Calcium receptor-active compounds

Abstract: The present invention features compounds of general formulae a), b), c), able to modulate one or more activities of an inorganic ion receptor and methods for treating diseases or disorders by modulating inorganic ion receptor activity. Preferably, the compound can mimic or block the effect of extracellular Ca 2+ on a calcium receptor.

Description: Field of the Invention This invention relates to the design, development, composition and use of compounds able to modulate one or more inorganic ion receptor activities. Background of the Invention Certain cells in the body respond not only to chemical signals, but also to ions such as extracellular calcium ions (Ca 2+ ). Changes in the concentration of extracellular Ca 2+ (referred to herein as "[Ca 2+ ]") alter the functional responses of these cells. One such specialized cell is the parathyroid cell which secretes parathyroid hormone (PTH). PTH is the principal endocrine factor regulating Ca 2+ homeostasis in the blood and extracellular fluids. PTH, by acting on bone and kidney cells, increases the level of Ca 2+ in the blood. This increase in [Ca 2+ ] then acts as a negative feedback signal, depressing PTH secretion. The reciprocal relationship between [Ca 2+ ] and PTH secretion forms the essential mechanism maintaining bodily Ca 2+ homeostasis. Extracellular Ca 2+ acts directly on parathyroid cells to regulate PTH secretion. The existence of a parathyroid cell surface protein which detects changes in [Ca 2+ ] has been confirmed. Brown et al. , 366 Nature 574, 1993. In parathyroid cells, this protein acts as a receptor for extracellular Ca 2+ ("the calcium receptor"), and detects changes in [Ca 2+ ] and to initiate a functional cellular response, PTH secretion. Extracellular Ca 2+ can exert effects on different cell functions, reviewed in Nemeth et al. , 11 Cell Calcium 319, 1990. The role of extracellular Ca 2+ in parafollicular (C-cells) and parathyroid cells is discussed in Nemeth, 11 Cell Calcium 323, 1990. These cells have been shown to express similar Ca 2+ receptor. Brown et al., 366 Nature 574, 1993; Mithal et al. , 9 Suppl. 1 J. Bone and Mineral Res. s282, 1994; Rogers et al., 9 Suppl. 1 J. Bone and Mineral Res. s409, 1994; Garrett et al. , 9 Suppl. 1 J . Bone and Mineral Res. s409, 1994. The role of extracellular Ca 2+ on bone osteoclasts is discussed by Zaidi, 10 Bioscience Reports 493, 1990. In addition keratinocytes, juxtaglomerular cells, trophoblasts, pancreatic beta cells and fat/adipose cells all respond to increases in extracellular calcium which likely reflects activation of calcium receptors of these cells. The ability of various compounds to mimic extracellular Ca 2+ in vitro is discussed by Nemeth et al. , (spermine and spermidine) in "Calcium-Binding Proteins in Health and Disease," 1987, Academic Press, Inc., pp. 33-35; Brown et al., ( e.g. , neomycin) 128 Endocrinology 3047, 1991; Chen et al., (diltiazem and its analog, TA-3090) 5 J. Bone and Mineral Res. 581, 1990; and Zaidi et al., (verapamil) 167 Biochem. Biophys. Res. Commun. 807, 1990. Nemeth et al. , PCT/US93/01642, International Publication Number WO 94/18959, and Nemeth et al. , PCT/US92/07175, International Publication Number WO 93/04373, describe various compounds which can modulate the effect of an inorganic ion on a cell having an inorganic ion receptor. The references provided in the background are not admitted to be prior art. Summary of the Invention The present invention features compounds able to modulate one or more activities of an inorganic ion receptor and methods for treating diseases or disorders by modulating inorganic ion receptor activity. The compounds can mimic or block the effect of extracellular calcium on a cell surface calcium receptor. Diseases or disorders which can be treated by modulating inorganic ion receptor activity include one or more of the following types: (1) those characterized by abnormal inorganic ion homeostasis, preferably calcium homeostasis; (2) those characterized by an abnormal amount of an extracellular or intracellular messenger whose production can be affected by inorganic ion receptor activity, preferably calcium receptor activity; (3) those characterized by an abnormal effect ( e.g. , a different effect in kind or magnitude) of an intracellular or extracellular messenger which can itself be ameliorated by inorganic ion receptor activity, preferably calcium receptor activity; and (4) other diseases or disorders in which modulation of inorganic ion receptor activity, preferably calcium receptor activity will exert a beneficial effect, for example, in diseases or disorders where the production of an intracellular or extracellular messenger stimulated by receptor activity compensates for an abnormal amount of a different messenger. Examples of extracellular messengers whose secretion and/or effect can be affected by modulating inorganic ion receptor activity include inorganic ions, hormones, neurotransmitters, growth factors, and chemokines. Examples of intracellular messengers include cAMP, cGMP, IP 3 , and diacylglycerol. Thus, a compound of this invention preferably modulates calcium receptor activity and is used in the treatment of diseases or disorders which can be affected by modulating one or more activities of a calcium receptor. Calcium receptor proteins enable certain specialized cells to respond to changes in extracellular Ca 2+ concentration. For example, extracellular Ca 2+ inhibits the secretion of parathyroid hormone from parathyroid cells, inhibits bone resorption by osteoclasts, and stimulates secretion of calcitonin from C-cells. In a preferred embodiment, the compound is used to treat a disease or disorder characterized by abnormal bone and mineral homeostasis, more preferably calcium homeostasis. Extracellular Ca 2+ is under tight homeostatic control and controls various processes such as blood clotting, nerve and muscle excitability, and proper bone formation. Abnormal calcium homeostasis is characterized. by one or more of the following activities: (1) an abnormal increase or decrease in serum calcium; (2) an abnormal increase or decrease in urinary excretion of calcium; (3) an abnormal increase or decrease in bone calcium levels, for example, as assessed by bone mineral density measurements; (4) an abnormal absorption of dietary calcium; (5) an abnormal increase or decrease in the production and/or release of messengers which affect serum calcium levels such as parathyroid hormone and calcitonin; and (6) an abnormal change in the response elicited by messengers which affect serum calcium levels. The abnormal increase or decrease in these different aspects of calcium homeostasis is relative to that occurring in the general population and is generally associated with a disease or disorder. Diseases and disorders characterized by abnormal calcium homeostasis can be due to different cellular defects such as a defective calcium receptor activity, a defective number of calcium receptors, or a defective intracellular protein acted on by a calcium receptor. For example, in parathyroid cells, the calcium receptor is coupled to the G i protein which in turn inhibits cyclic AMP production. Defects in G i protein can affect its ability to inhibit cyclic AMP production. Thus, a first aspect the invention features a compound having the structure: or a pharmaceutically acceptable salt or complex thereof. The compounds according to the invention therefore comprise a compound of structure (I) above as well as the pharmaceutically acceptable salts and complexes thereof. Compounds of this invention have preferred stereo-chemistry. The CH 3 of Structure I is at a chiral center and provides an α-(R)-methyl structure. Inorganic ion receptor activities are those processes brought about as a result of inorganic ion receptor activation. Such processes include the production of molecules which can act as intracellular or extracellular messengers. Inorganic ion receptor-modulating compound include ionomimetics, ionolytics, calcimimetics, and calcilytics. Ionomimetics are compounds which bind to an inorganic ion receptor and mimic ( i.e. , evoke or potentiate) the effects of an inorganic ion at an inorganic ion receptor. Preferably, the compound affects one or more calcium receptor activities. Calcimimetics are ionomimetics which effects one or more calcium receptor activities and bind to a calcium receptor. Ionolytics are compounds which bind to an inorganic ion receptor and block ( i.e. , inhibit or diminish) .one or more activities caused by an inorganic ion at an inorganic ion receptor. Preferably, the compound affects one or more calcium receptor activities. Calcilytics are ionolytics which block one or more calcium receptor activities evoked by extracellular calcium and bind to a calcium receptor. Ionomimetics and ionolytics may bind at the same receptor site as the native inorganic ion ligand binds or can bind at a different site ( e.g., allosteric site). For example, NPS R -467 binding to a calcium receptor results in calcium receptor activity and, thus, NPS R -467 is classified as a calcimimetic. However, NPS R -467 binds to the calcium receptor at a different site ( i.e ., an allosteric site) than extracellular calcium. A measure of a compounds effectiveness can be determined by calculating the EC 50 or IC 50 for that compound. The EC 50 is the concentration of a compound which causes a half maximal mimicking effect. The IC 50 is the concentration of compound which causes a half-maximal blocking effect. EC 50 and IC 50 for compounds at a calcium receptor can be determined by assaying one or more of the activities of extracellular calcium at a calcium receptor. Examples of assays for measuring EC 50 , and IC 50 are described Nemeth et al. , PCT/US93/01642, International Publication Number WO 94/18959, and Nemeth et al., PCT/US92/07175, International Publication Number WO 93/04373, (both of these publications are hereby incorporated by reference here) and below. Such assays include oocyte expression assays and measuring increases in intracellular calcium ion concentration ([Ca 2+ ] i ) due to calcium receptor activity. Preferably, such assays measure the release or inhibition of a particular hormone associated with activity of a calcium receptor. An inorganic ion receptor-modulating compound preferably selectively targets inorganic ion receptor activity in a particular cell. For example, selective targeting of a calcium receptor activity is achieved by a compound exerting a greater effect on a calcium receptor activity in one cell type than at another cell type for a given concentration of compound. Preferably, the differential effect is 10-fold or greater as measured in vivo or in vitro. More preferably, the differential effect is measured in vivo and the compound concentration is measured as the plasma concentration or extracellular fluid concentration and the measured effect is the production of extracellular messengers such as plasma calcitonin, parathyroid hormone, or plasma calcium. For example, in a preferred embodiment, the compound selectively targets PTH secretion over calcitonin secretion. Preferably, the compound is either a calcimimetic or calcilytic having an EC 50 or IC 50 at a calcium receptor of less than or equal to 5 µM, and even more preferably less than or equal to 1 µM, 100 nmolar, 10 nmolar, or 1 nmolar using one of the assays described below. More preferably, the assay measures intracellular Ca 2+ in HEK 293 cells transformed with nucleic acid expressing the human parathyroid calcium receptor and loaded with fura-2. Lower EC 50 ' s or IC 50 ' s are advantageous since they allow lower concentrations of compounds to be used in vivo or in vitro. The discovery of compounds with low EC 50 ' s and IC 50 's enables the design and synthesis of additional compounds having similar or improved potency, effectiveness, and/or selectivity. Another aspect of the present invention features a pharmaceutical composition comprising a compound according to the invention and a physiologically acceptable carrier. A "pharmacological composition" refers to a composition in a form suitable for administration into a mammal, preferably a human. Preferably, the pharmaceutical composition contains a sufficient amount of a compound according to the invention in a proper pharmaceutical form to exert a therapeutic effect on a human. Considerations concerning forms suitable for administration are known in the art and include toxic effects, solubility, route of administration, and maintaining activity. For example, pharmacological compositions injected into the blood stream should be soluble. Pharmaceutical compositions can also be formulated as pharmaceutically acceptable salts ( e.g. , acid addition salts) and complexes thereof. The preparation of such salts can facilitate the pharmacological use of a compound by altering its physical characteristics without preventing it from exerting a physiological effect. The compounds according to the invention may be used in a method for the preparation of a medicament for treating a patient by modulating inorganic ion receptor activity. The method involves administering to the patient a pharmaceutical composition containing a therapeutically effective amount of a compound according to the invention. In a preferred embodiment, the disease or disorder is treated by modulating calcium receptor activity by administering to the patient a therapeutically effective amount of a calcium receptor-modulating compound of the invention. These compounds, and compositions containing the compounds, can be used to treat patients. A "patient" refers to a mammal in which modulation of an inorganic ion receptor will have a beneficial effect. Patients in need of treatment involving modulation of inorganic ion receptors can be identified using standard techniques known to those in the medical profession. Preferably, a patient is a human having a disease or disorder characterized by one more of the following : (1) abnormal inorganic ion homeostasis, more preferably abnormal calcium homeostasis, (2) an abnormal level of a messenger whose production or secretion is affected by inorganic ion receptor activity, more preferably affected by calcium receptor activity, and (3) an abnormal level or activity of a messenger whose function is affected by inorganic ion receptor activity, more preferably affected by calcium receptor activity. Diseases characterized by abnormal calcium homeostasis include hyperparathyroidism, osteoporosis and other bone and mineral-related disorders, and the like (as described, e.g. , in standard medical text books, such as "Harrison's Principles of Internal Medicine"). Such diseases are treated using calcium receptor-modulating compounds which mimic or block one or more of the effects of extracellular Ca 2+ on a calcium receptor and, thereby, directly or indirectly affect the levels of proteins or other compounds in the body of the patient. By "therapeutically effective amount" is meant an amount of a compound which relieves to some extent one or more symptoms of the disease or disorder in the patient; or returns to normal either partially or completely one or more physiological or biochemical parameters associated with or causative of the disease or disorder. In a preferred embodiment, the patient has a disease or disorder characterized by an abnormal level of one or more calcium receptor-regulated components and the compound is active on a calcium receptor of a cell selected from the group consisting of: parathyroid cell, bone osteoclast, juxtaglomerular kidney cell, proximal tubule kidney cell, distal tubule kidney cell, central nervous system cell, peripheral nervous system cell, cell of the thick ascending limb of Henle's loop and/or collecting duct, keratinocyte in the epidermis, parafollicular cell in the thyroid (C-cell), intestinal cell, platelet, vascular smooth muscle cell, cardiac atrial cell, gastrin-secreting cell, glucagon-secreting cell, kidney mesangial cell, mammary cell, beta cell, fat/adipose cell, immune cell, GI tract cell, skin cell, adrenal cell, pituitary cell, hypothalamic cell and cell of the subfornical organ. More preferably, the cells are chosen from the group consisting of: parathyroid cell, central nervous system cell, peripheral nervous system cell, cell of the thick ascending limb of Henle's loop and/or collecting duct in the kidney, parafollicular cell in the thyroid (C-cell), intestinal cell, GI tract cell, pituitary cell, hypothalamic cell and cell of the subfornical organ. In a preferred embodiment, the compound is a calcimimetic acting on a parathyroid cell calcium receptor and reduces the level of parathyroid hormone in the serum of the patient. More preferably, the level is reduced to a degree sufficient to cause a decrease in plasma Ca 2+ . Most preferably, the parathyroid hormone level is reduced to that present in a normal individual. In another preferred embodiment, the compound is a calcilytic acting on a parathyroid cell calcium receptor and increases the level of parathyroid hormone in the serum of the patient. More preferably, the level is increased to a degree sufficient to cause an increase in bone mineral density of a patient. Patients in need of such treatments can be identified by standard medical techniques, such as blood or urine analysis. For example, by detecting a deficiency of protein whose production or secretion is affected by changes in inorganic ion concentrations, or by detecting abnormal levels of inorganic ions or hormones which effect inorganic ion homeostasis. In another aspect, the invention relates to the use of the compounds according to the invention for the preparation of a medicament for treating a disease or disorder characterised by abnormal bone and mineral homeostasis. Diseases or disorders that may be treated include hyperparathyroidism, Paget's disease, osteoporosis, hypertension and renal osteodystrophy. Various examples are used throughout the application. These examples are not intended in any way to limit the invention. Other features and advantages of the invention will be apparent from the following figures, detailed description of the invention, examples, and the claims. Brief Description of the Drawings Figs. 1 and 2 provided data for reference compound R-568 and the compound of structure (I) respectively. Description of the Preferred Embodiments The present invention features compounds able to modulate one or more inorganic ion receptor activities, preferably the compound can mimic or block an effect of an extracellular ion on a cell having an inorganic ion receptor, more preferably the extracellular ion is Ca 2+ and the effect is on a cell having a calcium receptor. Publications concerned with the calcium activity, calcium receptor and/or calcium receptor modulating compounds include the following: Brown et al., Nature 366 : 574, 1993; Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959; Nemeth et al. , PCT/US92/07175, International Publication Number WO 93/04373; Shoback and Chen, J. Bone Mineral Res. 9 : 293 (1994) ; and Racke et al. , FEBS Lett. 333 : 132, (1993). These publications are not admitted to be prior art to the claimed invention. I. Calcium Receptors Calcium receptors are present on different cell types and can have different activities in different cell types. The pharmacological effects of the following cells, in response to calcium, is consistent with the presence of a calcium receptor: parathyroid cell, bone osteoclast, juxtaglomerular kidney cell, proximal tubule kidney cell, distal tubule kidney cell, central nervous system cell, peripheral nervous system cell, cell of the thick ascending limb of Henle's loop and/or collecting duct, keratinocyte in the epidermis, parafollicular cell in the thyroid (C-cell), intestinal cell, platelet, vascular smooth muscle cell, cardiac atrial cell, gastrin-secreting cell, glucagon-secreting cell, kidney mesangial cell, mammary cell, beta cell, fat/adipose cell, immune cell, GI tract cell, skin cell, adrenal cell, pituitary cell, hypothalamic cell and cell of the subfornical organ. In addition, the presence of calcium receptors on parathyroid cell, central nervous system cell, peripheral nervous system cell, cell of the thick ascending limb of Henle's loop and/or collecting duct in the kidney, parafollicular cell in the thyroid (C-cell), intestinal cell, GI tract cell, pituitary cell, hypothalamic cell and cell of the subfornical organ, has been confirmed by physical data. The calcium receptor on these different cell types may be different. It is also possible that a cell can have more than one type of calcium receptor. Comparison of calcium receptor activities and amino acid sequences from different cells indicate that distinct calcium receptor types exist. For example, calcium receptors can respond to a variety of di- and trivalent cations. The parathyroid calcium receptor responds to calcium and Gd 3+ , while osteoclasts respond to divalent cations such as calcium, but do not respond to Gd 3+ . Thus, the parathyroid calcium receptor is pharmacologically distinct from the calcium receptor on the osteoclast. On the other hand, the nucleic acid sequences encoding calcium receptors present in parathyroid cells and C-cells indicate that these receptors have a very similar amino acid structure. Nevertheless, calcimimetic compounds exhibit differential pharmacology and regulate different activities at parathyroid cells and C-cells. Thus, pharmacological properties of calcium receptors may vary significantly depending upon the cell type or organ in which they are expressed even though the calcium receptors may have similar or even identical structures. Calcium receptors, in general, have a low affinity for extracellular Ca 2+ (apparent K d generally greater than about 0.5 mM). Calcium receptors may include a free or bound effector mechanism as defined by Cooper, Bloom and Roth, "The Biochemical Basis of Neuropharmacology", Ch. 4, and are thus distinct from intracellular calcium receptors, e.g. , calmodulin and the troponins. Calcium receptors respond to changes in extracellular calcium levels. The exact changes depend on the particular receptor and cell line containing the receptor. For example, the in vitro effect of calcium on the calcium receptor in a parathyroid cell includes the following: 1. An increase in internal calcium. The increase is due to the influx of external calcium and/or to mobilization of internal calcium. Characteristics of the increase in internal calcium include the following: (a) A rapid (time to peak < 5 seconds) and transient increase in [Ca 2+ ] i that is refractory to inhibition by 1 µM La 3+ or 1 µM Gd 3+ and is abolished by pretreatment with ionomycin (in the absence of extracellular Ca 2+ ); (b) The increase is not inhibited by dihydropyridines; (c) The transient increase is abolished by pretreatment for 10 minutes with 10 mM sodium fluoride; (d) The transient increase is diminished by pretreatment with an activator of protein kinase C (PKC) , such as phorbol myristate acetate (PMA), mezerein or (-)-indolactam V. The overall effect of the protein kinase C activator is to shift the concentration-response curve of calcium to the right without affecting the maximal response; and (e) Pretreatment with pertussis toxin (100 ng/ml for > 4 hours) does not affect the increase. 2. A rapid (< 30 seconds) increase in the formation of inositol-1,4,5-triphosphate or diacylglycerol. Pretreatment with pertussis toxin (100 ng/ml for > 4 hours) does not affect this increase; 3. The inhibition of dopamine- and isoproterenol-stimulated cyclic AMP formation. This effect is blocked by pretreatment with pertussis toxin (100 ng/ml for > 4 hours); and 4. The inhibition of PTH secretion. Pretreatment with pertussis toxin (100 ng/ml for > 4 hours) does not affect the inhibition in PTH secretion. Using techniques known in the art, the effect of calcium on other calcium receptors in different cells can be readily determined. Such effects may be similar in regard to the increase in internal calcium observed in parathyroid cells. However, the effect is expected to differ in other aspects, such as causing or inhibiting the release of a hormone other than parathyroid hormone. II. Inorganic Ion Receptor Modulating Compounds Inorganic ion receptor modulating compounds modulate one or more inorganic ion receptor activities. Preferred calcium receptor modulating compounds are calcimimetics and calcilytics. Inorganic ion receptor modulating compounds can be identified by screening compounds which are modelled after a compound shown to have a particular activity ( i.e. , a lead compound). A preferred method of measuring calcium receptor activity is to measure changes in [Ca 2+ ] i . Changes in [Ca 2+ ] i can be measured using different techniques such by using HEK 293 cells transduced with nucleic acid expressing the human parathyroid calcium receptor and loaded with fura-2; and by measuring an increase in Cl - current in a Xenopus oocyte injected with nucleic acid coding for a calcium receptor. (See Nemeth et al. , PCT/US93/01642, International Publication Number WO 94/18959.) For example, poly(A) + mRNA can be obtained from cells expressing a calcium receptor, such as a parathyroid cell, bone osteoclast, juxtaglomerular kidney cell, proximal tubule kidney cell, distal tubule kidney cell, cell of the thick ascending limb of Henle's loop and/or collecting duct, keratinocyte in the epidermis, parafollicular cell in the thyroid (C-cell), intestinal cell, central nervous cell, peripheral nervous system cell, platelet, vascular smooth muscle cell, cardiac atrial cell, gastrin-secreting cell, glucagon-secreting cell, kidney mesangial cell, mammary cell, beta cell, fat/adipose cell, immune cell, and GI tract cell. Preferably, the nucleic acid is from a parathyroid cell, C-cell, or osteoclast. More preferably, the nucleic acid encodes a calcium receptor and is present on a plasmid or vector. In preferred embodiments the calcium receptor modulating compound is a calcimimetic which inhibits bone resorption in vivo by an osteoclast; inhibits bone resorption in vitro by an osteoclast; stimulates calcitonin secretion in vitro or in vivo from a c-cell; inhibits parathyroid hormone secretion from a parathyroid cell in vitro and decreases PTH secretion in vivo; elevates calcitonin levels in vivo; or blocks osteoclastic bone resorption in vitro and inhibits bone resorption in vivo . In another preferred embodiment the calcium receptor modulating compound is a calcilytic which evokes the secretion of parathyroid hormone from parathyroid cells in vitro and elevates the level of parathyroid hormone in vivo. Preferably, the compound selectively targets inorganic ion receptor activity, more preferably calcium receptor activity, in a particular cell. By "selectively" is meant that the compound exerts a greater effect on inorganic ion receptor activity in one cell type than at another cell type for a given concentration of compound. Preferably, the differential effect is 10-fold or greater. Preferably, the concentration refers to blood plasma concentration and the measured effect is the production of extracellular messengers such as plasma calcitonin, parathyroid hormone or plasma calcium. For example, in a preferred embodiment, the compound selectively targets PTH secretion over calcitonin secretion. In another preferred embodiment, the compound has an EC 50 or IC 50 less than or equal to 5 µM at one or more, but not all cells chosen from the group consisting of: parathyroid cell, bone osteoclast, juxtaglomerular kidney cell, proximal tubule kidney cell, distal tubule kidney cell, central nervous system cell, peripheral nervous system cell, cell of the' thick ascending limb of Henle's loop and/or collecting duct, keratinocyte in the epidermis, parafollicular cell in the thyroid (C-cell) , intestinal cell, platelet, vascular smooth muscle cell, cardiac atrial cell, gastrin-secreting cell, glucagon-secreting cell, kidney mesangial cell, mammary cell, beta cell, fat/adipose cell, immune cell, GI tract cell, skin cell, adrenal cell, pituitary cell, hypothalamic cell and cell of the subfornical organ. More preferably, the cells are chosen from the group consisting of parathyroid cell, central nervous system cell, peripheral nervous system cell, cell of the thick ascending limb of Henle's loop and/or collecting duct in the kidney, parafollicular cell in the thyroid (C-cell), intestinal cell, GI tract cell, pituitary cell, hypothalamic cell and cell of the subfornical organ. The presence of a calcium receptor in this group of cells has been confirmed by physical data such as in situ hybridization and antibody staining. Preferably, inorganic ion receptor modulating compounds mimic or block the effects of an extracellular ion on a cell having an inorganic ion receptor, such that the compounds achieve a therapeutic effect. Inorganic ion receptor modulating compounds may have the same, or different, effects on cells having different types of inorganic ion receptor morphology ( e.g. , such as cells having normal inorganic ion receptors, a normal number of inorganic ion receptor, an abnormal inorganic ion receptor, and an abnormal number of inorganic ion receptors) . Calcium receptor modulating compounds preferably mimic or block all of the effects of extracellular ion in a cell having a calcium receptor. However, calcimimetics need not possess all the biological activities of extracellular Ca 2+ . Similarly, calcilytics need not block all of the activities caused by extracellular calcium. Additionally, different calcimimetics and different calcilytics do not need to bind to the same site on the calcium receptor as does extracellular Ca 2+ to exert their effects. Inorganic modulating compounds need not effect inorganic receptor activity to the same extent or in exactly the same manner as the natural ligand. For example, a calcimimetic may effect calcium receptor activity to a different extent, to a different duration, by binding to a different binding site, or by having a different affinity, compared to calcium acting at a calcium receptor. Calcimimetic Activity The ability of compounds to mimic the activity of Ca 2+ at calcium receptors can be determined using procedures known in the art and described by Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959. For example, calcimimetics possess one or more and preferably all of the following activities when tested on parathyroid cells in vitro: 1. The compound causes a rapid (time to peak < 5 seconds) and transient increase in intracellular calcium concentration that is refractory to inhibition by 1 µM La 3+ or 1 µM Gd 3+ . The increase in [Ca 2+ ] persists in the absence of extracellular Ca 2+ , but is abolished by pretreatment with ionomycin (in the absence of extracellular Ca 2+ ) ; 2. The compound potentiates increases in [Ca 2+ ] elicited by submaximal concentrations of extracellular Ca 2+ ; 3. The increase in [Ca 2+ ] i elicited by extracellular Ca 2+ is not inhibited by dihydropyridines; 4. The transient increase in [Ca 2+ ] i caused by the compound is abolished by pretreatment for 10 minutes with 10 mM sodium fluoride; 5. The transient increase in [Ca 2+ ] i caused by the compound is diminished by pretreatment with an activator of protein kinase C (PKC), such as phorbol myristate acetate (PMA), mezerein or (-)-indolactam V. The overall effect of the protein kinase C activator is to shift the concentration-response curve of the compound to the right without affecting the maximal response; 6. The compound causes a rapid (< 30 seconds) increase in the formation of inosicol-1,4,5-triphosphate and/or diacylglycerol; 7. The compound inhibits dopamine- or isoproterenol-stimulated cyclic AMP formation; 8. The compound inhibits PTH secretion; 9. Pretreatment with pertussis toxin (100 ng/ml for > 4 hours) blocks the inhibitory effect of the compound on cyclic AMP formation, but does not effect increases in [Ca 2+ ] i , inositol-1,4,5-triphosphate, or diacylglycerol, nor decreases in PTH secretion; 10. The compound elicits increases in Cl - current in Xenopus oocytes injected with poly(A) + -enriched mRNA from bovine or human parathyroid cells, but is without effect in Xenopus oocytes injected with water, or liver mRNA; and 11. Similarly, using a cloned calcium receptor from a parathyroid cell, the compound will elicit a response in Xenopus oocytes injected with the specific cDNA or mRNA encoding the receptor. Different calcium activities can be measured using available techniques. ( See , Nemeth et al. , PCT/US93/01642, International Publication Number WO 94/18959.) Parallel definitions of compounds mimicking. Ca 2+ activity on other calcium responsive cell, preferably at a calcium receptor, are evident from the examples provided herein and Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959. Preferably, the compound as measured by the bioassays described herein, or by Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959, has one or more, more preferably all of the following activities: evokes a transient increase in internal calcium, having a duration of less that 30 seconds (preferably by mobilizing internal calcium) ; evokes a rapid increase in [Ca 2+ ] i , occurring within thirty seconds; evokes a sustained increase (greater than thirty seconds) in [Ca 2+ ] i (preferably by causing an influx of external calcium); evokes an increase in inositol-1,4,5-triphosphate or diacylglycerol levels, preferably within less than 60 seconds; and inhibits dopamine- or isoproterenol-stimulated cyclic AMP formation. The transient increase in [Ca 2+ ] i is preferably abolished by pretreatment of the cell for ten minutes with 10 mM sodium fluoride, or the transient increase is diminished by brief pretreatment (not more than ten minutes) of the cell with an activator of protein kinase C, preferably, phorbol myristate acetate (PMA) , mezerein or (-) indolactam V. Calcilytics The ability of a compound to block the activity of extracellular calcium at a calcium receptor can be determined using standard techniques based on the present disclosure. ( See , also Nemeth et al. , PCT/US93/01642, International Publication Number WO 94/18959.) For example, compounds which block the effect of extracellular calcium, when used in reference to a parathyroid cell, possess one or more, and preferably all of the following characteristics when tested on parathyroid cells in vitro: 1. The compound blocks, either partially or completely, the ability of increased concentrations of extracellular Ca 2+ to: (a) increase [Ca 2+ ] i , (b) mobilize intracellular Ca 2+ , (c) increase the formation of inositol-1,4,5-triphosphate, (d) decrease dopamine- or isoproterenol-stimulated cyclic AMP formation, and (e) inhibit PTH secretion; 2. The compound blocks increases in Cl - current in Xenopus oocytes injected with poly(A) + -mRNA from bovine or human parathyroid cells elicited by extracellular Ca 2+ or calcimimetic compounds, but not in Xenopus oocytes injected with water or liver mRNA; 3. Similarly, using a cloned calcium receptor from a parathyroid cell, the compound will block a response in Xenopus oocytes injected with the specific cDNA, mRNA or cRNA encoding the calcium receptor, elicited by extracellular Ca 2+ or a calcimimetic compound. Parallel definitions of compounds blocking Ca 2+ activity on a calcium responsive cell, preferably at a calcium receptor, are evident from the examples provided herein and Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959. III. TREATMENT OF DISEASES OR DISORDERS Diseases or disorders which can be treated by modulating calcium receptor activity are known in the art. For example, diseases or disorders which can be treated by modulating calcium receptor activity can be identified based on the functional responses of cells regulated'by calcium receptor activity. Functional responses of cells regulated by calcium receptor are know in the art, including PTH secretion by parathyroid cells, calcitonin secretion by C-cells, and bone resorption by osteoclasts. Such functional responses are associated with different diseases or disorders. For example, hyperparathyroidism results in elevated levels of PTH in the plasma. Decreasing the plasma levels of PTH offers an effective means of treating hyperparathyroidism. Likewise, increasing plasma levels of calcitonin is associated with an inhibition of bone resorption. Inhibiting bone resorption is an effective treatment for osteoporosis. Thus, modulation of calcium receptor activity can be used to treat diseases such as hyperparathyroidism, and osteoporosis. Those compounds modulating inorganic ion receptor activity, preferably calcium receptor activity, can be used to confer beneficial effects to patients suffering from a variety of diseases or disorders. For example, osteoporosis is an age-related disorder characterized by loss of bone mass and increased risk of bone fracture. Compounds can be used to block osteoclastic bone resorption either directly ( e.g. , an osteoclast ionomimetic compound) or indirectly by increasing endogenous calcitonin levels ( e:g. , a C-cell calcimimecic). Alternatively, a calcilytic active on the parathyroid cell calcium receptor will increase circulating levels of parathyroid hormone, stimulating bone formation. All three of these approaches will result in beneficial effects to patients suffering from osteoporosis. In addition, it is known that intermittent low dosing with PTH results in an anabolic effect on bone mass and appropriate bone remodeling. Thus, compounds and dosing regimens evoking transient increases in parathyroid hormone ( e.g. , intermittent dosing with a parathyroid cell ionolytic) can increase bone mass in patients suffering from osteoporosis. Additional diseases or disorders can be identified by identifying additional cellular functional responses, associated with a disease or disorder, which are regulated by calcium receptor activity. Diseases or disorder which can be.treated by modulating other inorganic ion receptors can be identified in an analogous manner. The inorganic ion receptor-modulating compounds of the present invention can exert an affect at an inorganic ion receptor causing one or more cellular effects ultimately producing a therapeutic effect. Calcium receptor-modulating compounds of the present invention can exert an effect on calcium receptor causing one or more cellular effects ultimately producing a therapeutic effect. Different diseases can be treated by the present invention by targeting cells having a calcium receptor. For example, primary hyperparathyroidism (HPT) is characterized by hypercalcemia and abnormal elevated levels of circulating PTH. A defect associated with the major type of HPT is a diminished sensitivity of parathyroid cells to negative feedback regulation by extracellular Ca 2+ . Thus, in tissue from patients with primary HPT, the "set-point" for extracellular Ca 2+ is shifted to the right so that higher than normal concentrations of extracellular Ca 2+ are required to depress PTH secretion. Moreover, in primary HPT, even high concentrations of extracellular Ca 2+ often depress PTH secretion only partially. In secondary (uremic) HPT, a similar increase in the set-point for extracellular Ca 2+ is observed even though the degree to which Ca 2+ suppresses PTH secretion is normal. The changes in PTH secretion are paralleled by changes in [Ca 2+ ] i : the set-point for extracellular Ca 2+ -induced increases in [Ca 2+ ] i is shifted to the right and the magnitude of such increases is reduced. Patients suffering from secondary HPT may also have renal osteodystrophy. Calcimimetics appear to be useful for treating both abnormal PTH secretion and osteodystrophy in such patients. Compounds that mimic the action of extracellular Ca 2+ are beneficial in the long-term management of both primary and secondary HPT. Such compounds provide the added impetus required to suppress PTH secretion which the hypercalcemic condition alone cannot achieve and, thereby, help to relieve the hypercalcemic condition. Compounds with greater efficacy than extracellular Ca 2+ may overcome the apparent nonsuppressible component of PTH secretion which is particularly troublesome in the major form of primary HPT caused by adenoma of the parathyroid gland. Alternatively or additionally, such compounds can depress synthesis of PTH, as prolonged hypercalcemia has been shown to depress the levels of preproPTH mRNA in bovine and human adenomatous parathyroid tissue. Prolonged hypercalcemia also depresses parathyroid cell proliferation in vitro , so calcimimetics can also be effective in limiting the parathyroid cell hyperplasia characteristic of secondary HPT. Cells other than parathyroid cells can respond directly to physiological changes in the concentration of extracellular Ca 2+ . For example, calcitonin secretion from parafollicular cells in the thyroid (C-cells) is regulated by changes in the concentration of extracellular Ca 2+ . Isolated osteoclasts respond to increases in the concentration of extracellular Ca 2+ with corresponding increases in [Ca 2+ ] i that arise partly from the mobilization of intracellular Ca 2+ . Increases in [Ca 2+ ] i in osteoclasts are associated with the inhibition of bone resorption. Release of alkaline phosphatase from bone-forming osteoblasts is directly stimulated by calcium. Renin secretion from juxtaglomerular cells in the kidney, like PTH secretion, is depressed by increased concentrations of extracellular Ca 2+ . Extracellular Ca 2+ causes the mobilization of intracellular Ca 2+ . in these cells. Other kidney cells respond to calcium as follows: elevated Ca 2+ inhibits formation of 1,25(OH) 2 -vitamin D by proximal tubule cells, stimulates production of calcium-binding protein in distal tubule cells, and inhibits tubular reabsorption of Ca 2+ and Mg 2+ and the action of vasopressin on the thick ascending limb of Henle's loop (MTAL), reduces vasopressin action in the cortical collecting duct cells, and affects vascular smooth muscle cells in blood vessels of the renal glomerulus. Calcium also promotes the differentiation of intestinal goblet cells, mammary cells, and skin cells; inhibits atrial natriuretic peptide secretion from cardiac atria; reduces cAMP accumulation in platelets; alters gastrin and glucagon secretion; acts on vascular smooth muscle cells to modify cell secretion of vasoactive factors; and affects cells of the central nervous system and peripheral nervous system. Thus, there are sufficient indications to suggest that Ca 2+ , in addition to its ubiquitous role as an intracellular signal, also functions as an extracellular signal to regulate the responses of certain specialized cells. Compounds of this invention can be used in the treatment of diseases or disorders associated with disrupted Ca 2+ responses in these cells. Specific diseases and disorders which might be treated or prevented, based upon the affected cells, also include those of the central nervous system such as seizures, stroke, head trauma, spinal cord injury, hypoxia-induced nerve cell damage such as in cardiac arrest or neonatal distress, epilepsy, neurodegenerative diseases such as Alzheimer's disease, Huntington's disease and Parkinson's disease, dementia, muscle tension, depression, anxiety, panic disorder, obsessive-compulsive disorder, post-traumatic stress disorder, schizophrenia, neuroleptic malignant syndrome, and Tourette's syndrome; diseases involving excess water reabsorption by the kidney such as syndrome of inappropriate ADH secretion (SIADH), cirrhosis, congestive heart failure, and nephrosis; hypertension; preventing and/or decreasing renal toxicity from cationic antibiotics ( e.g. , aminoglycoside antibiotics); gut motility disorders such as diarrhea, and spastic colon; GI ulcer diseases; GI diseases with excessive calcium absorption such as sarcoidosis; and autoimmune diseases and organ transplant rejection. While calcium receptor-modulating compounds of the present invention will typically be used in therapy for human patients, they may also be used to treat similar or identical diseases in other warm-blooded animal species such as other primates, farm animals such as swine, cattle, and poultry; and sports animals and pets Such as horses, dogs and cats. IV. Administration The compounds described by the present invention can be used to treat different diseases or disorders by modulating inorganic ion receptor activity, preferably calcium receptor activity. The compounds of the invention can be formulated for a variety of modes of administration, including systemic and topical or localized administration. Techniques and formulations generally may be found in Remington's Pharmaceutical Sciences, Mack Publishing Co., Easton, PA. Administration of ionomimetics and ionolytics is discussed by Nemeth et al. , PCT/US93/01642, International Publication Number WO 94/18959. Suitable dosage forms, in part, depend upon the use or the route of entry, for example oral, transdermal, or by injection. Such dosage forms should allow the compound to reach a target cell whether the target cell is present in a multicellular host or in culture. For example, pharmacological compounds or compositions injected into the blood stream should be soluble. Other factors are known in the art, and include considerations such as toxicity and dosage form which retard the compound or composition from exerting its effect. The compound of structure (I) can also be formulated as pharmaceutically acceptable salts ( e.g. , acid addition salts) and complexes thereof. Pharmaceutically acceptable salts are non-toxic salts at the concentration at which they are administered. The preparation of such salts can facilitate the pharmacological use by altering the physical characteristic of the compound without preventing it from exerting its physiological effect. Useful alterations in physical properties include lowering the melting point to facilitate transmucosal administration and increasing the solubility to facilitate administering higher concentrations of the drug. Pharmaceutically acceptable salts include acid addition salts such as those containing sulfate, hydrochloride, maleate, phosphate, sulfamate, acetate, citrate, lactate, tartrate, methanesulfonate, ethanesulfonate, benzenesulfonate, p -toluenesulfonate, cyclohexylsulfamate and quinate. ( See e.g., PCT/US92/03736, hereby incorporated by reference herein.) Pharmaceutically acceptable salts can be obtained from acids such as hydrochloric acid, maleic acid, sulfuric acid, phosphoric acid, sulfamic acid, acetic acid, citric acid, lactic acid, tartaric acid, malonic acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p -toluenesulfonic acid, cyclohexylsulfamic acid, and quinic acid. Pharmaceutically acceptable salts can be prepared by standard techniques. For example, the free base form of a compound is dissolved in a suitable solvent, such as an aqueous or aqueous-alcohol solution, containing the appropriate acid and then isolated by evaporating the solution. In another example, a salt is prepared by reacting the free base and acid in an organic solvent. Carriers or excipients can also be used to facilitate administration of the compound. Examples of carriers and excipients include calcium carbonate, calcium phosphate, various sugars such as lactose, glucose, or sucrose, or types of starch, cellulose derivatives, gelatin, vegetable oils, polyethylene glycols and physiologically compatible solvents. The compositions or pharmaceutical composition can be administered by different routes including intravenously, intraperitoneal, subcutaneous, and intramuscular, orally, topically, or transmucosally. For systemic administration, oral administration is preferred. Alternatively, injection may be used, e.g. , intramuscular, intravenous, intraperitoneal, and subcutaneous. For injection, the compounds of the invention are formulated in liquid solutions, preferably in physiologically compatible buffers such as Hank's solution or Ringer's solution. In addition, the compounds may be formulated in solid form and redissolved or suspended immediately prior to use. Lyophilized forms can also be produced. Systemic administration can also be by transmucosal or transdermal means, or the compounds can be administered orally. For transmucosal or transdermal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are generally known in the art, and include, for example, for transmucosal administration, bile salts and fusidic acid derivatives. In addition, detergents may be used to facilitate permeation. Transmucosal administration may be through nasal sprays, for example, or using suppositories. For oral administration,. the compounds can be formulated into conventional oral administration dosage forms such as capsules, tablets, and liquid preparations. For topical administration, the compounds of the invention can be formulated into ointments, salves, gels, or creams, as is generally known in the art. The amounts of various compounds of this invention to be administered can be determined by standard procedures. Generally, a therapeutically effective amount is between about 1 nmole and 3 µmole of the compound, preferably 0.1 nmole and 1 µmole depending on its EC 50 or IC 50 and on the age and size of the patient, and the disease or disorder associated with the patient. Generally, it is an amount between about 0.1 and 50 mg/kg, preferably 0.01 and 20 mg/kg of the animal to be treated. V. Examples Examples are provided below illustrating different aspects and embodiments of the present invention. These examples are not intended to limit the claimed invention. Example 1: Cloning of Human Parathyroid Calcium Receptor From a Human Parathyroid Gland Adenoma Tumor This example describes the cloning of a human parathyroid calcium receptor from a human parathyroid gland adenoma tumor using pBoPCaR1 as a hybridization probe ( See , Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959) . The probe was used to identify nucleic acid encoding human parathyroid gland calcium receptor by cross-hybridization at reduced stringency. Messenger RNA was prepared from a human parathyroid gland adenoma tumor removed from a 39-year-old Caucasian male diagnosed with primary hyperparathyroidism. Northern blot analysis of this mRNA using pBoPCaR1 as a hybridization probe identified calcium receptor transcripts of about 5 Kb and about 4 Kb. A cDNA library was constructed from the mRNA. Double-stranded cDNA larger than 3 Kbp were size-selected on an agarose gel and ligated into the cloning vector lambda ZapII. Five hundred thousand primary recombinant phage were screened with the 5.2 Kbp cDNA insert of pBoPCaR1 as a hybridization probe. The pBoPCaR1 insert was labeled by random-primed synthesis using [ 32 P]-dCTP to a specific activity of 1 x 10 9 cpm/µg. Library screening was performed at a hybridization stringency of 400 mM Na + , 50% formamide at a temperature of 38°C. Plaque lift filters were hybridized at a probe concentration of 500,000 cpm/ml for 20 hours. Following hybridization, filters were washed in 1 x SSC at 40°C for 1 hr. The primary screen identified about 250 positive clones identified by hybridization to pBoPCaR1. Seven of these clones were taken through secondary and tertiary screens to isolate single clones that hybridized to the pBoPCaR1 probe. These seven clones were analyzed by restriction enzyme mapping and Southern blot analysis. Three of the clones contained cDNA inserts of about 5 Kbp and appear to be full-length clones corresponding to the 5 Kb mRNA. Two of the clones contain cDNA inserts of about 4 Kbp and appear to be full-length clones corresponding to the 4 Kb mRNA. Restriction enzyme mapping of the two different sized inserts indicate that they share regions of sequence similarity in their 5' ends, but diverge in their 3' end sequences. DNA sequence analyses indicate that the smaller insert may result from alternative polyadenylation upstream of the polyadenylation site used in the larger insert. Representative cDNA inserts for both size classes were subcloned into the plasmid vector pBluescript SK. Linearization followed by in vitro transcription using T7 RNA polymerase produced cRNA transcripts. The cRNA transcripts were injected into Xenopus oocytes (150 ng/µl RNA; 50 nl/oocyte) for functional analysis. Following incubation periods of 2-4 days, the oocytes were assayed for the presence of functional calcium receptors. Both clone types gave rise to functional calcium receptors as assessed by the stimulation of calcium-activated chloride currents upon addition of appropriate calcium receptor agonists. Known calcium receptor agonists, including NPS R -467 and NPS R -568 ( see , Nemeth et al ., PCT/US93/01642, International Publication Number WO 94/18959), activated the oocyte-expressed receptor at about the same concentrations known to be effective for the native parathyroid cell receptor. Thus, both clones encode a functional, human parathyroid cell calcium receptor. Plasmids were prepared by subcloning each size class of insert into pBluescript thereby producing pHuPCaR 5.2 and pHuCaR 4.0. The nucleic acid sequence, and amino acid sequence, of the inserts are shown in SEQ. ID. Nos. 1 and 2. Several differences were observed between the nucleic acid sequences of the two cDNA inserts. Sequence analyses of the two cDNA inserts indicate the existence of at least two sequence variants differing in the 3' untranslated region and which may result from alternative polyadenylation. In addition, sequence variation exists at the 5' end of the inserts. These distinct sequences correspond to untranslated regions and may have arisen due to alternative transcriptional initiation and/or splicing. Three additional sites of sequence variation are observed within the coding regions of cDNA clones pHuPCaR5.2 and pHuPCaR4.0 (see SEQ. ID. NOs. 1 and 2) demonstrating that these cDNA clones encode distinct proteins. Sequence analysis of the human CaR gene indicates that the additional 30 base pairs of DNA in cDNA clone pHuPCaR5.2, as compared to the pHuPCaR 4.0 cDNA clone, results from alternative mRNA splicing. The alternative mRNA splicing is predicted to insert 10 additional amino acids into the CaR polypeptide encoded by the pHuPCaR5.2 cDNA at a site between aa#536 and aa#537 in polypeptide encoded by pHuPCaR4.0 cDNA. In addition, pHuPCaR4.0 encodes glutamine (Gln) at aa#925 and glycine (Gly) at position 990 whereas pHuPCaR5.2 encodes arg (Arg) at both equivalent positions. The human CaR gene encodes for Gln and Arg, respectively, at these positions. The difference between the pHuPCaR4.0 cDNA compared to human DNA appears to represent a true sequence polymorphism within the human population while the single base change in pHuPCaR5.2 probably reflects a mutation which occurred during its cloning. Both cDNAs encode functional calcium receptors as demonstrated by the ability of Xenopus oocytes injected with cRNA prepared from these cDNA clones to respond to 10 mM extracellular calcium as ascertained by Cl- conductance. However, it is possible that these two receptor isoforms are functionally and/or pharmacologically distinct. Example 2: Selection of Stable Recombinant Cells Expressing the Calcium Receptor Clonal cell lines that stably express the two human and the bovine calcium receptors have been isolated. Calcium receptor cDNAs were subcloned in two different, commercially available expression vectors; pMSG (obtained from Pharmacia) and Cep4B (obtained from Invitrogen). The first vector contains the selectable marker gene for xanthine-guanine phosphoribosyltransferase (gpt) allowing stably transfected cells to overcome the blockade of the purine biosynthetic pathway imposed by addition of 2 µg/ml aminopterin and 25 µg/ml mycophenolic acid. The second vector encodes a gene conferring resistance to the antibiotic hygromycin (used at 200 µg/ml). HuPCaR 5.2 and HuPCaR 4.0 cDNAs (SEQ. ID. NOs. 1 and 2, respectively) were removed from the parent bluescript plasmid with Not I and Hind III restriction enzymes and then either ligated directly into Not I + Hind III digested Cep4B or treated with the klenow fragment of DNA polymerase prior to blunt-end ligation into Sma I digested pMSG. The pMSG subclone containing the HuPCaR 5.2 insert was transfected into CHO cells as discussed above. Selection has resulted in 20 resistant clones which are being characterized. The Cep4B subclone containing the HuPCaR 5.2 insert was transfected into HEK 293 cells as described above. Selection with hygromycin resulted in a pool of stable clones. Clones expressing the HuPCaR 4.0 receptor isoform were prepared similarly. Cells obtained from the pool of hygromycin selected HEK 293 cells transfected with Cep4B containing the HuPCaR 5.2 insert were plated on collagen coated Aklar squares which had been placed into individual wells of 12-well tissue culture plates. Two to six days later, medium was removed and the cells washed with balanced salt solution and 1 ml of buffer containing 1 µM fura2-AM, 1 mM CaCl 2 and 0.1% BSA and 1 mM CaCl 2 . Measurements of fluorescence in response to calcium receptor agonists were performed at 37°C in a spectrofluorimeter using excitation and emission wavelengths of 340 and 510 nm, respectively. For signal calibration, Fmax was determined after addition of ionomycin (40 µM) and the apparent Fmin was determined by addition of 0.3 M EGTA, 2.5 M Tris-HCl; pH 10. Robust increases in [Ca 2+ ] i were observed in response to the addition of the following calcium receptor agonists: Ca 2+ (10 mM), Mg 2+ (20 mM) and NPS R -467. Control cells expressing functional substance K receptors did not respond to these calcimimetic compounds. Additional clonal isolates of HEK 293 cells transfected with pHuPCaR4.0 sequence were obtained. These were tested for responsiveness to calcimimetics as described above except that the cells were tested while in suspension. Example 3: Using Fura-2 Loaded Parathyroid cells To Measure to Calcium Receptor Activity This section describes procedures used to obtain parathyroid cells from calves and humans, and to use the parathyroid cells to measure calcium receptor activity. Parathyroid glands were obtained from freshly slaughtered calves (12-15 weeks old) at a local abattoir and transported to the laboratory in ice-cold parathyroid cell buffer (PCB) which contains (mM): NaCl, 126; KCl, 4; MgCl 2 , 1; Na-HEPES, 20; pH 7.4; glucose, 5.6, and variable amounts of CaCl 2 , e.g. , 1.25 mM. Human parathyroid glands, were obtained from patients undergoing surgical removal of parathyroid tissue for primary or uremic hyperparathyroidism (uremic HPT) , and were treated similarly to bovine tissue. Glands were trimmed of excess fat and connective tissue and then minced with fine scissors into cubes approximately 2-3 mm on a side. Dissociated parathyroid cells were prepared by collagenase digestion and then purified by centrifugation in Percoll buffer. The resultant parathyroid cell preparation was essentially devoid of red blood cells, adipocytes, and capillary tissue as assessed by phase contrast microscopy and Sudan black B staining. Dissociated and purified parathyroid cells were present as small clusters containing 5 to 20 cells. Cellular viability, as indexed by exclusion of trypan blue or ethidium bromide, was routinely 95%. Although cells can be used for experimental purposes at this point, physiological responses ( e.g. , suppressibility of PTH secretion and resting levels of [Ca 2+ ] i ) should be determined after culturing the cells overnight. Primary culture also has the advantage that cells can be labeled with isotopes to near isotopic equilibrium, as is necessary for studies involving measurements of inositol phosphate metabolism. After purification on Percoll gradients, cells were washed several times in a 1:1 mixture of Ham's F12-Dulbecco's modified Eagle's medium (GIBCO) supplemented with 50 µg/ml streptomycin, 100 U/ml penicillin, 5 µg/ml gentamicin and ITS + , ITS + is a premixed solution containing insulin, transferrin, selenium, and bovine serum albumin (BSA)-linolenic acid (Collaborative Research, Bedford, MA). The cells were then transferred to plastic flasks (75 or 150 cm 2 ; Falcon) and incubated overnight at 37°C in a humid atmosphere of 5% CO 2 . No serum is added to these overnight cultures, since its presence allows the cells to attach to the plastic, undergo proliferation, and dedifferentiate. Cells cultured under the above conditions were readily removed from the flasks by decanting, and show the same viability as freshly prepared cells. Purified parathyroid cells were resuspended in 1.25 mM CaCl 2 -2% BSA-PCB containing 1 µM fura-2-acetoxymethylester and incubated at 37°C for 20 minutes. The cells were then pelleted, resuspended in the same buffer, but lacking the ester, and incubated a further 15 minutes at 37°C. The cells were subsequently washed twice with PCB containing 0.5 mM CaCl 2 and 0.5% BSA and maintained at room temperature (about 20°C). Immediately before use, the cells were diluted five-fold with prewarmed 0.5 mM CaCl 2 -PCB to obtain a final BSA concentration of 0.1%. The concentration of cells in the cuvette used for fluorescence recording was 1-2 x 10 6 /ml. The fluorescence of indicator-loaded cells was measured at 37°C in a spectrofluorimeter (Biomedical Instrumentation Group, University of Pennsylvania, Philadelphia, PA) equipped with a thermostated cuvette holder and magnetic stirrer using excitation and emission wavelengths of 340 and 510 nm, respectively. This fluorescence indicates the level of cytosolic Ca 2+ . Fluorescence signals were calibrated using digitonin (50 µg/ml, final) to obtain maximum fluorescence (F max ), and EGTA (10 mM, pH 8.3, final) to obtain minimal fluorescence (F min ) , and a dissociation constant of 224 nM. Leakage of dye is dependent on temperature and most occurs within the first 2 minutes after warming the cells in the cuvette. Dye leakage increases only very slowly thereafter. To correct the calibration for dye leakage, cells were placed in the cuvette and stirred at 37°C for 2-3 minutes. The cell suspension was then removed, the cells pelleted, and the supernatant returned to a clean cuvette. The supernatant was then treated with digitonin and EGTA to estimate dye leakage, which is typically 10-15% of the total Ca 2+ -dependent fluorescent signal. This estimate was subtracted from the apparent F min . Example 4: Using Fura-2 Loaded- HEK 293/pHuPCaR4. 0 Cells To Measure to Calcium Receptor Activity This section describes procedures used to assay calcium receptor activity using fura-2 loaded HEX 293/pHuPCaR4.0 cells. HEK 293 cells transfected with pHuPCaR4.0 were loaded with fura-2 by incubating the cells in Dulbecco's modified Eagle's media buffered with 20 mM HEPES containing about 5 µM fluo-3/AM for one hour at room temperature. Cell were then rinsed with Hank's balanced salt solution buffered with 20 mM HEPES containing 1 mM CaCl 2 and 1 mM MgCl 2 . Compounds to be tested were then added to the cells and fluorescence was measured (excitation and emission wavelengths of 340 and 510 nm, respectively). Example 5: Measuring the Ability of Compounds to Modulate Calcium Receptor Activity The ability of the compounds to modulate calcium receptor activity was assayed by measuring increases in [Ca 2+ ] i in HEK 293 cells transfected with nucleic acid encoding pHuPCaR4.0 using fura-2 loaded cells or using parathyroid cells loaded with using fura-2 loaded cells. Results of different experiments are summarized in Table 1. Table 1 summarizes the effects of compounds, at different concentrations, on calcium receptor activity assayed as described in Example 4 (i.e., using HEK 293 cells transfected with nucleic acid encoding pHuPCaR4.0, which were loaded with fura-2). Reference compound R-568 has the structure Calcimimetic compounds which produce greater than 40% response at 3 .3 ng/mL in HEK-293 cells expressing the human calcium receptor. Compound % activity at four concentrations (ng/mL) 3300 330 33 3.3 Reference compound R-568 95 69 24 Compound (1) 99 71 45 Example 6: Synthesis of Compounds The compounds described herein can be synthesized using standard techniques such as those described by Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959. SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: NPS Pharmaceuticals, Inc. (ii) TITLE OF INVENTION: CALCIUM RECEPTOR-ACTIVE COMPOUNDS (iii) NUMBER OF SEQUENCES: 2 (iv) CORRESPONDENCE ADDRESS: (A) ADDRESSEE: Lyon & Lyon (B) STREET: First Interstate World Center, Suite 4700 633 West Fifth Street (C) CITY: Los Angeles (D) STATE: California (E) COUNTRY: USA (F) ZIP: 90017 (v) COMPUTER READABLE FORM: (A) MEDIUM TYPE: 3.5" Diskette, 1.44 Mb storage (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: FastSeq (vi) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: (B) FILING DATE: C) CLASSIFICATION: (vii) PRIOR APPLICATION DATA: Prior applications total, including application described below: 2 (A) APPLICATION NUMBER: U.S. 08/353,784 (B) FILING DATE: 8 December, 1994 (A) APPLICATION NUMBER: PCT/US/94/12117 (B) FILING DATE: 21 October, 1994 (viii) ATTORNEY/AGENT INFORMATION: (A) NAME: Heber, Sheldon O. (B) REGISTRATION NUMBER: 38,179 (C) REFERENCE/DOCKET NUMBER: 215/304 (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: (213) 489-1600 (B) TELEFAX: (213) 955-0440 (C) TELEX: 67-3510 (2) INFORMATION FOR SEQ ID NO: 1: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 5006 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA to mRNA (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 436..3699 (D) OTHER INFORMATION: (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1: (2) INFORMATION FOR SEQ ID NO: 2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 3809 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA to mRNA (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 373..3606 (D) OTHER INFORMATION: (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 2:

Claims: A compound having the structure: or a pharmaceutically acceptable salt or complex thereof. A pharmaceutical composition comprising a compound, pharmaceutically acceptable salt or complex of claim 1 and a pharmaceutically acceptable carrier. Use of the compound, pharmaceutically acceptable salt or complex of claim 1 for the preparation of a medicament for treating a patient having a disease or disorder characterised by abnormal bone and mineral homeostasis. Use of the compound, pharmaceutically acceptable salt or complex of claim 1 for the preparation of a medicament for treating a patient having hyperparathyroidism. Use of the compound, pharmaceutically acceptable salt or complex of claim 1 for the preparation of a medicament for treating a patient having Paget's disease. Use of the compound, pharmaceutically acceptable salt or complex of claim 1 for the preparation of a medicament for treating a patient having osteoporosis. Use of the compound, pharmaceutically acceptable salt or complex of claim 1 for the preparation of a medicament for treating a patient having hypertension. Use of the compound, pharmaceutically acceptable salt or complex of claim 1 for the preparation of a medicament for treating a patient having renal osteodystrophy.

Inventors: BALANDRIN MANUEL F, DELMAR ERIC G, MOE SCOTT T, NEMETH EDWARD F, VAN WAGENEN BRADFORD C, BALANDRIN, MANUEL F., DELMAR, ERIC G., MOE, SCOTT T., NEMETH, EDWARD F., VAN WAGENEN, BRADFORD C.
Applicants: NPS PHARMA INC, NPS PHARMACEUTICALS, INC.
Application year: 1995
Main classification: C07C211
IPC codes: C07C211, C07C323, C07C225, C07C317, A61K31, C07D319, C07C217, G01N33