NMR Investigations of the Static and Dynamic Structures of Bisphosphonates on Human Bone: a Molecular Model

摘要

We report the results of an investigation of the binding of a series of bisphosphonate drugs to human bone using ~2H,~(13)C, (~15)N, and(~31)P nuclear magnetic resonance spectroscopy. The ~(31)P NMR results show that the bisphosphonate groups bind irrotationally to bone, displacing orthophosphate from the bone mineral matrix. Binding of pamidronate is well described by a Langmuir-like isotherm, from which we deduce an ～30-38 A2 surface area per pamidronate molecule and a △G = -4.3 kcal mol~(1-). TEDOR of [~(13)C_3,~（15)N] pamidronate on bone shows that the bisphosphonate binds in a gauche [N-C(1)] conformation. The results of ~(31)P as well as ~(15)N shift and cross-polarization measurements indicate that risedronate binds weakly, since it has a primarily neutral pyridine side chain, whereas zoledronate (with an imidazole ring) binds more strongly, since the ring is partially protonated. The results of~2H NMR measurements of side-chain ~2H-labeled pamidronate, alendronate, zoledronate, and risedronate on bone show that all side chains undergo fast but restricted motions. In pamidronate, the motion is well simulated by a gauche+lgauche-hopping motion of the terminal -CH_2-NH_3~+ group, due to jumps from one anionic surface group to another. The results of double-cross polarization experiments indicate that the NH_3~+-terminus of pamidronate is close to the bone mineral surface, and a detailed model is proposed in which the gauche side-chain hops between two bone PO_4~(3-) sites.