Abstract
The crystal structures of three salts ( 1-a−3-a), products of the reactions between 5-chloro ( 1), 5bromo ( 2) and 5-iodo ( 3) substituted (pyridin-2-yl)aminomethane-1,1-diphos phonic acids and 4aminopyridine were determined by single crystal X-ray diffraction and discussed with respect to molecular geometry and solid state organization. In all 1-a−3-a, bisphosphonate dianion adopts the opposite (E) conformation with respect to the C2 −N1 bond, compared with the parent zwitterion. This provides further evidence that int ermolecular N−H··· O hydrogen bonds involving both exocyclic and pyridinium N atoms as proton donors and an O atom of the phosphonic/phosphonate group as acceptor play a significant role in stabilizing the Z conformation of this particular subclass of acids. The solution behavior and complex-formation abilities of [(5-iodopyridin-2-yl)amino]methane-1,1 -diphosphonic acid (3) were also studied. Compound 3 exists in solution as the Z/E mixture. However, the barrier to rotation around t he C2 −N1 bond in 3 is lower, compared with 1 and 2. This is important for the complex-formation processes in the Zn(II), Mg(II) and Ca(II) solution s with 3.
Highlights
Bisphosphonates are widely used to treat bone resorption diseases such as osteoporosis, Paget ’s disease and osteolytic bone metastases.[1]
Zn(II), Mg(II) and Ca(II) complexes with 3 Recently we have demonstrated that the formation of soluble, protonated multinuclear complexes in the Zn(II), Mg(II) and Ca(II) solutions withaminomethane-1,1-diphosphonic acid and related 4- and 5-substituted derivatives is exceptionally slow on the NMR time-scale, compared with most of bisphosphonates
The crystal structures of 1-a−3-a have been determined, which demonstrate that a loss of conformational stabilization provided by intermolecular N−H···O hydrogen bonds upon proton release from the pyridinium N atom leads to opposite conformation of the dianions of 1, 2 and 3, compared with the parent zwitterions
Summary
Bisphosphonates are widely used to treat bone resorption diseases such as osteoporosis, Paget ’s disease and osteolytic bone metastases.[1]. Zn(II), Mg(II) and Ca(II) complexes with 3 Recently we have demonstrated that the formation of soluble, protonated multinuclear complexes in the Zn(II), Mg(II) and Ca(II) solutions with (pyridin-2-yl)aminomethane-1,1-diphosphonic acid and related 4- and 5-substituted derivatives is exceptionally slow on the NMR time-scale, compared with most of bisphosphonates.
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