Para-aminobenzoic acid structure

The following molecular model is a representation of para-aminobenzoic acid (PABA), the active ingredient in many sunscreens. Indicate the positions of the multiple bonds, and draw a skeletal structure (gray = C, red = O, blue = N, ivory - H). 

Sulfanilamides are antibiotics that serve as structural analogs of para-aminobenzoic acid (PABA), a substrate In the formation of folic acid by many bacteria. Substitution of the sulfanilamide compound In place of PABA In the reaction prevents formation of the critical coenzyme folic acid. 

To date, over 10 000 structural analogues of sulphanilamide, the parent of all sulpha drugs, have been synthesized and used in the SAR studies. However, only about 40 of them have ever been used as prescribed drugs. Sulpha drugs are bactereostatic, i.e. they inhibit bacterial growth but do not actively kill bacteria. These drugs act on the biosynthetic pathway of tetrahydrofolic acid, inhibit dihydropteroate synthetase and mimic the shape of PABA (para-aminobenzoic acid). 

Aminosalicylic acid (Paser, PAS) exerts its effects in a manner similar to the sulfonamide drugs that is, aminosalicylic acid is structurally similar to para-aminobenzoic acid (PABA) and inhibits folic acid synthesis by competing with PABA in tuberculosis... 

Finally, sulfonamides can interfere with intermediary metabolism. Because of their structural similarity to para-aminobenzoic acid (PABA), they can function as competitive inhibitors for dihydropteroate synthase. The result is interruption of microbial synthesis of folic acid by blocking formation of the folic acid precursor dihydropteroic acid. Sensitive microorganisms are those that must synthesize their own folic acid. Conversely, resistant bacteria and normal mammalian cells are unaffected since they do not synthesize folic acid but use the preformed vitamin. 

Figure 6.4 Structure of prontosil and sulfanilamide. PABA is para-aminobenzoic acid.

Folic acid is a conjugated molecule consisting of a pteridine ring structure linked to para-aminobenzoic acid (PABA) that forms pteroic acid. 

As shown in Scheme 19.5, however, prontosil is itself an inactive prodrug that, upon oral administration, requires metabolic reduction by the gut microflora to become sulfanilamide, 6. The latter is an active antimicrobial that is very effective against streptococcal infections upon its absorption into the body. Once this was understood, the birth of the sulfonamide antibiotics can be said to have occurred and both Domagk and his daughter lived happily-ever-after. It was later shown that the structure of 6 resembles that of para-aminobenzoic acid (PABA) because... 

FIGURE 43-1 Structural formulas of selected sulfonamides and para-aminobenzoic acid. The N of the para- blK group is designated as N4 that of the amide NH, as Nl. 

Folates exist in many chemical forms. The coenzyme form that functions in accepting one-carbon groups is tetrahydrofolate polyglutamate (Fig. 40.2), generally just referred to as tetrahydrofolate or FH4. It has three major structural components, a bicyclic pteridine ring, para-aminobenzoic acid, and a polyglutamate tail consisting... 

Para-aminosalicylic Acid (PAS), like the sulfonamides (see Chapter 44), is a structural analogue of p-aminobenzoic acid (PABA). It is a folate synthesis antagonist that interferes with the incorporation of PABA into folic acid. PAS is bacteriostatic, and in vitro, most strains of M. tuberculosis are sensitive to a concentra-... 

No pattern is obvious in the substitution of ortho versus meta versus para substituents by tritium. Differences do exist. For example, substitution of the amino group is considerably less probable in m-aminobenzoic acid than in either o- or p-aminobenzoic acid. It is possible that the crystal structure and the forces relative to the position of the groups in the lattice may affect the yields. 

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