Conformational polymorphism in peptidic and nonpeptidic drug molecules.

Macrolide ligands that bind FK506 binding proteins and cyclosporins that a bind cyclophilins are chemically dissimilar but can share a number of structural and biological properties. Both families of ligands have very different conformations in the free state compared to those adopted when complexed with their binding protein. These transformations involve twisting from cis to trans about specific amide bonds, which result in significant changes in the hydrogen-bonding capabilities of the molecular surfaces. The three-dimensional structure of a new cyclosporin-like ligand (SDZ214 - 103) is described in the free crystalline state and bound to cyclophilin, and is shown to have a very different conformation from cyclosporin A in the free crystal, but a very similar conformation when bound to cyclophilin.