Design and synthesis of conformationally constrained salinomycin derivatives.

Two conformationally restricted salinomycin derivatives by tethering the hydroxyl groups at C1 and C20 with different chain length were designed and synthesized. The cyclic derivatives showed better biological activities than C1/C20 modified derivatives, indicating the importance of the compact conformation for the ion binding capacity. In addition, the length of the connective chain plays critical role in the biological activities, thus cyclic the derivative 7 preserved some pharmacological activity but derivative 5 with two carbon atom shorter chain showed significantly reduced activity. The conformations of the two cyclic salinomycin derivatives were analyzed by ROESY spectrum in DMSO-d6, indicating derivative 7 may adopt more appropriate conformations for the coordinate with alkali metal ion than derivative 5, which has a closer distance between H3 and H25.