Sulfonamides, also known as sulfa drugs, are synthetic antimicrobial agents derived from sulfonic acid. In bacteria, these drugs are competitive inhibitors of para-aminobenzoic acid (PABA), a substrate of the enzyme dihydropteroate synthetase. This reaction is necessary in these organisms for the synthesis of folic acid.
The first sulfonamide was trade named prontosil. The first experiments with prontosil began in 1932 by the German chemist Gerhard Domagk, and the results were published in 1935 (after his employer, I. G. Farben, had obtained a patent on the compound). Prontosil was a red azo dye, and in mice had a protective action against streptococci. It had no effect in the test tube, and only exerted an antibacterial effect in the live animal itself. And, with war on the horizon, there was interest among the Allies to break the German patent.
Soon it was discovered (1936) that prontosil's active agent was a smaller, more effective compound known as sulfanilamide:
Sulfanilamide had a central role in preventing infection during World War II. American soldiers were issued a first aid kit containing sulfa powder and were told to sprinkle sulfa on any open wound. During the years 1942 to 1943, German/Nazi Doctors conducted sulfanilamide medical experiments on 74 Polish political prisoners in women's concentration camp in Ravensbrück.
An inadvertently toxic preparation of sulfanilamide also had a central influence on the US Food and Drug Administration. A preparation called Elixir Sulfanilamide contained ethylene glycol as a solvent, which is toxic. This preparation killed over one hundred people, mostly children, and led to the passage of the 1938 Food, Drug, and Cosmetic Act.
Many thousands of permutations of the sulfanilamide structure have been created since its discovery (by one account, over 5400 permutations by 1945), usually by the substitution of another functional group for a single amide hydrogen.
Certain sulfonamides (sulfadiazine or sulfamethoxazole) are sometimes mixed with the drug trimethoprim, which acts against dihydrofolate reductase.
Sulfa allergies are common enough that many medications are labeled as containing sulfonamides for this reason.
See also: antibiotic, timeline of antibiotics