Nonsteroidal Antiinflammatory Agents,XVIII: C-5 Functionalized 6,7-Diphenyl-2,3-dihydro-1H-pyrrolizines as Inhibitors of Bovine Cyclooxygenase and 5-Lipoxygenase

6-(4-Chlorophenyl)-7-phenyl-2,3-dihydro-1H-pyrrolizines with functional groups at position 5 of the heterocyclic moiety were synthesized and tested. To determine their antiinflammatory activity bovine blood was used as enzyme source for the cyclooxygenase and 5-lipoxygenase, respectively. The iminoxy acetic acid derivative and the iminotetrazole selectively inhibit the 5-lipoxygenase, all the other compounds show medium or low affinity to the active sites of cyclooxygenase and 5-lipoxygenase. In general all compounds inhibit 5-lipoxygenase more effectively than cyclooxygenase. Concerning the inhibition of 5-lipoxygenase the most active compounds found are equipotent to the corresponding propionic acid compounds, but they aren't well balanced dual inhibitors as shown for the carboxylic derivatives. A structure activity relationship and the enzyme selectivity are discussed.     

Nonsteriodal Antiinflammatory Agents,XVII: Inhibition of Bovine Cyclooxygenase and 5-Lipoxygenase by N-Alkyldiphenyl-pyrrolyl Acetic and Propionic Acid Derivatives

A series of 19 N-alkyl-diarylpyrrolyl-acetic and -propionic acid derivatives was synthesized and tested. Using bovine blood as enzyme source the inhibition of cyclooxygenase and 5-lipoxygenase, respectively, was applied to determine the antiinflammatory activity. In general all compounds tested inhibit 5-lipoxygenase more effectively than cyclooxygenase. A structure-activity relationship is discussed.     

Differential effects of a series of hydroxamic acid derivatives on 5-lipoxygenase and cyclooxygenase from neutrophils and 12-lipoxygenase from platelets and their in vivo effects on inflammation and anaphylaxis

The synthesis of a series of novel substituted hydroxamates has been described along with their profile of inhibitory activity against 5-lipoxygenase, 12-lipoxygenase, and cyclooxygenase enzymes. The structure--activity relationship suggests that future molecules could be designed to specifically inhibit one or more of these enzymes since there were definite differences in structure--activity relationships for these different enzymes. A representative number of these compounds have been tested in vivo and found to possess potent oral activity in a systemic anaphylaxis model mediated by leukotrienes and topical activity in an arachidonic acid induced inflammation model. One of these molecules, compound 20, demonstrated that a leukotriene antagonist pharmacophore can be modified such that it contains both antagonist activity and 5-lipoxygenase inhibitory activity.     

Novel 10-substituted antipsoriatic anthrones as inhibitors of epidermal 12-lipoxygenase and lipid peroxidation in membranes

The ability of novel 10-substituted anthrones to inhibit 12-lipoxygenase (12-LO) in mouse epidermal homogenate and lipid peroxidation in both bovine brain phospholipid liposomes and erythrocyte ghosts was investigated, and compared with their ability to inhibit 5-lipoxygenase (5-LO) in bovine leukocytes. The compounds were fairly potent inhibitors of epidermal 12-LO, in addition to their strong inhibitory effects against leukocyte 5-LO. Although the antipsoriatic drug, anthralin, predominantly inhibited epidermal 12-LO, the novel derivatives were more selective 5-LO inhibitors. Compounds with free phenolic groups in the attached aromatic ring were also potent inhibitors of nonenzymatic lipid peroxidation in both sources of lipid substrate. This property was not correlated with their ability to inhibit the 5- and 12-LO pathways, suggesting that their mechanism of 5-/12-LO inhibition is not simply due to scavenging of peroxyl radicals generated at the active site of the enzymes. The compounds are dual-purpose inhibitors and may play a protective role against oxidative damage to psoriatic skin, in addition to their antiinflammatory 5-LO and 12-LO inhibitory properties.     

New Pyrazolylhydrazone Derivatives as Inhibitors of Platelet Aggregation

Abstract— A series of 5-pyrazolylhydrazone derivatives was designed to be mixed hybrid isosteres of both BW755C and CBS-1108, which belong to the class of dual cyclo-oxygenase and 5-lipoxygenase inhibitors. Some derivatives of this series inhibit the in-vitro platelet aggregation of citrated platelet-rich rabbit plasma induced by ADP (5 μm ), collagen (5 μg mL^?1) and arachidonic acid (100 μm ). The structure-activity relationships of this class of compounds were determined from these results. When ADP is used as the aggregation inducer, the presence of free oxygenated substituents at the p-position in the phenyl subunit of the hydrazone moiety favours inhibitory activity; p-methoxyformylbenzene-5-(1-phenyl-3-methyl-4-nitropyrazolyl)hydrazone (100 μm ), which has a methoxy group at this position was the most active with 62·8% inhibition of aggregation. In contrast, substitution in the aryl ring does not affect the aggregation induced by collagen, whereas the non-substituted compound, formylbenzene-5-(1-phenyl-3-methyl-4-nitropyrazolyl)hydrazone, showed similar activity to those of substituted derivatives. In the arachidonic acid assays, the presence of an aryl ring linked to the hydrazone moiety, with an adequate electronic density at the ring due to the nature of its substitutents, is an important structural requirement for inhibitory activity.     

Dual inhibitors of thromboxane A2 synthase and 5-lipoxygenase with scavenging activity of active oxygen species. Synthesis of a novel series of (3-pyridylmethyl)benzoquinone derivatives

A novel series of (3-pyridylmethyl)benzoquinone derivatives was molecular designed and synthesized for the dual purpose of inhibiting thromboxane A2 and leukotriene biosynthesis enzymes and scavenging active oxygen species (AOS). They were evaluated for inhibition of TXA2 synthase, inhibition of 5-lipoxygenase, and for their scavenging activity of AOS using the thiobarbituric acid method. 2,3,5-Trimethyl-6-(3-pyridylmethyl)-1,4-benzoquinone (24, CV-6504) was the most promising derivative since it showed efficient AOS scavenging activity (inhibition of lipid peroxidation in rat brain homogenates: IC50 = 1.8 x 10(-6) M) as well as potent, specific, and well-balanced inhibitory effects on both enzymes (inhibitory effect on TXA2 synthase in human blood, IC50 = 3.3 x 10(-7) M; inhibitory effect on 5-lipoxygenase in human blood, IC50 = 3.6 x 10(-7) M). In adriamycin-induced proteinuria in a rat model, compound 24 at 10 mg/kg per day (po) suppressed proteinuria by more than 50%. The proteinuria, however, could not be reduced by single administration of an inhibitor specific for thromboxane A2 synthase [(E)-7-phenyl-7-(3-pyridyl)-6-heptenoic acid (2, CV-4151)] or for 5-lipoxygenase [2-(12-hydroxy-5,10-dodecadiynyl)-3,5,6-trimethyl-1,4-benzoquinone (1, AA-861)]. The proteinuria was also not reduced by administration of an AOS scavenger, 2-O-octadecylascorbic acid (4, CV-3611). Triple function compounds such as compound 24 that specifically inhibit both enzymes as well as scavenge AOS possess a variety of pharmacologically beneficial effects.     

Inhibition of cyclooxygenase/lipoxygenase from human platelets by polyhydroxylated/methoxylated flavonoids isolated from medicinal plants

Various flavonoid derivatives were previously reported to possess the inhibitory activity on cyclooxygenase/lipoxygenase. And these properties of flavonoids might contribute to their anti-inflammatory activity in vivo. In this study, several polyhydroxylated/methoxylated flavonoid derivatives such as oroxylin A, wogonin, skullcapflavone II, tectorigenin and iristectorigenin A were isolated from the medicinal plants. These compounds were evaluated for their inhibitory effects on cyclooxygenase/lipoxygenase from the homogenate of human platelets in vitro. It was found that isoflavones including daidzein and tectorigenin possessed the inhibitory activity on cyclooxygenase, although the potency of inhibition was far less than that of indomethacin. In addition, oroxylin A, baicalein and wogonin inhibited 12-lipoxygenase activity without affecting cyclooxygenase, which suggested that 5,6,7- or 5,7,8-trisubstitutions of A-ring of flavone gave favorable results. The IC50 values of oroxylin A and NDGA against 12-lipoxygenase were found to be 100 and 1.5 microM, respectively.     

Benzothiazole hydroxy ureas as inhibitors of 5-lipoxygenase: use of the hydroxyurea moiety as a replacement for hydroxamic acid.

A novel series of N-[(2-benzothiazolylthio)alkyl]-N'-hydroxyurea derivatives (9-25) was synthesized and evaluated for biological activity as inhibitors of 5-lipoxygenase both in vivo (mouse zymosan peritonitis assay) and in vitro (Ca2+ ionophore-stimulated human peripheral blood leukocyte model). The compounds of this series were based on the corresponding hydroxamic acid derivatives (1, 3, 4, and 5) which were moderately active in vitro but inactive in vivo. A number of compounds in the hydroxyurea series exhibited oral activity for 5-lipoxygenase inhibition. Results of studies relating structure to in vivo and in vitro 5-lipoxygenase activity are reported.     

Design and synthesis of novel 2-amino-5-hydroxyindole derivatives that inhibit human 5-lipoxygenase

Compounds that inhibit 5-lipoxygenase (5-LO), the key enzyme in the biosynthesis of leukotrienes (LTs), possess potential for the treatment of inflammatory and allergic diseases as well as of atherosclerosis and cancer. Here we present the design and the synthesis of a series of novel 2-amino-5-hydroxyindoles that potently inhibit isolated human recombinant 5-LO as well as 5-LO in polymorphonuclear leukocytes, exemplified by ethyl 2-[(3-chlorophenyl)amino]-5-hydroxy-1H-indole-3-carboxylate (3n, IC(50) value congruent with 300 nM). Introduction of an aryl/arylethylamino group or 4-arylpiperazin-1-yl residues into position 2 of the 5-hydroxyindoles was essential for biological activity. Whereas the 4-arylpiperazin-1-yl derivatives were more potent in cell-free assays as compared to intact cell test systems, aryl/arylethylamino derivatives inhibited 5-LO activity in intact cells and cell-free assays almost equally well. On the basis of their 5-LO inhibitory properties, these novel 2-amino-5-hydroxyindoles represent potential candidates for the pharmacological intervention with LT-associated diseases.     

New Class of 5-Lipoxygenase Inhibitors: Correlation Between Inhibition of LTB4 Production and Chemiluminescence of Human Polymorphonuclear Granulocytes

The effect of several series of compounds on the biosynthesis of leukotriene B₄ in human polymorphonuclear granulocytes (PMNL) was measured after stimulation of the cells by the Ca²⁺ ionophore A23187. Phenylhydrazone derivatives and some pyrrole derivatives strongly inhibited 5-lipoxygenase activity at 10 µM. In contrast, 4-aminopyrrolopyrimidines and 4-oxopyrrolopyrimidmes did not exhibit any effect. The compounds examined for inhibition of 5-lipoxygenase were also tested in a chemiluminescence assay for potential effects on the emission of photons as a measure of activated oxygen species generated by the stimulated granulocytes. There was a good correlation between lipoxygenase inhibition and suppression of chemiluminescence; however, some derivatives with no inhibitory activity against lipoxygenase still reduced chemiluminescence, which suggests that an alternative inhibitory mechanism of chemiluminescence must be present. Cyclooxygenase inhibitors such as aspirin did not suppress chemiluminescence of granulocytes. It is, therefore, unlikely that cyclooxygenase is required in the chemiluminescence reaction. In contrast, LTB₄ seems to play an important role in the zymosan-induced chemiluminescence of PMNL.     

Regulation of leukocyte and platelet lipoxygenases by hydroxyeicosanoids

During allergic and inflammatory reactions, arachidonic acid is oxidized by lipoxygenases to a variety of biologically active products, including leukotrienes. The mechanisms for regulation of the different lipoxygenase activities are not well defined. We report here that [14C]arachidonic acid metabolism by the 5- and 15-lipoxygenase activities in rabbit leukocytes and the 12-lipoxygenase in rabbit platelets is inhibited by various hydroxyeicosatetraenoic acids (HETEs). 15-HETE was the most effective inhibitor of the 5- and 12-lipoxygenases, whereas similar inhibitory potencies were observed for 5-HETE and 12-HETE acting on the 15-lipoxygenase. These three enzyme pathways were all least sensitive to their own products HETEs. To determine which structural characteristics of 15-HETE are essential for inhibition of the 5-lipoxygenase, various derivatives were prepared and purified by high pressure liquid chromatography, and their structures were confirmed by gas chromatography-mass spectrometry. The inhibitory potencies of 15-HETE analogs with different degrees of unsaturation were in the order of three double bonds greater than 4 greater than 2 greater than 0. 15-Hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) was four times more potent than 15-HETE. The 15-acetoxy, 15-keto and methyl ester derivatives were of comparable activity to 15-HETE, and the 15-acetoxy methyl ester derivative was less potent. Based upon the observed patterns of inhibition, we postulate that complex interregulatory relationships exist between the various lipoxygenases, and that cells containing these lipoxygenases may interact with each other via their lipoxygenase metabolites.     

Structure-activity analysis of a class of orally active hydroxamic acid inhibitors of leukotriene biosynthesis

The nature of the carbonyl and nitrogen substituents of hydroxamic acids has a major influence on the biological profile of these compounds. Hydroxamates with small groups such as methyl appended to the carbonyl and relatively large nitrogen substituents generally have longer duration in vivo, produce greater plasma concentrations, and often are more potent inhibitors of in vivo leukotriene biosynthesis than hydroxamic acids with the opposite arrangement. The structure-activity relationships that describe in vitro 5-lipoxygenase inhibitory activity and in vivo leukotriene biosynthesis inhibitory potency for a group of these hydroxamic acids were investigated. While most of the compounds examined were potent in vitro inhibitors of 5-lipoxygenase, their in vivo potencies varied widely. This discrepancy was usually attributable to differences in bioavailability. Substitution patterns are described that produce potent, orally active inhibitors of leukotriene biosynthesis.     

2-aminoethoxydiphenyl borate as a prototype drug for a group of structurally related calcium channel blockers in human platelets

We have synthesized a series of 2-aminoethoxydiphenyl borate (2-APB, 2,2-diphenyl-1,3,2-oxazaborolidine) analogs and tested their ability to inhibit thrombin-induced Ca(2+) influx in human platelets. The analogs were either synthesized by adding various substituents to the oxazaborolidine ring (methyl, dimethyl, tert-butyl, phenyl, methyl phenyl, and pyridyl) or increasing the size of the oxazaborolidine ring to seven- and nine-membered rings. NMR analysis of the boron-containing analogs suggests that each of them exist as a ring structure through the formation of an N-->B coordinate bond (except for the hexyl analog). The possibility that these boron-containing compounds formed dimers was also considered. All compounds dose-dependently inhibited thrombin-induced Ca(2+) influx in human platelets, with the 2,2-diphenyl-1,3,2-oxazaborolidine-5-one derivative having the weakest activity at 100 microM, whereas the (S)-4-benzyl and (R)-4-benzyl derivatives of 2-APB were approximately 10 times more potent than the parent 2-APB. Two nonboron analogs (3-methyl and 3-tert-butyl 2,2-diphenyl-1,3-oxazolidine) were synthesized; they had approximately the same activity as 2-APB, and this implies that the presence of boron was not necessary for inhibitory activity. All of the compounds tested were also able to inhibit thrombin-induced calcium release. We concluded that extensive modifications of the oxazaborolidine ring in 2-APB can be made, and Ca(2+)-blocking activity was maintained.     

Structural optimization and biological evaluation of 1,5-disubstituted pyrazole-3-carboxamines as potent inhibitors of human 5-lipoxygenase

Human 5-lipoxygenase (5-LOX) is a well-validated drug target and its inhibitors are potential drugs for treating leukotriene-related disorders. Our previous work on structural optimization of the hit compound 2 from our in-house collection identified two lead compounds, 3a and 3b, exhibiting a potent inhibitory profile against 5-LOX with IC₅₀ values less than 1 µmol/L in cell-based assays. Here, we further optimized these compounds to prepare a class of novel pyrazole derivatives by opening the fused-ring system. Several new compounds exhibited more potent inhibitory activity than the lead compounds against 5-LOX. In particular, compound 4e not only suppressed lipopolysaccharide-induced inflammation in brain inflammatory cells and protected neurons from oxidative toxicity, but also significantly decreased infarct damage in a mouse model of cerebral ischemia. Molecular docking analysis further confirmed the consistency of our theoretical results and experimental data. In conclusion, the excellent in vitro and in vivo inhibitory activities of these compounds against 5-LOX suggested that these novel chemical structures have a promising therapeutic potential to treat leukotriene-related disorders.KEY WORDS: 5-Lipoxygenase, 5-LOX inhibitors, Pyrazole derivatives, Leukotrienes-related diseases, In vivo, Benzo-fused heterocycle, Ischemic incults, Brain inflammation     

4-hydroxythiazole inhibitors of 5-lipoxygenase

4-Hydroxythiazoles have been identified as potent inhibitors of 5-lipoxygenase in vitro exhibiting IC50's of less than 1 microM. An investigation of structure-activity relationships showed that the most potent inhibitors of this series are the 5-phenyl derivatives. The corresponding thiazolidin-4-one analogues were found to be relatively inactive. The 4-hydroxythiazoles were active inhibitors against 5-lipoxygenase in both intact rat polymorphonuclear leukocytes and human whole blood. The compounds were also selective inhibitors of 5-lipoxygenase, displaying only weak activity against other related enzymes, cyclooxygenase and 12- and 15-lipoxygenase.     

New inhibitors of aromatase: synthesis and biological activity of pyridyl-substituted phenanthrenone derivatives]

The phenanthrenone derivatives 3-6 were synthesized and tested for their aromatase and desmolase inhibitory potency. Compounds 5 and 6 show a stronger inhibition of aromatase than aminoglutethimide not exceeding, however, the activity of the parent compounds 1 and 2. Compounds 4 and 5 do not inhibit desmolase.     

Synthesis and evaluation of chromone-2-carboxamide derivatives as cytotoxic agents and 5-lipoxygenase inhibitors

In the present study, we prepared a series of 21 chromone carboxamide derivatives bearing diverse amide side chains. Their potency to inhibit the proliferation of breast (MCF-7), ovarian (OVCAR and IGROV), and colon (HCT-116) cancer cell lines, was evaluated in vitro using the MTT assay. Among these compounds, 13 showed promising cytotoxic activity against at least one cancer cell line with IC₅₀ in the range 0.9–10?μM. Our compounds were also screened for their anti-inflammatory activity as putative inhibitors of 5-lipoxygenase.Structure-activity relationships studies on our chromone carboxamide derivatives revealed that the presence of a 6-fluoro substituent on the chromone nucleus (R₁) or propyl and 3-ethylphenyl groups on the amide side chain (R₂) has a positive impact on the cytotoxic activity. In terms of the anti-inflammatory activity, hydrophilic chromone carboxamide derivatives showed greater 5-lipoxygenase inhibition.The physico-chemical properties of chromone carboxamides are in accordance with the general requirements of drug development process and ligand efficiency values allow further structure optimization, with compound 4b as a lead.     

A new phenolic fatty acid ester with lipoxygenase inhibitory activity from Jacaranda filicifolia.

The dichloromethane extract of the stem of jacaranda filicifolia Don. showed inhibitory activity in vitro against soybean 5-lipoxygenase. Systematic fractionation to isolate the compounds responsible resulted in the isolation of three active compounds, 2 alpha, 3 alpha-dihydroxyurs-12-en-28-oic acid, beta-sitosterol, and one of which was new which was characterised as 2-(4-hydroxyphenyl)ethyl 1-dodecyloctadecanoate. This type of compound has not previously been reported to inhibit lipoxygenase.     

Synthesis and biological evaluation of pyrazolone analogues as potential anti-inflammatory agents targeting cyclooxygenases and 5-lipoxygenase

New pyrazolone derivatives structurally related to celecoxib and FPL 62064 were synthesized and biologically evaluated for their inhibitory activity against cyclooxygenases (COXs) and 5-lipoxygenase (5-LOX) and their selectivity indices were calculated. The results showed that compounds 3f , 3h , 3l , and 3p have an excellent COX-2 selectivity index. Moreover, they showed potent 5-LOX inhibitory activity relative to celecoxib and zileuton, as positive controls. These promising candidates were further investigated for anti-inflammatory activity using the carrageenan-induced rat paw edema method and ulcerogenic liability. The results showed no ulceration, which implies their gastric safety profile. Moreover, these compounds were evaluated for prostaglandin (PGE2) production in rat serum. Molecular docking in the COX-2 and 5-LOX active sites was performed to rationalize their anti-inflammatory activities. Strong binding interactions and effective docking scores were identified. The results indicated that these derivatives are good leads for dual-acting COX-2/5-LOX inhibitors to be used as potent and safe anti-inflammatory agents.     

Selectivity of neutrophil 5-lipoxygenase and cyclo-oxygenase inhibition by an anti-inflammatory flavonoid glycoside and related aglycone flavonoids

A newly described plant-derived flavonoid, hypolaetin-8-glucoside, which has anti-inflammatory and gastroprotective actions in-vivo, and its corresponding aglycone, hypolaetin, have been compared with 14 other flavonoids for inhibition of eicosanoid generation via the 5-lipoxygenase and cyclo-oxygenase pathways in elicited rat peritoneal leukocytes stimulated with calcium ionophore. Comparable results for the inhibitory profiles of the compounds were obtained using either radioimmunoassay of released eicosanoids or radio-TLC of metabolites formed from labelled arachidonate, but there were differences in absolute potency of the inhibitors. Hypolaetin-8-glucoside was a weak but selective inhibitor of 5-lipoxygenase (IC50 56 microM vs 5-lipoxygenase; greater than 1000 microM vs cyclo-oxygenase), whereas the aglycone hypolaetin was a more potent and selective 5-lipoxygenase inhibitor (IC50 4.5 microM vs 70 microM). Results with three other glycoside/aglycone pairs confirmed that addition of sugar residues greatly reduces inhibitory potency whilst retaining selectivity against 5-lipoxygenase. Analysis of 12 aglycone flavonoids showed that inhibitory potency and selectivity against 5-lipoxygenase is conferred by the presence of 3'4'-vicinal diol (catechol) in ring B as part of a 3,4-dihydroxycinnamoyl structure as proposed by others and by incorporation of additional hydroxyl substituents. In contrast, "cross-over" of inhibitory selectivity is observed in compounds containing few hydroxyl substituents (with none in ring B) which are selective against cyclo-oxygenase. These results are discussed in relation to possible mechanisms of hypolaetin-8-glucoside's protective actions and the concept that these inhibitory effects of flavonoids cannot be ascribed to a unitary free radical scavenging action.