This finding led to following studies designed to determine if they might also inhibit bone resorption [5]. The clarification of this property made BPs the most widely used and effective antiresorptive agents for the treatment of diseases in which there was an increase in the number or activity of osteoclasts, including tumor-associated osteolysis and hypercalcemia [6]. After more than three decades of research, first-, second-, and third-generation bisphosphonates have been developed. Changes in chemical structure have resulted in increased potency, without demineralization of bone [1]. There is now a growing body of evidence regarding the efficacy of

these drugs in Inhibitors,research,lifescience,medical clinical settings. All BPs that act significantly on the skeleton are characterized, Inhibitors,research,lifescience,medical as stated above, by P–C–P bond (Figure 1(a)), in contrast to pyrophosphate, which has a P–O–P bond (Figure 1(b)). Figure 1 Structures (a) and (b) show the basic structures of inorganic pyrophosphate and geminal bisphosphonate, respectively, where R1 and R2 represent different side chains for each bisphosphonate. Inhibitors,research,lifescience,medical This peculiarity confers stability both to heat and to most chemical reagents and is one of the most important properties of these compounds [4]. Extensive

chemical research programs have produced a wide range of molecules with various substituents attached to the carbon atom. Variations in potency and in the ability of the compounds to bind to 5-FU manufacturer crystals in bone one determined by the chemical and three-dimensional structure of the two side chains, R1 and R2, attached to the central, geminal carbon atom [1–4]. The bioactive moiety comprising the R2 chain of the molecule is considered primarily responsible for BPs’ effect on resorption, and Inhibitors,research,lifescience,medical small changes in this part of the structure can result in large differences in their antiresorptive potencies [4]. The uptake and

binding to bone mineral is Inhibitors,research,lifescience,medical determined by the bi- or tridentate ligand (hydroxybisphosphonate) of the molecule, which is also thought to be responsible for the physicochemical effects, the most important being the inhibition of growth of calcium crystals. The most effective structures for binding to bone mineral consist of the two phosphonate groups attached to the central however carbon and the substitution at R1 with a hydroxyl or amino group that provides tridentate binding [4]. In fact, the addition of a hydroxyl (OH) or primary amino (NH2) group increases the affinity for calcium ions, resulting in preferential localization of these drugs to sites of bone remodelling. Increasing the number of carbon atoms in the side chain initially increases and then decreases the magnitude of the effect on bone resorption [1–4]. The early compounds, clodronate (CLO) and etidronate (ETI), contained simple substituents (H, OH, Cl, CH3) and lacked a nitrogen atom (Figure 2).