The synthesis and properties of a new family of diastereomeric macrocyclic compounds are described which span two different types of internal cavities. The compounds are characterized by a polylactone ring and functionalized side chains arranged in either a “syn” or an “anti” configuration. The method of synthesis involves the use of cyclic tin-oxygen compounds as covalent templates and provides either of the diastereomers with high regio- and stereospecificity. Extensive spectroscopic data are given (NMR and X-ray analyses) and evidence for the different binding properties of the diastereomers for europium ions. The relationships of these compounds with naturally occurring ionophores is discussed and their possible application for the design of ion carriers or catalysts indicated.