O‐(Triazolyl)methyl Carbamates as a Novel and Potent Class of Fatty Acid Amide Hydrolase (FAAH) Inhibitors

Inhibition of fatty acid amide hydrolase (FAAH) activity is under investigation as a valuable strategy for the treatment of several disorders, including pain and drug addiction. A number of potent FAAH inhibitors belonging to different chemical classes have been disclosed to date; O‐aryl carbamates are one of the most representative families. In the search for novel FAAH inhibitors, a series of O‐(1,2,3‐triazol‐4‐yl)methyl carbamate derivatives were designed and synthesized exploiting a copper‐ catalyzed [3+2] cycloaddition reaction between azides and alkynes (click chemistry). Exploration of the structure–activity relationships within this new class of compounds identified potent inhibitors of both rat and human FAAH with IC₅₀ values in the single‐digit nanomolar range. In addition, these derivatives showed improved stability in rat plasma and kinetic solubility in buffer with respect to the lead compound. Based on the results of the study, the novel analogues identified can be considered to be promising starting point for the development of new FAAH inhibitors with improved drug‐like properties.     

MAO Inhibitory Activity of 2‐Arylbenzofurans versus 3‐Arylcoumarins: Synthesis,in vitro Study,and Docking Calculations

Monoamine oxidase (MAO) is an important drug target for the treatment of neurological disorders. Several 3‐arylcoumarin derivatives were previously described as interesting selective MAO‐B inhibitors. Preserving the trans‐stilbene structure, a series of 2‐arylbenzofuran and corresponding 3‐arylcoumarin derivatives were synthesized and evaluated as inhibitors of both MAO isoforms, MAO‐A and MAO‐B. In general, both types of derivatives were found to be selective MAO‐B inhibitors, with IC₅₀ values in the nano‐ to micromolar range. 5‐Nitro‐2‐(4‐methoxyphenyl)benzofuran ( 8 ) is the most active compound of the benzofuran series, presenting MAO‐B selectivity and reversible inhibition (IC₅₀=140 nM ). 3‐(4′‐Methoxyphenyl)‐6‐nitrocoumarin ( 15 ), with the same substitution pattern as that of compound 8 , was found to be the most active MAO‐B inhibitor of the coumarin series (IC₅₀=3 nM ). However, 3‐phenylcoumarin 14 showed activity in the same range (IC₅₀=6 nM ), is reversible, and also severalfold more selective than compound 15 . Docking experiments for the most active compounds into the MAO‐B and MAO‐A binding pockets highlighted different interactions between the derivative classes (2‐arylbenzofurans and 3‐arylcoumarins), and provided new information about the enzyme–inhibitor interaction and the potential therapeutic application of these scaffolds.     

3‐Aminoazetidin‐2‐one Derivatives as N‐Acylethanolamine Acid Amidase (NAAA) Inhibitors Suitable for Systemic Administration

N‐Acylethanolamine acid amidase (NAAA) is a cysteine hydrolase that catalyzes the hydrolysis of endogenous lipid mediators such as palmitoylethanolamide (PEA). PEA has been shown to exert anti‐inflammatory and antinociceptive effects in animals by engaging peroxisome proliferator‐activated receptor α (PPAR‐α). Thus, preventing PEA degradation by inhibiting NAAA may provide a novel approach for the treatment of pain and inflammatory states. Recently, 3‐aminooxetan‐2‐one compounds were identified as a class of highly potent NAAA inhibitors. The utility of these compounds is limited, however, by their low chemical and plasma stabilities. In the present study, we synthesized and tested a series of N‐(2‐oxoazetidin‐3‐yl)amides as a novel class of NAAA inhibitors with good potency and improved physicochemical properties, suitable for systemic administration. Moreover, we elucidated the main structural features of 3‐aminoazetidin‐2‐one derivatives that are critical for NAAA inhibition.     

Monoamine Oxidase (MAO) Inhibitory Activity: 3‐Phenylcoumarins versus 4‐Hydroxy‐3‐phenylcoumarins

Monoamine oxidase (MAO) is a useful target in the treatment of neurodegenerative diseases and depressive disorders. Both isoforms, MAO‐A and MAO‐B, are known to play critical roles in disease progression, and as such, the identification of novel, potent and selective inhibitors is an important research goal. Here, two series of 3‐phenylcoumarin derivatives were synthesized and evaluated against MAO‐A and MAO‐B. Most of the compounds tested acted preferentially on MAO‐B, with IC₅₀ values in the micromolar to nanomolar range. Only 6‐chloro‐4‐hydroxy‐3‐(2’‐hydroxyphenyl)coumarin exhibited activity against the MAO‐A isoform, while still retaining good selectivity for MAO‐B. 6‐Chloro‐3‐phenylcoumarins unsubstituted at the 4 position were found to be more active as MAO‐B inhibitors than the corresponding 4‐hydroxylated coumarins. For 4‐unsubstituted coumarins, meta and para positions on the 3‐phenyl ring seem to be the most favorable for substitution. Molecular docking simulations were used to explain the observed hMAO‐B structure–activity relationships for this type of compound. 6‐Chloro‐3‐(3’‐methoxyphenyl)coumarin was the most active compound identified (IC₅₀=0.001 μM ) and is several times more potent and selective than the reference compound, R‐(?)‐deprenyl hydrochloride. This compound represents a novel tool for the further investigation of the therapeutic potential of MAO‐B inhibitors.     

3‐Heterocycle‐Phenyl N‐Alkylcarbamates as FAAH Inhibitors: Design,Synthesis and 3D‐QSAR Studies

Carbamates are a well‐established class of fatty acid amide hydrolase (FAAH) inhibitors. Here we describe the synthesis of meta‐substituted phenolic N‐alkyl/aryl carbamates and their in vitro FAAH inhibitory activities. The most potent compound, 3‐(oxazol‐2yl)phenyl cyclohexylcarbamate ( 2 a ), inhibited FAAH with a sub‐nanomolar IC₅₀ value (IC₅₀=0.74 nM ). Additionally, we developed and validated three‐dimensional quantitative structure–activity relationships (QSAR) models of FAAH inhibition combining the newly disclosed carbamates with our previously published inhibitors to give a total set of 99 compounds. Prior to 3D‐QSAR modeling, the degree of correlation between FAAH inhibition and in silico reactivity was also established. Both 3D‐QSAR methods used, CoMSIA and GRID/GOLPE, produced statistically significant models with coefficient of correlation for external prediction (R²_PRED) values of 0.732 and 0.760, respectively. These models could be of high value in further FAAH inhibitor design.     

ω‐Imidazolyl‐ and ω‐Tetrazolylalkylcarbamates as Inhibitors of Fatty Acid Amide Hydrolase: Biological Activity and in vitro Metabolic Stability

Fatty acid amide hydrolase (FAAH) is a serine hydrolase that terminates the analgesic and anti‐inflammatory effects of endocannabinoids such as anandamide. Herein, structure–activity relationship studies on a new series of aryl N‐(ω‐imidazolyl‐ and ω‐tetrazolylalkyl)carbamate inhibitors of FAAH were investigated. As one result, a pronounced increase in inhibitory potency was observed if a phenyl residue attached to the carbamate oxygen atom was replaced by a pyridin‐3‐yl moiety. The most active compounds exhibited IC₅₀ values in the low nanomolar range. In addition, investigations on the metabolic properties of these inhibitors were performed. In rat liver homogenate and in porcine plasma, the extent of their degradation was shown to be strongly dependent on the kind of aryl residue bound to the carbamate as well as on the length and type of the alkyl spacer connecting the carbamate group with the heterocyclic system. With the aid of esterase inhibitors it was shown that in porcine plasma, carboxylesterase‐like enzymes and paraoxonase are involved in carbamate cleavage. Moreover, it was found that highly active pyridin‐3‐yl carbamates reacted with albumin, which led to covalent albumin adducts.     

Synthesis of N‐Hydroxycinnamides Capped with a Naturally Occurring Moiety as Inhibitors of Histone Deacetylase

Histone deacetylase (HDAC) inhibitors are regarded as promising therapeutics for the treatment of cancer. All reported HDAC inhibitors contain three pharmacophoric features: a zinc‐chelating group, a hydrophobic linker, and a hydrophobic cap for surface recognition. In this study we investigated the effectiveness of osthole, a hydrophobic Chinese herbal compound, as the surface recognition cap in hydroxamate‐based compounds as inhibitors of HDAC. Nine novel osthole‐based N‐hydroxycinnamides were synthesized and screened for enzyme inhibition activity. Compounds 9 d , 9 e , 9 g exhibited inhibitory activities (IC₅₀=24.5, 20.0, 19.6 nM ) against nuclear HDACs in HeLa cells comparable to that of suberoylanilide hydroxamic acid (SAHA; IC₅₀=24.5 nM ), a potent inhibitor clinically used for the treatment of cutaneous T‐cell lymphoma (CTCL). While compounds 9 d and 9 e showed SAHA‐like activity towards HDAC1 and HDAC6, compound 9 g was more selective for HDAC1. Compound 9 d exhibited the best cellular effect, which was comparable to that of SAHA, of enhancing acetylation of either α‐tubulin or histone H3. Molecular docking analysis showed that the osthole moiety of compound 9 d may interact with the same hydrophobic surface pocket exploited by SAHA and it may be modified to provide class‐specific selectivity. These results suggest that osthole is an effective hydrophobic cap when incorporated into N‐hydroxycinnamide‐derived HDAC inhibitors.     

Design,Synthesis, and SAR of Naphthyl‐Substituted Diarylpyrimidines as Non‐Nucleoside Inhibitors of HIV‐1 Reverse Transcriptase

A series of 38 2‐naphthyl‐substituted diarylpyrimidine (DAPY) analogues, characterized by various substitution patterns on the pyrimidine and naphthalene rings, was synthesized in a straightforward fashion by means of parallel synthesis and evaluated as inhibitors of the HIV‐1 wild‐type and double mutant (K103N+Y181C) strains. Most of the compounds displayed strong activity against wild‐type HIV‐1. The most active compound, with a cyano group at position C6 on the naphthalene ring, exhibited activity against wild‐type HIV‐1 with an EC₅₀ value of 0.002 μM and against the double mutant strain with an EC₅₀ value of 0.24 μM ; the selectivity index (SI) against wild‐type is >180 000, the highest SI value among DAPY analogues. The structure–activity relationship (SAR) of the newly synthesized DAPYs is presented herein.     

Rapid Development of a Potent Photo‐triggered Inhibitor of the Serine Hydrolase RBBP9

The serine hydrolases constitute a large class of enzymes that play important roles in physiology. There is great interest in the development of potent and selective pharmacological inhibitors of these proteins. Traditional active‐site inhibitors often have limited selectivity within this superfamily and are tedious and expensive to discover. Using the serine hydrolase RBBP9 as a model target, we designed a rapid and relatively inexpensive route to highly selective peptoid‐based inhibitors that can be activated by visible light. This technology provides rapid access to photo‐activated tool compounds capable of selectively blocking the function of particular serine hydrolases.     

Design,Synthesis, in vitro MAO‐B Inhibitory Evaluation,and Computational Studies of Some 6‐Nitrobenzothiazole‐Derived Semicarbazones

Monoamine oxidase B (MAO‐B) is an important drug target for the treatment of neurological disorders. A series of 6‐nitrobenzothiazole‐derived semicarbazones were designed, synthesized, and evaluated as inhibitors of the rat brain MAO‐B isoenzyme. Most of the compounds were found to be potent inhibitors of MAO‐B, with IC₅₀ values in the nanomolar to micromolar range. Molecular docking studies were performed with AutoDock 4.2 to deduce the affinity and binding mode of these inhibitors toward the MAO‐B active site. The free energies of binding (ΔG) and inhibition constants (K_i) of the docked compounds were calculated by the Lamarckian genetic algorithm (LGA) of AutoDock 4.2. Good correlations between the calculated and experimental results were obtained. 1‐[(4‐Chlorophenyl)(phenyl)methylene]‐4‐(6‐nitrobenzothiazol‐2‐yl)semicarbazide emerged as the lead MAO‐B inhibitor, with top ranking in both the experimental MAO‐B assay (IC₅₀: 0.004±0.001 μM ) and in computational docking studies (K_i: 1.08 μM ). Binding mode analysis of potent inhibitors suggests that these compounds are well accommodated by the MAO‐B active site through stable hydrophobic and hydrogen bonding interactions. Interestingly, the 6‐nitrobenzothiazole moiety is stabilized in the substrate cavity with the aryl or diaryl residues extending up into the entrance cavity of the active site. According to our results, docking experiments could be an interesting approach for predicting the activity and binding interactions of this class of semicarbazones against MAO‐B. Thus, a binding site model consisting of three essential pharmacophoric features is proposed, and this can be used for the design of future MAO‐B inhibitors.     

Development of Novel Selective Peptidomimetics Containing a Boronic Acid Moiety,Targeting the 20S Proteasome as Anticancer Agents

This paper describes the design, synthesis, and biological evaluation of peptidomimetic boronates as inhibitors of the 20S proteasome, a validated target in the treatment of multiple myeloma. The synthesized compounds showed a good inhibitory profile against the ChT‐L activity of 20S proteasome. Compounds bearing a β‐alanine residue at the P2 position were the most active, that is, 3‐ethylphenylamino and 4‐methoxyphenylamino (R)‐1‐{3‐[4‐(substituted)‐2‐oxopyridin‐1(2H)‐yl]propanamido}‐3‐methylbutylboronic acids ( 3 c and 3 d , respectively), and these derivatives showed inhibition constants (K_i) of 17 and 20 nM , respectively. In addition, they co‐inhibited post glutamyl peptide hydrolase activity ( 3 c , K_i=2.57 μM ; 3 d , K_i=3.81 μM ). No inhibition was recorded against the bovine pancreatic α‐chymotrypsin, which thus confirms the selectivity towards the target enzyme. Docking studies of 3 c and related inhibitors into the yeast proteasome revealed the structural basis for specificity. The evaluation of growth inhibitory effects against 60 human tumor cell lines was performed at the US National Cancer Institute. Among the selected compounds, 3 c showed 50 % growth inhibition (GI₅₀) values at the sub‐micromolar level on all cell lines.     

Design and Synthesis of Tricyclic JAK3 Inhibitors with Picomolar Affinities as Novel Molecular Probes

The Janus kinase (JAK) signaling pathway is of particular importance in the pathology of inflammatory diseases and oncological disorders, and the inhibition of Janus kinase 3 (JAK3) with small molecules has proven to provide therapeutic immunosuppression. A novel class of tricyclic JAK inhibitors derived from the 3‐methyl‐1,6‐dihydrodipyrrolo[2,3‐b:2′,3′‐d]pyridine scaffold was designed based on the tofacitinib–JAK3 crystal structure by applying a rigidization approach. A convenient synthetic strategy to access the scaffold via an intramolecular Heck reaction was developed, and a small library of inhibitors was prepared and characterized using in vitro biochemical as well as cellular assays. IC₅₀ values as low as 220 pM could be achieved with selectivity for JAK3 over other JAK family members. Both activity and selectivity were confirmed in a cellular STAT phosphorylation assay, providing also first‐time data for tofacitinib. Our novel inhibitors may serve as tool compounds and useful probes to explore the role of JAK3 inhibition in pharmacodynamics studies.     

Discovery of 7‐Aryl‐Substituted (1,5‐Naphthyridin‐4‐yl)ureas as Aurora Kinase Inhibitors

As part of our research projects to identify new chemical entities of biological interest, we developed a synthetic approach and the biological evaluation of (7‐aryl‐1,5‐naphthyridin‐4‐yl)ureas as a novel class of Aurora kinase inhibitors for the treatment of malignant diseases based on pathological cell proliferation. 1,5‐Naphthyridine derivatives showed excellent inhibitory activities toward Aurora kinases A and B, and the most active compound, 1‐cyclopropyl‐3‐[7‐(1‐methyl‐1H‐pyrazol‐4‐yl)‐1,5‐naphthyridin‐4‐yl]urea ( 49 ), displayed IC₅₀ values of 13 and 107 nM against Aurora kinases A and B, respectively. In addition, the selectivity toward a panel of seven cancer‐related protein kinases was highlighted. In vitro ADME properties were also determined in order to rationalize the difficulties in correlating antiproliferative activity with Aurora kinase inhibition. Finally, the good safety profile of these compounds imparts promising potential for their further development as anticancer agents.     

Glucosylceramide Mimics: Highly Potent GCase Inhibitors and Selective Pharmacological Chaperones for Mutations Associated with Types 1 and 2 Gaucher Disease

A series of iminoxylitol derivatives carrying a C‐linked di‐O‐acyl or di‐O‐alkyl glyceryl substituent were prepared and characterized. All of these compounds, which were designed as glucosylceramide (GlcCer) mimics, were nanomolar inhibitors of lysosomal β‐glucosidase (glucocerebrosidase, GCase). Two of these pseudoglycolipids were further evaluated for their ability to enhance the activity of mutant GCase in human Gaucher cells. Although the di‐O‐hexyl ether was surprisingly devoid of chaperoning activity on both N370S and L444P GCases, the di‐O‐decanoyl ester was a potent chaperone of the L444P hydrolase, capable of increasing the residual activity of the enzyme by a factor of two at a very low concentration (50 nM ); such a significant effect on the L444P mutation in human fibroblasts has not yet been observed. In heat‐stress studies, the diether was found to be much more effective in stabilizing the wild‐type enzyme than the diester. Four representative pseudoglycolipids were also assayed as inhibitors of GlcCer synthase, because such compounds could find use in the substrate reduction therapy approach to treat lysosomal storage diseases, but these compounds revealed only moderate activity. As efficient pharmacological chaperones, new structures such as the di‐C₁₀‐ester constitute leads for the development of therapeutic agents for types 2 and 3 Gaucher disease, the most severe neuronopathic forms of this lysosomal disease.     

Functionalization of Fluorinated Benzenesulfonamides and Their Inhibitory Properties toward Carbonic Anhydrases

Substituted tri‐ and tetrafluorobenzenesulfonamides were designed, synthesized, and evaluated as high‐affinity and isoform‐selective carbonic anhydrase (CA) inhibitors. Their binding affinities for recombinant human CA I, II, VA, VI, VII, XII, and XIII catalytic domains were determined by fluorescent thermal shift assay, isothermal titration calorimetry, and a stopped‐flow CO₂ hydration assay. Variation of the substituents at the 2‐, 3‐, and 4‐positions yielded compounds with a broad range of binding affinities and isoform selectivities. Several 2,4‐substituted‐3,5,6‐trifluorobenzenesulfonamides were effective CA XIII inhibitors with high selectivity over off‐target CA I and CA II. 3,4‐Disubstituted‐2,5,6‐trifluorobenzenesulfonamides bound CAs with higher affinity than 2,4‐disubstituted‐3,5,6‐trifluorobenzenesulfonamides. Many such fluorinated benzenesulfonamides were found to be nanomolar inhibitors of CA II, CA VII, tumor‐associated CA IX and CA XII, and CA XIII. X‐ray crystal structures of inhibitors bound in the active sites of several CA isoforms provide structure–activity relationship information for inhibitor binding affinities and selectivity.     

De Novo Design,Synthesis and Evaluation of Benzylpiperazine Derivatives as Highly Selective Binders of Mcl‐1

Considerable efforts have been made to the development of small‐molecule inhibitors of antiapoptotic B‐cell lymphoma 2 (Bcl‐2) family proteins (such as Bcl‐2, Bcl‐x_L, and Mcl‐1) as a new class of anticancer therapies. Unlike general inhibitors of the entire family, selective inhibitors of each member protein can hopefully reduce the adverse side effects in chemotherapy treatments of cancers overexpressing different Bcl‐2 family proteins. In this study, we designed four series of benzylpiperazine derivatives as plausible Bcl‐2 inhibitors based on the outcomes of a computational algorithm. A total of 81 compounds were synthesized, and their binding affinities to Bcl‐2, Bcl‐x_L, and Mcl‐1 measured. Encouragingly, 22 compounds exhibited binding affinities in the micromolar range (K_i<20 μM ) to at least one target protein. Moreover, some compounds were observed to be highly selective binders to Mcl‐1 with no detectable binding to Bcl‐2 or Bcl‐x_L, among which the most potent one has a K_i value of 0.18 μM for Mcl‐1. Binding modes of four selected compounds to Mcl‐1 and Bcl‐x_L were derived through molecular docking and molecular dynamics simulations. It seems that the binding affinity and selectivity of these compounds can be reasonably interpreted with these models. Our study demonstrated the possibility for obtaining selective Mcl‐1 inhibitors with relatively simple chemical scaffolds. The active compounds identified by us could be used as lead compounds for developing even more potent selective Mcl‐1 inhibitors with potential pharmaceutical applications.     

Covalent Inhibition of the Lymphoid Tyrosine Phosphatase

Covalent inhibitors of lymphoid tyrosine phosphatase (LYP) were identified from a screen of the NIH Molecular Libraries Small Molecules Repository (MLSMR). Both of the two lead compounds identified have phosphotyrosine‐mimetic benzoic acid moieties as well as electrophilic acrylonitrile groups. Inhibition kinetics of both compounds are consistent with covalent modification of the enzyme, with nanomolar K_I and reciprocal millisecond k_inact values, representing the best efficiency ratios (k_inact/K_I) among currently reported covalent LYP inhibitors. Covalent inhibitors can provide longer efficacy and better selectivity than more conventional noncovalent inhibitors, and these lead compounds are an important step toward the development of protein tyrosine phosphatase (PTP)‐targeted covalent therapeutic compounds.     

Discovery of 3‐Hydroxy‐3‐phenacyloxindole Analogues of Isatin as Potential Monoamine Oxidase Inhibitors

A series of 3‐hydroxy‐3‐phenacyloxindole analogues of isatin were designed, synthesized, and evaluated in vitro for their inhibitory activity toward monoamine oxidase (MAO) A and B. Most of the synthesized compounds proved to be potent and selective inhibitors of MAO‐A rather than MAO‐B. 1‐Benzyl‐3‐hydroxy‐3‐(4′‐hydroxyphenacyl)oxindole (compound 18 ) showed the highest MAO‐A inhibitory activity (IC₅₀: 0.009±0.001 μm , K_i: 3.69±0.003 nm ) and good selectivity (selectivity index: 60.44). Kinetic studies revealed that compounds 18 and 16 (1‐benzyl‐3‐hydroxy‐3‐(4′‐bromophenacyl)oxindole) exhibit competitive inhibition against MAO‐A and MAO‐B, respectively. Structure–activity relationship studies suggested that the 3‐hydroxy group is an essential feature for these analogues to exhibit potent MAO‐A inhibitory activity. Computational studies revealed the possible molecular interactions between the inhibitors and MAO isozymes. The computational data obtained are congruent with experimental results. Further studies on the lead inhibitors, including co‐crystallization of inhibitor–MAO complexes and in vivo evaluations, are essential for their development as potential therapeutic agents for the treatment of MAO‐associated neurological disorders.     

A Second Generation of Carbamate‐Based Fatty Acid Amide Hydrolase Inhibitors with Improved Activity in vivo

The fatty acid ethanolamides are a class of signaling lipids that include agonists at cannabinoid and α type peroxisome proliferator‐activated receptors (PPARα). In the brain, these compounds are primarily hydrolyzed by the intracellular serine enzyme fatty acid amide hydrolase (FAAH). O‐aryl carbamate FAAH inhibitors such as URB597 are being evaluated clinically for the treatment of pain and anxiety, but interactions with carboxylesterases in liver might limit their usefulness. Here we explore two strategies aimed at overcoming this limitation. Lipophilic N‐terminal substitutions, which enhance FAAH recognition, yield potent inhibitors but render such compounds susceptible to attack by broad‐spectrum hydrolases and inactive in vivo. By contrast, polar electron‐donating O‐aryl substituents, which decrease carbamate reactivity, yield compounds, such as URB694, that are highly potent FAAH inhibitors in vivo and less reactive with off‐target carboxylesterases. The results suggest that an approach balancing inhibitor reactivity with target recognition produces FAAH inhibitors that display significantly improved drug‐likeness.     

ω‐Phthalimidoalkyl Aryl Ureas as Potent and Selective Inhibitors of Cholesterol Esterase

Cholesterol esterase (CEase), a serine hydrolase thought to be involved in atherogenesis and thus coronary heart disease, is considered as a target for inhibitor development. We investigated recombinant human and murine CEases with a new fluorometric assay in a structure–activity relationship study of a small library of ω‐phthalimidoalkyl aryl ureas. The urea motif with an attached 3,5‐bis(trifluoromethyl)phenyl group and the aromatic character of the ω‐phthalimide residue were most important for inhibitory activity. In addition, an alkyl chain composed of three or four methylene groups, connecting the urea and phthalimide moieties, was found to be an optimal spacer for inhibitors. The so‐optimized compounds 2 [1‐(3,5‐bis(trifluoromethyl)phenyl)‐3‐(3‐(1,3‐dioxoisoindolin‐2‐yl)propyl)urea] and 21 [1‐(3,5‐bis(trifluoromethyl)phenyl)‐3‐(4‐(1,3‐dioxoisoindolin‐2‐yl)butyl)urea] exhibited dissociation constants (K_i) of 1–19 μm on the two CEases and showed either a competitive ( 2 on the human enzyme and 21 on the murine enzyme) or a noncompetitive mode of inhibition. Two related serine hydrolases—monoacylglycerol lipase and fatty acid amide hydrolase—were inhibited by ω‐phthalimidoalkyl aryl ureas to a lesser extent.