PABA

ANTIBACTERIALAGENTSSYNTHETIC - SULFONAMIDES] (Vol2) p-Ammobenzoic acid (PABA) [150-13-0]... 

The primary mode of action of the sulfonamides is, however, the interference with the uptake of PABA for the formation of foHc acid [59-30-3]. 

Subsequent knowledge of the stmcture, function, and biosynthesis of the foHc acid coenzyme gradually allowed a picture to be formed regarding the step in this pathway that is inhibited by sulfonamides. The biosynthetic scheme for foHc acid is shown in Figure 1. Sulfonamides compete in the step where condensation of PABA with pteridine pyrophosphate takes place to form dihydropteroate (32). The amino acids, purines, and pyrimidines that are able to replace or spare PABA are those with a formation that requkes one-carbon transfer catalyzed by foHc acid coenzymes (5). 

Development of Resistance. One of the principal disadvantages of sulfonamide therapy is the emergence of dmg-resistant strains of bacteria. Resistance develops by several mechanisms overproduction of PABA (38) altered permeabiUty of the organisms to sulfonamides (39) and reduced affinity of dihydropteroate synthetase for sulfonamides while the affinity for PABA is retained (40). Sulfonamides also show cross-resistance to other sulfonamides but not to other antibacterials. In plasmodia, resistance may occur by means of a bypass mechanism in which the organisms can use preformed foHc acid (41). 

Folic acid is synthesized both in microorganisms and in plants. Guanosine-5-ttiphosphate (GTP) (33), -aminobenzoic acid (PABA), and L-glutamic acid are the precursors. Reviews are available for details (63,64). The sequence of reactions responsible for the enzymatic conversion of GTP to 7,8-dihydrofohc acid (2) is shown. 

In E. coli GTP cyclohydrolase catalyzes the conversion of GTP (33) into 7,8-dihydroneoptetin triphosphate (34) via a three-step sequence. Hydrolysis of the triphosphate group of (34) is achieved by a nonspecific pyrophosphatase to afford dihydroneopterin (35) (65). The free alcohol (36) is obtained by the removal of residual phosphate by an unknown phosphomonoesterase. The dihydroneoptetin undergoes a retro-aldol reaction with the elimination of a hydroxy acetaldehyde moiety. Addition of a pyrophosphate group affords hydroxymethyl-7,8-dihydroptetin pyrophosphate (37). Dihydropteroate synthase catalyzes the condensation of hydroxymethyl-7,8-dihydropteroate pyrophosphate with PABA to furnish 7,8-dihydropteroate (38). Finally, L-glutamic acid is condensed with 7,8-dihydropteroate in the presence of dihydrofolate synthetase. 

The first are competitors of PABA (p-aminobenzoic acid) and thus intermpt host de novo formation of the tetrahydrofoUc acid required for nucleic acid synthesis. Examples of dmgs that fall into this group are the sulfones and sulfonamides. The most weU-known of the sulfones is dapsone (70, 4,4 -diaminodiphenyl sulfone, DDS), whose toxicity has discouraged its use. Production of foHc acid, which consists of PABA, a pteridine unit, and glutamate, is disturbed by the substitution of a sulfonamide (stmcturally similar to PABA). The antimalarial sulfonamides include sulfadoxine (71, Fanasd [2447-57-6]) sulfadiazine (25), and sulfalene (72, sulfamethoxypyrazine [152-47-6] Kelfizina). Compounds of this group are rapidly absorbed but are cleared slowly. 

Therapeutic Function Sunscreen agent, antirickettsial Chemical Name p-aminobenzolc acid Common Name Vitamin H, Vitamin B, PABA Structural Formula ... 

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). 

Para-aminobenzoic acid (PABA), HCjH NO is used in some sunscreen agents. A solution is made by dissolving 0.263 mol of PABA in enough water to make 750.0 mL of solution. The solution has [H+] = 2.6 X 10-3 M. What is Ka for PABA ... 

B. antagonize PABA, which some bacteria need to multiply... 

One excellent UV protector for foods is PABA, a B vitamin. Likewise, many of the same antioxidants we ingest as health supplements—such as vitamin C and a similar chemical, erythorbic acid vitamin E and lecithin, a source of the important nutrients choline and inositol—occur naturally in food. 

PABA 4-aminobenzoic acid p-aminobenzoic acid ethoxylated ethyl 4-aminobenzoic acid (PEG-25 PABA)... 

Para-amino benzoic acid (PABA) is considered to be in the B-complex vitamin family. The human body can make it from folic acid, since PABA forms the middle part of that vitamin ... 

This means that in the strictest sense, PABA is not a vitamin, because the body can manufacture it. But in this sense, too, vitamin A is not technically a vitamin, as the body makes that from beta-carotene. 

Bacteria in the intestines produce folic acid if there is PABA present. Microbes need PABA, but it is not strictly necessary for humans. A class of drugs that simulate PABA, sulfa drugs, can fool the microbes into trying to use them instead of PABA, which causes them to die. This is why people taking sulfa drugs are advised not to take PABA at the same time. 

PABA is taken orally in vitamin supplements. However, its widest use is as a sunscreen. Taking it orally will not protect a person from the sun as a sunscreen PABA acts as a topical dye that absorbs ultraviolet light. To block UV rays from the sun, a person needs to paint it directly onto the skin. 

PABA is acidic, which means it can sting if it gets in the eyes. Some people are sensitive to PABA when it is applied to their skin. PABA also darkens and can stain clothing. For these reasons, modified forms of PABA have become popular as sunscreens. PABA can be reacted with long-chain alcohols to form PABA esters, such as polyethylene glycol 25 PABA ... 

This PABA molecule eliminates the irritation and staining problems. Other PABA esters are glycerol PABA, padimate A, and padimate O. 

Denatonium benzoate is the bitterest-tasting substance known. It gets its name from denatured alcohol—alcohol that has been rendered unfit for drinking—and is often used in the denaturing process. Specially denatured alcohol 40, or SD-40, is ethanol that has been denatured by a tiny amount of denatonium benzoate. Denatonium benzoate is an ester of PABA, and is related to lidocaine, benzocaine, novocaine, and cocaine. 

You can learn more about molecules that absorb different colors in the section on para-amino benzoic acid (PABA). 

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