This review concentrates on advances in nitric oxide synthase (NOS) structure, function and inhibition made in the last seven years, during which time substantial advances have been made in our understanding of this enzyme family. There is now information on the enzyme structure at all levels from primary (amino acid sequence) to quaternary (dimerization, association with other proteins) structure. The crystal structures of the oxygenase domains of inducible NOS (iNOS) and vascular endothelial NOS (eNOS) allow us to interpret other information in the context of this important part of the enzyme, with its binding sites for iron protoporphyrin IX (haem), biopterin, L-arginine, and the many inhibitors which interact with them. The exact nature of the NOS reaction, its mechanism and its products continue to be sources of controversy. The role of the biopterin cofactor is now becoming clearer, with emerging data implicating one-electron redox cycling as well as the multiple allosteric effects on enzyme activity. Regulation of the NOSs has been described at all levels from gene transcription to covalent modification and allosteric regulation of the enzyme itself. A wide range of NOS inhibitors have been discussed, interacting with the enzyme in diverse ways in terms of site and mechanism of inhibition, time-dependence and selectivity for individual isoforms, although there are many pitfalls and misunderstandings of these aspects. Highly selective inhibitors of iNOS versus eNOS and neuronal NOS have been identified and some of these have potential in the treatment of a range of inflammatory and other conditions in which iNOS has been implicated.

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Nitric oxide synthases: structure, function and inhibition

Prostaglandins and glucocorticoids are potent mediators of inflammation. Non-steroidal anti-inflammatory drugs (NSAIDs) exert their effects by inhibition of prostaglandin production. The pharmacological target of NSAIDs is cyclooxygenase (COX, also known as PGH synthase), which catalyses the first committed step in arachidonic-acid metabolism. Two isoforms of the membrane protein COX are known: COX-1, which is constitutively expressed in most tissues, is responsible for the physiological production of prostaglandins; and COX-2, which is induced by cytokines, mitogens and endotoxins in inflammatory cells, is responsible for the elevated production of prostaglandins during inflammation. The structure of ovine COX-1 complexed with several NSAIDs has been determined. Here we report the structures of unliganded murine COX-2 and complexes with flurbiprofen, indomethacin and SC-558, a selective COX-2 inhibitor, determined at 3.0 to 2.5 A resolution. These structures explain the structural basis for the selective inhibition of COX-2, and demonstrate some of the conformational changes associated with time-dependent inhibition.

Structural basis for selective inhibition of cyclooxygenase-2 by anti-inflammatory agents.

The preparation of urea by Wöhler constituted a landmark achievement in organic chemistry, and it laid the ground for the early days of target-oriented organic synthesis.1 Since then, significant progress has been achieved in this discipline; many powerful single bond forming reactions and asymmetric variants have been developed. These discoveries have paved the way for the stereoselective assembly of complex organic molecules, a task deemed inconceivable by early practitioners. A great many strategies were invented by chemists in order to facilitate the synthesis of complex natural products.2 One avenue in emulating nature’s efficiency would * To whom correspondence should be addressed. E-mail: dennis.hall@ ualberta.ca. † Novartis Institute for Biomedical Research. ‡ Department of Chemistry, University of Alberta. Chem. Rev. 2009, 109, 4439–4486 4439

Natural product synthesis using multicomponent reaction strategies.

The abundance and activation of macrophages in the inflamed synovial membrane/pannus significantly correlates with the severity of rheumatoid arthritis (RA). Although unlikely to be the 'initiators' of RA (if not as antigen-presenting cells in early disease), macrophages possess widespread pro-inflammatory, destructive, and remodeling capabilities that can critically contribute to acute and chronic disease. Also, activation of the monocytic lineage is not locally restricted, but extends to systemic parts of the mononuclear phagocyte system. Thus, selective counteraction of macrophage activation remains an efficacious approach to diminish local and systemic inflammation, as well as to prevent irreversible joint damage.

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Macrophages in rheumatoid arthritis

Purpose. NSAIDs constitute an important class of drugs with therapeutic applications that have spanned several centuries. Treatment of inflammatory conditions such as rheumatoid arthritis (RA) and osteoarthritis (OA) starting from the classic drug aspirin to the recent rise and fall of selective COX-2 inhibitors has provided an enthralling evolution. Efforts to discover an ultimate magic bullet to treat inflammation continues to be an important drug design challenge. This review traces the origins of NSAIDs, their mechanism of action at the molecular level such as cyclooxygenase (COX) inhibition, development of selective COX-2 inhibitors, their adverse cardiovascular effects, and some recent developments targeted to the design of effective anti-inflammatory agents with reduced side effects. Methods. Literature data is presented describing important discoveries pertaining to the sequential development of classical NSAIDs and then selective COX-2 inhibitors, their mechanism of action, the structural basis for COX inhibition, and recent discoveries. Results. A brief history of the development of NSAIDs and the market withdrawal of selective COX-2 inhibitors is explained, followed by the description of prostaglandin biosynthesis, COX isoforms, structure and function. The structural basis for COX-1 and COX-2 inhibition is described along with methods used to evaluate COX-1/COX-2 inhibition. This is followed by a section that encompasses the major chemical classes of selective COX-2 inhibitors. The final section describes briefly some of the recent advances toward developing effective anti-inflammatory agents such as nitric oxide donor NO-NSAIDs, dual COX/LOX inhibitors and anti-TNF therapy. Conclusions. A great deal of progress has been made toward developing novel anti-inflammatory agents. In spite of the tremendous advances in the last decade, the design and development of a safe, effective and economical therapy for treating inflammatory conditions still presents a major challenge.

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Evolution of nonsteroidal anti-inflammatory drugs (NSAIDs): cyclooxygenase (COX) inhibition and beyond

The current invention discloses useful pharmaceutical compositions containing amidino derivatives of formula (I) as nitric oxide synthase inhibitors.

Amidino derivatives useful as nitric oxide synthase inhibitors

A class of pyrazolyl compounds is described for use in treating inflammation and inflammation-related disorders. Compounds of particular interest are defined by formula (II), wherein R1 is selected from alkyl, aralkyl, alkynyl, cyanoalkyl, carboxyalkyl, aminocarbonylalkyl, arylaminocarbonylalkyl, heterocyclicalkyl, and alkoxycarbonylalkyl; wherein R3 is aryl optionally substituted at a substitutable position with one or more radicals independently selected from halo, alkylthio, alkylsulfinyl, alkyl, cyano, carboxyl, alkoxycarbonyl, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, N-alkyl-N-arylaminocarbonyl, haloalkyl, hydroxyl, alkoxy, hydroxyalkyl, alkoxyalkyl, haloalkoxy, amino, alkylamino, arylamino, heterocyclo and nitro; wherein R4 is haloalkyl; and wherein R5 is selected from alkyl and amino; or a pharmaceutically acceptable salt thereof.

3,4-substituted pyrazoles for the treatment of inflammation

A class of substituted thiazolyl compounds is described for use in treating inflammation and inflammation-related disorders. Compounds of particular interest are defined by Formula (II), wherein R4 is selected from alkyl and amino, wherein R5 is selected from aryl, cycloalkyl, cycloalkenyl and heterocyclic; wherein R5 is optionally substituted at a substitutable position with one or more radicals selected from halo, alkylthio, alkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, aminosulfonyl, alkyl, alkenyl, alkynyl, cyano, carboxyl, carboxyalkyl, alkoxycarbonyl, aminocarbonyl, acyl, N-alkylaminocarbonyl, N-arylaminocarbonyl, N,N-dialkylaminocarbonyl, N-alkyl-N-arylaminocarbonyl, haloalkyl, hydroxyl, alkoxy, hydroxyalkyl, haloalkoxy, amino, N-alkylamino, N,N-dialkylamino, heterocyclic and nitro; and wherein R6 is selected from halo, amino, alkoxy, nitro, hydroxyl, aminocarbonyl, acyl, alkylaminocarbonyl, arylaminocarbonyl, alkenyl, alkynyl, haloalkoxy, alkylamino, arylamino, aralkylamino, alkoxycarbonylalkyl, alkylaminoalkyl, heterocycloalkyl, aralkyl, cyanoalkyl, N-alkylsulfonylamino, heteroarylsulfonylalkyl, heteroarylsulfonylhaloalkyl, aryloxyalkyl, aralkyloxyalkyl, aryl and heterocyclo, wherein the aryl and heterocyclo radicals are optionally substituted at a substitutable position with one or more radicals selected from halo, alkyl, alkoxy, alkylthio, alkylsulfinyl, haloalkyl, haloalkoxy, carboxyalkyl, alkoxycarbonyl, aminocarbonyl, amino, acyl and alkylamino; or a pharmaceutically-acceptable salt thereof.

Substituted thiazoles for the treatment of inflammation

One-pot synthesis of protected prostaglandins from alkynes and cyclopentenones. In situ generation of higher order cyanocuprates derived from alkenylzirconium intermediates

In the literature, the introduction of fluorine into bioactive molecules has been known to enhance the biological activity relative to the parent molecule. Described in this article is the synthesis of 4R-fluoro-L-NIL (12) and 4,4-difluoro-L-NIL (23) as part of our iNOS program. Both 12 and 23 were found to be selective iNOS inhibitors as shown in Table 2 below. Secondarily, methodology to synthesize orthogonally protected 4-fluoro-L-lysine and 4,4-difluoro-L-lysine has been developed.

Steven W. Kramer

Papers

Amidino derivatives useful as nitric oxide synthase inhibitors

3,4-substituted pyrazoles for the treatment of inflammation

Substituted thiazoles for the treatment of inflammation

One-pot synthesis of protected prostaglandins from alkynes and cyclopentenones. In situ generation of higher order cyanocuprates derived from alkenylzirconium intermediates

4-Fluorinated L-lysine analogs as selective i-NOS inhibitors: methodology for introducing fluorine into the lysine side chain