J>-Aminobenzoic acid

Closely related to the use of rhodium catalysts for the hydrogenation of phenols is their use in the reduction of anilines. The procedure gives details for the preparation of the catalyst and its use to carry out the low-pressure reduction of /j-aminobenzoic acid. Then, as in the preceding experiment, advantage is taken of the formation of a cyclic product to carry out the separation of a mixture of cis and trans cyclohexyl isomers. 

By oxidation of acet- -toluidide, followed by esterification of the J>-aminobenzoic acid. Chemnitius, Pharm. Zentralh. 68, 765 (1927). 

Table 3.2. /j-AMINOBENZOIC ACID UNIT ANALOGUES BENZENE MODIFICATIONS... 

Amphoteric molecules such as/j-aminobenzoic acid (H2NC6H4COOH, where. H2... 

The nature and extent of the immunological reaction does not generally relate directly to the chemical structure of the foreign compound which is acting as a hapten. Thus, many different compounds may elicit the same type of reaction. For example, nickel, /j-phenylenediamine,/j-aminobenzoic acid and neomycin all cause dermatitis. The antigen produced may have some bearing on the type of response, but there are many other factors. Thus, it can be stated that chemically similar foreign compounds may produce very different immunotoxic reactions and conversely different types of substance may elicit the... 

In this biotransformation B is the product of a Phase I reaction and is less active than A. An example would be the hydrolysis of the local anesthetic procaine (A) to j -aminobenzoic acid (B). 

The pteroic acid moiety of tetrahydrofolate consists of a reduced pteridine ring and j)-aminobenzoic acid. Folic acid from the diet is absorbed by the intestinal mucosa, and in two enzymic steps is reduced to tetrahydrofolate which is the active form of the coenzyme. Mammals cannot synthesize folate this normally does not present a problem because microorganisms of the intestinal tract do so in sufficient quantities. The two steps in the reduction of folic acid to tetrahydrofolate are catalyzed by dihydrofolate reductase. Both of these reactions require NADPH as a somce of electrons. 

There are antagonists of the biosynthesis of dihydrofolic acid, and antagonists of its utilization. The history of the discovery of the antibacterial sulfonamides, typical antagonists of biosynthesis, was given in Sections 2.1 and 6.3.1. In 1940, Woods showed that the anti-bacterial action of sulfanilamide depended on its competition with j -aminobenzoic acid (P.7), which is a natural metabolite (Woods, 1940). Later this competition was shown to take place at the site on the enzyme dihydrofolate synthetase, which uses j -aminobenzoic acid to build up the molecule of dihydrofolic acid (2.74) (G.M. Brown, 1962). 

Bacteria use/ -aminobenzoic acid only for conversion to 7.8-dihydrofolic acid (Griffin and Brown, 1964). Thus, E, coli condenses j -aminobenzoic acid (and, alternatively, -aminobenzoylglutamic acid) with 2-amino-4-oxo-6-hydroxy-methyl-7,8-dihydropteridine 9.21) (as the 6-pyrophosphate) to give dihydro-pteroic acid (and alternatively, dihydrofolic acid) (Jaenicke and Chan, 1960). The sulfonamides competitively inhibit the isolated enzyme dihydrofolate the-tase which catalyses these steps (G. Brown, 1962). From Lactobacillus plantamm two enzymes responsible for this synthesis have been isolated in a pure state (Shiota et al., 1969a). The first of these catalyses the esterification of the pteridine 9.21) to its pyrophosphoryl derivative. The second is Brown s dihydrofolate synthetase. This second enzyme has also been isolated from several strains of Pneumococcus, found to have a mol. wt. of 90000, and to need ATP and Mg " as coenzymes (Ortiz, 1970). 

Not all substances with an acidic and a basic group are zwitterions (internal salts), because there may be no pH at which both groups are ionized. The pH of the solution is another factor. Thus a substance is 90% or more in the zwitterionic state when the pH is at least one unit above the acidic pK and at least one unit below the basic p a- If this rule is applied to / -aminobenzoic acid (acidic pK 4.8 basic p a 2.7), it will at once be seen that this substance, unlike glycine, is exclusively anionic in neutral and alkaline solutions. For other tests to distinguish between zwitterionic and merely amphoteric substances (e.g. glycine and j -aminobenzoic acid respectively), see Albert and Serjeant (1984). 

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