6-Chlorochroman-2-carboxylic acids. Synthesis and biological evaluation as antagonists for cholesterol biosynthesis and lipolysis in vitro

Lipid-lowering properties of 6-benzoyl-2(3H)-benzothiazolone and structurally related compounds

Fifteen compounds derived from the 2(3H)-benzothiazolone template with an acyl side-chain in position-6 were evaluated for their lipid-lowering action in mice. Among these compounds, 6-benzoyl-2(3H)-benzothiazolone was found to be the most potent one both in mice models receiving a hypercholesterolemic diet (for 15 days) or a standard diet (for 21 days). 6-Benzoyl-2(3H)-benzothiazolone compares favorably with fenofibrate, the standard drug, both in terms of HDL-C/Chol (High Density Lipoprotein-Cholesterol/Total Cholesterol) ratio and absence of liver hepatomegaly.

Structural requisites of 2-(p-chlorophenoxy)propionic acid analogues for activity on native rat skeletal muscle chloride conductance and on heterologously expressed CLC-1

(1) The 2-(p-chlorophenoxy)propionic acid (CPP) modulates in a stereoselective manner the macroscopic chloride conductance (gCl), the electrical parameter sustained by the CLC-1 channel, of skeletal muscle. In order to determine the structural requirements for modulating native gCl and to identify high-affinity ligands, the effects of newly synthesised CPP analogues have been evaluated on gCl of rat EDL muscle fibres by means of the two-microelectrode current-clamp technique. (2) Each type of the following independent modification of CPP structure led to a three- to 10-fold decrease or to a complete lack of gCl-blocking activity: replacement of the electron-attractive chlorine atom of the aromatic ring, substitution of the oxygen atom of the phenoxy group, modification at the chiral centre and substitution of the carboxylic function with a phosphonate one. (3) The analogues bearing a second chlorophenoxy group on the asymmetric carbon atom showed a significant gCl-blocking activity. Similar to racemate CPP, the analogue with this group, spaced by an alkyl chain formed by three methylenic groups, blocked gCl by 45% at 100 micro M. (4) These latter derivatives were tested on heterelogously expressed CLC-1 performing inside-out patch-clamp recordings to further define how interaction between drug and channel protein could take place. Depending on the exact chemical nature of modification, these derivatives strongly blocked CLC-1 with K(D) values at -140 mV ranging from about 4 to 180 micro M. (5) In conclusion, we identified four molecular determinants pivotal for the interaction with the binding site on muscle CLC-1 channels: (a) the carboxylic group that confers the optimal acidity and the negative charge; (b) the chlorophenoxy moiety that might interact with a hydrophobic pocket; (c) the chiral centre that allows the proper spatial disposition of the molecule; (d) an additional phenoxy group that remarkably stabilises the binding by interacting with a second hydrophobic pocket.

Lipid lowering actions of 7-(2-methylene butyryl)-(2H)-1,4-benzoxazin-3-(4H)-one derivatives in mice, rats and Syrian hamsters

A series of compounds derived from 7-acyl-(2H)-1,4-benzoxazin-3-(4H)-one was synthesized and evaluated for its lipid lowering actions in animal models. These of three 7-(2-methylene butyryl) 4-methyl and 2,4 dimethyl or 2,2,4 trimethyl benzoxazinone showed very potent activity. Their hypocholesterolemic and hypotriglyceridemic activities were tested in normolipemic and in cholesterol-induced hyperlipidemic mice, rats and Syrian hamsters. Two key enzymatic activities (ACAT, HMG CoA Reductase) of the most active compound were also determined. Additional investigation with these products and other derivatives will be performed using a variety of hepatic enzyme activities to better determine their mechanisms of action.

Action of clofibrate and its analogs in rats dissociation of hypolipidemic effects and the induction of peroxisomal β-oxidation

Experiments were conducted to compare directly the effects of clofibrate (ethyl 2-(p-chlorophenoxy)isobutyrate) and its analogs on serum lipids and on the rate-limiting enzyme of the hepatic peroxisomal beta-oxidation pathway, fatty acyl-coenzyme A oxidase. Clofibrate feeding (5 g/kg diet) led to 8-10-fold increases in enzyme activity in 7 days. The enzyme remained elevated during the 28-day course of the experiment. The treatment did not lead to a lowering of serum cholesterol or triacylglycerol at any time during the experiment. In separate experiments rats were given clofibrate or one of five analogs by gastric intubation for 4 consecutive days. Four of the five analogs studied caused a significant lowering of serum triacylglycerol to about 50% of pretreatment level; another analog and clofibrate itself did not significantly affect serum triacylglycerol levels. None of the five analogs caused an induction of hepatic fatty acyl-CoA oxidase, while clofibrate treatment led to a 3-4-fold increase in enzyme activity. The results demonstrate a complete dissociation between the hypolipidemic action of these compounds and the induction of peroxisomal beta-oxidation. Thus it appears that the two phenomena are mechanistically unrelated.

Hypolipidemic effects of clofibrate and selected chroman analogs in fasted rats: II. High sucrose-fed animals

The hypolipidemic properties of ethyl 6-chlorochroman-2-carboxylate (II), 6-phenylchroman-2-carboxylate (III) and 6-cyclohexylchroman-2-carboxylate (IV) were compared to clofibrate (I) in sucrose-fed fasted male Sprague-Dawley rats. All compounds were administered at doses of 0.2 and 0.4 mmol/kg, orally, twice daily for 7 consecutive days. In this model, II was a more effective hypocholesterolemic drug than clofibrate, whereas III and IV were inactive. Chlorochroman II, like clofibrate, decreased serum alpha-lipoprotein cholesterol and pre-beta-lipoprotein triglyceride concentrations and concomitantly increased serum beta-lipoprotein triglyceride concentrations. In clofibrate-treated rats, serum free cholesterol concentrations increased concurrent with a reduction in serum lecithin: cholesterol acyltransferase activity, but no such correlation was observed for II. Only II lowered liver cholesterol levels and increased liver triglyceride levels. No consistent inhibition of liver microsomal 3-hydroxy-3-methylglutaryl-CoA reductase activity was observed with these analogs. The observed changes in triglyceride and cholesterol concentrations among serum lipoproteins were of a greater magnitude after chlorochroman II and clofibrate administration to sucrose-fed rats than in our previous studies using chow-fed fasted rats. These data suggest that chloro-substitution at the 6-position of the phenylchroman ring is important for hypolipidemic activity of these cyclic clofibrate analogs.

Hypolipidemic effects of clofibrate and selected chroman analogs in fasted rats: I. Chow-fed animals

The hypolipidemic properties of ethyl 6-chlorochroman-2-carboxylate (II), ethyl 6-phenylchroman-2-carboxylate (III) and ethyl 6-cyclohexylchroman-2-carboxylate (IV) were compared to clofibrate (I) in fasted normolipidemic rats. The chroman analog II, like its parent compound, clofibrate, reduced serum and alpha-lipoprotein cholesterol concentrations. Although analog III had no effect on serum cholesterol, it caused a slight elevation of alpha-lipoprotein cholesterol concentration. Serum free cholesterol was increased and LCAT activity was reduced in clofibrate-treated rats. The hypolipidemic agents had no consistent effect on liver lipid concentrations and liver microsomal HMG-CoA reductase activity. In addition, we have shown that drug efficacies varied directly with seasonal variations in serum lipid concentrations.

Antilipidemic activity of 4-oxo-functionalized ethyl 6-chlorochroman-2-carboxylate analogs and a related tricyclic lactone in three rat models

The synthesis of ethyl cis-6-chloro-4-hydroxychroman-2-carboxylate (IV) and 6-chloro-4-hydroxy-chroman-2-carboxylic acid lactone (V) are reported. The antilipidemic properties of these compounds in 3 rat models were compared to the activity obtained for the previously synthesized related analogs ethyl 6-chlorochroman-2-carboxylate (II), ethyl 6-chlorochromanone-2-carboxylate (III) and clofibrate (I). The biologically most interesting analog, ethyl 6-chlorochroman-2-carboyxlate (II) like clofibrate (I), was an effective antitriglyceridemic and anticholesterolemic agent in Triton WR-1339 hyperlipidemic rats, sucrose-fed hyperlipidemic rats and chow-fed normolipemic rats. Ethyl 6-chlorochromanone-2-carboxylate (III) was found to be active after 7 days of administration to sucrose-fed rats. In sucrose-fed, male Sprague-Dawley rats, the comparative effects of these analogs on various hepatic drug parameters also were carried out. Consistent with previous findings, results obtained with these compounds provide evidence showing that changes in hepatic HMG-CoA reductase activity bear no relationship to serum cholesterol lowering in the sucrose-fed model.

Potential hypocholesteremic derivatives of styrylacetic acid II: cis- and trans-3-methyl-4-phenyl-3-butenoic acid analogs

The synthesis and preliminary biological testing for in vitro cholesterol biosynthesis inhibitory activity of 2-indeneacetic acid, 2-methyl-1,2-dihydro-2-naphthoic acid, and their 5- and 7-chloro derivatives, respectively are described. These compounds were prepared as trans- and cis-analogs of the known antilipemic agent 3-methyl-4-phenyl-3-butenoic acid. Although both series of compounds showed cholesterol biosynthesis inhibitory properties, chloro substitution enhanced potency only in the cis-system. These findings are discussed in terms of a possible relationship between the cis-compounds and clofibrate-type antilipemic agents.

Comparison of hypocholesterolemic activity for cyclic analogs of clofibrate in normolipemic rats

Chronic administration of ethyl 2-methyl-2(4-chlorophenoxy)-propionate [clofibrate, CPIB], ethyl 6-cyclohexylchroman-2carboxylate, and ethyl 6-phenylchroman-2-carboxylate to normolipemic rats, in vivo, reduced serum cholesterol levels and inhibitid the activiry of hepatic 3-hydroxy-3methyl-glutaryl Coenzyme A. Only clofibrate was found to lower liver cholesterol content after pretreatment for 4 or 18 days. The cyclic analogs, ethyl 6-cholorochromone-2-carboxylate and 9-chloro-2,3-dihydro-5H-1,4-dioxepino [6,5-b] benzofuran were inaffective as cholesterol lowering agents in normolipemic rats. These findings indicate that appropriate modification of clofibrate can lead to the development of compounds which are selective and equally effective to clofibrate as potential hypocholesterolemic agents. Results obtained in these studies are also discussed in terms of the known structural requirements of biological activity for this series of cyclic analogs in the Triton WR-1339 hyperlipemic rat model and modes of action of the parent compound.