It was discovered by Lionel Whitby at the British firm May & Baker Ltd and logged in their Test Book on 2 November, 1937 under Code No M&B 693.
The drug sulfasalazine is structurally one molecule of mesalamine linked to one molecule of sulfapyridine with an azo bond.
M&B 693 was one of the first generation of sulphonamide antibiotics. It has been reported as the first chemical cure for pneumonia. It could either be taken in tablet form or the powder could be placed in wounds. It was used so widely during the Second World War that May & Baker had difficulty keeping up with demand. It was later largely superseded by penicillin and other sulfonamides.