Hydroxy acids decarboxylation

Benzimidazole-2-carboxylic acid decarboxylation, 5, 435 Benzimidazole-3-carboxylic acid, 1-hydroxy-ethyl ester synthesis, 6, 407 Benzimidazoles acidity, 5, 50, 385, 386 acylation, 5, 71, 391, 402, 417 2V-alkyl-... 

Chromone-5-carboxylic acid, 7-hydroxy-2-methyl-decarboxylation, 3, 711 Chromonecarboxylic acids decarboxylation, 3, 710 Chromone-2-carboxylic acids esters... 

Lumazine-6-carboxylic acid, 7-hydroxy-tautomerism, 3, 271 Lumazine-7-carboxylic acid synthesis, 3, 304 Lumazine-6,7-dicarboxylic acid decarboxylation, 3, 304 reactions, 3, 304 synthesis, 3, 320 Lumazine-6,7-dione catabolism, 3, 322... 

Glycol and o -hydroxy acid cleavage Oxidative decarboxylation Oxidative rearrangement of olefins... 

The NAD- and NADP-dependent dehydrogenases catalyze at least six different types of reactions simple hydride transfer, deamination of an amino acid to form an a-keto acid, oxidation of /3-hydroxy acids followed by decarboxylation of the /3-keto acid intermediate, oxidation of aldehydes, reduction of isolated double bonds, and the oxidation of carbon-nitrogen bonds (as with dihydrofolate reductase). 

Biochemical reactions include several types of decarboxylation reactions as shown in Eqs. (1)-(5), because the final product of aerobic metabolism is carbon dioxide. Amino acids result in amines, pyruvic acid and other a-keto acids form the corresponding aldehydes and carboxylic acids, depending on the cooperating coenzymes. Malonyl-CoA and its derivatives are decarboxylated to acyl-CoA. -Keto carboxylic acids, and their precursors (for example, the corresponding hydroxy acids) also liberate carbon dioxide under mild reaction conditions. 

As shown by Sato et al. N-phthaloyl derivatives of C-unprotected amino acids efficiently undergo decarboxylation upon irradiation [248,249]. In this case, the iV-phthaloyl a-amino acid of methionine 310 represents an exception, because the normal decarboxylation route is not followed. Two main products are obtained, the trans-hydroxy acid 313 and the tetracyclic lactone 314 [250, 251]... 

Kinetic studies of the oxidation of aspirin by bromamine-T, A-bromosuccinimide (NBS), and A-bromophthalimide (NBP) support a mechanism in which the unpro-tonated oxidant is the active species. " The ultimate product of the reaction is 2,4,6-tribromophenol, which arises through decarboxylation, bromination and loss of acetic acid. The NBP and NBS oxidations of -hydroxy acids are found to be similar in mechanism. 

Periodic acid reacts well in aqueous solution. Usually, if the reactant has to be run in organic solvents, lead tetraacetate is used as the reagent. Interestingly, periodic acid will not act on a-keto acids or a-hydroxy acids whereas lead tetraacetate wiU. The corresponding reactions are actually oxidative decarboxylations. 

OH hydroxy or tautomeric oxo form. b Mucochloric acid (decarboxylation). c R-7 = pyridyl, thienyl. d Meldrum s acid derivative. 

An interesting oxidative decarboxylation process was reported for a /(-hydroxy acid. Reaction of 2-ethyl-2-(l -hydroxycyclobutyl)butanoic acid with vanadium(III) chloride in the presence of 1 equivalent of l,8-bis(dimethylamino)naphthalcne (Proton Sponge) gave 3-cyclobutylidene-pentane (20).181... 

Linked oxidation and decarboxylation. Metabolic pathways often make use of oxidation of a (3-hydroxy acid to a (3-oxoacid followed by decarboxylation in the active site of the same enzyme. An example is conversion of L-malate to pyruvate (Eq. 13-45). The Mg2+ or Mn2+-dependent decarboxylating malic dehydrogenase that catalyzes the reaction is usually called the malic enzyme. It is found in most organisms.237-240 While a concerted decarboxylation and dehydrogenation may sometimes occur,241-242 the enzymes of this group appear usually to operate with bound oxoacid intermediates as in Eq. 13-45. 

Alpha oxidation and omega oxidation. Animal tissues degrade such straight-chain fatty acids as palmitic acid, stearic acid, and oleic acid almost entirely by (3 oxidation, but plant cells often oxidize fatty acids one carbon at a time. The initial attack may involve hydroxylation on the a-carbon atom (Eq. 17-3) to form either the d- or the L-2-hydroxy add.17 18-32 323 The L-hydroxy acids are oxidized rapidly, perhaps by dehydrogenation to the oxo acids (Eq. 17-3, step b) and oxidative decarboxylation, possibly utilizing H202 (see Eq. 15-36). The D-hydroxy acids tend to accumulate... 

Aminobenzo[6]thiophene-2-carhoxylic acids are conveniently obtained by reduction of the corresponding nitro compound.152,185,333, 334,33c, 338,497 Djazotization of these, followed by the usual replacement reactions of the diazonium group, provides many substituted benzo[6]thiophene-2-carboxylic acids, decarboxylation of which leads to some otherwise rather inaccessible benzo[6]thiophenes. 5-Hydroxy-benzo[6]thiophene-2-carboxylic acid is most conveniently prepared from the corresponding amino compound by means of the Bucherer reaction,338,497 in which the dicarboxylic acid (303) is formed as a by-product.152... 

H- Benzimidazole, 2,2-pentamethylene-reduction, 5, 423 Benzimidazole-2-carbaldehyde oximes, 5, 436 Benzimidazolecarbaldehydes oxidation, 5, 437 Benzimidazole-2-carbamates 5-substituted as anthelmintics, I, 202 Benzimidazole-l-carboxylic acid, 2-amino-methyl ester reactions, 5, 453 Benzimidazole-2-carboxylic acid decarboxylation, 5, 435 Benzimidazole-3-carboxylic acid, 1-hydroxy-ethyl ester synthesis, 6, 407 Benzimidazoles acidity, 5, 50, 385, 386 acylation, 5, 71, 391, 402, 417 N-alkyl-... 

H-Pyrazole-3-carboxylic acid, 4,5-dihydro-5-oxo-l-(4-sulfophenyl)-4-[(4-sulfophenyl)azo]-trisodium salt — see Tartrazine Pyrazole-5-carboxylic acid, 4-hydroxy-synthesis, 5, 276 Pyrazolecarboxylic acids decarboxylation, 5, 260 reactions... 

Free amino acids are further catabolized into several volatile flavor compounds. However, the pathways involved are not fully known. A detailed summary of the various studies on the role of the catabolism of amino acids in cheese flavor development was published by Curtin and McSweeney (2004). Two major pathways have been suggested (1) aminotransferase or lyase activity and (2) deamination or decarboxylation. Aminotransferase activity results in the formation of a-ketoacids and glutamic acid. The a-ketoacids are further degraded to flavor compounds such as hydroxy acids, aldehydes, and carboxylic acids. a-Ketoacids from methionine, branched-chain amino acids (leucine, isoleucine, and valine), or aromatic amino acids (phenylalanine, tyrosine, and tryptophan) serve as the precursors to volatile flavor compounds (Yvon and Rijnen, 2001). Volatile sulfur compounds are primarily formed from methionine. Methanethiol, which at low concentrations, contributes to the characteristic flavor of Cheddar cheese, is formed from the catabolism of methionine (Curtin and McSweeney, 2004 Weimer et al., 1999). Furthermore, bacterial lyases also metabolize methionine to a-ketobutyrate, methanethiol, and ammonia (Tanaka et al., 1985). On catabolism by aminotransferase, aromatic amino acids yield volatile flavor compounds such as benzalde-hyde, phenylacetate, phenylethanol, phenyllactate, etc. Deamination reactions also result in a-ketoacids and ammonia, which add to the flavor of... 

A further study on the oxidation of terpenoid compounds by mammalian systems (c/. p. 62) has shown that patchoulol (298) is oxidized by rabbits to give a mixture of diol (299) and hydroxy-acid (300).129 Subsequent oxidative decarboxylation of (300) provided norpatchoulenol (301), the major odour carrier of patchouli oil. It has been suggested that a similar oxidative transformation of patchoulol occurs during the biosynthesis of norpatchoulenol in the plant.129 Cedrol (72) has also been oxidized by rabbits (c/. p. 62) and it is interesting to note that the hydroxylated products are... 

The E2 Reaction. The stereochemistry of the E2 process is even less well understood. It is exemplified by the decarboxylative eliminations of the vinylogous /3-hydroxy acids 5.16 and 5.18, which are both largely, although not exclusively, syn. The corresponding E2 reaction with /3-hydroxy acids is highly anti selective, in the usual way for /3 eliminations. 

Dehydrative decarboxylation. The convc sion of p-hydroxy carboxylic acids to alkenes by reaction with a DMF dialkyl acetal iirvolves an r/n/Z-elimination, and thus is complementary to the known. yv/i-elimination of these hydroxy acids via a P-lactone (5, 22 9, 504). These reactions were used to obtain both the (E)- and the (Z)-l-alkoxy-l,3-... 

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