Thioester naming

Thiamin, structure of, 530, 1045 thiazolium ring in, 530 Thiamin diphosphate, p/Ca of, 1151 reaction with pyruvate, 1151-1153 structure of. 1151 ylide from. 1151 Thiazole, basicity of. 948 thio-, thioester name ending, 787 Thioacetal, synthesis of, 743 Thioanisole, electrostatic potential map of. 777... 

Thioesters are named like the corresponding esters. If the related ester has a common name, the prefix thio- is added to the name of the carboxylate acetate becomes thioacetate, for instance. If the related ester has a systematic name, the -oate or -carboxylate ending is replaced by -thioate or -carbothioate butanoate becomes butanelhioate and cyclohexanecarboxylate becomes cyclohexane-carbothioate, for instance. 

Steps 6-8 of Figure 29.5 Reduction and Dehydration The ketone carbonyl group in acetoacetyl ACP is next reduced to the alcohol /S-hydroxybutyry] ACP by yS-keto thioester reductase and NADPH, a reducing coenzyme closely related to NADH. R Stereochemistry results at the newly formed chirality center in the /3-hydroxy thioester product. (Note that the systematic name of a butyryl group is biitanoyl.)... 

Naming, acid anhydrides—cont d prostaglandins, 1069 sulfides, 668 thioesters. 787 thiols, 667... 

Methods for the A-acylation of similar heterocycles, such as simple thiazolidinethiones, have been reported since 1977, namely acyl chlorides in miscellaneous conditions,586 or carboxylic acids under DCC-activation.60,61 However the easiest and most effective method involves acyl chlorides or carboxylic anhydrides in the presence of an amine.47 Applying that procedure on carbohydrate scaffolds Rollin and co-workers62 reported the synthesis of diverse /V-acylated OZTs. The reactions were performed with good yields and the /V-selective acylation was ascertained by NMR— namely the thiocarbonyl 13C chemical shift (Scheme 41). Thanks to the dual nature of the carbanion drifting in the reaction,596 60 no competitive formation of the thioester, as mentioned by Plusquellec el al. in the case of benzothiazole, was observed. 

Although hydrolytic enzymes, esterases and amidases, are named after their major substrates, the same enzyme can often hydrolyze esters, thioesters, and amides therefore, the differentiation between esterases and amidases is sometimes artificial. The highest hydrolytic activity is in the liver, but the enzyme pseudocholinesterase is found in the serum. Gut bacteria also contain hydrolytic enzymes. 

A similar aldol reaction is encountered in the Krebs cycle in the reaction of acetyl-CoA and oxaloacetic acid (see Section 15.3). This yields citric acid, and is catalysed by the enzyme citrate synthase. This intermediate provides the alternative terminology for the Krebs cycle, namely the citric acid cycle. The aldol reaction is easily rationalized, with acetyl-CoA providing an enolate anion nucleophile that adds to the carbonyl of oxaloacetic acid. We shall see later that esters and thioesters can also be converted into enolate anions (see Section 10.7). 

In more recent investigations, the assumed multienzyme involved in cyclosporin A biosynthesis could be isolated from T. inflatum. A partially purified enzyme fraction was indeed capable of forming enzyme-substrate complexes by thioester linkage. Although de novo synthesis (in vitro) of cyclosporin A has not yet been achieved, the formation of a partial sequence, namely, the diketopiperazine cyclo(DAla-MeLeu), from D-alanine and L-leucine was observed under consumption of ATP and S-adenosyl-L-methio-nine [25]. 

Note the names given are for the appropriate fatty acid the structures shown are actually the thioesters involved in the conversions... 

Based on the identified homology of the cefD and cefDZ proteins with known eukaryotic enzymes, a mechanism for the A. chrysogenum two-component epimerization system which is different from the epimerization found in prokaryotes has been established <2002JBC46216>. Therefore, it was suggested that the cephalosporin biosynthesis pathway begins with the activation of the substrate isopenicillin N to its CoA, followed by an epimerization to the D-enantiomer, namely penicillinyl-CoA. Next, the required hydrolysis of the CoA-thioesters seems to occur in a nonstereoselective manner by different thioesterases. The resulting product, penicillin N, is the direct precursor of all cephalosporins and cephamycins. 

Thioesters are named like esters, using the prefix thio- before the name of the carboxylic acid. 

The enzyme systems are complex two reactions are catalyzed, namely formation of a thioester and its subsequent hydrolysis to free acid. Because little or no tritium or deuterium from solution is incorporated into the rearranged product, a hydride shift was assumed. With optically pure thiols like (36) the rearrangement of (37) to (10b) can be catalyzed (equation 21). The methyl mandelate formed has a very modest enantiomeric excess. ... 

Many types of reactive molecules are well known to medicinal chemists acyl halides, aldehydes, aliphatic esters, aliphatic ketones, alkyl halides, anhydrides, alpha-halocarbonyl compounds, aziridines, 1,2-dicarbonyl compounds, epoxides, halopyrimidines, heteroatom-heteroatom single bonds, imines, Michael acceptors and (l-heterosubstituted carbonyl compounds, perhalo ketones, phosphonate esters, thioesters, sulfonate esters, and sulfonyl halides, to name a few [14]. This is not to say that these functionalities are not useful - some even appear in approved drugs -but all of these can react covalently with proteins, and thus should be regarded with suspicion. However, molecules can react covalently with proteins even if they do not contain functionalities that raise alarm. Jonathan Baell has referred to these as pan assay interference compounds, or PAINS, and has published a list of moieties to watch out for, as well as strategies to detect them [15, 16]. 

Abeles and co-workers extended the work of Buckel on the properties and mechanism of the reductive dehydration of lactate to propionate in C. propionicum (234, 235). Studies by Abeles concluded that acrylate is indeed an intermediate in lactate dehydration, based on the observation of a primary kinetic isotope effect of 1.8 on the conversion of [3- H3]lactate to propionate, indicating that -hydrogen abstraction is at least partially rate limiting. The true substrates for the reaction were determined to be the CoA thioesters of lactate and acrylate, hence the enzyme has been aptly named lactyl-CoA dehydratase (234). The reaction was found to be mediated by two proteins, El and E2, and like the (R)-2-hydroxyglutarate-dehydrating enzyme from A. fermentans, both El and E2 from... 

---