Thiamine-diphosphate-dependent ThDP

The formation of acyloins (a-hydroxyketones), versatile intermediates for natural products syntheses, is catalyzed in nature by thiamine diphosphate-dependent (ThDP-dependent) enzymes. These enzymes belong to different families, transferases as transketolase cf 5.2.), lyases as benzaldehyde lyase (cf 5.1.), and different decarboxylases. They are generally highly enantioselective... 

Two-step cascade for the synthesis of (1/ ,2R)-norephedrine and (1/ ,2S)-ephedrine combining a thiamine diphosphate-dependent lyase (ThDP) acetohydroxyacid synthase (AHAS-I) with stereocomplementary co-TAs. 

Benzoylformate decarboxylase (BFD EC 4.1.1.7) belongs to the class of thiamine diphosphate (ThDP)-dependent enzymes. ThDP is the cofactor for a large number of enzymes, including pyruvate decarboxylase (PDC), benzaldehyde lyase (BAL), cyclohexane-1,2-dione hydrolase (CDH), acetohydroxyacid synthase (AHAS), and (lR,6] )-2-succinyl-6-hydroxy-2,4-cyclohexadiene-l-carboxylate synthase (SHCHC), which all catalyze the cleavage and formation of C-C bonds [1]. The underlying catalytic mechanism is summarized elsewhere [2] (see also Chapter 2.2.3). 

Various thiamine diphosphate (ThDP)-dependent a-keto acid decarboxylases have been described as catalyzing C-C bond formation and/or cleavage [48]. Extensive work has already been conducted on transketolase (TK) and pyruvate decarboxylase (PDC) from different sources [49]. Here attention should be drawn to some concepts based on the investigation of reactions catalyzed by the enzymes... 

For this type of C-C bond formation both stereoisomers of the hydroxyphenyl-propanone can be obtained using either the BFD mentioned above or the benz-aldehyde lyase (BAL). Both of these enzymes are dependent on thiamine diphosphate (ThDP) as cofactor [22]. For the enantioselective reduction of the intermediate also, both stereoisomers can be obtained by using two different ADH enzymes. Thus all four possible stereoisomers of the diol can be obtained in high optical purity (see Scheme. 3.1.1) [23]. 

As noted earlier, the conversion of benzoylformic acid to benzaldehyde is catalyzed by the thiamin diphosphate (ThDP)-dependent enzyme BFD. The proposed catalytic mechanism proceeds through two covalent... 

The deprotonation and addition of a base to thiazolium salts are combined to produce an acyl carbanion equivalent (an active aldehyde) [363, 364], which is known to play an essential role in catalysis of the thiamine diphosphate (ThDP) coenzyme [365, 366]. The active aldehyde in ThDP dependent enzymes has the ability to mediate an efScient electron transfer to various physiological electron acceptors, such as lipoamide in pyruvate dehydrogenase multienzyme complex [367], flavin adenine dinucleotide (FAD) in pyruvate oxidase [368] and Fc4S4 cluster in pyruvate ferredoxin oxidoreductase [369]. 

Pyruvate oxidase (Pyox) is a FAD- and thiamine diphosphate (ThDP)-dependent enzyme that catalyzes the reaction of pyruvate to give acetyl phosphate or vice versa (see Fig. 15). If used in the oxidative way, it can be activated and reactivated under nonaerobic conditions using ferrocene mediators. Kinetic parameters of the indirect electrochemical process using the enzyme incorporated into a biomimetic supported bilayer at a gold electrode have been reported [142]. Similarly, FAD-dependent amino oxidases may also be applied. 

Tittmann, K., Wille, G., Golbik, R., Weidner, a., Ghisia, S., Hubner, G. (2005b), Radical phosphate transfer mechanism for the thiamin diphosphate-and FAD-dependent pyruvate oxidase from Lactobacillus plantarum. Kinetic coupling of intercofactor electron transfer with phosphate transfer to acetyl-thiamin diphosphate via transient FAD semiquinone/hydroxyethyl-ThDP radical pair. Biochemistry 44, 13291-13303. 

Thiamin (Vitamin Bl), biosynthesized by most prokaryotes and eukaryotes in its active form thiamin diphosphate (ThDP), is an essential cofactor for several enzymes involved in carbohydrate and amino acid metabolism. Most bacteria, as well as fungi and plants, are able to produce thiamin de novo, while mammals depend solely on the dietary uptake [335-337],... 

The Importance of Vitamins in Biochemistry and Disease as Illustrated by Thiamine Diphosphate (ThDP) Dependent... 

An associated cascade process that combines a thiamine diphosphate (ThDP)-dependent ligase with enantiocomplementary m-TAs was described recently to access norephedrine (NE) and norpseudoephedrine (NPE) in only two steps from cheap starting materials [52]. The system uses the acetohydroxyacid synthase I (AHAS-I) from E. coli to yield (P)-phenylacetylcarbinol [(R)-PAC, 98% ee] via carboligation with benzaldehyde, which was then directly converted to the desired ephedrine derivatives (NE or NPE) by the appropriate choice of m-TA (Scheme 4.15). Moreover, a novel cascade was introduced with this system ( recycling cascade ) because the coproduct of the reductive amination (pyruvate) could be elegantly removed/recycled without addition of further catalyst, increasing thereby the intrinsic overall efficiency. Several aminotransferases were tested initially for the reductive amination because the benzaldehyde also serves as a suitable substrate for... 

Milller and co-workers recently developed an enantioselective benzoin dimerization using purified enzymes from Pseudomonas. The thiamine diphosphate (ThDP) dependent enzymes benzaldehyde lyase (BAL) and benzoylformate decarboxylase (BED) were found to catalyze the reversible benzoin condensation of aromatic aldehydes. The reaction is driven in the forward direction by the poor solubility of the benzoin products in aqueous media. A wide variety of aromatic aldehydes are accepted by BAL, and products of the (/ )-configuration are produced in excellent yield and enantiomeric purity. The (S)-enantiomer of benzoin is also available in high enantiomeric purity from a BAL-catalyzed kinetic resolution of rac-benzoin. In the presence of excess acetaldehyde, BAL selectively converts (i )-benzoin into (/ )-2-hydroxy-l-phenylpropanone, while the (iS)-benzoin enantiomer is not a substrate for the enzyme. At 49% conversion, (5)-benzoin is resolved to > 99% ee. BED can produce (i )-benzoin from benzaldehyde in comparable yield and enantiomeric purity with respect to BAL, but the substrate scope appears more limited. ... 

CARBON-CARBON BOND FORMATION USING THIAMIN DIPHOSPHATE (THDP)-DEPENDENT CARBOLIGASES... 

Thiamin diphosphate (ThDP)-dependent carboligases are a class of enzymes involved in a variety of metabolic pathways where they catalyze a broad range of bond cleavage and bond formation reactions between carbon and hydrogen. 

A. Cosp, C. Dresen, M. Pohl, L. Walter, C. Rohr, M. Muller, a,p-Unsaturated aldehydes as substrates for asymmetric C—C bond forming reactions with thiamin diphosphate (ThDP)-dependent enzymes, Adv. Synth. Catal 350 (2008) 759-771. 

Decarboxylation is one of the most common processes in natural metabolism. All decarboxylases [EC 4.1.1.-] cleave a substrate carboxylic group with or without the requirement of an enzymatic cofactor. There are three known decarboxylase types (i) thiamine diphosphate (ThDP)-dependent decarboxylases, (ii) pyridoxal phosphate (PLP)-dependent decarboxylases, and (iii) cofactor-independent decarboxylases (Figure 3.1) [1-4]. Cofactor-independent decarboxylases are specific for activated substrates. 

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