Uric acid formula

Birds excrete nitrogen as uric acid Uric acid is a purine having the molecular formula C5H4N4O3 it has no C—H bonds Write a structural formula for uric acid... 

In 1776, Scheele first prepared cyanuric acid by pyrolysis of uric acid (7) (B-1793MI22000). In 1830, the first correct analysis was obtained by Liebig and Wohler (1835MI22000), but the molecular formula was incorrectly assigned as C6H6N606. Dreschel deduced the correct molecular formula, C3H3N3O3, in 1875 (1875JPR(11)289). Cyanuric acid does not have many industrial applications itself, but many of its derivatives are valuable monomers (see Section 2.20.5). 

Widely used as a uric acid solvent and in many forms of rheumatism in combination with suitable alteratives— see formula in this volume. Also as a tonic with Damiana. The dose is 5-30 drops of the fluid extract. 

Three formulas have been suggested for uric acid ... 

The system was first named by Fischer 0899CB435) but the correct ring structure was proposed much earlier <1875LA( 175)243) in a formula for uric acid. In the general literature purine nomenclature has been to a large extent affected by the abundance of trivial names for compounds which were isolated before their structures were known and by variation in description of tautomeric forms. 

Purine derivatives are considered to be prebiotic molecules. Purine as well as adenine (HCN) can be formed from hydrogen cyanide in the presence of ammonia in a prebiotic atmosphere. Similar reaction in the presence of water can lead to other purines. Purine chemistry goes back to the roots of organic chemistry. Uric acid was the first purine isolated from bladder stones by Scheelc in 1776. The correct empirical formula of uric acid was established much later by Liebig and Mitscherlich. The correct structure was suggested by L. Medicus and was shown to be correct by the syntheses ofHorbaezewski. Behrend and Roosen, and unambiguously by E. Fischer. The development of purine chemistry by E. Fischer is a milestone in heterocyclic chemistry. 

Constitution.— The constitution of uric acid has been established by a remarkable set of syntheses based upon a study of the products of decomposition. In this work several men played an important part. The most comprehensive work which cleared up the question of the constitution not only of uric acid but of several related compounds, which we shall presently consider, was by Emil Fischer, whom we have already mentioned in connection with two other groups of compounds intimately connected with plants and animals, viz., the carbohydrates and the proteins (p. 393). Earlier important work was done by Liebig and Wohler, and the relationship of the decomposition products was mainly due to the work of Baeyer. The accepted formula was first suggested by Medicus, and the syntheses supporting it were worked out by Horbaczewski, and by Behrend and Roosen. 

Horbaczewski s Synthesis.—The syntheses which establish the above formula are several. The two best are those before mentioned, of Horbaczewski and of Behrend and Roosen. The former heated together tri-chlor lactic amide and urea and obtained uric acid. 

The assigning of the two types of formulas in some cases, Le.j the hydroxyl or alcohol formula (enol formula) and the ketone or carbonyl formula ketone formula), is due to the fact, not mentioned in the case of uric acid, that it is probably a tautomeric compound... 

The ureids and uric acid have also been explained by structural formulas of this ring type as follows ... 

As shown in the above formulas uric acid exists in tautomeric forms, having the constitution either of a hydroxyl compound, enol form, or of a ketone, keto form. The purine alkaloids which we have mentioned are similar hydroxyl or amino derivatives of purine. As tautomeric compounds they also exist in the two forms. Those which contain hydroxyl groups have the enol and the keto forms, while, if they contain ammonia residues instead of hydroxyl, they have the corresponding amino or imino forms. In the following formulas only one tautomeric form will be given, viz., the keto and the amino. 

The diureids may be considered as consisting of two molecules of urea united together by loss of hydrogen and interposition of a group of proper valence (see formula of uric acid, etc., below). The best known of the group is ... 

The synthesis of uric acid has been accomplished by heating together a mixture of glycocol and urea at 230" (446° F)., and purifying the product. From this synthesis and from the products of decomposition of uric acid its constitution has been established. Its molecule consists of two urea remainders, CO(NH)s, united unsymmetrioally by a group of three carbon and one oxygen atoms, in the manner represented by the formula ... 

Parabanic Acid, C3H2N2O3.—Under certain conditions an acid of this formula is obtained by oxidizing uric acid with nitric acid. The structure of parabanic acid is deduced from the decomposition which results when the acid is hydrolyzed by an alkali urea and oxalic acid are formed —... 

Allantoine, C4H6O3N4, is formed when uric acid is oxidized by potassium permanganate. The products of hydrolysis of allantoine, and its synthesis from glyoxylic acid and urea, lead to the structure which is represented by the formula,—... 

These facts lead to the view that the structure of uric acid is that represented by the formula,—... 

Many other facts, which can not be discussed here, lead to the same conclusion. With this structural formula as a guide, uric acid has been synthesized in a number of ways. 

Uric acid 33 (2,6,8-trihydroxypurine) was isolated from urinary calculi by Scheele (1774). After ascertaining its molecular formula (Liebig and Mitscherlich 1834), its structure was established by oxidative degradation and structural correlation with barbituric acid, alloxan, allantoin and hydantoin (Liebig, Wohler, Baeyer) ... 

Uric acid, a purine derivative found mainly in the excrement of snakes and birds, has the molecular formula CsHnNiiOa- On nitric acid oxidation it breaks down to urea and a hydrated compound called alloxan of formula CijRaNaOit HaO. Alloxan is readily obtained by oxidation of barbituric acid. What is the probable structure of alloxan and uric acid Why is alloxan hydrated ... 

Table 1 Serum and urinary uric acid values in normal subjects during their personal diet and after 7 days of ingestion of an isoenergetic, purine-free liquid formula diet.

We recently investigated the effect of oral purines on uric acid pool size and turnover rate in three normal subjects (Loffler et al., 1980a). The diet was an isoenergetic liquid formula diet free of purines and the purine supplement was 1 g AMP plus 1 g GMP per 70 kg body weight, which corresponds to about 4 g RNA as used by Powering et al. (1969). Results are shown in Table 3 and in Fig. 4. It is obvious that in normal subjects dietary purines lead to an increase in turnover rate of uric acid pool. 

We therefore reinvestigated this question using a purine-free liquid formula diet containing 12, 24, and 36 energy percent protein (Loffler et al., 1980b). The results of this study are shown in Table 6. It is obvious that not only renal excretion of uric acid increased, but also serum levels decreased under these conditions. We conclude from these results that formula diets give more consistent results in experimental studies than low-purine diets of conventional food. 

After the research of Wohler and Liebig (1838, see p. 333), uric acid and its derivatives were investigated by Schlieper. The latter showed that uric acid on reduction by hydriodic acid forms glycocoll and the decomposition products of urea (NH3 and CO2). Gerhardt formulated alloxan as the mesoxalyl, and parabanic acid as the oxalyl, derivatives of urea, which he then regarded as hydrate d oxyde de cyanammonium , giving complicated formulae, which were simplified by Kekule as ... 

The formula of uric acid was based on its decomposition on heating with acids into glycocoll, ammonia, and carbonic acid, and the formation of alloxan and urea on oxidation with alkaline permanganate, the alloxan readily forming urea and glyoxylic acid. The other formulae were not based on any experimental evidence, and a formula for uric acid proposed by Fittig was usually accepted. 

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