Inhibitors of acyl-CoA:cholesterol acyltransferase. 5. Identification and structure-activity relationships of novel beta-ketoamides as hypocholesterolemic agents

Targeting Sterol O-Acyltransferase/Acyl-CoA:Cholesterol Acyltransferase (ACAT): A Perspective on Small-Molecule Inhibitors and Their Therapeutic Potential

Sterol O-acyltransferase (SOAT) is a membrane-bound enzyme that aids the esterification of cholesterol and fatty acids to cholesterol esters. SOAT has been studied extensively as a potential drug target, since its inhibition can serve as an alternative to statin therapy. Two SOAT isozymes that have discrete functions in the human body, namely, SOAT1 and SOAT2, have been characterized. Over three decades of research has focused on candidate SOAT1 inhibitors with unsatisfactory results in clinical trials. Recent research has focused on targeting SOAT2 selectively. In this perspective, we summarize the literature covering various SOAT inhibitory agents and discuss the design, structural requirements, and mode of action of SOAT inhibitors.

Amide Bond Bioisosteres: Strategies, Synthesis, and Successes

The amide functional group plays a key role in the composition of biomolecules, including many clinically approved drugs. Bioisosterism is widely employed in the rational modification of lead compounds, being used to increase potency, enhance selectivity, improve pharmacokinetic properties, eliminate toxicity, and acquire novel chemical space to secure intellectual property. The introduction of a bioisostere leads to structural changes in molecular size, shape, electronic distribution, polarity, pK_a, dipole or polarizability, which can be either favorable or detrimental to biological activity. This approach has opened up new avenues in drug design and development resulting in more efficient drug candidates introduced onto the market as well as in the clinical pipeline. Herein, we review the strategic decisions in selecting an amide bioisostere (the why), synthetic routes to each (the how), and success stories of each bioisostere (the implementation) to provide a comprehensive overview of this important toolbox for medicinal chemists.

Application of the N-Dibenzyl Protective Group in the Preparation of β-Lactam Pseudopeptides

Despite the great importance of β-lactam antibiotics, there is still a limited number of synthetic approaches for the formation of β-lactam⁻containing dipeptides. In this study, we report upon the stereoselective preparation of β-lactam⁻containing pseudopeptides, where different reaction conditions and NH₂ protective groups were tested to obtain compounds that contain 3-amino-azetidin-2-one. We demonstrate that the protective group is essential for the outcome of the reaction. Successful implementation of dibenzyl-protected serine-containing dipeptides through the Mitsunobu reaction can provide the desired products at high yields and stereoselectivity.

Sonochemistry in organocatalytic enamine-azide [3+2] cycloadditions: A rapid alternative for the synthesis of 1,2,3-triazoyl carboxamides

We described herein the use of sonochemistry in the organocatalytic enamine-azide [3+2] cycloadditions of β-oxo-amides with a range of substituted aryl azides. These sonochemical promoted reactions were found to be amenable to a range of β-oxo amides or aryl azides, providing an efficient access to new N-aryl-1,2,3-triazoyl carboxamides in good to excellent yields and short times of reaction.

Prediction of IC50 values for ACAT inhibitors from molecular structure

A quantitative structure-activity study is performed on several series of compounds derived from N-chlorosulfonyl isocyanate to develop models that relate their structures to IC50 activity for inhibition of acyl-CoA:cholesterol O-acyltransferase (ACAT). Numerical descriptors are used to encode topological, electronic, and geometric information from the molecular structures of the inhibitors. A data set of 157 compounds showing triglyceride- and cholesterol-lowering activity is used to develop successful linear regression models and nonlinear computational neural network models. The models are validated using an external prediction set.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase (ACAT) as hypocholesterolemic agents: synthesis and structure-activity relationships of novel series of sulfonamides, acylphosphonamides and acylphosphoramidates

Sulfoacetic acid, phosphoramidate, and phosphoramide analogs of the ACAT inhibitors, CI-999 and CI-1011 were synthesized. The structure-activity relationships of these compounds as ACAT inhibitors are described.

Synthesis, X-ray crystal structure, and biological activity of FR186054, a novel, potent, orally active inhibitor of acyl-CoA:cholesterol O-acyltransferase (ACAT) bearing a pyrazole ring

The synthesis, single crystal X-ray structural analysis, and biological activity of FR186054 (2c), a new, potent, orally efficacious inhibitor of acyl-CoA:cholesterol O-acyltransferase (ACAT), containing a pyrazole ring are described. This compound displayed excellent in vitro efficacy, irrespective of dosing method, indicating superior characteristics compared to other ACAT inhibitors.

Heterocyclic ureas: inhibitors of acyl-CoA:cholesterol O-acyltransferase as hypocholesterolemic agents

A series of diaryl-substituted heterocyclic ureas was prepared, and their ability to inhibit acyl-CoA: cholesterol O-acyltransferase (ACAT) in vitro and to lower plasma total cholesterol in cholesterol-fed animal models in vivo was examined. N-(2,6-Diisopropylphenyl)-N'-tetrazole or isoxazole-substituted heterocyclic ureas proved optimal. A carbon chain of 11-14 carbons substituted 1,3 with respect to the amine provided the optimal side chain. Substitution of the alkyl chain generally lowered activity. Tetrazole urea 2i dosed at 3 mg/kg lowered plasma total cholesterol (TC) 67% in an acute, cholesterol-fed (C-fed) rat model of hypercholesterolemia and 47% in C-fed dogs. Tetrazole 2i, dosed at 10 mg/kg, also lowered TC 52% and raised HDL cholesterol 113% in rats with pre-established hypercholesterolemia.

Cholecystokinin B antagonists. Synthesis and quantitative structure-activity relationships of a series of C-terminal analogues of CI-988

A study of structure-activity relationships of a series of 'dipeptoid' CCK-B receptor antagonists was performed in which variations of the phenyl ring were examined while the [(2-adamantyloxy)carbonyl]-alpha-methyl-R)-tryptophan moiety of the potent antagonist CI-988 was kept constant. Since the main focus of this study was phenyl substituent variation, series design techniques were employed to insure an adequate spread of physicochemical properties (lipophilic, steric, electronic), as well as positional substitution. A QSAR analysis on sets of 26 and 16 analogues revealed that CCK-B affinity was related to a combination of the overall size and, marginally, lipophilicity of the phenyl ring substituents (i.e., smaller groups were associated with increased potency with an optimum pi near zero, respectively). Further exploration revealed that the dimensions and electronics of the para-phenyl substituent could be related to CCK-B affinity. Increased affinity was seen with short, bulky (branched) electron withdrawing groups. Analogs with small para-substituents appeared to be about 1000-fold CCK-B selective, indicating that selectivity for CCK-B binding is sensitive to phenyl ring substitution. The 4-F-phenyl dipeptoid, derived from this study, has extraordinary high affinity at the CCK-B receptor (IC50 = 0.08 nM) and was also very selective (940-fold CCK-B selective). Consistent with previous reports, (S)-configuration at the substituted phenethylamide center, a carboxylic acid and the presence of a phenyl ring were found to be associated with increased affinity at both CCK-A and CCK-B receptors.

Heterocyclic amides: inhibitors of acyl-CoA:cholesterol O-acyl transferase with hypocholesterolemic activity in several species and antiatherosclerotic activity in the rabbit

A series of heterocyclic amides were synthesized and evaluated as inhibitors of acyl-CoA: cholesterol O-acyltransferase (ACAT) in vitro and for cholesterol lowering in cholesterol-fed rats. Compounds were evaluated for cell-based macrophage ACAT inhibition, bioactivity, and adrenal toxicity. Candidates were selected for evaluation in cholesterol-fed dogs and, ultimately, the injured cholesterol-fed rabbit model of atherosclerosis. The heterocyclic amides potently inhibited rabbit liver ACAT (IC50's = 0.014-0.11 microM), and the majority of compounds significantly lowered plasma cholesterol (42-68%) in an acute cholesterol-fed rat model at 3 mg/kg. The most efficacious compounds in the rat were evaluated for bioactivity in vivo and arterial ACAT inhibition in a cell-based macrophage ACAT assay. Two highly bioactive analogs, (+/-)-2-(3-dodecylisoxazol-5-yl)-2-phenyl-N-(2,4,6-trimethoxypheny l) acetamide (13a) and (+/-)-2-(5-dodecylisoxazol-3-yl)-2-phenyl-N-(2,4,6-trimethoxypheny l) acetamide (16a), were selected for further study and were found to be nontoxic in a guinea pig model of adrenal toxicity. Compounds 13a and 16a lowered total cholesterol in the cholesterol-fed rat, rabbit, and dog models of pre-established hypercholesterolemia. Compound 13a in the injured cholesterol-fed rabbit model of atherosclerosis was effective in slowing the development of cholesteryl ester-rich thoracic aortic lesions, reducing lesion coverage by 53% at a dose of 1 mg/kg.

Bioisosterism in drug design: identification of and structure-activity relationships in a series of glycine anilide ACAT inhibitors

To examine the effects of bioisosteric replacement on the biological activity of our previously disclosed disubstituted urea inhibitors of the enzyme acyl-CoA:cholesterol acyltransferase (ACAT), we prepared a series of N'-substituted and N',N'-disubstituted glycine anilides. These compounds were tested for the ability to inhibit ACAT in vitro and lower plasma total cholesterol in cholesterol-fed rats given a single high-fat, high-cholesterol meal. ACAT inhibitory potency was greatest in compounds containing 2,6-diisopropyl substituents in the anilide portion with the glycine nitrogen substituted by a 1,1-diphenylmethyl moiety. Small improvements in potency in vitro were obtained by substitution of electron donating groups in the 2-, 3- or 5-positions of the aryl rings of the 1,1-diphenylmethyl moiety, but not by substitution in the 4-position. In vitro potency was maintained, but not improved by acylation of the glycine nitrogen. Through a QSAR analysis of in vitro ACAT inhibition for this set of compounds, an equation could be derived which accounted for 85% of the variance in the dataset. An optimal clogp of 6.65 was found, comparable to that found for other series of ACAT inhibitors. In general, compounds from this series displayed inhibitory potency against ACAT in vitro and hypocholesterolemic activity in the in vivo rat model of hypercholesterolemia comparable to that found with the ureas.

Imidazolylbenzopyrane derivatives: a new class of acyl-CoA: cholesterol acyltransferase (ACAT) inhibitors

Inhibitors of the enzyme Acyl-CoA: Cholesterol Acyltransferase are regarded as potentially useful agents in the treatment of hypercholesterolemia and atherosclerosis. We report here a novel series of 2, 6-disubstituted-3-imidazolylbenzopyrane derivatives with significant in vitro ACAT inhibitory activity (IC50 range 0.05-0.5 microM). Compounds of this series such as 26 are examples of a new, structurally distinct class of potent ACAT inhibitors with high specificity for the aortic subtype of the enzyme. The structure-activity relationships of the 3-imidazolylbenzopyrane ACAT inhibitors were investigated by systematic manipulation of two regions of the parent compound 1 and the inhibitory activity resulted linked to the substituent in position 6 of the benzopyrane ring and modulated by the size of lipophilic substituents in position 2. Investigation of the mechanism of the inhibitory effect leads to the conclusion that these compounds act in a non-competitive fashion.