Ten new pentangular polyphenols, namely amexanthomycins A-J (1-10) were isolated from the strain Amycolatopsis mediterranei S699a dagger rifA constructed by deleting the polyketide synthase genes responsible for the biosynthesis of rifamycins. Their structures were elucidated on the basis of 1D and 2D NMR spectroscopic data and high-resolution ESIMS. Amexanthomycins A-C (1-3) showed inhibitory activity against human DNA topoisomerases.