Carboxylic acid biological

Thiadiazole-4-carboxylic acids biological activity, 6, 462 photochemistry, 6, 462... 

The chemistry of carboxylic acids is the central theme of this chapter The impor tance of carboxylic acids is magnified when we realize that they are the parent com pounds of a large group of derivatives that includes acyl chlorides acid anhydrides esters and amides Those classes of compounds will be discussed m Chapter 20 Together this chapter and the next tell the story of some of the most fundamental struc tural types and functional group transformations m organic and biological chemistry... 

This difference in behavior for acetic acid in pure water versus water buffered at pH = 7 0 has some important practical consequences Biochemists usually do not talk about acetic acid (or lactic acid or salicylic acid etc) They talk about acetate (and lac tate and salicylate) Why Its because biochemists are concerned with carboxylic acids as they exist in di lute aqueous solution at what is called biological pH Biological fluids are naturally buffered The pH of blood for example is maintained at 7 2 and at this pH carboxylic acids are almost entirely converted to their carboxylate anions... 

In most biochemical reactions the pH of the medium is close to 7 At this pH car boxylic acids are nearly completely converted to their conjugate bases Thus it is common practice m biological chemistry to specify the derived carboxylate anion rather than the carboxylic acid itself For example we say that glycolysis leads to lactate by way of pyruvate... 

Pyromucic acid — see Furan-2-carboxylic acid Pyronaridine biological activity, 2, 625... 

AH-Pyrrolo[3,4-c]isoxazole, 3-amino-biological activity, 6, 1024 4H-Pyrrolo[3,4- c]isoxazole-5(6/7)-carboxylic acid, 3-amino-ethyl ester... 

Thieno[3,4-d]isothiazole, 2,3-dihydro-3-oxo-1,1-dioxide, 6, 989 biological activity, 6, 1024 Thieno[2,3-c]isothiazole-3-carboxylic acid synthesis, 6, 1023... 

Specific biological activity of carboxylic acids peroxide derivatives in compaiison with their oxidation ability and ionization degree in aqueous solutions has been considered. Peroxyoctanoic, diperoxynonandioic and diperoxydecandioic acids give the most intense bactericidal effect among researched cai boxylic acids peroxide derivatives. The perspectives of use of the aliphatic middle-chain peracid C8-C9 as anti-infective agents have been discussed. 

The discussion of acylation reactions in this chapter is focused on fluonnated carboxylic acid derivatives and their use to build up new fluorine-containing molecules of a general preparative interest Fifteen years ago, fluonnated carboxylic acids and their derivatives were used mainly for technical applications [/] Since then, an ever growing interest for selectively fluonnated molecules for biological applications [2, 3, 4, 5] has challenged many chemists to use bulk chemicals such as tnfluoroacetic acid and chlorodifluoroacetic acid as starting materials for the solution of the inherent synthetic problems [d, 7,, 9]... 

A third method of aldehyde synthesis is one that we ll mention here just briefly and then return to in Section 21.6. Certain carboxylic acid derivatives can be partially reduced to yield aldehydes. The partial reduction of an ester by dhsobutylaluminum hydride (DIBAH), for instance, is an important laboratory-scale method of aldehyde synthesis, and mechanistically related processes also occur in biological pathways. The reaction is normally carried out at —78 °C (dry-ice temperature) in toluene solution. 

Water can add reversibly to o ,/3-unsalurated aldehydes and ketones to yield /3-hydroxy aldehydes and ketones, although the position of the equilibrium generally favors unsaturated reactant rather than saturated adduct. A related addition to an c /S-unsaturated carboxylic acid occurs in numerous biological pathways, such as the citric acid cycle of food metabolism where ds-aconitate is converted into isocitrate by conjugate addition of water to a double bond. 

Carboxylic acids, RC02H, occupy a central place among carbonyl compounds. Not only are they valuable in themselves, they also serve as starting materials for preparing numerous acyl derivatives such as acid chlorides, esters, amides, and thioesters. In addition, carboxylic acids are present in the majority of biological pathways. We ll look both at acids and at their close relatives, nitriles (RC=N), in this chapter and at acyl derivatives in the next chapter. 

In acidic solution at low pH, a carboxylic acid is completely undissociated and exists entirely as RCO2H- In basic solution at high pH, a carboxylic acid is completely dissociated and exists entirely as RC02 - Inside living cells, however, the pH is neither acidic nor basic but is instead buffered to nearly neutral pH—in humans, to pH = 7.3, a value often referred to as physiological pH. In what form, then, do carboxylic acids exist inside cells The question is an important one for understanding the acid catalysts so often found in biological reactions. 

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