Bivalent Metal-Chelating Properties of Harzianic Acid Produced by Associated to the Gastropod .

Harzianic acid is a secondary metabolite of , structurally belonging to the dienyltetramic acid subgroup of the tetramic acids. Biological activities of harzianic acid are of great interest for its antimicrobial and plant growth-promoting activities, which might be related to its chelating properties. In the present work harzianic acid, isolated from cultures of a strain of associated to the gastropod , was studied as a complexant agent of a number of biologically relevant transition metals (i.e., Zn, Fe, Cu, and Mn), using UV-VIS, potentiometry, MS and NMR techniques. Our findings show the coordination capacity of harzianic acid toward the above cations through the formation of neutral or charged complexes in a variable ratio depending on the metal and pH conditions.