This application claims benefit of provi- sional application Serial No. 60/171, 950, filed December 23, 1999.

FIELD OF INVENTION The present invention relates to a series of compounds that are potent and selective inhibi- tors of cyclic adenosine 3', 5'-monophosphate spe- cific phosphodiesterase (cAMP specific PDE). In particular, the present invention relates to a se- ries of novel thiazole compounds that are useful for inhibiting the function of cAMP specific PDE, in particular, PDE4, as well as methods of making the same, pharmaceutical compositions containing the same, and their use as therapeutic agents, for exam- ple, in treating inflammatory diseases and other diseases involving elevated levels of cytokines and proinflammatory mediators.

BACKGROUND OF 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 interleukin-1 (IL-1), are produced by these activated cells. Accordingly, an agent that suppresses the activation of these cells, or their production of proinflammatory cytokines, would be useful in the therapeutic treatment of inflammatory diseases and other diseases involving elevated lev- els of cytokines.

Cyclic adenosine monophosphate (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 triphosphate (ATP) to cAMP. It is theorized that the agonist induced actions of cAMP within the cell are mediated predom- inately 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.

Elevated levels of cAMP in human myeloid and lymphoid lineage cells are associated with the suppression of cell activation. The intracellular enzyme family of PDEs, therefore, regulates the level of cAMP in cells. PDE4 is a predominant PDE isotype in these cells, and is a major contributor to cAMP degradation. Accordingly, the inhibition of

PDE function would prevent the conversion of cAMP to the inactive metabolite 5'-AMP and, consequently, maintain higher cAMP levels, and, accordingly, sup- press cell activation (see Beavo et al.,"Cyclic Nucleotide Phosphodiesterases : Structure, Regula- tion 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., Clin. Exp. Allergy, 22, pp. 337-344 (1992)).

In particular, PDE4 inhibitors, such as rolipram, have been shown to inhibit production of TNFa and partially inhibit IL-1/3 release by mono- cytes (see Semmler et al., Int. J. Immunopharmacol., 15, pp. 409-413, (1993) ; Molnar-Kimber et al., Medi- ators of Inflammation, 1, pp. 411-417, (1992)).

PDE4 inhibitors also have been shown to inhibit the production 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 in eosino- phils (see Dent et al., J. Pharmacol., 103, pp.

1339-1346, (1991)) ; and to inhibit the activation of human T-lymphocytes (see Robicsek et al., Biochem.

Pharmacol., 42, pp. 869-877, (1991)).

Inflammatory cell activation and excessive or unregulated cytokine (e. g., TNFa and IL) pro- duction are implicated in allergic, autoimmune, and inflammatory diseases and disorders, such as rheuma-

toid arthritis, osteoarthritis, gouty arthritis, spondylitis, thyroid associated ophthalmopathy, Behcet's disease, sepsis, septic shock, endotoxic shock, gram negative sepsis, gram positive sepsis, toxic shock syndrome, asthma, chronic bronchitis, adult respiratory distress syndrome, chronic pulmo- nary inflammatory disease, such as chronic obstruc- tive pulmonary disease, silicosis, pulmonary sarco- idosis, reperfusion injury of the myocardium, brain, and extremities, fibrosis, cystic fibrosis, 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 cytokine levels include brain injury due to moderate trauma (see Dhillon et al., J. Neurotrauma, 12, pp.

1035-1043 (1995) ; Suttorp et al., J. Clin. Invest., 91, pp. 1421-1428 (1993)), cardiomyopathies, such as congestive heart failure (see Bristow et al., Circu- lation, 97, pp. 1340-1341 (1998)), cachexia, cachex- ia 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, TNFa 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 in T-lymphocytic and monocytic cells (see Poli et al., Proc. Natl.

Acad. Sci. USA, 87, pp. 782-785, (1990)).

Several properties of TNFa, such as stimu- lation of collagenases, stimulation of angiogenesis in vivo, stimulation of bone resorption, and an ability to increase the adherence of tumor cells to endothelium, are consistent with a role for TNF in the development and metastatic spread of cancer in the host. TNFa recently has been directly impli- cated in 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 amino 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 amino acid identity. It is theorized that the role of these alternatively expressed PDE4 proteins allows a mechanism by which a cell can differentially localize these enzymes intracellularly and/or regulate the catalytic effi- ciency via post translational modification. Any given cell type that expresses the PDE4 enzyme typi-

cally expresses more than one of the four possible genes encoding these proteins.

Investigators have shown considerable interest in the use of PDE4 inhibitors as anti-in- 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 biogenic amines, such as histamine, have been attenuated in these cells by the action of PDE4 inhibitors. The PDE4 inhibitors also affect other cellular functions including T- cell proliferation, granulocyte transmigration in response to chemotoxic substances, and integrity of endothelial cell junctions within the vasculature.

The design, synthesis, and screening of various PDE4 inhibitors have been reported. Methyl- xanthines, such as caffeine and theophylline, 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 struc- tural formula, has a reported 50% Inhibitory Concen- tration (IC50) of about 200 nM (nanomolar) with re- spect 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 IC50 than rolipram, and that avoid the undesirable central nervous system (CNS) side effects, such as retching, vomiting, and sedation, associated with the adminis- tration of rolipram. One class of compounds is dis- closed 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 structural formula (I), has an IC5 (l with respect to human recombinant PDE4 of about 2 nM. Inasmuch as a favorable separa- tion of emetic side effect from efficacy was ob- served, these compounds did not exhibit a reduction in undesirable CNS effects.

In addition, several companies are now undertaking clinical trials of other PDE4 inhibi- tors. 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 ad- verse CNS side effects associated with prior PDE4 inhibitors, would be useful in the treatment of allergic and inflammatory diseases, and other dis- eases associated with excessive or unregulated pro- duction of cytokines, such as TNF. In addition, selective PDE4 inhibitors would be useful in 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 po- tent and selective PDE4 inhibitors useful in treat- ment 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 compounds having the structural formula (II) : wherein R1 is lower alkyl, bridged alkyl (e. g., norbornyl), aralkyl (e. g., indanyl), cyclo- alkyl, a 5-. or 6-membered saturated heterocycle (e. g., 3-tetrahydrofuryl), CI-3alkylenecycloalkyl (e. g., cyclopentylmethyl), aryl-or heteroaryl-sub- stituted propargyl (e. g., -CH2C=C-C6H5), aryl-or heteroaryl-substituted allyl (e. g.,-CH2CH=CH-C6Hs), or halocycloalkyl (e. g., fluorocyclopentyl) ; R2 is hydrogen, methyl, or halo-substituted methyl, e. g., CHF2 ; R3 is selected from the group consisting of C (=O) OR7, C (=O) R, C (=NH) NR8R9, C (=O) NR8R9, lower alkyl, bridged alkyl, cycloalkyl, haloalkyl, halo- cycloalkyl, Cl3alkylenecycloalkyl, a 5-or 6- membered saturated heterocycle, aryl, heteroaryl, heteroarylSO2, aralkyl, alkaryl, heteroaralkyl, heteroalkaryl, C1-2alkyleneC(=O)OR7, C (=O) C13alkyl- eneC (=O) OR, C1-3alkyleneheteroaryl, C (=O) C (=O) OR',

C (=O) C1-3alkyleneC(=O)OR7, C(=O)C1-3alkyleneNHC(=O)OR7, C (=O) Cl3alkyleneNH2, and NHC (=O) oR7 ; R'is hydrogen,. lower alkyl, haloalkyl, cycloalkyl, aryl, C (=O) R', OR8, NR8R9, or SR8 ; Rs is hydrogen, lower alkyl, haloalkyl, cycloalkyl, or aryl ; R'is selected from the group consisting of cycloalkyl, branched or unbranched lower alkyl, heteroaryl, a heterocycle, aralkyl, and aryl, and R7 is optionally substituted with one or more of OR8, NR8R9, or SR ; R8 and R9, same or different, are selected from the group consisting of hydrogen, lower alkyl, cycloalkyl, aryl, heteroaryl, alkaryl, heteroaralk- yl, heteroalkaryl, and aralkyl, or R and R9 are taken together form a 4-membered to 7-membered ring ; R10 is hydrogen, alkyl, haloalkyl, cyclo- alkyl, aryl, C (=O) alkyl, C (=O) cycloalkyl, C (=O) aryl, C (=O) Oalkyl, C (=O) Ocycloalkyl, C (=O) aryl, CHZOH, CH2Oalkyl, CHO, CN, NO2, or SO2R1l ; and Rll is alkyl, cycloalkyl, trifluoromethyl, aryl, aralkyl, or NR8R9.

The present invention also is directed to pharmaceutical compositions containing one or more of the compounds of structural formula (II), to use of the compounds and compositions containing the compounds in the treatment of a disease or disorder, and to methods of preparing compounds and intermedi- ates involved in the synthesis of the compounds of structural formula (II).

The present invention also is directed to methods of treating a mammal having a condition where inhibition of PDE4 provides a benefit, of

modulating cAMP levels in a mammal, of reducing TNFa levels in a mammal, of suppressing inflammatory cell activation in a mammal, and of inhibiting PDE4 func- tion in a mammal by administering to the mammal a therapeutically effective amount of a compound of structural formula (II), or a composition containing a composition of structural formula (II).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to com- pounds having the structural formula (II) : wherein R1 is lower alkyl, bridged alkyl (e. g., norbornyl), aralkyl (e. g., indanyl), cyclo- alkyl, a 5-or 6-membered saturated heterocycle (e. g., 3-tetrahydrofuryl), Cl3alkylenecycloalkyl (e. g., cyclopentylmethyl), aryl-or heteroaryl-sub- stituted propargyl (i. e.,-CH2C=C-C6H5), aryl-or heteroaryl-substituted allyl (e. g.,-CH2CH=CH-C6H5), or halocycloalkyl (e. g., fluorocyclopentyl) ; R2 is hydrogen, methyl, or halo-substituted methyl, e. g., CHF2 ;

R3 is selected from the group consisting of C (=0) OR', C (=O) R7, C (=NH) NR8R9, C (=O) NR8R9, lower alkyl, bridged alkyl, cycloalkyl, haloalkyl, halocycloalkyl, C1-3alkylenecycloalkyl, a 5-or 6- membered saturated heterocycle, aryl, heteroaryl, heteroaryl502, aralkyl, alkaryl, heteroaralkyl, heteroalkaryl, C1-3alkyleneC(=O)OR7, C (=O) C13alkyl- eneC (=O) OR7, C1-3alkyleneheteroaryl, C (=O) C (=O) oR7, C (=O) Cl3alkyleneC (=O)OR7, C(=O)C1-3alkyleneNHC(=O)OR7, C (=O) C13alkyleneNH2, and NHC (=O) OR7 ; R4 is hydrogen, lower alkyl, haloalkyl, cycloalkyl, aryl, C (=O) R7, OR8, NR8R9, or SR8 ; RI is hydrogen, lower alkyl, haloalkyl, cycloalkyl, or aryl ; R'is selected from the group consisting of cycloalkyl, branched or unbranched lower alkyl, heteroaryl, a heterocycle, aralkyl, and aryl, and R7 is optionally substituted with one or more of OR8, NR8R9, or SR8 ; and R8 and R9, same or different, are selected from the group consisting of hydrogen, lower alkyl, cycloalkyl, aryl, heteroaryl, alkaryl, heteroaralk- yl, heteroalkaryl, and aralkyl, or R8 and R9 are taken together form a 4-membered to 7-membered ring ; R1° is hydrogen, alkyl, haloalkyl, cyclo- alkyl, aryl, C (=O) alkyl, C (=O) cycloalkyl, C (=O) aryl, C (=O) Oalkyl, C (=O) Ocycloalkyl, C (=O) aryl, CH2OH, CH2Oalkyl, CHO, CN, NO2, or SO2R11 ; and R"is alkyl, cycloalkyl, trifluoromethyl, aryl, aralkyl, or NR8R9.

A compound of structural formula (II) can be used alone, either neat or in a composition that further contains a pharmaceutically acceptable car-

rier. A compound of structural formula (II) also can be administering in conjunction with a second active therapeutic agent, for example, a second antiinflammatory therapeutic agent, like an agent capable of targeting TNFa.

Compounds of structural formula (II) can be used to modulate cAMP levels in a mammal, reduce TNFa levels in a mammal, suppress inflammatory cell activation in a mammal, inhibit PDE4 function in a mammal, and treat conditions afflicting a mammal where inhibition of PDE4 provides a benefit.

As used herein, the term"alkyl, alone or in combination, is defined to include straight chain and branched chain, and bridged, saturated hydrocar- bon groups containing one to 16 carbon atoms. The term"lower alkyl"is defined herein as an alkyl group having one through six carbon atoms (Cl-C6).

Examples of lower alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, iso- butyl, n-butyl, neopentyl, n-hexyl, and the like.

The term"alkynyl"refers to an unsaturated alkyl group that contains a carbon-carbon triple bond.

The term"bridged alkyl'is defined herein as a C6-Cl6 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"allyl"is defined herein as CH2=CH-CH2-, optionally substituted, e. g., alkyl or aryl substituted.

The term"propargyl"is defined herein as CHEC-CH2-, optionally substituted, e. g., alkyl or aryl substituted.

The term"cycloalkyl"is defined herein to include cyclic C3-C7 hydrocarbon groups. Examples of cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclohexyl, and cyclo- pentyl.

The term"alkylene"refers to an alkyl group having a substituent. For example, the term ''Cl3alkylenecycloalkyl''refers to an alkyl group containing one to three carbon atoms, and substi- tuted with a cycloalkyl group.

The term"haloalkyl"is defined herein as an alkyl group substituted with one or more halo substituents, either fluro, chloro, bromo, iodo, or combinations thereof. Similarly,"halocycloalkyl" is defined as a cycloalkyl group having one or more halo substituents.

The term"aryl,"alone or in 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 in particular one to three, sub- stituents selected from halo, alkyl, hydroxy, hy- droxyalkyl, alkoxy, aryloxy, aralkoxy, alkoxyalkyl, aryloxyalkyl, aralkoxyalkyl, haloalkyl, nitro, amino, alkylamino, acylamino, alkylthio, alkylsul- finyl, and alkylsulfonyl. Exemplary aryl groups include phenyl, naphthyl, tetrahydronaphthyl, 2- chlorophenyl, 3-chlorophenyl, 4-chlorophenyl, 2- methylphenyl, 4-methoxyphenyl, 3-trifluoromethyl- phenyl, 4-nitrophenyl, 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 in an aromatic ring, and which can be unsubstituted or substituted, for example, with one or more, and in particular one to three, substituents, like halo, alkyl, hydroxy, hydroxyalkyl, alkoxy, aryloxy, aralkoxy, alkoxy- alkyl, aryloxyalkyl, aralkoxyalkyl, haloalkyl, ni- tro, amino, alkylamino, acylamino, alkylthio, alkyl- sulfinyl, and alkylsulfonyl. Examples of heteroaryl groups include thienyl, furyl, pyridyl, oxazolyl, quinolyl, isoquinolyl, indolyl,. triazolyl, isothi- azolyl, isoxazolyl, imidizolyl, benzothiazolyl, pyrazinyl, pyrimidinyl, 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 terms"heteroaralkyl"and"heteroal- karyl"are defined similarly as the term"aralkyl" and"alkaryl,"however, the aryl group is replaced by a heteroaryl group as previously defined.

The term"heterocycle"is defined as a 5- or 6-membered nonaromatic ring, optionally substi- tuted, having one or more heteroatoms selected from oxygen, nitrogen, and sulfur present in the ring.

Nonlimiting examples include tetrahydrofuran, piper-

idine, piperazine, sulfolane, morpholine, tetrahydropyran, dioxan, and the like.

The term"halogen"or"halo"is defined herein to include fluorine, chlorine, bromine, and iodine.

The terms"alkoxy,""aryloxy,"and"aral- koxy'§ 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 term"hydroxy"is defined as-OH.

The term"hydroxyalkyl"is defined as a hydroxy group appended to an alkyl group.

The term"amino"is defined as-NH2.

The term"alkylamino"is defined as-NR2 wherein at least one R is alkyl and the second R is alkyl or hydrogen.

The term"acylamino"is defined as RC (=O) N, wherein R is alkyl or aryl.

The term"nitro"is defined as-NO2.

The term"alkylthio"is defined as-SR, where R is alkyl.

The term"alkylsulfinyl"is defined as R-SO2, where R is alkyl.

The term "alkylsulfonyl" is defined as R-SO3, where R is alkyl.

In preferred embodiments, Rus ils hydrogen, R7 is methyl, R2 is methyl or difluoromethyl, R4 is selected from the group consisting of hydrogen, methyl, trifluoromethyl, cyclopropyl, acetyl, ethy-

nyl, benzoyl, phenyl, and NR8R9, wherein R8 and R9, independently, are hydrogen, lower alkyl, or cyclo- alkyl, or are taken together to form a 5-membered or 6-membered ring. Rl is selected from the group con- sisting of

R3 is selected from the group consisting of

In most preferred embodiments, Rl is se- lected from the group consisting of cyclopentyl, tetrahydrofuryl, indanyl, norbornyl, phenethyl, and phenylbutyl ; R2 is selected from the group consisting of methyl and difluoromethyl ; R3 is selected from the group consisting of CO2CH3, C (=O) CH2OH, C (=O) CH (CH3)- OH, C (=O) C (CH3) 20H, and C (=O)-C-OH / R4 is NR8R9 ; RI is hydrogen ; R'is methyl ; R8 and R9, independently, are selected from the group consist- ing of hydrogen and lower alkyl, or are taken to- gether form a 5-membered or 6-membered ring ; and Rl° is hydrogen.

The present invention includes all possi- ble stereoisomers and geometric isomers of compounds of structural formula (II), and includes not only racemic compounds but also the optically active isomers as well. When a compound of structural formula (II) 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 inter- mediate, or a starting material can be achieved by any suitable method known in the art. Additionally, in situations where tautomers of the compounds of

structural formula (II) are possible, the present invention is intended to include all tautomeric forms of the compounds. As demonstrated hereafter, specific stereoisomers exhibit an exceptional abil- ity to inhibit PDE4 without manifesting the adverse CNS side effects typically associated with PDE4 inhibitors.

In particular, it is generally accepted that biological systems can exhibit very sensitive activities with respect to the absolute stereochemi- cal nature of compounds. (See, E. J. Ariens, Medici- nal Research Reviews, 6 : 451-466 (1986) ; E. J. Ariens, Medicinal Research Reviews, 7 : 367-387 (1987) ; K. W.

Fowler, Handbook of Stereoisomers : Therapeutic Drugs, CRC Press, edited by Donald P. Smith, pp. 35- 63 (1989) ; and S. C. Stinson, Chemical and Engineer- ing News, 75 : 38-70 (1997).) For example, rolipram is a stereospecific PDE4 inhibitor that contains one chiral center. The (-)-enantiomer of rolipram has å higher pharmacolog- ical potency than the (+)-enantiomer, which could be related to its potential antidepressant action.

Schultz et al., Naunyn-Schmiedeberg's Arch Pharma- col, 333 : 23-30 (1986). Furthermore, the metabolism of rolipram appears stereospecific with the (+)- enantiomer exhibiting a faster clearance rate than the (-)-enantiomer. Krause et al., Xenobiotica, 18 : 561-571 (1988). Finally, a recent observation indicated that the (-)-enantiomer of rolipram (R- rolipram) is about ten-fold more emetic than the (+)-enantiomer (S-rolipram). A. Robichaud et al., Neuropharmacology, 38 : 289-297 (1999). This observa- tion is not easily reconciled with differences in

test animal disposition to rolipram isomers and the ability of rolipram to inhibit the PDE4 enzyme. The compounds of the present invention can have three chiral centers. As shown below, compounds of a specific stereochemical orientation exhibit similar PDE4 inhibitory activity and pharmacological activ- ity, but altered CNS toxicity and emetic potential.

Accordingly, preferred compounds of the present invention have the structural formula (III) : The compounds of structural formula (III) are potent and selective PDE4 inhibitors, and do not manifest the adverse CNS effects and emetic potential demon- strated by stereoisomers of a compound of structural formula (III).

Compounds of structural formula (II) 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 (II), 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, benzenesul- phonate, 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 (II), as well as pharmaceutically acceptable salts and sol- vates thereof.

The compounds of the present invention can be therapeutically administered as the neat chemi- cal, but it is preferable to administer compounds of structural formula (II) as a pharmaceutical composi- tion or formulation. Accordingly, the present in- vention further provides for pharmaceutical formula- tions comprising a compound of structural formula (II), together with one or more pharmaceutically acceptable carriers and, optionally, other therapeu- tic and/or prophylactic ingredients. The carriers are"acceptable"in the sense of being compatible with 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 in com- bination with a second antiinflammatory therapeutic agent, for example, a therapeutic agent targeting TNFa, such as ENBRELs or REMICADE@, which have util- ity in treating rheumatoid arthritis. Likewise, therapeutic utility of IL-1 antagonism has also been shown in animal models for rheumatoid arthritis.

Thus, it is envisioned that IL-1 antagonism, in combination with PDE4 inhibition, which attenuates TNFa, would be efficacious.

The present PDE4 inhibitors are useful in the treatment of a variety of allergic, autoimmune, and inflammatory diseases.

The term"treatment"includes preventing, lowering, stopping, or reversing the progression of 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 local- ized, protective response elicited by injury or destruction of tissues, which serves to destroy, dilute or wall off (i. e., sequester) both the inju- rious agent and the injured tissue. The term"in- flammatory disease,"as used herein, means any dis- ease in which an excessive or unregulated inflamma- tory response leads to excessive inflammatory symp- toms, host tissue damage, or loss of tissue func- tion. Additionally, the term"autoimmune disease," as used herein, means any group of disorders in which tissue injury is associated with humoral or cell-mediated responses to the body's own constitu- ents. The term"allergic disease,"as used herein, means any symptoms, tissue damage, or loss of tissue function resulting from allergy. The term"arth- ritic disease,"as used herein, means any of a large family of diseases that are characterized by inflam- matory lesions of the joints attributable to a vari- ety of etiologies. The term"dermatitis,"as used herein, means any of a large family of diseases of

the skin that are characterized by inflammation of the skin 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 thrombocytopenia.

The present invention also provides a method of modulating cAMP levels in a mammal, as well as a method of treating diseases characterized by elevated cytokine levels.

The term"cytokine,"as used herein, means any secreted polypeptide that affects the functions of other cells, and that modulates interactions between cells in the immune or inflammatory re- sponse. Cytokines include, but are not limited to monokines, lymphokines, and chemokines regardless of which cells produce them. For instance, a monokine is generally referred to as being produced and se- creted by a monocyte, however, many other cells produce monokines, such as natural killer cells, fibroblasts, basophils, neutrophils, endothelial cells, brain astrocytes, bone marrow stromal cells, epidermal keratinocytes, and B-lymphocytes. Lympho- kines are generally referred to as being produced by lymphocyte cells. Examples of cytokines include, but are not limited to, interleukin-1 (IL-1), inter- leukin-6 (IL-6), Tumor Necrosis Factor alpha (TNFa), and Tumor Necrosis Factor beta (TNF).

The present invention further provides a method of reducing TNF levels in 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 in vivo TNF levels in 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 in vivo TNF levels in a mammal to normal levels or below normal levels ; or c) inducing a down-regulation, by inhi- bition of the direct synthesis of TNF as a postrans- lational event.

Moreover, the compounds of the present invention are useful in suppressing inflammatory cell activation. The term"inflammatory cell acti- vation,"as used herein, means the induction by a stimulus (including, but not limited to, cytokines, antigens or auto-antibodies) of a proliferative cellular response, the production of soluble media- tors (including but not limited to cytokines, oxygen radicals, enzymes, prostanoids, or vasoactive amines), or cell surface expression of new or in- creased numbers of mediators (including, but not limited to, major histocompatability antigens or cell adhesion molecules) in inflammatory cells (in- cluding but not limited to monocytes, macrophages, T lymphocytes, B lymphocytes, granulocytes, poly- morphonuclear leukocytes, mast cells, basophils, eosinophils, dendritic cells, and endothelial cells). It will be appreciated by persons skilled

in the art that the activation of one or a combina- tion of these phenotypes in these cells can contrib- ute to the initiation, perpetuation, or exacerbation of an inflammatory condition.

The compounds of the present invention also are useful in causing airway smooth muscle relaxation, bronchodilation, and prevention of bronchoconstriction.

The compounds of. the present invention, therefore, are useful in 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, al- lergic conjunctivitis, vernal conjunctivitis, eosinophilic granuloma, adult (acute) respiratory distress syndrome (ARDS), chronic pulmonary inflam- matory disease (such as chronic obstructive pulmo- nary disease), silicosis, pulmonary sarcoidosis, reperfusion injury of the myocardium, brain or ex- tremities, 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 disor- ders (e. g., graft vs. host (GvH) reaction and allo- graft rejection), chronic glomerulonephritis, in- flammatory bowel diseases, such as Crohn's disease and ulcerative colitis, proliferative lymphocytic diseases, such as leukemias (e. g. chronic lympho- cytic 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 conges- tive heart failure, pyrexia, cachexia, cachexia secondary to infection or malignancy, cachexia sec- ondary to acquired immune deficiency syndrome (AIDS), ARC (AIDS-related complex), cerebral ma- laria, osteoporosis and bone resorption diseases, and fever and myalgias due to infection. In addi- tion, the compounds of the present invention are useful in the treatment of diabetes insipidus and central nervous system disorders, such as depression and multi-infarct 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 Pinsky et al., J. Clin. Invest., 92, pp. 2994-3002 (1993)) as well.

Selective PDE4 inhibitors also can be use- ful in the treatment of erectile dysfunction, espe- cially vasculogenic impotence (Doherty, Jr. et al.

U. S. Patent No. 6, 127, 363), diabetes insipidus (Kid- ney Int., 37, p. 362, (1990) ; Kidney Int., 35, p.

494, (1989)) and central nervous system disorders, such as multiinfarct dementia (Nicholson, Psycho- pharmacology, 101, p. 147 (1990)), depression (Eck- man et al., Curr. Ther. Res., 43, p. 291 (1988)), anxiety and stress responses (Neuropharmacology, 38, p. 1831 (1991)), cerebral ischemia (Eur. J. Pharma- col., 272, p. 107 (1995)), tardive dyskinesia (J.

Clin. Pharmocol., 16, 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"behav- ioral 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 Richel- son, 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 antide- pressants increase the brain-derived expression of PDE4 (J. Neuroscience, 19, p. 610 (1999)). There- fore, a selective PDE4 inhibitor can be used alone or in conjunction with a second therapeutic agent in a treatment for the four major classes of antide- pressants : electroconvulsive procedures, monoamine oxidase inhibitors, and selective reuptake inhibi- tors of serotonin or norepinephrine. Selective PDE4 inhibitors also can be useful in 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 in the present invention include those wherein the active ingredient is administered to a mammal in an effective amount to achieve its intended purpose. More specifically, a"therapeuti- cally effective amount@ means an amount effective to prevent development of, or to alleviate the existing symptoms of, the subject being treated. Determina-

tion of the effective amounts is well within the capability of those skilled in the art, especially in light of the detailed disclosure provided herein.

The term"mammal"as used herein includes males and females, and encompasses humans, domestic animals (e. g., cats, dogs), livestock (e. g., cattle, horses, swine), and wildlife (e. g., primates, large cats, zoo specimens).

A"therapeutically effective dose"refers to that amount of the compound that results in achieving the desired effect. Toxicity and thera- peutic efficacy of such compounds can be determined by standard pharmaceutical procedures in cell cul- tures or experimental animals, e. g., for determining the LDso (the dose lethal to 50% of the population) and the EDgo (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index, which is expressed as the ratio between LDso and ED50. Compounds which exhibit high therapeutic indices are preferred. The data obtained from such data can be used in formulating a dosage range for use in humans. The dosage of such compounds prefer- ably lies within a range of circulating concentra- tions that include the EDso with little or no toxic- ity. The dosage can vary within this range depend- ing upon the dosage form employed, and the route of administration utilized.

The exact formulation, route of adminis- tration, and dosage can be chosen by the individual physician in view of the patient's condition. Dos- age 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 in the art, reference herein to treatment extends to pro- phylaxis, as well as to treatment of established diseases or symptoms. It is further appreciated that the amount of a compound of the invention re- quired for use in 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 veterinar- ian. In general, however, doses employed for adult human treatment typically are in the range of 0. 001 mg/kg to about 100 mg/kg per day. The desired dose can be conveniently administered in 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 deter- mines the actual dosing regimen which is most suit- able for an individual patient, and the dosage var- ies 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 in- stances in which higher or lower dosages are mer- ited, and such are within the scope of the present invention.

Formulations of the present invention can be administered in a standard manner for the treat- ment of the indicated diseases, such as orally, parenterally, transmucosally (e. g., sublingually 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, intra- arterial, intraperitoneal, subcutaneous, intramuscu- lar, intrathecal, and intraarticular. Parenteral administration also can be accomplished using a high pressure technique, like POWDERJECTTM.

For buccal administration, the composition can be in the form of tablets or lozenges formulated in conventional manner. For example, tablets and capsules for oral administration can contain conven- tional excipients such as binding agents (for exam- ple, syrup, accacia, gelatin, sorbitol, tragacanth, mucilage of starch or polyvinylpyrrolidone), fillers (for example, lactose, sugar, microcrystalline, cellulose, maize-starch,'calcium phosphate or sorbi- tol), lubricants (for example, magnesium, stearate, stearic acid, talc, polyethylene glycol or silica), disintegrants (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 in the art.

Alternatively, the compounds of the pres- ent'invention can be incorporated into oral liquid preparations such as aqueous or oily suspensions, solutions, emulsions, syrups, or elixirs, for exam- ple. Moreover, formulations containing these com- pounds can be presented as a dry product for consti- tution 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, fraction- ated 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 glycerides. Compositions for inhalation typically can be provided in the form of a solution, suspen- sion, or emulsion that can be administered as a dry powder or in the form of an aerosol using a conven- tional propellant, such as dichlorodifluoromethane or trichlorofluoromethane. Typical topical and transdermal formulations comprise conventional aque- ous or nonaqueous vehicles, such as eye drops, creams, ointments, lotions, and pastes, or are in the form of a medicated plaster, patch, or membrane.

Additionally, compositions of the present invention can be formulated for parenteral adminis- tration by injection or continuous infusion. Formu- lations for injection can be in the form of suspen- sions, solutions, or emulsions in 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 in 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 inven- tion can be formulated with suitable polymeric or hydrophobic materials (e. g., an emulsion in an ac- ceptable oil), ion exchange resins, or as sparingly soluble derivatives (e. g., a sparingly soluble salt).

For veterinary use, a compound of formula (II), or nontoxic salts thereof, is administered as a suitably acceptable formulation in accordance with normal veterinary practice. The veterinarian can readily determine the dosing regimen and route of administration that is most appropriate for a par- ticular animal.

Thus, the invention provides in a further aspect a pharmaceutical composition comprising a compound of the formula (II), 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 (II), which process comprises mixing a compound of formula (II), together with a pharmaceutically acceptable diluent or carrier therefor.

A specific, nonlimiting example of a com- pound of structural formula (II) is provided below, the synthesis of which was performed in accordance with the procedure set forth below.

Generally, compounds of structural formula (II) can be prepared according to the following synthetic scheme. In the scheme described below, it is understood in the art that protecting groups can

be employed where necessary in accordance with gen- eral principles of synthetic chemistry. These pro- tecting groups are removed in the final steps of the synthesis under basic, acidic, or hydrogenolytic conditions which are readily apparent to those skilled in the art. By employing appropriate manip- ulation and protection of any chemical function- alities, synthesis of compounds of structural for- mula (II) not specifically set forth herein can be accomplished by methods analogous to the schemes set forth below.

Unless otherwise noted, all starting mate- rials were obtained from commercial suppliers and used without further purification. All reactions and chromatography fractions were analyzed by thin- layer chromatography on 250-mm silica gel plates, visualized with UV (ultraviolet) light or I2 (iodine) stain. Products and intermediates were purified by flash chromatography, or reverse-phase HPLC.

The compounds of general structural for- mula (II) can be prepared, for example, as set forth in the following Example 1. Other synthetic routes also are known to persons skilled in the art. The following reaction scheme provides a compound of structural formula (II), wherein Rl and R2, i. e., cyclopentyl and CH3, are determined by the starting materials. Proper selection of other starting mate- rials, or performing conversion reactions on inter- mediates and examples, provide compounds of general structural formula (II) having other recited R1 through R"substituents. The following example is provided for illustration and should not be con- strued as limiting.

Example 1 Preparation of (3S, 4R)-4- (3-Cyclopentyloxy-4- methoxyphenyl)-3-methyl-3- (2-methylaminothiazol-4- yl) pyrrolidine-l-carboxYlic acid methyl ester To a solution of 1-methyl-2-thiourea (0. 038 g, 0. 418 mmol) in methanol (1 mL), at 50°C, was added a solution of (3S, 4R)-3- (2-bromoethanoyl)- 4- (3-cyclopentyloxy-4-methoxyphenyl)-3-methyl- pyrrolidine-1-carboxylic acid methyl ester (0. 19 g, 0. 42 mmol) in methanol (1 mL). The temperature was raised to 70°C and refluxed for 2 hours. The reac- tion mixture then was concentrated under reduced pressure and dissolved in acetonitrile-water (CH3CN- H20) (1 mL) for purification by HPLC on a C18 column (Luna 10 µ, C18, 250xlOmm). Gradient elution of 50- 100% acetonitrile-water (0. 05% TFA) yielded the named product as a white powder after lyophilization (91 mg, 49%).

H NMR (300 MHz, CDCl3) 5 (ppm) : 11. 84 (s, lH, NH) 6. 95-6. 70 (m, 3H, aromatic), 6. 14 (m, 1H, aromatic), 4. 87-4. 82 (br. m, 1H), 3. 97-3. 5 (m, 4H), 3. 84 (s, 3H, OCH3), 3. 78 (s, 3H, OCH3), 3. 40-3. 36 (m, 1H),

3. 05 (s, 3H, NCH3), 2. 0-1. 6 (m, 8H, cyclopentyl), 1. 07 (s, 3H, CH3).

The compounds of structural formula (II) were tested for an ability to inhibit PDE4. The ability of a compound to inhibit PDE4 activity is related to the IC., value for the compound, i. e., the concentration of inhibitor required for 50% inhibi- tion of enzyme activity. The ICso value for com- pounds of structural formula (II) were determined using recombinant human PDE4.

The compounds of the present invention typically exhibit an IC50 value against recombinant human PDE4 of less than about 100 AIMl and preferably less than about 50 uM, and more preferably less than about 25 um. The compounds of the present invention typically exhibit an IC5e value against recombinant human PDE4 of less than about 5 AZMl and often less than about 1 uM. To achieve the full advantage of the present invention, a present PDE4 inhibitor has an IC50 of about 0. 05 DZM to about 15 µM.

The IC50 values for the compounds were determined from concentration-response curves typi- cally using concentrations ranging from 0. 1 pM to 500 uM. Tests against other PDE enzymes using stan- dard methodology, as described in 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.

The production of recombinant human PDEs and the IC50 determinations can be accomplished by well-known methods in the art. Exemplary methods are described as follows :

EXPRESSION OF HUMAN PDEs Expression in Baculovirus-Infected Spodoptera fuviperda (Sf9) Cells Baculovirus transfer plasmids were con- structed using either pBlueBacIII (Invitrogen) or pFastBac (BRL-Gibco). The structure of all plasmids was verified by sequencing across the vector junc- tions 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.

Diol. Chem., 271, pp. 796-806 (1996)) in pBlue- BacIII. Plasmid Hcam3aBB contained the complete open reading frame of PDE1C3 (Loughney et al.

(1996)) in pBlueBacIII. Plasmid pBB-PDE3A contained the complete open reading frame of PDE3A (Meacci et al., Proc. Natl. Acad. Sci., USA, 89, pp. 3721-3725 (1992)) in pBlueBacIII.

Recombinant virus stocks were produced using either the MaxBac system (Invitrogen) or the FastBac system (Gibco-BRL) according to the manufac- turer's protocols. In both cases, expression of recombinant human PDEs in the resultant viruses was driven off the viral polyhedron promoter. When using the MaxBac° system, virus was plaque purified twice in order to insure that no wild type (occ+) virus contaminated the preparation. Protein expres- sion was carried out as follows. Sf9 cells were grown at 27°C in Grace's Insect culture medium (Gibco-BRL) supplemented with 10% fetal bovine se- rum, 0. 33% TC yeastolate, 0. 33% lactalbumin hydro- lysate, 4. 2 mM NaHCO3, 10 Sg/mL gentamycin, 100

units/mL penicillin, and 100 Sg/mL streptomycin.

Exponentially growing cells were infected at a mul- tiplicity of approximately 2 to 3 virus particles per cell and incubated for 48 hours. were collected by centrifugation, washed with nonsup- plemented Grace's medium, and quick-frozen for stor- age.

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 in 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 in Price et al., Methods in 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. Trans- formed host cells were grown in 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. Approxi- mately 24 hr later, cells were harvested, washed, and stored at-70°C.

HUMAN PHOSPHODIESTERASE PREPARATIONS Phosphodiesterase Activity Determinations Phosphodiesterase activity of the prepara- tions was determined as follows. PDE assays utiliz- ing a charcoal separation technique were performed essentially as described in 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 in 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 guanosine 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 in a 100 AZL reaction mixture containing (final concentra- tions) 40 mM Tris HC1 (pH 8. 0), 1 AZM ZnSO4, 5 mM MgCl2, 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 CaCl2 and 10 Alg/mL calmodulin.

PDE enzyme was present in quantities that yield <30% total hydrolysis of substrate (linear assay condi- tions). 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) ig 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 AZL of activated charcoal (25 mg/mL suspension in 0. 1 M NaH2PO4, pH 4). After centrifugation (750 X g for

3 minutes) to sediment the charcoal, a sample of the supernatant was taken for radioactivity determina- tion in a scintillation counter and the. PDE activity was calculated.

Inhibitor analyses were performed simi- larly to the method described in Loughney et al., J.

Biol. Chem., 271, pp. 796-806 (1996), except both cGMP and cAMP were used, and substrate concentra- tions were kept below 32 nM, which is far below the Km of the tested PDEs.

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, uM ZnSO, 2 mM MgCl2, 14. 2 mM 2-mercapto- ethanol, 5 AZg/mL each of pepstatin, leupeptin, aprotinin, 20 AZg/mL each of calpain inhibitors I and II, and 2 mM benzamidine HCl). Cells were lysed in a French pressure cell (SLM-Amìnco@, Spectronic Instruments) at 10°C. The extract was centrifuged in a Beckman JA-10 rotor at 9, 000 rpm for 22 minutes at 4°C. The supernatant was removed and centrifuged in 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 in an ice bath and maintaining the pH between 7. 0 and 7. 5.

The precipitated proteins containing PDE4A were

collected via centrifugation in a Beckman JA-10 rotor at 9, 000 rpm for 22 minutes. The precipitate was resuspended in 50 mL of Buffer G (50 mM MOPS pH 7. 5, 10 µM ZnSO4, 5 mM MgCl2, 100 mM NaCl, 14. 2 mM 2- mercaptoethanol, 2 mM benzamidine HCl, 5, ug/mL each of leupeptin, pepstatin, and aprotinin, and 20, ug/mL each of calpain inhibitors I and II) and passed through a 0. 45 um 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, uM ZnSO4, 5 mM MgCl2, 14. 2 mM 2-mercaptoethanol, and 100 mM benzamidine HCl). The column was washed in suc- cession 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 M ZnSO, 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 pre- cipitated proteins were resuspended in Buffer X (25 mM MOPS pH 7. 5, 5 ; uM ZnS04, 50 mM NaCl, 1 mM DTT, and 1 mM benzamidine HCl), and desalted via gel po filtration on a Pharmacia PD-10 column per manufac-

turer's instructions. The 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 40 limol 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 benzamidine HC1, 5 Sg/mL each of pepstatin, leupeptin,-. aprotinin, calpain inhibi- tors 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 in a Beckman J2-21M centrifuge using a JA-10 rotor at 9, 000 rpm and 4°C. The supernatant was recovered and centrifuged in 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 stir- ring in an ice bath and maintaining the pH between, 7. 0 and 7. 5. This mixture was then centrifuged for 22 minutes in 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 200 mL of Buffer A (50 mM MOPS pH 7. 5, 5 mM MgCl2, 1 mM DTT, 1 mM benzamidine HC1, and 5 Sg/mL each of leupeptin,

pepstatin, and aprotinin). 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 in 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 HC1 pH 8, 2 mM EDTA, 2 mM EGTA, 1 mM DTT, 2 mM benzamidine 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 precipi- tated proteins were resuspended in Buffer X (25 mM MOPS pH 7. 5, 5 AZM ZnSO4, 50 mM NaCl, 1 mM DTT, and 1 mM benzamidine HCl) and desalted via gel filtration on a Pharmacia PD-10 column per manufacturer's instructions. The enzyme pool was dialyzed over- night 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 >90% pure by SDS-PAGE. These preparations had specific activities of about 10 to 50, ttmol 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 benzamidine HC1, 5 Sg/mL each of pepstatin, leupeptin, aprotinin, calpain inhibi- tors 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 in a Beckman J2-21M centrifuge using a JA-10 rotor at 9, 000 rpm and 4°C. The supernatant was recovered and centrifuged in 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 in an ice bath and maintaining the pH between 7. 0 and 7. 5.

Thirty minutes later, this mixture was'centrifuged for 22 minutes in 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 MgCl2, 1 mM DTT, 2 mM benzamidine HCl, and 5, ug/mL each of leupeptin, pepstatin, and aprotinin). 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 in Buffer A. The

sample was cycled through the column 4 to 6 times over the course of 12 hours. The column was washed in 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 benzamidine HC1, 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 pre- cipitated proteins were resuspended in Buffer X (25 mM MOPS pH 7. 2, 5 uM ZnSO4, 50 mM NaCl, 1 mM DTT, and 1 mM benzamidine HC1) and desalted via gel fil- tration on a Pharmacia PD-10@ column per manufac- turer'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 mol 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 AlM ZnSO4, 2 mM MgCl2, 14. 2 mM 2-mercaptoethanol, 2 mM benzamidine HCl, 5 Sg/mL each of pepstatin, leupeptin, aprotin- in, 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 mixing for 6 cycles of 30 sec each. The homogenate was centrifuged for 22 minutes in a Beckman J2-21M cen- trifuge using a JA-10 rotor at 9, 000 rpm and 4°C.

The supernatant was recovered and centrifuged in 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 super- natant) while stirring in an ice bath and maintain- ing the pH between 7. 0 and 7. 5. Thirty minutes later, this mixture was centrifuged for 22 minutes in a Beckman J2 centrifuge using a JA-10 rotor at 9, 000 rpm (12, 000 X g). The supernatant was dis- carded and the pellet was dissolved in 100 mL of Buffer A (50 mM MOPS pH 7. 5, 10 uM ZnSO4, 5 mM MgCl2, 14. 2 mM 2-mercaptoethanol, 100 mM benzamidine HC1, and 5 Sg/mL each of leupeptin, pepstatin, aprotinin, calpain inhibitor I and II). The pH and conductiv- ity were corrected to 7. 5 and 15-20 mS, respec- tively.

At a flow rate of 0. 67 mL/min, the resus- pended sample was loaded onto a 1. 6 X 20 cm column (10 mL) of Sigma Cibacron Blue Agarose-type 300 equilibrated in Buffer A. 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 then 10 to 20 mL of Buffer C (50 mM Tris HC1 pH 8, 10 SM ZnS04, 14. 2 mM 2-mercaptoethanol, 2 mM benzamidine HC1).

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 pre- cipitated proteins were resuspended in Buffer X (25 mM MOPS pH 7. 2, 5/M ZnSO,, 50 mM NaCl, 1 mM DTT, and 1 mM benzamidine HCl) and desalted via gel fil- tration on a Pharmacia PD-10 column per manufac- turer's instructions. The enzyme pool was dialyzed overnight against Buffer X containing 50% glycerol.

This enzyme preparation 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 20 to 50 Smol cAMP'hydrolyzed per minute per milligram protein. Example No. Molecular Weight PDE4 ICso (nM) 1 445. 58 4, 731. 1 The data presented above shows that the present compounds are potent inhibitors of PDE4, e. g., the compounds have an ICso vs. human recombi- nant PDE4 of about 0. 05/-zM to about 15 µM. Pre- ferred compounds have an IC50 of about 100 vM or less, and especially preferred compounds have an IC50 of about 50 lit or less.

The compounds of the present invention are useful for selectively inhibiting PDE4 activity in a mammal, without exhibiting the adverse CNS and emetic effects associated with prior PDE4 inhibi- tors.

Obviously, many modifications and varia- tions of the invention as hereinbefore set forth can be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated by the appended claims.