Effect of bile acids on the binding of drugs and dyes to human albumin

Chenodeoxycholic, cholic, deoxycholic and taurodeoxycholic acids were found to inhibit the binding of 2-(4'-hydroxybenzeneazo)benzoic acid, methyl orange, sulphadimethoxine and warfarin to human albumin. In addition, glycodeoxycholic acid inhibited the binding of sulphadimethoxine and warfarin. In contrast, these bile acids did not inhibit the binding of phenylbutazone. The extent of displacement was in the rank order of: dihydroxy acids (chenodeoxycholic and deoxycholic) greater than trihydroxy acid (cholic) greater than conjugates (glycodeoxycholic and taurodeoxycholic). Thus the introduction of polar groups into the steroid nucleus of bile acids reduces their effectiveness as binding inhibitors. Displacement was usually accompanied by a decrease in the apparent association constant which suggests that the mechanism of displacement may be competitive.     

Bile acid salt binding with colesevelam HCl is not affected by suspension in common beverages

It has been previously reported that anions in common beverages may bind to bile acid sequestrants (BAS), reducing their capacity for binding bile acid salts. This study examined the ability of the novel BAS colesevelam hydrochloride (HCl), in vitro, to bind bile acid sodium salts following suspension in common beverages. Equilibrium binding was evaluated under conditions of constant time and varying concentrations of bile acid salts in simulated intestinal fluid (SIF). A stock solution of sodium salts of glycochenodeoxycholic acid (GCDC), taurodeoxycholic acid (TDC), and glycocholic acid (GC), was added to each prepared sample of colesevelam HCl. Bile acid salt binding was calculated by high-performance liquid chromatography (HPLC) analysis. Kinetics experiments were conducted using constant initial bile acid salt concentrations and varying binding times. The affinity, capacity, and kinetics of colesevelam HCl binding for GCDC, TDC, and GC were not significantly altered after suspension in water, carbonated water, Coca-Cola, Sprite, grape juice, orange juice, tomato juice, or Gatorade. The amount of bile acid sodium salt bound as a function of time was unchanged by pretreatment with any beverage tested. The in vitro binding characteristics of colesevelam HCl are unchanged by suspension in common beverages.     

Potent antimalarial activity of 2-aminopyridinium salts, amidines, and guanidines

We describe the design, synthesis, and antimalarial activity of 60 bis-tertiary amine, bis-2(1 H)-imino-heterocycle, bis-amidine, and bis-guanidine series. Bis-tertiary amines with a linker from 12 to 16 methylene groups were active against the in vitro growth of Plasmodium falciparum within the 10 (-6)-10 (-7) M concentration range. IC 50 decreased by 2 orders of magnitude for bis-2-aminopyridinium salts, bis-amidines, and bis-guanidines (27 compounds with IC 50 < 10 nM). Increasing the alkyl chain length from 6 to 12 methylene groups led to increased activity, while beyond this antimalarial activity decreased. Antimalarial activities appear to be strictly related to the basicity of the cationic head with an optimal p K a over 12.5. Maximal activity occurs for bis-2-aminopyridinium, two C-duplicated bis-amidines, and three bis-guanidines, with IC 50 values lower than 1 nM. In comparison to similar quaternary ammonium salts, amidinium compounds have distinct structural requirements for antimalarial activity and likely additional binding opportunities on account of their hydrogen-bond-forming properties.     

lonization and Solubilization of 4 Alkyl Benzole Acids and 4 Alkyl Anilines in Sodium Taurodeoxycholate Solutions

Purpose. The aqueous solubility and the extent of solubilization and ionization constant in sodium taurodeoxycholate (NaTDC) solutions of a series of benzoic acid and aniline derivatives were measured as a basis to characterize and thereby help predict the nature of the interaction of drugs with bile aggregates. Methods. The aqueous solubility and the solubilization of two series of compounds, 4-alkyl benzoic acids and 4-alkyl anilines, was measured as a function of NaTDC in 0 and 150 mM NaCl. The ionization constants were determined in water and in 50 mM NaTDC at sodium chloride concentrations of 0, 75 and 150 mM by spectrophotometric titration. The diffusion coefficients of NaTDC and the solutes were measured by pulsed-field gradient spin echo NMR spectroscopy. Results. The aqueous solubilities decreased with increasing alkyl chain length in both series, and the aniline derivatives had larger solubilities than the benzoic acid derivatives. The number of moles of solute solubilized per mole of bile salt ranged from 0.17 to 0.31 for the benzoic acid derivatives and from 1.3 to 3.0 for the aniline derivatives. The pKa values of the benzoic acid derivatives in the presence of NaTDC were higher relative to the controls, and the difference in the pKa (pKa,obs) increased with increasing chain length. With the aniline derivatives, the pKa values were also shifted to higher values in NaTDC relative to the control but only in the absence of salt. The presence of the solute caused a decrease in the diffusion coefficient of NaTDC, and the diffusion coefficients of the solutes decreased with increasing alkyl chain length. With the hexyl derivatives, the diffusion coefficient of the solute was smaller than the diffusion coefficient of the bile salt. The chemical shift of the protons attached to carbon 18 and 19 of the bile salt were decreased to a greater extent in the presence of the solutes than the protons attached to carbon 26. Conclusions. Both the solubilization and ionization behavior of solutes were affected by the presence of bile salt aggregates. The surface potential and effective polarity of NaTDC aggregates were found to be dependent on the alkyl chain length for these two homologous series of solutes. The solubilization ratio was largely independent of alkyl chain length, but the unitary partition coefficient was dependent on both the alkyl chain length as well as ionization state. The derivatives reduced the diffusivity of the micelles suggesting the formation of larger sized aggregates and the solutes (hexyl derivatives) appear to favor association with the larger sized aggregates. The phenyl ring of the solutes appears to be oriented parallel to the plane of the steroid frame with preferential positioning near the hydrophobic rings.     

Effects of novel bile salts on cholesterol metabolism in rats and guinea-pigs

Novel bile salts (quaternary ammonium conjugates) inhibited cholic acid binding and transport in everted ileal sacs in vitro. The cationic piperazine conjugate of lithocholic acid (di-iodide salt, compound 8, BRL 39924A) appeared most active, inhibiting binding by 29% and transport by 59% in guinea-pig ileum (200 microM). BRL 39924A also inhibited taurocholate uptake into guinea-pig ileal sacs and cholate uptake into rat ileal sacs and was selected for further study in vivo. In hyperlipidaemic rats, BRL 39924A significantly raised cholesterol 7 alpha-hydroxylase activity and decreased hepatic accumulation of exogenous cholic acid. HDL cholesterol concentration in the serum increased and the level of VLDL plus LDL cholesterol decreased. In hyperlipidaemic guinea-pigs. BRL 39924A lowered serum total cholesterol and triglyceride levels. Although metabolic changes were less than those achieved with the bile acid sequestrant, cholestyramine, the doses of BRL 39924A used were much lower (100-500 mg/kg body wt). Selective inhibition of receptor mediated bile acid uptake may be associated with local side-effects but these novel bile salts are useful pharmacological tools to examine the effects of receptor blockade on lipoprotein metabolism.     

Assessment of the combined approach of N-alkylation and salt formation to enhance aqueous solubility of tertiary amines using bupivacaine as a model drug.

Quaternary prodrug types of poorly water-soluble tertiary amines have been shown to exhibit significantly enhanced solubilities as compared to the parent amine. In the present study the combined effect of N-alkylation and salt formation to enhance aqueous solubility of tertiary amines have been investigated using bupivacaine as a model compound. X-ray structure analyses of selected salts were included to investigate the potential existence of correlations between salt solubility and crystal packing modes. Alkyl groups were methyl, ethyl, propyl, and butyl and the derivatives were isolated as their iodide salts. Chloride, mesylate, formate, acetate, glycolate, and tosylate salts were obtained by anion exchange of the N-methyl-bupivacaine derivative. N-Alkylation and salt formation afforded quaternary ammonium salts possessing pH-independent aqueous solubilities far exceeding that of the parent tertiary amine (up to a factor of 3200 at pH 8). A moderate reduction in solubility with increasing length of the alkyl chain was observed for the iodide salts of the N-alkylated bupivacaine derivatives. In case of the N-methyl-bupivacaine derivative variation of the counterion had a significant impact on the solubility with the iodide salt being 200 times less soluble than the chloride salt. X-ray analysis revealed that both the alkyl substituent and the anionic counterion influenced salt packing modes, however, in an unpredictable manner making establishment of quantitative correlations between crystal packing and solubility difficult even for a series of closely related derivatives.     

Novel, highly potent adenosine deaminase inhibitors containing the pyrazolo[3,4-d]pyrimidine ring system. Synthesis, structure-activity relationships, and molecular modeling studies

This study reports the synthesis of a number of 1- and 2-alkyl derivatives of the 4-aminopyrazolo[3,4-d]pyrimidine (APP) nucleus and their evaluation as inhibitors of ADA from bovine spleen. The 2-substituted aminopyrazolopyrimidines proved to be potent inhibitors, most of them exhibiting K(i) values in the nanomolar/subnanomolar range. In this series the inhibitory activity is enhanced with the increase in length of the alkyl chain, reaching a maximum with the n-decyl substituent. Insertion of a 2'-hydroxy group in the n-decyl chain gave 3k, whose (R)-isomer displayed the highest inhibitory potency of the series (K(i) 0.053 nM), showing an activity 2 orders of magnitude higher than that of (+)-EHNA (K(i) 1.14 nM), which was taken as the reference standard. Docking simulations of aminopyrazolopyrimidines into the ADA binding site were also performed, to rationalize the structure-activity relationships of this class of inhibitors.     

Influence of various combinations of mucolytic agent and non-ionic surfactant on intestinal absorption of poorly absorbed hydrophilic compounds

The absorption enhancing effects of various combinations of a mucolytic agent and a non-ionic surfactant on the intestinal absorption of poorly absorbed hydrophilic compounds were examined. Fluorescein isothiocyanate-labeled dextran with an average molecular weight of ca. 4.4 kDa (FD-4) was used as a model compound. Cysteine derivatives such as N-acetylcysteine (NAC), S-carboxymethylcysteine (SCMC), S-ethylcysteine (SEC), and S-methylcysteine (SMC) were selected as mucolytic agents. A homogeneous series of single chain polyoxyethylene alkyl ethers were employed as non-ionic surfactants. Various dosing solutions were administered into rat jejunum, and the bioavailability of FD-4 was determined. Unlike NAC, the agents such as SCMC, SEC, and SMC, which do not possess a free thiol group, did not show any apparent enhancement of intestinal FD-4 absorption, when they were co-administered with p-t-octyl phenol polyoxyethylene-9.5 (Triton X-100, TX-100). In addition, the absorption enhancement was dependent on the kinds of polyoxyethylene alkyl ethers used, when used in combination with NAC. For a constant alkyl chain of 12 with a varying polyoxyethylene (POE) chain length, the surfactant with a short to medium POE chain length such as lauryl poly (4.2) oxyethylene ether (BL-4.2) and lauryl poly (9) oxyethylene ether (BL-9) were effective. In addition, for a constant alkyl chain of 18 with a varying POE chain length, the surfactants with a longer POE chain length such as oleyl poly (15) oxyethylene ether (BO-15) and stearyl poly (20) oxyethylene ether (BS-20) showed the effective enhancement. All these results suggest that a mucolytic agent not possessing a free thiol group is not effective for enhancing the intestinal absorption of poorly absorbed hydrophilic compounds. Also, they indicate that the combination of a mucolytic agent possessing a free thiol group and a non-ionic surfactant either with a short to medium POE chain length and a medium alkyl chain length, or with a longer POE chain length and a longer alkyl chain length shows the effective enhancement. This fundamental information might be useful for finding the optimal combination.     

Polymeric sorbents for bile acids. I: Comparison between cholestyramine and colestipol.

Isotherms for the sorption of bile acids at 20 degrees C, in tris(hydroxymethyl)aminomethane.HCl(tris) and KH2PO4-NaOH (phosphate) buffers (pH 7.4), indicate that the binding by cholestyramine and colestipol is mainly through ionic linkages, although hydrophobic interactions are also of importance. Cholestyramine has a higher sorption capacity for bile acids, in both buffers, than colestipol. The chloride form of cholestyramine has a higher capacity for cholate in tris buffer than the iodide form. Increased ionic strength of the medium leads to decreased amounts of sorption.     

Interactions of surface-active alkyltrimethylammonium salts with the plasma membrane of Acanthamoeba castellanii.

The interactions of three surface-active alkyltrimethylammonium salts (C12-C16) with the plasma membrane of Acanthamoeba castellanii were studied. The surfactants caused a release of K+ from the cells at premicellar concentrations. The lytic effectiveness of the surfactants increased with an increase in the length of the alkyl chain with about an order of magnitude for every two carbon atoms added to the alkyl chain. Binding studies with the C16 homologue revealed that at a concentration corresponding to 50% release of K+ there were about 1.9 x10(10) molecules bound per cell. At prelytic concentrations the surfactants stimulated phagocytosis and pinocytosis. The mode of action of the surfactants on the plasma membrane of Acanthamoeba castellanii is discussed and it is hypothesized that the stimulation of endocytosis is due to a "fluidizing" effect of the surfactants on the lipid bilayer of the plasma membrane.     

Preparation and Characterization of Reconstructed Small Intestinal Brush Border Membranes for Surface Plasmon Resonance Analysis

PURPOSE: To prepare the surface generated by small intestinal brush border membrane vesicles (BBMVs) for the surface plasmon resonance (SPR) analysis, which allows the real-time measurement of binding events occurring on the intestinal membrane. METHODS: BBMVs were isolated from Sprague-Dawley rats, suspended in HEPES-buffered saline, and flowed over the surface of a SPR sensor chip composed of dextran derivatives modified with lipophilic residues. The surface coverage was determined from binding of bovine serum albumin to BBMV-immobilized sensor chip. The performance of BBMVs immobilized was evaluated by their interaction with otilonium bromide and bile salts. RESULTS: The stable BBMV surface was achieved when BBMV suspension was flowed over the sensor chip for 8 h at a rate of 2 microl/min. The flow of otilonium bromide resulted in an increased SPR signal because of its binding to calcium channel, which is known to be distributed over the gastrointestinal tact. When bile salts were flowed over ileal and duodenal BBMV surfaces, respectively, a slightly higher SPR signal was observed in the ileal BBMV surface, indicating the specific interaction of bile salts with bile acid transporters. CONCLUSIONS: BBMV surfaces may be useful for the estimation of binding events on the intestinal membrane by SPR analysis, especially for the drugs that are orally administrated.     

On the anomalous sorption behaviour of chlorhexidine with poly(2-hydroxyethyl methacrylate)

General observations of solute: plastic interactions would suggest that the sorption of the cationic preservative, chlorhexidine, with poly (2-hydroxyethyl methacrylate) (PHEMA) is not only unexpected but also atypical in its properties. The polymer and preservative were investigated independently and the sorption of PHEMA with simple solutes, namely benzoic acid, benzocaine and aniline found to exhibit conventional properties. The single exception was the uptake of small amounts of benzocaine and aniline cations at acidic pH's. In order to elucidate the sorption characteristics of chlorhexidine a series of N¹-(p-chlorophenyl)-N⁵-alkylbiguanide acetates were synthesized. The anomalous sorption behaviour observed between PHEMA and the bis biguanide, chlorhexidine, was also found to be characteristic of these monofunctional biguanide derivatives. The extent of the interactions increased with increasing alkyl chain length (R = methyl to n-octyl), this being interpreted in terms of an interaction binding mechanism via the biguanide functional group stabilized by van der Waal's forces between the alkyl chain and the polymer backbone. Atypical sorption behaviour was observed for simple organic cations, biguanide and N¹-phenylbiguanide acetate with PHEMA, a possible inference being that this is a general characteristic of all cationic sorption with PHEMA.     

Dextran hydrogels for colon-specific drug delivery. V. Degradation in human intestinal incubation models

In the present study degradation of dextran hydrogels, potential drug carriers for colon-specific drug delivery, was studied in simulated small intestinal juices as well as in a human colonic fermentation model. Dextran hydrogels were shown to be stable when incubated at 37°C with the small intestinal enzymes amyloglucosidase, invertase and pancreatin. After a 24 h incubation, less than 3.3% of free glucose was released. However, the hydrogels were still intact as measured by the dry weight remaining. The fermentation of dextran hydrogels and several mono- and polysaccharides to short-chain fatty acids (SCFA) was investigated after anaerobic incubation in a human colonic fermentation model at 37°C for 0–72 h. In addition, the dextranase activity of the incubations was determined. The amounts and ratios of SCFA formed varied considerably in relation to the type of substrate fermented (glucose, maize starch, potato starch, cellulose, soluble dextran and dextran hydrogels). Detailed SCFA analysis demonstrated that fermentable saccharides resulted in an increased SCFA production, in contrast to the metabolic inert polysaccharide, cellulose. The hydrogels were found to be completely degraded in the human colonic fermentation model. An increased crosslinking density or a decreased degree of hydration resulted in a lower degradability. The pH of the incubations were found to be inversely proportional to the SCFA production as a result of the increased acid formation.     

Drug substances presented as sulfonic acid salts: overview of utility,safety and regulation

Objectives Controlling genotoxic impurities represents a significant challenge to both industry and regulators. The potential for formation of genotoxic short‐chain alkyl esters of sulfonic acids during synthesis of sulfonic acid salts is a long‐standing regulatory concern. This review provides a general overview of the utility of sulfonic acids as salt‐forming moieties and discusses strategies for effectively minimizing the potential for alkyl sulfonate formation during the synthesis and processing of sulfonate salt active pharmaceutical ingredients. The potential implications of the recent establishment of a substantial human threshold dose for ethyl methanesulfonate for the safety assessment of alkyl sulfonates in general are also discussed. Key findings The formation of alkyl sulfonates requires highly acidic conditions, possibly combined with long reaction times and/or elevated temperatures, to generate significant amounts, and these conditions are most unlikely to be present in the synthesis of active pharmaceutical ingredient sulfonate salts. It is possible to design salt formation conditions, using a short‐chain alcohol as solvent, to manufacture sulfonate salts that are essentially free of alkyl sulfonate impurities. Processes using non‐acidic conditions such as ethanol recrystallization or wet granulation should not raise any concerns of alkyl sulfonate formation. Summary An understanding of the mechanism of formation of alkyl sulfonates is critical in order to avoid restricting or over‐controlling sulfonic acid salts, which have many technical advantages as pharmaceutical counterions. Recent regulatory acceptance of a human threshold limit dose of 2 mg/kg per day for ethyl methanesulfonate, indicating that its toxicological risks have previously been considerably overestimated, could signal the beginning of the end over safety concerns on alkyl sulfonate residues, thus removing a major constraint from the exploitation of sulfonic acid counterions.     

Effects of chain-length and unsaturation on affinity and selectivity at muscarinic receptors.

1. Lengthening the chain in diphenylacetylcholine decreases affinity for muscarinic cholinoceptors in guinea-pig ileum. Diphenylacetoxypropyldimethylamine and its quaternary trimethylammonium salt are roughly equiactive: the dimethylamine and the piperidine have some selectivity for ileum compared with atria, but are not as active nor as selective as 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) methobromide (MeBr). With the weaker diphenylacetoxybutyl compounds the base is more active than the quaternary salt. 2. The diphenylacetoxybutyl-, cis-butenyl and trans-butenyl compounds have similar affinities. The quaternary salts are less active than the tertiary bases, but they are less selective than the butynyl analogues studied in earlier work. 3. 1,1-Diphenyl-1-hydroxy-2,4-hexadiynyl dimethylamine and its trimethylammonium salt are inactive in concentrations below 100 microM, as are the (+)-camphor-sulphonyl ester of 4-hydroxy-N-methyl piperidine and its methiodide. The (+/-)-phenylcyclopentylacetyl ester of 4-hydroxy-N-methylpiperidine methobromide is more active than its cyclohexyl analogue and than 4-DAMP MeBr but it is less selective than 4-DAMP MeBr. 4. The high selectivity of p-fluoro-hexahydrosila-diphenidol is confirmed but this compound has relatively low affinity (for ileum log K = 7.8). 5. The results indicate steric constraints to binding at muscarinic receptors which could be used to check molecular modelling of the receptor based on its known amino acid sequence. The group binding the charged nitrogen is probably at the mouth of a cavity which can accommodate two large rings (as in 4-DAMP MeBr) but with a depth less than about 7 A so that the rod-like hexadiynes cannot fit.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relations between the physico-chemical properties, the chemical reactivity and the local anesthetic activity. 32. (Part 1): Binding capacity of a structural protein (wool) to local anesthetics]

1. The general part deals with the molecular structure of nerve membranes and different local-anesthetic substances as well as the various possibilities of local-anesthetic binding to the nerve membrane. Albumin is usually chosen as a model protein in such investigations, a short extract of which is given. 2. The special part includes the chemical composition and properties of wool macroprotein, the model system used in the present paper. We determined its protein-binding values with cinchocain and tetracain homologues and various known commercial products of local anesthetics (oxybuprocain, parethoxyprocain and tetracain). The binding constants of these substances on wool protein are shown. 3. A statistically confirmed relationship between the alkyl chain length and the strength of protein binding is given. The free energy per CH2-group ranges between 400 and 500 cal/mol and its larger in cases of low pH values. 4. From the present data, a relationship between the binding constant and the partition constant of each substance of the homologous series studied could easily be observed, which further makes it possible to estimate the characteristic protein-binding constant Kp and also the change in pi-values with the change in free reaction energy of the substances. 5. The large differences in the binding values of the different binding mechanisms, which most probably are dependent on the variable binding affinities of the functional groups as well as on steric factors. But as in the homologous series, only substituents like alkyl amino and alkoxy could be changed, the possibility of some other binding process depending on the alkyl chain length of these groups could not be ruled out. Since the alky groups are non-polar, hydrophobic binding plays a role.     

Observations on the biopharmaceutical importance of chain length in chemically related compounds

The physicial properties of compounds which have a common parent structure, and differ only by the sequential addition of a methylene group to an alkyl side chain might be expected to demonstrate a linear variation in behaviour as a function of the length of the alkyl carbon chain. Although this is indeed so in many instances, there are many examples in the literature in which a break in the pattern of the behaviour of the product is observed at a chain length of five carbons (±1). In this paper, examples are highlighted in which this is true for solid-state properties (melting point, wettability), solubility, liquid properties, partition and biological response. NMR data demonstrate that certain substituent alkyl chains are essentially rigid until a chain length of 5 carbons is exceeded, after which the freedom of movement is increased; this is used as a basis to explain the observed behaviour.     

Functional group contribution of bile salt molecules to partitioning of a quaternary ammonium N,N-dimethyl derivative of propranolol

A quaternary ammonium N,N-dimethyl derivative of propranolol was extracted from pH 7.4 phosphate buffer into 1-octanol as ion-pairs with 12 different bile salts. The binding number, n, and the extraction constant, Ke, were determined. To obtain group contribution values of the bile salt molecule from the ion-pair extraction data, multiple linear regression analysis by the Free-Wilson technique was applied. The results showed that the fundamental premise of the functional group's contribution to the ion-pair extraction is valid. The functional groups of counterions contribute to the partitioning of the ammonium compound independently and additively in this system.     

Glucuronidation and excretion of nonylphenol in perfused rat liver.

Nonylphenol, an environmental estrogenic chemical, is reported to have adverse effects on the reproductive organs of animals. In this study, the metabolism of nonylphenol and that of other alkylphenols in the rat liver was investigated using liver perfusion. Alkylphenols (nonylphenol, hexylphenol, butylphenol, and ethylphenol) were glucuronidated by rat liver microsomes. Nonylphenol was found to be conjugated with glucuronic acid by an isoform of UDP-glucuronosyltransferase, UGT2B1, expressed in yeast AH22 cells. However, when nonylphenol was perfused into rat liver in situ, it was difficult for free nonylphenol and conjugated metabolite to be excreted into the bile or vein, and most of the perfused nonylphenol remained free and as a glucuronide conjugate in the liver tissue, even after 1 h of perfusion. After 1 h of perfusion of the other alkylphenols, most of them were excreted into the bile as glucuronides. Ethylphenol, which has the shortest alkyl chain, was excreted rapidly into both the bile and vein; however, the excretion rates of alkylphenols having longer alkyl chains tended to be slow. MRP-2-deficient Eisai hyperbilirubinemic rats could not secrete alkylphenol-glucuronides into the bile, indicating that alkylphenol-glucuronides are transported by MRP-2 to the bile in normal Sprague-Dawley rats. The results indicate that the kinetics of excretion of alkylphenol-glucuronides into the bile or vein depends on the length of alkyl chain and suggest that nonylphenol-glucuronide formed in the liver cannot be transported by MRP-2.     

Benzophenone dicarboxylic acid antagonists of leukotriene B4. 2. Structure-activity relationships of the lipophilic side chain

A series of lipophilic benzophenone dicarboxylic acid derivatives were found to inhibit the binding of the potent chemotaxin leukotriene B4 (LTB4) to its receptor on intact human neutrophils. Activity at the LTB4 receptor was determined by using a [3H]LTB4-binding assay. The structure-activity relationship for the lipophilic side chain was systematically investigated. Compounds with n-alkyl side chains of varying lengths were prepared and tested. Best inhibition of [3H]LTB4 binding was observed with the n-decyl derivative. Analogues with alkyl chains terminated with an aromatic ring showed improved activity. The 6-phenylhexyl side chain was optimal. Substitution on the terminal aromatic ring was also evaluated. Methoxyl, methylsulfinyl, and methyl substituents greatly enhanced the activity of the compound. For a given substituent, the para isomer had the best activity. Thus the nature of the lipophilic side chain can greatly influence the ability of the compounds to inhibit the binding of LTB4 to its receptor on intact human neutrophils. The most active compound from this series, 84 (LY223982), bound to the LTB4 receptor with an affinity approaching that of the agonist.