PHOSPHODIESTERASE-V MODULATOR DRUGS AND THEIR USES

Abstract: This invention relates to novel multibinding compounds that bind to the enzyme phosphodiesterase V (PDE V) and modulate its activity. The compounds of this invention comprise 2-10 PDE V modulator (particularly inhibitor) ligands covalently connected by a linker or linkers, wherein the ligands in their monovalent (i.e., unlinked) state bind to a PDE V enzyme. The manner of linking the ligands together is such that the multibinding agents thus formed demonstrate an increased biologic and/or therapeutic effect as compared to the same number of unlinked ligands made available for binding to PDE V. The invention also relates to methods of using such compounds and to methods of preparing them. The compounds of this invention are particularly useful for treating diseases and conditions of mammals that are mediated by PDE V. Accordingly, this invention also relates to pharmaceutical compositions comprising a pharmaceutically acceptable excipient and an effective amount of a compound of this invention.

Description: PHOSPHODIESTERASE-V MODULATOR DRUGS AND THEIR USES CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Applications Serial Nos. 60/088,448, filed June 8, 1998 and 60/093,072 filed July 16, 1998, the entire disclosures of which are incorporated herein by reference. BACKGROUND Field of the Invention This invention relates to novel multibinding compounds that bind to the enzyme phosphodiesterase V (PDE V) and modulate its activity. The compounds of this invention comprise 2-10 PDE V modulator (particularly inhibitor) ligands covalently connected by a linker or linkers, wherein the ligands in their monovalent (i.e. , unlinked) state bind to a PDE V enzyme. The manner of linking the ligands together is such that the multibinding agents thus formed demonstrate an increased biologic and/or therapeutic effect as compared to the same number of unlinked ligands made available for binding to PDE V. The invention also relates to methods of using such compounds and to methods of preparing them. The compounds of this invention are particularly useful for treating diseases and conditions of mammals that are mediated by PDE V. Accordingly, this invention also relates to pharmaceutical compositions comprising a pharmaceutically acceptable excipient and an effective amount of a compound of this invention. References The following publications are cited in this application as superscript numbers: 'Manganiello, V.C., et al., Artch. Biochem. Biophys. , 322, 1-13, 1995. 2 Beavo, J.A., et al., Mol. Pharmacol. , 46, 399-405, 1994. 3 Conti, M., et al., Endocrine Rev., 12, 218-234, 1991. 4 Beavo, J.A., et al., Trends Pharmacol., 11, 150-155, 1990. 5 McAllister-Lucas, L.M., et al., J. Biol. Chem., 270, 30671-30679, 1995. 6 Stroop, S.D., et al., Adv. Second Messenger Phosphoprotein Res. , 25, 55-71, 1992. 7 Beltman, J., et al., Mol. Cell Biochem. , 127/128, 239-253, 1993. 8 McAllister-Lucas, L., et al., J. Biol. Chem., 268, 22863-22873, 1993. 9 Charbonneau, H., et al., Proc. Natl. Acad. Sci. USA., 87, 288-292, 1990. 10 Thomas, M.K., et al., J. Biol. Chem., 265, 14964-14970, 1990. " Stroop, S.D., et al., /. Biol. Chem., 266, 23802-23809, 1991. 12 Francis, S.H., et al., in Cyclic Nucleotide Phoshpdiesterases: Structure, Regulation, and Drug Action (Beavo, J.A. and Houslay, M.D. Eds.), Wiley, Chichester, UK, 117-140, 1991. 13 Thomas, M.K., et al., J. Biol Chem. , 265, 14971-14978. 14 Chiu, P.J.S., et al., Arch. Pharmacol , 355, 463-469, 1997. 15 Christ, G.J., Urol. Clin. N. Am. , 22, 727-745, 1995. 16 Lue, T.F., et al., J. Urol , 130, 1237, 1983. 17 Andersson, K.E., et al., Physiology Review, 75, 191-236, 1995. 18 Trigo-Rocha, F., et al., J. Urol , 149, 872-877, 1993. 19 Burnett, A.L., Biol, Reprod.,, 52, 485-487, 1995. 20 Boolell, M., et al., /. Impot. Res. , 8, 47-52, 1996. 21 Goldstein, I., et al., N. Engl J. Med. , 338, 1397-1404, 1998. 22 Ballard, S.A., et al., J. Urol , 159, 2164-2171, 1998. ^Haynes, H., et al., Adv. Cyclic Nucleotide Prot. Phoshporyl Res. , 16, 245-259, 1984. 24 Sheth, S.B.„et al., Platelets, 6, 61-70, 1995. ^Chiu, P.J.S., et al., /. Biomed. Sci, 1, 43-48, 1994. 26 C, hintala, M.S., et al., J. Pharmacol Expt. Ther., 271, 1203-1208, 1994. "Vemulapalli, S., et al., Pharmacology, 52, 235-242, 1996. ^Vemulapalli, S., et al., Cardiovasc. Pharmacology, 28, 862-869, 1996. ^Thompson, W.J., et al., Biochem., 10, 311-316, 1971. 30 Thompson, W.J., et al., Biochem., 18, 5228-5237, 1979. 31 Chuang, A.J., et al., J. Urol, 160, 257-261, 1998. 32 Carter, A.J., et al., J. Urol, 160, 242-246, 1998. 33 Terrett, N.K., et al., Bioorg. Med. Chem. Lett., 6, 1819-1824, 1996. ^Moreland, R.B., et al., Life Sc , 62, 309-318, 1998. ^International Patent WO 98/17668 36 International Patent WO 98/06722 37- International Patent WO 99/00359 38 Toιphy, T.J., Am. J. Respir. Cut. Care Med., 157, 351-370, 1998. The disclosure of each of the above publications is incorporated herein by reference in its entirety to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference in its entirety. State of the Art Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) are critical intracellular second messengers that mediate biological responses generated by a variety of extracellular signals, including hormones, peptides, neurotransmitters and nitric oxide (Figure 1). By catalyzing the hydrolysis of the 3'- phosphoester bond of these cyclic nucleotides to form inactive 5 '-nucleotide monophosphate products, phosphodiesterases (PDEs) are important in regulating intracellular concentrations of and, consequently, biological responses to these signal-transducing molecules. Mammalian PDEs include a large group of structurally related isoenzymes which belong to at least nine genetically distinct families (Table 1), most of which include more than one gene product as well as multiple splice variants. The result of this diversity is a vast array of enzymes with distinct kinetic characteristics, regulatory properties, and subcellular distributions. The phosphodiesterases contain three functional domains 1 (Figure 2): a conserved catalytic core with considerable (>50%) sequence similarity between families, a regulatory N-terminus unique to the different PDE families (for example, calcium-calmodulin binding domain in PDE I or noncatalytic cGMP-binding domains in PDEs π, V, and VI), and a C- teπninus, whose function is less clear. The three domains are connected by a putative hinge region(s). Flexibility in these areas may allow the N- or C- terminal domains to fold onto the catalytic regions of the enzyme, thus modulating access of the substrate to the catalytic site. From a functional standpoint, the two major differentiating factors among the PDEs are their relative affinities for cAMP and cGMP. The cGMP-binding PDEs comprise a heterogeneous subgroup, all of which exhibit allosteric cGMP-binding sites (at the N-teπninal domain), distinct from the sites of cGMP hydrolysis 5 , which act to regulate enzyme activity 1, M . This group consists of at least three classes of PDEs: PDE π, PDE V, and PDE VI 1 . PDE V exists as a homodimer comprised of two 93 kDa subunits. Limited proteolysis studies have suggested that the dimerization domain of PDE V is within or near the allosteric cGMP-binding region, thus allowing for the formation of cGMP-binding sites through the interaction of two identical repeats residing on separate subunit_£ 8l 10"π . Studies of the dissociation kinetics of the binding sites 12, 13 have suggested that there is cooperativity between the allosteric cGMP-binding sites at the N-teπninal domain of the enzyme and the more distant catalytic cGMP-binding sites. The allosteric binding sites of the regulatory domain of PDE V (as with all the PDEs) may also serve autoinhibitory functions 1 . PDE V enzymes are present in most smooth muscle preparations, including vascular, tracheal, and corpus cavernosum tissue 8, 10"13 . It has also been isolated from platelets 14 and the kidney 30 . Its role in physiological processes is not well understood, but has traditionally been thought of mostly as a regulator of cGMP levels and function. Studies with the PDE V-selective inhibitor zaprinast have shown that co-stimulation with atrial natriuretic peptide (ANP) (in the presence of zaprinast) causes extensive loss of sodium and diuresis. This suggests a role for PDE V in modulating the effect of ANP (and other agents that alter cGMP synthesis) on renal handling of sodium. The inhibition of PDE V with dipyridamole suggests a role in decreasing pulmonary resistance 38 . In addition, the role of cGMP in nitric oxide-induced corpus cavernosum smooth muscle relaxation in penile tissue and in platelet aggregation suggests a role for PDE V therapy in erectile dysfunction and thromboembolic diseases. Thus, it is not surprising that the modulation of PDE V enzymes has been recognized as an attractive target for the therapy of many diseases, including erectile dysfunction (ED) platelet aggregation and cardiovascular disorders. Penile erection is a hemodynamic event under the control of the autonomic nervous system 15 , involving the relaxation of the smooth muscle of the corpus cavernosum and its associated arterioles. This relaxation increases blood flow into the trabecular spaces of the corpora cavernosa 16, 17 (Figure 3), which creates stretching and compressive effects on the subtunical venules, leading to a functionally rigid penile erection. The principle neural mediator in this smooth muscle relaxation is nitric oxide which, during sexual stimulation, is synthesized in the nerve terminals of parasympathetic nonadrenergic, non-cholinergic neurons in the penis, and by endothelial cells lining the blood vessels and lacunar spaces of the corpora cavernosa 18, 19 . Nitric oxide activates guanylate cyclase resulting in an increased conversion of guanosine triphosphate to cGMP, which provides the signal leading to the relaxation of smooth muscle of the corpus cavernosum and penile arterioles 19 . Levels of cGMP are regulated by balancing its rate of synthesis by guanylate cyclase and its rate of hydrolysis by PDE V. Therefore, agents that inhibit PDE V and thus prevent cGMP hydrolysis would be expected to improve and thereby have utility for the treatment of male ED. Sildenafil (Viagra™) is a selective inhibitor of PDE V 20 . Its clinical efficacy in male ED following oral aclministration has been established 20, 21 . There are, however, clinical shortcomings of Viagra, including headache, flushing of the face and indigestion. In addition, some users experience a predominantly bluish tinge to their vision, which lasts up to several hours after use, and is accompanied, in some cases, by sensitivity to light and blurred vision. FDA clinical trials demonstrated some retinal dysfunction, especially when higher doses of the medication were taken. A clinical study showed that electrical measures of retinal function dropped by 30 to 50% for at least five hours after a high dose of sildenafil. These effects of sildenafil on vision could be attributed to its cross-reactivity with PDE VI, which is found predominantly in the photoreceptors of the eye 22 . Antithrombotic drugs suppress platelet function and are used primarily to treat arterial thrombotic disease, which frequently leads to death or disability from stroke, peripheral arterial disease or myocardial infarction. Prevention of arterial thrombosis is the primary indication for antiplatelet therapy, and intense research has been conducted to develop novel antiplatelet agents with favorable safety profiles. Current antiplatelet therapy consists of aspirin, ticlopidine, and lamifiban. Although all of these agents have been shown to reduce vascular events, their mechanisms of action are via platelet-platelet interactions, i.e., they prevent platelet aggregation. Thus, none of these agents are effective in reducing platelet adhesion to the subendothelium nor do they prolong the reduced survival of platelets that is characteristic of thromboembolic disorders. Moreover, adverse effects of these agents are common, with most involving the gastrointestinal tract. In recent years, cGMP has also emerged as an important modulator of platelet function 23, 4 . Measures known to increase tissue cGMP have been shown to attenuate platelet aggregation in rat pulmonary microcirculation 25 , in rat kidneys following ischemia reperfusion 26 and at the sites of balloon catheter induced vascular injury in rat. 27, S . Platelets are among the tissues richest in PDE V, thus cGMP accumulation by selective inhibition of PDE V is associated with effective antiplatelet activity 7 . Hypertension, defined as a resting (supine) arterial pressure of 160/95 mg Hg or higher, is the most common of the cardiovascular diseases. It has been estimated that 15 to 20% of the adult population of the U.S. is affected with this condition. Since arterial blood pressure is a product of cardiac output and peripheral vascular resistance, treatment may consist of reducing cardiac output by inhibiting myocardial contractility, decreasing ventricular filling pressure (by actions on the venous tone or by actions on blood volume via renal effects), reducing peripheral resistance by relaxing the smooth muscle of resistance vessels, or interfering with the activity of systems that produce constriction of resistance vessels (e.g., the sympathetic nervous system). Similar to its role in penile erection, nitric oxide activates guanylate cyclase in the peripheral blood vessels, resulting in an increased conversion of guanosine triphosphate to cGMP. This provides the signal which leads to the relaxation of vascular smooth muscle. Since the levels of cGMP are regulated by balancing its rate of synthesis by guanylate cyclase and its rate of hydrolysis by PDE V, agents that inhibit PDE V and thus prevent cGMP hydrolysis would be expected to reduce peripheral resistance and thereby lower blood pressure, via a non-selective vascular smooth muscle relaxation. The PDE V inhibitors currently available for the treatment of erectile dysfunction, anti-thrombosis and hypertension have the clinical shortcomings of low efficacy, low affinity, poor safety profile or lack of selectivity for the intended receptor. Accordingly, it would be beneficial to develop agents that have improved affinity, efficacy, selectivity, onset of action or duration of action. SUMMARY OF THE INVENTION This invention is directed to novel multibinding compounds that bind to PDE V enzymes in mammalian tissues and can be used to treat diseases and conditions mediated by such enzymes. This invention is also directed to general synthetic methods for generating large libraries of diverse multimeric compounds which multimeric compounds are candidates for possessing multibinding properties for PDE V enzymes. The diverse multimeric compound libraries provided by this invention are synthesized by combining a linker or linkers with a ligand or ligands to provide for a library of multimeric compounds wherein the linker and ligand each have complementary functional groups permitting covalent linkage. The library of linkers is preferably selected to have diverse properties such as valency, linker length, linker geometry and rigidity, hydrophilicity or hydrophobicity, amphiphilicity, acidity, basicity and polarization. The library of ligands is preferably selected to have diverse attachment points on the same ligand, different functional groups at the same site of otherwise the same ligand, and the like. This invention is also directed to libraries of diverse multimeric compounds which multimeric compounds are candidates for possessing multibinding properties. These libraries are prepared via the methods described above and permit the rapid and efficient evaluation of what molecular constraints impart multibinding properties to a ligand or a class of ligands targeting a PDE V enzyme. Accordingly, in one of its composition aspects, this invention is directed to a multibinding compound and salts thereof comprising 2 to 10 ligands which may be the same or different and which are covalently attached to a linker or linkers, which may be the same or different, each of said ligands comprising a ligand domain capable of binding to a PDE V enzyme. The multibinding compounds of this invention are preferably represented by formula I: ( ) p (X) q ( I ) where each L is a ligand that may be the same or different at each occurrence; X is a linker that may be the same or different at each occurrence; p is an integer of from 2 to 10; and q is an integer of from 1 to 20; wherein each of said ligands comprises a ligand domain capable of binding to a PDE V enzyme. Preferably q is less than . Preferably, the binding of the multibinding compound to a PDE V enzyme in a mammal modulates diseases and conditions mediated by the PDE V enzyme. In another of its composition aspects, this invention is directed to a pharmaceutical composition comprising a pharmaceutically acceptable excipient and a therapeutically effective amount of one or more multibinding compounds (or pharmaceutically acceptable salts thereof) comprising 2 to 10 ligands which may be the same or different and which are covalently attached to a linker or linkers, which may be the same or different, each of said ligands comprising a ligand domain capable of binding to a PDE V enzyme of a cell mediating mammalian diseases or conditions, thereby modulating the diseases or conditions. In still another of its composition aspects, this invention is directed to a pharmaceutical composition comprising a pharmaceutically acceptable excipient and a therapeutically effective amount of one or more multibinding compounds represented by formula I: (L)p(X)q (I) or pharmaceutically acceptable salts thereof, where each L is a ligand that may be the same or different at each occurrence; X is a linker that may be the same or different at each occurrence; p is an integer of from 2 to 10; and q is an integer of from 1 to 20; wherein each of said ligands comprises a ligand domain capable of binding to a PDE V enzyme of a cell mediating mammalian diseases or conditions, thereby modulating the diseases or conditions. Preferably q is less than ?. In one of its method aspects, this invention is directed to a method for modulating the activity of a PDE V enzyme in a biologic tissue, which method comprises contacting a tissue having a PDE V enzyme with a multibinding compound (or pharmaceutically acceptable salts thereof) under conditions sufficient to produce a change in the activity of the enzyme in said tissue, wherein the multibinding compound comprises 2 to 10 ligands which may be the same or different and which are covalently attached to a linker or linkers, which may be the same or different, each of said ligands comprising a ligand domain capable of binding to a PDE V enzyme . In another of its method aspects, this invention is directed to a method for treating a disease or condition in a mammal resulting from an activity of a PDE V enzyme, which method comprises adπiinistering to said mammal a therapeutically effective amount of a pharmaceutical composition comprising a pharmaceutically acceptable excipient and one or more multibinding compounds (or pharmaceutically acceptable salts thereof) comprising 2 to 10 ligands which may be the same or different and which are covalently attached to a linker or linkers, which may be the same or different, each of said ligands comprising a ligand domain capable of binding a PDE V enzyme of a cell mediating mammalian diseases or conditions. In yet another of its method aspects, this invention is directed to a method for treating a disease or condition in a mammal resulting from an activity of a PDE V enzyme, which method comprises administering to said m_ιmmal a therapeutically effective amount of a pharmaceutical composition comprising a pharmaceutically acceptable excipient and one or more multibinding compounds represented by formula I: (L) p (X) q ( I ) and pharmaceutically acceptable salts thereof, where each L is a ligand that may be the same or different at each occurrence; X is a linker that may be the same or different at each occurrence; p is an integer of from 2 to 10; and q is an integer of from 1 to 20; wherein each of said ligands comprises a ligand domain capable of binding to a PDE V enzyme of a cell mediating mammalian diseases or conditions. Preferably q is less than p. In a further aspect, this invention provides processes for preparing the multibinding agents of Formula I. This can be accomplished by combining p appropriately functionalized ligands with q complementary functionalized linkers under conditions where covalent bond formation between the ligands and linkers occur. Alternatively linking portions of p appropriately functionalized ligands to q complementary functionalized linkers and then completing the synthesis of the ligands in a subsequent step may be performed to prepare these compounds. Another method which may be used involves linking ' appropriately functionalized ligands to portions of the linker(s) and then completing the synthesis of the linker(s) in a subsequent step. Coupling one or more of the appropriately functionalized ligand(s) to a complementary functionalized linker, and subsequently coupling one or more additional ligands to said linker or linkers may be done to prepare the claimed compounds. Coupling as described in the preceding sentence, wherein coupling of different appropriately functionalized linkers occurs simultaneously may also be used. In one of its method aspects, this invention is directed to a method for identifying multimeric ligand compounds possessing multibinding properties for PDE V enzymes, which method comprises: (a) identifying a ligand or a mixture of ligands wherein each ligand contains at least one reactive functionality; (b) identifying a library of linkers wherein each linker in said library comprises at least two functional groups having complementary reactivity to at least one of the reactive functional groups of the ligand; (c) preparing a multimeric ligand compound library by combining at least two stoichiometric equivalents of the ligand or mixture of ligands identified in (a) with the library of linkers identified in (b) under conditions wherein the complementary functional groups react to form a covalent linkage between said linker and at least two of said ligands; and „ (d) assaying the multimeric ligand compounds produced in (c) above to identify multimeric ligand compounds possessing multibinding properties. In another of its method aspects, this invention is directed to a method for identifying multimeric ligand compounds possessing multibinding properties for PDE V enzymes, which method comprises: (a) identifying a library of ligands wherein each ligand contains at least one reactive functionality; (b) identifying a linker or mixture of linkers wherein each linker comprises at least two functional groups having complementary reactivity to at least one of the reactive functional groups of the ligand; (c) preparing a multimeric ligand compound library by combining at least two stoichiometric equivalents of the library of ligands identified in (a) with the linker or mixture of linkers identified in (b) under conditions wherein the complementary functional groups react to form a covalent linkage between said linker and at least two of said ligands; and (d) assaying the multimeric ligand compounds produced in (c) above to identify multimeric ligand compounds possessing multibinding properties. The preparation of the multimeric ligand compound library is achieved by either the sequential or concurrent combination of the two or more stoichiometric equivalents of the ligands identified in (a) with the linkers identified in (b). Sequential addition is preferred when a mixture of different ligands is employed to ensure heterodimeric or multimeric compounds are prepared. Concurrent addition of the ligands occurs when at least a portion of the multimer comounds prepared are homomultimeric compounds. The assay protocols recited in (d) can be conducted on the multimeric ligand compound library produced in (c) above, or preferably, each member of the library is isolated by preparative liquid chromatography mass spectrometry (LCMS). In one of its composition aspects, this invention is directed to a library of multimeric ligand compounds which may possess multivalent properties for PDE V enzymes, which library is prepared by the method comprising: (a) identifying a ligand or a mixture of ligands wherein each ligand contains at least one reactive functionality; (b) identifying a library of linkers wherein each linker in said library comprises at least two functional groups having complementary reactivity to at least one of the reactive functional groups of the ligand; and (c) preparing a multimeric ligand compound library by combining at least two stoichiometric equivalents of the ligand or mixture of ligands identified in (a) with the library of linkers identified in (b) under conditions wherein the complementary functional groups react to form a covalent linkage between said linker and at least two of said ligands. In another of its composition aspects, this invention is directed to a library of multimeric ligand compounds which may possess multivalent properties for PDE V enzymes, which library is prepared by the method comprising: (a) identifying a library of ligands wherein each ligand contains at least one reactive functionality; (b) identifying a linker or mixture of linkers wherein each linker comprises at least two functional groups having complementary reactivity to at least one of the reactive functional groups of the ligand; and (c) preparing a multimeric ligand compound library by combining at least two stoichiometric equivalents of the library of ligands identified in (a) with the linker or mixture of linkers identified in (b) under conditions wherein the complementary functional groups react to form a covalent linkage between said linker and at least two of said ligands. In a preferred embodiment, the library of linkers employed in either the methods or the library aspects of this invention is selected from the group comprising flexible linkers, rigid linkers, hydrophobic linkers, hydrophilic linkers, linkers of different geometry, acidic linkers, basic linkers, linkers of different polarization and amphiphilic linkers. For example, in one embodiment, each of the linkers in the linker library may comprise linkers of different chain length and/or having different complementary reactive groups. Such linker lengths can preferably range from about 2 to lOOA. In another preferred embodiment, the PDE V enzyme ligand or mixture of ligands is selected to have reactive functionality at different sites on said ligands in order to provide for a range of orientations of said ligand on said multimeric ligand compounds. Such reactive functionality includes, by way of example, carboxylic acids, carboxylic acid halides, carboxyl esters, amines, halides, isocyanates, vinyl unsaturation, ketones, aldehydes, thiols, alcohols, anhydrides, and precursors thereof. It is understood, of course, that the reactive functionality on the ligand is selected to be complementary to at least one of the reactive groups on the linker so that a covalent linkage can be formed between the linker and the ligand. In other embodiments, the multimeric ligand compound is homomeric (i.e., each of the ligands is the same, although it may be attached at different points) or heterodimeric (i.e., at least one of the ligands is different from the other ligands). In addition to the combinatorial methods described herein, this invention provides for an interative process for rationally evaluating what molecular constraints impart multibinding properties to a class of multimeric compounds or ligands targeting a receptor. Specifically, this method aspect is directed to a method for identifying multimeric ligand compounds possessing multibinding properties for PDE V enzymes which method comprises: (a) preparing a first collection or iteration of multimeric compounds which is prepared by contacting at least two stoichiometric equivalents of the ligand or mixture of ligands which target a receptor with a linker or mixture of linkers wherein said ligand or mixture of ligands comprises at least one reactive functionality and said linker or mixture of linkers comprises at least two functional groups having complementary reactivity to at least one of the reactive functional groups of the ligand wherein said contacting is conducted under conditions wherein the complementary functional groups react to form a covalent linkage between said linker and at least two of said ligands; (b) assaying said first collection or iteration of multimeric compounds to assess which if any of said multimeric compounds possess multibinding properties; (c) repeating the process of (a) and (b) above until at least one multimeric compound is found to possess multibinding properties; (d) evaluating what molecular constraints imparted multibinding properties to the multimeric compound or compounds found in the first iteration recited in (a)- (c) above; (e) creating a second collection or iteration of multimeric compounds which elaborates upon the particular molecular constraints imparting multibinding properties to the multimeric compound or compounds found in said first iteration; (f) evaluating what molecular constraints imparted enhanced multibinding properties to the multimeric compound or compounds found in the second collection or iteration recited in (e) above; (g) optionally repeating steps (e) and (f) to further elaborate upon said molecular constraints. Preferably, steps (e) and (f) are repeated at least two times, more preferably at from 2-50 times, even more preferably from 3 to 50 times, and still more preferably at least 5-50 times. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 A and IB schematically illustrate the role of PDE in the regulation of cyclic nucleotide signal transduction. Figure 1A illustrates the cAMP system, while Figure IB illustrates the cGMP system. Figure 2 is a schematic of the structure of the phosphodiesterases, showing three functional domains connected by a hinge region. Figure 3 schematically illustrates the process of penile erection. Figure 4 illustrates a method for optimizing the linker geometry for presentation of ligands (filled circles) in bivalent compounds: A. phenyldiacetylene core structure B. cyclohexane dicarboxylic acid core structure Figure 5 shows exemplary linker "core"structures. Figure 6 illustrates examples of multi-binding compounds comprising (A) 2 ligands, (B) 3 ligands, (C) 4 ligands, and (D) >4 ligands attached in different formats to a linker. Figure 7 illustrates the ligand sildenafil, which may be used in preparing multi- binding compounds. Some potentially modifiable positions are indicated by arrows. Figure 8 illustrates numerous reactive functional groups and the resulting bonds formed by reaction therebetween. Figures 9A to 9J illustrate some homodimers and heterodimers of Sildenafil. Figures 10 to 15 illustrate convenient methods for preparing the multibinding •compounds of this invention. DETAILED DESCRIPTION OF THE INVENTION Biological systems in general are controlled by molecular interactions between bioactive ligands and their receptors, in which the receptor "recognizes" a molecule (which may be a ligand or a substrate) or a portion of a molecule (i.e., a hgand domain) to produce a biological effect. Thus, enzymatic processes are controlled by interaction of an enzyme with a ligand or substrate that is "recognized" by the enzyme. The result of this interaction can be either to initiate the desired biological effect of the enzyme, or alternatively to inhibit or alter (i.e. , to modulate) the normal function of the enzyme. Enzymes such as PDE V possess specific binding sites for ligands having agonist activities (i.e., those which could serve as substrates, cofactors or activators of the enzyme), and antagonist activities (i.e., those which would inhibit the activity of the enzyme). The binding of ligands to such sites modulates the activity of the enzyme; the enzyme activities are regulatable. Accordingly, diseases or conditions that involve or are mediated by PDE V enzymes can be treated with pharmacologically active ligands that interact with such enzymes to initiate, modulate, or abrogate activity. The interaction of a PDE V enzyme and a PDE V enzyme-binding ligand may be described in terms of "affinity" and "specificity". The "affinity" and "specificity" of any given ligand-enzyme interaction is dependent upon the complementarity of molecular binding surfaces and the energetic costs of complexation (i.e., the net difference in free energy between bound and free states). Affinity may be quantified by the equilibrium constant of complex formation, the ratio of on/off rate constants, and/or by the free energy of complex formation. Specificity relates to the difference in affinity between different ligands binding to the same enzyme. The net free energy of interaction of such ligand with PDE V is the difference between energetic gains (enthalpy gained through molecular complementarity and entropy gained through the hydrophobic effect) and energetic costs (enthalpy lost through decreased solvation and entropy lost through reduced translational, rotational and conformational degrees of freedom). The compounds of this invention comprise 2 to 10 PDE V-binding ligands covalently linked together and capable of acting as multibinding agents. Without wishing to be bound by theory, the enhanced activity of these compounds is believed to arise at least in part from their ability to bind in a multivalent manner with multiple ligand binding sites on a PDE V enzyme, which lowers the energetic costs of binding to the enzyme. Multivalent binding interactions are characterized by the contemporaneous interaction of multiple ligands with multiple receptors (enzymes). Multivalent interactions differ from collections of individual monovalent (univalent) interactions by being capable of providing enhanced biologic and/or therapeutic effect. Multivalent binding can amplify binding affinities and differences in binding affinities, resulting in enhanced binding specificity as well as affinity. Definitions As used herein: The term "alkyl" refers to a monoradical branched or unbranched saturated hydrocarbon chain, preferably having from 1 to 40 carbon atoms, preferably 1-10 carbon atoms, more preferably 1-6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n- butyl, secondary butyl, tert-butyl, n-hexyl, n-octyl, n-decyl, n-dodecyl, 2-ethyldodecyl, tetradecyl, and the like, unless otherwise indicated. The term "substituted alkyl" refers to an alkyl group as defined above having from 1 to 5 substituents selected from the group consisting of alkoxy, substituted alkoxy, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, acyl, acylamino, acyloxy, amino, aminoacyl, aminoacyloxy, oxyaminoacyl, azido, cyano, halogen, hydroxyl, keto, thioketo, carboxyl, carboxylalkyl, thioaryloxy, thioheteroaryloxy, thioheterocyclooxy, thiol, thioalkoxy, substituted thioalkoxy, aryl, aryloxy, heteroaryl, heteroaryloxy, heterocyclic, heterocyclooxy, hydroxyamino, alkoxy∑rmino, nitro, -SO- alkyl, -SO-aryl, -SO-heteroaryl, -SO 2 -alkyl, -SO 2 -aryl, -SO 2 -heteroaryl, and -NR a R b , wherein R a and R b may be the same or different and are chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic. The term "alkylene" refers to a diradical of a branched or unbranched saturated hydrocarbon chain, preferably having from 1 to 40 carbon atoms, preferably 1-10 carbon atoms, more preferably 1-6 carbon atoms. This term is exemplified by groups such as methylene (-CH 2 -), ethylene (-CHjCH--), the propylene isomers (e.g., -CHjCH-CHj- and -CH(CH 3 )CH 2 -) and the like. The term "substituted alkylene" refers to: (1) An alkylene group as defined above having from 1 to 5 substituents selected from the group consisting of alkoxy, substituted alkoxy, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, acyl, acylamino, acyloxy, amino, __minoacyl, aminoacyloxy, oxyacylamino, azido, cyano, halogen, hydroxyl, keto, thioketo, carboxyl, carboxylalkyl, thiol, thioalkoxy, substituted thioalkoxy, aryl, aryloxy, thioaryloxy, heteroaryl, heteroaryloxy, thioheteroaryloxy, heterocyclic, heterocyclooxy, thioheterocyclooxy, nitro, and -N j R,,, wherein R, and R^ may be the same or different and are chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic. Additionally, such substituted alkylene groups include those where 2 substituents on the alkylene group are fused to form one or more cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, aryl, heterocyclic or heteroaryl groups fused to the alkylene group; (2) An alkylene group as defined above that is interrupted by 1-20 atoms independently chosen from oxygen, sulfur and NR.-, where 1^ is chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic, or groups selected from carbonyl, carboxyester, carboxyamide and sulfonyl; and (3) An alkylene group as defined above that has both from 1 to 5 substituents as defined above and is also interrupted by 1-20 atoms as defined above. Examples of substituted alkylenes are chloromethylene (-CH(C1)-), aminoethylene (-CHCNKyCH j -), 2- carboxypropylene isomers (-CH 2 CH(CO 2 H)CH 2 -), ethoxyethyl (-ClrLCH-O-CHjCHj-), ethylmethylaminoethyl (-CH 2 CH 2 N(CH 3 )CH 2 CH 2 -), l-ethoxy-2-(2-ethoxy-ethoxy)ethane (-CH 2 CH 2 O-CH 2 CH 2 -OCH 2 CH 2 - OCH 2 CH 2 -), and the like. _ The term "alkaryl" or "aralkyl" refers to the groups -alkylene-aryl and -substituted alkylene-aryl in which alkylene and aryl are as defined herein. Such alkaryl groups are exemplified by benzyl, phenethyl and the like. The term "alkoxy" refers to the groups alkyl-O-, alkenyl-O-, cycloalkyl-O-, cycloalkenyl-O-, and alkynyl-O-, where alkyl, alkenyl, cycloalkyl, cycloalkenyl, and alkynyl are as defined herein. Preferred alkoxy groups are alkyl-O- and include, by way of example, methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, tert-butoxy, sec-butoxy, n- pentoxy, n-hexoxy, 1,2-dimethylbutoxy, and the like. The term "substituted alkoxy" refers to the groups substituted alkyl-O-, substituted alkenyl-O-, substituted cycloalkyl-O-, substituted cycloalkenyl-O-, and substituted alkynyl- O- where substituted alkyl, substituted alkenyl, substituted cycloalkyl, substituted cycloalkenyl and substituted alkynyl are as defined herein. The term "alkylalkoxy" refers to the groups -alkylene-O-alkyl, alkylene-O- substituted alkyl, substituted alkylene-O-alkyl and substituted alkylene-O-substituted alkyl wherein alkyl, substituted alkyl, alkylene and substituted alkylene are as defined herein. Examples of such groups are methylenemethoxy (-CH^OCR j ), ethylenemethoxy (-CH 2 CH 2 OCH 3 ), n-propylene-iso-propoxy (-CH 2 CH 2 CH 2 OCH(CH 3 ) 2 ), methylene-t-butoxy (-CH 2 -O-C(CH 3 ) 3 ) and the like. The term "alkylthioalkoxy" refers to the group -alkylene-S-alkyl, alkylene-S- substituted alkyl, substituted ∑ilkylene-S-alkyl and substituted alkylene-S-substituted alkyl wherein alkyl, substituted alkyl, alkylene and substituted alkylene are as defined herein. Preferred alkylthioalkoxy groups are alkylene-S-alkyl and include, by way of example, methylenethiomethoxy (-CH 2 SCH 3 ), ethylenethiomethoxy (-CHjCHjSCE,), n-propylene- iso-thiopropoxy and the like. "Alkenyl" refers to a monoradical of a branched or unbranched unsaturated hydrocarbon preferably having from 2 to 40 carbon atoms, preferably 2-10 carbon atoms, more preferably 2-6 carbon atoms, and preferably having 1-6 double bonds. This term is further exemplified by such radicals as vinyl, prop-2-enyl, pent-3-enyl, hex-5-enyl, 5- ethyldodec-3,6-dienyl, and the like. The term "substituted alkenyl" refers to an alkenyl group as defined above having from 1 to 5 substituents selected from the group consisting of alkoxy, substituted alkoxy, acyl, acylamino, acyloxy, amino, aminoacyl, aminoacyloxy, oxyaminoacyl, azido, cyano, halogen, hydroxyl, keto, thioketo, carboxyl, carboxylalkyl, thiol, thioalkoxy, substituted thioalkoxy, aryl, heteroaryl, heterocyclic, aryloxy, thioaryloxy, heteroaryloxy, thioheteroaryloxy, heterocyclooxy, thioheterocyclooxy, nitro, -SO-alkyl, -SO-substituted alkyl, -SO-aryl, -SO-heteroaryl, -SO 2 -alkyl, -SO 2 -substituted alkyl, -SO 2 -aryl, -SO 2 - heteroaryl, and, -NR'R 0 , wherein R a and R b may be the same or different and are chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic. "Alkenylene" refers to a diradical of an unsaturated hydrocarbon, preferably having from 2 to 40 carbon atoms, preferably 2-10 carbon atoms, more preferably 2-6 carbon atoms, and preferably having 1-6 double bonds. This term is further exemplified by such radicals as 1,2-ethenyl, l,3-prop-2-enyl, l,5-pent-3-enyl, l,4-hex-5-enyl, 5-ethyl-l,12- dodec-3,6-dienyl, and the like. The term "substituted alkenylene" refers to an alkenylene group as defined above having from 1 to 5 substituents, selected from the group consisting of alkoxy, substituted alkoxy, acyl, acylamino, acyloxy, amino, aminoacyl, aminoacyloxy, oxy acylamino, azido, cyano, halogen, hydroxyl, keto, thioketo, carboxyl, carboxylalkyl, thiol, thioalkoxy, substituted thioalkoxy, aryl, aryloxy, thioaryloxy, heteroaryl, heteroaryloxy, thioheteroaryloxy, heterocyclic, heterocyclooxy, thioheterocyclooxy, nitro, and NR a R b , wherein R a and R b may be the same or different and are chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic. Additionally, such substituted alkenylene groups include those where 2 substituents on the alkenylene group are fused to form one or more cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, aryl, heterocyclic or heteroaryl groups fused to the alkenylene group. "Alkynyl" refers to a monoradical of an unsaturated hydrocarbon, preferably having from 2 to 40 carbon atoms, preferably 2-10 carbon atoms, more preferably 2-6 carbon atoms, and preferably having 1-6 triple bonds. This term is further exemplified by such radicals as acetylenyl, prop-2-ynyl, pent-3-ynyl, hex-5-ynyl, 5-ethyldodec-3,6-diynyl, and the like. The term "substituted alkynyl" refers to an alkynyl group as defined above having from 1 to 5 substituents, selected from the group consisting of alkoxy, substituted alkoxy, acyl, acylarnino, acyloxy, amino, ∑iminoacyl, aminoacyloxy, oxyacylamino, azido, cyano, halogen, hydroxyl, keto, thioketo, carboxyl, carboxylalkyl, thiol, thioalkoxy, substituted thioalkoxy, aryl, aryloxy, thioaryloxy, heteroaryl, heteroaryloxy, thioheteroaryloxy, heterocyclic, heterocyclooxy, thioheterocycloxy, nitro, -SO-alkyl, -SO-substituted alkyl, -SO-aryl, -SO-heteroaryl, -SO 2 -alkyl, -SO 2 -substituted alkyl, -SO 2 -aryl, -SO 2 -heteroaryl, SO 2 - heterocyclic, NR a R b , wherein R a and R b may be the same or different and are chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic. "Alkynylene" refers to a diradical of an unsaturated hydrocarbon radical, preferably having from 2 to 40 carbon atoms, preferably 2-10 carbon atoms, more preferably 2-6 carbon atoms, and preferably having 1-6 triple bonds. This term is further exemplified by such radicals as l,3-prop-2-ynyl, l,5-pent-3-ynyl, l,4-hex-5-ynyl, 5-ethyl-l,12-dodec-3,6-diynyl, and the like. The term "acyl" refers to the groups -CHO, alkyl-C(O)-, substituted alkyl-C(O)-. cycloalkyl-C(O)-, substituted cycloalkyl-C(O)-, cycloalkenyl-C(O)-, substituted cycloalkenyl-C(O)-, aryl-C(O)-, heteroaryl-C(O)- and heterocyclic-C(O)- where alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, aryl, heteroaryl and heterocyclic are as defined herein. The term "acylamino" refers to the group -C(O)NRR where each R is independently hydrogen, alkyl, substituted alkyl, aryl, heteroaryl, heterocyclic or where both R groups are joined to form a heterocyclic group (e.g., morpholine) wherein alkyl, substituted alkyl, aryl, heteroaryl and heterocyclic are as defined herein. The term "aminoacyl" refers to the group -NRC(O)R where each R is independently hydrogen, alkyl, substituted alkyl, aryl, heteroaryl, or heterocyclic wherein alkyl, substituted alkyl, aryl, heteroaryl and heterocyclic are as defined herein. The term "aminoacyloxy" refers to the group -NRC(O)OR where each R is independently hydrogen, alkyl, substituted alkyl, aryl, heteroaryl, or heterocyclic wherein alkyl, substituted alkyl, aryl, heteroaryl and heterocyclic are as defined herein. The term "acyloxy" refers to the groups alkyl-C(O)O-, substituted alkyl-C(O)O-, cycloalkyl-C(O)O-, substituted cycloalkyl-C(O)O-, aryl-C(O)O-, heteroaryl-C(O)O-, and heterocyclic-C(O)O- wherein alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl, aryl, heteroaryl, and heterocyclic are as defined herein. The term "aryl" refers to an unsaturated aromatic carbocyclic group of from 6 to 20 carbon atoms having a single ring (e.g., phenyl) or multiple condensed (fused) rings (e.g., naphthyl or anthryl). Unless otherwise constrained by the definition for the aryl substituent, such aryl groups can optionally be substituted with from 1 to 5 substituents selected from the group consisting of acyloxy, hydroxy, thiol, acyl, alkyl, alkoxy, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, substituted alkyl, substituted alkoxy, substituted alkenyl, substituted alkynyl, substituted cycloalkyl, substituted cycloalkenyl, amino, aminoacyl, acylamino, alkaryl, aryl, aryloxy, azido, carboxyl, carboxylalkyl, cyano, halo, nitro, heteroaryl, heteroaryloxy, heterocyclic, heterocyclooxy, ∑tminoacyloxy, oxyacylamino, thioalkoxy, substituted thioalkoxy, thioaryloxy, thioheteroaryloxy, -SO-alkyl, -SO-substituted alkyl, -SO-aryl, -SO- heteroaryl, -SO 2 -alkyl, -SO 2 -substituted alkyl, -SO 2 -aryl, -SO 2 -heteroaryl, trihalomethyl, NR a R b , wherein R a and R b may be the same or different and are chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic. Preferred aryl substituents include alkyl, alkoxy, halo, cyano, nitro, trihalomethyl, and thioalkoxy. The term "aryloxy" refers to the group aryl-O- wherein the aryl group is as defined above, including optionally substituted aryl groups as also defined above. The term "arylene" refers to a diradical derived from aryl or substituted aryl as defined above, and is exemplified by 1,2-phenylene, 1,3-phenylene, 1,4-phenylene, 1,2-naphthylene and the like. The term "amino" refers to the group -NH 2 The term "substituted amino" refers to the group -NRR where each R is independently selected from the group consisting of hydrogen, alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, alkynyl, substituted alkynyl, aryl, heteroaryl and heterocyclic provided that both R=s are not hydrogen. The term "carboxyalkyl" refers to the group "-C(O)O-alkyl", "-C(O)O-substituted alkyl", H -C(O)O-cycloalkyl", "-C(O)O-substituted cycloalkyl", "-C(O)O-alkenyr, "-C(O)O- substituted alkenyl", "-C(O)O-alkynyl" and "-C(O)O-substituted alkynyl" where alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, substituted alkenyl, alkynyl and substituted alkynyl where alkynyl are as defined herein. The term "cycloalkyl" refers to cyclic alkyl groups of from 3 to 20 carbon atoms having a single cyclic ring or multiple condensed rings. Such cycloalkyl groups include, by way of example, single ring structures such as cyclopropyl, cyclobutyl, cyclopentyl, cyclooctyl, and the like, or multiple ring structures such as adamantanyl, and the like. The term "substituted cycloalkyl" refers to cycloalkyl groups having from 1 to 5 substituents selected from the group consisting of alkoxy, substituted alkoxy, cycloalkyl, cycloalkenyl, substituted cycloalkenyl, acyl, acyl_unino, acyloxy, -imino, aminoacyl, aminoacyloxy, oxyaminoacyl, azido, cyano, halogen, hydroxyl, keto, thioketo, carboxyl, carboxylalkyl, thioaryloxy, thioheteroaryloxy, thioheterocyclooxy, thiol, thioalkoxy, substituted thioalkoxy, aryl, aryloxy, heteroaryl, heteroaryloxy, heterocyclic, heterocyclooxy, hydroxyamino, aikoxy__rnino, nitro, -SO-alkyl, -SO-substituted alkyl, -SO- aryl, -SO-heteroaryl, -SO 2 -alkyl, -SO 2 -substituted alkyl, -SO 2 -aryl, -SO 2 -heteroaryl, and NR a R b , wherein R a and R b may be the same or different and are chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic. The term "cycloalkenyl" refers to cyclic alkenyl groups of from 4 to 20 carbon atoms having a single cyclic ring or fused rings and at least one point of internal unsaturation. Examples of suitable cycloalkenyl groups include, for instance, cyclobut-2-enyl, cyclopent-3- enyl, cyclooct-3-enyl and the like. The term "substituted cycloalkenyl" refers to cycloalkenyl groups having from 1 to 5 substituents selected from the group consisting of alkoxy, substituted alkoxy, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, acyl, acylamino, acyloxy, amino, aminoacyl, Eiminoacyloxy, oxyaminoacyl, azido, cyano, halogen, hydroxyl, keto, thioketo, carboxyl, carboxylalkyl, thioaryloxy, thioheteroaryloxy, thioheterocyclooxy, thiol, thioalkoxy, substituted thioalkoxy, aryl, aryloxy, heteroaryl, heteroaryloxy, heterocyclic, heterocyclooxy, hychoxyamino, alkoxyamino, nitro, -SO-alkyl, -SO-substituted alkyl, -SO- aryl, -SO-heteroaryl, -SO 2 -alkyl, -SO 2 -substituted alkyl, -SO 2 -aryl, -SO 2 -heteroaryl, and NR a R b , wherein R a and R b may be the same or different and are chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic. The term "halo" or "halogen" refers to fluoro, chloro, bromo and iodό. Ηaloalkyl" refers to alkyl as defined above substituted by 1-4 halo groups as defined above, which may be the same or different, such as 3-fluorododecyl, 12,12,12- trifluorododecyl, 2-bromooctyl, -3-bromo-6-chloroheptyl, and the like. The term "heteroaryl" refers to an aromatic group of from 1 to 15 carbon atoms and 1 to 4 heteroatoms selected from oxygen, nitrogen and sulfur within at least one ring (if there is more than one ring). Unless otherwise constrained by the definition for the heteroaryl substituent, such heteroaryl groups can be optionally substituted with 1 to 5 substituents selected from the group consisting of acyloxy, hydroxy, thiol, acyl, alkyl, alkoxy, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, substituted alkyl, substituted alkoxy, substituted alkenyl, substituted alkynyl, substituted cycloalkyl, substituted cycloalkenyl, amino, aminoacyl, acylamino, alkaryl, aryl, aryloxy, azido, carboxyl, carboxylalkyl, cyano, halo, nitro, heteroaryl, heteroaryloxy, heterocyclic, heterocyclooxy, ∑iminoacyloxy, oxyacylamino, thioalkoxy, substituted thioalkoxy, thioaryloxy, thioheteroaryloxy, -SO-alkyl, -SO- substituted alkyl, -SO-aryl, -SO-heteroaryl, -SO 2 -alkyl, -SO 2 -substituted alkyl, -SO 2 -aryl, -SOj-heteroaryl, trihalomethyl, mono-and di--_lkyl__mino, mono- and NR a R b , wherein R a and R b may be the same or different and are chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic. Preferred heteroaryls include pyridyl, pyrrolyl and furyl. The term "heteroaryloxy" refers to the group heteroaryl-O-. The term "heteroarylene" refers to the diradical group derived from heteroaryl or substituted heteroaryl as defined above, and is exemplified by the groups 2,6-pyridylene, 2,4-pyridiylene, 1,2-quinolinylene, 1,8-quinolinylene, 1,4-benzofuranylene, 2,5- pyridinylene, 1,3-morpholinylene, 2,5-indolenyl, and the like. The term "heterocycle" or "heterocyclic" refers to a morioradical saturated or unsaturated group having a single ring or multiple condensed rings, from 1 to 40 carbon atoms and from 1 to 10 hetero atoms, preferably 1 to 4 heteroatoms, selected from nitrogen, sulfur, phosphorus, and or oxygen within the ring. Unless otherwise constrained by the definition for the heterocyclic substituent, such heterocyclic groups can be optionally substituted with 1 to 5, and preferably 1 to 3 substituents, selected from the group consisting of alkoxy, substituted alkoxy, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, acyl, acylamino, acyloxy, amino, -tminoacyl, aminoacyloxy, oxyaminoacyl, cyano, halogen, hydroxyl, keto, thioketo, carboxyl, carboxylalkyl, thioaryloxy, thioheteroaryloxy, thioheterocyclooxy, thiol, thioalkoxy, substituted thioalkoxy, aryl, aryloxy, heteroaryl, heteroaryloxy, heterocyclic, heterocyclooxy, hydroxyamino, alkoxyamino, nitro, -SO-alkyl, -SO-substituted alkyl, -SO- aryl, -SO-heteroaryl, -SO 2 -alkyl, -SO 2 -substituted alkyl, -SO 2 -aryl, -SO 2 -heteroaryl, and NR^, wherein R and R b may be the same or different and are chosen from hydrogen, optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclic. Such heterocyclic groups can have a single ring or multiple condensed rings. Examples of nitrogen heterocycles and heteroaryls include, but are not limited to, pyrrole, imidazole, pyrazole, pyridine, pyrazine, pyrimidine, pyridazine, indolizine, isoindole, indole, indazole, purine, quinolizine, isoquinoline, quinoline, phthalazine, naphthylpyridine, quinoxaline, quinazoline, cinnoline, pteridine, carbazole, carboline, phenanthridine, acridine, phenanthroline, isothiazole, phenazine, isoxazole, phenoxazine, phenothiazine, imidazolidine, imidazoline, piperidine, piperazine, indoline, morpholino, piperidinyl, tetrahydrofuranyl, and the like as well as N-alkoxy-nitrogen containing heterocycles. A preferred class of heterocyclics include "crown compounds" which refers to a specific class of heterocyclic compounds having one or more repeating units of the formula [-(CH 2 -) m Y-] where m is equal to or greater than 2, and Y at each separate occurrence can be O, N, S or P. Examples of crown compounds include, by way of example only, [-(CHj MH, and the like. Typically such crown compounds can have from 4 to 10 heteroatoms and 8 to 40 carbon atoms. The term "heterocyclooxy" refers to the group heterocyclic-O-. The term "thioheterocyclooxy" refers to the group heterocyclic-S-. The term "heterocyclene" refers to the diradical group derived from a heterocycle as defined herein, and is exemplified by the groups 2,6-morpholino, 2,5-morpholino and the like. The term "oxyacylamino'' refers to the group -°C(O)NRR where each R is independently hydrogen, alkyl, substituted alkyl, aryl, heteroaryl, or heterocyclic wherein alkyl, substituted alkyl, aryl, heteroaryl and heterocyclic are as defined herein. The term "thiol" refers to the group -SH. The term "thioalkoxy" refers to the group -S-alkyl. The term "substituted thioalkoxy" refers to the group -S-substituted alkyl. The term "thioaryloxy" refers to the group aryl-S- wherein the aryl group is as defined above including optionally substituted aryl groups also defined above. The term "thioheteroaryloxy" refers to the group heteroaryl-S- wherein the heteroaryl group is as defined above including optionally substituted aryl groups as also defined above. As to any of the above groups which contain one or more substituents, it is understood, of course, that such groups do not contain any substitution or substitution patterns which are sterically impractical and/or synthetically non-feasible. In addition, the compounds of this invention include all stereochemical isomers arising from the substitution of these compounds. "Alkyl optionally interrupted by 1-5 atoms chosen from O, S, or N" refers to alkyl as defined above in which the carbon chain is interrupted by O, S, or N. Within the scope are ethers, sulfides, and amines, for example 1-methoxydecyl, 1-pentyloxynonane, l-(2- isopropoxyethoxy)-4-methylnonane, l-(2-ethoxyethoxy)dodecyl, 2-(t-butoxy)heptyl, 1- pentylsulfanylnonane, nonylpentylamine, and the like. "Heteroarylalkyl" refers to heteroaryl as defined above linked to alkyl as defined above, for example pyrid-2-ylmethyl, 8-quinolinylpropyl, and the like. "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances in which it does not. For example, optionally substituted alkyl means that alkyl may or may not be substituted by those groups enumerated in the definition of substituted alkyl. The term "pharmaceutically acceptable salt" refers to salts which retain the biological effectiveness and properties of the multibinding compounds of this invention and which are not biologically or otherwise undesirable. In many cases, the multibinding compounds of this invention are capable of forming acid and/or base salts by virtue of the presence of amino and/or carboxyl groups or groups similar thereto. Pharmaceutically acceptable base addition salts can be prepared from inorganic and organic bases. Salts derived from inorganic bases, include by way of example only, sodium, potassium, lithium, ammonium, calcium and magnesium salts. Salts derived from organic bases include, but are not limited to, salts of primary, secondary and tertiary amines, such as alkyl ∑unines, dialkyl amines, trialkyl amines, substituted alkyl amines, di(substituted alkyl) amines, tri(substituted alkyl) amines, alkenyl amines, dialkenyl amines, trialkenyl amines, substituted alkenyl amines, di(substituted alkenyl) amines, tri(substituted alkenyl) amines, cycloalkyl ∑tmines, di(cycloalkyl) amines, tri(cycloalkyl) amines, substituted cycloalkyl ∑tmines, disubstituted cycloalkyl amine, trisubstituted cycloalkyl amines, cycloalkenyl ∑tmines, di(cycloalkenyl) amines, tri(cycloalkenyl) amines, substituted cycloalkenyl amines, disubstituted cycloalkenyl amine, trisubstituted cycloalkenyl amines, aryl .tmines, diaryl amines, triaryl amines, heteroaryl amines, diheteroaryl amines, triheteroaryl amines, heterocyclic amines, diheterocyclic amines, triheterocyclic __mines, mixed di- and fri-amines where at least two of the substituents on the amine are different and are selected from the group consisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, aryl, heteroaryl, heterocyclic, and the like. Also included are amines where the two or three substituents, together with the amino nitrogen, form a heterocyclic or heteroaryl group. Examples of suitable amines include, by way of example only, isopropylamine, trimethyl amine, diethyl amine, tri σ-propyl) amine, tri(/2-propyl) amine, eth-mol_umne, 2-dimethylaminoethanol, tiomethamine, lysine, arginine, histidine, caffeine, procaine, hydrabamine, choline, betaine, ethylenediamine, glucosamine, N-alkylglucamines, theobromine, purines, piperazine, piperidine, morpholine, N-ethylpiperidine, and the like. It should also be understood that other carboxylic acid derivatives would be useful in the practice of this invention, for example, carboxylic acid amides, including carboxamides, lower alkyl carboxamides, dialkyl carboxamides, and the like. Pharmaceutically acceptable acid addition salts may be prepared from inorganic and organic acids. Salts derived from inorganic acids include hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, and the like. Salts derived from organic acids include acetic acid, propionic acid, glycolic acid, pyruvic acid, oxalic acid, malic acid, malonic acid, succinic acid, maleic acid, fumaric acid, tartaric acid, citric acid, benzoic acid, cinnamic acid, mandelic acid, methanesulfonic acid, ethanesulfonic acid, p- toluene-sulfonic acid, salicylic acid, and the like. The term "protecting group" or "blocking group" refers to any group which when bound to one or more hydroxyl, thiol, __mino or carboxyl groups of the compounds prevents reactions from occurring at these groups and which protecting group can be removed by conventional chemical or enzymatic steps to reestablish the hydroxyl, thiol, ∑αnino or carboxyl group. See, generally, T.W. Greene & P.G.M. Wuts, Protective Groups in Organic Synthesis, 2 nd Ed., 1991, John Wiley and Sons, N.Y. The particular removable blocking group employed is not critical and preferred removable hydroxyl blocking groups include conventional substituents such as allyl, benzyl, acetyl, chloroacetyl, thiobenzyl, benzylidine, phenacyl, t-butyl-diphenylsilyl and any other group that can be introduced chemically onto a hydroxyl functionaUty and later selectively removed either by chemical or enzymatic methods in mild conditions compatible with the nature of the product. Preferred removable amino blocking groups include conventional substituents such as t-butyoxycarbonyl (t-BOC), benzyloxycarbonyl (CBZ), fluorenylmethoxycarbonyl (FMOC), allyloxycarbonyl (ALOC) and the like, which can be removed by conventional conditions compatible with the nature of the product. Preferred carboxyl protecting groups include esters such as methyl, ethyl, propyl, f-butyl etc. which can be removed by mild hydrolysis conditions compatible with the nature of the product. As used herein, the terms "inert organic solvent" or "inert solvent" mean a solvent inert under the conditions of the reaction being described in conjunction therewith [including, for example, benzene, toluene, acetonitrile, tetrahydrofuran ("THF"), dimethylformamide ("DMF"), chloroform ("CHC1 3 "), methylene chloride (or dichloromethane or "CE^Cl-"), diethyl ether, ethyl acetate, acetone, methylethyl ketone, methanol, ethanol, propanol, isopropanol, tert-butanol, dioxane, pyridine, and the like]. Unless specified to the contrary, the solvents used in the reactions of the present invention are inert solvents. The terms "phosphodiesterase", "PDE" or "PDE enzyme" refer to a family of enzymes which function to catalyze the hydrolysis of cyclic nucleotides. The terms "phosphodiesterase V" or "PDE V" or "PDE V enzyme" refer to a subgroup of the PDE enzymes which are cGMP specific and contain a high-affinity non- catalytic cGMP binding site. They are the predominant form of PDE isozyme in corpus cavernosum smooth muscle. They are also found in platelets and the cardiovascular system. "Ligand" as used herein denotes a compound that is a binding partner for a PDE V enzyme , and is bound thereto, for example, by complementarity. The specific region or regions of the ligand molecule that is recognized by the ligand binding site of PDE V is designated as the "ligand domain". A ligand may be either capable of binding to an enzyme by itself, or may require the presence of one or more non-ligand components for binding (e.g., ions, a lipid molecule, a solvent molecule, and the like). Ligands useful in this invention comprise PDE V modulators such as dipyrimadole, IBMX, NM-702, SCH51866 28, Sildenafil 22, 31 - 34 , E-4021 14 , Zaprinast 22, 33 , pyrazolo[4,5-d] pyrimidin-7-one derivatives, thienopyrimidine derivatives 35, 36 , and sulfonylamide derivatives 37 . See Table 2 for structures of various PDE V inhibitor ligands. While it is contemplated that many PDE V ligands that are currently known can be used in the preparation of multibinding compounds of this invention, it should be understood that portions of the ligand structure that are not essential for molecular recognition and binding activity (i.e. , that are not part of the ligand domain) may be varied substantially, replaced with unrelated structures and, in some cases, omitted entirely without affecting the binding interaction. Accordingly, it should be understood that the term "ligand" is not intended to be limited to compounds known to be useful as PDE V - binding compounds (e.g., known drugs), in that ligands that exhibit marginal activity or lack useful activity as monomers can be highly active as multibinding compounds, because of the biological benefit conferred by multivalency. The primary requirement for a ligand as defined herein is that it has a ligand domain, as defined above, which is available for binding to a recognition site on a PDE V enzyme. For purposes of the present invention, the term "ligand" or "ligands" is intended to include the racemic ligands as well as the individual stereoisomers of the ligands, including pure enantiomers and non-racemic mixtures thereof. The scope of the invention as described and claimed encompasses the racemic forms of the ligands as well as the individual enantiomers and non-racemic mixtures thereof. The term "ligand binding site" as used herein denotes a site on a PDE V enzyme that recognizes a ligand domain and provides a binding partner for the ligand. The ligand binding site may be defined by monomeric or multimeric structures. This interaction may be capable of producing a unique biological effect, for example agonism, antagonism, modulation, or may maintain an ongoing biological event, and the like. It should be recognized that the ligand binding sites of a PDE V enzyme that participate in biological multivalent binding interactions are constrained to varying degrees by their intra- and intermolecular associations. For example, PDE V ligand binding sites may be covalently joined in a single structure, noncovalently associated in one or more multimeric structures, embedded in a membrane or biopolymer matrix, and so on, and therefore have less translational and rotational freedom than if the same sites were present as monomers in solution. The terms "agonism" and "antagonism" are well known in the art. As used herein, the term "agonist" refers to a ligand that when bound to a PDE V enzyme stimulates enzymatic activity. The term "antagonist" refers to a ligand that when bound to a PDE V enzyme inhibits enzymatic activity. Enzyme inhibition (block) or activation may result from allosteric effects of ligand binding to the enzyme rather than occupancy of the active site. These allosteric effects may produce changes in protein conformation that affect PDE V binding sites. The term "modulatory effect" is intended to refer to the ability of a ligand to change the biological activity of an agonist or antagonist through binding to an enzyme. A "multibinding agent or multibinding compound" refers herein to a compound that has from 2 to 10 ligands as defined herein (which may be the same or different) covalently bound to one or more linkers (which may be the same or different), and is capable of multivalency, as defined below. A multibinding compound provides an improved biologic and/or therapeutic effect compared to that of the same number of unlinked ligands available for binding to the ligand binding sites on a PDE V enzyme. Examples of improved "biologic and/or therapeutic effect" include increased ligand-receptor binding interactions (e.g., increased affinity, increased ability to elicit a functional change in the target, improved kinetics), increased selectivity for the target, increased potency, increased efficacy, decreased toxicity, increased therapeutic index, improved duration of action, improved bioavailability, improved pliaπnacokinetics, improved activity spectrum, and the like. The multibinding compounds of this invention will exhibit at least one, and preferably more than one, of the above-mentioned effects. "Univalency" as used herein refers to a single binding interaction between one ligand with one ligand binding site as defined herein. It should be noted that a compound having multiple copies of a ligand (or ligands) exhibits univalency when only one ligand of that compound interacts with a hgand binding site. Examples of univalent interactions are depicted below. univalent interaction "Multivalency" as used herein refers to the concurrent binding of from 2 to 10 linked ligands, which may be the same or different, and two or more corresponding ligand binding sites, which may be the same or different. An example of trivalent binding is depicted below for illustrative purposes. trivalent interaction It should be understood that not all compounds that contain multiple copies of a ligand attached to a linker necessarily exhibit the phenomena of multivalency, i.e., that the biologic and/or therapeutic effect of the multibinding agent is greater than that of the same number of unlinked ligands made available for binding to the ligand binding sites. For multivalency to occur, the ligand domains of the ligands that are linked together must be presented to their cognate ligand binding sites by the linker or linkers in a specific manner in order to bring about the desired hgand-orienting result, and thus produce a multibmding interaction. The term "library" refers to at least 3, preferably from 10 2 to 10 9 and more preferably from 10 2 to 10 4 multimeric compounds. Preferably, these compounds are prepared as a multiplicity of compounds in a single solution or reaction mixture which permits facile synthesis thereof. In one embodiment, the library of multimeric compounds can be directly assayed for multibinding properties. In another embodiment, each member of the library of multimeric compounds is first isolated and, optionally, characterized. This member is then assayed for multibinding properties. The term "collection" refers to a set of multimeric compounds which are prepared either sequentially or concurrently (e.g., combinatorially). The collection comprises at least 2 members; preferably from 2 to 10 9 members and still more preferably from 10 to 10 4 members. The term "multimeric compound" refers to compounds comprising from 2 to 10 ligands covalently connected through at least one linker which compounds may or may not possess multibinding properties (as defined herein). The term "pseudohalide" refers to functional groups which react in displacement reactions in a manner similar to a halogen. Such functional groups include, by way of example, mesyl, tosyl, azido and cyano groups. The term "linker", identified where appropriate by the symbol X, refers to a group or groups that covalently links from 2 to 10 ligands (as defined above) in a manner that provides a compound capable of multivalency. The linker is a ligand-orienting entity that permits attachment of multiple copies of a ligand (which may be the same or different) thereto. The term "linker" includes eveiything that is not considered to be part of the ligand, e.g., ancillary groups such as solubilizing groups, lipophilic groups, groups that alter pharmacodynamics or ph-trmacokinetics, groups that modify the diffusability of the multibinding compound, spacers that attach the ligand to the linker, groups that aid the ligand-orienting function of the linker, for example, by imparting flexibility or rigidity to the linker as a whole, or to a portion thereof, and so on. The term "linker" does not, however, cover solid inert supports such as beads, glass particles, rods, and the like, but it is to be understood that the multibinding compounds of this invention can be attached to a solid support if desired, for example, for use in separation and purification processes and for similar applications. The extent to which the previously discussed enhanced activity of multibinding compounds is realized in this invention depends upon the efficiency with which the linker or linkers that joins the Ugands presents them to their array of ligand binding sites. Beyond presenting these ligands for multivalent interactions with ligand binding sites, the linker spatially constrains these interactions to occur within dimensions defined by the linker. The linkers used in this invention are selected to allow multivalent binding of ligands to any desired ligand binding sites of PDE V, whether such sites are located within the conserved catalytic domain of the enzyme, the regulatory domain of the enzyme, or at any intermediate position thereof. The preferred linker length will vary depending on the distance between adjacent ligand binding sites, and the geometry, flexibility and composition of the linker. The length of the linker will preferably be in the range of about 2A to about 100A, more preferably from about lλ to about 5θA and even more preferably from about 5A to about 2θA. The ligands are covalently attached to the linker or linkers using conventional chemical techniques. The reaction chemistries resulting in such linkage are well known in the art and involve the use of reactive functional groups present on the linker and ligand. Preferably, the reactive functional groups on the linker are selected relative to the functional groups available on the hgand for coupling, or which can be introduced onto the ligand for this purpose. Again, such reactive functional groups are well known in the art. For example, reaction between a carboxylic acid of either the linker or the ligand and a primary or secondary amine of the ligand or the linker in the presence of suitable well- known activating agents results in formation of an amide bond covalently linking the ligand to the linker; reaction between an ∑tmine group of either the linker or the ligand and a sulfonyl halide of the ligand or the linker results in formation of a sulfonamide bond covalently linking the ligand to the linker; and reaction between an alcohol or phenol group of either the linker or the ligand and an alkyl or aryl halide of the ligand or the linker results in formation of an ether bond covalently linking the ligand to the linker. The table below and Figure 8 illustrate numerous reactive functional groups and the resulting bonds formed by reaction therebetween. Where functional groups are lacking, they can be created by suitable chemistries that are described in standard organic chemistry texts such as J. March, Advanced Organic Chemistry, 4 th Ed., (Wiley-Interscience, N.Y., 1992). Complementary Binding Chemistries First Reactive Group Second Reactive Group Linkage hydroxyl isocyanate urethane amine . epoxide β-hy<froxy_unine sulfonyl halide amine sulfonamide carboxyl amine amide hydroxyl alkyl/aryl halide ether The linker is attached to the ligand at a position that retains ligand domain-ligand binding site interaction and specifically which permits the ligand domain of the hgand to orient itself to bind to the ligand-binding site. Such positions and synthetic protocols for linkage are well known in the art. The term linker embraces everything that is not considered to be part of the ligand. The relative orientation in which the ligand domains are displayed depends both on the particular point or points of attachment of the ligands to the linker, and on the framework geometry. The determination of where acceptable substitutions can be made on a hgand is typically based on prior knowledge of structure-activity relationships of the ligand and/or congeners and/or structural information about ligand-receptor complexes (e.g., X-ray crystallography, NMR, and the like). Such positions and synthetic protocols for linkage are well known in the art and can be determined by those with ordinary skill in the art (see METHODS OF PREPARATION, Examples 1-10 and Figures 10-15). Following attachment of a ligand to the linker or linkers, or to a significant portion thereof (e.g., 2-10 atoms of linker), the linker-ligand conjugate may be tested for retention of activity in a relevant assay system (see Utilit y and Testing below for representative assays). At present, it is preferred that the multibinding compound is a bivalent compound in which two ligands are covalently linked, or a trivalent compound, in which three ligands are covalently linked. Linker design is further discussed under METHODS OF PREPARATION. "Potency" as used herein refers to the minimum concentration at which a ligand is able to achieve a desirable biological or therapeutic effect. The potency of a Ugand is typicaUy proportional to its ∑iffinity for its receptor. In some cases, the potency may be non-linearly correlated with its affinity. In comparing the potency of two drugs, e.g., a multibinding agent and the aggregate of its unlinked Ugand, the dose-response curve of each is determined under identical test conditions (e.g., in an in vitro or in vivo assay, in an appropriate ∑uiimal model (such as a human patient)). The finding that the multibinding agent produces an equivalent biologic or therapeutic effect at a lower concentration than the aggregate unlinked Ugand (e.g., on a per weight, per mole or per Ugand basis) is indicative of enhanced potency. "Selectivity" or "specificity" is a measure of the binding preferences of a Ugand for different receptors. The selectivity of a Ugand with respect to its target receptor relative to another receptor is given by the ratio of the respective values of K- j (i.e. , the dissociation constants for each ligand-receptor complex) or, in cases where a biological effect is observed below the K,,, the ratio of the respective EC^s or IC 50 s (i.e., the concentrations that produce 50% of the maximum response for the Ugand interacting with the two distinct receptors). The term "treatment" refers to any treatment of a disease or condition in a mammal, particularly a human, and includes: (i) preventing the disease or condition from occurring in a subject which may be predisposed to the condition but has not yet been diagnosed with the condition and, accordingly, the treatment constitutes prophylactic treatment for the pathologic condition; (ii) inhibiting the disease or condition, i.e., arresting its development; (Ui) relieving the disease or condition, i.e. , causing regression of the disease or condition; or (iv) relieving the symptoms resulting from the disease or condition without addressing the underlying disease or condition, e.g., relieving symptoms of angina pectoris and other conditions of ischemia but not an underlying cause such as, for example, atherosclerotic disease or hypertension. The phrase "disease or condition which is modulated by treatment with a multibinding PDE V ligand" covers aU disease states and/or conditions that are generaUy acknowledged in the art to be usefuUy treated with a Ugand for PDE V in general, and those disease states and/or conditions that have been found to be usefully treated by a specific multibinding compound of our invention, i.e., the compounds of Formula I. Such disease states include, by way of example only, erectile dysfunction, thrombosis, hypertension and the like. The term "therapeuticaUy effective amount" refers to that amount of multibinding compound that is sufficient to effect treatment, as defined above, when administered to a mammal in need of such treatment. The therapeuticaUy effective amount wUl vary depending upon the subject and disease condition being treated, the weight and age of the subject, the severity of the disease condition, the manner of aα'ministration and the like, which can readtty be determined by one of ordinary skiU in the art. The term "phaπnaceuticaUy acceptable excipient" is intended to include vehicles and carriers capable of being coadministered with a multibinding compound to faciUtate the performance of its intended function. The use of such media for pharmaceuticaUy active substances is weU known in the art. Examples of such vehicles and carriers include solutions, solvents, dispersion media, delay agents, emulsions and the like. Any other conventional carrier suitable for use with the multibinding compounds also faUs within the scope of the present invention. METHODS OF PREPARATION Linkers The linker or linkers, when covalently attached to multiple copies of the Ugands, provides a biocompatible, substantiaUy non-immunogenic multibinding compound. The biological activity of the multibinding PDE V modulator compound is highly sensitive to the geometry, composition, size, length, flexibttity or rigidity, the presence or absence of anionic or cationic charge, the relative hydrophobicity/hydrophiUcity, and similar properties of the linker. Accordingly, the linker is preferably chosen to maximize the biological activity of the compound. The linker may be biologicaUy "neutral, i.e., not itself contribute any additional biological activity to the multibinding compound, or it may be chosen to further enhance the biological activity of the compound. In general, the linker may be chosen from any organic molecule construct that orients two or more ligands for binding to the receptors to permit multivalency. In this regard, the linker can be considered as a "framework" on which the ligands are arranged in order to bring about the desired Ugand-orienting result, and thus produce a multibinding compound. For example, different orientations of ligands can be achieved by varying the geometry of the framework (linker) by use of mono- or polycyclic groups, such as aryl and/or heteroaryl groups, or structures incorporating one or more carbon-carbon multiple bonds (alkenyl, alkenylene, alkynyl or alkynylene groups). The optimal geometry and composition of frameworks (linkers) used in the multibinding compounds of this invention are based upon the properties of their intended receptors. For example, it is preferred to use rigid cyclic groups (e.g., aryl, heteroaryl), or non-rigid cycUc groups (e.g., cycloalkyl or crown groups) to reduce conformational entropy when such may be necessary to achieve energeticaUy coupled binding. Different hydrophobic/nydrophiUc characteristics of the linker as weU as the presence or absence of charged moieties can readUy be controlled by the skilled artisan. For example, the hydrophobic nature of a linker derived from hexamethylene diamine or related polyamines can be modified to be substantially more hydrophiUc by replacing the alkylene group with a poly(oxyalkylene) group such as found in the commerciaUy avaUable "Jeffamines" (class of surfactants). Different frameworks can be designed to provide preferred orientations of the ligands. The identification of an appropriate framework geometry for ligand domain presentation is an important first step in the construction of a multi binding agent with enhanced activity. Systematic spatial searching strategies can be used to aid in the identification of preferred frameworks through an iterative process. Figure 4 iUustrates a useful strategy for detepnining an optimal framework display orientation for Ugand domains and can be used for preparing the bivalent compounds of this invention. Various alternative strategies known to those skiUed in the art of molecular design can be substituted for the one described here. As shown in Figure 4, the ligands (shown as filled circles) are attached to a central core structure such as phenyldiacetylene (Panel A) or cyclohexane dicarboxyUc acid (Panel B). The Ugands are spaced apart from the core by an attaching moiety of variable lengths m and n. If the Ugand possesses multiple attachment sites (see discussion below), the orientation of the ligand on the attaching moiety may be varied as well. The positions of the display vectors around the central core structures are varied, thereby generating a coUection of compounds. Assay of each of the individual compounds of a coUection generated as described wiU lead to a subset of compounds with the desired enhanced activities (e.g., potency, selectivity). The analysis of this subset using a technique such as Ensemble Molecular Dynamics wiU suggest a framework orientation that favors the properties desired. The process may require the use of multiple copies of the same central core structure or combinations of different types of display cores. It is to be noted that core structures other than those shown here can be used for determining the optimal framework display orientation of the ligands. The above-described technique can be extended to trivalent compounds and compounds of higher-order valency. A wide variety of linkers is commercially available (Chem Sources USA and Chem Sources International; the ACD electronic database; and Chemical Abstracts). Many of the linkers that are suitable for use in this invention faU into this category. Others can be readily synthesized by methods known in the art, and as described below. Examples of linkers include aliphatic moieties, aromatic moieties, steroidal moieties, peptides, and the like. Specific examples are peptides or polyamides, hydrocarbons, aromatics, heterocyclics, ethers, Upids, cationic or anionic groups, or a combination thereof. Examples are given below and in Figure 5, but it should be understood that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. For example, properties of the linker can be modified by the addition or insertion of anciUary groups into the linker, for example, to change the solubiUty of the multibinding compound (in water, fats, Upids, biological fluids, etc.), hydrophobicity, hydrophilicity, linker flexibility, antigenicity, stabiUty, and the like. For example, the introduction of one or more polyethylene glycol) (PEG) groups onto the linker enhances the hydrophilicity and water solubility of the multibinding compound, increases both molecular weight and molecular size and, depending on the nature of the unPEGylated linker, may increase the in vivo retention time. Further, PEG may decrease antigenicity and potentiaUy enhances the overall rigidity of the linker. AnciUary groups that enhance the water solubility/hydrophUicity of the linker, and accordingly, the resulting multibinding compounds, are useful in practicing this invention. Thus, it is within the scope of the present invention to use anciUary groups such as, for example, smaU repeating units of ethylene glycols, alcohols, polyols, (e.g., glycerin, glycerol propoxylate, saccharides, including mono-, oligosaccharides, etc.) carboxylates (e.g., small repeating units of glutamic acid, acrylic acid, etc.), amines (e.g., tettaethylenepentamine), and the like to enhance the water solubiUty and/or hydrophUicity of the multibinding compounds of this invention. In preferred embodiments, the ancillary group used to improve water solubility/hydrophilicity wiU be a polyether. In particularly preferred embodiments, the ancillary group will contain a small number of repeating ethylene oxide (-CI^CH-O-) units. The incorporation of lipophilic ancillary groups within the structure of the linker to enhance the Upophilicity and/or hydrophobicity of the compounds of Formula I is also within the scope of this invention. LipophUic groups useful with the linkers of this invention include, but are not limited to, lower alkyl, aromatic groups and polycyclic aromatic groups. The aromatic groups may be either unsubstituted or substituted with other groups, but are at least substituted with a group which aUows their covalent attachment to the linker. As used herein the term "aromatic groups" incorporates both aromatic hydrocarbons and heterocyclic aromatics. Other UpophUic groups useful with the linkers of this invention include fatty acid derivatives which may or may not form miceUes in aqueous medium and other specific lipophilic groups which modulate interactions between the multibinding compound and biological membranes. Also within the scope of this invention is the use of anciUary groups which result in the compound of Formula I being incorporated into a vesicle, such as a Uposome, or a miceUe. The term "tipid" refers to any fatty acid derivative that is capable of foπning a bUayer or miceUe such that a hydrophobic portion of the lipid material orients toward the bUayer while a hydrophilic portion orients toward the aqueous phase. Hydrophilic characteristics derive from the presence of phosphato, carboxylic, sulfato, amino, sulfhydryl, nitro and other like groups weU known in the art. Hydrophobicity could be conferred by the inclusion of groups that include, but are not limited to, long chain saturated and unsaturated aliphatic hydrocarbon groups of up to 20 carbon atoms and such groups substituted by one or more aryl, heteroaryl, cycloalkyl, and or heterocyclic group(s). Preferred Upids are phosphoglycerides and sphingolipids, representative examples of which include phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, phosphatidic acid, palmitoyleoyl phosphatidylcholine, lysophosphatidylcholine, lysophosphatidyl-etl__mol--m_ne, dipalmitoylphosphatidylcholine, dioleoylphosphatidyl-choline, distearoyl- phosphatidylchoUne and diUnoleoylphosphatidylcholine. Other compounds lacking phosphorus, such as sphingoUpid and glycosphingolipid families, are also within the group designated as Upid. AdditionaUy, the amphipathic Upids described above may be mixed with other Upids including triglycerides and sterols. The flexibiUty of the linker can be manipulated by the inclusion of anciUary groups which are bulky and/or rigid. The presence of bulky or rigid groups can hinder free rotation about bonds in the linker, or bonds between the linker and the ancillary group(s), or bonds between the linker and the functional groups. Rigid groups can include, for example, those groups whose conformational freedom is restrained by the presence of rings and/or π-bonds, for example, aryl, heteroaryl and heterocyclic groups. Other groups which can impart rigidity include polypeptide groups such as ohgo- or polyproline chains. Rigidity can also be imparted electrostaticaUy. Thus, if the anciUary groups are either positively or negatively charged, the similarly charged anciUary groups wiU force the linker into a configuration affording the inaximum distance between each of the like charges. The energetic cost of bringing the like-charged groups closer to each other, which is inversely related to the square of the distance between the groups, will tend to hold the linker in a configuration that mamtains the separation between the like-charged ancillary groups. Further, ancUlary groups bearing opposite charges wUl tend to be attracted to their oppositely charged counterparts and potentially may enter into both inter- and intramolecular ionic bonds. This non-covalent mechanism wiU tend to hold the linker in a conformation which aUows bonding between the oppositely charged groups. The addition of anciUary groups which are charged, or alternatively, protected groups that bear a latent charge which is unmasked, foUowing addition to the linker, by deprotection, a change in pH, oxidation, reduction or other mechanisms known to those skiUed in the art, is within the scope of this invention. Bulky groups can include, for example, large atoms, ions (e.g., iodine, sulfur, metal ions, etc.) or groups containing large atoms, polycyclic groups, including aromatic groups, non-aromatic groups and structures incorporating one or more carbon-carbon -bonds (i.e., alkenes and alkynes). Bulky groups can also include oUgomers and polymers which are branched- or straight-chain species. Species that are branched are expected to increase the rigidity of the structure more per unit molecular weight gain than are straight-chain species. In preferred embodiments, rigidity (entropic control) is imparted by the presence of alicyclic (e.g., cycloalkyl), aromatic and heterocyclic groups. In other preferred embodiments, this comprises one or more six-membered rings. In stiU further preferred embodiments, the ring is an aryl group such as, for example, phenyl or naphthyl, or a macrocyclic ring such as, for example, a crown compound. In view of the above, it is apparent that the appropriate selection of a linker group providing suitable orientation, entropy and physico-chemical properties is weU within the skiU of the art. Eliminating or reducing antigenicity of the multibinding compounds described herein is also within the scope of this invention. In certain cases, the antigenicity of a multibinding compound may be eliminated or reduced by use of groups such as, for example, polyethylene glycol). The Compounds of Formula I As explained above, the multibinding compounds described herein comprise 2-10 ligands attached covalently to a linker that links the ligands in a manner that allows their multivalent binding to ligand binding sites of PDE V enzyme. The linker spatiaUy constrains these interactions to occur within dimensions defined by the linker. This and other factors increases the biologic and/or therapeutic effect of the multibinding compound as compared to the same number of ligands used in monobinding form. The compounds of this invention are preferably represented by the empirical formula (L) p (X) q where L, X, p and q are as defined above. This is intended to include the several ways in which the Ugands can be linked together in order to achieve the objective of multivalency, and a more detailed explanation is provided below. As noted previously, the linker may be considered as a framework to which Ugands are attached. Thus, it should be recognized that the ligands can be attached at any suitable position on this framework, for example, at the termini of a linear chain or at any intermediate position thereof. The simplest and most preferred multibinding compound is a bivalent compound which can be represented as L-X-L, where L is a Ugand and is the same or different and X is the linker. A trivalent compound could also be represented in a linear fashion, i.e., as a sequence of repeated units L-X-L-X-L, in which L is a ligand and is the same or different at each occurrence, as is X. However, a trivalent compound can also comprise three ligands attached to a central core, and thus be represented as (L)gX, where the linker X could include, for example, an aryl or cycloalkyl group. Tetravalent compounds can be represented in a linear array:L-X-L-X-L-X-L, or a branched array: L-X-L-X-L I L i.e., a branched construct analogous to the isomers of butane (n-butyl, wø-butyl, .sec-butyl, and t- butyl). Alternatively, it could be represented as an aryl or cycloalkyl derivative as described above with four (4) ligands attached to the core linker. The same considerations apply to higher multibinding compounds of this invention containing from 5-10 ligands. However, for multibinding agents attached to a central linker such as an aryl, cycloalkyl or heterocyclyl group, or a crown compound, there is a self- evident constraint that there must be sufficient attachment sites on the linker to accommodate the number of ligands present; for example, a benzene ring could not accommodate more than 6 Ugands, whereas a multi-ring linker (e.g., biphenyl) could accommodate a larger number of ligands. The formula (L) p (X) q is also intended to represent a cyclic compound of formula (-L- X-) n , where n is 2-10. All of the above variations are intended to be within the scope of the invention defined by the formula (L) p (X) q . Examples of bivalent and higher-order valency compounds of this invention are provided in Figures 6 A to 6D. With the foregoing in mind, a preferred linker may be represented by the foUowing formula: -X'-Z-(Y'-Z) m -Y"-Z-X'- in which: m is an integer of from 0 to 20; X' at each separate occurrence is -O-, -S-, -S(O)-, -S(O) 2 -, -NR-, -N + R R\ -C(O>, -C(O)O-, -C(O)NH-, -C(S), -C(S)O-, -C(S)NH- or a covalent bond, where R and R' at each separate occurrence are as defined below for R' and R"; Z is at each separate occurrence selected from alkylene, substituted alkylene, alkylalkoxy, cycloalkylene, substituted cycloalkylene, alkenylene, substituted alkenylene, alkynylene, substituted alkynylene, cycloalkenylene, substituted alkenylene, arylene, substituted arylene, heteroarylene, heterocyclene, substituted heterocyclene, crown compounds, or a covalent bond; Y' and Y" at each separate occurrence are selected from the group consisting of -S(0) n -CR-R"-, -S(0) n -NR'-, -S-S- or covalent bond; in which: n is 0, 1 or 2; and R' and R" at each separate occurrence re selected from hydrogen, alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl, heteroaryl or heterocycUc. Additionally, the linker moiety can be optionally substituted at any atom therein by one or more alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl, heteroaryl and heterocyclic group. As indicated above, the simplest (and preferred) construct is a bivalent compound which can be represented as L-X-L, where L is a PDE V Ugand that is the same or different at each occurrence, and X is the linker. Accordingly, examples of the preparation of a bivalent Ugand are given below as an illustration of the manner in which multibinding compounds of Formula I are obtained. The reaction schemes that follow illustrate preferred linking strategies for linking pyrazolo[4,5-d]pyrimadin-7-one derivative (sildenafil, zaprinast) classes of PDE V modulators. These strategies are intended to apply as weU to any PDE V Ugand that includes, or can be functionalized with, groups compatible with the chosen linker. As was previously discussed, the linker or linkers can be attached to different positions on the ligand molecule to achieve different orientations of the ligand domains and thereby facilitate multivalency. For example, the positions that are potentiaUy available for linking a pyrazolo[4,5-d]pyrimadin-7-one derivative such as sildenafil are indicated by arrows in the structure shown in Figure 7. Certain PDE V ligands may be chiral and exhibit stereoselectivity. the most active enantiomers are preferably used as ligands in the multibinding compounds of this invention. The chiral resolution of enantiomers is accomplished by weU known procedures that result in the formation of diastereomeric derivatives or salts, followed by conventional separation by chromatographic procedures or by fractional crystaUization (see, e.g., Bossert, et al., Agnew. Chem. Int. Ed., 20:762-769 (1981) and U.S. Patent No. 5,571,827 and references cited therein.) The ligands are covalently attached to the linker using conventional chemical techniques. The reaction chemistries resulting in such linkage are weU known in the art and involve the coupling of reactive functional groups present on the linker and ligand. In some cases, it may be necessary to protect portions of the ligand that are not involved in linking reactions. Protecting groups for this purpose are well known in the art and are indicated generally in the reaction schemes by the symbols PG and PG'. Preferably, the reactive functional groups on the linker are selected relative to the functional groups on the Ugand that are available for coupling, or can be introduced onto the ligand for this purpose. In some embodiments, the linker is coupled to Ugand precursors, with the completion of Ugand synthesis being carried out in a subsequent step. Where functional groups are lacking, they can be created by suitable chemistries that are described in standard organic chemistry texts such as J. March, Advanced Organic Chemistry, 4 th Ed. (Wiley-Interscience, N.Y., 1992). Examples of the chemistry for connecting ligands by a linker are shown in Figure 8, where R 1 and R 2 represent a ligand and/or the linking group. One skilled in the art wiU appreciate that synthetically equivalent coupling reactions can be substituted for the reactions Ulustrated herein. The linker to which the ligands or Ugand precursors are attached comprises a "core" molecule having two or more functional groups with reactivity that is complementary to that of the functional groups on the Ugand. Figure 5 illustrates the diversity of "cores" that are useful for varying the linker size, shape, length, orientation, rigidity, acidity/basicity, hydrophobicity hydrophilicity, hydrogen bonding characteristics and number of Ugands connected. This pictorial representation is intended only to iUustrate the invention, and not to limit its scope to the structures shown. In the Figures and reaction schemes that foUow, a solid circle is used to genericaUy represent a core molecule. The solid circle is equivalent to a linker as defined above after reaction. The preferred compounds of Formula I are bivalent. Accordingly, and for the purpose of simplicity, the figures and reaction schemes below Ulustrate the synthesis of bivalent PDE V modulators. Figures 9A to 9J illustrate some exemplary homodimer and heterodimer analogs of Sildenafil. It should be noted, however, that the same techniques can be used to generate higher order multibinding compounds, i.e., the compounds of the invention where/? is 3-10. Reactions performed under standard amide coupling conditions are carried out in an inert polar solvent (e.g., DMF, DMA) in the presence of a hindered base (e.g., TEA, DIPEA) and standard amide coupling reagents (e.g., DPP A, PyBOP, HATU, DCC). Several methods for preparing bivalent pyrazolo[4,5-d]pyrimadin-7-one derivative compounds, as exemplified here for sildenafil, zaprinast and structurally analogous molecules, are illustrated in the reaction schemes shown in Figure 10-15. The strategies for preparing compounds of Formula I discussed above involve coupling the ligand directly to a homobifunctional core. Another strategy that can be used with all ligands, and for the preparation of both bivalent and higher order multibinding compounds, is to introduce a "spacer" before coupling to a central core. Such a spacer can itself be selected from the same set as the possible core compounds. Compounds of formula I of higher order valency, i.e., p>2, can be prepared by simple extension of the above strategies. Compounds are prepared by coupling ligands to a central core bearing multiple functional groups. The reaction conditions are the same as described above for the preparation of bivalent compounds, with appropriate adjustments made in the molar quantities of ligand and reagents. Ligands may be coupled to a polypeptide core with a sidechain spacer. SoUd phase peptide synthesis can be used to produce a wide variety of peptidic core molecules. Techniques well-known to those skilled in the art (including combinatorial methods) are used to vary the distance between ligand attachment sites on the core molecule, the number of attachment sites available for coupling, and the chemical properties of the core molecule. Orthogonal protecting groups are used to selectively protect functional groups on the core molecule, thus allowing ancillary groups to be inserted into the linker of the multibinding compound and/or the preparation of "heterovalomers" (i.e., multibinding compounds with non-identical ligands). Certain of the synthetic strategies described above employ a step in which the ligand, attached to spacers or not, is symmetrically linked to functionally equivalent positions on a central core. Compounds of formula I can also be synthesized using an asymmetric linear approach. This strategy is preferred when linking two or more different ligands and/or the same Ugand at different points of connectivity. Isolation and Purification of the Compounds Isolation and purification of the compounds and intermediates described herein can be effected, if desired, by any suitable separation or purification such as, for example, filtration, extraction, crystallization, column chromatography, thin-layer chromatography, thick-layer chromatography, preparative low or high-pressure liquid chromatography or a combination of these procedures, Characterization is preferably by NMR and mass spectroscopy. Utility and Testing The multibinding compounds of this invention can be used to modulate PDE V activity in various tissues including smooth muscle and platelets. They will typicaUy be used for the treatment of diseases and conditions in mammals that involve or are mediated by PDE V, such as erectile dysfunction, thromboembolic diseases, hypertension and the like. The multibinding compounds of this invention are tested in weU-known and reliable assays and their activities are compared with those of the corresponding unlinked (i.e., monovalent) Ugands. Binding affinity to and inhibition of phosphodiesterases The in-vitro inhibitory activity of the multibinding compounds against cGMP and cAMP are determined by measurement of the concentration of multibinding compound required for 50% inhibition of PDE V activity (IC 50 value), essentially by the method of Thompson and Appleman 29 . The required PDE V enzymes are isolated from a variety of sources essentially using the method of Thompson et al. 30 , or Ballard et al 22 . Results from these tests will show that the compounds of the present invention are potent and selective inhibitors of PDE V. Effect on corpus cavernosum smooth muscle (CCSM) The effect of compounds of this invention of the relaxation of CCSM may be determined in vitro using isolated strips of rabbit corpus cavernosum 31 , or in strips of human corpus cavernosum 22 . In each case, the abUity of compounds of the present invention to relax phenylephrine-induced contractions of CCSM in a dose-dependent fashion is measured. Effect on erectile function The effect of compounds of this invention on erectile function may be determined in vitro in dogs 32 . The effects of increasing doses of multibinding compounds on electrically stimulated intracavernosal pressure, penile blood flow, blood pressure, and heart-rate are evaluated. Effect on platelet aggregation The effect of compounds of this invention on platelet aggregation may be determined in vitro in guinea pigs 14 or rat pulmonary microcirculation 25 , where platelet aggregation is elicited by collagen, or in kidneys following iscehmia-reperfusion 26 , or at the sites of balloon catheter induced vasular injury 25 in rats. Combinatorial Libraries The methods described above lend themselves to combinatorial approaches for identifying multimeric compounds which possess multibinding properties for PDE V enzymes. Specifically, factors such as the proper juxtaposition of the individual ligands of a multibinding compound with respect to the relevant array of binding sites on a target or targets is important in optimizing the interaction of the multibinding compound with its target(s) and to maximize the biological advantage through multivalency. One approach is to identify a library of candidate multibinding compounds with properties sp-inning the multibinding parameters that are relevant for a particular target. These parameters include: (1) the identity of ligand(s), (2) the orientation of ligands, (3) the valency of the construct, (4) linker length, (5) linker geometry, (6) linker physical properties, and (7) linker chemical functional groups. Libraries of multimeric compounds potentially possessing multibinding properties (i.e., candidate multibinding compounds) and comprising a multiplicity of such variables are prepared and these Ubraries are then evaluated via conventional assays corresponding to the ligand selected and the multibinding parameters desired. Considerations relevant to each of these variables are set forth below: Selection of Ugand(s) A single ligand or set of ligands is (are) selected for incorporation into the libraries of candidate multibinding compounds which library is directed against a particular biological target or targets. The only requirement for the ligands chosen is that they are capable of interacting with the selected target(s). Thus, ligands may be known drugs, modified forms of known drugs, substructures of known drugs or substrates of modified forms of known drugs (which are competent to interact with the target), or other compounds. Ligands are preferably chosen based on known favorable properties that may be projected to be carried over to or amplified in multibinding forms. Favorable properties include demonstrated safety and efficacy in human patients, appropriate PK/ADME profiles, synthetic accessibility, and desirable physical properties such as solubUity, logP, etc. However, it is crucial to note that Ugands which display an unfavorable property from among the previous list may obtain a more favorable property through the process of multibmding compound formation; i.e., ligands should not necessarily be excluded on such a basis. For example, a Ugand that is not sufficiently potent at a particular target so as to be efficacious in a human patient may become highly potent and efficacious when presented in multibinding form. A ligand that is potent and efficacious but not of utility because of a non-mechanism-related toxic side effect may have increased therapeutic index (increased potency relative to toxicity) as a multibinding compound. Compounds that exhibit short in vivo half-lives may have extended half-lives as multibinding compounds. Physical properties of ligands that limit their usefulness (e.g., poor bioavaUabiUty due to low solubiUty, hydrophobicity, hydrophilicity) may be rationaUy modulated in multibinding forms, providing compounds with physical properties consistent with the desired utility. Orientation: selection of ligand attachment points and linking chemistry Several points are chosen on each ligand at which to attach the ligand to the linker. The selected points on the ligand/linker for attachment are functionalized to contain complementary reactive functional groups. This permits probing the effects of presenting the ligands to their receptor(s) in multiple relative orientations, an important multibinding design parameter. The only requirement for choosing attachment points is that attaching to at least one of these points does not abrogate activity of the Ugand. Such points for attachment can be identified by structural information when avaUable. For example, inspection of a co-crystal structure of a protease inhibitor bound to its target aUows one to identify one or more sites where linker attachment wUl not preclude the enzyme: inhibitor interaction. Alternatively, evaluation of ligandVtarget binding by nuclear magnetic resonance wiU permit the identification of sites non-essential for ligand/target binding. See, for example, Fesik, et al., U.S. Patent No. 5,891,643. When such structural information is not available, utilization of structure-activity relationships (SAR) for ligands wiU suggest positions where substantial structural variations are and are not allowed. In the absence of both structural and SAR information, a library is merely selected with multiple points of attachment to allow presentation of the ligand in multiple distinct orientations. Subsequent evaluation of this Ubrary wUl indicate what positions are suitable for attachment. It is important to emphasize that positions of attachment that do abrogate the activity of the monomeric ligand may also be advantageously included in candidate multibinding compounds in the library provided that such compounds bear at least one ligand attached in a manner which does not abrogate intrinsic activity. This selection derives from, for example, heterobivalent interactions within the context of a single target molecule. For example, consider a receptor antagonist ligand bound to its target receptor, and then consider modifying this Ugand by attaching to it a second copy of the same ligand with a linker which aUows the second ligand to interact with the same receptor molecule at sites proximal to the antagonist binding site, which include elements of the receptor that are not part of the formal antagonist binding site and/or elements of the matrix surrounding the receptor such as the membrane. Here, the most favorable orientation for interaction of the second ligand molecule with the receptor/matrix may be achieved by attaching it to the linker at a position which abrogates activity of the ligand at the formal antagonist binding site. Another way to consider this is that the SAR of individual ligands within the context of a multibinding structure is often different from the SAR of those same Ugands in momomeric form. The foregoing discussion focused on bivalent interactions of dimeric compounds bearing two copies of the same Ugand joined to a single linker through different attachment points, one of which may abrogate the binding/activity of the monomeric Ugand. It should also be understood that bivalent advantage may also be attained with heterodimeric constructs bearing two different ligands that bind to common or different targets. For example, a 5HT 4 receptor antagonist and a bladder-selective muscarinic M 3 antagonist may be joined to a linker through attachment points which do not abrogate the binding affinity of the monomeric ligands for their respective receptor sites. The dimeric compound may achieve enhanced affinity for both receptors due to favorable interactions between the 5HT 4 Ugand and elements of the M 3 receptor proximal to the formal M 3 antagonist binding site and between the M 3 ligand and elements of the 5HT 4 receptor proximal to the formal 5HT 4 antagonist binding site. Thus, the dimeric compound may be more potent and selective antagonist of overactive bladder and a superior therapy for urinary urge incontinence. Once the ligand attachment points have been chosen, one identifies the types of chemical linkages that are possible at those points. The most preferred types of chemical linkages are those that are compatible with the overaU structure of the ligand (or protected forms of the ligand) readily and generaUy formed, stable and intrinsicaUy inocuous under typical chemical and physiological conditions, and compatible with a large number of available linkers. Amide bonds, ethers, amines, carbamates, ureas, and sulfonamides are but a few examples of preferred linkages. Linkers: spanning relevant multibinding parameters through selection of valency, linker length, linker geometry, rigidity, physical properties, and chemical functional groups In the library of linkers employed to generate the library of candidate multibinding compounds, the selection of linkers employed in this Ubrary of linkers takes into consideration the foUowing factors: Valency. In most instances the library of linkers is initiated with divalent linkers. The choice of Ugands and proper juxtaposition of two Ugands relative to their binding sites permits such molecules to exhibit target binding affinities and specificities more than sufficient to confer biological advantage. Furthermore, divalent linkers or constructs are also typicaUy of modest size such that they retain the desirable biodistribution properties of smaU molecules. Linker length. Linkers are chosen in a range of lengths to aUow the sp-tnning of a range of inter-ligand distances that encompass the distance preferable for a given divalent interaction. In some instances the preferred distance can be estimated rather precisely from high-resolution structural information of targets, typically enzymes and soluble receptor targets. In other instances where high-resolution structural information is not available (such as 7TM G-protein coupled receptors), one can make use of simple models to estimate the maximum distance between binding sites either on adjacent receptors or at different locations on the same receptor. In situations where two binding sites are present on the same target (or target subunit for multisubunit targets), preferred linker distances are 2-20 A, with more preferred linker distances of 3-12 A. In situations where two binding sites reside on separate (e.g., protein) target sites, preferred linker distances are 20-100 A, with more preferred distances of 30-70 A. Linker geometry and rigidity. The combination of ligand attachment site, linker length, linker geometry, and linker rigidity determine the possible ways in which the ligands of candidate multibinding compounds may be displayed in three dimensions and thereby presented to their binding sites. Linker geometry and rigidity are nominaUy determined by chemical composition and bonding pattern, which may be controUed and are systematically varied as another spaiining function in a multibinding array. For example, linker geometry is varied by attaching two ligands to the ortho, meta, and para positions of a benzene ring, or in cis- or trα/w-arrangements at the 1,1- vs. 1,2- vs. 1,3- vs. 1,4- positions around a cyclohexane core or in cis- or tr /w-arrangements at a point of ethylene unsaturation. Linker rigidity is varied by controlling the number and relative energies of different conformational states possible for the linker. For example, a divalent compound bearing two ligands joined by 1,8-octyl linker has many more degrees of freedom, and is therefore less rigid than a compound in which the two ligands are attached to the 4,4' positions of a biphenyl linker. Linker physical properties. The physical properties of linkers are nominally determined by the chemical constitution and bonding patterns of the linker, and linker physical properties impact the overaU physical properties of the candidate multibinding compounds in which they are included. A range of linker compositions is typically selected to provide a range of physical properties (hydrophobicity, hydrophilicity, amphiphilicity, polarization, acidity, and basicity) in the candidate multibinding compounds. The particular choice of linker physical properties is made within the context of the physical properties of the ligands they join and preferably the goal is to generate molecules with favorable PK ADME properties. For example, linkers can be selected to avoid those that are too hydrophUic or too hydrophobic to be readUy absorbed and/or distributed in vivo. Linker chemical functional groups. Linker chemical functional groups are selected to be compatible with the chemistry chosen to connect linkers to the ligands and to impart the range of physical properties sufficient to span initial examination of this parameter. Combinatorial synthesis Having chosen a set of n ligands (n being deteπnined by the sum of the number of different attachment points for each ligand chosen) and m linkers by the process outlined above, a library of (nl)m candidate divalent multibinding compounds is prepared which spans the relevant multibinding design parameters for a particular target. For example, an array generated from two ligands, one which has two attachment points (Al, A2) and one which has three attachment points (Bl, B2, B3) joined in all possible combinations provide for at least 15 possible combinations of multibinding compounds: Al-Al A1-A2 Al-Bl A1-B2 A1-B3 A2-A2 A2-B1 A2-B2 A2-B3 Bl-Bl B1-B2 B1-B3 B2-B2 B2-B3 B3-B3 When each of these combinations is joined by 10 different linkers, a library of 150 candidate multibinding compounds results. Given the combinatorial nature of the library, common chemistries are preferably used to join the reactive functionalies on the ligands with complementary reactive functionalities on the linkers. The library therefore lends itself to efficient paraUel synthetic methods. The combinatorial tibrary can employ soUd phase chemistries well known in the art wherein the ligand and/or linker is attached to a solid support. Alternatively and preferably, the combinatorial libary is prepared in the solution phase. After synthesis, candidate multibinding compounds are optionally purified before assaying for activity by, for example, chromatographic methods (e.g., HPLC). Analysis of array by biochemical, analytical, pharmacological, and computational methods Various methods are used to characterize the properties and activities of the candidate multibinding compounds in the library to determine which compounds possess multibinding properties. Physical constants such as solubUity under various solvent conditions and logD/clogD values can be determined. A combination of NMR spectroscopy and computational methods is used to determine low-energy conformations of the candidate multibinding compounds in fluid media. The ability of the members of the library to bind to the desired target and other targets is determined by various standard methods, which include radioligand displacement assays for receptor and ion channel targets, and kinetic inhibition analysis for many enzyme targets. In vitro efficacy, such as for receptor agonists and antagonists, ion channel blockers, and antimicrobial activity, can also be determined. Pharmacological data, including oral absorption, everted gut penetration, other pharmacokinetic parameters and efficacy data can be determined in appropriate models. In this way, key structure-activity relationships are obtained for multibinding design parameters which are then used to direct future work. The members of the Ubrary which exhibit multibmding properties, as defined herein, can be readUy determined by conventional methods. First those members which exhibit multibinding properties are identified by conventional methods as described above including conventional assays (both in vitro and in vivo). Second, ascertaining the structure of those compounds which exhibit multibinding properties can be accomplished via art recognized procedures. For example, each member of the library can be encrypted or tagged with appropriate information allowing determination of the structure of relevant members at a later time. See, for example, Dower, et al., International Patent Application Publication No. WO 93/06121; Brenner, et al., Proc. Natl Acad. ScL, USA, 89:5181 (1992); GaUop, et al., U.S. Patent No. 5,846,839; each of which are incorporated herein by reference in its entirety. Alternatively, the structure of relevant multivalent compounds can also be deteπnined from soluble and untagged libaries of candidate multivalent compounds by methods known in the art such as those described by Hindsgaul, et al., Canadian Patent Application No. 2,240,325 which was pubUshed on July 11, 1998. Such methods couple frontal affinity chromatography with mass spectroscopy to determine both the structure and relative binding affinities of candidate multibinding compounds to receptors. The process set forth above for dimeric candidate multibinding compounds can, of course, be extended to trimeric candidate compounds-and higher analogs thereof. Follow-up synthesis and analysis of additional aιrw(s) Based on the information obtained through analysis of the initial Ubrary, an optional component of the process is to ascertain one or more promising multibinding "lead" compounds as defined by particular relative ligand orientations, tinker lengths, linker geometries, etc. Additional libraries can then be generated around these leads to provide for further information regarding structure to activity relationships. These arrays typicaUy bear more focused variations in linker structure in an effort to further optimize target -tffinity and/or activity at the target (antagonism, partial agonism, etc.), and/or alter physical properties. By iterative redesign/analysis using the novel principles of multibinding design along with classical medicinal chemistry, biochemistry, and pharmacology approaches, one is able to prepare and identify optimal multibinding compounds that exhibit biological advantage towards their targets and as therapeutic agents. To further elaborate upon this procedure, suitable divalent linkers include, by way of example only, those derived from dicarboxyUc acids, disulfonylhalides, dialdehydes, diketones, dihalides, dUsocy_mates,diamines, diols, mixtures of carboxyUc acids, sulfonylhalides, aldehydes, ketones, halides, isocyanates, amines and diols. In each case, the carboxylic acid, sulfonylhaUde, aldehyde, ketone, halide, isocyanate, amine and diol functional group is reacted with a complementary functionality on the Ugand to form a covalent linkage. Such complementary functionality is weU known in the art as iUustrated in the foUowing table: COMPLEMENTARY BINDING CHEMISTRIES First Reactive Group Second Reactive Group in age hydroxyl isocyanate urethane amine epoxide β-hyα oxyamine sulfonyl halide amine sulfonamide carboxyl acid amine amide hydroxyl alkyl/aryl halide ether aldehyde amine/NaCNBH 4 amine ketone amine/NaCNBH 4 amine amine isocyanate carbamate Exemplary linkers include the foUowing linkers identified as X-1 through X-418 as set forth below: Representative ligands for use in this invention include, by way of example, pyrazolo[4,5-d]pyrimadin-7-one compounds such as sUdenafil compounds (designated L-1; e.g., structures 5, 7, 9 and 11 of Figures 10 and 11) and zaprinast compounds (designated L-2; e.g., structures 1 and 3 of Figure 10). Combinations of Ugands (L) and linkers (X) per this invention include, by way example only, homo- and hetero-dimers wherein a first ligand is selected from L-1 through L-2 above and the second ligand and linker is selected from the following: L-l/X-1- L-l/X-2- L-l/X-3- L-l/X-4- L-l/X-5- L-l/X-6- L-l/X-7- L-l/X-8- L-l/X-9- L-l/X-10- L-l/X-11- L-l/X-12- L-l/X-13- L-l/X-14- L-l/X-15- L-l/X-16- L-l/X-17- L-l/X-18- L-l/X-19- L-l/X-20- L-l/X-21- L-l/X-22- L-l/X-23- L-l/X-24- L-l/X-25- L-l/X-26- L-l/X-27- L-l/X-28- L-l/X-29- L-l/X-30- L-l/X-31- L-l/X-32- L-l/X-33- L-l/X-34- L-l/X-35- L-l/X-36- L-l/X-37- L-l/X-38- L-l/X-39- L-l/X-40- L-l/X-41- L-l/X-42- L-l/X-43- L-l/X-44- L-l/X-45- L-l/X-46- L-l/X-47- L-l/X-48- L-l/X-49- L-l/X-50- L-l/X-51- L-l/X-52- L-l/X-53- L-l/X-54- L-l/X-55- L-l/X-56- L-l/X-57- L-l/X-58- L-l/X-59- L-l/X-60- L-l/X-61- L-l/X-62- L-l/X-63- L-l/X-64- L-l/X-65- L-l/X-66- L-l/X-67- L-l/X-68- L-l/X-69- L-l/X-70- L-l/X-71- L-l/X-72- L-l/X-73- L-l/X-74- L-l/X-75- L-l/X-76- L-l/X-77- L-l/X-78- L-l/X-79- L-l/X-80- L-l/X-81- L-l/X-82- L-l/X-83- L-l/X-84- L-l/X-85- L-l/X-86- L-l/X-87- L-l/X-88- L-l/X-89- L-l/X-90- L-l/X-91- L-l/X-92- L-l/X-93- L-l/X-94- L-l/X-95- L-l/X-96- L-l/X-97- L-l/X-98- L-l/X-99- L-l/X-100- L-l/X-101- L-l/X-102- L-l/X-103- L-l/X-104- L-l/X-105- L-l/X-106- L-l/X-107- L-l/X-108- L-l/X-109- L-l/X-110- L-l/X-111- L-l/X-112- L-l/X-113- L-l/X-114- L-l/X-115- L-l/X-116- L-l/X-117- L-l/X-118- L-l/X-119- L-l/X-120- L-l/X-121- L-l/X-122- L-l/X-123- L-l/X-124- L-l/X-125- L-l/X-126- L-l/X-127- L-l/X-128- L-l/X-129- L-l/X-130- L-l/X-131- L-l/X-132- L-l/X-133- L-l/X-134- L-l/X-135- L-l/X-136- L-l/X-137- L-l/X-138- L-l/X-139- L-l/X-140- L-l/X-141- L-l/X-142- L-l/X-143- L-l/X-144- L-l/X-145- L-l/X-146- L-l/X-147- L-l/X-148- L-l/X-149- L-l/X-150- L-l/X-151- L-l/X-152- L-l/X-153- L-l/X-154- L-l/X-155- L-l/X-156- L-l/X-157- L-l/X-158- L-l/X-159- L-l/X-160- L-l/X-161- L-l/X-162- L-l/X-163- L-l/X-164- L-l/X-165- L-l/X-166- L-l/X-167- L-l/X-168- L-l/X-169- L-l/X-170- L-l/X-171- L-l/X-172- L-l/X-173- L-l/X-174- L-l/X-175- L-l/X-176- L-l/X-177- L-l/X-178- L-l/X-179- L-l/X-180- L-l/X-181- L-l/X-182- L-l/X-183- L-l/X-184- L-l/X-185- L-l/X-186- L-l/X-187- L-l/X-188- L-l/X-189- L-l/X-190- L-l/X-191- L-l/X-192- L-l/X-193- L-l/X-194- L-l/X-195- L-l/X-196- L-l/X-197- L-l/X-198- L-l/X-199- L-l/X-200- L-l/X-201- L-l/X-202- L-l/X-203- L-l/X-204- L-l/X-205- L-l/X-206- L-l/X-207- L-l/X-208- L-l/X-209- L-l/X-210- L-l/X-211- L-l/X-212- L-l/X-213- L-l/X-214- L-l/X-215- L-l/X-216- L-l/X-217- L-l/X-218- L-l/X-219- L-l/X-220- L-l/X-221- L-l/X-222- L-l/X-223- L-l/X-224- L-l/X-225- L-l/X-226- L-l/X-227- L-l/X-228- L-l/X-229- L-l/X-230- L-l/X-231- L-l/X-232- L-l/X-233- L-l/X-234- L-l/X-235- L-l/X-236- L-l/X-237- L-l/X-238- L-l/X-239- L-l/X-240- L-l/X-241- L-l/X-242- L-l/X-243- L-l/X-244- L-l/X-245- L-l/X-246- L-l/X-247- L-l/X-248- L-l/X-249- L-l/X-250- L-l/X-251- L-l/X-252- L-l/X-253- L-l/X-254- L-l/X-255- L-l/X-256- L-l/X-257- L-l/X-258- L-l/X-259- L-l/X-260- L-l/X-261- L-l/X-262- L-l/X-263- L-l/X-264- L-l/X-265- L-l/X-266- L-l/X-267- L-l/X-268- L-l/X-269- L-l/X-270- L-l/X-271- L-l/X-272- L-l/X-273- L-l/X-274- L-l/X-275- L-l/X-276- L-l/X-277- L-l/X-278- L-l/X-279- L-l/X-280- L-l/X-281- L-l/X-282- L-l/X-283- L-l/X-284- L-l/X-285- L-l/X-286- L-l/X-287- L-l/X-288 L-l/X-289- L-l/X-290- L-l/X-291- L-l/X-292- L-l/X-293- L-l/X-294 L-l/X-295- L-l/X-296- L-l/X-297- L-l/X-298- L-l/X-299- L-l/X-300 L-l/X-301- L-l/X-302- L-l/X-303- L-l/X-304- L-l/X-305- L-l/X-306 L-l/X-307- L-l/X-308- L-l/X-309- L-l/X-310- L-l/X-311- L-l/X-312 L-l/X-313- L-l/X-314- L-l/X-315- L-l/X-316- L-l/X-317- L-l/X-318- L-l/X-319- L-l/X-320- L-l/X-321- L-l/X-322- L-l/X-323- L-l/X-324 L-l/X-325- L-l/X-326- L-l/X-327- L-l/X-328- L-l/X-329- L-l/X-330 L-l/X-331- L-l/X-332- L-l/X-333- L-l/X-334- L-l/X-335- L-l/X-336- L-l/X-337- L-l/X-338- L-l/X-339- L-l/X-340- L-l/X-341- L-l/X-342- L-l/X-343- L-l/X-344- L-l/X-345- L-l/X-346- L-l/X-347- L-l/X-348- L-l/X-349- L-l/X-350- L-l/X-351- L-l/X-352- L-l/X-353- L-l/X-354- L-l/X-355- L-l/X-356- L-l/X-357- L-l/X-358- L-l/X-359- L-l/X-360- L-l/X-361- L-l/X-362- L-l/X-363- L-l/X-364- L-l/X-365- L-l/X-366- L-l/X-367- L-l/X-368- L-l/X-369- L-l/X-370- L-l/X-371- L-l/X-372- L-l/X-373- L-l/X-374- L-l/X-375- L-l/X-376- L-l/X-377- L-l/X-378- L-l/X-379- L-l/X-380- L-l/X-381- L-l/X-382- L-l/X-383- L-l/X-384 L-l/X-385- L-l/X-386- L-l/X-387- L-l/X-388- L-l/X-389- L-l/X-390- L-l/X-391- L-l/X-392- L-l/X-393- L-l/X-394- L-l/X-395- L-l/X-396 L-l/X-397- L-l/X-398- L-l/X-399- L-l/X-400- L-l/X-401- L-l/X-402 L-l/X-403- L-l/X-404- L-l/X-405- L-l/X-406- L-l/X-407- L-l/X-408 L-l/X-409- L-l/X-410- L-1/X 11- L-l/X-412- L-l/X-413- L-l/X-414 L-l/X-415- L-l/X-416- L-l/X-417- L-l/X-418- L-2/X-1- L-2/X-2- L-2 X-3- L-2/X-4- L-2/X-5- L-2/X-6- L-2/X-7- L-2/X-8- L-2/X-9- L-2/X-10- L-2/X-11- L-2/X-12- L-2/X-13- L-2/X-14- L-2/X-15- L-2/X-16- L-2/X-17- L-2/X-18- L-2/X-19- L-2/X-20- L-2/X-21- L-2/X-22- L-2/X-23- L-2/X-24- L-2/X-25- L-2/X-26- L-2/X-27- L-2/X-28- L-2/X-29- L-2/X-30- L-2/X-31- L-2/X-32- L-2/X-33- L-2/X-34- L-2/X-35- L-2/X-36- L-2/X-37- L-2/X-38- L-2/X-39- L-2/X-40- L-2/X-41- L-2/X-42- L-2/X-43- L-2/X-44- L-2/X-45- L-2/X-46- L-2/X-47- L-2/X-48- L-2/X-49- L-2/X-50- L-2/X-51- L-2/X-52- L-2/X-53- L-2/X-54- L-2/X-55- L-2/X-56- L-2/X-57- L-2/X-58- L-2/X-59- L-2/X-60- L-2/X-61- L-2/X-62- L-2/X-63- L-2/X-64- L-2/X-65- L-2/X-66- L-2/X-67- L-2/X-68- L-2/X-69- L-2/X-70- L-2/X-71- L-2/X-72- L-2/X-73- L-2/X-74- L-2/X-75- L-2/X-76- L-2/X-77- L-2/X-78- L-2/X-79- L-2/X-80- L-2/X-81- L-2/X-82- L-2/X-83- L-2/X-84- L-2/X-85- L-2/X-86- L-2/X-87- L-2/X-88- L-2/X-89- L-2/X-90- L-2/X-91- L-2/X-92- L-2/X-93- L-2/X-94- L-2/X-95- L-2/X-96- L-2/X-97- L-2/X-98- L-2/X-99- L-2/X-100- L-2/X-101- L-2/X-102- L-2/X-103- L-2/X-104- L-2/X-105- L-2/X-106- L-2/X-107- L-2/X-108- L-2/X-109- L-2/X-110- L-2/X-U1- L-2/X-112- L-2/X-113- L-2/X-114- L-2/X-115- L-2/X-116- L-2/X-117- L-2/X-118- L-2/X-119- L-2/X-120- L-2/X-121- L-2/X-122- L-2/X-123- L-2/X-124- L-2/X-125- L-2/X-126- L-2/X-127- L-2/X-128- L-2/X-129- L-2/X-130- L-2/X-131- L-2/X-132- L-2/X-133- L-2/X-134- L-2/X-135- L-2/X-136- L-2/X-137- L-2/X-138- L-2/X-139- L-2/X-140- L-2/X-141- L-2/X-142- L-2/X-143- L-2/X-144- L-2/X-145- L-2/X-146- L-2/X-147- L-2/X-148- L-2/X-149- L-2/X-150- L-2/X-151- L-2/X-152- L-2/X-153- L-2/X-154- L-2/X-155- L-2/X-156- L-2/X-157- L-2/X-158- L-2/X-159- L-2/X-160- L-2/X-161- L-2/X-162- L-2/X-163 L-2/X-164 L-2/X-165 L-2/X-166 L-2/X-167 L-2/X-168 L-2/X-169 L-2/X-170 L-2/X-171 L-2/X-172 L-2/X-173- L-2/X-174- L-2/X-175- L-2/X-176- L-2/X-177- L-2/X-178- L-2/X-179- L-2/X-180- L-2/X-181- L-2/X-182- L-2/X-183- L-2/X-184- L-2/X-185- L-2/X-186- L-2/X-187- L-2/X-188- L-2/X-189- L-2/X-190- L-2/X-191- L-2/X-192- L-2/X-193- L-2/X-194- L-2/X-195- L-2/X-196- L-2/X-197- L-2/X-198- L-2/X-199- L-2/X-200- L-2/X-201- L-2/X-202- L-2/X-203- L-2/X-204- L-2/X-205- L-2/X-206- L-2/X-207- L-2/X-208- L-2/X-209- L-2/X-210- L-2/X-211- L-2/X-212- L-2/X-213- L-2/X-214- L-2/X-215- L-2/X-216- L-2/X-217- L-2/X-218- L-2/X-219- L-2/X-220- L-2/X-221- L-2/X-222- L-2/X-223- L-2/X-224- L-2/X-225- L-2/X-226- L-2/X-227- L-2/X-228- L-2/X-229- L-2/X-230- L-2/X-231- L-2/X-232- L-2/X-233- L-2/X-234- L-2/X-235- L-2/X-236- L-2/X-237- L-2/X-238- L-2/X-239- L-2/X-240- L-2/X-241- L-2/X-242- L-2/X-243- L-2 X-244- L-2/X-245- L-2/X-246- L-2/X-247- L-2/X-248- L-2/X-249- L-2/X-250- L-2/X-251- L-2/X-252- L-2/X-253- L-2/X-254- L-2/X-255- L-2/X-256- L-2/X-257- L-2/X-258- L-2/X-259- L-2/X-260- L-2/X-261- L-2/X-262- L-2/X-263- L-2/X-264- L-2/X-265- L-2/X-266- L-2/X-267- L-2/X-268- L-2/X-269- L-2/X-270- L-2/X-271- L-2/X-272- L-2/X-273- L-2/X-274- L-2/X-275- L-2/X-276- L-2/X-277- L-2/X-278- L-2/X-279- L-2/X-280- L-2/X-281- L-2/X-282- L-2/X-283- L-2/X-284- L-2/X-285- L-2/X-286- L-2/X-287- L-2/X-288- L-2/X-289- L-2/X-290- L-2/X-291- L-2/X-292- L-2/X-293- L-2/X-294- L-2/X-295- L-2/X-296- L-2/X-297- L-2/X-298- L-2/X-299- L-2/X-300- L-2/X-301- L-2/X-302- L-2/X-303- L-2/X-304- L-2/X-305- L-2/X-306- L-2/X-307- L-2/X-308- L-2/X-309- L-2/X-310- L-2/X-311- L-2/X-312- L-2/X-313- L-2/X-314- L-2/X-315- L-2/X-316- L-2/X-317- L-2/X-318- L-2/X-319- L-2/X-320- L-2/X-321- L-2/X-322- L-2/X-323- L-2/X-324- L-2/X-325- L-2/X-326- L-2/X-327- L-2/X-328- L-2/X-329- L-2/X-330- L-2/X-331- L-2/X-332- L-2/X-333- L-2/X-334- L-2/X-335- L-2/X-336- L-2/X-337- L-2/X-338- L-2/X-339- L-2/X-340- L-2/X-341- L-2/X-342- L-2/X-343- L-2/X-344- L-2/X-345- L-2/X-346- L-2/X-347- L-2/X-348- L-2/X-349- L-2/X-350- L-2/X-351- L-2/X-352- L-2/X-353- L-2/X-354- L-2/X-355- L-2/X-356- L-2/X-357- L-2/X-358- L-2/X-359- L-2/X-360- L-2/X-361- L-2/X-362- L-2/X-363- L-2/X-364- L-2/X-365- L-2/X-366- L-2/X-367- L-2/X-368- L-2/X-369- L-2/X-370- L-2/X-371- L-2/X-372- L-2/X-373- L-2/X-374- L-2/X-375- L-2/X-376- L-2/X-377- L-2/X-378- L-2/X-379- L-2/X-380- L-2/X-381- L-2/X-382- L-2/X-383- L-2/X-384- L-2/X-385- L-2/X-386- L-2/X-387- L-2/X-388- L-2/X-389- L-2/X-390- L-2/X-391- L-2/X-392- L-2/X-393- L-2/X-394- L-2/X-395- L-2/X-396- L-2/X-397- L-2/X-398- L-2/X-399- L-2/X-400- L-2/X-401- L-2/X-402- L-2/X-403- L-2/X-404- L-2/X-405- L-2/X-406- L-2/X-407- L-2/X-408- L-2/X-409- L-2/X-410- L-2/X-411- L-2/X-412- L-2/X-413- L-2/X-414- L-2/X-415- L-2/X-416- L-2/X-417- L-2/X-418-. Pharmaceutical Formulations When employed as pharmaceuticals, the compounds of Formula I are usually administered in the form of pharmaceutical compositions. This invention therefore provides pharmaceutical compositions which contain, as the active ingredient, one or more of the compounds of Formula I above or a pharmaceutically acceptable salt thereof and one or more pharmaceutically acceptable excipients, carriers, diluents, permeation enhancers, solubilizers and adjuvants. The compounds may be administered alone or in combination with other therapeutic agents (e.g., other antihypertensive drugs, diuretics and the like). Such compositions are prepared in a manner well known in the pharmaceutical art (see, e.g., Remington 's Pharm. Set, Mack Publishing Co., Philadelphia, PA, 17 th Ed., 1985 and Modern Pharm., Marcel Dekker, Inc., 3 rd Ed. (G.S. Banker & C.T. Rhodes, Eds.). The compounds of Formula I may be administered by any of the accepted modes of administration of agents having similar utilities, for example, by oral, parenteral, rectal, buccal, intranasal or transdermal routes. The most suitable route wiU depend on the nature and severity of the condition being treated. Oral aclministration is a preferred route for the compounds of this invention. In making the compositions of this invention, the active ingredient is usually diluted by an excipient or enclosed within such a carrier which can be in the form of a capsule, sachet, paper or other container. When the excipient serves as a chluent, it can be a solid, semi-solid, or liquid material, which acts as a vehicle, carrier or medium for the active ingredient. Thus, the compositions can be in the form of tablets, pills, powders, lozenges, sachets, cachets, elixirs, suspensions, emulsions, solutions, syrups, aerosols (as a solid or in a liquid medium), ointments containing, for example, up to 10% by weight of the active compound, soft and hard gelatin capsules, suppositories, sterile injectable solutions, and sterile packaged powders. Pharmaceutically acceptable salts of the active agents may be prepared using standard procedures known to those skilled in the art of synthetic organic chemistry and described, e.g., by J. March, Advanced Organic Chem. Reactions, Mechanisms and Structure, 4 th Ed. (N.Y.: Wiley-Interscience, 1992). Some examples of suitable excipients include lactose, dextrose, sucrose, sorbitol, mannitol, starches, gum acacia, calcium phosphate, alginates, tragacanth, gelatin, calcium silicate, microcrystalUne cellulose, polyvinylpyrrolidone, cellulose, sterile water, syrup, and methyl cellulose. The formulations can additionally include: lubricating agents such as talc, magnesium stearate, and mineral oil; wetting agents; emulsifying and suspending agents; preserving agents such as methyl- and propylhydroxy-benzoates; sweetening agents; and flavoring agents. The compositions of the invention can be formulated so as to provide quick, sustained or delayed release of the active ingredient after admimstration to the patient by employing procedures known in the art. Controlled release drug delivery systems for oral administration include osmotic pump systems and dissolutional systems containing polymer-coated reservoirs or drug-polymer matrix formulations. Examples of controUed release systems are given in U.S. Patent Nos. 3,845,770; 4,326,525; 4,902,514; and 5,616,345. Another preferred formulation for use in the methods of the present invention employs transdeπnal deUvery devices ("patches"). Such transdermal patches may be used to provide continuous or discontinuous infusion of the compounds of the present invention in controUed amounts. The construction and use of transdermal patches for the delivery of pharmaceutical agents is well known in the art. See, e.g., U.S. Patent Nos. 5,023,252; 4,992,445 and 5,001,139. Such patches may be constructed for continuous, pulsatile, or on demand delivery of pharmaceutical agents. The compositions are preferably formulated in a unit dosage form. The term "unit dosage forms" refers to physically discrete units suitable as unitary dosages for human subjects and other mammals, each unit containing a predetermined quantity of active material calculated to produce the desired therapeutic effect, in association with a suitable pharmaceutical excipient (e.g., a tablet, capsule, ampoule). The active compound is effective over a wide dosage range and is generally administered in a pharmaceuticaUy effective amount. Preferably, for oral administration, each dosage unit contains firom 1-1000 mg of a compound of Formula I, and for parenteral administration, preferably from 0.1 to 600 mg of a compound of Formula I or a pharmaceutically acceptable salt thereof. It will be understood, however, that the amount of the compound actually administered will be determined by a physician, in the Ught of the relevant circumstances, including the condition to be treated, the chosen route of aclministration, the actual compound administered and its relative activity, the age, weight, and response of the individual patient, the severity of the patient's symptoms, and the like. For preparing solid compositions such as tablets, the principal active ingredient is mixed with a pharmaceutical excipient to form a solid preformulation composition containing a homogeneous mixture of a compound of the present invention. When referring to these preformulation compositions as homogeneous, it is meant that the active ingredient is dispersed evenly throughout the composition so that the composition may be reacUly subdivided into equally effective unit dosage forms such as tablets, piUs and capsules. The tablets or pills of the present invention may be coated or otherwise compounded to provide a dosage form affording the advantage of prolonged action. For example, the tablet or pUl can comprise an inner dosage and an outer dosage component, the latter being in the form of an envelope over the former. The two components can be separated by an enteric layer which serves to resist disintegration in the stomach and permit the inner component to pass intact into the duodenum or to be delayed in release. A variety of materials can be used for such enteric layers or coatings, such materials including a number of polymeric acids and mixtures of polymeric acids with such materials as * shellac, cetyl alcohol, and cellulose acetate. The liquid forms in which the novel compositions of the present invention may be incorporated for administration orally or by injection include aqueous solutions, suitably flavored syrups, aqueous or oil suspensions, and flavored emulsions with edible oils such as corn oil, cottonseed oU, sesame oil, coconut oil, or peanut oU, as well as elixirs and similar pharmaceutical vehicles. Compositions for inhalation or insufflation include solutions and suspensions in pharmaceutically acceptable, aqueous or organic solvents, or mixtures thereof, and powders. The Uquid or soUd compositions may contain suitable pharmaceutically acceptable excipients as described supra. Preferably the compositions are administered by the oral or nasal respiratory route for local or systemic effect. Compositions in preferably pharmaceutically acceptable solvents may be nebulized by use of inert gases. Nebulized solutions may be inhaled directly firom the nebulizing device or the nebuUzing device may be attached to a face mask tent, or intermittent positive pressure breathing machine. Solution, suspension, or powder compositions may be administered, preferably orally or nasally, firom devices which deliver the formulation in an appropriate manner. The following formulation examples Ulustrate representative pharmaceutical compositions of the present invention. Formulation Example 1 Hard gelatin capsules containing the following ingredients are prepared: Quantity Ingredient (mg/capsule Active Ingredient 30.0 Starch 305.0 Magnesium stearate 5.0 The above ingredients are mixed and fiUed into hard gelatin capsules in 340 mg quantities. Formulation Example 2 A tablet formula is prepared using the ingredients below: Quantity Ingredient (mg/tablet) Active Ingredient 25.0 Cellulose, microcrystalline 200.0 Colloidal silicon dioxide 10.0 Stearic acid 5.0 The components are blended and compressed to form tablets, each weighing 240 mg. Formulation Example 3 A dry powder inhaler formulation is prepared containing the following components: Ingredient Weight % Active Ingredient 5 Lactose 95 The active ingredient is mixed with the lactose and the mixture is added to a dry powder inhaling appUance. Formulation Example 4 Tablets, each containing 30 mg of active ingredient, are prepared as follows: Quantity Ingredient fmg/tablet. Active Ingredient 30.0 Starch 45.0 Microcrystalline cellulose 35.0 PolyvinylpyrroUdone (as 10% solution in sterile water) 4.0 Sodium carboxymethyl starch 4.5 Magnesium stearate 0.5 Talc 1.0 Total 120.0 The active ingredient, starch and cellulose are passed through a No. 20 mesh U.S. sieve and mixed thoroughly. The solution of polyvinylpyrroUdone is mixed with the resultant powders, which are then passed through a 16 mesh U.S. sieve. The granules so produced are dried at 50°C to 60°C and passed through a 16 mesh U.S. sieve. The sodium carboxymethyl starch, magnesium stearate, and talc, previously passed through a No. 30 mesh U.S. sieve, are then added to the granules which, after mixing, are compressed on a tablet machine to yield tablets each weighing 120 mg. Formulation Example 5 Capsules, each containing 40 mg of medicament are made as follows: Quantity Ingredient (mg/capsule) Active Ingredient 40.0 Starch 109.0 Magnesium stearate 1.0 Total 150.0 The active ingredient, starch, and magnesium stearate are blended, passed through a No. 20 mesh U.S. sieve, and filled into hard gelatin capsules in 150 mg quantities. Formulation Example 6 Suppositories, each containing 25 mg of active ingredient are made as foUows: Ingredient; Ampunt Active Ingredient 25.0 mg Saturated fatty acid glycerides to 2,000.0 mg The active ingredient is passed through a No. 60 mesh U.S. sieve and suspended in the saturated fatty acid glycerides previously melted using the minimum heat necessary. The mixture is then poured into a suppository mold of nominal 2.0 g capacity and aUowed to cool. Formulation Example 7 Suspensions, each containing 50 mg of medicament per 5.0 mL dose are made as follows: Ingredient Amount Active Ingredient 50.0 mg Xanthan gum 4.0 mg Sodium carboxymethyl cellulose (11%) Microcrystalline cellulose (89%) 50.0 mg Sucrose 1.75 g Sodium benzoate 10.0 mg Flavor and Color q.v. Purified water to 5.0 ml The active ingredient, sucrose and xanthan gum are blended, passed through a No. 10 mesh U.S. sieve, and then mixed with a previously made solution of the microcrystalline cellulose and sodium carboxymethyl cellulose in water. The sodium benzoate, flavor, and color are diluted with some of the water and added with stirring. Sufficient water is then added to produce the required volume. Formulation Example 8 Quantity Ingredient .mg/capsule Active Ingredient 15.0 mg Starch 407.0 mg Magnesium stearate 3.0 mg Total 425.0 mg The active ingredient, starch, and magnesium stearate are blended, passed through a No. 20 mesh U.S. sieve, and filled into hard gelatin capsules in 425.0 mg quantities. Formulation Example 9 A subcutaneous formulation may be prepared as foUows: Ingredient Quantity Active Ingredient 5.0 mg Corn Oil 1.0 mL Frequently, it will be desirable or necessary to introduce the pharmaceutical composition to the brain, either directly or indirectly. Direct techniques usually involve placement of a drug delivery catheter into the host's ventricular system to bypass the blood-brain barrier. One such implantable delivery system used for the transport of biological factors to specific anatomical regions of the body is described in U.S. Patent 5,011,472 which is herein incorporated by reference. Synthesis Examples Preparation 1: tert-butyl-3-chlorocarbonyl-4-ethoxybenzoate, 21. (Figure 13A) A. 3-Carbomethoxy-4-ethoxybenzoic acid, prepared as described in BoU. Chim. Farm., 1969, 108, 619, (0.1 mol) is dissolved in CH 2 C1 2 (100 mL) and SOCl 2 (0.2 mol) and DMF (0.1 mL) are added. After 6 hours, the volatile components are removed under vacuum, and the residue is dissolved in CH2CI2 (100 mL) and E-3N (0.2 mol) and tert-BuOH (0.5 mol) are added. After 12 hours, the solution is washed with water, then dried and evaporated. The residue is chromatographed to afford tert-butyl-3-carbomethoxy-4-ethoxybenzoate, 19. B. The compound 19 (0.1 mol) is dissolved in THF (200 mL) and a solution of LiOH, H2O (0.1 mol) in water (200 mL) is added. The progress of the reaction is monitored by thin layer chromatography (tic). When it is complete, the reaction mixture is added to water, and washed with ether. The aqueous solution is acidified with dUute HCl, then extracted with EtOAc. The extract is dried and evaporated, and the residue is chromatographed to afford tert-butyl-3-carboxy-4-ethoxybenzoate, 20. C. The compound 20 (0.1 mol) is dissolved in CH2CI2 (200 mL) and SOCI2 (0.2 mol) and DMF (0.1 mL) are added. After 6 hours the volatile components are removed under vacuum. The residue is redissolved in CH2CI2 (100 mL) and the solvent is again removed under vacuum, to afford the compound 21. Preparation 2: 5-(5-carboxy-2-ethoxy)phenyl-l-methyl-3-propyl-l,6-d_hydro- 7H-pyrazolo[4^-d]pyrimidin-7-one, (3), in which R is methyl and R2 is propyl. (Figure 13B) A. Tert-butyl-3-chlorocarbonyl-4-ethoxybenzoate, 21, (50 mmol) is dissolved in CH2CI2 (100 mL) and the solution is added to a solution of 4-amino-l-methyl-3- propylpyrazole-5-carboxamide, 22, prepared as described in European Patent 463756, (30 mmol), 4-cUmemyl-_minopyridine (0.1 mmol) and Et3N (100 mmol) in CH2CI2 (100 mL) at 0°C. The progress of the reaction is monitored by tic. When it is complete, the reaction mixture is washed with dilute HCl, then dried and evaporated. The residue is chromatographed to afford 4-[(2-ethoxy-5-tert-butoxycarbonyl)benzamido]-l-methyl-3- propylpyrazole-5-carboxamide, 23, in which R\ is methyl and R2 is propyl. B. The above compound 23, (25 mmol) is added in portions to a solution of NaOH (50 mmol) and 30% H2O2 (8 mL) in water (75 mL) and EtOH (10 mL). The mixture is heated at reflux, and the progress of the reaction is monitored by tic. When it is complete, the reaction mixture is cooled and the solvents are removed under vacuum. To the residue is added dilute HCl (30 mL); the mixture is then extracted with CH2CI2, and the extract is washed with aqueous Na2CO3, then is dried and evaporated. The residue is chromatographed tθ -u%rd 5-[(5-tert-butoxycarbonyl-2-ethoxy)phenyl]-l-methyl-3-propyl-l,6-dihydro-7H- pyrazolo[4,3-d]pyrimidin-7-one, 24, in which Rj is methyl and R2 is propyl. C. The above compound 23, (5 mmol) is dissolved in CH2CI2 (50 mL) and TFA (10 mL) is added. The progress of the reaction is monitored by tic. When it is complete, the reaction mixture is evaporated under vacuum, and the residue is chromatographed to afford 5- [(5-c_trboxy-2-etUoxy)phenyl]-l-methyl-3-propyl-l,6-dihydro-7H-pyrazolo[4,3-d]pyrimidm 7-one, 3, in which R\ is methyl and R2 is propyl. Preparation 3 : 5-[2-ethoxy-5-(piperazin-l-ylsulfonyl)phenyl]-l-methyl-3-propyI-l,6- dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one, 5, in which Rj is methyl and R2 is propyl. (Figure 13C) A. 4-(Tert-butoxycarbonyl)piperazine (5 mmol) is added to a suspension of 5- [(2-ethoxy-5-cUorosulfonyl)phenyl]-l-methyl-3-propyl-l,6-dihydro-7H-pyrazolo[4,3- d]pyrimidin-7-one, 1, in which R\ is methyl and R2 is propyl, prepared as described in European Patent 463756, (2 mmol) in EtOH (50 mL). The mixture is stirred at room temperature, and the progress of the reaction is monitored by tic. When it is complete, the solvent is removed under vacuum, and the residue is redissolved in 9:1 CH2C-2:MeOH (100 mL); the solution is washed with aqueous Na2CO3, then dried and evaporated. The residue is chromatographed to afford 5-[2-ethoxy-5-(4-fert-butoxycarbonylpiρerazin-l- ylsulfonyl)phenyl]-l-methyl-3-propyl-l,6-clihydro^ 26, in which R\ is methyl and R2 is propyl. B. The above compound 26 (2 mmol) is dissolved in CH2CI2 (25 mL) and TFA (3 mL) is added. The progress of the reaction is monitored by tic. When it is complete, the solvents are removed under vacuum, and the residue is dissolved in CH2CI2 (50 mL); the solution is washed with dUute N-1HCO3, then dried and evaporated. The residue is chromatographed to afford the title compound 5, in which R\ is methyl and R2 is propyl. Preparation 4: l-(2-am_noethyl)-5-[2-ethoxy-5-(4-methylpiperazin-l- ylsulfonyl)phenyl)]-3-propyl-l,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one, 7, in which n is 2 and R2 is propyl. (Figure 14) A. Ethyl 3-propylpyrazole-5-carboxylate 27, prepared as described in Chem. Pharm. Bull., 1984, 32, 1568, (25 mmol) is dissolved in DMF (20 mL) containing K2CO3 (1 g) and KI (25 mg).2-(Bromoethyl)phthalimide 28, in which n is 2, (30 mmol) is added, and the mixture is heated at 60°. The progress of the reaction is monitored by tic. When it is complete, the mixture is added to water and extracted with EtOAc. The extract is then dried and evaporated. The residue is chromatographed to afford ethyl l-(2-phthaIimidoethyl)-3- propylpyr__zole-5-carboxylate, 29, in which n is 2 and R2 is propyl. B. Using the conditions of Preparation IB, the above ester 29 (10 mmol) is converted into the corresponding acid, l-(2-phthalimidoethyl)-3-propylpyrazole-5-carboxyUc acid, 30, in which n is 2 and R2 is propyl. C. The above compound 30 (10 mmol) is added in portions to a mixture of oleum (5 mL) and iuming nitric acid (5 mL), at 60°C. After 12 hours the mixture is cooled and added to ice. The mixture is extracted with EtOAc, and the extract is dried and evaporated under vacuum, The residue is chromatographed to afford l-(2-phthalimidoethyl)-4-nitro-3- propylpyrazole-5-carboxylic acid, 31, in which n is 2 and R2 is propyl. D. Using the conditions of Preparation 1C, the above acid 31 is converted into the corresponding acid chloride. This compound (10 mmol) is dissolved in acetone, (10 mL) and the solution is added with vigorous stirring to concentrated NH4OH (10 mL). After 1 hour the mixture is diluted with 3 volumes of water, and extracted with EtOAc. The extract is dried and evaporated and the residue is chromatographed to afford l-(2-phthalimidoethyl)-4- nitro-3-propylpyr__zole-5-carboxamide, 32, in which n is 2 and R2 is propyl. E. The above compound 32 (10 mmol) and SnC_2 dihydrate (40 mmol) are suspended in EtOH (30 mL) and the mixture is heated at reflux. The progress of the reaction is monitored by tic. When it is complete, the mixture is cooled and basified by addition of dUute NaOH. The solution is extracted with CH2CI2, and the extract is dried and evaporated. The residue is chromatographed to afford 4-ammo-l-(2-phthalimidoethyl)-3-propylpyrazole- 5-carboxamide, 33, in which n is 2 and R2 is propyl. F. Using the conditions of Preparation 2A, the above compound 33 is reacted with 2-ethoxybenzoyl chloride 34 to afford the compound 4-[(2-ethoxybenzamido]-l-(2- phthalimidoethyl)-3-propylpyrazole-5-carbox--mide, 35 in which n is 2 and R2 is propyl. G. Using the conditions of Preparation 2B, the above compound 35 is converted into the cyclized compound 5- [2-ethoxyphenyl]- 1 -(2-phthalimidoethyl)-3 -propyl- 1 ,6- dihycko-7H-pyr_-Zolo[4,3-d]pyrimidin-7-one, 36, in which n is 2 and R2 is propyl. H. The above compound 36 (10 mmol) is added to chlorosulfonic acid (10 mL) at 0°C under nitrogen. The mixture is maintained at 0°C for 12 hours, and is then added to water (100 mL). The solution is extracted with CH2CI2, and the extract is dried and evaporated to afford 5-[2-ethoxy-5-cMoros fonylphenyl]-l-(2-phthalimidoethyl)-3-propyl-l,6-dihydro-7H- pyr__zolo[4,3-d]pyrimidin-7-one, 37, in which n is 2 and R2 is propyl. I. Using the conditions of Preparation 3 A, the above compound 37 is reacted with N-methylpiperazine to afford 5-[2-ethoxy-5-(4-methylpiperaz_n-l-ylsulfonyl)phenyl]-l- (2-phtlιalintidoemyl)-3-propyl-l,6-dihycho-7H-pyrazolo[4,3-d]pyrinή 38, in which n is 2 and R2 is propyl. J. The above compound 38 (10 mmol) is dissolved in EtOH (10 mL) and hydrazine hydrate (2 mL) is added. The progress of the reaction is monitored by tic. When it is complete, the mixture is added to water and extracted with CH2CI2. The extract is dried and evaporated, and the residue is chromatographed to afford l-(2-aminoethyl)-5-[2-ethoxy- 5-(4-memylpiper_ __in-l-ylsulfonyl)phenyl]-3-propyl-l,6-dihydro-7H-pyrazolo[4,3- d]pyrimidin-7-one, 7, in which n is 2 and R2 is propyl. K. Using the above procedures A-J, but employing in step A different haloalkyl phthalimides 28 in which n is 3-20, there are obtained the corresponding compounds 7 in which n is 3-20. Preparation 5 : 5- [2-ethoxy-5-(4-methy lpiperazm-l -ylsul όnyl)phenyl)] -3-(3- bromopropyl-l,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one, 9, in which n is 3 and Rj is methyl. (Figure 15A) A. Ethyl oxalate (40) (0.1 mol) is dissolved in dry THF (100 mL) at 0°C and sodium ethoxide (0.1 mol) is added in portions with stirring. After 1 hour, a solution of 4- bromobutyroyl chloride (39 in which n is 3), (0.1 mol) in dry THF (50 mL) is added. The mixture is stirred for 24 hours, and then is added to dilute HCl. The aqueous solution is extracted with ether, and the extract is dried and evaporated. The residue is chromatographed to afford the compound ethyl 7-bromo-2,3,5-trioxoheptanoate, 41 in which n is 3. B. The above compound 41 (0.1 mol) is dissolved in EtOH (100 mL) and 85% hydrazine hydrate (0.2 mol) is added. The progress of the reaction is monitored by tic. When it is complete, the mixture is added to water and extracted with CH2CI2; the extract is dried and evaporated and the residue is chromatographed to afford ethyl 3-(3- bromopropyl)pyrazole-5-carboxylate, 42, in which R] is H and n is 3. C. A mixture of the above compound 42 (75 mmol) and dimethyl sulfate (75 mmol) is heated to 90°C for 3 hours. The mixture is then cooled and dissolved in CH2CI2. The solution is washed with dUute Na2CO3, and then dried and evaporated. The residue is chromatographed to afford ethyl 3-(3-bromopropyl)-l-methylpyrazole-5-carboxylate, 42, in which R\ is methyl and n is 3. D. Using the procedures of Preparation IB, 4C, 4D and 4E, the above compound 42 is converted into 4-ammo-3-(3-bromopropyl)-l-methylpyrazole-5-carboxamide, 43, in which R\ is methyl and n is 3. E. Using the conditions of Preparation 2 A, the above compound 43 is reacted with 2-ethoxybenzoyl chloride, and the product thus obtained is subjected to the cyclization conditions of Preparation 2B, to afford 3-(3-bromopropyl)-5-[2-ethoxyphenyl)]-l-methyl-l,6- d^ydro-7H-pyrazolo[4,3-d]pyrimidin-7-one, 44, in which n is 3 and R\ is methyl. F. The above compound 44 is then reacted under the conditions of Preparation 4H to afford the corresponding 5-chlorosulfonyl compound, which is reacted withN-methyl piperazine under the conditions of preparation 3A, to afford the compound 3-(3- bromopropyl)-5-[2-ethoxy-5-(4-memylpiper-_-dn-l-ylsulfonyl)phenyl]-l-memyl-l,6-α^ihydro- 7H-pyr_tzolo[4,3-d]pyirimidin-7-one, 9, in which n is 3 and R\ is methyl. G. Using the above procedures A-F, but employing in Step A different haloalkanoyl chlorides, in which n is 4-20, there are obtained the corresponding compounds 9 in which n is 4-20. Preparation 6: dimeric 3,3'-propyl pyrazolopyrimidine sulfonyl chlorides, 49, in which R is methyl and X is as specified herein. (Figure 15B) A. Using the conditions of Preparation 5 A, one molar equivalent of 1 ,8- di(chlorocarbonyl)octane (45), in which X is (CH2)2 . is reacted with two molar equivalents of ethyl oxalate (40) to afford the dimeric diketoester 46 in which X is (CH2)2- This compound is reacted with hyclrazine using the conditions of Preparation 5B, to afford the bis(propylpyrazole) compound 47 in which X is (CH2)2 and R\ is H, and then methylation, using the procedure of Preparation 5C, affords the compound 47 in which X is (CH2)2- B. The above compound 47 is reacted under the conditions of Preparations 1 A, (ester hydrolysis), 4C, (nitration), 4D (amide formation), 4E (reduction of the nitro group to amino), and 4F/G (acylation with 2-ethoxybenzoyl chloride, followed by cyclization) to afford the dimeric pyr∑tzolopyrimidine 48, in which X is (CH2)2 and R\ is methyl. C. The latter compound is chlorosulfonated, using the procedure of Preparation 4H, to afford the bis (sulfonyl chloride), 49, in which X is (CH2)2 and Rj is methyl. D. Using the above procedures A-C, but employing in Step A different bis-(acid chlorides) 45, in which X is, for example, (CH2) n , where n is 0 to 14, (CH2) n C6H4(CH2) n where n is 0 to 10, and the like, there are obtained the corresponding compounds 49 in which X is (CH2) n , where n is 0 to 14, (CH2) n C6HL4(CH2) n where n is 0 to 10, and the like. Example 1. (Figures 9A and 10A) Homodimers Type 1: sulfonamide-Iinked homodimer 2 in which Link is p- (CH 2 )2OC 6 H 4 O(CH2)2 A. A solution of 2-[4-(2-_ιmmoethoxy)phenoxy]ethylamine 50 (5 mmol) in CH2CI2 (20 mL) is added over a period of 6 hours to a solution of the sulfonyl chloride 1, prepared as described in European Patent 463756, (10 mmol) in CH2CI2 (20 mL) and diisopropylethylamine (20 mmol). The progress of the reaction is monitored by tic. When it is complete, the solution is washed with dilute NaHCO3, then dried and evaporated. The residue is chromatographed to afford the product 51. B. Using the above procedure, but employing different diamines, as described herein, in place of 50, there are obtained the corresponding compounds 2. Example 2. (Figures 9B and 10B) Homodimers Type 2: amide linked homodimer 4 in which Link is p- (CH 2 )2C6H4(CH 2 )2 Rl is methyl and R 2 is propyl. A. A solution of 2-[4-(2-ammoethyl)phenyl]ethylamine 51 (10 mmol) in DMF (10 mL) is added to a solution of 3 (20 mmol) and dicyclohexylcarbodiimide (25 mmol) in DMF (20 mL). The progress of the reaction is monitored by tic. When it is complete, the solution is added to water and extracted with CH2CI2. The extract is dried and evaporated, and the residue is chromatographed to afford the compound 53 in which R\ is methyl and R2 is propyl. B. Using the above procedure, but employing different diamines, as described herein, in place of 51, there are obtained the corresponding linked compounds 4. Example 3. (Figures 9C and IOC) Homodimers Type 3: carbon linked homodimer 6 in which Link is (CH2) Ri is methyl and R2 is propyl. A. 1 ,4-Dibromobutane (10 mmol) and the piperazine 5, (20 mmol) are heated at 60°C in DMF (20 mL) containing K2CO3 (1 g) and KI (25 mg). The progress of the reaction is monitored by tic. When it is complete, the solution is added to water and extracted with CH2CI2. The extract is dried and evaporated, and the residue is chromatographed to afford the compound 6, in which Link is (CH2)4 i is methyl and R2 is propyl. B. Using the same procedure, but employing different dibromo compounds, as described herein, there are obtained the corresponding dimeric compounds 6. Example 4. (Figures 9D and 10D) Homodimers Type 4: amine linked homodimer 8 in which Link is (CH2)s an( * ^2 s propyl. A. Using the procedure of Example 3 A, 1 ,8-bromooctane is reacted with the bromoethyl compound 7, to afford the dimeric compound 56, in which Link is (CH2)s and R2 is propyl. B. Using the above procedure, but employing different dibromo compounds, as described herein, in place of 1,8-dibromooctane, there are obtained the corresponding compounds 8. Example 5. (Figures 9E and 11A) Homodimers Type 5: amine and thioether linked dimers 58 in which Link is (CH2)4 or p-CβHφ A. Using the procedure of Example 4 A, 1 ,4-diaminobutane (57, in which A and B are NH, and Link is (CH2)4) is reacted with the bromo compound 9, in which n is 3, to afford the compound 58, in which A and B are NH, Link is (CH2)4) and n is 3 and R\ is methyl. B. Using the above procedure, but employing different diamines 57, as described herein, the corresponding compounds 10, in which X is NH, are obtained. C. A solution of 1 ,4-dimercaptobenzene (57, in which A and B are S, and Link is p-Cβl ) (5 mmol) in THF (25 mmol) is added to a solution of the bromo compound 9, in which n is 3, (10 mmol) in THF (25 mL) and diisopropyle yl-imine (1 mL) at -20°C under nitrogen. The progress of the reaction is monitored by tic. When it is complete, the mixture is added to water and extracted with CH2CI2. The extract is dried and evaporated, and the residue is chromatographed to afford the compound 58 in which A and B are S, Link is p- CgH4 and n is 3. D. Using the above procedure, but employing different dimercaptans, as described herein, there are obtained the corresponding compounds 10 in which X is S. Example 6. (Figure 9F and 11B) Homodimers Type 6: oxygen-linked dimer 12 in which Link is m-CH2C<jH4CH2, Rj is methyl and R2 is propyl. A. l,3-Di-(Bromomethyl)benzene, (5 mmol) is added to a solution of the phenolic compound 11 (2 mmol) in DMF (25 mL) containing K2CO3 (2 g). The progress of the reaction is monitored by tic. When it is complete, the solution is added to water and extracted with CH2CI2. The extract is dried and evaporated and the residue is chromatographed to afford the compound 12 in which Link is Ri is methyl and R2 is propyl. B. Using the above procedure, but employing different dibromo compounds, as described herein, in place of 59, there are obtained the corresponding compounds 12. Example 7. (Figure 9G and llC) Homodimers Type 7: carbon-linked dimer 60 in which X is (CH2)2 and Rj is methyl. A. The dimeric sulfonyl chloride 49, in which X is (CH2)2 and R is methyl (2 mmol) and N-methylpiperazine (10 mmol) are reacted together under the conditions of Preparation 3 A, to afford the compound 60, in which X is (CH2)2 and R\ is methyl. B. Using the same procedure, but employing different __mines, as described herein, in place of 4-methyl piperazine, and different sulfonyl chlorides 49, there are obtained the corresponding compounds 14. Example 8. (Figures 9H and 12A) Heterodimers Type 1: amide-sulfonamide dimer 62 in which Link is (CH2)2O(CH2)2» Rj is methyl, R2 is propyl. A. Using the procedure of Example 2A, four molar equivalents of l,5-di__mino-3- oxapentane are reacted with one molar equivalent of the carboxylic acid 3, in which R\ is methyl, and R2 is propyl, to afford the intermediate compound 61, in which Link is (CH2)2O(CH2)2 . l is methyl, R2 is propyl. This compound is then reacted with the sulfonyl chloride 1, using the conditions of Preparation 3 A, to afford the compound 62 in which Link is (CH2)2θ(CH2)2 > Rl is methyl, R2 is propyl. B. In a similar manner, by employing different diamines, as described herein, in place of l,5-di_ι___ino-3-oxapentane, there are obtained the corresponding compounds 15. Example 9. (Figures 91 and 12B) Heterodimers Type 2: amine-sulfonamide linked dimer 16 in which Link is (CH2)4, Ri is methyl, R2 is propyl. A. Using the conditions of Preparation 3 A, the sulfonyl chloride 1 is reacted with 4-aminobutanol, 63, in which Link is (CH2)4, and R3 is OH, to afford the compound 64, in which Link is (CH2)4, and R3 is OH. This compound (1 mmol) is dissolved in pyridine (10 mL) and p-toluenesulfonyl chloride (1.1 mmol) is added. The progress of the reaction is monitored by tic. When it is complete, the mixture is added to water and extracted with CH2O2; the extract is dried and evaporated, and the residue is chromatographed to afford the compound 64 in which Link is (CH2)4, Ri is methyl, R2 is propyl and R3 is p- toluenesulfonyloxy. One molar equivalent of this compound is then reacted with one molar equivalent of the amine 5, under the conditions of Preparation 4A, to afford the compound 16, in which Link is (CH2)4, R] is methyl and R2 is propyl. B. Using the above procedures, but employing different amines 63, as described herein, there are obtained the corresponding compounds 16. Example 10. (Figures 9J and 12C) Heterodimers Type 3: amine-linked compound 17 in which Link is P-CH2C6H4CH2. A. Using the conditions of Preparation 3 A, except that the reaction is conducted at room, temperature, equimolar amounts of the .tmine 5, in which Rj is methyl and R2 is propyl, and the dibromide 65 are reacted together to afford the compound 66 in which R\ is methyl, R2 is propyl and Link is P-CH2C6H4CH2. This compound is then reacted as described above, with the amine 7, in which R is methyl and n is 2, to afford the compound 17, in which R is methyl, R2 is propyl, n is 2 and Link is P-CH2C6H4CH2. B. Using the above conditions, but employing different dibromo compounds, as described herein, there are obtained the corresponding compounds 17. Wh e the present invention has been described with reference to the specific embodiments thereof, it should be understood by those skiUed in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process step or steps, to the objective spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended thereto. All of the publications, patent applications and patents cited in this application are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent application or patent was specificaUy and individuaUy indicated to be incorporated by reference in its entirety. TABLE 1: Phosphodiesterase Isoenzymes TABLE 2. Structure of Various PDE V Ligands Zaprinast romboβmbolism, Clinical NM-702, Nissan Chemical E-4021 Sildenafil Table 2. Structure of Various PDE V Ligands (Continued) Pfizer Pfizer Glaxo Weilcome SA Tanabe Bayer AG Glaxo Wellcome pic

Claims: What is claimed is: 1. A multibinding compound comprising 2 to 10 ligands which may be the same or different and which are covalently attached to a linker or linkers, which may be the same or different, each of said Ugands comprising a Ugand domain capable of binding to a phosphodiesterase V (PDE V) enzyme. 2. The multibinding compound of Claim 1 wherein said ligand is selected from the group consisting of dipyrimadole, IBMX, NM-702, SCH51866, Sildenafil, E-4021, Zaprinast, pyrazolo[4,5-d] pyrimidin-7-one derivatives, tWenopyrimidine derivatives, and sulfonylamide derivatives. 3. The multibinding compound of Claim 1 which has 2 Ugands. 4. The multibinding compound represented by Formula I: (L) p (X)q I where each L is a Ugand that may be the same or different at each occurrence; X is a linker that may be the same or different at each occurrence; p is an integer of from 2 to 10; and q is an integer of from 1 to 20; wherein each of said Ugands comprises a Ugand domain capable of binding to a PDE V enzyme. 5. The multibinding compound of Claim 4 wherein q is less than p. 6. The multibinding compound of Claim 4 wherein said Ugand is selected firom the group consisting of dipyrimadole, IBMX, NM-702, SCH51866, Sildenafil, E-4021, Zaprinast, pyrazolo[4,5-d] pyrimidin-7-one derivatives, t enopyrimidine derivatives, and sulfonylamide derivatives. 7. The multibinding compound of Claim 4 wherein q is 2 map is 1. 8. A pharmaceutical composition comprising a pharmaceutically acceptable excipient and a therapeutically effective amount of one or more multibinding compounds, or pharmaceutically acceptable salts thereof, comprising 2 to 120 Ugands which may be the same or different and which are covalently attached to a linker or linkers, which may be the same or different, each of said ligands comprising a ligand domain capable of binding to PDE V enzyme mediating mammalian diseases or conditions, thereby modulating the diseases or conditions. 9. The pharmaceutical composition of Claim 8 wherein said ligand is selected from the group consisting of dipyrimadole, IBMX, NM-702, SCH51866, Sildenafil, E- 4021, Zaprinast, pyrazolo[4,5-d] pyrimidin-7-one derivatives, tWenopyrimidine derivatives, and sulfonylamide derivatives. 10. The pharmaceutical composition of Claim 8 which has 2 ligands. 11. A pharmaceutical composition comprising a pharmaceutically acceptable excipient and a therapeutically effective amount of one or more multibinding compounds represented by Formula I: (L) p (X)q and pharmaceutically acceptable salts thereof; where each L is a ligand that may be the same or different at each occurrence; X is a linker that may be the same or different at each occurrence; p is an integer of from 2 to 10; and q is an integer of from 1 to 20; wherein each of said Ugands comprises a ligand domain capable of binding to a PDE V enzyme mediating mammalian diseases or conditions, thereby modulating the diseases or conditions. 12. The pharmaceutical composition of Claim 11 wherein said ligand is selected from the group consisting of dipyrimadole, IBMX, NM-702, SCH51866, SUdenafil, E- 4021, Zaprinast, pyrazolo[4,5-d] pyrimidin-7-one derivatives, tMenopyrimidine derivatives, and sulfonylamide derivatives. 13. The pharmaceutical composition of Claim 11 which has 2 Ugands. 14. A method for modulating the activity of a phosphodiesterase V (PDE V) enzyme in a biologic tissue, which method comprises contacting a tissue having PDE V enzyme with a multibinding compounds, or a pharmaceutically acceptable salt thereof, under conditions sufficient to produce a change in the activity of the enzyme in said tissue, wherein the multibinding compounds comprises 2 to 10 ligands which may be the same of different and which are covalently attached to a linker or linkers, which may be the same or different, each of said ligands comprising a ligand domain capable of binding to a PDE V enzyme. 15. The method of Claim 14 wherein said Ugand is selected from the group consisting of dipyrimadole, IBMX, NM-702, SCH51866, SUdenafil, E-4021, Zaprinast, pyrazolo[4,5-d] pyrimidin-7-one derivatives, tMenopyrimidine derivatives, and sulfonylamide derivatives. 16. The method of Claim 14 wherein the multibinding compound has 2 Ugands. 17. A method for treating a disease or condition in a mammal resulting from an activity of a phosphodiesterase V (PDE V) enzyme, which method comprises administering to said mammal a therapeutically effective amount of a pharmaceutical composition comprising a pharmaceutically acceptable excipient and one or more multibinding compounds, or pharmaceutically acceptable salts thereof, comprising 2 to 10 ligands which may be the same or different and which are covalently attached to a linker or linkers, which may be the same or different, each of said ligands comprising a Ugand domain capable of binding to a PDE V enzyme of a cell mediating mammalian diseases or conditions. 18. The method of Claim 17 wherein said Ugand is selected from the group consisting of dipyrimadole, IBMX, NM-702, SCH51866, SUdenafil, E-4021, Zaprinast, pyrazolo[4,5-d] pyrimidin-7-one derivatives, tMenopyrimidine derivatives, and sulfonylamide derivatives. 19. The method of Claim 17 wherein the multibinding compound has 2 ligands. 20. A method for treating a disease or condition in a mammal resulting from an activity of PDE V enzyme, which method comprises _tdministering to said mammal a therapeutically effective amount of a pharmaceutical composition comprising a pharmaceutically acceptable excipient and one or more multibinding compounds represented by Formula I: (L) p (X)q (I ) and pharmaceuticaUy acceptable salts thereof; where each L is a Ugand that may be the same or different at each occurrence; X is a linker that may be the same or different at each occurrence; p is an integer of from 2 to 10; and q is an integer of from 1 to 20; wherein each of said Ugands comprises a ligand domain capable of binding to a PDE V enzyme a cell mediating mammalian diseases or conditions. 21. The method of Claim 20 wherein said Ugand is selected from the group consisting of dipyrimadole, IBMX, NM-702, SCH51866, SUdenafil, E-4021, Zaprinast, pyrazolo[4,5-d] pyrimidin-7-one derivatives, tMenopyrimidine derivatives, and sulfonylamide derivatives. 22. The method of Claim 20 wherein the multibinding compound has 2 ligands. 23. A method for identifying multimeric ligand compounds possessing multibinding properties for PDE V enzymes, wMch method comprises: (a) identifying a ligand or a mixture of Ugands wherein each ligand contains at least one reactive functionality; (b) identifying a library of linkers wherein each linker in said library comprises at least two functional groups having complementary reactivity to at least one of the reactive functional groups of the ligand; (c) preparing a multimeric ligand compound library by combining at least two stoicMometric equivalents of the Ugand or mixture of ligands identified in (a) with the library of linkers identified in (b) under conditions wherein the complementary functional groups react to form a covalent linkage between said linker and at least two of said ligands; and (d) assaying the multimeric ligand compounds produced in the Ubrary prepared in (c) above to identify multimeric ligand compounds possessing multibinding properties. 24. A method for identifying multimeric Ugand compounds possessing multibinding properties for PDE V enzymes, wMch method comprises: (a) identifying a library of ligands wherein each Ugand contains at least one reactive functionaUty; (b) identifying a linker or mixture of linkers wherein each linker comprises at least two functional groups having complementary reactivity to at least one of the reactive functional groups of the Ugand; (c) preparing a multimeric Ugand compound library by combining at least two stoicMometric equivalents of the Ubrary of ligands identified in (a) with the linker or mixture of linkers identified in (b) under conditions wherein the complementary functional groups react to form a covalent linkage between said Imker and at least two of said Ugands; and (d) assaying the multimeric ligand compounds produced in the library prepared in (c) above to identify multimeric Ugand compounds possessing multibinding properties. 25. The method according to Claim 23 or 24 wherein the preparation of the multimeric ligand compound Ubrary is acMeved by either the sequential or concurrent combination of the two or more stoicMometric equivalents of the Ugands identified in (a) with the linkers identified in (b). 26. The method according to Claim 25 wherein the multimeric ligand compounds comprising the multimeric Ugand compound Ubrary are dimeric. 27. The method according to Claim 26 wherein the dimeric Ugand compounds comprising the dimeric Ugand compound Ubrary are heterodimeric. 28. The method according to Claim 27 wherein the heterodimeric Ugand compound Ubrary is prepared by sequential addition of. a first and second Ugand. 29. The method according to Claim 23 or 24 wherein, prior to procedure (d), each member of the multimeric ligand compound library is isolated from the Ubrary. 30. The method according to Claim 29 wherein each member of the library is isolated by preparative liquid cMomatography mass spectrometry (LCMS). 31. The method according to Claim 23 or 24 wherein the linker or linkers employed are selected from the group comprising flexible linkers, rigid linkers, hydrophobic linkers, hydrophiUc linkers, linkers of different geometry, acidic linkers, basic tinkers, linkers of different polarization and ampMp lic linkers. 32. The method according to Claim 31 wherein the linkers comprise linkers of different chain length and/or having different complementary reactive groups. 33. The method according to Claim 32 wherein the linkers are selected to have different linker lengths ranging from about 2 to lOOA. 34. The method according to Claim 23 or 24 wherein the Ugand or mixture of Ugands is selected to have reactive functionality at different sites on said Ugands. 35. The method according to Claim 34 wherein said reactive functionality is selected from the group consisting of carboxylic acids, carboxylic acid halides, carboxyl esters, amines, halides, pseudohaUdes, isocyanates, vinyl unsaturation, ketones, aldehydes, t ols, alcohols, anhydrides, boronates, and precursors thereof wherein the reactive functionality on the ligand is selected to be complementary to at least one of the reactive groups on the linker so that a covalent linkage can be formed between the linker and the Ugand. 36. The method according to Claim 23 or Claim 24 wherein the multimeric ligand compound library comprises homomeric ligand compounds. 37. The method according to Claim 23 or Claim 24 wherein the multimeric Ugand compound library comprises heteromeric ligand compounds. 38. A library of multimeric Ugand compounds wMch may possess multivalent properties for PDE V enzymes, wMch Ubrary is prepared by the method comprising: (a) identifying a ligand or a mixture of ligands wherein each Ugand contains at least one reactive functionality; (b) identifying a library of linkers wherein each linker in said Ubrary comprises at least two functional groups having complementary reactivity to at least one of the reactive functional groups of the ligand; and (c) preparing a multimeric ligand compound library by combining at least two stoicMometric equivalents of the ligand or mixture of ligands identified in (a) with the library of linkers identified in (b) under conditions wherein the complementary functional groups react to form a covalent linkage between said linker and at least two of said ligands. 39. A library of multimeric ligand compounds wMch may possess multivalent properties for PDE V enzymes, wMch library is prepared by the method comprismg: (a) identifying a Ubrary of Ugands wherein each ligand contains at least one reactive functionaUty; (b) identifying a linker or mixture of linkers wherein each linker comprises at least two functional groups having complementary reactivity to at least one of the reactive functional groups of the ligand; and (c) preparing a multimeric ligand compound library by combining at least two stoicMometric equivalents of the library of Ugands identified in (a) with the linker or mixture of linkers identified in (b) under conditions wherein the complementary functional groups react to form a covalent linkage between said linker and at least two of said Ugands. 40. The library according to Claim 38 or Claim 39 wherein the linker or linkers employed are selected from the group comprising flexible linkers, rigid tinkers, hydrophobic linkers, hydropMlic linkers, tinkers of different geometry, acidic linkers, basic linkers, linkers of different polarization and ampMpMlic linkers. 41. The library according to Claim 40 wherein the linkers comprise linkers of different chain length and/or having different complementary reactive groups. 42. The Ubrary according to Claim 41 wherein the linkers are selected to have different linker lengths ranging from about 2 to 100A. 43. The library according to Claim 38 or 39 wherein the ligand or mixture of ligands is selected to have reactive functionality at different sites on said Ugands. 44. The library according to Claim 43 wherein said reactive functionaUty is selected from the group consisting of carboxylic acids, carboxylic acid halides, carboxyl esters, amines, halides, pseudohalides, isocyanates, vinyl unsaturation, ketones, aldehydes, tMols, alcohols, anhydrides, boronates, and precursors thereof wherein the reactive functionality on the ligand is selected to be complementary to at least one of the reactive groups on the linker so that a covalent linkage can be formed between the linker and the Ugand. 45. The library according to Claim 38 or Claim 39 wherein the multimeric ligand compound Ubrary comprises homomeric ligand compounds. 46. The library according to Claim 38 or Claim 39 wherein the multimeric ligand compound library comprises heteromeric ligand compounds. 47. An interative method for identifying multimeric Ugand compounds possessing multibinding properties for PDE V enzymes, wMch method comprises: (a) preparing a first coUection or iteration of multimeric compounds wMch is prepared by contacting at least two stoicMometric equivalents of the ligand or mixture of Ugands wMch target a receptor with a linker or mixture of linkers wherein said Ugand or mixture of Ugands comprises at least one reactive functionality and said tinker or mixture of linkers comprises at least two functional groups having complementary reactivity to at least one of the reactive functional groups of the ligand wherein said contacting is conducted under conditions wherein the complementary functional groups react to form a covalent linkage between said linker and at least two of said Ugands; (b) assaying said first coUection or iteration of multimeric compounds to assess wMch if any of said multimeric compounds possess multibinding properties; (c) repeating the process of (a) and (b) above until at least one multimeric compound is found to possess multibinding properties; (d) evaluating what molecular constraints imparted or are consistent with imparting multibinding properties to the multimeric compound or compounds found in the first iteration recited in (a)- (c) above; (e) creating a second coUection or iteration of multimeric compounds wMch elaborates upon the particular molecular constraints imparting multibinding properties to the multimeric compound or compounds found in said first iteration; (f) evaluating what molecular constraints imparted or are consistent with imparting enhanced multibmding properties to the multimeric compound or compounds found in the second coUection or iteration recited in (e) above; (g) optionally repeating steps (e) and.(f) to further elaborate upon said molecular constraints. 48. The method according to Claim 47 wherein steps (e) and (f) are repeated from 2-50 times. 49. The method according to Claim 47 wherein steps (e) and (f) are repeated from 5-50 times.

Inventors: GRIFFIN JOHN H, KLEIN UWE, ZHU YAN, GRIFFIN, JOHN, H., KLEIN, UWE, ZHU, YAN
Applicants: ADVANCED MEDICINE INC, GRIFFIN JOHN H, KLEIN UWE, ZHU YAN, ADVANCED MEDICINE, INC., GRIFFIN, JOHN, H., KLEIN, UWE, ZHU, YAN
Application year: 1999
Main classification: A61K38
IPC codes: A01N57, A61K31, A61K38, A61K39, A61K47, A61K51, A61P31, A61P43, C07B61, C07C233, C07C237, C07C271, C07C275, C07C335, C07D207, C07D211, C07D215, C07D233, C07D235, C07D263, C07D265, C07D401, C07D405, C07D413, C07D453, C07D471, C07D473, C07D475, C07D477, C07D487, C07D493, C07D495, C07D498, C07D499, C07D501, C07D519, C07H15, C07H17, C07H19, C07K2, C07K4, C12N9, C12P19, C12Q1, C40B30, C40B40, G01N33, G01N37