PYRAZOLE CYCLIC AMP-SPECIFIC PDE INHIBITORS

Abstract: Pyrazole compounds (I) that are potent and selective inhibitors of PDE4, as well as methods of making the same, are disclosed. Use of the compounds in the treatment of inflammatory diseases and other diseases involving elevated levels of cytokines, as well as central nervous system (CNS) disorders, also is disclosed (I) wherein Y is O or NOH; Z is O or NH; R<1> - R<4> are as claimed.

Description: PYKAZOLE CYCLIC AMP - SPECIFIC PDE INHIBITORS CROSS - REFERENCE TO RELATED APPLICATION Thi s appl icat ion claims the benef i t of provi s ional appl i cat ion Serial No . 60 / 172 , 067 , f i l ed December 23 , 1999 . FIELD OF INVENTION The present invention relates to a series of compounds that are potent and selective inhibitors of cyclic adenosine 3 ' , 5 ' -monophosphate specific phosphodiesterase (cAMP specific PDE) . In particular, the present invention relates to a series of novel pyrazole compounds which are useful for inhibiting the function of cAMP specific PDE, m particular, PDE4 , as well as methods of making the same, pharmaceutical compositions containing the same, and their use as therapeutic agents, for example, m treating inflammatory diseases and other diseases involving elevated levels of cytokines and proinflammatory mediators. BACKGROUND QF THE INVENTION Chronic inflammation is a multi-factorial disease complication characterized by activation of multiple types of inflammatory cells, particularly cells of lymphoid lineage (including T lymphocytes) and myeloid lineage (including granulocytes , macro- phages, and monocytes) . Proinflammatory mediators, including cytokines, such as tumor necrosis factor (TNF) and mterleukm-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 m the therapeutic treatment of inflammatory diseases and other diseases involving elevated levels of cytokines. Cyclic adenosine onophosphate (cAMP) is a second messenger that mediates the biologic re- sponses 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 tπphosphate (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 structures of cAMP and 5'- AMP are illustrated below. cAMP 5 ' -AMP Elevated levels of cAMP m 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 m cells. PDE4 is a predominant PDE isotype m 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, sup ¬ press cell activation (see Beavo et al , "Cyclic Nucleotide Phosphodiesterases Structure, Regulation and Drug Action," Wiley and Sons, Chichester, pp 3-14, (1990)); Torphy et al , Drug News and Perspectives, 6, pp. 203-214 (1993) ; Giembycz et al , Clm . Exp . Allergy, 22 , pp. 337-344 (1992) . In particular, PDE4 inhibitors, such as rolipram, have been shown to inhibit production of TNFα and partially inhibit IL-1. release by monocytes (see Semmler et al . , Int . J. Immunopharmacol . , 15 , pp. 409-413 (1993); Molnar-Kimber et al . , Media tors of Inflammation, 1, pp. 411-417 (1992)). PDE4 inhibitors also have been shown to inhibit the pro- duction of superoxide radicals from human poly- morphonuclear 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 m eosmophils (see Dent et al., J. Pharmacol . , 103 , pp. 1339-1346 (1991)); and to inhibit the activation of human T-lymphocytes (see Robicsek et al . , Bioche . Pharmacol . , 42 , pp. 869-877 (1991) ) . Inflammatory cell activation and excessive or unregulated cytokme (e.g , TNFα and I -15) production are implicated m allergic, autoimmune, and inflammatory diseases and disorders, such as rheumatoid arthritis, osteoarthπtis , gouty arthritis, spondylitis, thyroid associated ophthalmopathy, Behce ' s disease, sepsis, septic shocκ, endotoxic snock, gram negative sepsis, gram positive sepsis, toxic shock syndrome, asthma, chronic bronchitis, adult respiratory distress syndrome, chronic pulmo- nary inflammatory disease, such as chronic obstructive pulmonary disease, silicosis, pulmonary sarco- ldosis, reperfusion injury of the myocardium, brain, and extremities, fibrosis, cystic fibros s, keloid formation, scar formation, atherosclerosis, trans- plant rejection disorders, such as graft vs. host reaction and allograft rejection, chronic glomerulo- nephritis, lupus, inflammatory bowel disease, such as Crohn's disease and ulcerative colitis, prolif- erative lymphocyte diseases, such as leukemia, and inflammatory dermatoses, such as atopic dermatitis, psoriasis, and urticaria. Other conditions characterized by elevated cytokme levels include brain injury due to moderate trauma (see Dhillon et al . , J. Neurotrauma, 12 , pp. 1035-1043 (1995); Suttorp et al . , J " . Clm . Invest . , 91 , pp. 1421-1428 (1993)), cardiomyopathies , such as congestive heart failure (see Bπstow et al . , Circu la tion , 97, pp. 1340-1341 (1998)), cachexia, cachexia secondary to infection or malignancy, cachexia secondary to acquired immune deficiency syndrome (AIDS) , ARC (AIDS related complex) , fever myalgias due to infection, cerebral malaria, osteoporosis and bone resorption diseases, keloid formation, scar tissue formation, and pyrexia In particular, TNFα has been identified as having a role with respect to human acquired immune deficiency syndrome (AIDS) . AIDS results from the infection of T-lymphocytes with Human Immunodefi- ciency Virus (HIV) . Although HIV also infects and is maintained in myeloid lineage cells, TNF has been shown to upregulate HIV infection m T-lymphocytic and monocytic cells (see Poll et al . , Proc . Na zi . Acad . Sci . USA, 87 , pp. 782-785 (1990)). 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 m the development and metastatic spread of cancer m the host. TNFα recently has been directly implicated m the promotion of growth and metastasis of tumor cells (see Orosz et al . , J " . Exp . Med . , 177, pp. 1391-1398 (1993) ) . PDE4 has a wide tissue distribution. There are at least four genes for PDE4 of which multiple transcripts from any given gene can yield several different proteins that share identical catalytic sites. The ammo acid identity between the four possible catalytic sites is greater than 85%. Their shared sensitivity to inhibitors and their kinetic similarity reflect the functional aspect of this level of ammo acid identity. It is theorized that the role of these alternatively expressed PDE4 proteins allows a mechanism by wnich a cell can differentially localize these enzymes mtracellularly and/or regulate the catalytic efficiency via post translational modification. Any given cell type that expresses the PDE4 enzyme typically expresses more than one of the four possmle genes encoding these proteins. Investigators have shown considerable interest the use of PDE4 inhibitors as anti-m- flammatory agents. Early evidence indicates that PDE4 inhibition has beneficial effects on a variety of inflammatory cells such as monocytes, macro- phages, T-cells of the Th-1 lineage, and granulo- cytes . The synthesis and/or release of many proinflammatory mediators, such as cytokines, lipid mediators, superoxide, and biogemc amines, such as histamme, have been attenuated these cells by the action of PDE4 inhibitors. The PDE4 inhibitors also affect other cellular functions including T- cell proliferation, granulocyte transmigration response to chemotoxic substances, and integrity of endothelial cell junctions withm the vasculature. The design, synthesis, and screening of various PDE4 inhibitors have been reported. Methyl- xanthmes, such as caffeine and theophyll e, were the first PDE inhibitors discovered, but these com- pounds are nonselective with respect to which PDE is inhibited. The drug rolipram, an antidepressant agent, was one of the first reported specific PDE4 inhibitors. Rolipram, having the following structural formula, has a reported 50% Inhibitory Concen- tration (IC 50 ) of about 200 nM (nanomolar) with respect to inhibiting recombinant human PDE4. Rolipram 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. One class of compounds is disclosed in Feldman et al . U.S. Patent No. 5,665,754. The compounds disclosed therein are substituted pyrrolidines having a structure similar to rolipram. One particular compound, having the following structural formula, has an IC 50 with respect to human recombinant PDE4 of about 2 nM . Inasmuch as a favorable separation of emetic side effect from efficacy was observed, these compounds did not exhibit a reduction in undesirable CNS effects. 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 , and that reduce or eliminate the adverse CNS 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 the treatment of diseases that are associated with ele- vated cAMP levels or PDE4 function in a particular target tissue. SUMMARY OF THE INVENTION The present invention is directed to potent and selective PDE4 inhibitors useful in treatment of diseases and conditions where inhibition of PDE4 activity is considered beneficial. The present PDE4 inhibitors unexpectedly reduce or eliminate the adverse CNS side effects associated with prior PDE4 inhibitors . In particular, the present invention is directed to pyrazole compounds having the structural formula (I) : ( I ) wherein Y is O or NOH; R 1 is selected from the group consisting of optionally substituted alkyl, cycloalkyl, aryl , heteroaryl, alkaryl, aralkyl , heteroaralkyl , and heteroalkaryl ; R 2 is selected from the group consisting of optionally substituted hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, alkoxyalkyl, aryloxyalkyl , aral- koxyalkyl , (alkylthio) alkyl , (arylthio) alkyl , and (aralkylthio) alkyl ; and R 3 and R 4 , independently, are selected from the group consisting of hydrogen, alkyl, haloalkyl, alkoxyalkyl, aryl, C(=0) alkyl, and C (=0) CH=CHNR 5 R 6 ; R 5 and R 6 , independently, are hydrogen or alkyl, or R 5 and R 6 are taken together to form a 5- or 6-membered ring. The present invention also is directed to pharmaceutical compositions containing one or more of the compounds of structural formula (I) , to use of the compounds and compositions containing the compounds the treatment of a disease or disorder, and to methods of preparing the compounds and inter- mediates involved in the synthesis of the compounds of structural formula (I) . BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 contains plots of TNFα concentra ¬ tion m serum (pg/mL) vs. concentration of PDE4 inhibitors . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to compounds having a structural formula: wherein Y is O or NOH; Z is O or NH; R 1 is selected from the group consisting of optionally substituted alkyl, cycloalkyl, aryl, alkaryl, aralkyl, heteroaralkyl, and heteroalkaryl; R 2 is selected from the group consisting of optionally substituted hydrogen, methyl, C 3 16 alkyl, aryl, heteroaryl, alkoxyalkyl, aryloxyalkyl, aral- koxyalkyl , (alkylthio) alkyl , (arylthio) alkyl , and (aralkylthio) alkyl ; R 3 and R " * , independently, are selected from the group consisting of hydrogen, alkyl, haloalkyl, and aryl ; with the proviso that when R x is unsubsti- tuted phenyl, R 2 is different from unsubstituted phenyl, unsubstituted pyridinyl , or p-tolyl. The present invention also is directed to compounds having a structural formula: wherein Y is O or NOH; Z is O or NH; p is 0 or 1; R 1 is selected from the group consisting of alkyl, aryl, heteroaryl, alkaryl, aralkayl, heteroaralkyl, and heteroalkaryl; R 2 is ethyl; R 3 and R 4 , independently, are selected from the group consisting of hydrogen, alkyl, alkoxyalkyl, aryl, C(=0) alkyl, and C (=0) CH=CHNR 5 R 6 ; R 5 and R 6 , independently, are hydrogen or alkyl, or R 5 and R 6 are taken together to form a 5- or 6-membered ring, with the proviso that R 1 is different from nitro-substituted pyridinyl, amino-substituted phenyl, nitro- substituted phenyl, trichlorophenyl, and chlorotrifluorophenyl . The present invention is further directed to compounds having a structural formula: , and An important feature of the present invention is a method treating a disease or condition wherein inhibition of PDE activity is beneficial . The method comprises administering a therapeutically effective amount of a compound of structural formula (I ) to a mammal . R J (I) wherein Y is 0 or NOH; p is 0 or 1 ; R 1 is selected from the group consisting of optionally substituted alkyl, cycloalkyl, aryl, heteroaryl, alkaryl, aralkyl, heteroaralkyl, and heteroalkaryl ; R- is selected from the group consisting of optionally substituted hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, alkoxyalkyl, aryloxyalkyl, aralkoxyalkyl , (alkylthio) alkyl , (arylthio) alkyl , and (aralkylthio) alkyl ; and R and R J , independently, are selected from the group consisting of hydrogen, alkyl, haloalkyl, alkoxyalkyl, aryl, C(=0) alkyl, and C (=0) CH=CHNR=R ; R ^ and R" , independently, are hydrogen or alkyl, or R 5 and R " are taken together to form a 5- or 6-membered ring. A compound of structural formula (I) can be used alone, either neat or a composition that further contains a pharmaceutically acceptable carrier. A compound of structural formula (I) also can be administered conjunction with a second active therapeutic agent, for example, a second antiinflammatory therapeutic agent, like an agent capable of targeting TNFα. Compounds of structural formula (I) can be used to modulate cAMP levels a mammal, reduce TNFα levels m a mammal, suppress inflammatory cell activation m a mammal, inhibit PDE4 function a mammal, and treat conditions in a mammal when inhibition of PDE4 provides a benefit. As used herein, the term "mammals" includes males and females, and encompasses humans, domestic pets (e.g., cats, dogs), livestock (e.g., cattle, horses, pigs), and wildlife (e.g., primates, large felines, mammalian zoo specimens) . As used herein, the term "alkyl," alone or combination, is defined to include straight chain and branched chain, and bridged, saturated hydrocarbon groups containing one to 16 carbon atoms. "C_,_alkyl" refers to an alkyl group containing m to n carbon atoms. The term "lower alkyl" is defined herein as an alkyl group having one through six carbon atoms (C_-C . Examples of lower alkyl groups include, but are not limited to, methyl, ethyl, n- propyl , isopropyl, isobutyl, n-butyl , neopentyl , n- hexyl , and the like. The term "bridged alkyl" is defined herein as a C 6 -C lo bicyclic or polycyclic hydrocarbon group, for example, norboryl , adamantyl , bicyclo [2.2.2] - octyl, bicyclo [2.2.1] heptyl , bicyclo [3.2.1] octyl , or decahydronaphthyl . The term "cycloalkyl" is defined herein to include cyclic C 3 -C 7 hydrocarbon groups. Examples of cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl , cyclohexyl, and cyclo- pentyl . The term "haloalkyl" is defined herein as an alkyl group substituted with one or more halo substituents, either fluro, chloro, bromo, lodo, or combinations thereof. Similarly, "halocycloalkyl " is defined as a cycloalkyl group having one or more halo substituents. The term "aryl," alone or m combination, is defined herein as a monocyclic or polycyclic aromatic group, preferably a monocyclic or bicyclic aromatic group, e.g., phenyl or naphthyl , that can be unsubstituted or substituted, for example, with one or more, and m particular one to three, substituents selected from halo, alkyl, hydroxy, hy- droxyalkyl, alkoxy, alkoxyalkyl, haloalkyl, nitro, amino, alkylammo, acylammo, benzenesulfonylammo, alkylthio, alkylsulfmyl , and alkylsulfonyl . Exemplary aryl groups include phenyl, naphthyl , tetra- hydronaphthyl , 2 -chlorophenyi , 3 -chlorophenyl , 4- chlorophenyl, 2-methylphenyl , 4-methoxyphenyl , 3- tπfluoromethyl -phenyl , 4-nιtrophenyl , and the like. The term "heteroaryl" is defined herein as a monocyclic or bicyclic ring system containing one or two aromatic rings and containing at least one nitrogen, oxygen, or sulfur atom m an aromatic ring, and which can be unsubstituted or substituted, for example, with one or more, and m particular one to three, substituents, like halo, alkyl, hydroxy, hydroxyalkyl , alkoxy, alkoxyalkyl, haloalkyl, nitro, ammo, alkylammo, acylammo, benzenesulfonylammo, alkylthio, alkylsulf yl , and alkylsulfonyl . Examples of heteroaryl groups include thienyl, furyl , pyπdyl , oxazolyl , qu olyl , isoquinolyl, mdolyl, triazolyl, isothiazolyl , isoxazolyl, lmidizolyl, benzothiazolyl , pyrazmyl, pyrimid yl , thiazolyl , and thiadiazolyl . The term "aralkyl" is defined herein as a previously defined alkyl group, wherein one of the hydrogen atoms is replaced by an aryl group as de- fined herein, for example, a phenyl group optionally having one or more substituents, for example, halo, alkyl, alkoxy, and the like. An example of an aralkyl group is a benzyl group. The term "alkaryl" is defined herein as a previously defined aryl group, wherein one of the hydrogen atoms is replaced by an alkyl, cycloalkyl, haloalkyl, or halocycloalkyl group. The term "heteroaralkyl" and "heteroalkaryl" are defined similarly as the term "aralκ/1" and "alkaryl," however, the aryl group is replaced by a heteroaryl group as previously defined. The term "heterocycle" or "heterocyclic ring" is defined as a 5- or 6-membered nonaromatic ring having one or more heteroatoms selected from oxygen, nitrogen, and sulfur present m the ring. Nonlimiting examples include tetrahydrofuran, piper- ldine, piperazme, sulfolane, morpholme, tetrahy- dropyran, dioxane, and the like. A "carbocyclic ring" is similarly defined, but the ring contains solely carbon atoms. The term "halogen" or "halo" is defined herein to include fluorine, chlorine, bromine, and iodine . The term "alkoxy," "aryloxy," and "aralkoxy" are defined as -OR, wherein R is alkyl, aryl, and aralkyl, respectively. The term "alkoxyalkyl" is defined as an alkoxy group appended to an alkyl group. The terms "aryloxyalkyl" and "aralkoxyalkyl " are similarly defined as an aryloxy or aralkoxy group appended to an alkyl group. The terms " (alkylthio) alkyl , " " (arylthio) alkyl, " and " (aralkylthio) alkyl " are defined similarly as the three above-identifled groups, except a sulfur atom, rather than an oxygen atom, is present. The term "hydroxy" is defined as -OH. The term "hydroxya1kyl " is defined as a hydroxy group appended to an alkyl group. The term "ammo" is defined as -NH 2 . The tern "alkylammo" is defmed as -Nj_r_ where at least one R is alkyl and the second R is alkyl or hydrogen The term "acylammo" is defined as RC(=0)NH, wherein R is alkyl or aryl. The term "nitro" is defined as -NO, . The terms "alkylthio," "arylthio," and "aralkylthio" are defined as -SR, where R is alkyl, aryl, and aralkyl, respectively. The term "alkylsulfmyl " is defined as R-S(0) 2 , where R is alkyl. The term "alkylsulfonyl " is defined as R-S(0 3 ), where R is alkyl. In preferred embodiments, R 1 is selected from the group consisting of optionally substituted alkyl, aryl, alkaryl, and heteroaryl; R 2 is selected from the group consisting of optionally substituted hydrogen, alkyl, and aryl; and R 3 and R 4 , independently, are selected from the group consisting of optionally substituted alkyl, aryl, hydrogen, C(=0) alkyl, and C (=0) CH=CHNR 5 R° . In most preferred embodiments, R is aryl, cycloalkyl, or heteroaryl, optionally substituted with one or more of nitro, ammo, lower alkyl, alkoxy, halo, tπfluoromethyl , - , , and -NH-C-0(CH 3 ) 3 R 1 typically is phenyl, pyridyl, or cyclohexyl, optionally substituted. In most preferred embodiments, R 2 is alkyl, hydrogen, or Typically, R 2 is ethyl, methyl, or hydrogen, p is 1, and Y and Z are O . In most preferred embodiments, R J and R 4 , independently, are alkyl, hydrogen, trifluoromethyl , -C(=0)CH=CHN(CH 3 ) 2 , -C(=0)CH 3 , or -CH 2 OCH 3 . Typically, R 3 and R 4 are methyl or hydrogen. The present invention includes all possible stereoisomers and geometric isomers of compounds of structural formula (I), and includes not only racemic compounds but also the optically active isomers as well. When a compound of structural formula (I) is desired as a single enantiomer, it can be obtained either by resolution of the final product or by stereospecifIC synthesis from either isomerically pure starting material or use of a chiral auxiliary reagent, for example, see Z. Ma et al . , Tetrahedron; Asymmetry, 8 (6) , pages 883-888 (1997) . Resolution of the final product, an intermediate, or a starting material can be achieved by any suitable method known m the art. Additionally, m situations where tautomers of the compounds of structural formula (I) are possible, the present invention is intended to include all tautomeric forms of the compounds. As demonstrated hereafter, specific stereoisomers exhibit an exceptional ability to inhibit PDE4 without manifesting the adverse CNS side effects typically associated with PDE4 inhibitors. Compounds of structural formula (I) which contain acidic moieties can form pharmaceutically acceptable salts with suitable cations. Suitable pharmaceutically acceptable cations include alkali metal (e.g., sodium or potassium) and alkaline earth metal (e.g., calcium or magnesium) cations. The pharmaceutically acceptable salts of the compounds of structural formula (I) , which contain a basic center, are acid addition salts formed with pharma- ceutically acceptable acids. Examples include the hydrochloride , hydrobromide, sulfate or bisulfate, phosphate or hydrogen phosphate, acetate, benzoate, succinate, fumarate, maleate, lactate, citrate, tartrate, gluconate, methanesulfonate, benzene- sulphonate, and p-toluenesulphonate salts. In light of the foregoing, any reference to compounds of the present invention appearing herein is intended to include compounds of structural formula (I) , as well as pharmaceutically acceptable salts and solvates thereof . The compounds of the present invention can be therapeutically administered as the neat chemical, but it is preferable to administer compounds of structural formula (I) as a pharmaceutical composi- tion or formulation. Accordingly, the present invention further provides for pharmaceutical formulations comprising a compound of structural formula (I), or pharmaceutically acceptable salts thereof, together wit . one or more pharmaceutically acceptable carriers and, optionally, other therapeutic and/or prophylactic ingredients. The carriers are "acceptable" m the sense of being compatible witn the other ingredients of the formulation and not deleterious to the recipient thereof . In particular, a selective PDE4 inhibitor of the present invention is useful alone or m combination with a second antiinflammatory therapeutic agent, for example, a therapeutic agent targeting TNFα, such as ENBREL ® or REMICADE ® , which have utility m treating rheumatoid arthritis. Likewise, therapeutic utility of IL-1 antagonism has also been shown m animal models for rheumatoid arthritis. Thus, it is envisioned that IL-1 antagonism, combination with PDE4 inhibition, which attenuates TNFα, would be efficacious. The present PDE4 inhibitors are useful m the treatment of a variety of allergic, autoimmune, and inflammatory diseases. The term "treatment" includes preventing, lowering, stopping, or reversing the progression or severity of the condition or symptoms being treated. As such, the term "treatment" includes both medical therapeutic and/or prophylactic administration, as appropriate . In particular, inflammation is a localized, protective response elicited by injury or destruction of tissues, which serves to destroy, dilute or wall off (i.e., sequester) both the injurious agent and the injured tissue. The term "inflammatory disease," as used herein, means any disease m which an excessive or unregulated mflamma- tory response leads to excessive inflammatory symptoms, host tissue damage, or loss of tissue function. Additionally, the term "autoimmune disease," as used herein, means any group of disorders m which tissue injury is associated with humoral or cell -mediated responses to the body's own constituents. The term "allergic disease," as used herein, means any symptoms, tissue damage, or loss of tissue function resulting from allergy. The term "arth- πtic disease," as used herein, means any of a large family of diseases that are characterized by inflammatory lesions of the joints attributable to a variety of etiologies. The term "dermatitis," as used herein, means any of a large family of diseases of the skm that are characterized by inflammation of the skm attributable to a variety of etiologies. The term "transplant rejection," as used herein, means any immune reaction directed against grafted tissue (including organ and cell (e.g., bone mar- row) ) , characterized by a loss of function of the grafted and surrounding tissues, pain, swelling, leukocytosis and thrombocytopema . The present invention also provides a method of modulating cAMP levels m a mammal, as well as a method of treating diseases characterized by elevated cytok e levels. The term "cytokme," as used herein, means any secreted polypeptide that affects the functions of other cells, and that modulates interactions between cells m the immune or inflammatory response. Cytokines include, but are not limited to monokmes, lymphokmes, and chemokmes regardless of which cells produce them. For instance, a monokme is generally referred to as being produ^^d and secreted by a monocyte, however, many other cells produce monokmes, such as natural killer cells, fibroblasts, basophils, neutrophils, endothelial cells, brain astrocytes, bone marrow stromal cells, epidermal keratmocytes , and B- lymphocytes . Lymphokmes are generally referred to as being produced by lymphocyte cells. Examples of cytokines include, but are not limited to, mterleukm-1 (IL-1) , lnter- leukm-6 (IL-6) , Tumor Necrosis Factor alpha (TNFα) , and Tumor Necrosis Factor beta (TNF?) . The present invention further provides a method of reducing TNF levels m a mammal, which comprises administering an effective amount of a compound of structural formula (II) to the mammal. The term "reducing TNF levels, " as used herein, means either: a) decreasing excessive m vivo TNF levels a mammal to normal levels or below normal levels by inhibition of the in vivo release of TNF by all cells, including but not limited to monocytes or macrophages; or b) inducing a down-regulation, at the translational or transcription level, of excessive m vivo TNF levels m a mammal to normal levels or below normal levels; or c) inducing a down-regulation, by inhibition of the direct synthesis of TNF as a postrans- lational event . Moreover, the compounds of the present invention are useful m suppressing inflammatory cell activation. The term "inflammatory cell activation, " as used herein, means the induction by a stimulus (including, but not limited to, cyto es, antigens or auto-antibodies) of a proliferat ve cellular response, the production of soluble mediators (including but not limited to cytokines, oxygen radicals, enzymes, prostanoids, or vasoactive amines) , or cell surface expression of new or increased numbers of mediators (including, but not limited to, major histocompatability antigens or cell adhesion molecules) m inflammatory cells (m- eluding but not limited to monocytes, macrophages, T lymphocytes, B lymphocytes, granulocytes , poly- morphonuclear leukocytes, mast cells, basophils, eosmophils, dendritic cells, and endothelial cells) . It will be appreciated by persons skilled in the art that the activation of one or a combination of these phenotypes m these cells can contribute to the initiation, perpetuation, or exacerbation of an inflammatory condition. The compounds of the present invention also are useful m causing airway smooth muscle relaxation, bronchodilation, and prevention of bronchoconstπction . The compounds of the present invention, therefore, are useful m treating such diseases as arthritic diseases (such as rheumatoid arthritis) , osteoarthritis , gouty arthritis, spondylitis, thyroid-associated ophthalmopathy , Behcet disease, sepsis, septic shock, endotoxic shock, gram negative sepsis, gram positive sepsis, toxic shock syndrome, asthma, chronic bronchitis, allergic rhinitis, allergic conjunctivitis, vernal conjunctivitis, eosmophilic granuloma, adult (acute) respiratory distress syndrome (ARDS) , chronic pulmonary mflam- matory disease isuch as chronic obstructive pulmonary disease) , silicosis, pulmonary sarcoidosis, reperfusion injury of the myocardium, brain or extremities, brain or spinal cord injury due to minor trauma, fibrosis including cystic fibrosis, keloid formation, scar tissue formation, atherosclerosis, autoimmune diseases, such as systemic lupus erythematosus (SLE) and transplant rejection disorders (e.g., graft vs. host (GvH) reaction and allo- graft rejection), chronic glomerulonephritis , inflammatory bowel diseases, such as Crohn's disease and ulcerative colitis, proliferative lymphocytic diseases, such as leukemias (e.g. chronic lymphocytic leukemia; CLL) (see Mentz et al . , Blood 88 , pp. 2172-2182 (1996)), and inflammatory dermatoses, such as atopic dermatitis, psoriasis, or urticaria. Other examples of such diseases or related conditions include cardiomyopathies , such as congestive heart failure, pyrexia, cachexia, cachexia secondary to infection or malignancy, cachexia secondary to acquired immune deficiency syndrome (AIDS) , ARC (AIDS-related complex) , cerebral malaria, osteoporosis and bone resorption diseases, and fever and myalgias due to infection. In addi- tion, the compounds of the present invention are useful m the treatment of diabetes msipidus and central nervous system disorders, such as depression and multi-mfarct dementia. Compounds of the present invention also have utility outside of that typically known as therapeutic. For example, the present compounds can function as organ transplant preservatives (see Pmsky et al . , J. Clm. Invest., 92, pp. 2994-3002 (1993) ) as well . Selective PDE4 inhibitors also can be useful m the treatment of diabetes msipidus (Kid- ney Int., 37, p. 362 (1990); Kidney Int., 35, p. 494 (1989)) and central nervous system disorders, such as multiinfarct dementia (Nicholson, Psychopharma- cology, 101, p. 147 (1990)), depression (Eckman et al . , Curr. Ther. Res., 43, p. 291 (1988)), anxiety and stress responses {Neuropharmacology, 38, p. 1831 (1991)), cerebral ischemia (Eur. J. Pharmacol., 272, p. 107 (1995)), tardive dyskinesia {J. Clin. Pharmo- col . , 1 i p. 304 (1976)), Parkinson's disease (see Neurology, 25, p. 722 (1975) ; Clin. Exp . Pharmacol , Physiol . , 26, p. 421 (1999)), and premenstrual syndrome. With respect to depression, PDE4-selective inhibitors show efficacy in a variety of animal models of depression such as the "behavioral despair" or Porsolt tests (Eur. J. Pharmacol., 47, p. 379 (1978); Eur. J. Pharmacol., 57, p. 431 (1979); Antidepressants : neurochemical , behavioral and clinical prospectives , Enna, Malick, and Richelson, eds., Raven Press, p. 121 (1981)), and the "tail suspension test" (Psychopharmacology, 85, p. 367 (1985)) . Recent research findings show that chronic in vivo treatment by a variety of antidepressants increase the bram-deπved expression of PDE4 {J. Neuroscience, 19, p. 610 (1999)). Therefore, a selective PDE4 inhibitor can be used alone or conjunction with a second therapeutic agent in a treatment for the four major classes of antidepressants: electroconvulsive procedures, monoamme oxidase inhibitors, and selective reuptake inhibitors of serotonin or norepinephrme . Selective PDE4 inhibitors also can be useful m applications that modulate bronchodilatory activity via direct action on bronchial smooth muscle cells for the treatment of asthma. Compounds and pharmaceutical compositions suitable for use m the present invention include those wherein the active ingredient is administered m an effective amount to achieve its intended purpose. More specifically, a "therapeutically effective amount" means an amount effective to prevent development of, or to alleviate the existing symptoms of, the subject being treated. Determination of the effective amounts is well withm the capability of those skilled in the art, especially m light of the detailed disclosure provided herein. A "therapeutically effective dose" refers to that amount of the compound that results m achieving the desired effect. Toxicity and therapeutic efficacy of such compounds can be determined by standard pharmaceutical procedures m cell cultures or experimental animals, e.g., for determining the LD 50 (the dose lethal to 50% of the population) and the ED 50 (the dose therapeutically effective m 50% of the population) . The dose ratio between toxic and therapeutic effects is the therapeutic index, which is expressed as the ratio between LD 5 and ED 50 . Compounds which exhibit high therapeutic indices are preferred. The data obtained from such data can be used m formulating a dosage range for use m humans. The dosage of such compounds preferably lies withm a range of circulating concentra- tions that include the ED C1 with little nr no toxicity. The dosage can vary with tnis range depending upon the dosage form employed, and the route of administration utilized. The exact formulation, route of administration, and dosage can be chosen by the individual physician m view of the patient's condition. Dosage amount and interval can be adjusted individually to provide plasma levels of the active moiety which are sufficient to maintain the therapeutic effects. As appreciated by persons skilled m the art, reference herein to treatment extends to prophylaxis, as well as to treatment of established diseases or symptoms. It is further appreciated that the amount of a compound of the invention required for use m treatment varies with the nature of the condition being treated, and with the age and the condition of the patient, and is ultimately determined by the attendant physician or vetermar- lan. In general, however, doses employed for adult human treatment typically are m the range of 0.001 mg/kg to about 100 mg/kg per day. The desired dose can be conveniently administered m a single dose, or as multiple doses administered at appropriate intervals, for example as two, three, four or more subdoses per day. In practice, the physician determines the actual dosing regimen which is most suitable for an individual patient, and the dosage varies with the age, weight, and response of the par- ticular patient. The above dosages are exemplary of the average case, but there can be individual instances m wnich higher or lower dosages are mer- ited, and such are withm the scope or tre present inven ion . Formulations of the present invention can be administered m a standard manner for the treat - ment of the indicated diseases, such as orally, parenterally , transmucosally (e.g., subl gually or via buccal administration) , topically, trans- dermally, rectally, via inhalation (e.g., nasal or deep lung inhalation) . Parenteral administration includes, but is not limited to intravenous, mtra- arterial, mtrapeπtoneal , subcutaneous, intramuscular, mtrathecal, and mtraarticular . Parenteral administration also can be accomplished using a high pressure technique, like POWDERJECT™ . For buccal administration, the composition can be m the form of tablets or lozenges formulated m conventional manner. For example, tablets and capsules for oral administration can contain conventional excipients such as binding agents (for exam- pie, syrup, accacia, gelatin, sorbitol, tragacanth, mucilage of starch or polyvmylpyrrolidone) , fillers (for example, lactose, sugar, microcrystallme , cellulose, maize-starch, calcium phosphate or sorbitol), lubricants (for example, magnesium, stearate, steaπc acid, talc, polyethylene glycol or silica), dismtegrants (for example, potato starch or sodium starch glycollate) , or wetting agents (for example, sodium lauryl sulfate) . The tablets can be coated according to methods well known m the art. Alternatively, the compounds of the present invention can be incorporated into oral liquid preparations such as aqueous or oily suspensions, solutions, emulsions, syrups, or elixirs, for exam- pie. Moreover, formulations containing these compounds can be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid preparations can contain conven- tional additives, such as suspending agents, such as sorbitol syrup, methyl cellulose, glucose/sugar syrup, gelatin, hydroxyethylcellulose, hydroxy- propylmethylcellulose, carboxymethyl cellulose, aluminum stearate gel, and hydrogenated edible fats; emulsifying agents, such as lecithin, sorbitan mono- oleate, or acacia; nonaqueous vehicles (which can include edible oils), such as almond oil, fractionated coconut oil, oily esters, propylene glycol, and ethyl alcohol; and preservatives, such as methyl or propyl p-hydroxybenzoate and sorbic acid. Such preparations also can be formulated as suppositories, e.g., containing conventional suppository bases, such as cocoa butter or other glyceπdes . Compositions for inhalation typically can be provided m the form of a solution, suspension, or emulsion that can be administered as a dry powder or m the form of an aerosol using a conventional propellant, such as dichlorodifluoromethane or trichlorofluoromethane . Typical topical and transdermal formulations comprise conventional aqueous or nonaqueous vehicles, such as eye drops, creams, ointments, lotions, and pastes, or are m the form of a medicated plaster, patch, or membrane. Additionally, compositions of the present invention can be formulated for parenteral administration by injection or continuous infusion. Formulations for injection can be m the form of suspensions, solutions, or emulsions m oily or aqueous vehicles, and can contain formulation agents, such as suspending, stabilizing, and/or dispersing agents. Alternatively, the active ingredient can be in powder form for constitution with a suitable vehicle (e.g., sterile, pyrogen-free water) before use . A composition m accordance with the present invention also can be formulated as a depot preparation. Such long acting formulations can be administered by implantation (for example, subcuta- neously or intramuscularly) or by intramuscular injection. Accordingly, the compounds of the invention can be formulated with suitable polymeric or hydrophobic materials (e.g., an emulsion m an ac- ceptable oil) , ion exchange resms, or as sparingly soluble derivatives (e.g., a sparingly soluble salt) . For veterinary use, a compound of formula (I) or a nontoxic salt thereof, is administered as a suitably acceptable formulation m accordance with normal veterinary practice. The veterinarian can readily determine the dosing regimen and route of administration that is most appropriate for a particular animal . Thus, the invention provides m a further aspect a pharmaceutical composition comprising a compound of the formula (I) , together with a pharmaceutically acceptable diluent or carrier therefor. There is further provided by the present invention a process of preparing a pharmaceutical composition comprising a compound of formula (I), which process comprises mixing a compound of formula (I) , together with a pharmaceutically acceptable diluent or carrier therefor. Specific, nonlimiting examples of compounds of structural formula (I) are provided below, the synthesis of which were performed m accordance with the procedures set forth below. Generally, compounds of structural formula (I) can be prepared according to the following synthetic scheme. In the scheme described below, it is understood m the art that protecting groups can be employed where necessary m accordance with general principles of synthetic chemistry. These protecting groups are removed m the final steps of the synthesis under basic, acidic, or hydrogenolytic condi- tions which are readily apparent to those skilled m the art. By employing appropriate manipulation and protection of any chemical functionalities, synthesis of compounds of structural formula (I) not specifically set forth herein can be accomplished by methods analogous to the scheme set forth below. Unless otherwise noted, all starting materials were obtained from commercial suppliers and used without further purification. All reactions and chromatography fractions were analyzed by thm- layer chromatography on 250-mm silica gel plates, visualized with UV (ultraviolet) light and I 2 (iodine) stain. Flash column chromatography was carried out using Biotage 40M silica gel (230-400 mesh) . Products and intermediates were purified by flash chromatography and reverse -phase HPLC . As illustrated below, the compounds of general structural formula (I) are prepared by reacting a hydraz e of structural formula (II) with a butryπc acid derivative of structural formula (III) , m the presence of pyπdme, in a cyclization reaction, as set forth below: o 0 HN-NH 2 + R 4 C- C- C-OR 2 pyridme ( I ) R 1 c=o (ID (III) Intermediate 1 Preparation of (5-nitropyridin-2-yl) hydrazine To a solution of 2 -chloro- 5 -nitropyπdine (30mmol, 5.0g) m absolute ethanol was added a solution of hydrazine hydrate (320mmol, 15.8g) m ethanol using syringe pump. At the end of the addition, the reaction was refrigerated. The named product precipitated from the reaction medium, was collected by filtration, and recrystallized from ethanol. Example 1 Preparation of 1- (4-bromophenyl) -3 , 5 -dimethyl- lH-pyrazole-4-carboxylic acid ethyl ester p-Bromophenylhydrazme hydrochloride (lOmmol, 2.5g) was added to 2-acetyl-3 -oxo-butyric acid ethyl ester (lOmmol, 1.7g) m ethanol (lOmL) and pyπdme (lOmL) . The mixture was stirred overnight at room temperature. Thin layer chromatographic (TLC) analysis using chloroform indicated the reaction was complete. The solvents were removed under vacuum. The residue was dissolved m 150mL ether, then washed with 50mL water to remove the pyridme . The ether was dried over sodium sulfate (NaS0 4 ) , the solids filtered, then the solvents were removed under vacuum. The resulting oil was purified on a silica column. The named product crystallized upon standing the column effluent, m.p. 71°C-73°C. Analysis by -NMR and lj C-NMR verified synthesis the named product . Example 2 Preparation of 3 , 5 -dimethyl- 1- (3 -nitrophenyl) lH-pyrazole-4-carboxylic acid ethyl ester Similar to Example 1, m-nitrophenylhydrazine hydrochloride (lOmmol, 1.9g) and 2-acetyl-3-oxo- butyric acid ethyl ester (lOmmol, 1.7g) were mixed in a 50% solution of pyridine in ethanol. A precipitate was formed in the reaction medium, and was collected by filtration. Analysis confirmed synthe- sis of the named product, m.p., 107.7°C-109.2°C . Exa p1e 3 Preparation of 3 , 5-dιmethyl-l-phenyl-1H- pyrazole-4-carboxylic acid ethyl ester Similar to Example 1, phenyl hydrazine (7.5mmol, 0.8g) and 2 -acetyl-3-oxo-butyπc acid ethyl ester (7.5mmol, 1.3g) were mixed m a solution of 50% pyπdme m ethanol . The solvents were removed under vacuum and the oil resuspended m chloroform. The resulting suspension was washed with 5% sodium bicarbonate, 5% hydrochloric acid, and then brine. The organic layer was dried over NaS0 4 , the solids filtered, and the solvents removed under vacuum. The crude material was purified over silica gel to yield the named product as an oil. ^-NMR (CDC1 3 , ppm) : 1.37 t (3H) ; 2.51 s (6H); 4.32 q (2H); 7.42 bs (5H) . Examp le 4 Preparation of 3 , 5-dimethyl- 1-p-tolyl-lH- pyrazole-4-carboxylic acid ethyl ester Similar to Example 1, p-tolylhydrazme (lOmmol, 1.8g) and 2-acetyl-3-oxo-butyπc acid ethyl ester (lOmmol, 1.7g) were mixed m a solution of 50% pyri- dme m ethanol . The solvents were removed under vacuum. The named product was purified over silica gel (m.p. 47°C-49°C) . Example 5 Preparation of 3 , 5-dimethyl- 1- (2 -nitrophenyl) lH-pyrazole-4-carboxylic acid ethyl ester Similar to Example 1, o-mtrophenylhydrazme (20mmol, 3.4g) and 2 -acetyl -3 -oxo-butyric acid ethyl ester (20mmol, 3.4g) were mixed m a solution of 50% pyπdme m ethanol and heated under reflux. The solvents then were removed under vacuum, and the residue was resuspended in chloroform. The resulting mixture was washed with water and dried over NaS0_ . The solids then were filtered, and the solvents removed under vacuum. A precipitate formed when the oily solid was dissolved in a solution of 20% hexane m chloroform. The solid was collected and discarded, and the filtrate was purified over silica gel. The named product was contaminated, then was further purified by recrystallization from ethanol to yield a solid having a melting point of 128°C-130°C. Exa p1e 6 Preparation of 3 , 5 -dimethyl -1- ( 2 - aminophenyl ) lH-pyrazole-4-carboxylic acid ethyl ester To a solution of 3 , 5-dimethyl -1- (2 -nitrophenyl) -1H- pyrazole-4 -carboxylic acid ethyl ester (0.4g) m a solution of equal proportions of ethanol and ethyl acetate was added 5% Pd/C (37mg) . The solution was treated with hydrogen gas at 45 psi. Upon completion of the reaction, the mixture was filtered through Celite, then the filtrate concentrated under vacuum. The named product was collected as an oil, which then was purified by flash chromatography to provide a solid product having a melting point of 59°C-61°C. Example 7 Preparation of 3 , 5-dimethyl- 1- ( 5-nitropyridin-2 ■ yl) -lH-pyrazole-4-carboxylic acid ethyl ester The named product was purchased from Maybridge Chemical Co., Ltd., Cornwall, UK, and used without further purification. Example 8 Preparation of 3 , 5-dimethyl-l-pyridin-2 -yl-lH- pyrazole-4-carboxylic acid ethyl ester Similar to Example 1, 2 -pyridylhydrazme (7.5mmol, 0.8g) and 2 -acetyl-3 -oxo-butyric acid ethyl ester (7.5mmol, 1.3g) were mixed m a solution of 50% pyπdme m ethanol, then heated under reflux. The solvents were removed under vacuum and the residue purified over silica. The named product crystal - lized upon standing (m.p. 49°C-50°C) . Example 9 Preparation of 1- ( 3 - aminophenyl ) -3 , 5-dimethyl- lH-pyrazole-4-carboxylic acid ethyl ester The compound of Example 2 (1.8g) was dissolved in ethanol then 0.2g 5% Pd/C was added to the solution. The mixture was treated with hydrogen gas at 45 psi. Upon completion of the reaction, the solution was filtered through Celite, and the filtrate concentrated under vacuum. The named product slowly crys- tallized upon standing (m.p. 93°C-95°C) . Example 10 Preparation of 3 , 5 -dimethyl- 1- (3 -nitropyridin- 2-yl) -lH-pyrazole-4-carboxylic acid ethyl ester 3 The named product was purchased from Maybπdge Chemical Co., and used without further purification. Examp1e 11 Preparation of 3 , 5-dimethyl- 1- (4 -aminophenyl) lH-pyrazole-4-carboxylic acid ethyl ester The named product was purchased from Maybridge Chemical Co., and used without further purification. Example 12 Preparation of 1- (3-aminopyridin-2 -yl) -3 , 5- dimethyl-lH-pyrazole-4-carboxylic acid ethyl ester The compound of Example 10 was reduced using sodium borohydride (NaBH (17.2 mmole) m methanol (15ml ) . Following normal workup, the prod ¬ uct was purified over silica gel. The named product was analyzed by H-NMR (CDC1 3 , ppm) : 1.38 t (3H) ; 2.50 S (3H) ; 2.60 s (3H) ; 4.33 q (2H) ; 4.44 S (2H); 7.16 m (2H) ; 7.93 dd (1H) . Example 13 Preparation of 1- [4 - (4 -methoxybenzenesulfonylamino) phenyl] -3 , 5 -dimethyl-lH-pyrazole-4 -carboxylic acid ethyl ester The named compound was purchased from Maybridge Chemical Co., and used without further purification . Example 14 Preparation of 1- [4- (2 , 2 -dimethylpropionylamino) phenyl] -3 , 5 -dimethyl- lH-pyrazole-4 -carboxylic acid ethyl ester , The named compound was purchased from Maybridge Chemical Co., and used without further purification. Example 15 3 , 5 -dimethyl -1 -phenyl -lH-pyrazole- 4- carboxylic acid p-tolyl ester The named compound was purchased from Maybridge Chemical Co., and used without further purification. Example 16 Preparation of 3 , 5-dimethyl- 1- (3 -nitropyridin-2 • yl) -lH-pyrazole-4-carboxylic acid The compound of Example 10 (0.34mmol, O.lg) was treated with lithium hydroxide (LiOH-H 2 0) (0.51mmol, 0.021g) in a 50% solution of metahnol in water at 80°C. The methanol was removed under vacuum, the resulting solution was acidified to pH 2-3, and the product extracted with ethyl acetate and dried over sodium sulfate (Na 2 S0 4 ) . The solids were removed by filtration, and solvents removed under vacuum. The resulting solid was used without further purification, and ^-NMR analysis determined the solid to be the named compound '-H-NMR (CDC1 3 , ppm) : 2.48 Ξ (3H) ; 2.76 s (3H); 7.58 dd (1H); 7.32 dd (1H) ; 8.76 dd (1H) . Example 17 Preparation of 3 , 5 -dimethyl- 1- ( 5-nitropyrιdin-2 yl) -lH-pyrazole-4-carboxylic acid ethyl ester Similar to Example 1, equimolar amounts of (5-nιtropyπdm-2-yl) hydrazine and 2-acetyl-3 -oxo- butyric acid ethyl ester were combined m a solution of 50% pyπdme m ethanol. Analysis confirmed synthesis of the named product (m.p. 117°C-119°C) . Example 18 Preparation of 1- (4 -aminophenyl) -3 , 5 -dimethyl- lH-pyrazole-4 -carboxylic acid Similar to Example 16, the compound of Example 11 (0.38mmol, O.lg) was treated with LιOH-H 2 0 (0.57mmol, 0.024g) m a 50% solution of methanol m water. The resulting solid was determined to be the named compound by -H-NMR (CDC1 3 , ppm) : 2.46 sd (3H); 2.57 s (2H) ; 2.75 sd (3H); 7.85 dd (2H); 8.42 dd (2H) . Example 19 Preparation of 1-cyclohexyl -3 , 5-dimethyl-lH- pyrazole-4-carboxylxc acid ethyl ester Similar to Example 1, equimolar amounts of cyclohexyl hydrazine hydrochloride and 2 -acetyl-3 - oxobutyric acid ethyl ester were combined a solution of 50% pyπdme m ethanol. Analysis confirmed synthesis of the named product (m.p. 66°C-67°C) . Example 20 Preparation of l-benzyl-3 , 5-dimethyl -1H- pyrazole-4 -carboxylic acid ethyl ester Similar to Example 1, equimolar amounts of benzylhydrazme dihydrochloride and 2 -acetyl-3 -oxo- butyric acid ethyi ester were combined m a solution of 50% pyπdme ethanol. The resulting oil was determined to be the named product by Η-NMR (CDC1,, ppm) : 1.35 t (3H); 2.44 s < 3H) ; 2.45 s (3H) ; 4.38 a (2H) ; 5.25 s (2H); 7.08 d (2H); 7.29 m (3H) . Example 21 Preparation of 1- (3 -chlorophenyl) -3 , 5 -dimethyl - lH-pyrazole-4 -carboxylic acid ethyl ester Similar to Example 1, equimolar amounts of 3 -chlorophenylhydrazme hydrochloride and 2-acetyl- 3 -oxo-butyric acid ethyl ester were combined m a solution of 50% pyridme m ethanol. Analysis confirmed that the resulting solid was determined to be the named product (m.p. 56°C-57°C) . Example 22 Preparation of 3 , 5-dimethyl- 1-m- tolyl-lH- pyrazole-4 -carboxylic acid ethyl ester Similar to Example 1, equimolar amounts of m-tolylhydrazine hydrochloride and 2 -acetyl-3-oxo- butyric acid ethyl ester were combined in a solution of a 50% pyridine in ethanol. The resulting oil was purified by flash chromatography to yield the named product as a solid (m.p. 46.5°C-47.5°C) . Example 23 Preparation of 1- (3-fluorophenyl) -3 , 5-dimethyl- lH-pyrazole-4 -carboxylic acid ethyl ester Similar to Example 1, equimolar amounts of 3-fluorophenylhydrazine hydrochloride and 2-acetyl- 3 -oxo-but ric acid ethyl ester were combined a solution of 50% pyridme m ethanol. Analysis showed that resulting solid was the named product (m.p. 55°C-56.1°C) . Example 24 Preparation of 1- (3 -methoxyphenyl) -3 , 5-dimethyl- lH-pyrazole-4 -carboxylic acid ethyl ester Similar to Example 1, equimolar amounts of 3-methoxyphenylhydrazme hydrochloride and 2-acetyl- 3 -oxo-butyric acid ethyl ester were combined m a solution of 50% pyridme m ethanol. The resulting solid was determined to be the named product by X H-NMR (CDC1 3 , ppm) : 1.38 t (3H) ; 2.50 s (3H) ; 2.52 s (3H) ; 3.84 s (3H); 4.32 q (2H) ; 6.96 m (3H); 7.3 st (1H) . Example 25 Preparation of 1- ( 3 -bromophenyl) -3 , 5 -dimethyl- lH-pyrazole-4 -carboxylic acid ethyl ester Similar to Example 1, equimolar amounts of 3 -bromophenylhydrazine hydrochloride and 2 -acetyl-3 - oxo-butyric acid ethyl ester were combined in a solution of 50% pyridine in ethanol. Analysis showed that the resulting solid was the named product (m.p. 34°C-35°C) . Example 26 Preparation of 3 -methyl-l-pyridin-2-yl-lH- pyrazole-4-carboxylic acid ethyl ester Similar to Example 1, equimolar amounts of 2 -pyridylhydrazme and 2 - formyl -3 -oxo-butyric acid ethyl ester were combined m a solution of 50% pyridme m ethanol . Analysis showed that the resulting solid was determined to be the named product (m.p. 49°C-50°C) . Example 27 Preparation of 1- (4 -aminophenyl) -5- trifluoromethyl- lH-pyrazole-4 -carboxylic acid ethyl ester To 1- (4 -nitrophenyl) -5-trιfluoromethyl -1H- pyrazole-4-carboxylιc acid ethyl ester (0.5g, 1.5mmol) dissolved m methanol (4mL) was added pal- ladium on carbon and ammonium formate (0.428g, 6.8mmol) . This mixture was stirred at room temperature overnight . The solvent was removed under vacuum, then the material was resuspended m chloroform, and washed with water (twice) and saturated sodium bicarbonate (once) , and the organic layer dried over magnesium sulfate (MgS0 4 ) . The solid was filtered and the solvents removed under vacuum. The reaction product was purified over silica gel to yield the named product (m.p. 102 °C-103 °C) . The following Examples 28-37 were purchased from Maybridge Chemical Co., Ltd. (Exs. 29, 30, 32-37), ACROS Organics, Pittsburgh, PA (Ex. 28), or Bionet Research Ltd., Cornwall, UK (Ex. 31), and used without further purification. Example 28 3 , 5-Dimethyl- 1-phenyl- IH-pyrazole-4 -carboxaldehyde Example 29 5- (3-Dimethylaminoacryloyl) -1- (6-methyl-4- trifluoromethylpyridin-2 -yl) -IH-pyrazole- 4 -carboxylic acid methyl ester Example 3 0 1- (4 -Nitrophenyl) -5-trifluoromethyl - lH-pyrazole-4-carboxylic acid ethyl ester Example 31 1- (3-Chloro-5-trifluoromethylpyridin-2-yl) - 5-methyl-lH-pyrazole-4-carboxylic acid ethyl ester Example 32 1- [5-Methyl-l- ( 6 -methyl -4 -trifluoromethyl - pyridin-2 -yl) -lH-pyrazol-4 -yl] -ethanone oxime -OH Example 33 5-Acetyl - 1- ( 6 -methyl-4 - trifluoromethyIpyridin- 2-yl) -lH-pyrazole-4 -carboxylic acid methyl ester o Example 34 3 , 5-Dimethyl-l-phenyl-lH-pyrazole- 4-carboxylic acid pyridin-4-ylamide Example 35 5-Methoxymethyl-l- (2,4, 6- trichlorophenyl) -1H- yrazole-4 -carboxylic acid ethyl ester Example 3 6 3 , 5 -Dimethyl-1-phenyl- IH-pyrazole- 4 -carboxylic acid phenylamide Example 37 5-Acetyl-1-pyridin-2 -y1- 1H- pyrazole-4-carboxylic acid methyl ester The compounds of structural formula (I) were tested for an ability to inhibit PDE4. The ability of a compound to inhibit PDE4 activity is related to the IC 50 value for the compound, i.e., the concentration of inhibitor required for 50% inhibition of enzyme activity. The IC 50 value for com- pounds of structural formula (I) were determined using human recombinant PDE4. The compounds of the present invention typically exhibit an IC 5 , value against recombinant human PDE4 of less than about 100 μM , and preferably less than about 50 μM, and more preferably less than about 25 μm . The compounds of the present invention typically exhibit an IC 50 value against recombinant human PDE4 of less than about 10 μM , and often less than about 1 μM . To achieve the full advantage of the present invention, a present PDE4 inhibitor has an IC 50 of about 0.05 μM to about 25 uM . The IC 50 values for the compounds were determined from concentration-response curves typi- cally using concentrations ranging from 0.1 pM to 500 μM . Tests against other PDE enzymes using standard methodology, as described m Loughney et al . , J " . Biol . Chem . , 271 , pp. 796-806 (1996), also showed that compounds of the present invention are highly selective for the cAMP-specifIC PDE4 enzyme. In particular, a compound of the present invention, i.e., Example 2, has an IC 50 vs. human recombinant PDE4B of 0.1 μM , but has an IC 50 vs. PDE1A of 25.1 μM, vs. PDE1B of 25.7 μM , vs. PDE1C of 30.2 μM , vs. PDE2 of 21.8 μM , vs. PDE3A of 137 μM , vs. PDE5 of 25.6 μM , and vs. PDE7 of 39 μM . This illustrates the selectivity of the present compound with respect to inhibiting PDE4. The compounds of structural formulae (I) and (II) were tested for an ability to reduce TNFα secretions m human peripheral blood lymphocytes. The ability of a compound to reduce TNFα secretion is related to the EC S0 value for the compound (i.e., the effective concentration of the compound capable of inhibiting 50% of the total TNFα) . The compounds of the present invention typically exhibit an EC ςo value of less than about 50 μM , and preferably less than about 20 μM , and more preferably less than about 15 μm . The compounds of the present invention preferably exhibit a PBL/TNFa EC 50 value of less than about 10 μM , and often less than about 5 μM . To achieve the full advantage of the present invention, a present PDE4 inhibitor has an EC 50 of about 0.01 μM to about 15 μM . The production of recombinant human PDEs and the IC_ and EC 50 determinations can be accomplished by well-known methods m the art. Exemplary methods are described as follows: EXPRESSION OF HUMAN PDEs Expression in Baculovirus-Infected Spodoptera fuqriperda (Sf9) Cells Baculovirus transfer plasmids were constructed using either pBlueBacIII (Invitrogen) or pFastBac (BRL-Gibco) . The structure of all plasmids was verified by sequencing across the vector junctions and by fully sequencing all regions generated by PCR. Plasmid pBB-PDElA3/6 contained the complete open reading frame of PDE1A3 (Loughney et al . , J . Biol . Chem . , 271 , pp. 796-806 (1996)) m pBlueBacIII. Plasmid HcatτϋaBB contained the complete open reading frame of PDE1C3 (Loughney et al . (1996)) pBlueBacIII. Plasmid pBB-PDE3A contained the complete open reading frame of PDE3A (Meacci et al . , Proc . Na tl . Acad . Sci . , USA, 89 , pp. 3721-3725 (1992)) m pBlueBacIII Recombinant virus stocks were produced using either the axBac system (Invitrogen) or the FastBac system (G_.bco-BRL) according to the manufacturer's protocols In both cases, expression of recombinant human PDEs m the resultant viruses was driven off the viral polyhedron promoter. When using the MaxBac ® system, virus was plaque purified twice m order to insure that no wild type (occ+) virus contaminated the preparation. Protein expression was carried out as follows. Sf9 cells were grown at 27°C m Grace's Insect culture medium (Gibco-BRL) supplemented with 10% fetal bovine se- rum, 0.33% TC yeastolate, 0.33% lactalbumm hydro- lysate, 4.2 mM NaHCO,, 10 μg/mL gentamycm, 100 units/mL penicillin, and 100 /jg/mL streptomycin. Exponentially growing cells were infected at a multiplicity of approximately 2 to 3 virus particles per cell and incubated for 48 hours. Cells were collected by centrifugation, washed with nonsup- plemented Grace's medium, and quick-frozen for storage . Expression in Saccharomyces cerevisiae (Yeast) Recombinant production of human PDE1B, PDE2, PDE4A, PDE4B, PDE4C, PDE4D, PDE5 , and PDE7 was carried out similarly to that described m Example 7 of U.S. Patent No. 5,702,936, incorporated herein by reference, except that the yeast transformation vector employed, which is derived from the basic ADH2 plasmid described m Price et al . , Methods m Enzymology, 185 , pp. 308-318 ^1990), incorporated yeast ADH2 promoter and terminator sequences and the Saccharomyces cerevisiae host was the protease-defI- cient strain BJ2-54 deposited on August 31, 1998 with the American Type Culture Collection, Manassas, Virginia, under accession number ATCC 74465. Transformed host cells were grown m 2X SC-leu medium, pH 6.2, with trace metals, and vitamins. After 24 hours, YEP medium-containing glycerol was added to a final concentration of 2X YET/3% glycerol. Approximately 24 hr later, cells were harvested, washed, and stored at -70°C. CALMODULIN PURIFICATION Calmodulm used for activation of the PDE1 enzymes was purified from bovine testes essentially as described by Dedman et al . , Methods in Enzymology, 102 , pp. 1-8 (1983) using the Pharmacia Phenyl -Sepharose ® procedure. IMMOBILIZATION OF CALMODULIN ON AGAROSE Calmodulm was immobilized on BioRad Affi- Gel ® 15 per manufacturer's instructions. HUMAN PHOSPHODIESTERASE PREPARATIONS Phosphodiesterase Activity Determinations Phosphodiesterase activity of the preparations was determined as follows. PDE assays utilizing a charcoal separation technique were performed essentially as described m Loughney et al. (1996) . In this assay, PDE activity converts [32P]cAMP or [32P]cGMP to the corresponding [32P] 5 ' -AMP or [32P]5'-GMP m proportion to the amount of PDE ac- tivity present. The [32P] 5 ' -AMP or [32P]5'-GMP then was quantitatively converted to free [32P] phosphate and unlabeled adenosine or guanosme by the action of snake venom 5 ' -nucleotidase . Hence, the amount of [32P] phosphate liberated is proportional to en- zyme activity. The assay was performed at 30°C m a 100 μh reaction mixture containing (final concentrations) 40 mM Tπs HC1 (pH 8.0), 1 μM ZnS0 4 , 5 mM MgCl 2 , and 0.1 mg/mL bovine serum albumin (BSA) . Alternatively, in assays assessing PDEl-specifIC activity, incubation mixtures further incorporated the use of 0.1 mM CaCl 2 and 10 μg/mL calmodulm. PDE enzyme was present m quantities that yield <30% total hydrolysis of substrate (linear assay conditions) . The assay was initiated by addition of substrate (1 mM [32P] cAMP or cGMP) , and the mixture was incubated for 12 minutes. Seventy-five (75) μg of Crotalus atrox venom then was added, and the incubation was continued for 3 minutes (15 minutes total) . The reaction was stopped by addition of 200 μh of activated charcoal (25 mg/mL suspension m 0.1 M NaH 2 P0 4 , pH 4) . After centrifugation (750 X g for 3 minutes) to sediment the charcoal, a sample of the supernatant was taken for radioactivity determination m a scintillation counter and the PDE activity was calculated. Inhibitor analyses were performed similarly to the method described m Loughney et al . , J . Biol . Chem . , 271 , pp. 796-806 (1996), except both cGMP and cAMP were used, and substrate concentrations were kept below 32 nM, which is far oelo.. tne Km of the tested PDE5. Purification of PDE1A3 from SF9 Cells Cell pellets (5 g) were mixed with 10 mL of Lysis Buffer (50 mM MOPS pH 7.5 , 2 mM dithio- threitol (DTT) , 2 mM benzamidme HC1 , 5 μM ZnSO, , 0.1 mM CaCl 2 , 20 ug/mL calpam inhibitors I and II, and 5 g/mL each of leupept , pepstatm, and aprotmm) at room temperature. The cells were lysed by passage through a French ® pressure ceil (SLM-Ammco ® , Spectronic Instruments, Inc., Roches- ter NY) . The resultant lysate was centπfuged m a Beckman ultracentrifuge using a type T180 rotor at 45,000 rpm for 1 hr. The supernatant was recovered and filtered through a 0.2 μ filter. This filtrate was applied to a 2.6 X 90 cm column of SEPHACRYL ® S-300 equilibrated m Column Buffer A (Lysis Buffer containing 100 mM NaCl, and 2 mM MgCl ) . The column flow rate was adjusted to 1 mL/mm and fractions of 7 mL were collected. Active fractions were pooled and supplemented with 0.16 mg of calmodulm. The enzyme was applied overnight at a flow rate of 0.2 mL/mm to an ACC-1 agarose immunoaffmity column as described m Hansen et al . , Methods m Enzymology 159 , pp. 453-557 (1988) . The column was washed with 5 volumes of Column Buffer B (Column Buffer A with- out NaCl) and followed by 5 volumes of Column Buffer C (Column Buffer A containing 250 mM NaCl) . The column was eluted with Column Buffer D (50 mM MOPS pH 7.5, 1 mM EDTA, 1 mM EGTA, 1 mM DTT, 1 mM benzamidme HCl, 100 mM NaCl, 20 μg/mL calpam inhibitors I and II, and 5 g/mL each of leupeptm, pepstatm, and aprotmm) by applying one column volume at 0 1 mL/mm, stopping flow for 1 hour, and then continuing elution at the same flow rate. Fractions of 0.5 mL were collected. Fractions displaying activity were pooled, and first dialyzed against dialysis buffer containing 25 mM MOPS pH 7.5, 100 mM NaCl, 10 μM ZnS0 4 , 1 mM CaCl 2 , 1 mM DTT, and 1 mM benzamidme HCl. A subsequent dialysis against dialysis buffer containing 50% glycerol was performed prior to quick-freezing the sample with dry ice and storage at -70°C. The resultant preparations were about 10 to 15% pure by SDS-PAGE. These preparations had specific activities of about 5 to 20 μmol cAMP hydrolyzed per minute per milligram protein. Purification of PDE1B from S . cerevisiae Yeast cells (50 g) were thawed by mixing with 100 mL glass beads (0.5 mM, acid washed) and 200 mL Buffer A at room temperature. Buffer A consisted of 50 mM MOPS pH 7.5 , 1 mM DTT, 2 mM benzamidme HCl, 0.01 mM ZnS0 4 , 5 mM MgCl 2 , 20 μg/mL calpam inhibitors I and II, and 5 μg/mL each of leupeptm, pepstatm, and aprotmm. The mixture was cooled to 4°C, transferred to a Bead-Beater ® , and the cells lysed by rapid mixing for 6 cycles of 30 seconds each. The homogenate was centπfuged for 15 minutes m a Beckman J2-21M centrifuge using a JA-10 rotor at 9,000 rpm and 4°C. The supernatant was recovered and centπfuged in a Beckman XL-80 ultracentπfuge using a TI45 rotor at 36,000 rpm for 45 minutes at 4°C. The supernatant was recovered and PDE1B was precipitated by the addition of solid ammonium sulfate (0.33 g/mL supernatant) while stir- ring m an ice bath and maintaining the pH between 7.0 and 7.5. This mixture then was centπfuged for 22 minutes m a Beckman J2 centrifuge using a JA-10 rotor at 9,000 rpm (12,000 X g) . The supernatant was discarded and the pellet was dissolved m 100 mL of buffer B (50 mM MOPS pH 7.5 , 1 mM DTT, 1 mM benzamidme HCl, 0.01 mM ZnS0 4 , 2 mM MgCl 2 , 2 mM CaCl 2 , and 5 μg/mL each of leupeptm, pepstatm, and aprotmm) . The pH and conductivity were corrected to 7.5 and 15-20 milliSiemens (mS) , respectively. This solution was loaded onto a 20 mL column of calmodulm-Agarose that had been equilibrated with 10 column volumes of Buffer B at a rate of 1 mL/mm. The flow-through was reapplied to the column at least 5 times. The column was washed with 5 volumes of Buffer B, 5 volumes of buffer B containing 250 mM NaCl, and 2 volumes of Buffer B without NaCl again. Elution was accomplished by applying one volume of Buffer C (50 mM MOPS pH 7.5 , 1 mM EDTA, 1 mM EGTA, 1 mM DTT, 1 mM benzamidme HCl) at 0.33 mL/mm, then stopping flow for 1 hour before continuing the elution. Fractions of aoout 4 mL were collected and assayed for PDE activity. Active fractions were pooled and concentrated to a volume of 5 mL, using an Amicon ultraflltration system. The concentrate was then applied to a 320 mL Sephacryl ® S-300 column (1.6 X 150 cm) that had been equilibrated with at least 2 volumes of Buffer D (25 mM MOPS pH 7.5 , 1 mM DTT, 1 mM benzamidme HCl, 0.01 mM ZnS0 4 , 2 mM CaCl 2 , and 100 mM NaCl) . The column was developed at a flow rate of 1 mL/mm (11 cm/hr) , and 5 mL fractions were collected. The activity peak was pooled and dialyzed overnight against Buffer D containing 50% glycerol. The purified enzyme was frozen on dry ice and stored at -70°C. The resultant preparations were about >90% pure by SDS-PAGE These preparations had specific activities of about 10 to 30 μmol cGMP hydrolyzed per minute per milligram protein. Purification of PDE1C3 from Sf9 Cells Cell pellets (5 g) were thawed on ice with 20 mL of Lysis Buffer (50 mM MOPS pH 7.4, 10 μM ZnS0 4 , 0.1 mM CaCl 2 , 1 mM DTT, 2 mM benzamidme HCl, 5 μg/mL each of pepstatm, leupeptm, and aprotmm) . Cells were lysed by passage through a French ® pressure cell (SLM-Ammco ® , Spectronic Instruments) while temperatures were maintained below 10°C. The resultant cell homogenate was centrifuged at 36,000 rpm at 4°C for 45 mm in a Beckman ultra- centrifuge using a Type TI45 rotor. The supernatant was discarded and the resultant pellet was resuspended with 40 mL of Solubilization Buffer (Lysis Buffer containing 1 M NaCl, 0.1 M MgCl 2 , 1 mM CaCl 2 , 20 μg/mL calmodulm, and 1% Sulfobetame SB12 (Z3-12) by sonicating using a VibraCell tuner with a microtip for 3 X 30 seconds. This was performed m a crushed ice/salt mix for cooling. Following sonication, the mixture was slowly mixed for 30 minutes at 4°C to finish solubilizing membrane bound proteins. This mixture was centrifuged m a Beckman ultracentπfuge using a type TI45 rotor at 36,000 rpm for 45 minutes. The supernatant was diluted with Lysis Buffer containing 10 μg/mL calpam inhibitors I and II. The precipitated protein was centrifuged for 20 minutes at 9,000 rpm m a Beckman JA-10 rotor. The recovered supernatant then was subjected to Mimetic Blue ® AP Agarose Chromatography. To run the Mimetic Blue ® AP Agarose Column, the resin initially was shielded by the appli- cation of 10 bed volumes of 1% polyvmylpyrrolidone (i.e., MW of 40,000) to block nonspecific binding sites. The loosely bound PVP-40 was removed by washing with 10 bed volumes of 2 M NaCl, and 10 mM sodium citrate pH 3.4. Just prior to addition of the solubilized PCE1C3 sample, the column was equilibrated with 5 bed volumes of Column Buffer A (50 mM MOPS pH 7.4, 10 μM ZnS0 4 , 5 mM MgCl 2 , 0.1 mM CaCl 2 , 1 mM DTT, 2 mM benzamidme HCl) . The solubilized sample was applied to the column at a flow rate of 2 mL/mm with recycling such that the total sample was applied 4 to 5 times m 12 hours. After loading was completed, the column was washed with 10 column volumes of Column Buffer A, followed by 5 column volumes of Column Buffer B (Column Buffer A containing 20 mM 5 ' -AMP) , and followed by 5 column volumes of Column Buffer C (50 mM MOPS pH 7.4, 10 μM ZnS0 4 , 0.1 mM CaCl 2 , 1 mM DTT, and 2 mM benzamidme HCl) . The enzyme was eluted into three successive pools. The first pool consisted of enzyme from a 5-bed volume wash with Column Buffer C containing 1 mM cAMP . The second pool consisted of enzyme from a 10 -bed volume wash with Column Buffer C containing 1 M NaCl. The final pool of enzyme consisted of a 5 -bed volume wasn with Column Buffer C containing 1 M NaCl and 20 mM cAMP Tne active pools of enzyme were collected and the cyclic nucleotide removed via conventional gel filtration chromatography or chromatography on hydroxyapatite resms. Following removal of cyclic nucleotides, the enzyme pools were dialyzed against Dialysis Buffer containing 25 mM MOPS pH 7.4, 10 μM ZnS0 4 , 500 mM NaCl, 1 mM CaCl 2 , 1 mM DTT, 1 mM benzamidme HCl, followed by dialysis against Dialysis buffer containing 50% glycerol. The enzyme was quick-frozen with the aid of dry ice and stored at -70°C. The resultant preparations were about >90% pure by SDS-PAGE. These preparations had specific activities of about 0.1 to 1.0 μmol cAMP hydrolyzed per minute per milligram protein. Purification of PDE2 from S . cerevisiae Frozen yeast cell pellets from strain YI34 (lOg, stored at -70°C) were allowed to thaw on ice 25 mL of Lysis Buffer (50 mM MOPS, pH 7.2 , 1 mM EDTA, 1 mM EGTA, 0.1 mM DTT, 0.1 mM 4-(2-ammo- ethyl) benzenesulfonyl fluoride (AEBSF), 1 μg/mL of pepstatm, leupeptm, aprotmm, calpam inhibitors I and II, and 2 mM benzamidme) . Cells were lysed by three passages through a French ® pressure cell (SLM-Ammco ® , Spectronic Instruments) . The lysate was centrifuged at 36,000 rpm a Beckman Ultracen- trifuge rotor Type 45Tι for 60 minutes at 4°C. The supernatant was separated from sediment and passed through a 15 mL Epoxy-cGMP Sepharos ® resm at 4°C two times at about 0.5 mL/mm. The column subsequently was washed with 45 mL of Wash Buffer 1 (50 mM MOPS, pH 7.2, 0.1 mM EDTA, 0.1 mM DTT) . Following this wash, the column was washed with 45 mL of Wash Buffer 2 (Wash Buffer 1 containing 0.5 M NaCl) . Following this salt wash, the column was washed with 15 mL of Wash Buffer 3 (Wash Buffer 1 containing 0.25 M NaCl) . The column was transferred to room temperature and allowed to warm. Approximately 25 mL of Elution Buffer (Wash Buffer 3 containing 10 mM cGMP, maintained at room temperature) was applied to the column and the effluent was collected in 2 mL fractions. Small aliquots of each of the fractions were diluted 20-fold PBS containing 5 mM MgCl 2 to allow hydrolysis of the competing ligand and to aid detection of PDE2 activity. Active fractions were passed through a Pharmacia PD-10 ® gel filtration column to exchange into Wash Buffer 3. This exchanged pool was diluted 50% v/v with sterile 80% glycerol and stored at -20°C. The resultant preparations were greater than 85% pure as judged by SDS- PAGE with subsequent staining of protein by Coomassie R-250. These preparations had specific activities of about 150 to 250 μmol cGMP hydrolyzed per minute per milligram protein. Preparation of PDE3A from Sf9 Cells Cells (2 X 1010) were suspended m Lysis Buffer containing 50 mM MOPS pH 7.5 , 2 mM DTT, 2 mM benzamidme HCl, 5 μM ZnS0 4 , 0.1 mM CaCl 2 , 20 μg/mL calpam inhibitors I and II, and 5 μg/mL each of leupeptm, pepstatm, and aprotmm. The mixture was sonicated twice for 30 seconds and the cells were lysed m a French ® pressure cell (SLM-Ammco ® , Spectronic Instruments) at 4°C The lysate was centrifuged 100,000 X g for 45 minutes. The pellet was washed once m Lysis Buffer and suspended m 46 mL Lysis Buffer with a Dounce homogenizer. Aliquots were stored at -70°C. These preparations had specific activities of about 1 to 2 nmol cAMP hydrolyzed per minute per milligram protein. HUMAN PDE4A, 4B, 4C, 4D PREPARATIONS Preparation of PDE4A from S . cerevisiae Yeast cells (50 g of yeast strain YI26 harboring HDUN1.46) were thawed at room temperature by mixing with 50 mL of Lysis Buffer (50 mM MOPS pH 7.5, 10 μM ZnS0 4 , 2 mM MgCl 2 , 14.2 mM 2-mercapto- ethanol , 5 μg/mL each of pepstatm, leupeptm, aprotmm, 20 μg/mL each of calpam inhibitors I and II, and 2 mM benzamidme HCl) . Cells were lysed m a French ® pressure cell (SLM-Ammco ® , Spectronic Instruments) at 10°C. The extract was centrifuged m a Beckman JA-10 rotor at 9,000 rpm for 22 minutes at 4°C. The supernatant was removed and centrifuged m a Beckman TI45 rotor at 36,000 rpm for 45 minutes at 4°C. PDE4A was precipitated from the high-speed supernatant by the addition of solid ammonium sul- fate (0.26 g/mL supernatant) while stirring m an ice bath and maintaining the pH between 7.0 and 7.5. The precipitated proteins containing PDE4A were collected via centrifugation m a Beckman JA-10 rotor at 9,000 rpm for 22 minutes. The precipitate was resuspended m 50 mL of Buffer G (50 mM MOPS pH 7.5, 10 μM ZnS0 4 , 5 mM MgCl 2 , 100 mM NaCl, 14.2 mM 2- mercaptoethanol , 2 mM benzamidine HCl, 5 zig/mL each of leupeptin, pepstatin, and aprotinin, and 20 ug/mL each of calpain inhibitors I and II) and passed through a 0.45 μm filter. The resuspended sample (50 to 100 mL) was loaded onto a 5 X 100 cm column of Pharmacia SEPHACRYL ® S-300 equilibrated in Buffer G. Enzyme activity was eluted at a flow rate of 2 mL/min and pooled for later fractionation. The PDE4A isolated from gel filtration chromatography was applied to a 1.6 X 20 cm column of Sigma Cibacron Blue Agarose-type 300 (10 mL) equilibrated in Buffer A (50 mM MOPS pH 7.5, 10 μM ZnS0 4 , 5 mM MgCl 2 , 14.2 mM 2-mercaptoethanol , and 100 mM benzamidine HCl) . The column was washed in succession with 50 to 100 mL of Buffer A, 20 to 30 mL of Buffer A containing 20 mM 5 '-AMP, 50 to 100 mL of Buffer A containing 1.5 M NaCl, and 10 to 20 mL of Buffer C (50 mM Tris HCl pH 8 , 10 μM ZnS0 4 , 14.2 mM 2 -mercaptoethanol , and 2 mM benzamidine HCl) . The enzyme was eluted with 20 to 30 mL of Buffer C con- taining 20 mM cAMP . The PDE activity peak was pooled, and precipitated with ammonium sulfate (0.33 g/mL enzyme pool) to remove excess cyclic nucleotide. The precipitated proteins were resuspended in Buffer X (25 mM MOPS pH 7.5, 5 μM ZnS0 4 , 50 mM NaCl, 1 mM DTT, and 1 mM benzamidine HCl) , and desalted via gel filtration on a Pharmacia PD-10 ® column per manufac- turer s instructions. The enzyme was quιcκ- frozen m a dry ice/ethanol bath and stored at -70°C The resultant preparations were about .80- pure by SDS-PAGE These preparations had specific activities of about 10 to 40 μmol cAMP hydrolyzed per minute per milligram protein. Preparation of PDE4B from S . cerevisiae Yeast cells (150 g of yeast strain YI23 harboring HDUN2.32) were thawed by mixing with 100 mL glass beads (0.5 mM, acid washed) and 150 mL Lysis Buffer (50 mM MOPS pH 7.2 , 2 mM EDTA, 2 mM EGTA, 1 mM DTT, 2 mM benzamidme HCl, 5 μg/mL each of pepstatm, leupeptin, aprotmm, calpam inhibitors I and II) at room temperature. The mixture was cooled to 4°C, transferred to a Bead-Beater ® , and the cells lysed by rapid mixing for 6 cycles of 30 seconds each. The homogenate was centrifuged for 22 minutes m a Beckman J2-21M centrifuge using a JA-10 rotor at 9,000 rpm and 4°C. The supernatant was recovered and centrifuged m a Beckman XL-80 ultra- centrifuge using a TI45 rotor at 36,000 rpm for 45 minutes at 4°C. The supernatant was recovered and PDE4B was precipitated by the addition of solid ammonium sulfate (0.26 g/mL supernatant) while stirring m an ice bath and maintaining the pH between 7.0 and 7.5. This mixture was then centrifuged for 22 minutes m a Beckman J2 centrifuge using a JA-10 rotor at 9,000 rpm (12,000 X g) The supernatant was discarded and the pellet was dissolved m 200 mL of Buffer A (50 mM MOPS pH 7.5, 5 mM MgCl 2 , 1 mM DTT, 1 mM benzamidme HCl, and 5 μg/mL each of leupeptin, pepstatm, and aprotmm) . The pH and conductivity were corrected to 7.5 and 15-20 mS , respectively. The resuspended sample was loaded onto a 1.6 X 200 cm column (25 mL) of Sigma Cibacron Blue Agarose-type 300 equilibrated in Buffer A. The sample was cycled through the column 4 to 6 times over the course of 12 hours . The column was washed m succession with 125 to 250 mL of Buffer A, 125 to 250 mL of Buffer A containing 1.5 M NaCl, and 25 to 50 mL of Buffer A. The enzyme was eluted with 50 to 75 mL of Buffer E (50 mM Tris HCl pH 8 , 2 mM EDTA, 2 mM EGTA, 1 mM DTT, 2 mM benzamidme HCl, and 20 mM cAMP) and 50 to 75 mL of Buffer E containing 1 M NaCl. The PDE activity peak was pooled, and precip- itated with ammonium sulfate (0.4 g/mL enzyme pool) to remove excess cyclic nucleotide. The precipitated proteins were resuspended m Buffer X (25 mM MOPS pH 7.5, 5 μM ZnS0 4 , 50 mM NaCl, 1 mM DTT, and 1 mM benzamidme HCl) and desalted via gel filtration on a Pharmacia PD-10 ® column per manufacturer's instructions. The enzyme pool was dialyzed overnight against Buffer X containing 50% glycerol . This enzyme was quick- frozen m a dry ice/ethanol bath and stored at -70°C. The resultant preparations were about >90% pure by SDS-PAGE. These preparations had specific activities of about 10 to 50 μmol cAMP hydrolyzed per minute per milligram protein. Preparation of PDE4C from S . cerevisiae Yeast cells (150 g of yeast strain YI30 harboring HDUN3.48) were thawed by mixing with 100 mL glass beads (0.5 mM, acid washed) and 150 mL Lysis Buffer (50 mM MOPS pH 7.2 , 2 mM EDTA, 2 mM EGTA, 1 mM DTT, 2 mM benzamidme HCl, 5 μg/mL each of pepstatin, leupeptin, aprotmm, calpam inhibitors I and II) at room temperature. The mixture was cooled to 4°C, transferred to a BEAD-BEATER ® , and the cells lysed by rapid mixing for 6 cycles of 30 sec each. The homogenate was centrifuged for 22 minutes m a Beckman J2-21M centrifuge using a JA-10 rotor at 9,000 rpm and 4°C. The supernatant was recovered and centrifuged m a Beckman XL- 80 ultra- centrifuge using a TI45 rotor at 36,000 rpm for 45 minutes at 4°C. The supernatant was recovered and PDE4C was precipitated by the addition of solid ammonium sulfate (0.26 g/mL supernatant) while stirring m an ice bath and maintaining the pH between 7.0 and 7.5. Thirty minutes later, this mixture was centrifuged for 22 minutes m a Beckman J2 centrifuge using a JA-10 rotor at 9,000 rpm (12,000 X g) . The super- natant was discarded and the pellet was dissolved in 200 mL of Buffer A (50 mM MOPS pH 7.5 , 5 mM MgCl 2 , 1 mM DTT, 2 mM benzamidme HCl, and 5 μg/mL each of leupeptin, pepstatin, and aprotmm) . The pH and conductivity were corrected to 7.5 and 15-20 mS , respectively. The resuspended sample was loaded onto a 1.6 X 20 cm column (25 mL) of Sigma Cibacron Blue Agarose-type 300 equilibrated m Buffer A. The sample was cycled through the column 4 to 6 times over the course of 12 hours . The column was washed m succession with 125 to 250 mL of Buffer A, 125 to 250 mL of Buffer A containing 1.5 M NaCl, and then 25 to 50 mL of Buffer A. The enzyme was eluted with 50 to 75 mL of Buffer E (50 mM Tris HCl pH 8 , 2 mM EDTA, 2 mM EGTA, 1 mM DTT, 2 mM benzamidme HCl, and 20 mM cAMP) and 50 to 75 mL of Buffer E containing 1 M NaCl. The PDE4C activity peak was pooled, and precipitated with ammonium sulfate (0.4 g/mL enzyme pool) to remove excess cyclic nucleotide. The precipitated proteins were resuspended m Buffer X (25 mM MOPS pH 7.2, 5 μM ZnS0 4 , 50 mM NaCl, 1 mM DTT, and 1 mM benzamidine HCl) and desalted via gel fil- tration on a Pharmacia PD-10 ® column per manufacturer's instructions. The enzyme pool was dialyzed overnight against Buffer X containing 50% glycerol . This enzyme was quick- frozen in a dry ice/ethanol bath and stored at -70°C. The resultant preparations were about >80% pure by SDS-PAGE. These preparations had specific activities of about 10 to 20 μmol cAMP hydrolyzed per minute per milligram protein. Preparation of PDE4D from S . cerevisiae Yeast cells (100 g of yeast strain YI29 harboring HDUN4.11) were thawed by mixing with 150 mL glass beads (0.5 mM, acid washed) and 150 mL Lysis Buffer (50 mM MOPS pH 7.2 , 10 μM ZnS0 4 , 2 mM MgCl 2 , 14.2 mM 2 -mercaptoethanol , 2 mM benzamidine HCl, 5 μg/mL each of pepstatm, leupeptin, aprotinin, calpain inhibitors I and II) at room tempera- ture The mixture was cooled to 4°C, transferred to a Bead-Beater', and the cells lysed by rapid τ ιxmg for 6 cycles of 30 sec each. The homogenate was centrifuged for 22 minutes m a Beckman J2-21M cen- tπfuge using a JA-10 rotor at 9,000 rpm and 4°C The supernatant was recovered and centrifuged a Beckman XL-80 ultracentrifuge using a TI45 rotor at 36,000 rpm for 45 minutes at 4°C. The supernatant was recovered and PDE4D was precipitated by the addition of solid ammonium sulfate (0.33 g/mL supernatant) while stirring m an ice bath and maintaining the pH between 7.0 and 7.5. Thirty minutes later, this mixture was centrifuged for 22 minutes m a Beckman J2 centrifuge using a JA-10 rotor at 9,000 rpm (12,000 X g) . The supernatant was discarded and the pellet was dissolved in 100 mL of Buffer A (50 mM MOPS pH 7.5, 10 μM ZnS0 4 , 5 mM MgCl 2 , 14.2 mM 2-mercaptoethanol , 100 mM benzamidme HCl, and 5 μg/mL each of leupeptin, pepstatin, aprotmm, calpam inhibitor I and II) . The pH and conductivity were corrected to 7.5 and 15-20 mS , respectively. At a flow rate of 0.67 mL/mm, the resuspended sample was loaded onto a 1.6 X 20 cm column (10 mL) of Sigma Cibacron Blue Agarose-type 300 equilibrated m Buffer A. The column was washed m succession with 50 to 100 mL of Buffer A, 20 to 30 mL of Buffer A containing 20 mM 5 '-AMP, 50 to 100 mL of Buffer A containing 1.5 M NaCl, and then 10 to 20 mL of Buffer C (50 mM Tris HCl pH 8 , 10 μM ZnS0 4 , 14.2 mM 2-mercaptoethanol, 2 mM benzamidme HCl) . The enzyme was eluted with 20 to 30 mL of Buffer C containing 20 mM cAMP . The PDE4D activity peak was pooled and precipitated with ammonium sulfate (0.4 g/mL enzyme pool) to remove excess cyclic nucleotide. The precipitated proteins were resuspended Buffer X (25 mM MOPS pH 7.2, 5 μM ZnSO ^ , 50 mM NaCl, 1 mM DTT, and 1 mM benzamidme HCl) and desalted via gel filtration on a Pharmacia PD-10^ column per manufacturer's instructions. The enzyme pool was dialyzed overnight against Buffer X containing 50% glycerol. This enzyme preparation was quick-frozen m a dry ice/ethanol bath and stored at -70°C. The resultant preparations were about >80% pure by SDS-PAGE. These preparations had specific activities of about 20 to 50 μmol cAMP hydrolyzed per minute per milligram protein. Purification of PDE5 from S . cerevisiae Cell pellets (29 g) were thawed on ice with an equal volume of Lysis Buffer (25 mM Tris HCl, pH 8, 5 mM MgCl 2 , 0.25 mM DTT, 1 mM benzamidme, and 10 μM ZnS0 4 ) . Cells were lysed m a Micro- fluidizer ® (Microfluidics Corp.) using nitrogen at 20,000 psi. The lysate was centrifuged and filtered through 0.45 μm disposable filters. The filtrate was applied to a 150 mL column of Q SEPHAROSE ® Fast- Flow (Pharmacia) . The column was washed with 1.5 volumes of Buffer A (20 mM Bis-Tπs Propane, pH 6.8, 1 mM MgCl 2 , 0.25 mM DTT, 10 μM ZnS0 4 ) and eluted with a step gradient of 125 mM NaCl m Buffer A followed by a linear gradient of 125-1000 mM NaCl m Buffer A. Active fractions from the linear gradient were applied to a 180 mL hydroxyapatite column m Buffer B (20 mM Bis-Tns Propane (pH 6.8^, 1 mM MgCi,, 0.25 mM DTT, 10 μM ZnSO, , and 250 mM KCl) . After loading, the column was washed with 2 volumes of Buffer B and eluted with a linear gradient of 0-125 mM potassium phosphate m Buffer B. Active fractions were pooled, precipitated with 60% ammonium sulfate, and resuspended m Buffer C (20 mM Bis-Tns Propane, pH 6.8, 125 mM NaCl, 0.5 mM DTT, and 10 μM ZnSO . The pool was applied to a 140 mL column of SEPHACRYL ® S-300 HR and eluted with Buffer C. Active fractions were diluted to 50% glycerol and stored at -20°C. The resultant preparations were about 85% pure by SDS-PAGE. These preparations had specific activities of about 3 μmol cGMP hydrolyzed per minute per milligram protein. Preparation of PDE7 from S . cerevisiae Cell pellets (126 g) were thawed and resuspended at room temperature for about 30 minutes with an equal volume of Lysis Buffer (50 mM Tris HCl, pH 8, 1 mM EDTA, 1 mM DTT, 50 mM NaCl, 2 mM benzamidme HCl, and 5 μg/mL each of pepstatin, leupeptin, and aprotmm) . The cells were lysed at 0-4°C with the a d of glass beads (125 mL) m a Bead-Beater ® for 6 X 30 second cycles. The lysate was centrifuged and filtered through 0.45 μ disposable filters. The filtered extract (178 mL) was distributed into 4 mL aliquots, quick-frozen with dry ice, and stored m a freezer at -70°C. These preparations were stable to several cycles of freezing and thawing and had specific activities of about 50 to 100 pmol cAMP hydrolyzed per minute per milligram protein. Lipopolysaccharide-Stimulated TNFα Release from Human Peripheral Blood Lymphocytes To assess the ability of a compound to reduce TNFα secretion m human peripheral blood lymphocytes (PBL) , the following tests were performed. Previous studies have demonstrated that incubation of human PBL with cAMP-elevatmg agents, such as prostaglandm E21 forskolm, 8 -bromo-cAMP, or dibutryl-cAMP, inhibits the secretion of TNFα by the cells when stimulated by lipopolysaccharide (LPS; endotoxm) . Accordingly, preliminary experiments have been performed to demonstrate that selective PDE4 inhibitors, such as rolipram, inhibit LPS- mduced TNFα secretion from human lymphocytes m a dose-dependent fashion. Hence, TNFα secretion from human PBL was used as a standard for the ability of a compound to elevate intracellular cAMP concentrations and/or to inhibit PDE4 activity withm the cell. Heparmized blood (approximately 30 mL) drawn from human volunteers was mixed 1:1 with Dulbecco ' s modified phosphate-buffered saline. This mixture was mixed 1:1 with HISTOPAQUE ® and centrifuged at 1,500 rpm at room temperature without brak- mg m the swinging bucket of a Beckman model TJ6 centrifuge. Erythrocytes were centrifuged to the bottom of the tubes, and serum remained at the surface of the tubes. A layer containing lymphocytes sedimented between the serum and HISTOPAQUE ® layers, and was removed by aspiration to a fresh tube. Tne cells were quantified and adjusted to 3 X 10 cells/mL and a 100 μL aliquot is placed into the wells of a 96 well plate. Test compounds and RPMI media (Gibco/BRL Life Sciences) are added to each of the wells 15 minutes prior to addition of bacterial LPS (25 mg/mL) . The mixture was allowed to incubate for 20 hours at 37 °C m a humidified chamber. The cells then were separated by centrifugmg at 800 rpm for 5 minutes at room temperature. An aliquot of 180 μL of supernatant was transferred to a new plate for determination of TNFα concentration. TNFα protein m the cell supernatant fluids was measured using a commercially available enzyme-lmked lmmuno- sorbent assay (ELISA) (CYTOSCREEN ® Immunoassay Kit from Biosource International) . The cell -based assay provided the following results for various compounds of the present invention. The EC 50 values (i.e., effective concen- tration of the compound capable of inhibiting 50% of the total TNFα) illustrate the ability of the present compounds to inhibit LPS -stimulated TNFα release from human PBL. The following summarizes the IC 50 values determined for compounds of structural formula (I) against human recombinant PDE4. In the following table, R 3 and R" 1 are both methyl, Y and Z are 0, and p is 1, unless otherwise noted. The data presented above shows that compounds of formula (I) are potent and selective inhibitors of PDE4 , e.g., the compounds have an IC 50 vs . human recombinant PDE4 of about 0.1 to about 180μM. As an important added advantage, the com- pounds of formula (I) reduced or eliminated the adverse side effects, such as CNS effects and e esis, associated with prior PDE4 inhibitors. In particular, compounds of formula (I) were tested m cell-based assays and m animal models to illustrate the efficacy of the compounds with respect to inhibiting PDE4 both vi tro and vivo . The cell -based assay provided the following results for various pyrazole compounds of the present invention. The EC 5λj values (i.e., effective concentrations of the compound capable of inhibiting 50% of the total TNFα) illustrate the ability of the present compounds to inhibit LPS-stimulated TNFα release from human peripheral blood lymphocytes. The above table illustrates the ability of compounds of formula (I) to inhibit PDE4 activity and TNFα release. Preferred compounds have a PBL/TNFα EC_, r about 50 nM or less, and preferably about 20 nM or less. More preferred compounds have a PBL/TNFα EC- C of 15 nM or less. To achieve the full advantages of the present invention, the compound has an IC, 0 vs. human recombinant PDE4 of about 100 nM or less and a PBL/TNFα EC 50 of about 50 nM or less. More prefera- bly, the compound has an IC of about 5n nM or less and a PBL/TNFα EC of about 10 nM or less. Animal models Assay for Inhibition of Serum TNFα Levels in Mammals (Mouse/TNFα ED cn (mg/kg) ) In order to assess the ability of a com- pound to reduce serum TNFα levels m mammals, the following protocol was employed. Those skilled m the art appreciate that previous studies have demonstrated that incubation of LPS-activated human monocytes with agents that can elevate cAMP, like PGE2 , forskolm, and the dbcAMP, inhibited secretion of TNFα. PDE4 inhibitors like rolipram, which also elevate cAMP, have been found to inhibit serum TNFα as well. Rolipram has also been found to inhibit secretion of TNFα from LPS-activated mouse macro- phages . Accordingly, vivo efficacy of a PDE4 reducing compound was shown by dosing with compound and measuring reduction of serum TNFα levels m LPS- m ected mice. Female C3H mice, 20-25 gm body weight, were fasted overnight and dosed mtrapeπ- toneally with test compound m appropriate vehicle 60 minutes before LPS injection. Five μg of LPS was then injected mtraperitoneally into the mice. Ninety minutes after LPS injection, mice were bled from the heart. Blood was allowed to clot overnight at 4°C. Samples were centrifuged for 10 minutes m a microcentπfuge and the serum removed and stored at -20°C until analysis. Serum levels of TNFα were subsequently measured using a commercially available ELISA kit (Genzyme) following the protocol enclosed m the kit. The inhibition of serum TNFα levels caused by the compound was determined relative to serum TNFα levels m control mice receiving vehicle alone. The results are summarized m the plots of FIG. 1. Combined Mouse endotoxin- stimulated TNFα Release and Locomotor Activity Assay (ED 50 (mg/kg) ) The purpose of this study was to determine the efficacy of PDE4 inhibitors in vi vo m an LPS mouse model together with a determination with respect to central nervous system (CNS) side-effects manifested by a decrease m spontaneous mobility. The test animals were female Balb/c mice, having an average weight of about 20 g. The PDE4 inhibitors, formulated m 30% Cremophor ® EL, were administered via mtraperitoneal (i.p.) injections at doses of 0.1, 1.0, 10.0, and 100 mg/kg. Individual dose volumes (about 150 μL) were adjusted based on the body weights measured. One hour later, 5 mg/kg LPS in a final volume of 200 μL was injected via the tail vein to each animal . Ninety minutes following the LPS treatment, the animals were bled and serum samples were collected before being stored at -70°C until assayed. For efficacy determination, the serum samples were diluted two- fold and TNFα levels were determined using the CYTOSCREEN ® Immunoassay Kit (Biosource International) . The data were averaged between triplicate sample subjects for each of the tested compounds . For side-effect profiling, a suo ective visual scoring system was utilized at 5mm and 2Cmm after administration of PDE4 inhibitors. Vehicle control animals were rated a single "+" and animals that were effectively immobilized and stretched out on the bottom of the cage with little detectable movement were rated as "++++." Alternatively, a semi -automated "open field" system (e.g., a Photo- beam Activity Measurement System as sold by San Diego Instruments) for monitoring movements was used for assessing the effect of PDE4 inhibitors on mice and/or rats. In this instance, the subjects could be monitored continuously over pre-set intervals. Movement of the X-Y plane, or rearing up on the hmd legs, was quantified by counting the number of "light-beam" crosses per unit of time. A decrease m the number of activity events is directly proportional to the mobility or immobilization of the animal. The quantitative scoring corre- lated well with the subjective measurements described above. trans-3 - (3 -cyclopentoxy- -methoxyphenyl) - l-met_loxycarbonyl- 4 -methyl-4 - (methylcarbonyl) pyrrolidine , l e , Example 12 of Feldman et al . U.S. Patent No 5,665,754, incorporated herein by reference The data presented above show that com- pounds of formula (I) are potent and selective inhibitors of PDE4. As an important added advantage, the compounds of formula (I) also reduced or eliminated the adverse CNS side effects associated with prior PDE4 inhibitors. Compounds of formula (I) were further tested for emetogenic properties m animal models to further illustrate the efficacy of the compounds. The method and results of the emetogenic test are set forth below. The results show that the compounds of the present invention are useful for selectively inhibiting PDE4 activity m a mammal, without exhibiting the adverse CNS and emetic effects associated with prior PDE4 inhibitors. Obviously, many modifications and variations of the invention as hereinbefore set forth can be made without departing from the spirit and scope thereof and, therefore, only such limitations snould be imposed as are indicated by the appended claims.

Claims: WHAT IS CLAIMED IS: 1. A compound having a formula: wherein Y is 0 or NOH; Z is 0 or NH; R 1 is selected from the group consisting of optionally substituted alkyl, cycloalkyl, aryl, alkaryl, aralkyl, heteroaralkyl, and heteroalkaryl; R 2 is selected from the group consisting of optionally substituted hydrogen, methyl, C 3 16 alkyl , aryl, heteroaryl, alkoxyalkyl, aryloxyalkyl, aral- koxyalkyl, (alkylthio) alkyl , (arylthio) alkyl , and (aralkylthio) alkyl ; R 3 and R" , independently, are selected from the group consisting of hydrogen, alkyl, haloalkyl, and aryl ; with the proviso that when R 1 is unsubstituted phenyl, R is different from unsubstituted phenyl, unsubstituted pyridinyl, and p-tolyl. 2. The compound of claim 1 wherein R is selected from the group consisting of optionally substituted alkyl, aryl, alkaryl, and heteroaryl. 3. The compound of claim 1 wherein R 1 is selected from the group consisting of aryl, alkyl, or heteroaryl, optionally substituted with one or more of nitro, ammo, lower alkyl, alkoxy, halo, trifluoromethyl , , and -NH-C-0(CH 3 ) 3 4. The compound of claim 1 wnerem R is phenyl, pyridyl, or cyclohexyl, optionally substituted. 5. The compound of claim 1 wherein R" is selected from the group consisting of hydrogen, optionally substituted alkyl, and optionally substituted aryl . 6. The compound of claim 1 wherein R 2 is selected from the group consisting of hydrogen, XX, , and 7. The compound of claim 1 wherein R J and R , independently, are selected from the group consisting of alkyl, aryl, and hydrogen. 8. The compound of claim 1 wherein R 3 and R 4 , independently, are selected from the group consisting of alkyl, hydrogen, and trifluoromethyl . 9. The compound of claim 1 wherein R is phenyl or pyridyl, optionally substituted; R- is methyl or hydrogen; R J and R 4 , independently, are methyl or hydrogen; and Y and Z are 0. 10. The compound of claim 1 selected from the group consisting of : 1- (4 -bromophenyl ) -3 , 5-dimethyl -IH-pyrazole-4 -carboxylic acid ethyl ester; 3 , 5 -dimethyl- 1- (3 -nitrophenyl ) -IH-pyrazole-4 -carboxylic acid ethyl ester; 3 , 5 -dimethyl -1 -phenyl - IH-pyrazole-4 -carboxylic acid ethyl ester; 3 , 5 -dimethyl -1-p-tolyl -IH-pyrazole-4 -carboxylic acid ethyl ester; 3 , 5-dιmethyl-l- (2 -nitrophenyl ) -IH-pyrazole-4 -carboxylic acid ethyl ester; 3 , 5 -dimethyl -1- (2 -aminophenyl ) -lH-pyrazole-4-carboxylic acid ethyl ester; 3 , 5-dimethyl -1-pyrιdm-2 -yl-lH-pyrazole-4-carboxylic acid ethyl ester; 1- (3 -aminophenyl) -3 , 5 -dimethyl -lH-pyrazole-4-carboxylic acid ethyl ester; 3 , 5 -dimethyl -1- (4 -aminophenyl) -IH-pyrazole-4 -carboxylic acid ethyl ester; 1- (3 -ammopyrιdm-2 -yl) -3 , 5 -dimethyl -IH-pyrazole-4 - carboxylic acid ethyl ester; 3 , 5 -dimethyl -1- (3 -nιtropyrιdm-2-yl ) - IH-pyrazole- 4 - carboxylic acid 3 , 5-dιmethyl-l- (5-nιtropyrιdm-2 -yl ) -IH-pyrazole-4 - carboxylic acid ethyl ester; 1- (4 -aminophenyl) -3 , 5 -dimethyl -IH-pyrazole-4 -carbox¬ 1- cyclohexyl -3 , 5 -dimethyl -IH-pyrazole-4 -carboxylic acid ethyl ester; 1 -benzyl -3 , 5 -dimethyl- IH-pyrazole-4 -carboxylic acid ethyl ester; 1- (3 -chlorophenyl ) -3, 5-dιme hyl- IH-pyrazole-4 -carboxylic acid ethyl ester; 3 , 5-dimethyl -1-m-tolyl- IH-pyrazole-4 -carboxylic acid ethyl ester; l-(3 -fluorophenyl ) -3 , 5 -dimethyl - IH-pyrazole-4 -car- boxylliicc acid ethyl ester; 1- (3 -methoxyphenyl) -3 , 5 -dimethyl - IH-pyrazole-4 -carboxylic acid ethyl ester; 1- (3 -bromophenyl) -3 , 5 -dimethyl- IH-pyrazole -4 -carboxylic acid ethyl ester; 3 -methyl -1 -pyridin-2 -yl -IH-pyrazole-4 -carboxylic acid ethyl ester; and l -- ((4 -aminophenyl) -5- trifluoromethyl-lH-pyrazole-4- caarboxylic acid ethyl ester. 11. The compound of claim 1 selected from the group consisting of : 3 , 5 -dimethyl -1- (3 -nitrophenyl ) - IH-pyrazole-4 -carboxylic acid ethyl ester; 3 , 5 -dimethyl -1 -phenyl -IH-pyrazole -4 -carboxylic acid ethyl ester; 3 , 5-dιmethyl-l- (2 -aminophenyl ) - IH-pyrazole-4 -carboxylic acid ethyl ester; 3 , 5 -dimethyl -1- (2 -nitrophenyl) - IH-pyrazole-4 -carboxylic acid ethyl ester; 1- (3 -aminophenyl) -3 , 5 -dimethyl - IH-pyrazole-4 -carboxylic acid ethyl ester; 3 , 5 -dimethyl- 1- (4 -aminophenyl) - IH-pyrazole-4 -carboxylic acid ethyl ester; and 1- (3-ammopyrιdm-2-yl) -3 , 5 -dimethyl - IH-pyrazole-4 - carboxylic acid ethyl ester. 12. The compound of claim 1 having an IC s. human recombinant PDE4 of about 0.05 _.M to aoout 25 LM. 13. The compound of claim 1 having a PBL/TNFo EC of about 0.01 μM to about 15 μM . 14. The compound of claim 1 having an IC vs. human recombinant PDE4 of about 0.05 ^M to about 25 μM, and a PBL/TNFα EC 50 of about 0.01 μM to about 15 μM. 15. The compound of claim 1 having an IC bC vs. human recombinant PDE4 of about 100 μM or less. 16. The compound of claim 1 having an IC 5C vs. human recombinant PDE4 of about 50 μM or less. 17. The compound of claim 1 having a PBL/TNFα EC 50 of about 50 μM or less. 18. The compound of claim 1 having a PBL/TNFα EC 50 of about 20 μM or less. 19. The compound of claim 1 having an IC 50 vs. human recombinant PDE4 of about 100 μM or less and a PBL/TNFα EC DC of about 50 μM or less. 20. A pharmaceutical composition comprising a compound of claim 1, a pharmaceutically acceptable carrier, and, optionally, a second anti- mflammatory therapeutic agent. 21 A compound having a formula: wherein Y is 0 or NOH; Z is 0 or NH; p is 0 or 1 ; R 1 is selected from the group consisting of alkyl, aryl, heteroaryl, alkaryl, aralkyl, heteroaralkyl, and heteroalkaryl; R 2 is ethyl; R 3 and R 4 , independently, are selected from the group consisting of hydrogen, alkyl, akloxyalkyl, aryl, C(=0) alkyl, and C (=0) CH=CHNR=R 6 ; R 5 and R°, independently, are hydrogen or alkyl, or R ς and R 6 are taken together to form a 5- or 6-membered ring, with the proviso that R 1 is different from nitro-substituted pyridinyl, ammo-substituted phenyl, nitro-substituted phenyl, trichlorophenyl, and chlorotπfluorophenyl . 22. A compound having a structure , or 23. A method of treating a mammal having a condition where inhibition of a cAMP-specifIC PDE is of therapeutic benefit, said method comprising administering to said mammal a therapeutically effective amount of a compound having a formula wherein Y is O or NOH; R 1 is selected from the group consisting of optionally substituted alkyl, cycloalkyl, aryl, heteroaryl, alkaryl, aralkyl, heteroaralkyl, and heteroalkaryl ; R 2 is selected from the group consisting of optionally substituted hydrogen, alkyl, aryl, heteroaryl, alkoxyalkyl, aryloxyalkyl, aralkoxyalkyl , (alkylthio) alkyl , (arylthio) alkyl , and (aralkyl - thio) alkyl ; R 3 and R" , independently are selected from the group consisting of hydrogen, alkyl, haloalkyl, alkoxyalkyl, aryl C(=0) alkyl, and C (=0) CH=CHNR 5 R 6 ; R 5 and R D , independently, are hydrogen or alkyl, or R 5 and R° are taken together to form a 5- or 6-membered ring. 24. A method of modulating cAMP levels m a mammal comprising administering to said mammal an effective amount of a compound having a formula wherein Y is O or NOH; p is 0 or 1 ; R 1 is selected from the group consisting of optionally substituted alkyl, cycloalkyl, aryl, heteroaryl, alkaryl, aralkyl, heteroaralkyl, and heteroalkaryl ; R 2 is selected from the group consisting of optionally substituted hydrogen, alkyl, aryl, heteroaryl, alkoxyalkyl, aryloxyalkyl, aralkoxyalkyl , (alkylthio) alkyl , (arylthio) alkyl , and (aralkyl - thio) alkyl ; R 3 and R 4 , independently are selected from the group consisting of hydrogen, alkyl, haloalkyl, alkoxyalkyl, aryl C(=0) alkyl, and C (=0) CH=CHNRR°; R 5 and R 6 , independently, are hydrogen or alkyl, or R 5 and R 6 are taken together to form a 5- or 6-membered ring. 25. A method of treating a mammal having a condition where inhibition of a cAMP-specific PDE is of a therapeutic benefit comprising administering to said mammal a therapeutically effective amount of a pharmaceutical composition comprising a compound having a formula wherein Y is 0 or NOH; Z is O or NH; R 1 is selected from the group consisting of optionally substituted alkyl, cycloalkyl, aryl, heteroaryl, alkaryl, aralkyl, heteroaralkyl, and heteroalkaryl ; R 2 is selected from the group consisting of optionally substituted hydrogen, alkyl, aryl, heteroaryl, alkoxyalkyl, aryloxyalkyl, aralkoxyalkyl , (alkylthio) alkyl , (arylthio) alkyl , and (aralkyl - thio) alkyl ■ R 3 and R 4 , independently are selected from the group consisting of hydrogen, alkyl, haloalkyl, alkoxyalkyl, aryl C(=0) alkyl, and C (=0) CH=CHNR " R D ; R 5 and R 6 , independently, are hydrogen or alkyl, or R 5 and R 6 are taken together to form a 5- or 6-membered ring, - I l l - a pharmaceutically acceptable carrier, and, optionally, a second antiinflammatory therapeutic agent . 26. The method of claim 25 wherein the condition is an allergic disease, an autoimmune disease, an inflammatory disease, an arthritic disease, or dermititis. 27. The method of claim 25 wherein the condition is rheumatoid arthritis, osteoarthπtis , gouty arthritis, or spondylitis. 28. The method of claim 25 wherein the condition is thyroid-associated ophthalmopathy, Behcet disease, sepsis, septic shock, endotoxic shock, gram negative sepsis, gram positive sepsis, toxic shock syndrome, allergic con unctivitis, vernal conjunctivitis, or eosmophilic granuloma. 29. The method of claim 25 wherein the condition is asthma, chronic bronchitis, allergic rhinitis, adult respiratory distress syndrome, chronic pulmonary inflammatory disease, chronic obstructive pulmonary disease, silicosis, or pulmonary sarcoidosis. 30. The method of claim 25 wherein the condition is reperfusion injury of the myocardium, brain or extremities as a brain or spinal cord injury due to trauma. 31. The method of claim 25 wherein the condition is a fibrosis, keloid formation, or scar tissue formation. 32. The method of claim 25 wherein the condition is systemic lupus erythematosus , a transplant rejection disorder, a graft vs. host reaction, or an allograft rejection. 33. The method of claim 25 wherein the condition is chronic glomerulonephritis , an inflammatory bowel disease, Crohn's disease, or ulcerative colitis . 34. The method of claim 25 wherein the condition is proliferative lymphocytic disease or a leukemia . 35. The method of claim 25 wherein the condition is an inflammatory dermatosis, atopic dermatitis, psoriasis, or urticaria. 36. The method of claim 25 wherein the condition is a cardiomyopathy, congestive heart failure, atherosclerosis, pyrexia, cachexia, cachexia secondary to infection or malignancy, cachexia secondary to acquired immune deficiency syndrome, ARC, cerebral malaria, osteoporosis, a bone resorption disease, fever and myalgias due to infection, diabetes msipidus, a central nervous system disorder, depression, or multi-mfarct dementia . 37. The method of claim 25 wherein the mammal is free of an emetic response. 38. The method of claim 27 wnerem the mammal exhibits a minimal emetic response. 39. The method of claim 25 wherein the mammal exhibits minimal adverse central nervous system side effects . 40. The method of claim 25 wherein the mammal is free of adverse central nervous system side effects. 41. The method of claim 25 wherein the second antimflammatory therapeutic agent is capable of targeting TNFα. 42. A method of reducing TNF levels m a mammal comprising administering to said mammal a therapeutically effective amount of a compound having a formula wherein Y is O or NOH; Z is 0 or NH; p is 0 or 1; R 1 is selected from the group consisting of optionally substituted alkyl, cycloalkyl, aryl, heteroaryl, alkaryl, aralkyl, heteroaralkyl, and heteroalkaryl ; R 2 is selected from the group consisting of optionally substituted hydrogen, alkyl, aryl, heteroaryl, alkoxyalkyl, aryloxyalkyl, aralkoxyalkyl , (alkylthio) alkyl , (arylthio) alkyl , and (aralkyl - thio) alkyl ; R 3 and R 4 , independently are selected from the group consisting of hydrogen, alkyl, haloalkyl, alkoxyalkyl, aryl C(=0) alkyl, and C (=0) CH=CHNR 5 R 6 ; R 5 and R 6 , independently, are hydrogen or alkyl, or R 5 and R 6 are taken together to form a 5- or 6-membered ring. 43. A method of suppressing inflammatory cell activation m a mammal comprising administering to said mammal a therapeutically effective amount of a compound having a formula wherein Y is O or NOH; Z is O or NH; p is 0 or 1 ; R 1 is selected from the group consisting of optionally substituted alkyl, cycloalkyl, aryl, heteroaryl, alkaryl, aralkyl, heteroaralkyl, and heteroalkaryl ; R 2 is selected from the group consisting of optionally substituted hydrogen, alkyl, aryl, heteroaryl, alkoxyalkyl, aryloxyalkyl, aralkoxyalkyl , (alkylthio) alkyl , (arylthio) alkyl , and (aralkyl - thio) alkyl ; R 3 and R 4 , independently are selected from the group consisting of hydrogen, alkyl, haloalkyl, alkoxyalkyl, aryl C(=0) alkyl, and C (=0) CH=CHNR S R C ; R 5 and R 6 , independently, are hydrogen or alkyl, or R 5 and R 6 are taken together to form a 5- or 6-membered ring. 44. A method of inhibiting PDE4 function m a mammal comprising administering to said mammal a therapeutically effective amount of a compound having a formula wherein Y is 0 or NOH; Z is 0 or NH; p is 0 or 1 ; R 1 is selected from the group consisting of optionally substituted alkyl, cycloalkyl, aryl, heteroaryl, alkaryl, aralkyl, heteroaralkyl, and heteroalkaryl ; R 2 is selected from the group consisting of optionally substituted hydrogen, alkyl, aryl, heteroaryl, alkoxyalkyl, aryloxyalkyl, aralkoxyalkyl , (alkylthio) alkyl , (arylthio) alkyl , and (aralkyl - thio) alkyl ; R 3 and R 4 , independently are selected from the group consisting of hydrogen, alkyl, haloalkyl, alkoxyalkyl, aryl C(=0) alkyl, and C (=0) CH=CHNR 5 R 6 ; R 5 and R 6 , independently, are hydrogen or alkyl, or R 5 and R δ are taken together to form a 5- or 6-membered ring.

Inventors: FOWLER KERRY W, HERTEL CARMEN C, MARTINS TIMOTHY J, OLIVER AMY, FOWLER, KERRY, W., HERTEL, CARMEN, C., MARTINS, TIMOTHY, J., OLIVER, AMY
Applicants: ICOS CORP, ICOS CORPORATION
Application year: 2000
Main classification: C07D401
IPC codes: A61K31, A61K45, A61P5, A61P9, A61P11, A61P13, A61P17, A61P19, A61P25, A61P29, A61P31, A61P35, A61P37, C07D231, C07D401