Studies on chemical modification of monensin VIII. Synthesis of 7-O-substituted-25-carboxymonensins and their Ca2+ ion transport activity

Monensin (1), an ionophore antibiotic agent, was converted to 25-carboxymonensin (2) and 7-O-substituted-25-carboxyl derivatives (3a–d), which have two carboxyl groups at both ends of the molecule. Ca2+ ion transport activity of the dicarboxylic monensins was evaluated by the CHCl3 liquid membrane method, and 25-carboxymonensins (2 and 3a–d) were shown to transport the Ca2+ ion through the CHCl3 liquid membrane.