Inhibitors of acyl-CoA:cholesterol O-acyltransferase (ACAT). Part 1: identification and structure-activity relationships of a novel series of substituted N-alkyl-N-biphenylylmethyl-N'-arylureas

Solid Phase synthesis of Amides Using Mukaiyama'S Reagent

A new solid-phase synthetic method using Mukaiyama's reagent under mild conditions is reported to prepare amides in high purity without purification after cleavage from the resins.

Isoform-specific inhibitors of ACATs: recent advances and promising developments

Acyl-CoA:cholesterol acyltransferase (ACAT) is a promising therapeutic target for cardiovascular diseases. Although a number of synthetic ACAT inhibitors have been developed, they have failed to show efficacy in clinical trials. Now, the presence of two ACAT isoforms with distinct functions, ACAT1 and ACAT2, has been discovered. Thus, the selectivity of ACAT inhibitors toward the two isoforms is important for their development as novel anti-atherosclerotic agents. The selectivity study indicated that fungal pyripyropene A (PPPA) is only an ACAT2-specific inhibitor. Furthermore, PPPA proved orally active in atherogenic mouse models, indicating it possessed cholesterol-lowering and atheroprotective activities. Certain PPPA derivatives, semi-synthetically prepared, possessed more potent and selective in vitro activity than PPPA against ACAT2. This review covers these studies and describes the future prospects of ACAT2-specific inhibitors.

A Functional Slow Recycling Pathway of Transferrin is Required for Growth of Chlamydia

An inhibitor of host cell lysophospholipid acyltransferase, an enzyme involved in lipid metabolism blocked growth of the obligate intracellular pathogen Chlamydia through its action on the transport of transferrin (Tf) via the slow pathway of recycling. A detailed characterization of this inhibition revealed that Tf accumulated in vesicles positive for Rab11, with a concomitant reduction in the level of Tf found within the transport intermediate Rab4/11 hybrid vesicles. The net result was the failure to be recycled to the plasma membrane. In chlamydiae-infected cells, the Tf-containing Rab11-positive vesicles were typically found intimately associated with the inclusion, and treatment with the inhibitor caused their accumulation, suggesting that the timely progression and completion of Tf recycling was necessary for proper chlamydial growth. Growth inhibition by the compound could be negated by the simple removal of the Tf-containing fraction of the serum, a further indication that accumulation of Tf around the chlamydial inclusion was deleterious to the pathogen. Thus, it appears that manipulating the slow recycling pathway can have biological consequences for Chlamydia and implies the need to regulate carefully the interaction of the inclusion with this host trafficking pathway.

Design, synthesis, molecular modeling, and anti-HIV-1 integrase activity of a series of photoactivatable diketo acid-containing inhibitors as affinity probes

The diketo acid (DKA) class of HIV-1 integrase (IN) inhibitors is thought to function by chelating divalent metal ions on the enzyme catalytic site. However, differences in mutations conferring resistance to various DKA inhibitors suggest that multiple binding orientations may exist. In order to facilitate identification of DKA binding sites, a series of photoactivable analogues of two potent DKAs was prepared as novel photoaffinity probes. In cross-linking assays designed to measure disruption of substrate DNA binding, the photoprobes behaved similarly to a reference DKA inhibitor. Molecular modeling studies suggest that such photoprobes interact within the IN active site in a manner similar to that of the parent DKAs. Analogues Ia-c are novel photoaffinity ligands useful in clarifying the HIV-1 binding interactions of DKA inhibitors.

Detergent-mediated phospholipidation of plasma lipoproteins increases HDL cholesterophilicity and cholesterol efflux via SR-BI

Cellular cholesterol efflux is an early, obligatory step in reverse cholesterol transport, the putative antiatherogenic mechanism by which human plasma high-density lipoproteins (HDL) transport cholesterol from peripheral tissue to the liver for recycling or disposal. HDL-phospholipid content is the essential cholesterol-binding component of lipoproteins and therefore a major determinant of cholesterol efflux. Thus, increased phospholipidation of lipoproteins, particularly HDL, is one strategy for increasing cholesterol efflux. This study validates a simple, new detergent perturbation method for the phospholipidation of plasma lipoproteins; we have quantified the cholesterophilicity of human plasma lipoproteins and the effects of lipoprotein phospholipidation on cholesterophilicity and cellular cholesterol efflux mediated by the class B type I scavenger receptor (SR-BI). We determined that low-density lipoproteins (LDL) are more cholesterophilic than HDL and that LDL has a higher affinity for phospholipids than HDL whereas HDL has a higher phospholipid capacity than LDL. Phospholipidation of total human plasma lipoproteins enhances cholesterol efflux, an effect that occurs largely through the preferential phospholipidation of HDL. We conclude that increasing HDL phospholipid increases its cholesterophilicity, thereby making it a better acceptor of cellular cholesterol efflux. Phospholipidation of lipoproteins by detergent perturbation is a simple way to increase HDL cholesterophilicity and cholesterol efflux in a way that may be clinically useful.

Development of Selective Inhibitors and Substrate of Matrix Metalloproteinase-12

Four phosphinic peptide libraries with compounds having the general formula p-Br-Ph-(PO2-CH2)-Xaa'-Yaa'-Zaa'-NH2 have been prepared and screened against 10 matrix metalloproteinases (MMPs). We identified two phosphinic peptides with Ki values of 0.19 and 4.4 nM toward MMP-12 (macrophage elastase) that are more than 2-3 orders of magnitude less potent toward the other MMPs tested. These highly selective MMP-12 inhibitors contain a Glu-Glu motif in their Yaa'-Zaa' positions. Incorporation of this Glu-Glu motif into the sequence of a nonspecific fluorogenic peptide cleaved by MMPs provides a highly selective substrate for MMP-12. A model of one of these inhibitors interacting with MMP-12 suggests that the selectivity observed might be due, in part, to the presence of two unique polar residues in MMP-12, Thr239 and Lys177. These MMP-12-selective inhibitors may have important therapeutic applications to diseases in which MMP-12 has been suggested to play a key role, such as in emphysema, atherosclerosis, and aortic abdominal aneurysm.

Synthesis and structure–activity relationship studies on a novel series of naphthylidinoylureas as inhibitors of acyl-CoA:cholesterol O -acyltransferase (ACAT)

The synthesis and structure-activity relationships of N-phenyl-N'-[3-(4-phenylnaphthylidinoyl)]urea derivatives 3 as a novel structural class of potent ACAT inhibitors is described. A 3-methoxy group substituted on the naphthylidinone 4-phenyl ring, together with a 1-N-(n)butyl substitution, SM-32504 (3m), gave a potent ACAT inhibitor, in vitro, respectively. The most potent compound, SM-32504 (3m), decreased the serum cholesterol level significantly in a high fat and high cholesterol-fed mouse model.

A novel action of terpendole E on the motor activity of mitotic Kinesin Eg5

To reveal the mechanism of mitosis, the development of M phase-specific inhibitors is an important strategy. We have been screening microbial products to find specific M phase inhibitors that do not directly target tubulins, and rediscovered terpendole E (TerE) as a novel Eg5 inhibitor. TerE did not affect microtubule integrity in interphase, but induced formation of a monoastral spindle in M phase. TerE inhibited both motor and microtubule-stimulated ATPase activities of human Eg5, but did not affect conventional kinesin from either Drosophila or bovine brain. Although terpendoles have been reported as inhibitors of acyl-CoA:cholesterol O-acyltransferase (ACAT), the Eg5 inhibitory activity of TerE was independent of ACAT inhibition. Taken together, we demonstrate that TerE is a novel Eg5 inhibitor isolated from a fungal strain.

Solid-phase synthesis of linear ureas tethered to hydantoins and thiohydantoins

An efficient method for the solid-phase synthesis of hydantoins and thiohydantoins tethered to ureas, starting from a resin-bound amino acid, is presented. Following reduction of the amide with borane-THF, a second amino acid was selectively coupled to the primary amine followed by treatment of the secondary amine by an isocyanate to generate the corresponding urea. Hydantoin and thiohydantoin formation was achieved through the use of carbonyldiimidazole and thiocarbonyldiimidazole, respectively. Cleavage from the solid support using hydrogen fluoride, followed by extraction and lyophilization, provided the desired urea-linked heterocyclic compounds in good yield and high purity.

5-Phenyl substituted 1-methyl-2-pyridones and 4'-substituted biphenyl-4-carboxylic acids. synthesis and evaluation as inhibitors of steroid-5alpha-reductase type 1 and 2

The synthesis of a series of 5-phenyl substituted 1-methyl-2-pyridones (I) and 4'-substituted biphenyl-4-carboxylic acids (II) as novel A-C ring steroidomimetic inhibitors of 5alpha-reductase (5alphaR) is described. Compounds 1-4 (I) were synthesized by palladium catalyzed cross coupling (Ishikura) reaction between diethyl(3-pyridyl)borane and aryl halides (1b-4b) followed by alpha-oxidation with sodium ferrocyanate of the 1-methyl-pyridinium salt. Inhibitors II (5-18) were obtained either by two successive Friedel-Crafts acylations from biphenyl (5a-10a) followed by saponification to yield the corresponding carboxylic acids (5-10) or by Suzuki cross coupling reaction to give the 4'-substituted biphenyl-4-carbaldehydes 11a-18a. The latter compounds were subjected to a Lindgren oxidation to yield compounds 11-18. The compounds were tested for inhibitory activity toward human and rat 5alphaR1 and 2. The test compounds inhibited 5alphaR, showing a broad range of inhibitory potencies. The best compound in series I was the N-(dicyclohexyl)-4-(1,2-dihydro-1-methyl-2-oxopyrid-5-yl)benzamide 4 exhibiting an IC(50) value for the human type 2 enzyme of 10 microM. In series II, the most active compound toward human type 2 isozyme was the 4'-(dicyclohexyl)acetyl-4-biphenyl carboxylic acid (10; IC(50)=220nM). Both series showed only marginal activity toward the human type 1 isozyme. In conclusion, the biphenyl carboxylic acids (II) are more appropriate for 5alphaR inhibition than the 5-phenyl-1-methyl-2-pyridones (I). Especially the 4'-carbonyl compounds 5-10 represent new lead structures for the development of novel human type 2 inhibitors.

Solution-phase synthesis of an aminomethyl-substituted biaryl library via sequential amine N-alkylation and Suzuki cross-coupling

Described herein is the semiautomated preparation of a 20-member aminomethyl-substituted biaryl library. The two-step solution-phase synthesis was achieved via sequential N-alkylation of various amines with either 3- or 4-bromobenzyl bromide and Suzuki cross-coupling of the resultant aryl bromides with various boronic acids.

Tethered libraries: solid-phase synthesis of substituted urea-linked bicyclic guanidines

The general concept of tethered combinatorial libraries of compounds in which two pharmacophores are found is described. In particular, an improved method for the solid-phase synthesis of bicyclic guanidines from reduced N-acylated dipeptides, and its use in the synthesis of urea-linked bicyclic guanidines, is described. The exhaustive reduction of glutamine-containing resin-bound N-acylated dipeptides, using borane-THF, generated compounds containing three secondary amines and one primary amine. Following selective trityl protection of the primary amine, treatment of the three secondary amines with thiocarbonyldiimidazole (CSIm2) and mercuric acetate (Hg(OAc)2) generated the resin-bound bicyclic guanidines. Following trityl deprotection, an Fmoc-amino acid was coupled. Upon removal of the Fmoc protecting group, the resulting primary amine was treated with hexyl isocyanate to generate the urea-linked bicyclic guanidines. The desired products were cleaved from the resin using hydrogen fluoride. The selection of building blocks and characterization of controls for the synthesis of a combinatorial library is discussed.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. 3. Discovery of a novel series of N-alkyl-N-[(fluorophenoxy)benzyl]-N'-arylureas with weak toxicological effects on adrenal glands

A series of N-alkyl-N-[(fluorophenoxy)benzyl]-N'-arylureas were prepared and evaluated for their ability to inhibit intestinal acyl-CoA:cholesterol O-acyltransferase and to inhibit accumulation of cholesteryl esters in macrophages in vitro. In vivo hypocholesterolemic activity was assessed in cholesterol-fed rats by oral administration as a dietary admixture and/or by gavage in a PEG400 vehicle. Modification of the alkyl substituent on the N'-aryl moiety and on the urea nitrogen significantly influenced macrophage assay in vitro. Toxicological study revealed a distinct relationship between macrophage assay and the toxicity observed in adrenal glands of rabbits treated with representatives of this series of compounds. Investigations utilizing the macrophage assay as an indicator for adrenal toxicity led to the identification of compounds 1g (FR190809) and 1k (FR186485, or FR195249 as its hydrochloride salt) as potent, nonadrenotoxic, orally efficacious ACAT inhibitors irrespective of the administration method.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. 2. Identification and structure-activity relationships of a novel series of N-alkyl-N-(heteroaryl-substituted benzyl)-N'-arylureas

A series of N-alkyl-N-(heteroaryl-substituted benzyl)-N'-arylurea and related derivatives represented by 2 and 3 have been prepared and evaluated for their ability to inhibit acyl-CoA:cholesterol O-acyltransferase in vitro and to lower plasma cholesterol levels in cholesterol-fed rats in vivo. Among these novel compounds, the type 3 series was superior. A pyrazol-3-yl group on the N-benzyl group of this trisubstituted urea (i.e. 3, Ar1 = pyrazol-3-yl) was identified as a heteroaromatic ring providing a good profile of biological activity. As a result of optimization of the combination with the N-alkyl group (R) and N-aryl group (Ar3), compound 3aq (FR186054) was identified as a new, orally efficacious ACAT inhibitor, which exhibited potent in vitro ACAT inhibitory activity (rabbit intestinal microsomes IC50 = 99 nM) and excellent hypocholesterolemic effects in cholesterol-fed rats, irrespective of administration mode (ED50 = 0.046 mg/kg dosed via the diet, ED50 = 0. 44 mg/kg administered by gavage in PEG400 vehicle). Moreover, a toxicological study revealed compound 3aq to be nontoxic to the adrenal glands of dogs when tested at a single dose of 10 mg/kg po.