2,3,6-Pyridine tricarboxylic acid

The position in which the veratryl residue is attached to this isoquinoline nueleus in papaveraldine and papaverine is determined by the formation of pyridine-2 3 4-tricarboxylic acid in the oxidation of papaverine by hot permanganate. On the basis of these results, Goldschmiedt assigned the following formula to papaveraldine —... 

Papaverinic acid, CieHjjO N. HjO, crystallises in small tablets, m.p. 233°. It is dibasic, readily forms an anhydride, furnishes an oxime and a phenylhydrazone, contains two methoxyl groups, and on oxidation yields veratric and pyridine-2 3 4-tricarboxylic acids, and hence is represented by the following formula —... 

Cinchoninic Acid.—(2) Carboxylic acids. The only quinoline carboxylic acid of importance is known as cinchoninic acid because it is obtained by oxidizing cinchonine, one of the alkaloids of cinchona bark. It is the quinoline 4-carboxylic acid and by loss of carbon dioxide yields quinoline. By oxidation cinchoninic acid yields pyridine 2-3-4 tricarboxylic acid (p. 858) which by loss of carbon dioxide (3 mol.) yields pyridine. 

Permanganate oxidation of papaverine in neutral medium furnishes m-hemipinic acid (V), veratric acid (VI), papaverinic acid (a-veratroylcincho-meronic acid) (VII), and pyridine-2,3,4-tricarboxylic acid (VIII). The last-named product (VIII) may serve as evidence for the point of attachment of the nitrogen-free portion of the isoquinoline system. Dimethoxy-isoquinolines are oxidized to pyridine-3,4-dicarboxylic (cinchomeronic) acid, but papaverine yields VIII under analogous conditions, thus marking position 1 as the connecting point. 

The ready decarboxylation of pyridine-carboxylic acids was also early appreciated. Historically, the reaction played an important role in the orientation of quinoline, isoquinoline and the benzoquinolines . Decarboxylation occurs more readily than with benzene-carboxylic acids, and in the sequence 2 > 4 > 3 (see p. 367). The decarboxylation temperatures of solid pyridine-dicarboxylic acids depend roughly on their strengths as acids— the stronger the acid the lower the temperature . At 185 -190 , pyridine-2,3,4-tricarboxylic acid gives pyridine-3,4-dicarboxylic acid, which above... 

Wt % was obtained from each benzene-ether extract. Determination was made from the gas chromatograms of their methyl esters. Thiophene- and pyridine carboxylic acids for Samples 2-6, and pyridine tricarboxylic acids for Sample 1. 

The bicyclic nature of the labile adduct (79) from 3-methyl-pyridine was established by Acheson and Taylor who found that hydrogenation, yielding (80), followed by oxidation gave pyridine-3,4,5-tricarboxylic acid. This conclusion is consistent with Diels and Alder s observations that acid hydrolysis of the labile pyridine adduct gave pyridine and some crotonaldehyde, whereas alkaline hy-... 

JMJD2 demethylases are inhibited by analogues of the cofactor 2-OG that include N-oxalylamino acids, pyridine dicarboxylates, and related bipyridyl derivatives. Other chemotypes that are also presumed to bind to the active-site Fe(II) include catechols, hydroxamic acids (including the clinically used HD AC inhibitor SAHA/Vorinostat), and tricarboxylic acid cycle intermediates, such as succinate and fumarate [59,62]. 

If the CH, is on the benzene ring, oxidation gives only 2,3-pyridinedicarboxylic acid, regardless of the position of the CH,. If the CH, is on the pyridine ring, there are three possible tricarboxylic acids ... 

The aglycone of betaniu, the red-violet pigment of the beet (Beta vulgaris var. rubra), known as betanidin, has recently been shown to have the structure depicted in structural formula 113.170,282 Betanidin had previously been reported by Piattelli and Minale to contain a dopachrome unit in its structure and consequently would have been formulated as 114.109 The Italian workers obtained pyrrole-2,3,5-tricarboxylic acid and pyridine-2,4,6-tricarboxylic acid on permanganate oxidation of betanidin and they also prepared a semi-carbazone of the pigment, the absorption spectrum of which showed the pH dependency expected for an aminochrome semicarbazone.169... 

Pyrazinecarboxylic acid has been obtained by selenious acid oxidation in pyridine of methylpyrazine or aqueous permanganate oxidation of ethylpyrazine, in yields of 64 and 48%, respectively.171,218 It has also been obtained in 70% yield by partial decarboxylation of pyrazine-2,3-dicarboxylic acid on heating in vacuo at 210°.219 Aqueous permanganate oxidation of 2,5-distyrylpyrazine gives the 2,5-dicarboxylic acid.220 Pyrazine-2,5-dicarboxylic acid has also been prepared in 45% yield by direct carboxylation of pyrazine with carbon dioxide at 50 atm pressure at 250° for 3 hours in the presence of a potassium carbonate and calcium fluoride catalyst.221 Pyrazine-tricarboxylic acid (57), obtainable in only very poor yields by oxidation of 2,5-dimethyl-3-ethylpyrazine, is prepared in 87% yield by alkaline permanganate oxidation of 2-(D-arabo)tetrahydroxybutyl-quinoxaline (56).222 Decarboxylation of the tricarboxylic acid by... 

As for chloroplast membranes, various compounds in mitochondrial membranes accept and donate electrons. These electrons originate from biochemical cycles in the cytosol as well as in the mitochondrial matrix (see Fig. 1-9) —most come from the tricarboxylic acid (Krebs) cycle, which leads to the oxidation of pyruvate and the reduction of NAD+ within mitochondria. Certain principal components for mitochondrial electron transfer and their midpoint redox potentials are indicated in Figure 6-8, in which the spontaneous electron flow to higher redox potentials is toward the bottom of the figure. As for photosynthetic electron flow, only a few types of compounds are involved in electron transfer in mitochondria—namely, pyridine nucleotides, flavoproteins, quinones, cytochromes, and the water-oxygen couple (plus some iron-plus-sulfur-containing centers or clusters). 

When dehydrogenated with palladium nupharamine (XXXII) is converted to the pyridine derivative (XXXIII) and this can be oxidized with permanganate to pyridine-2,3,6-tricarboxylic acid (XXXIV) which indicates the location of the substituents (35). 

As indicated previously in Eq. (68), triester 193 can be hydrolyzed to the tricarboxylic acid 194 which can then be decarboxylated to 195. It has also been reported6 that pyrrolol 1,2-ftlpyridazines of type 195 could not be quaternized under conditions that usually convert pyridines or pyridazines into their quaternary derivatives. 

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