Potent and selective alpha-ketoheterocycle-based inhibitors of the anandamide and oleamide catabolizing enzyme, fatty acid amide hydrolase

Novel trifluoromethyl ketone derivatives as oral cPLA2/COX-2 dual inhibitors for resolution of inflammation in rheumatoid arthritis

Thirty-five trifluoromethyl hydrazones and seventeen trifluoromethyl oxime esters were designed and synthesized via molecular hybridization. All the target compounds were initially screened for in vitro anti-inflammatory activity by assessing their inhibitory effect on NO release in LPS-stimulated RAW264.7 cells, and the optimal compound was finally identified as 2-(3-Methoxyphenyl)-N'-((6Z,9Z,12Z,15Z)-1,1,1-trifluorohenicosa-6,9,12,15-tetraen-2-ylidene)acetohydrazide (F26, IC50 = 4.55 ± 0.92 μM) with no cytotoxicity. Moreover, F26 potently reduced the production of PGE2 in LPS-stimulated RAW264.7 cells compared to indomethacin. The interaction of F26 with COX-2 and cPLA2 was directly verified by the CETSA technique. F26 was found to modulate the phosphorylation levels of p38 MAPK and NF-κB p65, as well as the protein expression of IκB, cPLA2, COX-2, and iNOS in LPS-stimulated rat peritoneal macrophages. Additionally, F26 was observed to prevent the nuclear translocation of NF-κB p65 in LPS-stimulated rat peritoneal macrophages by immunofluorescence localization. Therefore, the aforementioned in vitro experiments demonstrated that F26 blocked the p38 MAPK and NF-κB pathways by binding to COX-2 and cPLA2. In the adjuvant-induced arthritis model, F26 demonstrated a significant effect in preventing arthritis symptoms and inflammatory status in rats, exerting an immunomodulatory role by regulating the homeostasis between Th17 and Treg through inhibition of the p38 MAPK/cPLA2/COX-2/PGE2 and NF-κB pathways. Encouragingly, F26 caused less acute ulcerogenicity in rats at a dose of 50 mg/kg compared to indomethacin. Overall, F26 is a promising candidate worthy of further investigation for treating inflammation and associated pain with lesser gastrointestinal irritation, as well as other symptoms in which cPLA2 and COX-2 are implicated in the pathophysiology.

Copper-Catalyzed C4-selective Carboxylation of Pyridines with CO2 via Pyridylphosphonium Salts

Pyridine motifs are widespread pharmacophores in many drugs. Installing various substituents through pyridine C-H bond functionalization is significant for new drug design and discovery. Developments of late-stage functionalization reactions enrich the strategies for selective functionalization of pyridines. However, late-stage C-H carboxylation of pyridines is a long-standing challenge, especially selectively carboxylation with CO2 on pyridine motifs. Herein, we describe a practical method for C4-H carboxylation of pyridines via one-pot C-H phosphination and copper-catalyzed carboxylation of the resulted phosphonium salts with CO2 . The reaction is conducted under mild conditions and compatible with multiple active groups and several pyridine drugs, providing diverse valuable isonicotinic acid compounds, demonstrating the application potential of this strategy.

Discovery of novel NSAID hybrids as cPLA2/COX-2 dual inhibitors alleviating rheumatoid arthritis via inhibiting p38 MAPK pathway

A series of NSAIDs hybrid molecules were synthesized and characterized, and their ability to inhibit NO release in LPS-induced RAW264.7 macrophages was evaluated. Most of the compounds showed significant anti-inflammatory activity in vitro, of which (2E,6Z,9Z,12Z,15Z)-1,1,1-trifluorohenicosa-2,6,9,12,15-pentaen-2-yl 2-(4-benzoylphenyl) propanoate (VI-60) was the most optimal (IC50 = 3.85 ± 0.25 μΜ) and had no cytotoxicity. In addition, VI-60 notably reduced the production of PGE2 in LPS-stimulated RAW264.7 cells compared to ketoprofen. Futhur more, VI-60 significantly inhibited the expression of iNOS, cPLA2, and COX-2 and the phosphorylation of p38 MAPK in LPS-stimulated RAW264.7 cells. The binding of VI-60 to cPLA2 and COX-2 was directly verified by the CETSA technique. In vivo studies illustrated that VI-60 exerted an excellent therapeutic effect on adjuvant-induced arthritis in rats by regulating the balance between Th17 and Treg through inhibiting the p38 MAPK/cPLA2/COX-2/PGE2 pathway. Encouragingly, VI-60 showed a lower ulcerative potential in rats at a dose of 50 mg/kg compared to ketoprofen. In conclusion, the hybrid molecules of NSAIDs and trifluoromethyl enols are promising candidates worthy of further investigation for the treatment of inflammation, pain, and other symptoms in which cPLA2 and COX-2 play a role in their etiology.

The Use of 5-Hydroxymethylfurfural towards Fine Chemicals: Synthesis and Direct Arylation of 5-HMF-Based Oxazoles

5-Hydroxymethylfurfural (5-HMF) is a renewable platform chemical used as a source for obtaining diverse fine chemicals. In this letter, we report the synthesis of 5-HMF-based oxazole compounds. While 5-HMF could be easily converted into the oxazole derivative through the Van Leusen reaction, the direct arylation step needed to access the final compounds was problematic at first. After optimization, a palladium-catalyzed procedure has been developed and used for the synthesis of a series of 33 derivatives. This article reports an extension of the late-stage CH arylation reaction as an application to the oxazole platform derived from biosourced 5-HMF. The challenges in the preparation of the derivatives containing some electron-withdrawing substituents were overcome by the use of a palladium-free method.

Heteroarylureas with fused bicyclic diamine cores as inhibitors of fatty acid amide hydrolase

A series of mechanism-based heteroaryl urea fatty acid amide hydrolase (FAAH) inhibitors with fused bicyclic diamine cores is described. In contrast to compounds built around a piperazine core, most of the fused bicyclic diamine bearing analogs prepared exhibited greater potency against rFAAH than the human enzyme. Several compounds equipotent against both species were identified and profiled in vivo.

The endocannabinoid hydrolase FAAH is an allosteric enzyme

Fatty acid amide hydrolase (FAAH) is a membrane-bound homodimeric enzyme that in vivo controls content and biological activity of N-arachidonoylethanolamine (AEA) and other relevant bioactive lipids termed endocannabinoids. Parallel orientation of FAAH monomers likely allows both subunits to simultaneously recruit and cleave substrates. Here, we show full inhibition of human and rat FAAH by means of enzyme inhibitors used at a homodimer:inhibitor stoichiometric ratio of 1:1, implying that occupation of only one of the two active sites of FAAH is enough to fully block catalysis. Single W445Y substitution in rat FAAH displayed the same activity as the wild-type, but failed to show full inhibition at the homodimer:inhibitor 1:1 ratio. Instead, F432A mutant exhibited reduced specific activity but was fully inhibited at the homodimer:inhibitor 1:1 ratio. Kinetic analysis of AEA hydrolysis by rat FAAH and its F432A mutant demonstrated a Hill coefficient of ~1.6, that instead was ~1.0 in the W445Y mutant. Of note, also human FAAH catalysed an allosteric hydrolysis of AEA, showing a Hill coefficient of ~1.9. Taken together, this study demonstrates an unprecedented allosterism of FAAH, and represents a case of communication between two enzyme subunits seemingly controlled by a single amino acid (W445) at the dimer interface. In the light of extensive attempts and subsequent failures over the last decade to develop effective drugs for human therapy, these findings pave the way to the rationale design of new molecules that, by acting as positive or negative heterotropic effectors of FAAH, may control more efficiently its activity.

N-Acyl pyrazoles: Effective and tunable inhibitors of serine hydrolases

A series of N-acyl pyrazoles was examined as candidate serine hydrolase inhibitors in which the active site acylating reactivity and the leaving group ability of the pyrazole could be tuned not only through the nature of the acyl group (reactivity: amide > carbamate > urea), but also through pyrazole C4 substitution with electron-withdrawing or electron-donating substituents. Their impact on enzyme inhibitory activity displayed pronounced effects with the activity improving substantially as one alters both the nature of the reacting carbonyl group (urea > carbamate > amide) and the pyrazole C4 substituent (CN > H > Me). It was further demonstrated that the acyl chain of the N-acyl pyrazole ureas can be used to tailor the potency and selectivity of the inhibitor class to a targeted serine hydrolase. Thus, elaboration of the acyl chain of pyrazole-based ureas provided remarkably potent, irreversible inhibitors of fatty acid amide hydrolase (FAAH, apparent K_i = 100-200 pM), dual inhibitors of FAAH and monoacylglycerol hydrolase (MGLL), or selective inhibitors of MGLL (IC₅₀ = 10-20 nM) while simultaneously minimizing off-target activity (e.g., ABHD6 and KIAA1363).

The Difference a Single Atom Can Make: Synthesis and Design at the Chemistry-Biology Interface

A Perspective of work in our laboratory on the examination of biologically active compounds, especially natural products, is presented. In the context of individual programs and along with a summary of our work, selected cases are presented that illustrate the impact single atom changes can have on the biological properties of the compounds. The examples were chosen to highlight single heavy atom changes that improve activity, rather than those that involve informative alterations that reduce or abolish activity. The examples were also chosen to illustrate that the impact of such single-atom changes can originate from steric, electronic, conformational, or H-bonding effects, from changes in functional reactivity, from fundamental intermolecular interactions with a biological target, from introduction of a new or altered functionalization site, or from features as simple as improvements in stability or physical properties. Nearly all the examples highlighted represent not only unusual instances of productive deep-seated natural product modifications and were introduced through total synthesis but are also remarkable in that they are derived from only a single heavy atom change in the structure.

Merging gold catalysis, organocatalytic oxidation, and Lewis acid catalysis for chemodivergent synthesis of functionalized oxazoles from N-propargylamides

Novel catalytic systems consisting of cationic gold complexes, N-hydroxyphthalimide (NHPI), and transition-metal-based Lewis acids have been developed for the one-pot synthesis of functionalized oxazoles.

Copper(ii)-mediated formation of oxazole-4-carbonitrile from acetophenone and coordinated cyanide anion via a radical coupling

A protocol for the direct synthesis of 4-aryloxazole-5-carbonitrile from acetophenone was first described.

Design, synthesis and biological evaluation of potent FAAH inhibitors

A new series of 3-carboxamido-5-aryl-isoxazoles was designed, synthesized and evaluated for their biological activity. Different pharmacomodulations have been explored and the lipophilicity of these compounds was assessed. Investigation of the in vitro biological activity led to the identification of 5 compounds as potent FAAH inhibitors, their good FAAH inhibition capacity is probably correlated with their suitable lipophilicity. Specifically, compound 25 showed similar inhibition potency against FAAH in comparison with URB597, one of the most potent FAAH inhibitor known to date.

Discovery of Uracil Derivatives as Potent Inhibitors of Fatty Acid Amide Hydrolase

Fatty Acid Amide Hydrolase (FAAH) is an intracellular serine enzyme involved in the biological degradation of the fatty acid ethanolamide family of signaling lipids, which exerts neuroprotective, anti-inflammatory, and analgesic properties. In the present study, a conjugated 2,4-dioxo-pyrimidine-1-carboxamide scaffold was confirmed as a novel template for FAAH inhibitors, based on which, a series of analogues had been prepared for an initial structure-activity relationship (SAR) study. Most of the synthesized compounds displayed moderate to significant FAAH inhibitory potency. Among them, compounds 11 and 14 showed better activity than others, with IC₅₀ values of 21 and 53 nM. SAR analysis indicated that 2,4-dioxopyrimidine-1-carboxamides represented a novel class of potent inhibitors of FAAH, and substitution at the uracil ring or replacement of the N-terminal group might favor the inhibitory potency. Selected compounds of this class may be used as useful parent molecules for further investigation.

Preclinical Characterization of the FAAH Inhibitor JNJ-42165279

The pre-clinical characterization of the aryl piperazinyl urea inhibitor of fatty acid amide hydrolase (FAAH) JNJ-42165279 is described. JNJ-42165279 covalently inactivates the FAAH enzyme, but is highly selective with regard to other enzymes, ion channels, transporters, and receptors. JNJ-42165279 exhibited excellent ADME and pharmacodynamic properties as evidenced by its ability to block FAAH in the brain and periphery of rats and thereby cause an elevation of the concentrations of anandamide (AEA), oleoyl ethanolamide (OEA), and palmitoyl ethanolamide (PEA). The compound was also efficacious in the spinal nerve ligation (SNL) model of neuropathic pain. The combination of good physical, ADME, and PD properties of JNJ-42165279 supported it entering the clinical portfolio.

Discovery libraries targeting the major enzyme classes: the serine hydrolases

Two libraries of modestly reactive ureas containing either electron-deficient acyl anilines or acyl pyrazoles were prepared and are reported as screening libraries for candidate serine hydrolase inhibitors. Within each library is a small but powerful subset of compounds that serve as a chemotype fragment screening library capable of subsequent structural diversification. Elaboration of the pyrazole-based ureas provided remarkably potent irreversible inhibitors of fatty acid amide hydrolase (FAAH, apparent Ki=100-200 pM) complementary to those previously disclosed enlisting electron-deficient aniline-based ureas.

α-Ketoheterocycle inhibitors of fatty acid amide hydrolase: exploration of conformational constraints in the acyl side chain

A series of α-ketooxazoles containing heteroatoms embedded within conformational constraints in the C2 acyl side chain of 2 (OL-135) were synthesized and evaluated as inhibitors of fatty acid amide hydrolase (FAAH). The studies reveal that the installation of a heteroatom (O) in the conformational constraint is achievable, although the potency of these novel derivatives is reduced slightly relative to 2 and the analogous 1,2,3,4-tetrahydronaphthalene series. Interestingly, both enantiomers (R and S) of the candidate inhibitors bearing a chiral center adjacent to the electrophilic carbonyl were found to effectively inhibit FAAH.

Design, synthesis, and characterization of α-ketoheterocycles that additionally target the cytosolic port Cys269 of fatty acid amide hydrolase

A series of α-ketooxazoles incorporating electrophiles at the C5 position of the pyridyl ring of 2 (OL-135) and related compounds were prepared and examined as inhibitors of fatty acid amide hydrolase (FAAH) that additionally target the cytosolic port Cys269. From this series, a subset of the candidate inhibitors exhibited time-dependent FAAH inhibition and noncompetitive irreversible inactivation of the enzyme, consistent with the targeted Cys269 covalent alkylation or addition, and maintained or enhanced the intrinsic selectivity for FAAH versus other serine hydrolases. A preliminary in vivo assessment demonstrates that these inhibitors raise endogenous brain levels of anandamide and other FAAH substrates upon intraperitoneal (i.p.) administration to mice, with peak levels achieved within 1.5–3 h, and that the elevations of the signaling lipids were maintained >6 h, indicating that the inhibitors effectively reach and remain active in the brain, inhibiting FAAH for a sustained period.

Rational design of fatty acid amide hydrolase inhibitors that act by covalently bonding to two active site residues

The design and characterization of α-ketoheterocycle fatty acid amide hydrolase (FAAH) inhibitors are disclosed that additionally and irreversibly target a cysteine (Cys269) found in the enzyme cytosolic port while maintaining the reversible covalent Ser241 attachment responsible for their rapid and initially reversible enzyme inhibition. Two α-ketooxazoles (3 and 4) containing strategically placed electrophiles at the C5 position of the pyridyl substituent of 2 (OL-135) were prepared and examined as inhibitors of FAAH. Consistent with the observed time-dependent noncompetitive inhibition, the cocrystal X-ray structure of 3 bound to a humanized variant of rat FAAH revealed that 3 was not only covalently bound to the active site catalytic nucleophile Ser241 as a deprotonated hemiketal, but also to Cys269 through the pyridyl C5-substituent, thus providing an inhibitor with dual covalent attachment in the enzyme active site. In vivo characterization of the prototypical inhibitors in mice demonstrates that they raise endogenous brain levels of FAAH substrates to a greater extent and for a much longer duration (>6 h) than the reversible inhibitor 2, indicating that the inhibitors accumulate and persist in the brain to completely inhibit FAAH for a prolonged period. Consistent with this behavior and the targeted irreversible enzyme inhibition, 3 reversed cold allodynia in the chronic constriction injury model of neuropathic pain in mice for a sustained period (>6 h) beyond that observed with the reversible inhibitor 2, providing effects that were unchanged over the 1-6 h time course monitored.

Sulfonyl fluoride inhibitors of fatty acid amide hydrolase

Sulfonyl fluorides are known to inhibit esterases. Early work from our laboratory has identified hexadecyl sulfonylfluoride (AM374) as a potent in vitro and in vivo inhibitor of fatty acid amide hydrolase (FAAH). We now report on later generation sulfonyl fluoride analogs that exhibit potent and selective inhibition of FAAH. Using recombinant rat and human FAAH, we show that 5-(4-hydroxyphenyl)pentanesulfonyl fluoride (AM3506) has similar inhibitory activity for both the rat and the human enzyme, while rapid dilution assays and mass spectrometry analysis suggest that the compound is a covalent modifier for FAAH and inhibits its action in an irreversible manner. Our SAR results are highlighted by molecular docking of key analogs.

Aryl Piperazinyl Ureas as Inhibitors of Fatty Acid Amide Hydrolase (FAAH) in Rat, Dog, and Primate

A series of aryl piperazinyl ureas that act as covalent inhibitors of fatty acid amide hydrolase (FAAH) is described. A potent and selective (does not inhibit FAAH-2) member of this class, JNJ-40355003, was found to elevate the plasma levels of three fatty acid amides: anandamide, oleoyl ethanolamide, and palmitoyl ethanolamide, in the rat, dog, and cynomolgous monkey. The elevation of the levels of these lipids in the plasma of monkeys suggests that FAAH-2 may not play a significant role in regulating plasma levels of fatty acid ethanolamides in primates.

Rat and human fatty acid amide hydrolases: overt similarities and hidden differences

Fatty acid amide hydrolase (FAAH) is a membrane protein that plays a relevant role in the metabolism of fatty acid amides and esters. It degrades important neurotransmitters such as oleamide and anandamide, and it has been involved in a number of human pathological conditions, representing therefore a valuable target for biochemical and pharmacological research. In this study, we have investigated in vitro the structure-function relationship of rat and human FAAHs. In particular circular dichroism, fluorescence spectroscopy and light scattering measurements have been performed, in order to characterize the structural features of the two proteins, both in the presence and absence of the irreversible inhibitor methoxyarachidonyl-fluorophosphonate. The results demonstrate that the structural dynamics of the two FAAHs are different, despite their high sequence homology and overall similarity in temperature-dependence. Additionally, membrane binding and kinetic assays of both FAAHs indicate that also the functional properties of the two enzymes are different in their interaction with lipid bilayers and with exogenous inhibitors. These findings suggest that pre-clinical studies of FAAH-dependent human diseases based only on animal models should be interpreted with caution, and that the efficacy of new drugs targeted to FAAH should be tested in vitro, on both rat and human enzymes.

α-Ketoheterocycle-based Inhibitors of Fatty Acid Amide Hydrolase (FAAH)

A summary of the initial discovery and characterization of the enzyme fatty acid amide hydrolase (FAAH), and the subsequent advancement of an important class of competitive, reversible, potent and selective inhibitors is presented. Initially explored using substrate-inspired inhibitors bearing electrophilic carbonyls, the examination of α-ketoheterocyle-based inhibitors of FAAH with the benefit of a unique activity-based protein-profiling (ABPP)-based proteome-wide selectivity assay, a powerful in vivo biomarker-based in vivo screen, and subsequent retrospective X-ray co-crystal structures with the enzyme, is summarized. These efforts defined the impact of the central activating heterocycle and its key substituents, provided key simplifications in the C2 acyl side chain and clear interpretations for the unique role and subsequent optimization of the central activating heterocycle, and established the basis for the recent further conformational constraints in the C2 acyl side chain, providing potent, long-acting, orally-active FAAH inhibitors.

Approximating protein flexibility through dynamic pharmacophore models: application to fatty acid amide hydrolase (FAAH)

A structure-based drug discovery method is described that incorporates target flexibility through the use of an ensemble of protein conformations. The approach was applied to fatty acid amide hydrolase (FAAH), a key deactivating enzyme in the endocannabinoid system. The resultant dynamic pharmacophore models are rapidly able to identify known FAAH inhibitors over drug-like decoys. Different sources of FAAH conformational ensembles were explored, with both snapshots from molecular dynamics simulations and a group of X-ray structures performing well. Results were compared to those from docking and pharmacophore models generated from a single X-ray structure. Increasing conformational sampling consistently improved the pharmacophore models, emphasizing the importance of incorporating target flexibility in structure-based drug design.

Design, synthesis and evaluation of polar head group containing 2-keto-oxazole inhibitors of FAAH

2-α-Keto oxazoles containing polar head groups in their C5-side chains were designed as fatty acid amide hydrolase (FAAH) inhibitors. Variation in the spacer length resulted in submicromolar α-keto-oxazole FAAH inhibitor (IC(50)=436 nM) presenting electrostatic stabilizing interactions between its polar head group contained in the C5-side chain and the hydrophilic pocket of the enzyme.

The discovery and development of inhibitors of fatty acid amide hydrolase (FAAH)

A summary of the discovery and advancement of inhibitors of fatty acid amide hydrolase (FAAH) is presented.

Mechanism of inhibition of fatty acid amide hydrolase by sulfonamide-containing benzothiazoles: long residence time derived from increased kinetic barrier and not exclusively from thermodynamic potency

Fatty acid amide hydrolase (FAAH) has emerged as a potential target for developing analgesic, anxiolytic, antidepressant, sleep-enhancing, and anti-inflammatory drugs, and tremendous efforts have been made to discover potent and selective inhibitors of FAAH. Most known potent FAAH inhibitors described to date employ covalent mechanisms, inhibiting the enzyme either reversibly or irreversibly. Recently, a benzothiazole-based analogue (1) has been described possessing a high potency against FAAH yet lacking a structural feature previously known to interact with FAAH covalently. However, covalent inhibition of FAAH by 1 has not been fully ruled out, and the issue of reversibility has not been addressed. Confirming previous reports, 1 inhibited recombinant human FAAH (rhFAAH) with high potency with IC(50) ~2 nM. It displayed an apparently noncompetitive and irreversible inhibition, titrating rhFAAH stoichiometrically within normal assay times. The inhibition appeared to be time dependent, but the time dependence only improved potency by a small degree (from ~8 to ~2 nM). However, mass spectrometric analyses of the reaction mixture failed to reveal any cleavage product or covalent adduct and showed full recovery of the parent compound, ruling out covalent, irreversible inhibition. Dialysis revealed recovery of enzyme activity from enzyme-inhibitor complex over a prolonged time (>10 h), demonstrating that 1 is indeed a reversible, albeit slowly dissociating inhibitor of FAAH. Molecular docking indicated that the sulfonamide group of 1 could form hydrogen bonds with several residues involved in catalysis, thereby mimicking the transition state. The long residence time displayed by 1 does not appear to derive exclusively from great thermodynamic potency and is consistent with an increased kinetic energy barrier that prevents dissociation from happening quickly.

Reversible competitive α-ketoheterocycle inhibitors of fatty acid amide hydrolase containing additional conformational constraints in the acyl side chain: orally active, long-acting analgesics

A series of α-ketooxazoles containing conformational constraints in the C2 acyl side chain of 2 (OL-135) were examined as inhibitors of fatty acid amide hydrolase (FAAH). Only one of the two possible enantiomers displayed potent FAAH inhibition (S vs R enantiomer), and their potency is comparable or improved relative to 2, indicating that the conformational restriction in the C2 acyl side chain is achievable. A cocrystal X-ray structure of the α-ketoheterocycle 12 bound to a humanized variant of rat FAAH revealed its binding details, confirmed that the (S)-enantiomer is the bound active inhibitor, shed light on the origin of the enantiomeric selectivity, and confirmed that the catalytic Ser241 is covalently bound to the electrophilic carbonyl as a deprotonated hemiketal. Preliminary in vivo characterization of the inhibitors 12 and 14 is reported demonstrating that they raise brain anandamide levels following either intraperitoneal (ip) or oral (po) administration indicative of effective in vivo FAAH inhibition. Significantly, the oral administration of 12 caused dramatic accumulation of anandamide in the brain, with peak levels achieved between 1.5 and 3 h, and these elevations were maintained over 9 h. Additional studies of these two representative members of the series (12 and 14) in models of thermal hyperalgesia and neuropathic pain are reported, including the demonstration that 12 administered orally significantly attenuated mechanical (>6 h) and cold (>9 h) allodynia for sustained periods consistent with its long-acting effects in raising the endogenous concentration of anandamide.

Fluoride-mediated capture of a noncovalent bound state of a reversible covalent enzyme inhibitor: X-ray crystallographic analysis of an exceptionally potent α-ketoheterocycle inhibitor of fatty acid amide hydrolase

Two cocrystal X-ray structures of the exceptionally potent α-ketoheterocycle inhibitor 1 (K(i) = 290 pM) bound to a humanized variant of rat fatty acid amide hydrolase (FAAH) are disclosed, representing noncovalently and covalently bound states of the same inhibitor with the enzyme. Key to securing the structure of the noncovalently bound state of the inhibitor was the inclusion of fluoride ion in the crystallization conditions that is proposed to bind the oxyanion hole precluding inhibitor covalent adduct formation with stabilization of the tetrahedral hemiketal. This permitted the opportunity to detect important noncovalent interactions stabilizing the binding of the inhibitor within the FAAH active site independent of the covalent reaction. Remarkably, noncovalently bound 1 in the presence of fluoride appears to capture the active site in the same "in action" state with the three catalytic residues Ser241-Ser217-Lys142 occupying essentially identical positions observed in the covalently bound structure of 1, suggesting that this technique of introducing fluoride may have important applications in structural studies beyond inhibiting substrate or inhibitor oxyanion hole binding. Key insights to emerge from the studies include the observations that noncovalently bound 1 binds in its ketone (not gem diol) form, that the terminal phenyl group in the acyl side chain of the inhibitor serves as the key anchoring interaction overriding the intricate polar interactions in the cytosolic port, and that the role of the central activating heterocycle is dominated by its intrinsic electron-withdrawing properties. These two structures are also briefly compared with five X-ray structures of α-ketoheterocycle-based inhibitors bound to FAAH recently disclosed.

Label-free quantification of membrane-ligand interactions using backscattering interferometry

Although membrane proteins are ubiquitous within all living organisms and represent the majority of drug targets, a general method for direct, label-free measurement of ligand binding to native membranes has not been reported. Here we show that backscattering interferometry (BSI) can accurately quantify ligand-receptor binding affinities in a variety of membrane environments. By detecting minute changes in the refractive index of a solution, BSI allows binding interactions of proteins with their ligands to be measured at picomolar concentrations. Equilibrium binding constants in the micromolar to picomolar range were obtained for small- and large-molecule interactions in both synthetic and cell-derived membranes without the use of labels or supporting substrates. The simple and low-cost hardware, high sensitivity and label-free nature of BSI should make it readily applicable to the study of many membrane-associated proteins of biochemical and pharmacological interest.

Fatty acid amide signaling molecules

Key studies leading to the discovery and definition of the role of endogenous fatty acid amide signaling molecules are summarized.

Synthesis and evaluation of paracetamol esters as novel fatty acid amide hydrolase inhibitors

Fatty acid amide hydrolase (FAAH) is the key hydrolytic enzyme for the endogenous cannabinoid receptor ligand anandamide. The synthesis and evaluation for their FAAH inhibitory activities of a series of 18 paracetamol esters are described. Structure-activity relationship studies indicated that the ester (33) with a 2-(4-(2-(trifluoromethyl)pyridin-4-ylamino)phenyl)acetic acid substituent was the most potent analogue in this series. The compound inhibited FAAH activity in a competitive manner with a K(i) value of 0.16 microM. The compound was also able to inhibit the FAAH activity in rat basophilic leukemia cells as assessed by measuring either the hydrolysis of anandamide, the FAAH-dependent cellular accumulation of anandamide, or the FAAH-dependent recycling of tritium to the cell membranes. The compound also inhibited the activity of monoacylglycerol lipase (MGL), the enzyme responsible for the hydrolysis of the endogenous cannabinoid receptor ligand 2-arachidonoylglycerol, with an IC(50) value of 1.9 microM. It is concluded that the compound may be a useful template for the design of potent novel inhibitors of FAAH.

X-ray crystallographic analysis of alpha-ketoheterocycle inhibitors bound to a humanized variant of fatty acid amide hydrolase

Three cocrystal X-ray structures of the alpha-ketoheterocycle inhibitors 3-5 bound to a humanized variant of fatty acid amide hydrolase (FAAH) are disclosed and comparatively discussed alongside those of 1 (OL-135) and its isomer 2. These five X-ray structures systematically probe each of the three active site regions key to substrate or inhibitor binding: (1) the conformationally mobile acyl chain-binding pocket and membrane access channel responsible for fatty acid amide substrate and inhibitor acyl chain binding, (2) the atypical active site catalytic residues and surrounding oxyanion hole that covalently binds the core of the alpha-ketoheterocycle inhibitors captured as deprotonated hemiketals mimicking the tetrahedral intermediate of the enzyme-catalyzed reaction, and (3) the cytosolic port and its uniquely important imbedded ordered water molecules and a newly identified anion binding site. The detailed analysis of their key active site interactions and their implications on the interpretation of the available structure-activity relationships are discussed providing important insights for future design.

beta-Lactams derived from a carbapenem chiron are selective inhibitors of human fatty acid amide hydrolase versus human monoacylglycerol lipase

A library of 30 beta-lactams has been prepared from (3R,4R)-3-[(R)-1'-(tbutyldimethylsilyloxy)-ethyl]-4-acetoxy-2-azetidinone, and the corresponding deacetoxy derivative, by sequential N- and O-functionalizations with various omega-alkenoyl and omega-arylalkanoyl chains. All compounds were selective inhibitors of hFAAH versus hMGL, and IC(50) values in the nanomolar range (5-14 nM) were recorded for the best representatives. From time-dependent preincubation and rapid dilution studies, and from docking analyses in a homology model of the target enzyme, a reversible mechanism of inhibition of hFAAH is proposed.

Refined homology model of monoacylglycerol lipase: toward a selective inhibitor

Monoacylglycerol lipase (MGL) is primarily responsible for the hydrolysis of 2-arachidonoylglycerol (2-AG), an endocannabinoid with full agonist activity at both cannabinoid receptors. Increased tissue 2-AG levels consequent to MGL inhibition are considered therapeutic against pain, inflammation, and neurodegenerative disorders. However, the lack of MGL structural information has hindered the development of MGL-selective inhibitors. Here, we detail a fully refined homology model of MGL which preferentially identifies MGL inhibitors over druglike noninhibitors. We include for the first time insight into the active-site geometry and potential hydrogen-bonding interactions along with molecular dynamics simulations describing the opening and closing of the MGL helical-domain lid. Docked poses of both the natural substrate and known inhibitors are detailed. A comparison of the MGL active-site to that of the other principal endocannabinoid metabolizing enzyme, fatty acid amide hydrolase, demonstrates key differences which provide crucial insight toward the design of selective MGL inhibitors as potential drugs.

Pain and beyond: fatty acid amides and fatty acid amide hydrolase inhibitors in cardiovascular and metabolic diseases

Fatty acid amide hydrolase (FAAH) is responsible for the hydrolysis of several important endogenous fatty acid amides (FAAs), including anandamide, oleoylethanolamide and palmitoylethanolamide. Because specific FAAs interact with cannabinoid and vanilloid receptors, they are often referred to as 'endocannabinoids' or 'endovanilloids'. Initial interest in this area, therefore, has focused on developing FAAH inhibitors to augment the actions of FAAs and reduce pain. However, recent literature has shown that these FAAs - through interactions with unique receptors (extracellular and intracellular) - can induce a diverse array of effects that include appetite suppression, modulation of lipid and glucose metabolism, vasodilation, cardiac function and inflammation. This review gives an overview of FAAs and diverse FAAH inhibitors and their potential therapeutic utility in pain and non-pain indications.

Binding and inactivation mechanism of a humanized fatty acid amide hydrolase by alpha-ketoheterocycle inhibitors revealed from cocrystal structures

The cocrystal X-ray structures of two isomeric alpha-ketooxazole inhibitors (1 (OL-135) and 2) bound to fatty acid amide hydrolase (FAAH), a key enzymatic regulator of endocannabinoid signaling, are disclosed. The active site catalytic Ser241 is covalently bound to the inhibitors' electrophilic carbonyl groups, providing the first structures of FAAH bound to an inhibitor as a deprotonated hemiketal mimicking the enzymatic tetrahedral intermediate. The work also offers a detailed view of the oxyanion hole and an exceptional "in-action" depiction of the unusual Ser-Ser-Lys catalytic triad. These structures capture the first picture of inhibitors that span the active site into the cytosolic port providing new insights that help to explain FAAH's interaction with substrate leaving groups and their role in modulating inhibitor potency and selectivity. The role for the activating central heterocycle is clearly defined and distinguished from that observed in prior applications with serine proteases, reconciling the large electronic effect of attached substituents found unique to this class of inhibitors with FAAH. Additional striking active site flexibility is seen upon binding of the inhibitors, providing insights into the existence of a now well-defined membrane access channel with the disappearance of a spatially independent portion of the acyl chain-binding pocket. Finally, comparison of the structures of OL-135 (1) and its isomer 2 indicates that they bind identically to FAAH, albeit with reversed orientations of the central activating heterocycle, revealing that the terminal 2-pyridyl substituent and the acyl chain phenyl group provide key anchoring interactions and confirming the distinguishing role of the activating oxazole.

Fatty acid amide hydrolase as a potential therapeutic target for the treatment of pain and CNS disorders

BACKGROUND: Fatty acid amide hydrolase (FAAH) is an integral membrane enzyme that hydrolyzes the endocannabinoid anandamide and related amidated signaling lipids. Genetic or pharmacological inactivation of FAAH produces analgesic, anti-inflammatory, anxiolytic, and antidepressant phenotypes without showing the undesirable side effects of direct cannabinoid receptor agonists, indicating that FAAH may be a promising therapeutic target. OBJECTIVES: This review highlights advances in the development of FAAH inhibitors of different mechanistic classes and their in vivo efficacy. Also highlighted are advances in technology for the in vitro and in vivo selectivity assessment of FAAH inhibitors employing activity-based protein profiling (ABPP) and click chemistry-ABPP, respectively. Recent reports on structure-based drug design for human FAAH generated by protein engineering using interspecies active site conversion are also discussed. METHODS: The literature searches of Medline and SciFinder databases were used. CONCLUSIONS: There has been tremendous progress in our understanding in FAAH and development of FAAH inhibitors with in vivo efficacy, selectivity, and drug like pharmacokinetic properties.