The interest of the German industry for the dyes was at the basis of the discovery of the sulphonamides, the first broad-spectrum antibacterial agents. The compound was the result of an accidental discovery as often happens doing research. In 1932 an experimental pathologist (Gerhard Domagk),  was testing the dyes synthetized by his colleagues, Fritz Mietzsch and Josef Klarer at the IG Farbenindustrie consortium, which was part of Bayer. Prontosil red, was one of the tested compounds and contained a sulphonamide group that was introduced with the aim of improving the binding to bacterial cells in analogy to its ability to bind to fibres. Interestingly, Prontosil red was able to protect mice infected with  with  haemolytic streptococci,  however, when the compound was tested in vitro against streptococci  it failed to show antibacterial activity. This paradox was explained by showing that when the compound reached systemic circulation, sulphanilamide was liberated from the dye. It was this colourless compound that was responsible for the astonishing properties of Prontosil, which in fact probably the first prodrug ever made, even though unintentionally.

Bayer was unable to patent the discovery as a chemical sulphanilamide had been synthesized and described as early as 1908. As a consequence, several firms market the drug so that by 1940 sulphanilamide itself was available under many different trade names. One version marketed in the USA, Elixir Sulfanilamide, was formulated in diethylene glycol and killed over 100 people. This accident led to a law assigning the Food and Drug Administration the power to regulate the licensing of new drugs in the USA.

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