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Preparation, properties and biological activity of natural and semisynthetic urethanes of monensin.

Conversion of the monovalent polyether antibiotic monensin into a series of urethane derivatives substituted at C-26 causes a ten-fold increase in the cation transporting properties of the antibiotic as well as making the resulting semisynthetic urethanes divalent ionophores. These changes must in part account for the enhanced antimicrobial activities of the urethanes. The most active derivatives are the phenylurethanes which are ten times more active in vitro against Gram-positive bacteria and unlike monensin are active against Candida albicans and Penicillium digitatum. Another novel activity exhibited by four of the urethanes was against Plasmodium berghei, the causative agent for malaria.