Disclosed are antioxidative natural compounds, their salts, chelates and cleavage derivatives that exhibit a superior combination of properties. The compounds can be used for a variety of purposes, including the stabilization of polymers. The compounds can be prepared by substantially cleaving a humic acid of formula I followed by esterification to provide at least one antioxidant compounds of formula V, formula VI, formula VII, formula VIII, salts thereof, or chelates thereof.