Positioning and configuration of key atoms influence the topology of [13]-macrodiolides.

Key atoms at specific positions along the ring govern the shape, or "topology" of a group of [13]-macrodiolides. Here we report the synthesis of these macrocycles and their characterization by functional and structural methods. The [13]-macrodiolides are organized by three four-atom planar units that help to rigidify them and one hinge atom that enables the planar units to orient themselves. The driving force for the organization of the structures is the minimization of steric strain on groups attached to the key atoms. When the key atom is a stereocenter, a macrocycle with planar chirality is observed. An alternative cup-like topology arises when the key atom bears two alkyl groups. Additionally, the key atoms can work in a coordinated fashion to guide one topology over another. The synthesis relied on an acylation-ring closing metathesis sequence. Rigidity was demonstrated by variable-temperature NMR experiments and diastereoselective epoxidation reactions. X-ray crystal structures of representative [13]-macrodiolides served as the basis of the structural observations made. The results provide a framework for the design of new macrocycles with well-defined structures as well as for understanding some general principles that influence the topology of natural product macrocycles.