ω-(5-Phenyl-2H-tetrazol-2-yl)alkyl-substituted glycine amides and related compounds as inhibitors of the amine oxidase vascular adhesion protein-1 (VAP-1).

Vascular adhesion protein-1 (VAP-1), also known as plasma amine oxidase or semicarbazide-sensitive amine oxidase, is an enzyme that degrades primary amines to aldehydes with the formation of hydrogen peroxide and ammonia. Among others, it plays a role in inflammatory processes as it can mediate the migration of leukocytes from the blood to the inflamed tissue. We prepared a series of ω-(5-phenyl-2H-tetrazol-2-yl)alkyl-substituted glycine amides and related compounds and tested them for inhibition of purified bovine plasma VAP-1. Compounds with submicromolar activity were obtained. Studies on the mechanism of action revealed that the glycine amides are substrate inhibitors, i.e., they are also converted to an aldehyde derivative. However, the reaction proceeds much more slowly than that of the substrate used in the assay, whose conversion is thus blocked. Examination of the selectivity of the synthesized glycine amides with respect to other amine oxidases showed that they inhibited diamine oxidase, which is structurally related to VAP-1, but only to a much lesser extent. In contrast, the activity of monoamine oxidase A and B was not affected. Selected compounds also inhibited VAP-1 in human plasma. The IC50 values measured were higher than those determined with the bovine enzyme. However, the structure-activity relationships obtained with the glycine amides were similar for both enzymes.

Synthesis, activity and metabolic stability of propan-2-one substituted tetrazolylalkanoic acids as dual inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase.

The serine hydrolases cytosolic phospholipase A2α (cPLA2α) and fatty acid amide hydrolase (FAAH) are interesting targets for the development of new anti-inflammatory and analgesic drugs. Structural modifications of a potent dual inhibitor with a propan-2-one substituted tetrazolylpropionic acid moiety led to compounds with also nanomolar activity against both enzymes but better physicochemical properties. The structure-activity relationships showed that the variations had partially divergent effects on the inhibitory activity of the compounds towards cPLA2α and FAAH reflecting differences in the binding mode to the enzymes. Furthermore, the metabolic stability of the target structures was investigated in vitro.

Synthesis, activity, metabolic stability and cell permeability of new cytosolic phospholipase A2α inhibitors with 1-indolyl-3-phenoxypropan-2-one structure.

Cytosolic phospholipase A2α (cPLA2α), the key enzyme of the arachidonic acid cascade, is considered to be an interesting target for the development of new anti-inflammatory drugs. Potent inhibitors of the enzyme include indole-5-carboxylic acids with propan-2-one residues in position 1 of the indole. Previously, it was found that central pharmacophoric elements of these compounds are their ketone and carboxylic acid groups, which unfortunately are subject to pronounced metabolism by carbonyl reductases and glucuronosyltransferases, respectively. Here we show that the metabolic stability of these inhibitors can be improved by introducing alkyl substituents in the vicinity of the ketone group or by increasing their rigidity. Furthermore, permeability tests with Caco-2 cells revealed that the indole derivatives have only low permeability, which can be attributed to their affinity to efflux transporters. Among other things, the polar ketone group in the center of the molecules seems to be a decisive factor for their reverse transport. After its removal, the permeability increased significantly. The enhancement in metabolic stability and permeability achieved by the structural variations carried out was accompanied by a more or less pronounced decrease in the inhibitory potency of the compounds against cPLA2α.

Synthesis and pharmacokinetic properties of novel cPLA2α inhibitors with 1-(carboxyalkylpyrrolyl)-3-aryloxypropan-2-one structure.

Indole-5-carboxylic acids with 3-aryloxy-2­oxopropyl residues in position 1 have been shown to be potent inhibitors of cytosolic phospholipase A2α (cPLA2α), an enzyme involved in the formation of pro-inflammatory lipid mediators. Unfortunately, in animal experiments, only very low plasma concentrations could be achieved after peroral administration of this type of compound. Since insufficient metabolic stability was suspected as the cause, structural modifications were made to optimize this property. These included the conversion of the aromatic into an aliphatic carboxylic acid function as well as the rigidification of the lipophilic structural elements. A selected pyrrole-3-propionic acid was tested for its peroral in vivo bioavailability in mice. However, higher plasma concentrations could not be achieved also with this compound. Using the Caco2 cell permeation assay, substances investigated were found to be very good substrates for gastrointestinal efflux transporters, which explains their poor peroral absorption.

HPLC fluorescence assay for measuring the activity of diacylglycerol lipases and the action of inhibitors thereof.

1,2-Diacylglycerol lipases (DAGLs) are the most important enzymes for the biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG), and their role in various pathophysiological conditions is currently under investigation. We synthesized a new 1,2-diacylglycerol substrate for these enzymes with a fluorogenic 4-(pyren-1-yl)butanoyl residue in sn-2 position. Using the fluorescent substrate, we measured DAGL activity in rat liver S9 fraction and brain microsomes. To this end, 2-acylglycerol release was directly determined via HPLC and fluorescence detection without further sample clean-up. The method was used to evaluate the action of several known DAGL inhibitors. These showed partly significant differences in their inhibitory effect on DAGLs in liver versus brain preparations. The method was verified by measuring the IC50 values for a subset of inhibitors by HPLC and single-quad MS detection using the deuterated natural DAGL substrate 1-stearoyl-2-arachidonoyl-sn-glycerol-d8. DAGL activity could also be measured with the new pyrene-labeled substrate by HPLC and UV instead of fluorescence detection, if larger quantities of the samples were injected into the HPLC system. Furthermore, using intact human sperm, we show that the substrate is also converted by DAGL enzymes in human cells.

ω-(5-Phenyl-2H-tetrazol-2-yl)alkyl-substituted hydrazides and related compounds as inhibitors of amine oxidase copper containing 3 (AOC3).

Amine oxidase copper containing 3 (AOC3), also known as plasma amine oxidase, semicarbazide-sensitive amine oxidase, or vascular adhesion protein-1, catalyzes the oxidative deamination of primary amines to aldehydes using copper and a quinone as cofactors. Because it is involved in the transmigration of inflammatory cells through blood vessels into tissues, AOC3 is thought to play an important role in inflammatory diseases. Therefore, inhibitors of this enzyme could lead to new therapeutics for the treatment of inflammation-related diseases. Recently, 6-(5-phenyl-2H-tetrazol-2-yl)hexan-1-amine was found to be a tight-binding substrate of AOC3. To obtain novel inhibitors of the enzyme, the amino group of this substrate was replaced with functional groups that occur in known AOC3 inhibitors, such as hydrazide or glycine amide moieties. In addition, derivatives of the compounds obtained in this way were prepared. The obtained hydrazide 5, which proved to be the most effective, was subjected to further structural modifications. Selected hydrazides were evaluated for selectivity toward some other amine oxidases.

Hexafluoroisopropyl Carbamates as Selective MAGL and Dual MAGL/FAAH Inhibitors: Biochemical and Physicochemical Properties.

A series of hexafluoroisopropyl carbamates with indolylalkyl- and azaindolylalkyl-substituents at the carbamate nitrogen was synthesized and evaluated for inhibition of the endocannabinoid degrading enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). The synthesized derivatives with butyl to heptyl spacers between the heteroaryl and the carbamate moiety were inhibitors of both enzymes. For investigated compounds in which the alkyl chain was partially incorporated into a piperidine ring, different results were obtained. Compounds with a methylene spacer between the piperidine ring and the heteroaromatic system were found to be selective MAGL inhibitors, while an extension of the alkyl spacer to two to four atoms resulted in dual inhibition of FAAH/MAGL. The only small change in enzyme inhibitory activity with variation of the heteroaromatic system indicates that the reactive hexafluoroisopropyl carbamate group is mainly responsible for the strength of the inhibitory effect of the compounds. Selected derivatives were also tested for hydrolytic stability in aqueous solution, liver homogenate and blood plasma as well as for aqueous solubility and for permeability in a Caco-2 cell model. Some compounds showed a slightly higher MAGL inhibitory effect than the known selective MAGL inhibitor ABX-1431 and also partly surpassed this substance with regard to certain physicochemical and biochemical properties such as water solubility and cell permeability.

Aryl N-[ω-(6-Fluoroindol-1-yl)alkyl]carbamates as Inhibitors of Fatty Acid Amide Hydrolase, Monoacylglycerol Lipase, and Butyrylcholinesterase: Structure-Activity Relationships and Hydrolytic Stability.

A series of aryl N-[ω-(6-fluoroindol-1-yl)alkyl]carbamates with alkyl spacers of varying lengths between the indole and the carbamate group and with differently substituted aryl moieties at the carbamate oxygen were synthesized and tested for inhibition of the pharmacologically interesting serine hydrolases fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), butyrylcholinesterase (BuChE), and acetylcholinesterase (AChE). Furthermore, the chemical stability in an aqueous solution and the metabolic stability toward esterases in porcine liver homogenate and porcine blood plasma were determined. While most of the synthesized derivatives were potent inhibitors of FAAH, a considerable inhibition of MAGL and BuChE was elicited only by compounds with a high carbamate reactivity, as evidenced by a significant hydrolysis of these compounds in an aqueous solution. However, the high inhibitory potency of some compounds toward MAGL and BuChE, especially that of the ortho-carboxyphenyl derivative 37, could not be explained by chemical reactivity alone. Several of the carbamates studied possessed varying degrees of stability toward esterases from liver and blood plasma. In some cases, marked inactivation by the pseudo-esterase activity of plasma albumin was observed. Mass spectrometric studies showed that such carbamates formed covalent bonds with albumin at several sites.

Tetrazolylpropan-2-ones as inhibitors of fatty acid amide hydrolase: Studies on structure-activity relationships and metabolic stability.

A series of derivatives of 1-(4-octylphenoxy)-3-(2H-tetrazol-2-yl)propan-2-one (3) and 1-(4-octylphenoxy)-3-(1H-tetrazol-1-yl)propan-2-one (4) was synthesized and tested for fatty acid amide hydrolase (FAAH) inhibitory potency and phase I metabolic stability. Introduction of certain substituents like 4-chlorophenyl, 4-methoxycarbonylphenyl and carboxyl in position 5 of the tetrazole ring of 3 led to a significant increase of the metabolic stability of the scissile ketone pharmacophore, while the high activity towards FAAH was not affected markedly. In contrast, substituents in position 5 of the heterocyclic system of 4 did not have a considerable impact on the undesired ketone reduction. Furthermore, the effect of shielding the ketone group of some derivatives of 3 by a methyl substituent in position 3 of the propan-2-one scaffold and the consequences of the replacement of the lipophilic octyl residue of these compounds by more drug-like substituents were examined.

1-Heteroarylpropan-2-ones as inhibitors of fatty acid amide hydrolase: Studies on structure-activity relationships and metabolic stability.

The serine hydrolase fatty acid amide hydrolase (FAAH) catalyzes the degradation of the endocannabinoid anandamide, which possesses analgesic and anti-inflammatory effects. A new series of 1-heteroarylpropan-2-ones was synthesized and evaluated for FAAH inhibition. Structure-activity relationship studies revealed that 1H-benzotriazol-1-yl, 1H-7-azabenzotriazol-1-yl, 1H-tetrazol-1-yl and 2H-tetrazol-2-yl substituents have the highest impact on inhibitory potency. Furthermore, attempts were made to increase the limited metabolic stability of the ketone functionality of these compounds towards metabolic reduction by introduction of shielding alkyl substituents in proximity of this serine reactive group.

Structure-activity relationship studies on 1-(2-oxopropyl)indole-5-carboxylic acids acting as inhibitors of cytosolic phospholipase A2α: Effect of substituents at the indole 3-position on activity, solubility, and metabolic stability.

Cytosolic phospholipase A2α (cPLA2α) is a key enzyme in the biosynthesis of pro-inflammatory lipid mediators and therefore represents an attractive target for the development of new anti-inflammatory drugs. Recently, we have found that 1-[3-(4-octylphenoxy)-2-oxopropyl]indole-5-carboxylic acid (4) is a potent inhibitor of the enzyme. In this work, we evaluate the effect of butanoyl- and hexanoyl-substituents in position 3 of the indole scaffold of this compound bearing terminal groups of varying polarity. As a result, inhibitory potency was not affected considerably in most cases, while metabolic phase I and phase II in vitro stability and aqueous solubility could be influenced and modulated by the structural modifications performed.

(Indolylalkyl)piperidine carbamates as inhibitors of fatty acid amide hydrolase (FAAH).

A series of phenyl 4-[(indol-1-yl)alkyl]piperidine carbamates was synthesized and tested for inhibition of the endocannabinoid degrading enzyme fatty acid amide hydrolase (FAAH) and for metabolic stability in rat liver S9 fractions and porcine blood plasma. Structure-activity relationship studies revealed that variation of the length of the alkyl spacer connecting the indole and the piperidine heterocycle, introduction of substituents into the indole ring, replacement of the piperidine by a piperazine scaffold as well as opening of the piperidine ring system affect activity significantly. The metabolic stability of this compound class proved to be significantly higher than that of corresponding phenyl N-(indol-1-ylalkyl)carbamates.

1-(5-Carboxyindazol-1-yl)propan-2-ones as dual inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase: bioisosteric replacement of the carboxylic acid moiety.

Indazole-5-carboxylic acids with 3-aryloxy-2-oxopropyl residues in position 1 were previously reported to be potent dual inhibitors of cytosolic phospholipase A2α (cPLA2α) and fatty acid amide hydrolase (FAAH). In continuation of our structure-activity studies on cPLA2α and FAAH inhibitors, a number of derivatives of these substances characterized by bioisosteric replacement of the carboxylic acid functionality by inverse amides, sulfonylamides, carbamates and ureas were prepared. The biological evaluation of the obtained compounds showed that the carboxylic acid functionality of the lead compounds is of special importance for a pronounced inhibition of cPLA2α and FAAH.

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.

Structure-activity relationship studies on 1-heteroaryl-3-phenoxypropan-2-ones acting as inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase: replacement of the activated ketone group by other serine traps.

Cytosolic phospholipase A2α (cPLA2α) and fatty acid amide hydrolase (FAAH) are serine hydrolases. cPLA2α is involved in the generation of pro-inflammatory lipid mediators, FAAH terminates the anti-inflammatory effects of endocannabinoids. Therefore, inhibitors of these enzymes may represent new drug candidates for the treatment of inflammation. We have reported that certain 1-heteroarylpropan-2-ones are potent inhibitors of cPLA2α and FAAH. The serine reactive ketone group of these compounds, which is crucial for enzyme inhibition, is readily metabolized resulting in inactive alcohol derivatives. In order to obtain metabolically more stable inhibitors, we replaced this moiety by α-ketoheterocyle, cyanamide and nitrile serine traps. Investigations on activity and metabolic stability of these substances revealed that in all cases an increased metabolic stability was accompanied by a loss of inhibitory potency against cPLA2α and FAAH, respectively.

1-Heteroaryl-3-phenoxypropan-2-ones as inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase: Effect of the replacement of the ether oxygen with sulfur and nitrogen moieties on enzyme inhibition and metabolic stability.

Cytosolic phospholipase A2α (cPLA2α) and fatty acid amide hydrolase (FAAH) are enzymes, which have emerged as attractive targets for the development of analgesic and anti-inflammatory drugs. We recently reported that certain 3-phenoxy-substituted 1-heteroarylpropan-2-ones are inhibitors of cPLA2α and/or FAAH. Starting from 1-[2-oxo-3-(4-phenoxyphenoxy)propyl]indole-5-carboxylic acid (3) and 1-(1H-benzotriazol-1-yl)-3-(4-phenoxyphenoxy)propan-2-one (4), the effect of the replacement of the oxygen in position 3 of the propan-2-one scaffold by sulfur and nitrogen containing moieties on inhibition of cPLA2α and fatty acid amide hydrolase as well as on metabolic stability in rat liver S9 fractions was investigated. As a result of these structure-activity relationship studies it was found that the ether oxygen is of great importance for enzyme inhibitory potency. Replacement by sulfur led to an about 100-fold decrease of enzyme inhibition, nitrogen and substituted nitrogen atoms at this position even resulted in inactivity of the compounds. The effect of the structural variations performed on metabolic stability of the important ketone pharmacophore was partly different in the two series of compounds. While introduction of SO and SO2 significantly increased stability of the ketone against reduction in case of the indole-5-carboxylic acid 3, it had no effect in case of the benzotriazole 4. Further analysis of the metabolism of 3 and 4 in rat liver S9 fractions revealed that the major metabolite of 3 was the alcohol 53 formed by reduction of the keto group. In contrast, in case of 4 beside keto reduction an excessive hydroxylation of the terminal phenoxy group occurred leading to the dihydroxy compound 50. Experiments with enzyme inhibitors showed that the phenylhydroxylation of 4 was catalyzed by tranylcypromine sensitive cytochrome P450 isoforms, while the reduction of the ketone function of 3 and 4 was mainly caused by cytosolic short chain dehydrogenases/reductases (cSDR).

Involvement of microsomal NADPH-cytochrome P450 reductase in metabolic reduction of drug ketones.

Recently, it was found that the carbonyl group of 1-[3-(4-phenoxyphenoxy)-2-oxopropyl]indole-5-carboxylic acid (5), an inhibitor of the pro-inflammatory enzyme cytosolic phospholipase A2 α, is easily reduced by rat liver S9 fractions in vitro. Determination of the inhibitory potency of certain putative inhibitors of carbonyl reducing enzymes on the transformation of the ketone derivative 5 to its alcohol 6 by recombinant microsomal NADPH-cytochrome P450 reductase and by recombinant cytosolic carbonyl reductase-1 now reveals that these compounds show a lack of specificity for these two enzymes in part. Thus, an assignment of the roles of different carbonyl reductases in metabolic keto reduction by the use of inhibitors is problematic. In addition, the ability of NADPH-cytochrome P450 reductase and carbonyl reductase-1 to reduce the ketone groups of the drugs haloperidol and daunorubicin was examined. Under the conditions applied, a pronounced reductive metabolism was only observed for daunorubicin in the presence of microsomal NADPH-cytochrome P450 reductase. Similarly, in rat liver S9 fractions a marked reduction of daunorubicin was seen, while haloperidol was only slightly metabolized to its alcohol. After separation of the S9 homogenate into a microsomal and a cytosolic fraction, it became evident that the ketone groups of daunorubicin, haloperidol and compound 5 were mainly reduced by cytosolic enzymes. However, since microsomes also catalysed these carbonyl reductions to some extent, it can be concluded that microsomal NADPH-cytochrome P450 reductase can contribute to metabolic keto reductions in xenobiotics. Copyright © 2015 John Wiley & Sons, Ltd.

Convergent and enantioselective syntheses of cytosolic phospholipase A(2)α inhibiting N-(1-indazol-1-ylpropan-2-yl)carbamates.

Cytosolic phospholipase A2α (cPLA2α) is an important enzyme of the inflammation cascade. Therefore, inhibitors of cPLA2α are assumed to be promising drug candidates for the treatment of inflammatory disorders. Recently we have found that indole-5-carboxylic acid with a 3-(4-octylphenoxy)-2-(phenoxycarbonylamino)propyl substituent in position 1 is an inhibitor of cPLA2α. We have now synthesized a corresponding derivative with the indole heterocycle replaced by an indazole (4) employing an analogous reaction sequence as for the synthesis of the indole derivative. Besides, a more convergent synthesis for 4 was established using an aziridine as central intermediate. Furthermore, a chiral-pool based enantioselective synthesis was developed for the synthesis of (R)- and (S)-4. Starting compound for both enantiomers was the (R)-serine derived oxazolidine (R)-25. Compound 4 proved to be a moderate inhibitor of cPLA2α, with the S-enantiomer being twice as active as the R-enantiomer. The racemate 4 and the enantiomers (R)- and (S)-4 showed a high in vitro metabolic stability in rat liver S9 fractions.

Investigations on the metabolic stability of cytosolic phospholipase A2α inhibitors with 1-indolylpropan-2-one structure.

Cytosolic phospholipase A2α (cPLA2α) plays a key role in the pathogenesis of many inflammatory diseases, such as rheumatoid arthritis, atopic dermatitis and Alzheimer's disease. Therefore, inhibition of this enzyme is assumed to provide a novel therapeutic option for the treatment of these maladies. In this study we investigated the metabolism of the potent cPLA2α inhibitors 1-[3-(4-phenoxyphenoxy)-2-oxopropyl]indole-5-carboxylic acid (1) and 3-isobutanoyl-1-[3-(4-phenoxyphenoxy)-2-oxopropyl]indole-5-carboxylic acid (2). Incubation of 1 with a mixture of human recombinant CYP1A2, 2C8, 2C9, 2C19, 2D6, 3A4 and NADPH-cytochrome P450 reductase enzymes led to reduction of its keto group and to hydroxylation at the terminal phenoxy residue. To identify the enzymes responsible for the observed reactions, experiments with isoform inhibitors were performed. In rat liver S9 fractions the only metabolite found was the alcohol 3 formed by the reduction of the keto group of 1. This reaction here was mainly catalyzed by cytosolic short-chain dehydrogenases/reductases (cSDR) as shown by inhibition experiments with different carbonyl reductase inhibitors. Furthermore, the metabolic stability of 2 in mouse brains was studied after intracerebroventricular application of this compound into the right brain hemispheres of mice. HPLC/MS analyses revealed that 2 is also readily reduced in the brain to an inactive alcohol metabolite most likely by carbonyl reductases.

(4-Phenoxyphenyl)tetrazolecarboxamides and related compounds as dual inhibitors of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL).

Inhibitors of the enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), the principle enzymes involved in the degradation of endogenous cannabinoids like anandamide and 2-arachidonoylglycerol, have potential utility in the treatment of several disorders including pain, inflammation and anxiety. In the present study, the effectivity and selectivity of eight known FAAH and MAGL inhibitors for inhibition of the appropriate enzyme were measured applying in vitro assays, which work under comparable conditions. Because many of the known FAAH and MAGL inhibitors simply consist of a lipophilic scaffold to which a heterocyclic system is bound, furthermore, different heterocyclic structures were evaluated for their contribution to enzyme inhibition by attaching them to the same lipophilic backbone, namely 4-phenoxybenzene. One of the most active compound synthesized during this investigation was N,N-dimethyl-5-(4-phenoxyphenyl)-2H-tetrazole-2-carboxamide (16) (IC50 FAAH: 0.012 µM; IC50 MAGL: 0.028 µM). This inhibitor was systematically modified in the lipophilic 4-phenoxyphenyl region. Structure-activity relationship studies revealed that the inhibitory potency against FAAH and MAGL, respectively, could still be increased by replacement of the phenoxy residue of 16 by 3-chlorophenoxy (45) or pyrrol-1-yl groups (49). Finally, the tetrazolecarboxamide 16 and some related compounds were tested for metabolic stability with rat liver S9 fractions showing that these kind of FAAH/MAGL inhibitors are readily inactivated by cleavage of the bond between the tetrazole ring and its carboxamide substituent.