Benzylamine antioxidants: relationship between structure, peroxyl radical scavenging, lipid peroxidation inhibition, and cytoprotection.

Three homologous series of 3,5-dialkoxy-4-hydroxybenzylamines were prepared and tested (1) as peroxyl radical scavengers in homogeneous aqueous solution, (2) as inhibitors of iron-dependent peroxidation of rabbit brain vesicular membrane lipids, and (3) as cytoprotective agents using primary cultures of rat hippocampal neurons exposed to hydrogen peroxide. The structural requirements for efficient radical trapping in homogeneous solution differed from those for effective lipid peroxidation inhibition: In homogeneous solution a kinetic preference existed for smaller, less sterically encumbered substituents flanking the reactive phenolic hydroxyl group. Lipid peroxidation inhibition, on the other hand, required longer more lipophilic substituents. Consequently, a lipophilic alkoxyl substituent at C3 and a small substituent at C5 appeared optimal for efficient radical scavenging activity in both lipid and homogeneous solution. Maximal cytoprotection of rat hippocampal neurons exposed to hydrogen peroxide was also associated with more lipophilic derivatives although substituent length and substituent bulk may represent independent parameters for relating structure and efficacy in this system.

Phenothiazines as lipid peroxidation inhibitors and cytoprotective agents.

A series of phenothiazines was synthesized and evaluated as in vitro inhibitors of iron-dependent lipid peroxidation. The MIC (minimum tested concentration that gave greater than or equal to 50% inhibition) for 2-(10H-phenothiazin-2-yloxy)-N,N-dimethylethanolamine methanesulfonate (6) was 0.26 microM. Whereas methyl substitution at N-10 diminished activity nearly 100-fold, other structural modifications such as varying the amine group, the distance separating the amine substituent from the phenothiazine nucleus, and the linking group had little effect. Compound 6 was more effective than probucol, a known antioxidant, in blocking Cu2+ catalyzed oxidation of low-density lipoprotein (LDL) as measured by competitive scavenger receptor mediated degradation of 125I-labeled acetyl-LDL by mouse peritoneal macrophage cells in vitro. At a concentration of 5 microM, compound 6 also protected primary cultures of rat hippocampal neurons exposed to hydrogen peroxide (50 microM) when assessed 18 h later by fluorescein diacetate and propidium iodide uptake.

N(2)-Aroylanthranilamide inhibitors of human factor Xa.

Reversal of the A-ring amide link in 1,2-dibenzamidobenzene 1 (fXa K(ass) = 0.81 x 10(6) L/mol) led to a series of human factor Xa (hfXa) inhibitors based on N(2)-aroylanthranilamide 4. Expansion of the SAR around 4 showed that only small planar substituents could be accommodated in the A-ring for binding to the S1 site of hfXa. Bulky groups such as 4-isopropyl, 4-tert-butyl, and 4-dimethylamino were favored in the B-ring to interact with the S4 site of hfXa. The central (C) ring containing a 5-methanesulfonamido group yielded greater activity than carbamoyl groups. Combining the beneficial features from the B- and C-ring SAR, compound 55 represents the most potent hfXa inhibitor in the N(2)-aroylanthranilamide 4 series with hfXa K(ass) = 58 x 10(6) L/mol (K(i) = 11.5 nM).

Fused bicyclic Gly-Asp beta-turn mimics with specific affinity for GPIIb-IIIa.

Disubstituted isoquinolones 2 and 3 have affinity for GPIIb-IIIa and represent leads for further structural evaluation. Structure-activity studies centered on the bicyclic beta-turn mimic contained in these molecules indicated that this moiety could accommodate a variety of modifications. Specifically, monocyclic, 6, 5-bicyclic, and 6,7-bicyclic structures provide compounds with affinity for GPIIb-IIIa. Within the 6,6-series, isoquinoline, tetralin, tetralone, and benzopyran nuclei yield potent antagonists that are specific for GPIIb-IIIa. Attachment of the arginine isostere (benzamidine) to the supporting nucleus can be accomplished with an ether or amide linkage, although the latter enhances activity. Several compounds in this series provided measurable blood levels after oral dosing. Conversion of the acid moiety in these molecules to an ester generally provided compounds which gave greater systemic exposure after oral administration. Absolute bioavailabilities in the rat for the ethyl ester prodrug derivatives of the tetralin, tetralone, and benzopyran analogues of 3 were 28%, 23%, and 24%, respectively.

1,2-Dibenzamidobenzene inhibitors of human factor Xa.

High-throughput screening of a combinatorial library of diamidophenols yielded lead compounds with the ability to inhibit human factor Xa (fXa) at micromolar concentrations (e.g. compound 4, fXa apparent K(ass) = 0.64 x 10(6) L/mol). SAR studies in this novel structural series of fXa inhibitors showed that the phenolic hydroxyl group was not essential for activity. The best activity was found in substituted 1,2-dibenzamidobenzenes in which the phenyl group of one benzoyl group (A-ring) was substituted in the 4-position with relatively small lipophilic or polarizable groups such as methoxy, vinyl, or chloro and the phenyl group of the other benzoyl group (B-ring) was substituted in the 4-position with larger lipophilic groups such as tert-butyl or dimethylamino. The central phenyl ring (C-ring) tolerated a wide variety of substituents, but methoxy, methanesulfonamido, hydroxyl, and carboxyl substitution produced slightly higher levels of activity than other substituents when present in combination with favorable B-ring substitution. Methylation of the amide nitrogen atoms was found to greatly decrease activity. Compound 12 is the highest affinity fXa inhibitor in this group of compounds, having fXa apparent K(ass) = 25.5 x 10(6) L/mol, about 40x more active than the original lead. This lead series does not show potent inhibition of human thrombin. A model for the binding of these ligands to the fXa active site is proposed. The model is consistent with the observed SAR and can serve to guide future SAR studies.

Cardiovascular effect and stimulus-dependent inhibition of superoxide generation from human neutrophils by tibenelast, 5,6-diethoxybenzo(b)thiophene-2-carboxylic acid, sodium salt (LY186655).

Tibenelast (LY186655), 5,6,-diethoxybenzo(b)thiophene-2-carboxylic acid, sodium salt, is an orally active anti-anaphylactic compound in guinea pigs, and has been shown to prevent bronchospasm in moderately severe asthmatic patients. Pharmacological studies with tibenelast demonstrated that it is a selective phosphodiesterase (PDE) inhibitor in that it is moderately active against the lung and stomach enzyme while being a very weak inhibitor of the heart enzyme. The compound was without cardiovascular effects at anti-anaphylactic doses. In contrast to theophylline, tibenelast did not have a direct inotropic effect in the cat papillary muscle system. The concentration that inhibited 50% of the enzymatic activity (IC50) for tibenelast was 20- to 30-fold lower for neutrophil PDE than for PDE of other tissues. It was 100 times more potent than aminophylline in inhibiting superoxide generation from platelet-activating factor (PAF)-primed polymorphonuclear leukocytes (PMNL) challenged with chemotactic factor, N-formyl-methionyl-leucyl-phenylalanine. However, tibenelast was less effective in the tumor necrosis factor-primed system, and did not inhibit superoxide generation during phagocytosis or when other soluble stimuli, such as phorbo-12-myristate-13-acetate or the calcium ionophore A23187, were used. Furthermore, tibenelast did not inhibit enzymes involved in arachidonic acid metabolism. These results suggest that tibenelast probably inhibits superoxide release from PMNL via a selective inhibition on PDE.

Purification and characterization of fatty acid cyclooxygenase from human platelets.

The fatty acid cyclooxygenase (EC 1.14.99.1) that produces the prostaglandin, thromboxane, and prostacyclin precursor (PGH2), was solubilized from human platelet microsomes in 20 sucrose and 1.0% Triton X-100. The enzyme was purified 300-fold by electrofocusing, Sephadex G-200 gel filtration, and hydrophobic chromatography on ethyl agarose. The cyclooxygenase catalyzed the conversion of arachidonic acid to prostaglandin endoperioxide, PGH2, that was trapped at -25 degrees C and separated on TLC at -20 degrees C. PGH2 was hydrolyzed to HHT in acidic pH, or was chemically converted to PGE2 in slightly alkaline pH in the absence of cofactors. The enzyme showed a broad pH optimum in the range of 7-9. Hemin containing substances such as methemoglobin were absolutely required as cofactors, while tryptophan, epinephrine, phenol, and hydroquinone stimulated the PGH2 formation. Metal ions, such as ZN2+ and Cd2+ inhibited the enzyme reaction at 0.1 to 1 mM. The molecular weight of the purified enzyme was estimated at 79,432 by sodium dodecyl sulfate disc gel electrophoresis at pH 8.0. The properties of the human platelet enzyme was generally similar to the sheep vesicular enzyme in the method of solubilization, pH optimum, and molecular weight.

Dog liver 3-hydroxy-3-methylglutaryl coenzyme A reductase.

A rapid and sensitive assay method for 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-coA reductase, EC 1.1.1.34) is described. HMG-coA reductase is demonstrated in dog liver microsomes, and the converted reaction product has been identified as mevalonolactone. The enzyme activity undergoes cyclic variation and increases by more than tenfold 5 h after feeding. The properties of dog liver enzyme are generally similar to the rat liver enzyme in the method of solubilization, cold inactivation, pH optimum, and Km values.

Anti-inflammatory effects of LY221068 and LY269415.

LY221068, 5-[[3,5-bis(1,1-dimethylethyl)-4-hydroxy phenyl]methylene]-3-(dimethylamino)-4-thiazolidinone, and the monomethylamino analog, LY269415, are anti-oxidants and potent inhibitors of iron dependent lipid peroxidation and 5-lipoxygenase enzyme. Since oxygen radical species, lipid peroxides and products of the arachidonic acid cascade have been implicated as important mediators in a variety of inflammatory diseases including arthritis, LY221068 and LY269415 were studied in the Freund's Complete Adjuvant Induced Arthritis (FCA) model in rats. The compounds were administered orally and inhibition of bone damage and paw swelling of both the injected and uninjected paws was assessed. At 50 mg/kg p.o., LY221068 inhibited soft tissue swelling in the uninjected paw by 72% while LY269415 at 25 mg/kg p.o. exhibited 74% inhibition. Bone damage was also significantly inhibited by both compounds. In a dose response study, the minimum effective dose for LY221068 was 10 mg/kg p.o. and for LY269415 was 5 mg/kg p.o. In the established FCA model in rats, LY221068 at 50 mg/kg p.o. inhibited the uninjected paw swelling by 71% while LY269415 at 25 mg/kg p.o. inhibited 70%. These results suggest that LY221068 and LY269415 may be useful in the treatment of arthritis.

The anti-inflammatory effects of LY178002 and LY256548.

LY178002 (5-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methylene-4-thiazolidinon e) and its N-methyl analog, LY256548, inhibit the enzymatic activity of phospholipase A2, 5-lipoxygenase and fatty acid cycloxygenase. They also inhibit leukotriene B4 production from human polymorphonuclear leukocytes stimulated with the calcium ionophore A23187. Since products of the arachidonic acid cascade have been implicated as important mediators in a variety of inflammatory diseases including arthritis, LY178002 and LY256548 were studied in the Freund's Complete Adjuvant-Induced Arthritis (FCA) model in rats. The compounds were administered orally and inhibition of bone damage and paw swelling was assessed of both the injected and uninjected paws. At 50 mg/kg LY178002 inhibited soft tissue swelling in the uninjected paw by 81% while LY256548 exhibited 57% inhibition. Bone damage was also significantly inhibited by both compounds. A dose response was conducted. The minimum effective dose for LY178002 was 10 mg/kg p.o. In the established FCA model LY178002 at 50 mg/kg p.o. inhibited the uninjected paw swelling by 75% while LY256548 did not show this level of activity. These results suggest that LY178002 and LY256548 may be useful in the treatment of arthritis.

Characterization of LY233569 on 5-lipoxygenase and reperfusion injury of ischemic myocardium.

LY233569 produced concentration-dependent inhibition of isolated guinea pig 5-lipoxygenase (5-LPO) and 5-LPO activity of human polymorphonuclear leukocytes in vitro; IC50 values were 0.4 and 0.1 microM, respectively. LY233569 also inhibited (IC50 approximately 1.8 microM) zymosan-stimulated production of leukotriene B4 in canine whole blood but had little or no concomitant effect on the production of thromboxane B2. Concentrations of LY233569 as high as 10 microM did not inhibit production or scavenge superoxide from activated human neutrophils. In normal anesthetized dogs, infusion of LY233569 (0.11 mg/kg/min, i.v.) for 6 hr produced persistent inhibition (approximately 80%) of leukotriene B4 production in blood challenged ex vivo with zymosan; the plasma concentration (approximately 4 microM) of LY233569 was consistent with in vitro data illustrating selective and maximal inhibition of 5-LPO. In subsequent experiments, myocardial infarct size was measured after 1 hr of occlusion of the circumflex coronary artery and 5 hr of reperfusion. Continuous infusion of LY233569 (0.11 mg/kg/min, i.v.) had little or no effect on base-line systolic arterial pressure, cardiac rate and the pressure rate product when compared with time-related changes observed in control dogs. LY233569 infusion also did not alter the degree of ST-segment deviation or the intensity and duration of cardiac arrhythmias associated with coronary artery occlusion and reperfusion. Resultant myocardial infarct sizes were 45 +/- 5% of the left ventricle placed at risk in control dogs and 43 +/- 4% in dogs given LY233569. Myeloperoxidase activity of infarcted myocardium did not differ between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Xanthine oxidase inhibition does not limit canine infarct size.

BACKGROUND: Evidence supporting the role of xanthine oxidase in myocardial reperfusion injury is based on studies with pharmacological interventions used to inhibit enzyme function. Controversy exists, however, regarding the true role of xanthine oxidase in reperfusion injury. This study was performed to determine whether xanthine oxidase inhibition limits myocardial injury due to coronary artery occlusion and reperfusion. METHODS AND RESULTS: Anesthetized dogs underwent coronary artery occlusion (90 minutes) and reperfusion (6 hours). Oxypurinol (28 mg/kg) or amflutizole (30 mg/kg), chemically unrelated inhibitors of xanthine oxidase, or vehicle was infused intravenously 15 minutes before and 3 hours after reperfusion. Regional myocardial blood flow was determined with radiolabeled microspheres. Infarct size was determined with the tetrazolium method. Myocardial infarct size (percent of risk region) was less in oxypurinol-treated dogs, 32 +/- 16%, compared with that of the control group, 46 +/- 15%. Infarct size for the amflutizole-treated dogs, 40 +/- 21%, was not significantly different from that of the control group. There were no differences in rate-pressure product or collateral blood flow to account for differences in infarct size. Uric acid concentration in the coronary venous plasma increased after reperfusion in the dogs treated with vehicle but not in the drug-treated dogs. Xanthine oxidase inhibition was demonstrated in each of the drug treatment groups, but only oxypurinol limited the extent of myocardial injury. CONCLUSIONS: Previously reported cardioprotective effects of allopurinol, noted to occur only when the drug was administered chronically, may be related to a property of oxypurinol, a major metabolite of allopurinol. The beneficial effect of oxypurinol is unrelated to inhibition of superoxide formation during xanthine oxidase-catalyzed oxidation of xanthine and hypoxanthine.

Fused bicyclic Gly-Asp beta-turn mimics with potent affinity for GPIIb-IIIa. Exploration of the arginine isostere.

6-[4-Amidinobenzoyl]amino]-tetralone-2-acetic acid is a potent antagonist of GPIIb-IIIa. Substitution in the meta position of the benzamidine, or replacement with a heteroaryl amidine was tolerated in this series. Use of an acyl-linked 4-alkyl piperidine as an arginine isostere also provided active compounds. Compounds from this series provided substantial systemic exposure in the rat following oral administration.