Prontosil

In spite of the rationale on which the testing of dyestuffs as antibiotics rested subsequent research re vealed that the antibacterial properties of Prontosil had nothing at all to do with its being a dye In the body Prontosil undergoes a reductive cleavage of its azo linkage to form sulfanilamide which is the sub stance actually responsible for the observed biological activity This is why Prontosil is active in vivo but not in vitro... 

Sulphonamides were introduced by Domagk in 1935. It had been shown that a red azo dye, prontosil (Fig. 5.16B), had a curative effect on mice infected with /3-haemolytic streptococci it was subsequently found that in vivo, prontosil was converted into sulphanilamide. Chemical modifications of the nucleus of sulphanilamide (see Fig. 5.16A) e compounds with higher antibacterial activity, although this was often accompanied by greater toxicity. In general, it may be stated that the sulphonamides... 

Fig. 5.16 A, some sulphonamides B, prontosil rabram C, unsubstituted diaminobenzylpyrimidines D, trimethoprim E, tetroxoprim F, dapsone.

The classic example is that of Prontosil (Figure 2.12) in which the compound is active against bacterial infection in animals though inactive against the bacteria in pure culture. The toxicity in animals is the result of reduction to the sulfanilamide (4-aminobenzenesulfonamide) that competitively blocks the incorporation of 4-aminobenzoate into the vitamin folic acid. 

Possibly the most significant discovery in the metabolism of aromatic azo compounds had implications that heralded the age of modem chemotherapy. It was shown that the bactericidal effect of the azo dye Prontosil in vivo was in fact due to the action of its transformation product, sulfanilamide, which is an antagonist of 4-aminobenzoate that is required for the synthesis of the vitamin folic acid. Indeed, this reduction is the typical reaction involved in the first stage of the biodegradation of aromatic azo compounds. 

Therefore, Gerhardt Domagk s announcement of Prontosil in 1935 (4, sparked scant initial interest and the usual skepticism. The British bacteriologist Ronald Hare assumed Prontosil to be "[alnother of those damned compounds from Germany with a trade name and of unknown composition that are no use anyway" (6). Domagk s data were too sketchy, his perfect results in animal experiments too pat, the accompanying clinical reports too resonant with a testimonial tone (2 ). 

French scientists at the Pasteur Institute, however, promptly dispelled some of Prontosil s mystery, splitting the molecule into a red dye component and an old chemical, sulfanilamide, its 1909 patent long since lapsed (2 ). The suspicion arose that Domagk, an I. G. Farbenindustrie researcher, had rediscovered sulfanilamide, and that the manufacturer had held it off the market until it could be presented in a new, complex, disguised, and patentable form (2, 3 ) Whether or not the suspicion was true, the French scientists, by showing that sulfanilamide was the therapeutically active fraction of Prontosil, shattered the gigantic Germany company s profitable plans. 

Persuasive proof of sulfanilamide s true antibacterial prowess came from Leonard Colebrook and his team of researchers in the maternity ward of Queen Charlotte s Hospital in London (7, 8, 9). Managing to obtain samples of Prontosil late in 1935, Colebrook quickly demonstrated the drug s remarkable effectiveness in curbing puerperal fever. The utility was soon expanded to other severe streptococcal infections. 

Two of these systems were studied as models—the acetylation of choline in brain to give acetyl choline (Hebb, Nachmansohn), and of sulfanilamide (the active component in prontosil, Chapter 3) in liver (Lipmann). Sulfanilamide is rapidly inactivated by acetylation on the p-amino group and then excreted. Sulfanilamide is easily diazotized the diazonium salt formed can be coupled with N-( 1 -naphthyl)ethylenedi-amine dihydrochloride to give a pink derivative (Bratton and Marshall, 1939). This formed the basis for an elegant colorimetric assay. Only the free p-amino group reacts, so that as acetylation proceeded color formation diminished. 

D.D.Woods. Prontosil bacteriostatic because its active principle inhibited the utilization of />-aminobenzoic acid. 

Domagk also observed that prontosil rubrum was ineffective against bacteria in test tube studies. This was an unusual finding. In current practice, activity at the... 

It was discovered that the active part of the prontosil molecule was not the azo group but the 4-aminobenzenesulpha-mide (sulphanilamide) which was released from the parent compound within the patient. Other sulphanilamide drugs... 

Similar success was achieved in the synthesis of analogs of prontosil and sulfanilamide. A number of these analogs were prepared and tested and found to he effective against a variety of infectious diseases. 

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