8-Acyloxy-1,3-benzoxazine-2,4-diones as siderophore components for antibiotics.

8-Acyloxy-1,3-benzoxazine-2,4-diones as masked catechol derivatives represent a novel type of siderophore components, whose growth promoting activity is low or not existing if tested alone. But after conjugation with beta-lactam antibiotics the resulting conjugates show a significantly increased antibacterial activity against Gram-negative bacteria compared with their parent antibiotics. Investigations using a set of penetration and iron transport mutants demonstrated that the conjugates use iron transport systems to penetrate the bacterial outer membrane. Title compounds were synthesized from (2,3-dimethoxycarbonyloxy)-benzoic acid and different amino compounds. Conjugates with penicillins and cephalosporins were prepared.