Decarboxylation spontaneous

The ester 322A is made by ester exchange with ethyl acetoacetate and a suitable alcohol. The product 322B decarboxylates spontaneously on heating. Draw out the whole sequence starting from ethyl acetoacetate. 

Hydroxylated amino acids (eg, 4-hydroxyproline, 5-hydroxylysine) and A/-methylated amino acids (eg, /V-methylhistidine) are obtained by the acid hydrolysis of proteins. y-Carboxyglutamic acid occurs as a component of some sections of protein molecules it decarboxylates spontaneously to L-glutamate at low pH. These examples are formed upon the nontranslational modification of protein and are often called secondary protein amino acids... 

Pyridines with an a- or y-carboxymethyl group (e.g. 685) undergo facile decarboxylation by a zwitterion mechanism (685 — 688) somewhat similar to that for the decarboxylation of 3-keto acids (cf. Section 3.2.3.1.1). Carboxymethylpyridines often decarboxylate spontaneously on formation thus, hydrolysis of (689) gives (690). The corresponding 2- and 4-pyridone and 2- and 4-pyrone acids are somewhat more stable, e.g. (691) decarboxylates at 170°C. 3-Pyridineacetic acid shows no pronounced tendency to decarboxylate. 

Some 25 papers have been published on various aspects of the metal ion-promoted decarboxylation of oxaloacetic acid and its derivatives338-340 and this system can be used to illustrate many features of these reactions. The /3-oxo acids decarboxylate spontaneously in aqueous solution... 

Fig. 4.37. Three El eliminations in the deprotection of a protected tripeptide. For the sake of brevity, a single formula in the second row of the scheme shows how the three tert-Bu—0 bonds het-erolyze. Of course, they are activated and broken one after the other. In the deprotection of the tert-butylated lysine side chain, the leaving group is a carbamic acid. Carbamic acids decarboxylate spontaneously (Figure 8.3, 8.5 and 8.6), which explains the final transformation. The preparation of the protected tripeptide is shown in Figure 4.41.

The product 322B decarboxylates spontaneously on heating. Draw out the whole sequence starting from ethyl acetoacetate. 

The procedure reported in Scheme 13.11 describes deracemization of an amino acid involving oxidation with an L-specific enzyme and transamination with a D-amino transferase using D-aspartate 10, which is generated from L-aspartate 11 by aspartate racemase, as the amino donor. The oxidative enzyme is defined as an L-amino acid deaminase, a flavoprotein from Proteus myxofadens [34]. The transamination reaction is shifted towards the product since the oxalacetate 12 formed decarboxylates spontaneously to give pyruvate and carbon dioxide. 

The n-complex of the alkene and Pd(II) allows nucleophilic attack by the amide on the nearer end and in a cis fashion because the nucleophile is tethered to the alkene by only two carbon atoms. Nucleophilic attack and elimination of palladium(O) occur in the usual way. The removal of the C02Bn group would normally be by hydrogenolysis but in this case ester hydrolysis by, say, HBr treatment would be preferred to avoid reduction of the alkene. The free acid decarboxylates spontaneously. 

The keto intermediate decarboxylates spontaneously to 7-/ -(4-carboxybutanami-do)-cephalosporanic acid (glutaryl-7-ACA) and carbon dioxide by chemical reaction with the hydrogen peroxide formed during the enzymatic reaction. The occurrence of the byproduct 7-ACA-sulfoxide is possible. In general a reaction mixture is produced, caused by the catalase also produced by the yeast. However, the a-ke-toacid intermediate reacts poorly with the deacylation enzyme in the second step. 

The relatively selective methylation (85 15, N-2 N-1) of 5-cyanotetrazole can be used to prepare pure 2-methyltetrazole by utilising the very large difference in stabilities of 1- and 2-methyl-tetrazole-5-carboxylic acids. The mixture of methylated nitriles can be hydrolysed to the carboxylate salts and, upon acidification, the 1-methyl acid decarboxylates spontaneously. The resulting 1-methyltetrazole and 2-methyltetrazole-5-carboxylic acid can be easily separated, then the latter decarboxylated at 200 °C to give pure 2-methyl tetrazole." ... 

Kumagai and coworkers11131 developed an enzymatic procedure to produce d-alanine from fumarate by means of aspartase (E. C. 4.3.1.1), aspartate racemase, and D-amino acid aminotransferase (Fig. 17-12). Aspartase catalyzes conversion of fumarate into L-aspartate, which is racemized to form D-aspartate. D-Amino acid aminotransferase catalyzes transamination between D-aspartate and pyruvate to produce D-alanine and oxalacetate. This 2-oxo acid is easily decarboxylated spontaneously to form pyruvate in the presence of metals. Thus, the transamination proceeds exclusively toward the direction of D-alanine synthesis, and total conversion of fumarate into D-alanine was achieved. 

The alcohol once formed is oxidized by an NAD(P)H- and 02-dependent oxygenase to the aldehyde and then to the carboxylic acid. The 4a-carboxylic acid is oxidized by an NAD " -dependent enzyme to the 3-oxo-4a-carboxylic acid. This enzyme has been solubilized and purified from rat liver microsomes. The enzyme has a of 7 juM for the sterol substrate and is maximally active at alkaline pH. The preparation was free of the hydroxylase activities and was uninfluenced by treatment with several phospholipases. It is not known whether the j8-oxo acid formed decarboxylates spontaneously or enzymatically [105]. 

The diaryliodonium carboxylate route to benzynes (Type B2) has been adapted to the polymer-bound precursor 58, prepared from Merrifield s resin by standard methods". (An earlier example of a polymer-bound h nzyne has been described. ) The polymer afforded benzyne 59 when heated above 200 °C, as demonstrated by trapping with 2-furoic acid the initial cycloadduct decarboxylates spontaneously at that temperature, affording naphthols 60 in about 20% yield. The three-phase test involving transfer of aryne from 58 to a... 

The protecting group is removed by hydrogenolysis after the coupling reaction. The substituted carbamic acid generated by benzyl hydrogenolysis decarboxylates spontaneously ... 

Acetoacetyl Co A is built from two acetyl Co A molecules. Free acetoacetic acid is either formed from acetoacetyl CoA or from /5-hydroxybutyric acid (Fig. 50). Acetoacetic acid decarboxylates spontaneously to acetone. Reduction of acetoacetyl CoA yields j8-hydroxybutyryl CoA which may be transformed to a polymeric derivative (Fig. 50), to butyric acid, or to butanol (Fig. 51). 

Furfural, oxygen, and GOg passed at 350° over UgOg-on-AlgOg furan. Y 77%. —The intermediate acid is decarboxylated spontaneously. L. Meszaros, Acta Univ. Szegediensis, Acta Phys. et Ghem. 6, 97 (1960) G. A. 55, 25905b. 

Important evidence that a-acetolactate and a-aceto-a-hydroxybutyrate are precursors of valine and isoleucine, respectively, was obtained by Wagner et cd. 164). These investigators isolated and identified acetyl-methylcarbinol and acetylethylcarbinol from a mutant strain of Neurospora blocked in the biosynthesis of valine and isoleucine. The two carbinol compounds were obtained as pteridine derivatives. They would be formed by decarboxylation of acetolactate and aceto-a-hydroxybutyrate. That the latter compounds are the probable sources of the carbinols is indicated by the fact that Neurospora possesses an active decarboxylase which catalyzes the conversion of acetolactate and aceto-a-hydroxybutyrate to their respective carbinol. Furthermore, since the aceto compounds are 3-keto acids, they would be expected also to decarboxylate spontaneously. 

Another feature of 2-pyrone 87 is its ability to undergo Diels-Alder reactions with acetylenes. The cycloadducts decarboxylate spontaneously to form benzene rings bearing the CF3 group. The substitution pattern is determined by the regioselectivity of the [4-1-2] cycloaddition step. Thus, the reaction of 87 with l-(NJ -diethylamind)-l-propyne takes place at 0 °C to produce 92 as a single isomer. Less electron rich acetylenes require heating at 140-200 C. Treatment of 87 with acetylene at 200 C leads to 93, while with dimethyl acetylenedicarboxylate triester 94 is formed [37] (Scheme 28). 

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