A decarboxylation

A decarboxylation route provides an alternative entry to perfluorovinylmer-cury compounds [182] (equation 129). 

One of the amino acids in Table 27.1 is the biological precursor to y-aminobutyric acid (4-aminobutanoic acid), which it forms by a decarboxylation reaction. Which amino acid is this ... 

How many of the 14 NADPH needed to form one palmitate (Eq. 25.1) can be made in this way The answer depends on the status of malate. Every citrate entering the cytosol produces one acetyl-CoA and one malate (Figure 25.1). Every malate oxidized by malic enzyme produces one NADPH, at the expense of a decarboxylation to pyruvate. Thus, when malate is oxidized, one NADPH is produced for every acetyl-CoA. Conversion of 8 acetyl-CoA units to one palmitate would then be accompanied by production of 8 NADPH. (The other 6 NADPH required [Eq. 25.1] would be provided by the pentose phosphate pathway.) On the other hand, for every malate returned to the mitochondria, one NADPH fewer is produced. 

Mammals can add additional double bonds to unsaturated fatty acids in their diets. Their ability to make arachidonic acid from linoleic acid is one example (Figure 25.15). This fatty acid is the precursor for prostaglandins and other biologically active derivatives such as leukotrienes. Synthesis involves formation of a linoleoyl ester of CoA from dietary linoleic acid, followed by introduction of a double bond at the 6-position. The triply unsaturated product is then elongated (by malonyl-CoA with a decarboxylation step) to yield a 20-carbon fatty acid with double bonds at the 8-, 11-, and 14-positions. A second desaturation reaction at the 5-position followed by an acyl-CoA synthetase reaction (Chapter 24) liberates the product, a 20-carbon fatty acid with double bonds at the 5-, 8-, IT, and ITpositions. 

The third and fourth steps in the synthesis of Hagemann s ester from ethyl acetoacetate and formaldehyde (Problem 23.50) are an intramolecular aklol cyclization to yield a substituted cyclohexenone, and a decarboxylation reaction. Write both reactions, and show the products of each step. 

Benzoxepins require drastic conditions for the thermal rearrangement to naphthols. When 3-benzoxepin-2,4-dicarboxylic acid is heated to 300 C, a decarboxylation reaction takes place and 3-hydroxynaphthalene-2-carboxylic acid (10) is formed in 44% yield.91... 

The use of microwave irradiation for decarboxylation reactions is well appreciated [107-110]. Still, only one example of a decarboxylation performed on 2-pyridone starting materials has been reported (Fig. 10) [111]. Notably, this decarboxylation reaction is a selective and reagent-free method performed in N-methyl-2-pyrrohdin one (NMP) and microwave irradiation at 220 °C for 10 min. The products 65 were isolated in excellent yields (92-99%) by a simple aqueous work-up (Fig. 10). 

A divergent synthesis of tropane alkaloid ferruginine was reported by Node and coworkers [59]. The P-ketoester intermediate was prepared by a novel PLE-catalyzed asymmetric dealkoxycarbonylation (hydrolysis followed by a decarboxylation) of a symmetric tropinone-type diester (Figure 6.12). Dimethyl sulfoxide was added to the phosphate buffer pH 8 (1 9) to reduce the activity of PLE and prevent over-deal-koxycarbonylation leading to tropinone. 

The biosynthesis of polyketides (including chain initiation, elongation, and termination processes) is catalyzed by large multi-enzyme complexes called polyketide synthases (PKSs). The polyketides are synthesized from starter units such as acetyl-CoA, propionyl-CoA, and other acyl-CoA units. Extender units such as malonyl-CoA and methylmalonyl-CoA are repetitively added via a decarboxylative process to a growing carbon chain. Ultimately, the polyketide chain is released from the PKS by cleavage of the thioester, usually accompanied by chain cyclization [49]. 

Hydrocarbon formation involves the removal of one carbon from an acyl-CoA to produce a one carbon shorter hydrocarbon. The mechanism behind this transformation is controversial. It has been suggested that it is either a decarbonylation or a decarboxylation reaction. The decarbonylation reaction involves reduction to an aldehyde intermediate and then decarbonylation to the hydrocarbon and releasing carbon monoxide without the requirement of oxygen or other cofactors [88,89]. In contrast, other work has shown that acyl-CoA is reduced to an aldehyde intermediate and then decarboxylated to the hydrocarbon, releasing carbon dioxide [90]. This reaction requires oxygen and NADPH and is apparently catalyzed by a cytochrome P450 [91]. Whether or not a decarbonylation reaction or a decarboxylation reaction produces hydrocarbons in insects awaits further research on the specific enzymes involved. 

As predicted, l,2,3,4-13C-labeled acetone dicarboxylate (15) provided an intact three-carbon chain into lycopodine. It also helped to explain why two molecules of pelletierine (12) were not incorporated (Scheme 6.3) [12]. As before, lysine (6) is converted to piperideine (8) via a decarboxylation. Then a Mannich reaction of labeled 15 with 8 provides pelletierine 12. The other half of the molecule to be incorporated must be pelletierine-like (12-CC>2Na), still containing one of the carboxylates. An aldol reaction of the two pelletierine fragments and a series of transformations leads to phlegmarine 9. Oxidation of 9 involving imine formation between N-C5, isomerization to the enamine and then cyclization onto an imine (at N-C13), provides lycopodine 10. Phlegmarine 9 and lycopodine 10 are proposed as... 

The bioluminescence of the American firefly (Photinus pyralis) is certainly the best-known bioluminescent reaction, thanks to the work of Me Elroy and coworkers and E. H. White and his group (for references see P, p. 138, 6,168,169)) The substrate of this enzyme-catalyzed chemiluminescent oxidation is the benzothiazole derivative 107 (Photinus luciferin) which yields the ketone 109 in a decarboxylation reaction. The concept of a concerted cleavage of a dioxetane derivative has been applied to this reaction 170> (see Section II. C.). Recent experiments with 18C>2 have challenged this concept, as no 180-containing carbon dioxide was detected from the oxidation of 107 171>. 

Methylthiobutyl glucosinolate derives from L-methionine by a complex elongation process leading to dihomomethionine. Four of the five carbons of methionine are retained, one being lost in a decarboxylation. The two necessary additional carbons each derive from a methyl group of acetyl-S-CoA by a complex, multi-step condensation mechanism (Equation 11) ... 

Sphingolipids are biosynthesized by adding head groups to the ceramide moiety. Sphinganine, also termed dihy-drosphingosine, is biosynthesized by a decarboxylating condensation of serine with palmitoyl-CoA to form a keto intermediate, which is then reduced by NADPH (Fig. 3-9). 

JEZ, J.M., FERRER, J.-L., BOWMAN, M.E., DIXON, R.A., NOEL, J.P., Dissection of malonyl-coenzyme A decarboxylation from polyketide formation in the reaction mechanism of a plant polyketide synthase, Biochemistry, 2000, 39, 890-902. 

Claisen A Decarboxylation Elimination JK Miscellaneous > Ester Synthesis ... 

Serotonin (5-hydroxytrptamine, 5-HT) synthesis involves an hydroxylation reaction (catalysed by tryptophan mono-oxygenase) and a decarboxylation step, similar to that in adrenaline (epinephrine) synthesis. 

Following the conversion of pyruvate into oxaloacetate, phosphoenolpyruvate carboxykinase (PEP CK) catalyses a decarboxylation to form PEP (Figure 6.42). This... 

Dauben et al. found that the CCI3 radical produced by sonolysis of carbon tetrachloride can be used in a decarboxylation-halogenation sequence (Scheme 3.5) [43]. Sonication of a thiohydroxamic ester at 33 °C for 10 - 50 min in carbon tetrachloride leads to the corresponding chloride in high yield. In the presence of bromotrichloromethane or iodoform, bromides and iodides are formed in yields > 80 %. This reaction can be successfully applied to primary, secondary, or tertiary esters and offers an interesting variant to the usual Hunsdiecker procedure. 

Allylic substitution with free carbamate nucleophiles was not accomplished until advanced catalyst precursors were developed. However, products from substitution with carbamate nucleophiles were generated by a decarboxylative allylation. In this process, the imidodicarbonate was shown to undergo decarboxylation to form the carbamate nucleophile, and reaction of the resulting carbamate with the 7i-allyliridium intermediate formed branched allylic carbamate products (Scheme 17) [92, 95]. 

Labeling experiments with l-deoxy-l-(dibenzylamino)-D-[l- C]-aruI>-mo-2-hexulosuronic acid [l- C] 112 indicated that the C label corresponded to the 5-methyl group of 111 (see Ref. 234). This is also consistent with a l-deoxy-2,3-dicarbonyl intermediate (115), and indicates that 111 is a decarboxylation product (see Scheme 22). The precise step entailing decarboxylation has not yet been determined. The carboxyl group could be carried through to ring closure (furanone formation). Such a step would provide a 2-carboxylate which is a /3-keto acid subject to ready decarboxylation. The labeling information and the initial steps of the mechanism in Scheme 22 are also consistent with the formation of 111 from D-[l- C]ribose and a secondary amine. ... 

The assay of carbenicillin in biological fluids presents problems in that it may be accompanied by traces of benzylpenicillin (probably arising by a-decarboxylation of carbenicillin) to which the usual test organism, Sarcina lutea, is extremely... 

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