cytotoxicity against the HT-29 colon cancer cell line with an IC₅₀ value of 6.4 μM. During this study we confirmed that the brominated gentisyl alcohol (2) was formed by chemical conversion of 4 during bromide salt addition to culture media.