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Alexander Fries

Bio: Alexander Fries is an academic researcher from University of Freiburg. The author has contributed to research in topics: Biocatalysis & Michael reaction. The author has an hindex of 6, co-authored 7 publications receiving 143 citations. Previous affiliations of Alexander Fries include Facultad de Ciencias Exactas y Naturales.

Papers
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Journal ArticleDOI
TL;DR: The results show that fungi use highly specific cytochrome P450 enzymes for regio- and stereoselective phenol coupling and suggest that bimolecular phenoxy radical couplings in nature can be catalyzed by phenol-coupling P450 heme enzymes, which might also apply to the plant kingdom.
Abstract: For almost 100 years, phenoxy radical coupling has been known to proceed in nature. Because of the linkage of their molecular halves (regiochemistry) and the configuration of the biaryl axis (stereochemistry), biaryls are notoriously difficult to synthesize. Whereas the intramolecular enzymatic coupling has been elucidated in detail for several examples, the bimolecular intermolecular coupling could not be assigned to one single enzyme in the biosynthesis of axially chiral biaryls. As these transformations often take place regio- and stereoselectively, enzyme-catalyzed control is reasonable. We now report the identification and expression of fungal cytochrome P450 enzymes that catalyze regio- and stereoselective intermolecular phenol couplings. The cytochrome P450 enzyme KtnC from the kotanin biosynthetic pathway of Aspergillus niger was expressed in Saccharomyces cerevisiae. The recombinant cells catalyzed the coupling of the monomeric coumarin 7-demethylsiderin both regio- and stereoselectively to the 8...

75 citations

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TL;DR: It is shown that SgvM from Streptomyces griseoviridis features an extended substrate scope with respect to the nucleophile as well as the electrophile, and could be a valuable tool for asymmetric biocatalytic C-alkylation reactions.
Abstract: S-Adenosylmethionine-dependent methyltransferases (MTs) play a decisive role in the biosynthesis of natural products and in epigenetic processes. MTs catalyze the methylation of heteroatoms and even of carbon atoms, which, in many cases, is a challenging reaction in conventional synthesis. However, C-MTs are often highly substrate-specific. Herein, we show that SgvM from Streptomyces griseoviridis features an extended substrate scope with respect to the nucleophile as well as the electrophile. Aside from its physiological substrate 4-methyl-2-oxovalerate, SgvM catalyzes the (di)methylation of pyruvate, 2-oxobutyrate, 2-oxovalerate, and phenylpyruvate at the β-carbon atom. Chiral-phase HPLC analysis revealed that the methylation of 2-oxovalerate occurs with R selectivity while the ethylation of 2-oxobutyrate with S-adenosylethionine results in the S enantiomer of 3-methyl-2-oxovalerate. Thus SgvM could be a valuable tool for asymmetric biocatalytic C-alkylation reactions.

39 citations

Journal ArticleDOI
TL;DR: Asymmetric mixed carboligation reactions of α-ketoglutarate with different aldehydes were explored with the thiamine diphosphate dependent enzymes SucA, Kgd and MenD to selectively deliver chiral δ-hydroxy-γ-keto acids with moderate to excellent stereoselectivity.

31 citations

Journal ArticleDOI
TL;DR: This facile and robust method developed for 25OHVD3 synthesis is a novel example for the concept of substrate-engineered catalysis and offers an attractive alternative to chemical or O2 /electron-donor-dependent enzymatic procedures.
Abstract: The hydroxylation of vitamin D3 (VD3, cholecalciferol) side chains to give 25-hydroxyvitamin D3 (25OHVD3) is a crucial reaction in the formation of the circulating and biologically active forms of VD3. It is usually catalyzed by cytochrome P450 monooxygenases that depend on complex electron donor systems. Cell-free extracts and a purified Mo enzyme from a bacterium anaerobically grown with cholesterol were employed for the regioselective, ferricyanide-dependent hydroxylation of VD3 and proVD3 (7-dehydrocholesterol) into the corresponding tertiary alcohols with greater than 99 % yield. Hydroxylation of VD3 strictly depends on a cyclodextrin-assisted isomerization of VD3 into preVD3, the actual enzymatic substrate. This facile and robust method developed for 25OHVD3 synthesis is a novel example for the concept of substrate-engineered catalysis and offers an attractive alternative to chemical or O2 /electron-donor-dependent enzymatic procedures.

16 citations

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TL;DR: Unexpectedly, as the identified residues such as Arg107 are highly conserved, some of the designed variations can be found in wild‐type SEPHCHC synthases from other bacteria (Arg107Lys, 0.3 %).
Abstract: Chorismate and isochorismate constitute branch-point intermediates in the biosynthesis of many aromatic metabolites in microorganisms and plants. To obtain unnatural compounds, we modified the route to menaquinone in Escherichia coli. We propose a model for the binding of isochorismate to the active site of MenD ((1R,2S, 5S,6S)-2-succinyl-5-enolpyruvyl-6-hydroxycyclohex-3-ene-1-carboxylate (SEPHCHC) synthase) that explains the outcome of the native reaction with α-ketoglutarate. We have rationally designed variants of MenD for the conversion of several isochorismate analogues. The double-variant Asn117Arg-Leu478Thr preferentially converts (5S,6S)-5,6-dihydroxycyclohexa-1,3-diene-1-carboxylate (2,3-trans-CHD), the hydrolysis product of isochorismate, with a >70-fold higher ratio than that for the wild type. The single-variant Arg107Ile uses (5S,6S)-6-amino-5-hydroxycyclohexa-1,3-diene-1-carboxylate (2,3-trans-CHA) as substrate with >6-fold conversion compared to wild-type MenD. The novel compounds have been made accessible in vivo (up to 5.3 g L-1 ). Unexpectedly, as the identified residues such as Arg107 are highly conserved (>94 %), some of the designed variations can be found in wild-type SEPHCHC synthases from other bacteria (Arg107Lys, 0.3 %). This raises the question for the possible natural occurrence of as yet unexplored branches of the shikimate pathway.

8 citations


Cited by
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TL;DR: A review of biocatalysis with a special focus on scalable chemical production using enzymes discusses the opportunities and limitations of enzymatic syntheses using distinct examples and provides an outlook on emerging enzyme classes.
Abstract: Biocatalysis has found numerous applications in various fields as an alternative to chemical catalysis. The use of enzymes in organic synthesis, especially to make chiral compounds for pharmaceuticals as well for the flavors and fragrance industry, are the most prominent examples. In addition, biocatalysts are used on a large scale to make specialty and even bulk chemicals. This review intends to give illustrative examples in this field with a special focus on scalable chemical production using enzymes. It also discusses the opportunities and limitations of enzymatic syntheses using distinct examples and provides an outlook on emerging enzyme classes.

538 citations

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TL;DR: The review provides a guide to the use of biocatalytic methods in the area of chemical synthesis with focused attention on retrosynthetic considerations and analysis and is expected to lead to better understanding of the characteristics and distinctions of the two complementary approaches.
Abstract: Recent developments of stereoselective biocatalytic and chemocatalytic methods are discussed. The review provides a guide to the use of biocatalytic methods in the area of chemical synthesis with focused attention on retrosynthetic considerations and analysis. The transformations presented are organized according to bond disconnections and attendant synthetic methods. The review is expected to lead to better understanding of the characteristics and distinctions of the two complementary approaches. It depicts for researchers in bio- and chemocatalysis a road map of challenges and opportunities for the evolution (and at times revolution) in chemical synthesis.

204 citations

Journal ArticleDOI
TL;DR: This review presents an update on the current knowledge of the secondary metabolite potential of the major fungal species used in industrial biotechnology, i.e., Aspergillus niger, As pergillus oryzae, and Trichoderma reesei, and a description of all known secondary metabolites produced by these species.
Abstract: This review presents an update on the current knowledge of the secondary metabolite potential of the major fungal species used in industrial biotechnology, i.e., Aspergillus niger, Aspergillus oryzae, and Trichoderma reesei. These species have a long history of safe use for enzyme production. Like most microorganisms that exist in a challenging environment in nature, these fungi can produce a large variety and number of secondary metabolites. Many of these compounds present several properties that make them attractive for different industrial and medical applications. A description of all known secondary metabolites produced by these species is presented here. Mycotoxins are a very limited group of secondary metabolites that can be produced by fungi and that pose health hazards in humans and other vertebrates when ingested in small amounts. Some mycotoxins are species-specific. Here, we present scientific basis for (1) the definition of mycotoxins including an update on their toxicity and (2) the clarity on misclassification of species and their mycotoxin potential reported in literature, e.g., A. oryzae has been wrongly reported as an aflatoxin producer, due to misclassification of Aspergillus flavus strains. It is therefore of paramount importance to accurately describe the mycotoxins that can potentially be produced by a fungal species that is to be used as a production organism and to ensure that production strains are not capable of producing mycotoxins during enzyme production. This review is intended as a reference paper for authorities, companies, and researchers dealing with secondary metabolite assessment, risk evaluation for food or feed enzyme production, or considerations on the use of these species as production hosts.

173 citations

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TL;DR: In this paper, the authors present representative advances for the catalyst-stereocontrolled synthesis of atropisomeric scaffolds with a focus on axially chiral motifs frequently utilized in catalysis or medicinal chemistry.
Abstract: Owing to their favorable molecular topology, atropisomers represent particularly valuable chiral scaffolds for numerous applications throughout academic research and industry. Nevertheless, whereas various well-established catalyst-controlled methodologies allow addressing stereocenter configuration, efficient procedures to prepare axially chiral compounds in high isomeric purity are still scarce. Complementary to the comprehensive reviews in the area, this Perspective features representative advances for the catalyst-stereocontrolled synthesis of atropisomeric scaffolds. With a focus on axially chiral motifs frequently utilized in catalysis or medicinal chemistry, selected recent examples encompassing unique stereoselective transition metal, hydrogen bond, ion pairing, chiral phosphoric acid, and amine catalysis are highlighted.

171 citations

Journal ArticleDOI
TL;DR: This Review highlights functional group interconversions catalyzed by enzymes, and provides some basic guidelines to choose the most appropriate enzyme for a targeted reaction keeping in mind aspects like commercial availability, cofactor-requirement, solvent tolerance, use of isolated enzymes or whole cell recombinant microorganisms aiming to assist organic chemists in the use of enzymes for synthetic applications.
Abstract: For the planning of an organic synthesis route, the disconnection approach guided by retrosynthetic analysis of possible intermediates and the chemical reactions involved, back to ready available starting materials, is well established In contrast, such concepts just get developed for biocatalytic routes In this Review we highlight functional group interconversions catalyzed by enzymes The article is organized rather by chemical bonds formed-exemplified for C-N, C-O- and C-C-bonds-and not by enzyme classes, covering a broad range of reactions to incorporate the desired functionality in the target molecule Furthermore, the successful use of biocatalysts, also in combination with chemical steps, is exemplified for the synthesis of various drugs and advanced pharmaceutical intermediates such as Crispine A, Sitagliptin and Atorvastatin This Review also provides some basic guidelines to choose the most appropriate enzyme for a targeted reaction keeping in mind aspects like commercial availability, cofactor-requirement, solvent tolerance, use of isolated enzymes or whole cell recombinant microorganisms aiming to assist organic chemists in the use of enzymes for synthetic applications

147 citations