Oudemansin A is a natural product first isolated from the basidiomycete fungus Oudemansiella mucida. Its chemical structure was determined by X-ray crystallography in 1979 and absolute stereochemistry by total synthesis. Two closely related derivatives, oudemansin B and X have also been isolated from other basidiomycetes. They are all biologically active against many filamentous fungi and yeasts but with insufficient potency and stability to become useful commercial products. However, their discovery, together with the strobilurins led to agricultural fungicides including azoxystrobin with the same mechanism of action.