text: Natural products containing acid anhydrides have been isolated from animals, bacteria and fungi. Examples include cantharidin from species of blister beetle, including the Spanish fly, Lytta vesicatoria, and tautomycin, from the bacterium Streptomyces spiroverticillatus. The maleidride family of fungal secondary metabolites, which possess a wide range of antibiotic and antifungal activity, are alicyclic compounds with maleic anhydride functional groups.
  A number of proteins in prokaryotes and eukaryotes undergo spontaneous cleavage between the amino acid residues aspartic acid and proline via an acid anhydride intermediate. In some cases, the anhydride may then react with nucleophiles of other cellular components, such as at the surface of the bacterium Neisseria meningitidis or on proteins localized nearby.