Patent Publication Number: US-2015086480-A1

Title: Heteroaryl inhibitors of pde4

Description:
This application claims the benefit of U.S. Provisional Application No. 61/882,808, filed Sep. 26, 2013, the disclosure of which is hereby incorporated by reference as if written herein in its entirety. 
    
    
     Disclosed herein are new bicyclic heteroaryl compounds and compositions and their application as pharmaceuticals for the treatment, of disease. Methods of inhibition of phosphodiesterase 4 (PDE4) activity in a human or animal subject are also provided for the treatment diseases such as inflammatory diseases and other diseases involving elevated levels of cytokines and proinflammatory mediators. 
     Chronic inflammation is a multi-factorial disease complication characterized by activation of multiple types of inflammatory cells, for example cells of lymphoid lineage (including T lymphocytes) and myeloid lineage (including granulocytes, macrophages, and monocytes). Proinflammatory mediators, including cytokines, such as tumor necrosis factor (TNF) and interleukin-1 (IL-1), are produced by these activated cells. Accordingly, an agent that suppresses the activation of these cells, or their production of proinflammatory cytokines, would be useful in the therapeutic treatment of inflammatory diseases and other diseases involving elevated levels of cytokines. 
     Cyclic adenosine monophosphate (cAMP) is a second messenger that mediates the biologic responses of cells to a wide range of extracellular stimuli. When the appropriate agonist binds to specific cell surface receptors, adenylate cyclase is activated to convert adenosine triphosphate (ATP) to cAMP. It is theorized that the agonist induced actions of cAMP within the cell are mediated predominately by the action of cAMP-dependent protein kinases. The intracellular actions of cAMP are terminated by either a transport of the nucleotide to the outside of the cell, or by enzymatic cleavage by cyclic nucleotide phosphodiesterases (PDEs), which hydrolyze the 3′-phosphodiester bond to form 5′-adenosine monophosphate (5′-AMP). 5′-AMP is an inactive metabolite. 
     The superfamily of PDEs is subdivided into two major classes, class I and class II, which have no recognizable sequence similarity. Class I includes all known mammalian PDEs and is comprised of 11 identified families that are products of separate genes. Some PDEs are highly specific for hydrolysis of cAMP (PDE4, PDE7, PDE8), some are highly cGMP-specific (PDE5, PDE6, PDE9), and some have mixed specificity (PDE1, PDE2, PDE3, PDE10, PDE11). All of the characterized mammalian PDEs are dimeric, but the importance of the dimeric structure for function in each of the PDEs is unknown. 
     The PDE4 subfamily is comprised of 4 members: PDE4A, PDE4B, PDE4C, and PDE4D. These enzymes possess N-terminal regulatory domains that presumably mediate dimerization, which results in optimally regulated PDE activity. In addition, activity is regulated via cAMP-dependent protein kinase phosphorylation sites in this upstream regulatory domain. PDE4 enzymes are broadly expressed and distributed. 
     Elevated levels of cAMP in human myeloid and lymphoid lineage cells are associated with the suppression of cell activation. The intracellular enzyme family of PDEs, therefore, regulates the level of cAMP in cells. PDE4 is a predominant PDE isotype in these cells, and is a major contributor to cAMP degradation. Accordingly, the inhibition of PDE function would prevent the conversion of cAMP to the inactive metabolite 5′-AMP and, consequently, maintain higher cAMP levels, and, accordingly, suppress cell activation. 
     PDE4 inhibitors have been shown to inhibit production of TNFα and partially inhibit IL-1β release by monocytes (see Semmler et al.,  Int. J. Immunopharmacol.,  15, pp. 409-413, (1993); Molnar-Kimber et al.,  Mediators of Inflammation,  1, pp. 411-417, (1992)). PDE4 inhibitors also have been shown to inhibit the production of superoxide radicals from human polymorphonuclear leukocytes (see Verghese et al.,  J. Mol. Cell. Cardiol.,  21 (Suppl. 2), S61 (1989); Nielson et al.,  J. Allergy Immunol.,  86, pp. 801-808, (1990)); to inhibit the release of vasoactive amines and prostanoids from human basophils (see Peachell et al.,  J. Immunol.,  148, pp. 2503-2510, (1992)); to inhibit respiratory bursts in eosinophils (see Dent et al.,  J. Pharmacol.,  103, pp. 1339-1346, (1991)); and to inhibit the activation of human T-lymphocytes (see Robicsek et al.,  Biochem. Pharmacol.,  42, pp. 869-877, (1991)). 
     Inflammatory cell activation and excessive or unregulated cytokine (e.g., TNFα and IL-1β) production are implicated in allergic, autoimmune, and inflammatory diseases and disorders, discussed herein. 
     Additionally, several properties of TNFα, such as stimulation of collagenases, stimulation of angiogenesis in vivo, stimulation of bone resorption, and an ability to increase the adherence of tumor cells to endothelium, are consistent with a role for TNF in the development and metastatic spread of cancer in the host. TNFα recently has been directly implicated in the promotion of growth and metastasis of tumor cells (see Orosz et al.,  J. Exp. Med.,  177, pp. 1391-1398, (1993)). 
     Investigators have shown considerable interest in the use of PDE4 inhibitors as anti-inflammatory agents. Early evidence indicates that PDE4 inhibition has beneficial effects on a variety of inflammatory cells such as monocytes, macrophages, T-cells of the Th-1 lineage, and granulocytes. The synthesis and/or release of many proinflammatory mediators, such as cytokines, lipid mediators, superoxide, and biogenic amines, such as histamine, have been attenuated in these cells by the action of PDE4 inhibitors. The PDE4 inhibitors also affect other cellular functions including T-cell proliferation, granulocyte transmigration in response to chemotoxic substances, and integrity of endothelial cell junctions within the vasculature. 
     The design, synthesis, and screening of various PDE4 inhibitors have been reported. Methylxanthines, such as caffeine and theophylline, were the first PDE inhibitors discovered, but these compounds are nonselective with respect to which PDE is inhibited. The drug rolipram, an antidepressant agent, was one of the first reported specific PDE4 inhibitors, with a reported IC 50  of about 200 nM with respect to inhibiting recombinant human PDE4. 
     Investigators have continued to search for PDE4 inhibitors that are more selective with respect to inhibiting PDE4, that have a lower IC 50  than rolipram, and that avoid the undesirable central nervous system (CNS) side effects, such as retching, vomiting, and sedation, associated with the administration of rolipram. In addition, several companies are now undertaking clinical trials of other PDE4 inhibitors. However, problems relating to efficacy and adverse side effects, such as emesis and central nervous system disturbances, remain unsolved. 
     Accordingly, compounds that selectively inhibit PDE4, isoforms PDE4D, or a PDE4 isoform containing a UCR1 activating mutation (such as PDE4D7 containing UCR1 activating mutation S54D, PDE4D7*), and that reduce or eliminate the adverse side effects associated with prior PDE4 inhibitors, would be useful in the treatment of allergic and inflammatory diseases, and other diseases associated with excessive or unregulated production of cytokines, such as TNF. In addition, selective PDE4 inhibitors would be useful in the treatment of diseases that would benefit from elevated cAMP levels or reduced PDE4 function in a particular target tissue. 
     Compounds and pharmaceutical compositions, certain of which have been found to inhibit PDE4 have been discovered, together with methods of synthesizing and using the compounds including methods for the treatment of PDE4-mediated diseases in a patient by administering the compounds, as well as methods of use as imaging agents for positron emission imaging (e.g., positronemission tomography (PET) imaging) used in the diagnosis and monitoring of diseases in a patient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows inhibition of the cAMP hydrolysis by human phosphodiesterase Type 4D (PDE4D) by increasing concentrations of Example 1. PDE4D inhibition is measured by the method of Burgin et al, (2010) Design of Phosphodiesterase Type 4D (PDE4D) Allosteric Modulators for Cognition with Improved Safety.  Nature Biotechnology  28:63-70. Each concentration of Example 1 was tested in duplicate (round symbols). One-half maximal inhibition of PDE4D occurs at a concentration of Example 1 equal to 0.15 nM. 
     
    
    
     Accordingly, provided herein are compounds of structural Formula I: 
     
       
         
         
             
             
         
       
     
     or a salt thereof, wherein: 
     X is chosen from O, NH, NR 3 , and C(R 3 ) 2 ; 
     R 1  and R 2  are each independently chosen from aryl, heteroaryl, heterocycloalkyl, and cycloalkyl, any of which may be optionally substituted; 
     each R 3  is independently chosen from hydrogen and lower alkyl. 
     In certain embodiments, X is CH 2 . 
     In certain embodiments, R 1  is optionally substituted aryl. 
     In certain embodiments, R 1  is optionally substituted phenyl. 
     In certain embodiments, R 1  is phenyl optionally substituted with one or two substituents chosen from halogen, lower alkyl, hydroxyl, lower hydroxyalkyl, cyano, urea, amido, methoxy, trifluoromethyl, trifluoromethoxy, COOH, and NO 2 . 
     In certain embodiments, R 1  is phenyl para-substituted with fluoro. 
     In certain embodiments, R 1  is phenyl para-substituted with  18 F. 
     In certain embodiments, R 2  is optionally substituted aryl. 
     In certain embodiments, R 2  is optionally substituted phenyl. 
     In certain embodiments, R 2  is phenyl optionally substituted with one or two substituents chosen from halogen, lower alkyl, hydroxyl, cyano, methoxy, trifluoromethyl, trifluoromethoxy, and NO 2 . 
     In certain embodiments, R 2  is phenyl meta-substituted with NO 2 . 
     In certain embodiments, R 2  is optionally substituted heteroaryl. 
     In certain embodiments, R 2  is optionally substituted thiophene. 
     In certain embodiments, R 2  is chloro-thiophene. 
     Also provided are embodiments wherein any of embodiment above in paragraphs [017]-[030] above may be combined with any one or more of these embodiments, provided the combination is not mutually exclusive or redundant. As used herein, two embodiments are “mutually exclusive” when one is defined to be something which cannot overlap with the other. For example, an embodiment wherein X is CH 2  is mutually exclusive with an embodiment wherein X is NR 3 . However, an embodiment wherein R 2  is optionally substituted aryl is not mutually exclusive with an embodiment wherein R 1  is optionally substituted aryl, and this an embodiment wherein both wherein R 2  is optionally substituted aryl and R 1  is optionally substituted aryl is contemplated. As used herein, two embodiments are “redundant” when one recited group wholly encompasses the other. For example, “R 1  is optionally substituted aryl” wholly encompasses “R 1  is phenyl para-substituted with fluoro,” and the two would not make sense combined with each other in an embodiment. 
     For example, in certain embodiments: 
     X is C(R 3 ) 2 ; 
     R 1  is phenyl optionally substituted with one or two substituents chosen from halogen, lower alkyl, hydroxyl, lower hydroxyalkyl, cyano, urea, amido, methoxy, trifluoromethyl, trifluoromethoxy, COOH, and NO 2 ; 
     R 2  is phenyl optionally substituted with one or two substituents chosen from halogen, lower alkyl, hydroxyl, cyano, methoxy, trifluoromethyl, trifluoromethoxy, and NO 2 ; and 
     each R 3  is independently chosen from hydrogen and lower alkyl. 
     In further embodiments: 
     X is CH 2 ; 
     R 1  is phenyl para-substituted with fluoro; and 
     R 2  is phenyl meta-substituted with NO 2 . 
     Also provided is a compound chosen from the Examples disclosed herein. In certain embodiments, the compound is Example 1. In certain embodiments, the compound is Example 2. 
     Also provided is a compound as disclosed herein for use in the manufacture of a medicament for the treatment of a PDE4-mediated disease. 
     In certain embodiments, the PDE4 is PDE4D. 
     Also provided is a compound as disclosed herein for use in the manufacture of a medicament for the modulation of a PDE4-mediated function, wherein: 
     the PDE4 is PDE4D; 
     the modulation is enhancement; and 
     the function is cognition. 
     Also provided is the use of a compound as disclosed herein for the treatment of a PDE4-mediated disease. 
     In certain embodiments, the PDE4 is PDE4D. 
     The use of a compound as disclosed herein for the modulation of a PDE4-mediated function, wherein: 
     the PDE4 is PDE4D; 
     the modulation is enhancement; and 
     the function is cognition. 
     Also provided is the use of a compound as disclosed herein as a medicament for the treatment of a PDE4-mediated disease. 
     Also provided is a pharmaceutical composition comprising a compound as disclosed herein, together with a pharmaceutically acceptable carrier. 
     In certain embodiments, additionally comprising another therapeutic agent. 
     In certain embodiments, the additional therapeutic agent is an antidepressant. 
     In certain embodiments, the pharmaceutical composition is formulated as a tablet or capsule. 
     Also provided is a method of treatment of a PDE4-mediated disease in a subject comprising the administration of a therapeutically effective amount of a compound as disclosed herein. 
     In certain embodiments, the PDE4 is PDE4D. 
     Also provided is a method of modulation of a PDE4-mediated function in a subject comprising the administration of a therapeutically effective amount of a compound as disclosed herein, wherein: 
     the PDE4 is PDE4D; 
     the modulation is enhancement; and 
     the function is cognition. 
     Also provided is a method for achieving an effect in a patient comprising the administration of a therapeutically effective amount of a compound as disclosed herein to a patient, wherein the effect is cognition enhancement. 
     Also provided is a method of inhibiting PDE4 comprising contacting PDE4 with a compound as disclosed herein. 
     The present invention also relates to a method of inhibiting at least one PDE4 function comprising the step of contacting the PDE4 with a compound of Formula I, as described herein. The cell phenotype, cell proliferation, activity of PDE4, change in biochemical output produced by active PDE4, expression of PDE4, or binding of PDE4 with a natural binding partner may be monitored. Such methods may be modes of treatment of disease, biological assays, cellular assays, biochemical assays, or the like. 
     Also provided herein is a method of treatment of a PDE4-mediated disease comprising the administration of a therapeutically effective amount of a compound as disclosed herein, or a salt thereof, to a patient in need thereof. 
     In certain embodiments, the disease is chosen from depression, depression secondary to illness, Alzheimer&#39;s disease, and traumatic brain injury. 
     Also provided herein is a compound as disclosed herein for use as a medicament. 
     Also provided is the use of a compound as disclosed herein as a medicament for the treatment of a PDE4-mediated disease. 
     Also provided is a compound as disclosed herein for use in the manufacture of a medicament for the treatment of a PDE4-mediated disease. 
     Also provided is the use of a compound as disclosed herein for the treatment of a PDE4-mediated disease. 
     Also provided herein is a method of inhibition of PDE4 comprising contacting PDE4 with a compound as disclosed herein, or a salt thereof. 
     Also provided herein is a method for achieving an effect in a patient comprising the administration of a therapeutically effective amount of a compound as disclosed herein, or a salt thereof, to a patient, wherein the effect is chosen from cognition enhancement. 
     Compounds of the present invention may be selective amongst the PDE4 isoforms PDE4A, PDE4B, PDE4C, and PDE4D in various ways. For example, compounds described herein may be selective for PDE4D over the other two isoforms, be a pan-inhibitor of all the isoforms, or be selective for only one isoform. In certain embodiments, compounds of the present invention may be selective for PDE4B over other isoforms. 
     In certain embodiments, the PDE4 is PDE4D. 
     In certain embodiments, the PDE4B-mediated disease is chosen from depression and depression secondary to illness. 
     Also provided is a method of modulation of a PDE4-mediated function in a subject comprising the administration of a therapeutically effective amount of a compound as disclosed herein. 
     In certain embodiments, the PDE4 is PDE4D. 
     In certain embodiments, the modulation is enhancement. 
     In certain embodiments, the function is cognition. 
     Also provided is a method of positron emission tomography (PET) imaging of a subject which employs a radiolabeled compound as disclosed herein as an imaging agent. 
     In certain embodiments, the method of PET imaging comprises:
         a) administering a radiolabeled compound as disclosed herein to a patient; and   b) imaging the subject using PET.       

     Also provided is a method of a diagnosing a PDE4-mediated disease in a patient which employs a radiolabeled compound as disclosed herein as a positron emission tomography (PET) imaging agent. 
     In certain embodiments, the method of diagnosing comprises:
         a) administering a radiolabeled compound as disclosed herein to a patient;   b) determining at least one of the presence, amount, or location of the compound; and   c) correlating the result of the determination made in (ii) with the presence, absence, or state of the disease or disorder.       

     Also provided is a method of monitoring therapy of a PDE4-mediated disease in a patient which employs a radiolabeled compound as disclosed herein as a positron emission tomography (PET) imaging agent. 
     In certain embodiments, the method of monitoring comprises:
         a) administering an amount of a radiolabeled compound as disclosed herein to a patient;   b) determining at least one of the presence, amount, or location of the compound;   c) correlating the result of the determination made in (ii) with the presence, absence, or state of the disease or disorder.       

     In certain embodiments, the method of monitoring further comprises:
         d) administering first, a therapeutically effective amount of a compound as disclosed herein to the patient;   e) administering a second amount of a radiolabeled compound as disclosed herein to a patient;   f) determining at least one of the presence, amount, or location of the compound;   g) correlating the result of the determination made in (ii) with the presence, absence, or state of the disease or disorder; and   h) administering a second therapeutically effective amount of a compound as disclosed herein to the patient.       

     Also provided is the use of a radiolabeled compound as disclosed herein in positron emission tomography (PET) imaging. 
     In certain embodiments of any of the foregoing embodiments where a radiolabeled compound is used, the radiolabeled compound comprises  18 F. 
     In further embodiments of any of the foregoing embodiments where a radiolabeled compound is used, the compound is Example 2. 
     Also provided is a pharmaceutical composition comprising a compound as disclosed herein, together with a pharmaceutically acceptable carrier. 
     In certain embodiments, the pharmaceutical composition is formulated for oral administration. 
     As used herein, the terms below have the meanings indicated. 
     When ranges of values are disclosed, and the notation “from n 1  . . . to n 2 ” or “between n 1  . . . and n 2 ” is used, where n 1  and n 2  are the numbers, then unless otherwise specified, this notation is intended to include the numbers themselves and the range between them. This range may be integral or continuous between and including the end values. By way of example, the range “from 2 to 6 carbons” is intended to include two, three, four, five, and six carbons, since carbons come in integer units. Compare, by way of example, the range “from 1 to 3 μM (micromolar),” which is intended to include 1 μM, 3 μM, and everything in between to any number of significant figures (e.g., 1.255 μM, 2.1 μM, 2.9999 μM, etc.). When n is set at 0 in the context of “0 carbon atoms”, it is intended to indicate a bond or null. 
     The term “about,” as used herein, is intended to qualify the numerical values which it modifies, denoting such a value as variable within a margin of error. When no particular margin of error, such as a standard deviation to a mean value given in a chart or table of data, is recited, the term “about” should be understood to mean that range which would encompass the recited value and the range which would be included by rounding up or down to that figure as well, taking into account significant figures. 
     The term “acyl,” as used herein, alone or in combination, refers to a carbonyl attached to an alkenyl, alkyl, aryl, cycloalkyl, heteroaryl, heterocycle, or any other moiety where the atom attached to the carbonyl is carbon. An “acetyl” group refers to a —C(O)CH 3  group. An “alkylcarbonyl” or “alkanoyl” group refers to an alkyl group attached to the parent molecular moiety through a carbonyl group. Examples of such groups include methylcarbonyl and ethylcarbonyl. Examples of acyl groups include formyl, alkanoyl and aroyl. 
     The term “alkenyl,” as used herein, alone or in combination, refers to a straight-chain or branched-chain hydrocarbon group having one or more double bonds and containing from 2 to 20 carbon atoms. In certain embodiments, said alkenyl will comprise from 2 to 6 carbon atoms. The term “alkenylene” refers to a carbon-carbon double bond system attached at two or more positions such as ethenylene [(—CH═CH—),(—C::C—)]. Examples of suitable alkenyl groups include ethenyl, propenyl, 2-methylpropenyl, 1,4-butadienyl and the like. Unless otherwise specified, the term “alkenyl” may include “alkenylene” groups. 
     The term “alkoxy,” as used herein, alone or in combination, refers to an alkyl ether group, wherein the term alkyl is as defined below. Examples of suitable alkyl ether groups include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, iso-butoxy, sec-butoxy, tert-butoxy, and the like. 
     The term “alkyl,” as used herein, alone or in combination, refers to a straight-chain or branched-chain alkyl group containing from 1 to 20 carbon atoms. In certain embodiments, said alkyl will comprise from 1 to 10 carbon atoms. In further embodiments, said alkyl will comprise from 1 to 6 carbon atoms. Alkyl groups may be optionally substituted as defined herein. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, iso-amyl, hexyl, octyl, noyl and the like. The term “alkylene,” as used herein, alone or in combination, refers to a saturated aliphatic group derived from a straight or branched chain saturated hydrocarbon attached at two or more positions, such as methylene (—CH 2 —). Unless otherwise specified, the term “alkyl” may include “alkylene” groups. 
     The term “alkylamino,” as used herein, alone or in combination, refers to an alkyl group attached to the parent molecular moiety through an amino group. Suitable alkylamino groups may be mono- or dialkylated, forming groups such as, for example, N-methylamino, N-ethylamino, N,N-dimethylamino, N,N-ethylmethylamino and the like. 
     The term “alkylidene,” as used herein, alone or in combination, refers to an alkenyl group in which one carbon atom of the carbon-carbon double bond belongs to the moiety to which the alkenyl group is attached. 
     The term “alkylthio,” as used herein, alone or in combination, refers to an alkyl thioether (R—S—) group wherein the term alkyl is as defined above and wherein the sulfur may be singly or doubly oxidized. Examples of suitable alkyl thioether groups include methylthio, ethylthio, n-propylthio, isopropylthio, n-butylthio, iso-butylthio, sec-butylthio, tert-butylthio, methanesulfonyl, ethanesulfinyl, and the like. 
     The term “alkynyl,” as used herein, alone or in combination, refers to a straight-chain or branched-chain hydrocarbon group having one or more triple bonds and containing from 2 to 20 carbon atoms. In certain embodiments, said alkynyl comprises from 2 to 6 carbon atoms. In further embodiments, said alkynyl comprises from 2 to 4 carbon atoms. The term “alkynylene” refers to a carbon-carbon triple bond attached at two positions such as ethynylene (—C:::C—, —C≡C—). Examples of alkynyl groups include ethynyl, propynyl, hydroxypropynyl, butyn-1-yl, butyn-2-yl, pentyn-1-yl, 3-methylbutyn-1-yl, hexyn-2-yl, and the like. Unless otherwise specified, the term “alkynyl” may include “alkynylene” groups. 
     The terms “amido” and “carbamoyl,” as used herein, alone or in combination, refer to an amino group as described below attached to the parent molecular moiety through a carbonyl group, or vice versa. The term “C-amido” as used herein, alone or in combination, refers to a —C(═O)—NR 2  group with R as defined herein. The term “N-amido” as used herein, alone or in combination, refers to a RC(═O)NH— group, with R as defined herein. The term “acylamino” as used herein, alone or in combination, embraces an acyl group attached to the parent moiety through an amino group. An example of an “acylamino” group is acetylamino (CH 3 C(O)NH—). 
     The term “amino,” as used herein, alone or in combination, refers to —NRR′, wherein R and R′ are independently chosen from hydrogen, alkyl, hydroxyalkyl, acyl, heteroalkyl, aryl, cycloalkyl, heteroaryl, and heterocycloalkyl, any of which may themselves be optionally substituted. Additionally, R and R′ may combine to form heterocycloalkyl, either of which may be optionally substituted. 
     The term “amino acid”, as used herein, alone or in combination, refers to a —NHCHRC(O)O— group, which may be attached to the parent molecular moiety to give either an N-terminus or C-terminus amino acid, wherein R is independently chosen from hydrogen, alkyl, aryl, heteroaryl, heterocycloalkyl, aminoalkyl, amido, amidoalkyl, carboxyl, carboxylalkyl, guanidinealkyl, hydroxyl, thiol, and thioalkyl, any of which themselves may be optionally substituted. The term C-terminus, as used herein, alone or in combination, refers to the parent molecular moiety being bound to the amino acid at the amino group, to give an amide as described herein, with the carboxyl group unbound, resulting in a terminal carboxyl group, or the corresponding carboxylate anion. The term N-terminus, as used herein, alone or in combination, refers to the parent molecular moiety being bound to the amino acid at the carboxyl group, to give an ester as described herein, with the amino group unbound resulting in a terminal secondary amine, or the corresponding ammonium cation. In other words, C-terminus refers to —NHCHRC(O)OH or to —NHCHRC(O)O −  and N-terminus refers to H 2 NCHRC(O)O— or to H 3 N + CHRC(O)O—. 
     The term “aryl”, as used herein, alone or in combination, means a carbocyclic aromatic system containing one, two or three rings wherein such polycyclic ring systems are fused together. The term “aryl” embraces aromatic groups such as phenyl, naphthyl, anthracenyl, and phenanthryl. 
     The term “arylalkenyl” or “aralkenyl,” as used herein, alone or in combination, refers to an aryl group attached to the parent molecular moiety through an alkenyl group. 
     The term “arylalkoxy” or “aralkoxy,” as used herein, alone or in combination, refers to an aryl group attached to the parent molecular moiety through an alkoxy group. 
     The term “arylalkyl” or “aralkyl,” as used herein, alone or in combination, refers to an aryl group attached to the parent molecular moiety through an alkyl group. 
     The term “arylalkynyl” or “aralkynyl,” as used herein, alone or in combination, refers to an aryl group attached to the parent molecular moiety through an alkynyl group. 
     The term “arylalkanoyl” or “aralkanoyl” or “aroyl,” as used herein, alone or in combination, refers to an acyl group derived from an aryl-substituted alkanecarboxylic acid such as benzoyl, naphthoyl, phenylacetyl, 3-phenylpropionyl(hydrocinnamoyl), 4-phenylbutyryl, (2-naphthyl)acetyl, 4-chlorohydrocinnamoyl, and the like. 
     The term aryloxy as used herein, alone or in combination, refers to an aryl group attached to the parent molecular moiety through an oxy. 
     The terms “benzo” and “benz,” as used herein, alone or in combination, refer to the divalent group C 6 H 4 =derived from benzene. Examples include benzothiophene and benzimidazole. 
     The term “carbamate,” as used herein, alone or in combination, refers to an ester of carbamic acid (—NHCOO—) which may be attached to the parent molecular moiety from either the nitrogen or acid end, and which may be optionally substituted as defined herein. 
     The term “O-carbamyl” as used herein, alone or in combination, refers to a —OC(O)NRR′ group, with R and R′ as defined herein. 
     The term “N-carbamyl” as used herein, alone or in combination, refers to a ROC(O)NR′— group, with R and R′ as defined herein. 
     The term “carbonyl,” as used herein, when alone includes formyl [—C(O)H] and in combination is a —C(O)— group. 
     The term “carboxyl” or “carboxy,” as used herein, refers to —C(O)OH (“carboxylic acid”) or the corresponding “carboxylate” anion, such as is in a carboxylic acid salt. An “O-carboxy” group refers to a RC(O)O— group, where R is as defined herein. A “C-carboxy” group refers to a —C(O)OR groups where R is as defined herein. 
     The term “cyano,” as used herein, alone or in combination, refers to —CN. 
     The term “cycloalkyl,” or, alternatively, “carbocycle,” as used herein, alone or in combination, refers to a saturated or partially saturated monocyclic, bicyclic or tricyclic alkyl group wherein each cyclic moiety contains from 3 to 12 carbon atom ring members and which may optionally be a benzo fused ring system which is optionally substituted as defined herein. In certain embodiments, said cycloalkyl will comprise from 5 to 7 carbon atoms. Examples of such cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, tetrahydronapthyl, indanyl, octahydronaphthyl, 2,3-dihydro-1H-indenyl, adamantyl and the like. “Bicyclic” and “tricyclic” as used herein are intended to include both fused ring systems, such as decahydronaphthalene, octahydronaphthalene as well as the multicyclic (multicentered) saturated or partially unsaturated type. The latter type of isomer is exemplified in general by, bicyclo[1,1,1]pentane, camphor, adamantane, and bicyclo[3,2,1]octane. 
     The term “ester,” as used herein, alone or in combination, refers to a carboxy group bridging two moieties linked at carbon atoms. 
     The term “ether,” as used herein, alone or in combination, refers to an oxy group bridging two moieties linked at carbon atoms. 
     The term “guanidine”, as used herein, alone or in combination, refers to —NHC(═NH)NH 2 , or the corresponding guanidinium cation. 
     The term “halo,” or “halogen,” as used herein, alone or in combination, refers to fluorine (F), chlorine (Cl), bromine (Br), or iodine (I). Isotopes of halogens, such as  18 F, are included within this term. 
     The term “haloalkoxy,” as used herein, alone or in combination, refers to a haloalkyl group attached to the parent molecular moiety through an oxygen atom. 
     The term “haloalkyl,” as used herein, alone or in combination, refers to an alkyl group having the meaning as defined above wherein one or more hydrogen atoms are replaced with a halogen. Specifically embraced are monohaloalkyl, dihaloalkyl and polyhaloalkyl groups. A monohaloalkyl group, for one example, may have an iodo, bromo, chloro or fluoro atom within the group. Dihalo and polyhaloalkyl groups may have two or more of the same halo atoms or a combination of different halo groups. Examples of haloalkyl groups include fluoromethyl, difluoromethyl, trifluoromethyl, chloromethyl, dichloromethyl, trichloromethyl, pentafluoroethyl, heptafluoropropyl, difluorochloromethyl, dichlorofluoromethyl, difluoroethyl, difluoropropyl, dichloroethyl and dichloropropyl. “Haloalkylene” refers to a haloalkyl group attached at two or more positions. Examples include fluoromethylene (—CFH—), difluoromethylene (—CF 2 —), chloromethylene (—CHCl—) and the like. 
     The term “heteroalkyl,” as used herein, alone or in combination, refers to a stable straight or branched chain, or cyclic hydrocarbon group, or combinations thereof, fully saturated or containing from 1 to 3 degrees of unsaturation, consisting of the stated number of carbon atoms and from one to three heteroatoms chosen from O, N, and S, and wherein the nitrogen and sulfur atoms may optionally be oxidized and the nitrogen heteroatom may optionally be quaternized. The heteroatom(s) O, N and S may be placed at any interior position of the heteroalkyl group. Up to two heteroatoms may be consecutive, such as, for example, —CH 2 —NH—OCH 3 . 
     The term “heteroaryl,” as used herein, alone or in combination, refers to a 3 to 7 membered unsaturated heteromonocyclic ring, or a fused monocyclic, bicyclic, or tricyclic ring system in which at least one of the fused rings is aromatic, which contains at least one atom chosen from B, O, S, and N. In certain embodiments, said heteroaryl will comprise from 5 to 7 carbon atoms. The term also embraces fused polycyclic groups wherein heterocyclic rings are fused with aryl rings, wherein heteroaryl rings are fused with other heteroaryl rings, wherein heteroaryl rings are fused with heterocycloalkyl rings, or wherein heteroaryl rings are fused with cycloalkyl rings. Examples of heteroaryl groups include pyrrolyl, pyrrolinyl, imidazolyl, pyrazolyl, pyridyl, pyrimidinyl, pyrazinyl, pyridazinyl, triazolyl, pyranyl, furyl, thienyl, oxazolyl, isoxazolyl, oxadiazolyl, thiazolyl, thiadiazolyl, isothiazolyl, indolyl, isoindolyl, indolizinyl, benzimidazolyl, quinolyl, isoquinolyl, quinoxalinyl, quinazolinyl, indazolyl, benzoxaborole, benzotriazolyl, benzodioxolyl, benzopyranyl, benzoxazolyl, benzoxadiazolyl, benzothiazolyl, benzothiadiazolyl, benzofuryl, benzothienyl, chromonyl, coumarinyl, benzopyranyl, tetrahydroquinolinyl, tetrazolopyridazinyl, tetrahydroisoquinolinyl, thienopyridinyl, furopyridinyl, pyrrolopyridinyl and the like. Exemplary tricyclic heterocyclic groups include carbazolyl, benzidolyl, phenanthrolinyl, dibenzofuranyl, acridinyl, phenanthridinyl, xanthenyl and the like. 
     The terms “heterocycloalkyl” and, interchangeably, “heterocycle,” as used herein, alone or in combination, each refer to a saturated, partially unsaturated, or fully unsaturated monocyclic, bicyclic, or tricyclic heterocyclic group containing at least one heteroatom as a ring member, wherein each said heteroatom may be independently chosen from nitrogen, oxygen, and sulfur. In certain embodiments, said hetercycloalkyl will comprise from 1 to 4 heteroatoms as ring members. In further embodiments, said hetercycloalkyl will comprise from 1 to 2 heteroatoms as ring members. In certain embodiments, said hetercycloalkyl will comprise from 3 to 8 ring members in each ring. In further embodiments, said hetercycloalkyl will comprise from 3 to 7 ring members in each ring. In yet further embodiments, said hetercycloalkyl will comprise from 5 to 6 ring members in each ring. “Heterocycloalkyl” and “heterocycle” are intended to include sulfones, sulfoxides, N-oxides of tertiary nitrogen ring members, and carbocyclic fused and benzo fused ring systems; additionally, both terms also include systems where a heterocycle ring is fused to an aryl group, as defined herein, or an additional heterocycle group. Examples of heterocycle groups include aziridinyl, azetidinyl, 1,3-benzodioxolyl, dihydroisoindolyl, dihydroisoquinolinyl, dihydrocinnolinyl, dihydrobenzodioxinyl, dihydro[1,3]oxazolo[4,5-b]pyridinyl, benzothiazolyl, dihydroindolyl, dihydropyridinyl, 1,3-dioxanyl, 1,4-dioxanyl, 1,3-dioxolanyl, isoindolinyl, morpholinyl, piperazinyl, methylpiperazinyl, N-methylpiperazinyl, pyrrolidinyl, tetrahydropyridinyl, piperidinyl, thiomorpholinyl, diazepanyl, and the like. The heterocycle groups may be optionally substituted unless specifically prohibited. 
     The term “hydrazinyl” as used herein, alone or in combination, refers to two amino groups joined by a single bond, i.e., —N—N—. 
     The term “hydroxy,” as used herein, alone or in combination, refers to —OH. 
     The term “hydroxyalkyl,” as used herein, alone or in combination, refers to a hydroxy group attached to the parent molecular moiety through an alkyl group. 
     The term “hydroxamic acid”, as used herein, alone or in combination, refers to —C(═O)NHOH, wherein the parent molecular moiety is attached to the hydroxamic acid group by means of the carbon atom. 
     The term “imino,” as used herein, alone or in combination, refers to ═N—. 
     The term “iminohydroxy,” as used herein, alone or in combination, refers to ═N(OH) and ═N—O—. 
     The phrase “in the main chain” refers to the longest contiguous or adjacent chain of carbon atoms starting at the point of attachment of a group to the compounds of any one of the formulas disclosed herein. 
     The term “isocyanato” refers to a —NCO group. 
     The term “isothiocyanato” refers to a —NCS group. 
     The phrase “linear chain of atoms” refers to the longest straight chain of atoms independently selected from carbon, nitrogen, oxygen and sulfur. 
     The term “lower,” as used herein, alone or in a combination, where not otherwise specifically defined, means containing from 1 to and including 6 carbon atoms. 
     The term “lower aryl,” as used herein, alone or in combination, means phenyl or naphthyl, which may be optionally substituted as provided. 
     The term “lower heteroaryl,” as used herein, alone or in combination, means either 1) monocyclic heteroaryl comprising five or six ring members, of which between one and four said members may be heteroatoms chosen from O, S, and N, or 2) bicyclic heteroaryl, wherein each of the fused rings comprises five or six ring members, comprising between them one to four heteroatoms chosen from O, S, and N. 
     The term “lower cycloalkyl,” as used herein, alone or in combination, means a monocyclic cycloalkyl having between three and six ring members. Lower cycloalkyls may be unsaturated. Examples of lower cycloalkyl include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. 
     The term “lower heterocycloalkyl,” as used herein, alone or in combination, means a monocyclic heterocycloalkyl having between three and six ring members, of which between one and four may be heteroatoms chosen from O, S, and N. Examples of lower heterocycloalkyls include pyrrolidinyl, imidazolidinyl, pyrazolidinyl, piperidinyl, piperazinyl, and morpholinyl. Lower heterocycloalkyls may be unsaturated. 
     The term “lower amino,” as used herein, alone or in combination, refers to —NRR′, wherein R and R′ are independently chosen from hydrogen, lower alkyl, and lower heteroalkyl, any of which may be optionally substituted. Additionally, the R and R′ of a lower amino group may combine to form a five- or six-membered heterocycloalkyl, either of which may be optionally substituted. 
     The term “mercaptyl” as used herein, alone or in combination, refers to an RS— group, where R is as defined herein. 
     The term “nitro,” as used herein, alone or in combination, refers to —NO 2 . 
     The terms “oxy” or “oxa,” as used herein, alone or in combination, refer to —O—. 
     The term “oxo,” as used herein, alone or in combination, refers to ═O. 
     The term “perhaloalkoxy” refers to an alkoxy group where all of the hydrogen atoms are replaced by halogen atoms. 
     The term “perhaloalkyl” as used herein, alone or in combination, refers to an alkyl group where all of the hydrogen atoms are replaced by halogen atoms. 
     The term “phosphonate,” as used herein, alone or in combination, refers to a —P(O)(OR) 2  group, wherein R is chosen from alkyl and aryl. The term “phosphonic acid”, as used herein, alone or in combination, refers to a —P(O)(OH) 2  group. 
     The term “phosphoramide”, as used herein, alone or in combination, refers to a —P(O)(NR) 3  group, with R as defined herein. 
     The terms “sulfonate,” “sulfonic acid,” and “sulfonic,” as used herein, alone or in combination, refer to the —SO 3 H group and its anion as the sulfonic acid is used in salt formation. 
     The term “sulfanyl,” as used herein, alone or in combination, refers to —S—. 
     The term “sulfinyl,” as used herein, alone or in combination, refers to —S(O)—. 
     The term “sulfonyl,” as used herein, alone or in combination, refers to —S(O) 2 —. 
     The term “N-sulfonamido” refers to a RS(O) 2 NR′— group with R and R′ as defined herein. 
     The term “S-sulfonamido” refers to a —S(O) 2 NRR′, group, with R and R′ as defined herein. 
     The terms “thia” and “thio,” as used herein, alone or in combination, refer to a —S— group or an ether wherein the oxygen is replaced with sulfur. The oxidized derivatives of the thio group, namely sulfinyl and sulfonyl, are included in the definition of thia and thio. 
     The term “thiol,” as used herein, alone or in combination, refers to an —SH group. 
     The term “thiocarbonyl,” as used herein, when alone includes thioformyl —C(S)H and in combination is a —C(S)— group. 
     The term “N-thiocarbamyl” refers to an ROC(S)NR′— group, with R and R′ as defined herein. 
     The term “O-thiocarbamyl” refers to a —OC(S)NRR′, group with R and R′ as defined herein. 
     The term “thiocyanato” refers to a —CNS group. 
     The term “trihalomethoxy” refers to a X 3 CO— group where X is a halogen. 
     Any definition herein may be used in combination with any other definition to describe a composite structural group. By convention, the trailing element of any such definition is that which attaches to the parent moiety. For example, the composite group alkylamido would represent an alkyl group attached to the parent molecule through an amido group, and the term alkoxyalkyl would represent an alkoxy group attached to the parent molecule through an alkyl group. 
     When a group is defined to be “null,” what is meant is that said group is absent. When any one or more of G 1 , G 2 , and G 3  of —(CH 2 ) s G 1 G 2 G 3  is designated to be “null”, said group condenses to either a bond if it occupies an interior position (as with G 1  and G 2 ), or is absent if it occupies a terminal position (as with G 3 ). Thus, for example, if G 1  and G 3  are both null, then —(CH 2 ) s G 1 G 2 G 3  condenses to —(CH 2 ) s G 2 . If G 2  and G 3  are both null, then —(CH 2 ) s G 1 G 2 G 3  condenses to —(CH 2 ) s G 1 . Similarly, if G 1  and G 2  are both null, then —(CH 2 ) s G 1 G 2 G 3  condenses to —(CH 2 ) s G 3 . When s is designated to be 0, then the (CH 2 ) s  portion of —(CH 2 ) s G 1 G 2 G 3  collapses to a bond connecting O to G 1 G 2 G 3 . Each of G 1 , G 2 , and G 3  are not meant to be null simultaneously and only two of G 1 , G 2 , and G 3  may be null at once. 
     The term “optionally substituted” means the anteceding group may be substituted or unsubstituted. When substituted, the substituents of an “optionally substituted” group may include, without limitation, one or more substituents independently selected from the following groups or a particular designated set of groups, alone or in combination: lower alkyl, lower alkenyl, lower alkynyl, lower alkanoyl, lower heteroalkyl, lower heterocycloalkyl, lower haloalkyl, lower haloalkenyl, lower haloalkynyl, lower perhaloalkyl, lower perhaloalkoxy, lower cycloalkyl, phenyl, aryl, aryloxy, lower alkoxy, lower haloalkoxy, oxo, lower acyloxy, carbonyl, carboxyl, lower alkylcarbonyl, lower carboxyester, lower carboxamido, cyano, hydrogen, halogen, hydroxy, amino, lower alkylamino, arylamino, amido, nitro, thiol, lower alkylthio, lower haloalkylthio, lower perhaloalkylthio, arylthio, sulfonate, sulfonic acid, trisubstituted silyl, N 3 , SH, SCH 3 , C(O)CH 3 , CO 2 CH 3 , CO 2 H, pyridinyl, thiophene, furanyl, lower carbamate, and lower urea. Two substituents may be joined together to form a fused five-, six-, or seven-membered carbocyclic or heterocyclic ring consisting of zero to three heteroatoms, for example forming methylenedioxy or ethylenedioxy. An optionally substituted group may be unsubstituted (e.g., —CH 2 CH 3 ), fully substituted (e.g., —CF 2 CF 3 ), monosubstituted (e.g., —CH 2 CH 2 F) or substituted at a level anywhere in-between fully substituted and monosubstituted (e.g., —CH 2 CF 3 ). Where substituents are recited without qualification as to substitution, both substituted and unsubstituted forms are encompassed. Where a substituent is qualified as “substituted,” the substituted form is specifically intended. Additionally, different sets of optional substituents to a particular moiety may be defined as needed; in these cases, the optional substitution will be as defined, often immediately following the phrase, “optionally substituted with.” 
     The term R or the term R′, appearing by itself and without a number designation, unless otherwise defined, refers to a moiety chosen from hydrogen, alkyl, cycloalkyl, heteroalkyl, aryl, heteroaryl and heterocycloalkyl, any of which may be optionally substituted. Such R and R′ groups should be understood to be optionally substituted as defined herein. Whether an R group has a number designation or not, every R group, including R, R′ and R n  where n=(1, 2, 3, . . . n), every substituent, and every term should be understood to be independent of every other in terms of selection from a group. Should any variable, substituent, or term (e.g. aryl, heterocycle, R, etc.) occur more than one time in a formula or generic structure, its definition at each occurrence is independent of the definition at every other occurrence. Those of skill in the art will further recognize that certain groups may be attached to a parent molecule or may occupy a position in a chain of elements from either end as written. Thus, by way of example only, an unsymmetrical group such as —C(O)N(R)— may be attached to the parent moiety at either the carbon or the nitrogen. 
     Asymmetric centers exist in the compounds disclosed herein. These centers are designated by the symbols “R” or “S,” depending on the configuration of substituents around the chiral carbon atom. It should be understood that the invention encompasses all stereochemical isomeric forms, including diastereomeric, enantiomeric, and epimeric forms, as well as d-isomers and 1-isomers, and mixtures thereof. Individual stereoisomers of compounds can be prepared synthetically from commercially available starting materials which contain chiral centers or by preparation of mixtures of enantiomeric products followed by separation such as conversion to a mixture of diastereomers followed by separation or recrystallization, chromatographic techniques, direct separation of enantiomers on chiral chromatographic columns, or any other appropriate method known in the art. Starting compounds of particular stereochemistry are either commercially available or can be made and resolved by techniques known in the art. Additionally, the compounds disclosed herein may exist as geometric isomers. The present invention includes all cis, trans, syn, anti, entgegen (E), and zusammen (Z) isomers as well as the appropriate mixtures thereof. Additionally, compounds may exist as tautomers; all tautomeric isomers are provided by this invention. Additionally, the compounds disclosed herein can exist in unsolvated as well as solvated forms with pharmaceutically acceptable solvents such as water, ethanol, and the like. In general, the solvated forms are considered equivalent to the unsolvated forms. 
     The term “bond” refers to a covalent linkage between two atoms, or two moieties when the atoms joined by the bond are considered to be part of larger substructure. A bond may be single, double, or triple unless otherwise specified. A dashed line between two atoms in a drawing of a molecule indicates that an additional bond may be present or absent at that position. 
     The term “disease” as used herein is intended to be generally synonymous, and is used interchangeably with, the terms “disorder” and “condition” (as in medical condition), in that all reflect an abnormal condition of the human or animal body or of one of its parts that impairs normal functioning, is typically manifested by distinguishing signs and symptoms, and causes the human or animal to have a reduced duration or quality of life. 
     The term “combination therapy” means the administration of two or more therapeutic agents to treat a therapeutic condition or disorder described in the present disclosure. Such administration encompasses co-administration of these therapeutic agents in a substantially simultaneous manner, such as in a single capsule having a fixed ratio of active ingredients or in multiple, separate capsules for each active ingredient. In addition, such administration also encompasses use of each type of therapeutic agent in a sequential manner. In either case, the treatment regimen will provide beneficial effects of the drug combination in treating the conditions or disorders described herein. 
     “PDE4 inhibitor” is used herein to refer to a compound that exhibits an IC 50  with respect to PDE4 activity of no more than about 100 μM and more typically not more than about 50 μM, as measured in the PDE4 assay described generally hereinbelow. “IC 50 ” is that concentration of inhibitor which reduces the activity of an enzyme (e.g., PDE4) to half-maximal level. Certain representative compounds of the present invention have been discovered to exhibit inhibition against PDE4. In certain embodiments, compounds will exhibit an IC 50  with respect to PDE4 of no more than about 10 μM; in further embodiments, compounds will exhibit an IC 50  with respect to PDE4 of no more than about 5 μM; in yet further embodiments, compounds will exhibit an IC 50  with respect to PDE4 of not more than about 1 μM, as measured in the PDE4 assay described herein. In yet further embodiments, compounds will exhibit an IC 50  with respect to PDE4 of not more than about 200 nM. 
     The phrase “therapeutically effective” is intended to qualify the amount of active ingredients used in the treatment of a disease or disorder. This amount will achieve the goal of reducing or eliminating the said disease or disorder. 
     The term “therapeutically acceptable” refers to those compounds (or salts, prodrugs, tautomers, zwitterionic forms, etc.) which are suitable for use in contact with the tissues of patients without undue toxicity, irritation, and allergic response, are commensurate with a reasonable benefit/risk ratio, and are effective for their intended use. 
     As used herein, reference to “treatment” of a patient is intended to include prophylaxis. The term “patient” means all mammals including humans. Examples of patients include humans, cows, dogs, cats, goats, sheep, pigs, and rabbits. Preferably, the patient is a human. 
     The term “prodrug” refers to a compound that is made more active in vivo. Certain compounds disclosed herein may also exist as prodrugs, as described in  Hydrolysis in Drug and Prodrug Metabolism: Chemistry, Biochemistry, and Enzymology  (Testa, Bernard and Mayer, Joachim M. Wiley-VHCA, Zurich, Switzerland 2003). Prodrugs of the compounds described herein are structurally modified forms of the compound that readily undergo chemical changes under physiological conditions to provide the compound. Additionally, prodrugs can be converted to the compound by chemical or biochemical methods in an ex vivo environment. For example, prodrugs can be slowly converted to a compound when placed in a transdermal patch reservoir with a suitable enzyme or chemical reagent. Prodrugs are often useful because, in some situations, they may be easier to administer than the compound, or parent drug. They may, for instance, be bioavailable by oral administration whereas the parent drug is not. The prodrug may also have improved solubility in pharmaceutical compositions over the parent drug. A wide variety of prodrug derivatives are known in the art, such as those that rely on hydrolytic cleavage or oxidative activation of the prodrug. An example, without limitation, of a prodrug would be a compound which is administered as an ester (the “prodrug”), but then is metabolically hydrolyzed to the carboxylic acid, the active entity. Additional examples include peptidyl derivatives of a compound. 
     The compounds disclosed herein can exist as therapeutically acceptable salts. The present invention includes compounds listed above in the form of salts, including acid addition salts. Suitable salts include those formed with both organic and inorganic acids. Such acid addition salts will normally be pharmaceutically acceptable. However, salts of non-pharmaceutically acceptable salts may be of utility in the preparation and purification of the compound in question. Basic addition salts may also be formed and be pharmaceutically acceptable. For a more complete discussion of the preparation and selection of salts, refer to  Pharmaceutical Salts: Properties, Selection , and Use (Stahl, P. Heinrich. Wiley-VCHA, Zurich, Switzerland, 2002). 
     The term “therapeutically acceptable salt,” as used herein, represents salts or zwitterionic forms of the compounds disclosed herein which are water or oil-soluble or dispersible and therapeutically acceptable as defined herein. The salts can be prepared during the final isolation and purification of the compounds or separately by reacting the appropriate compound in the form of the free base with a suitable acid. Representative acid addition salts include acetate, adipate, alginate, L-ascorbate, aspartate, benzoate, benzenesulfonate (besylate), bisulfate, butyrate, camphorate, camphorsulfonate, citrate, digluconate, formate, fumarate, gentisate, glutarate, glycerophosphate, glycolate, hemisulfate, heptanoate, hexanoate, hippurate, hydrochloride, hydrobromide, hydroiodide, 2-hydroxyethansulfonate (isethionate), lactate, maleate, malonate, DL-mandelate, mesitylenesulfonate, methanesulfonate, naphthylenesulfonate, nicotinate, 2-naphthalenesulfonate, oxalate, pamoate, pectinate, persulfate, 3-phenylproprionate, phosphonate, picrate, pivalate, propionate, pyroglutamate, succinate, sulfonate, tartrate, L-tartrate, trichloroacetate, trifluoroacetate, phosphate, glutamate, bicarbonate, para-toluenesulfonate (p-tosylate), and undecanoate. Also, basic groups in the compounds disclosed herein can be quaternized with methyl, ethyl, propyl, and butyl chlorides, bromides, and iodides; dimethyl, diethyl, dibutyl, and diamyl sulfates; decyl, lauryl, myristyl, and steryl chlorides, bromides, and iodides; and benzyl and phenethyl bromides. Examples of acids which can be employed to form therapeutically acceptable addition salts include inorganic acids such as hydrochloric, hydrobromic, sulfuric, and phosphoric, and organic acids such as oxalic, maleic, succinic, and citric. Salts can also be formed by coordination of the compounds with an alkali metal or alkaline earth ion. Hence, the present invention contemplates sodium, potassium, magnesium, and calcium salts of the compounds disclosed herein, and the like. 
     Basic addition salts can be prepared during the final isolation and purification of the compounds by reaction of a carboxy group with a suitable base such as the hydroxide, carbonate, or bicarbonate of a metal cation or with ammonia or an organic primary, secondary, or tertiary amine. The cations of therapeutically acceptable salts include lithium, sodium, potassium, calcium, magnesium, and aluminum, as well as nontoxic quaternary amine cations such as ammonium, tetramethylammonium, tetraethylammonium, methylamine, dimethylamine, trimethylamine, triethylamine, diethylamine, ethylamine, tributylamine, pyridine, N,N-dimethylaniline, N-methylpiperidine, N-methylmorpholine, dicyclohexylamine, procaine, dibenzylamine, N,N-dibenzylphenethylamine, 1-ephenamine, and N,N′-dibenzylethylenediamine. Other representative organic amines useful for the formation of base addition salts include ethylenediamine, ethanolamine, diethanolamine, piperidine, and piperazine. 
     A salt of a compound can be made by reaction of the appropriate compound, in the form of the free base, with the appropriate acid. 
     While it may be possible for the compounds of the subject invention to be administered as the raw chemical, it is also possible to present them as a pharmaceutical formulation (equivalently, a “pharmaceutical composition”). Accordingly, provided herein are pharmaceutical formulations which comprise one or more of certain compounds disclosed herein, or one or more pharmaceutically acceptable salts, esters, prodrugs, amides, or solvates thereof, together with one or more pharmaceutically acceptable carriers thereof and optionally one or more other therapeutic ingredients. The carrier(s) must be “acceptable” in the sense of being compatible with the other ingredients of the formulation and not deleterious to the recipient thereof. Proper formulation is dependent upon the route of administration chosen. Any of the well-known techniques, carriers, and excipients may be used as suitable and as understood in the art; e.g., in Remington&#39;s Pharmaceutical Sciences. The pharmaceutical compositions disclosed herein may be manufactured in any manner known in the art, e.g., by means of conventional mixing, dissolving, granulating, dragee-making, levigating, emulsifying, encapsulating, entrapping or compression processes. 
     The formulations include those suitable for oral, parenteral (including subcutaneous, intradermal, intramuscular, intravenous, intraarticular, and intramedullary), intraperitoneal, transmucosal, transdermal, rectal and topical (including dermal, buccal, sublingual and intraocular) administration although the most suitable route may depend upon for example the condition and disorder of the recipient. The formulations may conveniently be presented in unit dosage form and may be prepared by any of the methods well known in the art of pharmacy. Typically, these methods include the step of bringing into association a compound of the subject invention or a pharmaceutically acceptable salt, ester, amide, prodrug or solvate thereof (“active ingredient”) with the carrier which constitutes one or more accessory ingredients. In general, the formulations are prepared by uniformly and intimately bringing into association the active ingredient with liquid carriers or finely divided solid carriers or both and then, if necessary, shaping the product into the desired formulation. 
     Formulations of the compounds disclosed herein suitable for oral administration may be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amount of the active ingredient; as a powder or granules; as a solution or a suspension in an aqueous liquid or a non-aqueous liquid; or as an oil-in-water liquid emulsion or a water-in-oil liquid emulsion. The active ingredient may also be presented as a bolus, electuary or paste. 
     Pharmaceutical preparations which can be used orally include tablets, push-fit capsules made of gelatin, as well as soft, sealed capsules made of gelatin and a plasticizer, such as glycerol or sorbitol. Tablets may be made by compression or molding, optionally with one or more accessory ingredients. Compressed tablets may be prepared by compressing in a suitable machine the active ingredient in a free-flowing form such as a powder or granules, optionally mixed with binders, inert diluents, or lubricating, surface active or dispersing agents. Molded tablets may be made by molding in a suitable machine a mixture of the powdered compound moistened with an inert liquid diluent. The tablets may optionally be coated or scored and may be formulated so as to provide slow or controlled release of the active ingredient therein. All formulations for oral administration should be in dosages suitable for such administration. The push-fit capsules can contain the active ingredients in admixture with filler such as lactose, binders such as starches, and/or lubricants such as talc or magnesium stearate and, optionally, stabilizers. In soft capsules, the active compounds may be dissolved or suspended in suitable liquids, such as fatty oils, liquid paraffin, or liquid polyethylene glycols. In addition, stabilizers may be added. Dragee cores are provided with suitable coatings. For this purpose, concentrated sugar solutions may be used, which may optionally contain gum arabic, talc, polyvinyl pyrrolidone, carbopol gel, polyethylene glycol, and/or titanium dioxide, lacquer solutions, and suitable organic solvents or solvent mixtures. Dyestuffs or pigments may be added to the tablets or dragee coatings for identification or to characterize different combinations of active compound doses. 
     The compounds may be formulated for parenteral administration by injection, e.g., by bolus injection or continuous infusion. Formulations for injection may be presented in unit dosage form, e.g., in ampoules or in multi-dose containers, with an added preservative. The compositions may take such forms as suspensions, solutions or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilizing and/or dispersing agents. The formulations may be presented in unit-dose or multi-dose containers, for example sealed ampoules and vials, and may be stored in powder form or in a freeze-dried (lyophilized) condition requiring only the addition of the sterile liquid carrier, for example, saline or sterile pyrogen-free water, immediately prior to use. Extemporaneous injection solutions and suspensions may be prepared from sterile powders, granules and tablets of the kind previously described. 
     Formulations for parenteral administration include aqueous and non-aqueous (oily) sterile injection solutions of the active compounds which may contain antioxidants, buffers, bacteriostats and solutes which render the formulation isotonic with the blood of the intended recipient; and aqueous and non-aqueous sterile suspensions which may include suspending agents and thickening agents. Suitable lipophilic solvents or vehicles include fatty oils such as sesame oil, or synthetic fatty acid esters, such as ethyl oleate or triglycerides, or liposomes. Aqueous injection suspensions may contain substances which increase the viscosity of the suspension, such as sodium carboxymethyl cellulose, sorbitol, or dextran. Optionally, the suspension may also contain suitable stabilizers or agents which increase the solubility of the compounds to allow for the preparation of highly concentrated solutions. 
     In addition to the formulations described previously, the compounds may also be formulated as a depot preparation. Such long acting formulations may be administered by implantation (for example subcutaneously or intramuscularly) or by intramuscular injection. Thus, for example, the compounds may be formulated with suitable polymeric or hydrophobic materials (for example as an emulsion in an acceptable oil) or ion exchange resins, or as sparingly soluble derivatives, for example, as a sparingly soluble salt. 
     For buccal or sublingual administration, the compositions may take the form of tablets, lozenges, pastilles, or gels formulated in conventional manner. Such compositions may comprise the active ingredient in a flavored basis such as sucrose and acacia or tragacanth. 
     The compounds may also be formulated in rectal compositions such as suppositories or retention enemas, e.g., containing conventional suppository bases such as cocoa butter, polyethylene glycol, or other glycerides. 
     Certain compounds disclosed herein may be administered topically, that is by non-systemic administration. This includes the application of a compound disclosed herein externally to the epidermis or the buccal cavity and the instillation of such a compound into the ear, eye and nose, such that the compound does not significantly enter the blood stream. In contrast, systemic administration refers to oral, intravenous, intraperitoneal and intramuscular administration. 
     Formulations suitable for topical administration include liquid or semi-liquid preparations suitable for penetration through the skin to the site of inflammation such as gels, liniments, lotions, creams, ointments or pastes, and drops suitable for administration to the eye, ear or nose. The active ingredient for topical administration may comprise, for example, from 0.001% to 10% w/w (by weight) of the formulation. In certain embodiments, the active ingredient may comprise as much as 10% w/w. In other embodiments, it may comprise less than 5% w/w. In certain embodiments, the active ingredient may comprise from 2% w/w to 5% w/w. In other embodiments, it may comprise from 0.1% to 1% w/w of the formulation. 
     Topical ophthalmic, otic, and nasal formulations of the present invention may comprise excipients in addition to the active ingredient. Excipients commonly used in such formulations include, but are not limited to, tonicity agents, preservatives, chelating agents, buffering agents, and surfactants. Other excipients comprise solubilizing agents, stabilizing agents, comfort-enhancing agents, polymers, emollients, pH-adjusting agents and/or lubricants. Any of a variety of excipients may be used in formulations of the present invention including water, mixtures of water and water-miscible solvents, such as C1-C7-alkanols, vegetable oils or mineral oils comprising from 0.5 to 5% non-toxic water-soluble polymers, natural products, such as alginates, pectins, tragacanth, karaya gum, guar gum, xanthan gum, carrageenan, agar and acacia, starch derivatives, such as starch acetate and hydroxypropyl starch, and also other synthetic products such as polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, polyethylene oxide, preferably cross-linked polyacrylic acid and mixtures of those products. The concentration of the excipient is, typically, from 1 to 100,000 times the concentration of the active ingredient. In preferred embodiments, the excipients to be included in the formulations are typically selected on the basis of their inertness towards the active ingredient component of the formulations. 
     Relative to ophthalmic, otic, and nasal formulations, suitable tonicity-adjusting agents include, but are not limited to, mannitol, sodium chloride, glycerin, sorbitol and the like. Suitable buffering agents include, but are not limited to, phosphates, borates, acetates and the like. Suitable surfactants include, but are not limited to, ionic and nonionic surfactants (though nonionic surfactants are preferred), RLM 100, POE 20 cetylstearyl ethers such as Procol® CS20 and poloxamers such as Pluronic® F68. 
     The formulations set forth herein may comprise one or more preservatives. Examples of such preservatives include p-hydroxybenzoic acid ester, sodium perborate, sodium chlorite, alcohols such as chlorobutanol, benzyl alcohol or phenyl ethanol, guanidine derivatives such as polyhexamethylene biguanide, sodium perborate, polyquaternium-1, amino alcohols such as AMP-95, or sorbic acid. In certain embodiments, the formulation may be self-preserved so that no preservation agent is required. 
     For ophthalmic, otic, or nasal administration, the formulation may be a solution, a suspension, or a gel. In preferred aspects, the formulations are for topical application to the eye, nose, or ear in aqueous solution in the form of drops. The term “aqueous” typically denotes an aqueous formulation wherein the formulation is &gt;50%, more preferably &gt;75% and in particular &gt;90% by weight water. These drops may be delivered from a single dose ampoule which may preferably be sterile and thus render bacteriostatic components of the formulation unnecessary. Alternatively, the drops may be delivered from a multi-dose bottle which may preferably comprise a device which extracts any preservative from the formulation as it is delivered, such devices being known in the art. 
     For ophthalmic disorders, components of the invention may be delivered to the eye as a concentrated gel or a similar vehicle, or as dissolvable inserts that are placed beneath the eyelids. 
     The formulations of the present invention that are adapted for topical administration to the eye are preferably isotonic, or slightly hypotonic in order to combat any hypertonicity of tears caused by evaporation and/or disease. This may require a tonicity agent to bring the osmolality of the formulation to a level at or near 210-320 milliosmoles per kilogram (mOsm/kg). The formulations of the present invention generally have an osmolality in the range of 220-320 mOsm/kg, and preferably have an osmolality in the range of 235-300 mOsm/kg. The ophthalmic formulations will generally be formulated as sterile aqueous solutions. 
     In certain ophthalmic embodiments, the compositions of the present invention are formulated with one or more tear substitutes. A variety of tear substitutes are known in the art and include, but are not limited to: monomeric polyols, such as, glycerol, propylene glycol, and ethylene glycol; polymeric polyols such as polyethylene glycol; cellulose esters such hydroxypropylmethyl cellulose, carboxy methylcellulose sodium and hydroxy propylcellulose; dextrans such as dextran 70; vinyl polymers, such as polyvinyl alcohol; and carbomers, such as carbomer 934P, carbomer 941, carbomer 940 and carbomer 974P. Certain formulations of the present invention may be used with contact lenses or other ophthalmic products. 
     In certain embodiments, formulations are prepared using a buffering system that maintains the formulation at a pH of about 4.5 to a pH of about 8. A most preferred formulation pH is from 7 to 8. 
     In certain embodiments, a formulation of the present invention is administered once a day. However, the formulations may also be formulated for administration at any frequency of administration, including once a week, once every 5 days, once every 3 days, once every 2 days, twice a day, three times a day, four times a day, five times a day, six times a day, eight times a day, every hour, or any greater frequency. Such dosing frequency is also maintained for a varying duration of time depending on the therapeutic regimen. The duration of a particular therapeutic regimen may vary from one-time dosing to a regimen that extends for months or years. The formulations are administered at varying dosages, but typical dosages are one to two drops at each administration, or a comparable amount of a gel or other formulation. One of ordinary skill in the art would be familiar with determining a therapeutic regimen for a specific indication. 
     Gels for topical or transdermal administration may comprise, generally, a mixture of volatile solvents, nonvolatile solvents, and water. In certain embodiments, the volatile solvent component of the buffered solvent system may include lower (C1-C6)alkyl alcohols, lower alkyl glycols and lower glycol polymers. In further embodiments, the volatile solvent is ethanol. The volatile solvent component is thought to act as a penetration enhancer, while also producing a cooling effect on the skin as it evaporates. The nonvolatile solvent portion of the buffered solvent system is selected from lower alkylene glycols and lower glycol polymers. In certain embodiments, propylene glycol is used. The nonvolatile solvent slows the evaporation of the volatile solvent and reduces the vapor pressure of the buffered solvent system. The amount of this nonvolatile solvent component, as with the volatile solvent, is determined by the pharmaceutical compound or drug being used. When too little of the nonvolatile solvent is in the system, the pharmaceutical compound may crystallize due to evaporation of volatile solvent, while an excess may result in a lack of bioavailability due to poor release of drug from solvent mixture. The buffer component of the buffered solvent system may be selected from any buffer commonly used in the art; in certain embodiments, water is used. A common ratio of ingredients is about 20% of the nonvolatile solvent, about 40% of the volatile solvent, and about 40% water. There are several optional ingredients which can be added to the topical composition. These include, but are not limited to, chelators and gelling agents. Appropriate gelling agents can include, but are not limited to, semisynthetic cellulose derivatives (such as hydroxypropylmethylcellulose) and synthetic polymers, galactomannan polymers (such as guar and derivatives thereof), and cosmetic agents. 
     Lotions include those suitable for application to the skin or eye. An eye lotion may comprise a sterile aqueous solution optionally containing a bactericide and may be prepared by methods similar to those for the preparation of drops. Lotions or liniments for application to the skin may also include an agent to hasten drying and to cool the skin, such as an alcohol or acetone, and/or a moisturizer such as glycerol or an oil such as castor oil or arachis oil. 
     Creams, ointments or pastes are semi-solid formulations of the active ingredient for external application. They may be made by mixing the active ingredient in finely-divided or powdered form, alone or in solution or suspension in an aqueous or non-aqueous fluid, with the aid of suitable machinery, with a greasy or non-greasy base. The base may comprise hydrocarbons such as hard, soft or liquid paraffin, glycerol, beeswax, a metallic soap; a mucilage; an oil of natural origin such as almond, corn, arachis, castor or olive oil; wool fat or its derivatives or a fatty acid such as steric or oleic acid together with an alcohol such as propylene glycol or a macrogel. The formulation may incorporate any suitable surface active agent such as an anionic, cationic or non-ionic surfactant such as a sorbitan ester or a polyoxyethylene derivative thereof. Suspending agents such as natural gums, cellulose derivatives or inorganic materials such as silicaceous silicas, and other ingredients such as lanolin, may also be included. 
     Drops may comprise sterile aqueous or oily solutions or suspensions and may be prepared by dissolving the active ingredient in a suitable aqueous solution of a bactericidal and/or fungicidal agent and/or any other suitable preservative, and, in certain embodiments, including a surface active agent. The resulting solution may then be clarified by filtration, transferred to a suitable container which is then sealed and sterilized by autoclaving or maintaining at 98-100° C. for half an hour. Alternatively, the solution may be sterilized by filtration and transferred to the container by an aseptic technique. Examples of bactericidal and fungicidal agents suitable for inclusion in the drops are phenylmercuric nitrate or acetate (0.002%), benzalkonium chloride (0.01%) and chlorhexidine acetate (0.01%). Suitable solvents for the preparation of an oily solution include glycerol, diluted alcohol and propylene glycol. 
     Formulations for topical administration in the mouth, for example buccally or sublingually, include lozenges comprising the active ingredient in a flavored basis such as sucrose and acacia or tragacanth, and pastilles comprising the active ingredient in a basis such as gelatin and glycerin or sucrose and acacia. 
     For administration by inhalation, compounds may be conveniently delivered from an insufflator, nebulizer pressurized packs or other convenient means of delivering an aerosol spray. Pressurized packs may comprise a suitable propellant such as dichlorodifluoromethane, trichlorofluoromethane, dichlorotetrafluoroethane, carbon dioxide or other suitable gas. In the case of a pressurized aerosol, the dosage unit may be determined by providing a valve to deliver a metered amount. Alternatively, for administration by inhalation or insufflation, the compounds according to the invention may take the form of a dry powder composition, for example a powder mix of the compound and a suitable powder base such as lactose or starch. The powder composition may be presented in unit dosage form, in for example, capsules, cartridges, gelatin or blister packs from which the powder may be administered with the aid of an inhalator or insufflator. 
     Preferred unit dosage formulations are those containing an effective dose, as herein below recited, or an appropriate fraction thereof, of the active ingredient. 
     It should be understood that in addition to the ingredients particularly mentioned above, the formulations described above may include other agents conventional in the art having regard to the type of formulation in question, for example those suitable for oral administration may include flavoring agents. 
     Compounds may be administered orally or via injection at a dose of from 0.1 to 500 mg/kg per day. The dose range for adult humans is generally from 5 mg to 2 g/day. Tablets or other forms of presentation provided in discrete units may conveniently contain an amount of one or more compounds which is effective at such dosage or as a multiple of the same, for instance, units containing 5 mg to 500 mg, usually around 10 mg to 200 mg. 
     The amount of active ingredient that may be combined with the carrier materials to produce a single dosage form will vary depending upon the host treated and the particular mode of administration. 
     The compounds can be administered in various modes, e.g. orally, topically, or by injection. The precise amount of compound administered to a patient will be the responsibility of the attendant physician. The specific dose level for any particular patient will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, sex, diets, time of administration, route of administration, rate of excretion, drug combination, the precise disorder being treated, and the severity of the indication or condition being treated. Also, the route of administration may vary depending on the condition and its severity. 
     In certain instances, it may be appropriate to administer at least one of the compounds described herein (or a pharmaceutically acceptable salt, ester, or prodrug thereof) in combination with another therapeutic agent. By way of example only, if one of the side effects experienced by a patient upon receiving one of the compounds herein is hypertension, then it may be appropriate to administer an anti-hypertensive agent in combination with the initial therapeutic agent. Or, by way of example only, the therapeutic effectiveness of one of the compounds described herein may be enhanced by administration of an adjuvant (i.e., by itself the adjuvant may only have minimal therapeutic benefit, but in combination with another therapeutic agent, the overall therapeutic benefit to the patient is enhanced). Or, by way of example only, the benefit of experienced by a patient may be increased by administering one of the compounds described herein with another therapeutic agent (which also includes a therapeutic regimen) that also has therapeutic benefit. By way of example only, in a treatment for diabetes involving administration of one of the compounds described herein, increased therapeutic benefit may result by also providing the patient with another therapeutic agent for diabetes. In any case, regardless of the disease, disorder or condition being treated, the overall benefit experienced by the patient may simply be additive of the two therapeutic agents or the patient may experience a synergistic benefit. 
     Specific, non-limiting examples of possible combination therapies include use of the compounds of the invention with antidepressants, nootropics, anti-acetylcholinesterases, N-methyl D-aspartate (NMDA) receptor antagonists, amyloid beta therapeutics, and tau therapeutics, neurotrophic growth factors, cell based therapies and other regenerative medicine therapies for treatment of neurodegenerative diseases, amongst other therapies which will be apperent to one skilled in the art. 
     Antidepressants include, for example:
         selective serotonin reuptake inhibitors (SSRIs), such as citalopram, dapoxetine, escitalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline;   serotonin-norepinephrine reuptake inhibitors (SNRIs), such as venlafaxine, desvenlafaxine, minalcipran, levominalcipran, duloxetine, sibutramine, and bicifadine;   noradrenergic and specific serotonergic antidepressants (NaSSAs), such as mianserin, mirtazepine, esmirtazepine, and setiptiline;   norepinephrine reuptake inhibitors (NRIs), such asatomoxetine, mazindol, reboxetine, esreboxetine, viloxazine, and other specific and nonspecific agents which prevent or mitigate reuptake of norepinephrine (e.g., SNRIs, NDRIs);   norepinephrine-dopamine reuptake inhibitors (NDRIs), such as buproprion;   selective serotonin reuptake enhancers, such as tianeptine and amineptine;   norepinephrine-dopamine disinhibitors (NDDIs), such agomelatine   tricyclic antidepressants, including tertiary and secondary amine varieties, such as amitriptyline, clomipramine, doxepin, imipramine, trimipramine, desipramine, nortriptyline, and protriptyline; and   monoamine oxidase inhibitors (MAOIs), such as isocarboxazid, moclobemide, phenelzine, selegiline, and tranylcyrpomine.       

     Nootropic drugs, also known as cognition enhancers, include stimulants, dopaminergics, cholinergics, serotonergics, and many of the antidepressants listed above, as well as certain natural products (e.g., caffeine, tryptophan, 5-HTP, nicotine).
         racetams such as piracetam, pramiracetam, oxiracetam, and aniracetam   amphetamine analogues such as amphetamine (Adderall, Dexedrine), lisdexamfetamine, and methamphetamine;   wakefulness nehancers such as modafinil;   dopamine reuptake inhibitors such as methylphenidate, and possibly modafinil;   acetylcholinesterase inhibitors used to treat Alzheimer&#39;s disease such as tacrine, donepezil, galantamine, rivastigmine;   NMDA receptor antagonists such as memantine   Selective 5-HT6 receptor antagonists such as Lu AE58054;   Nicotinic alpha-7 receptor agonists such as EVP-6124;       

     Amyloid beta (a-beta or αβ) therapies and tau therapies target the pathological accumulation of a-beta and tau proteins associated with neurodegenerative diseases such as Alzheimer&#39;s disease and progressive supernuclear palsy, respectively. A-beta therapies include β-secretase inhibitors, γ-secretase inhibitors, Aβ 42 -lowering agents (e.g. tarenflurbil), anti-aggregation agents (e.g. apomorphine), antibodies and other immunotherapies. Tau therapies include Tau phosphorylation inhibitors, tau fibrillization inhibitors, and tau degradation enhancers. 
     In any case, the multiple therapeutic agents (at least one of which is a compound disclosed herein) may be administered in any order or even simultaneously. If simultaneously, the multiple therapeutic agents may be provided in a single, unified form, or in multiple forms (by way of example only, either as a single pill or as two separate pills). One of the therapeutic agents may be given in multiple doses, or both may be given as multiple doses. If not simultaneous, the timing between the multiple doses may be any duration of time ranging from a few minutes to four weeks. 
     Thus, in another aspect, the present invention provides methods for treating PDE4-mediated disorders in a human or animal subject in need of such treatment comprising administering to said subject an amount of a compound of the present invention effective to reduce or prevent said disorder in the subject in combination with at least one additional agent for the treatment of said disorder that is known in the art. In a related aspect, the present invention provides therapeutic compositions comprising at least one compound of the present invention in combination with one or more additional agents for the treatment of PDE4-mediated disorders. 
     The compounds of the subject invention may also be useful for the treatment of certain diseases and disorders of the nervous system. Central nervous system disorders in which PDE4 inhibition may be useful include cortical dementias including Alzheimer&#39;s disease, AIDS-related dementia (HIV dementia), and mild cognitive impairment (MCI). Neurodegenerative disorders in which PDE4 inhibition may be useful include nerve degeneration or nerve necrosis in disorders such as hypoxia, hypoglycemia, epilepsy, and in cases of central nervous system (CNS) trauma (such as spinal cord and head injury), hyperbaric oxygen convulsions and toxicity, dementia e.g. pre-senile dementia, and HIV-associated neurodegenerative disorder (HAND), cachexia, Sydenham&#39;s chorea, Huntington&#39;s disease, Parkinson&#39;s Disease, amyotrophic lateral sclerosis (ALS), Korsakoff&#39;s syndrome, and impairment relating to a cerebral vessel disorder. Further disorders in which PDE4 inhibition might prove useful include neuropathies of the central and peripheral nervous system, including, for example, IgA neuropathy, membranous neuropathy, idiopathic neuropathy, drug-induced peripheral neuropathy, diabetic neuropathy, HIV-associated neuropathy, and chronic inflammatory demyelinating polyneuropathy; as well as transverse myelitis, Gullain-Barre disease, encephalitis, and cancers of the nervous system. Compounds disclosed herein may also be used in the treatment of psychological disorders including anxiety, depression, major depressive disorder (MDD), bipolar disorder, and post-traumatic stress disorder. Compounds disclosed herein may also be used in the treatment of nervous system damage, for example that resulting from stroke, ischemias including cerebral ischemia (both focal ischemia, thrombotic stroke and global ischemia, for example, secondary to cardiac arrest and ischemic heart disease) and ischemia/reperfusion, ototoxicity and hearing loss, acute insults to the inner ear, including acoustic trauma, blast noise (for example, as experienced by military personnel), exposure to ototoxic chemotherapeutic agents for cancer therapy (such as cisplatin) and treatment with aminoglycoside antibioticsand other nervous system trauma. 
     Compounds disclosed herein may also be used in the treatment of traumatic brain injury (TBI), spinal cord injury (SCI), or a symptom thereof. In certain embodiments, a selective PDE4D inhibitor as disclosed herein will be used to treat SCI, in an amount sufficient to cause a detectable improvement in one or more symptoms, or a reduction in the progression of one or more symptoms of SCI. Additionally, the selective PDE4D inhibitor can be administered in combination with transplantation into the spinal cord of cells. Contemplated cells include stem cells and glial (e.g., Schwann) cells. 
     Furthermore, compounds of the subject invention may be used in the treatment or prevention of opiate tolerance in patients needing protracted opiate analgesics, and benzodiazepine tolerance in patients taking benzodiazepines, and other addictive behavior, for example, nicotine addiction, alcoholism, and eating disorders. Moreover, the compounds and methods of the present invention may be useful in the treatment or prevention of drug withdrawal symptoms, for example treatment or prevention of symptoms of withdrawal from opiate, alcohol, or tobacco addiction. 
     Compounds disclosed herein may also be used in the treatment of acute and chronic pain and inflammation. The compounds of the present invention may be useful to treat patients with neuropathy, neuropathic pain, or inflammatory pain such as reflex sympathetic dystrophy/causalgia (nerve injury), peripheral neuropathy (including diabetic neuropathy), intractable cancer pain, complex regional pain syndrome, and entrapment neuropathy (carpel tunnel syndrome). The compounds may also be useful in the treatment of pain associated with acute herpes zoster (shingles), postherpetic neuralgia (PHN), and associated pain syndromes such as ocular pain. The compounds may further be useful as analgesics in the treatment of pain such as surgical analgesia, or as an antipyretic for the treatment of fever. Pain indications include, but are not limited to, post-surgical pain for various surgical procedures including post-cardiac surgery, dental pain/dental extraction, pain resulting from cancer, muscular pain, mastalgia, pain resulting from dermal injuries, lower back pain, headaches of various etiologies, including migraine, and the like. The compounds may also be useful for the treatment of pain-related disorders such as tactile allodynia and hyperalgesia. The pain may be somatogenic (either nociceptive or neuropathic), acute and/or chronic. The PDE4 inhibitors of the subject invention may also be useful in conditions where NSAIDs, morphine or fentanyl opiates and/or other opioid analgesics would traditionally be administered. 
     In addition, compounds disclosed herein may be used in the treatment of insulin resistance and other metabolic disorders such as atherosclerosis that are typically associated with an exaggerated inflammatory signaling. 
     Compounds disclosed herein may also be used in the treatment of respiratory disease or conditions, including therapeutic methods of use in medicine for preventing and treating a respiratory disease or condition including: asthmatic conditions including allergen-induced asthma, exercise-induced asthma, pollution-induced asthma, cold-induced asthma, and viral-induced-asthma; asthma-related diseases such as airway hyperreactivity and small airway disease; chronic obstructive pulmonary diseases including chronic bronchitis with normal airflow, chronic bronchitis with airway obstruction (chronic obstructive bronchitis), emphysema, asthmatic bronchitis, and bullous disease; and other pulmonary diseases involving inflammation including bronchiolitis, bronchioectasis, cystic fibrosis, pigeon fancier&#39;s disease, farmer&#39;s lung, acute respiratory distress syndrome, pneumonia, pneumonitis, aspiration or inhalation injury, fat embolism in the lung, acidosis inflammation of the lung, acute pulmonary edema, acute mountain sickness, acute pulmonary hypertension, persistent pulmonary hypertension of the newborn, perinatal aspiration syndrome, hyaline membrane disease, acute pulmonary thromboembolism, heparin-protamine reactions, sepsis, status asthamticus, hypoxia, dyspnea, hypercapnea, hyperinflation, hypoxemia, and cough. Further, compounds disclosed herein would find use in the treatment of allergic disorders such as delayed type hypersensitivity reaction, allergic contact dermatitis, allergic rhinitis, and chronic sinusitis. 
     Compounds disclosed herein may also be used in the treatment of inflammation and related disorders. The compounds disclosed herein may be useful as anti-inflammatory agents with the additional benefit of having significantly less harmful side effects. The compounds may be useful to treat arthritis, including but not limited to rheumatoid arthritis, spondyloarthropathies, gouty arthritis, osteoarthritis, juvenile arthritis, acute rheumatic arthritis, enteropathic arthritis, neuropathic arthritis, psoriatic arthritis, reactive arthritis (Reiter&#39;s syndrome), and pyogenic arthritis, and autoimmune diseases, including systemic lupus erythematosus, hemolytic syndromes, autoimmune hepatitis, autoimmune neuropathy, vitiligo (autoimmune thyroiditis), Hashimoto&#39;s thyroiditis, anemias, myositis including polymyositis, alopecia greata, Goodpasture&#39;s syndrome, hypophytis, and pulmonary fibrosis. 
     Compounds disclosed herein may also be used in the treatment of osteoporosis and other related bone disorders. 
     Compounds disclosed herein may also be used in the treatment of gastrointestinal conditions such as reflux esophagitis, diarrhea, inflammatory bowel disease, Crohn&#39;s disease, gastritis, irritable bowel syndrome, Graves&#39; disease (hyperthyroidism), necrotizing enterocolitis, and ulcerative colitis. The compounds may also be used in the treatment of pulmonary inflammation, such as that associated with viral infections and cystic fibrosis. 
     In addition, compounds of invention may also be useful in organ transplant patients either alone or in combination with conventional immunomodulators. Examples of conditions to be treated in said patients include graft vs. host reaction (i.e., graft vs. host disease), allograft rejections (e.g., acute allograft rejection, and chronic allograft rejection), transplant reperfusion injury, and early transplantation rejection (e.g., acute allograft rejection). 
     Yet further, the compounds of the invention may be useful in the treatment of pruritis and vitiligo. 
     Compounds disclosed herein may also be used in the treatment of tissue damage in such diseases as vascular diseases, migraine headaches, periarteritis nodosa, thyroiditis, aplastic anemia, Hodgkin&#39;s disease, sclerodoma, rheumatic fever, type I diabetes, neuromuscular junction disease including myasthenia gravis, white matter disease including multiple sclerosis, sarcoidosis, nephritis, nephrotic syndrome, Langerhans&#39; cell histiocytosis, glomerulonephritis, reperfusion injury, pancreatitis, interstitial cystitis, Behcet&#39;s syndrome, polymyositis, gingivitis, periodontis, hypersensitivity, swelling occurring after injury, ischemias including myocardial ischemia, cardiovascular ischemia, and ischemia secondary to cardiac arrest, cirrhosis, septic shock, endotoxic shock, gram negative sepsis, toxic shock syndrome, stroke, ischemia reperfusion injury, multi-organ dysfunction, restenosis including restenosis following coronary bypass surgery, and the like. 
     Furthermore, the compounds disclose herein may also be useful in inhibiting PDE4 activity for the amelioration of systemic disorders including systemic hypotension associated with septic and/or toxic hemorrhagic shock induced by a wide variety of agents; as a therapy with cytokines such as TNF, IL-1 and IL-2; and as an adjuvant to short term immunosuppression in transplant therapy. 
     Compounds disclosed herein may also be used in the treatment of cancer, such as colorectal cancer, and cancer of the breast, lung, prostate, bladder, cervix and skin. Compounds of the invention may be used in the treatment and prevention of neoplasias including but not limited to brain cancer, bone cancer, leukemia, lymphoma, epithelial cell-derived neoplasia (epithelial carcinoma) such as basal cell carcinoma, adenocarcinoma, gastrointestinal cancer such as lip cancer, mouth cancer, esophageal cancer, small bowel cancer and stomach cancer, colon cancer, liver cancer, bladder cancer, pancreas cancer, ovary cancer, cervical cancer, lung cancer, breast cancer and skin cancer, such as squamous cell and basal cell cancers, prostate cancer, renal cell carcinoma, and other known cancers that effect epithelial cells throughout the body. The neoplasia can be selected from gastrointestinal cancer, liver cancer, bladder cancer, pancreas cancer, ovary cancer, prostate cancer, cervical cancer, lung cancer, breast cancer and skin cancer, such as squamous cell and basal cell cancers. The present compounds and methods may also be used to treat the fibrosis which occurs with radiation therapy. The present compounds and methods may be used to treat subjects having adenomatous polyps, including those with familial adenomatous polyposis (FAP). Additionally, the present compounds and methods may be used to prevent polyps from forming in patients at risk of FAP. 
     Compounds disclosed herein may also be used in the treatment of otic diseases and otic allergic disorders, including eustachian tube itching. 
     Compounds disclosed herein may also be used in the treatment of ophthalmic diseases, such as ophthalmic allergic disorders, including allergic conjunctivitis, vernal conjunctivitis, vernal keratoconjunctivitis, and giant papillary conjunctivitis, dry eye, glaucoma, corneal neovascularization, optic neuritis, Sjogren&#39;s syndrome, retinal ganglion degeneration, ocular ischemia, retinitis, retinopathies, uveitis, ocular photophobia, and of inflammation and pain associated with acute injury to the eye tissue. Specifically, the compounds may be used to treat glaucomatous retinopathy and/or diabetic retinopathy. The compounds may also be used to treat post-operative inflammation or pain as from ophthalmic surgery such as cataract surgery and refractive surgery. In certain embodiments, the compounds of the present invention are used to treat an allergic eye disease chosen from allergic conjunctivitis; vernal conjunctivitis; vernal keratoconjunctivitis; and giant papillary conjunctivitis. 
     Moreover, compounds of the subject invention may be used in the treatment of menstrual cramps, dysmenorrhea, premature labor, endometriosis, tendonitis, bursitis, skin-related conditions such as psoriasis, eczema, burns, sunburn, dermatitis, pancreatitis, hepatitis, lichen planus, scleritis, scleroderma, dermatomyositis, and the like. Other conditions in which the compounds of the subject invention may be used include diabetes (type I or type II), atherosclerosis, congestive heart failure, myocarditis, atherosclerosis, cerebral ischemia, angiogenesis, pulmonary hypertension, and aortic aneurysm. 
     The compounds disclosed herein may also be used in co-therapies, partially or completely, in place of other conventional anti-inflammatory therapies, such as together with steroids, NSAIDs, COX-2 selective inhibitors, 5-lipoxygenase inhibitors, LTB4 antagonists and LTA4 hydrolase inhibitors. Additional co-therapies comprising the compounds disclosed herein with biologics include:
         tumor necrosis factor alpha (TNFα) blockers such as etanercept (Enbrel), infliximab       

     (Remicade), adalimumab (Humira), certolizumab pegol (Cimzia), and golimumab (Simponi);
         Interleukin 1 (IL-1) blockers such as anakinra (Kineret);   monoclonal antibodies against B cells such as rituximab (Rituxan);   T cell costimulation blocker such as abatacept (Orencia); and   Interleukin 6 (IL-6) blockers such as tocilizumab (RoActemra or Actemra, an anti-IL-6 receptor antibody).       

     Compounds disclosed herein may also be used to prevent tissue damage when therapeutically combined with antibacterial or antiviral agents. In certain embodiments, the compounds disclosed hereinmay be combined with neuraminidase inhibitors for the treatment of a viral disease such as influenza. 
     Compounds disclosed herein may also be used in methods of positron emission tomography (PET) imaging and related methods of diagnosis, monitoring, and treatment of diseases. 
     Fluorine (F) exists as one of six isotopes:  17 F,  18 F,  19 F,  20 F,  21 F, and  22 F. The natural abundance of  19 F is 100%. The radioisotope  18 F can be prepared using conventional means (e.g., by bombarding 180-enriched water with high energy protons) and has a half-life of about 110 minutes. 
     Labelling of compounds with  18 F permits their use as positron emission tomography (PET) imaging agents. PET is a powerful non-invasive molecular imaging technique. It is used to study and visualize in vivo biological disorders at the molecular level, by detection of positron-emitting radiotracers, before anatomical changes become apparent. 
     Therefore, PET may be used for detection and monitoring of diseases, as well as investigating the efficacy of drugs. The information that PET provides at molecular level about biochemical processes (functional information) is not available from other conventional imaging techniques such as Computed Tomography (CT) or Magnetic Resonance Imaging (MRI). On the other hand, these imaging modalities provide a detailed picture of the body&#39;s internal anatomy (anatomical information). The combination of PET with one of these imaging tools allows the matching of functional and anatomical information. For example, the combined PET/CT technique provides complete information both on disease location and status. 
     Besides being useful for human treatment, imaging, and related processes, certain compounds and formulations disclosed herein may also be useful for veterinary treatment imaging, and related processes in companion animals, exotic animals and farm animals, including mammals, rodents, and the like. More preferred animals include horses, dogs, and cats. 
     All references, patents or applications, U.S. or foreign, cited in the application are hereby incorporated by reference as if written herein in their entireties. Where any inconsistencies arise, material literally disclosed herein controls. 
     General Synthetic Methods for Preparing Compounds 
     The invention is further illustrated by the following examples. 
     EXAMPLE 1 
     5-[(4-fluorophenyl)methyl]-7-(3-nitrophenyl)-2,3-dihydrobenzofuran 
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     Step 1: (7-bromo-2,3-dihydrobenzofuran-5-yl)-(4-fluorophenyl)methanol 
     
       
         
         
             
             
         
       
     
     A 25-mL round bottom flask, with stirrer bar, was charged with 7-bromo-2,3-dihydrobenzofuran-5-carbaldehyde (250 mg, 1.1 m mol, 1.0 eq.) and THF (5.0 mL). A solution of 4-fluorophenylmagnesium bromide (0.75 mL, 2.0M in ether, 1.5 mmol, 1.3 eq.) was added dropwise over 5 minute at −78° C. After stirring for 1.5 hrs at at −78° C., Methanol (0.2 ml) was added. The reaction mixture was allowed to warm to room temperature and partitioned between ether (15 ml) and NH 4 Cl aq (15 ml). The organic layer was separated and dried over Na 2 SO 4 . Removal of solvent under reduced pressure gave the crude product (7-bromo-2,3-dihydrobenzofuran-5-yl)-(4-fluorophenyl)methanol (407 mg, 100% yield). The product thus obtained was forwarded to the next step without any further purification. 
     Step 2: 7-bromo-5-[(4-fluorophenyl)methyl]-2,3-dihydrobenzofuran 
     
       
         
         
             
             
         
       
     
     A 18-mL vial, with stirrer bar, was charged with (7-bromo-2,3-dihydrobenzofuran-5-yl)-(4-fluorophenyl)methanol (407 mg, 1.1 mmol, 1 eq.) and dichloromethane (4 ml). To the solution at 0° C. was added Et 3 SiH (1 ml) followed by trifluoroacetic acid (2 ml) slowly. After the addition was complete, the resulting mixture was stirred at 0° C.˜rt until the starting material was consumed (2 hrs). The mixture was then added to NaHCO 3  aq (5 g, 20 ml) at 0° C. and extracted with ether (10 ml X 3). The organics were combined and dried over Na 2 CO 3 . Removal of solvent under reduced pressure gave the title compound (332 mg, 98% yield). The product thus obtained was forwarded to the next step without any further purification. 
     Step 3: 5-[(4-fluorophenyl)methyl]-7-(3-nitrophenyl)-2,3-dihydrobenzofuran 
     
       
         
         
             
             
         
       
     
     A 18-mL vial, with stirrer bar, was charged with 7-bromo-5-[(4-fluorophenyl)methyl]-2,3-dihydrobenzofuran (330 mg, 1.07 mmol, 1 eq.), 3-nitrophenylboronic acid (270 mg, 1.6 mmol, 1.5 eq.), Pd(PPh 3 ) 4  (100 mg, 0.087 mmol, 0.08 eq.), powdered K 3 PO 4  (480 mg, 2.26 mmol, 2 eq.), 1,2-dimethoxyethane (6 ml), ethanol (1.5 ml) and water (1.5 ml). The mixture was purged with Ar for 15 minutes and then stirred at 80° C. overnight. After cooling to room temperature, the volatile material was removed under reduced pressure and the residue was partitioned between water (10 ml) and dichloromethane (15 ml). The organic layer was separated and dried over Na 2 SO 4 . Solvent was removed under reduced pressure to give a residue, which was purified by chromatography on silica gel using hexane/dichloromethane (9:1) as eluent to give the title compound as a yellowish solid (108 mg, 29% yield). MW=351.37.  1 H NMR (DMSO-d 6 , 400 MHz) δ 8.55 (s, 1H), 8.17 (m, 2H), 7.73 (dd, J=8.0 and 8.0 Hz, 1H), 7.38 (s, 1H), 7.32 (m, 2H), 7.15 (s, 1H), 3H). 7.11 (dd, J=8.8 and 9.2 Hz, 2H), 4.61 (t, J=8.8 Hz, 2H), 3.93 (s, 2H), 3.21 (t, J=8.8 Hz, 2H). 
     EXAMPLE 2 
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     The title compound may be prepared using methods analogous to those disclosed herein, particularly as disclosed in Scheme II above, and by methods known in the art. 
     Biological Assays 
     The activity of the compounds in Example 1 as a PDE4 inhibitor is illustrated in the following assay. Certain compounds listed above, which have not yet been made and/or tested, such as Example 2, are predicted to have activity in this assay as well. 
     Kinetic Assay of PDE4 Activity 
     PDE4 activity may be measured by any method known in the art. Here, a kinetic assay of cAMP hydrolysis by purified PDE4 was used, in which PDE4 activity was measured by coupling the formation of the PDE4 reaction product, 5′-adenosine monophosphate, to the oxidation of reduced nicotinamide adenine dinucleotide (NADH) by the use of three coupling enzymes (myokinase, pyruvate kinase and lactate dehydrogenase), which allows fluorescent determination of reaction rates. Assays are performed in 96-well plates in a total volume of 200 μl/well. Compounds are dissolved in dimethylsulfoxide (DMSO) and added to plates in a volume of 10 μl followed by addition of 165 μl of assay mix. Plates are pre-incubated at 25° C. for 15 min and the reactions are initiated by the addition of 25 μl of cAMP followed by thorough mixing. Reaction rates are measured by monitoring the decrease in fluorescence using excitation at 355 nm and emission at 460 nm for a period of 10 min in a fluorescence plate reader. Initial rates (slopes) are determined from linear portions of the progress curves. Final concentrations of assay components are as follows: 50 mM Tris, pH 8, 10 mM MgCl 2 , 50 mM KCl, 2% DMSO, 5 mM tris(2-carboxyethyl)phosphine (TCEP), 0.4 mM phosphenolpyruvate (PEP), 0.01 mM NADH, 0.04 mM adenosine triphosphate (ATP), 0.004 mM cAMP, 7.5 units myokinase from yeast, 1.6 units pyruvate kinase, 2 units lactate dehydrogenase, and 0.5 nM human PDE4D7. All data are percent normalized relative to controls and are presented as percent inhibition. An inhibitory concentration 50% (IC 50 ) value is calculated by fitting of a sigmoidal dose response curve. Human PDE4D7 contained a mutation of serine 54 to aspartic acid to mimic activation by cAMP-dependent protein kinase A (PKA). These methods were adapted from Burgin, A. B. et al., “Design of Phosphodiesterase Type 4D (PDE4D) Allosteric Modulators for Cognition with Improved Safety,”  Nature Biotechnology  28, 63-70 (2010). 
     Results for Example 1 are shown in  FIG. 1 . It is expected that other compounds disclosed herein, such as Example 2, will demonstrate similar activity. 
     In Vivo Assays 
     Depression 
     PDE4 inhibitors may be shown to be effective in an animal model of depression (such as forced swimming test) and animal model of memory (such as maze test). See Saccomano, N. A. et al.,  J. Med. Chem.  34, p 291-298, 1991; O&#39;Donnell, J. M. and Zhang, H. T.,  Trends Pharmacal. Sci.,  25, p 158-163 (2004; Zhang, H. T. and O&#39;Donnell, J. M,  Psychopharmacology,  150, p 311-316, 2000. Since these improvements are hypothesized to be caused by activation of the central nerve system as a result of increase of the intracellular cAMP level, the compound of the invention, compounds disclosed herein are expected to be effective in diseases that are improved by activation of the central nervous system. Examples of such diseases include depression, anxiety, degradation of learning and memory ability, Alzheimer&#39;s disease, arteriosclerotic dementia, Parkinson&#39;s disease, Huntington&#39;s disease and late motor disorders. 
     The forced-swim test (FST) is the most widely used test of antidepressant drug action. In the FST, a rat is placed in an inescapable cylinder of water. (See Krishnan V and Nestler EJ, “Animal models of depression: molecular perspectives,”  Current topics in behavioral neurosciences  2011; 7:121-47; and Bergner C L et al., “Mouse models for studying depression-like states and antidepressant drugs,”  Methods Mol Biol  2010; 602:267-82.) This causes stress to the animal and following an initial period of swimming and climbing, the rat eventually displays a floating or immobile posture. The rat is removed from the water after 15 minutes. Immobility has been interpreted as an expression of behavioral despair or entrapment and is reversed by the single dose administration of almost all available antidepressants. 
     Intact, adult male or female rats are used for the FST. Either outbred or inbred strains of rats may be used for the study. The rats are group housed and allowed to acclimate for 7 days after arrival. All rats will be housed on standard bedding, kept under a reversed 12:12 hr light:dark (lights on ˜6 pm:6 am), and will receive food and water ad lib. 
     Comparison is made between a group of 10 rats that is dosed with vehicle only versus groups of 10 rats that are dosed with varying amounts of the test compound. Typically, test compounds are dosed at 0.1, 0.3, 1, 3, and 10 mg/kg by oral gavage. The dosing volume will be 10 ml/Kg for PO. The vehicle for dosing will be chosen based on the solubility of the compound. For oral dosing, the compound may be dosed in solution or may be dosed in suspension depending upon solubility. PO dosing is performed by oral gavage while the rat is restrained by hand using a flexible tube appropriate for rat. 
     For the FST, rats are placed in a cylindrical 5 gallon tank so the animals can swim or float without touching the bottom with their tails. The test is recorded via video camera for analysis offline or scored in real time by an observer. Behavior is scored by categorizing behavior as active escape (swimming, climbing), passive (floating immobile) or neutral (quiet paddling or grooming behaviors). For each rat, onset to the first 5 second bout of immobility, the number of bouts of immobility, and total time spent immobile is recorded. Immobility may be compared during the first 5 min of the FST or during the last 5 min of the FST. Comparison of data between groups is by ANOVA. 
     Compounds disclosed herein are expected to demonstrate activity in the models disclosed above, and to have utility in the treatment of diseases disclosed herein, including disorders of the central nervous system, psychological disorders, and disorders of cognition. 
     Traumatic Brain Injury 
     Restoration of Cognitive Function in Brain Injured Rats 12 Weeks After Traumatic Brain Injury. 
     Sprague Dawley rats may be subjected to moderate parasagittal fluid-percussion brain injury using methods described in Atkins et al,  J Neurosci Res  90, 1861-71 (2012). Adult male Sprague Dawley rats (280-300 g; Charles Rivers Laboratories) are anesthetized with 3% isoflurane, 70% N 2 O, and 30% O 2  and received a 4.8-mm craniotomy (3.8 mm posterior to bregma, 2.5 mm lateral to the midline) over the right parietal cortex. Twenty-four hours after the craniotomy, the animals are re-anesthetized (3% isoflurane, 70% N 2 O, and 30% O 2 ); immobilized with pancuronium bromide (1.0 mg/kg); and mechanically ventilated with 1% isoflurane, 70% N 2 O, and 30% O 2 . When physiological measurements had stabilized, the animals receive a fluid-percussion pulse (1.8-2.2 atmospheres, 14-16 msec) or sham injury with the fluid-percussion brain injury device. Blood gases, blood pH, and mean arterial blood pressure are monitored for 30 min prior to the fluid percussion brain injury or sham surgery and for up to 1 hr post-injury to maintain normal levels. Injured and sham injured rats are coded such that the investigator assessing the behavior of the animals would not know their injury status. 
     Compounds disclosed herein as test articles may be dissolved in 100% dimethylsulfoxide (DMSO) at 1 mg/ml and then diluted 20 fold into 0.9% sodium chloride (saline) with 2 molar equivalents of sodium hydroxide (0.258 mM) to yield a final concentration of 0.05 mg/ml in 5% DMSO saline. Rats treated with vehicle receive 5% DMSO in saline. Four treatment groups may be studied; TBI rats treated with vehicle, TBI rats treated with Compound, sham rats treated with vehicle, and sham rats treated with Compound. Compound and vehicle are delivered by intraperitoneal injection. Compound may be administered at a dose of 0.3 mg/kg. Twelve weeks after surgery, rats are tested for cognitive ability using the water maze test. Animals received vehicle or Compound (0.3 mg/kg, i.p.) 30 min prior to water maze training. The circular pool (122 cm diameter, 60 cm deep) is filled with opaque water at 24° C. and surrounded by distinct, invariant extramaze cues. An escape platform, 9.3 cm in diameter, is submerged 1.5 cm below the water surface. Animals receive four 60 s acquisition trials per day for 4 days with inter-trial intervals of 4 min. If the rat fails to navigate to reach the platform within 60 s, it is guided to the platform and remained on the platform for 10 s. Path length to reach the platform, escape latency, and swim speed are analyzed, for example with EthoVision software (Noldus Information Technology). After 4 training days, a probe trial (30 s duration) is given with the platform removed and no drug treatment is given prior to the probe trial. 
     During acquisition, TBI animals are expected to display progressive learning. Even on the 4th day of training, TBI animals treated with vehicle typically have significantly longer escape latencies and path lengths as compared to sham animals treated with vehicle. In contrast, TBI animals treated with Compound are expected to display a progressive decrease in escape latency and path length to reach the hidden platform and these indices of learning are expected to be comparable to sham animals treated with vehicle or Compound on the 4th day of acquisition. 24 h after the last acquisition trial, animals are tested for retention during a probe trial with the platform removed. TBI animals treated with vehicle are expected to spend less time in the target quadrant as compared to Compound-treated TBI animals or sham animals treated with vehicle or Compound. 
     To assess working memory in TBI animals, a working memory version of the water maze task is used on week 14 post-surgery. At 30 min prior to testing, animals receive Compound or vehicle. Four paired trials are given each day for 2 days with inter-trial intervals of 4 min. Trial duration is 60 s. The hidden platform remains invariant in location for each pair of trials. Upon reaching the platform, the animal remains on the platform for 10 s. After a 5 s delay, the animal is released into the water maze to again search for the hidden platform in the same location. Escape latency differences between the first location trial and subsequent match trial are measured. There is expected to be a significant impairment in working memory in TBI animals treated with vehicle as compared to sham animals, and this deficit is expected to be rescued by treatment of TBI animals with compounds disclosed herein. 
     Human Clinical Trial to Demonstrate Pro-cognitive Benefit in Subjects with Traumatic Brain Injury. 
     Compounds disclosed herein may be assessed in a 4 week, double-blind, randomized, multiple dose, placebo controlled, cross-over study to examine pro-cognitive benefit in otherwise healthy male or female subjects who have sustained a TBI 1-5 years previously and continue to have measurable cognitive impairment. The TBI may or may not have resulted in hospitalization. To be included in the study, subjects will have sustained a closed head injury resulting in moderate-to-severe impairment of consciousness. Impairment of consciousness will have been assessed using the Glasgow Coma Scale (GCS) or similar clinical scale. Subjects included in the study will have sustained a TBI that resulted in impairment of consciousness of GCS &lt;9 indicating severe loss of consciousness, or GCS &lt;13 indicating moderate loss of consciousness. The TBI will have resulted in measureable cognitive impairment 1-5 years after injury. The advantage of the crossover design is that each subject will act as their own control and fewer subjects will be required than a between-group design. In the first stage of the trial, subjects are randomized to receive either the PDE4B inhibitor or placebo for 4 weeks. After a two week washout, subjects cross-over to the second stage of the trial in which those that previously received the PDE4B inhibitor now receive placebo for 4 weeks. Correspondingly, those that received placebo previously cross over to receive the PDE4B inhibitor for 4 weeks. The primary outcome measure is assessment of cognitive function. Compounds disclosed herein are expected to show pro-cognitive benefit. 
     PET Assay 
     Molecular imaging (MRI, SPECT, and PET) has the potential to detect disease progression or therapeutic effectiveness earlier than most conventional methods in the fields of cardiology neurology, and oncology. Positron emission tomography (PET) is of particular interest for drug development because of its high sensitivity and ability to provide quantitative and kinetic data. 
     Positron emitting isotopes, including [ 11 C]-carbon, [ 13 N]-nitrogen, [ 15 O]-oxygen, and [ 18 F]-fluorine, can substitute for non-radioactive isotopes in target compounds and produce PET imagining tracers that are biologically equivalent to the original molecules and are useful as in vivo imaging agents targeting and visualizing diseases of the brain. Among these isotopes, [ 18 F]-fluorine (t1/2=109.7 min; β+=97%) has become widely popular because [ 18 F]-fluoride ion can be produced in high amounts and in high no-carrier-added (NCA) specific radioactivity. 
     [ 18 F]-Fluoride can be incorporated covalently into radiotracers having diverse structure and molecular weight. The nucleophilic aromatic and aliphatic [ 18 F]-fluoro-fluorination reaction has shown great utility in the synthesis of [ 18 F]-fluoro labelled radiopharmaceuticals, provided that suitably reactive precursors can be prepared for classical SN2 or SNAr reactions. Aryl C- 18 F bonds are generally favored in PET radiotracers because of their usual resistance to cleavage in vivo. Several methods are known for incorporating  18 F to an aromatic ring, including triarylsulfonium salts and diaryl sulfoxides. The use of diaryl iodonium salts has also been used to direct labeling of low molecular weight radiotracers. 
     Radiolabeled compounds disclosed herein, such as those incorporating  18 F, are expected to be useful as PET imaging agents. 
     Solubility Protocol 
     To measure compound solubility in aqueous buffer, about 5 mg of a compound may be mixed with 500 μL of pH 7.4, 0.1 M sodium phosphate buffer. The mixture is adjusted to the original pH of 7.4 and then mixed overnight or longer via rotary mixing. The sample is checked for pH and then filtered through a 0.45 μm filter. If the pH drifted away, the sample is adjusted to its original pH and mixed for at least 15 minutes before filtration. The filtrate is analyzed using HPLC. Generally, solubility ≧1 mg/mL is considered to be better than solubility of &lt;1 mg/mL, as it is generally easier to formulate for oral delivery. Certain compounds disclosed herein are expected to have solubility of ≧1 mg/mL. However, ideal solubility may vary; for example, an aqueous formulation may benefit from an even higher solubility. Conversely, a formulation containing hydrophilic carriers and one or more surfactants may be used to deliver a compound of low aqueous solubility. 
     Shelf Stability Protocol 
     To provide a measure of compound stability, about 3 mg of a compound may be dissolved in 3 mL of acetonitrile/water mixture (50/50). 100 μL of the stock solution is added to 20 mL each of 0.025 M pH 5.0 sodium acetate buffer (A5.0), 0.025 M pH 5.0 citrate buffer (C5.0) and 0.025 M pH 7.4 sodium phosphate buffer (P7.4). A two mL aliquot of each solution is kept in a glass vial equipped a cap lined with Teflon. Two vials containing the solution may be stored at 4° C. or −20° C. as control. Other aliquots may be stressed at RT, 45° C. or 75° C. for specified time check points, e.g. 1 day, 1 week, 2 weeks, 4 weeks, 8 weeks, or 12 weeks. The stressed samples in duplicate are assayed against the control using HPLC. The results are reported in % degradation. Preliminary shelf life (T90) is estimated assuming the rate of chemical degradation is double when the temperature is up 10° C. 
     It is expected that certain compounds disclosed herein, when tested, will be sufficiently shelf-stable. 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.