Structural evolution and pharmacology of a novel series of triacid angiotensin II receptor antagonists

Gold-Catalyzed Formal [3 + 2] Cycloaddition of Ynamides with 4,5-Dihydro-1,2,4-oxadiazoles: Synthesis of Functionalized 4-Aminoimidazoles

A gold-catalyzed formal [3 + 2] cycloaddition of ynamides with 4,5-dihydro-1,2,4-oxadiazoles has been developed. The reaction provides a concise and regioselective access to highly functionalized 4-aminoimidazoles likely via the formation of an α-imino gold carbene intermediate followed by cyclization. 4,5-Dihydro-1,2,4-oxadiazole was found to act as an efficient N-iminonitrene equivalent in these reactions.

4R- and 4S-iodophenyl hydroxyproline, 4R-pentynoyl hydroxyproline, and S-propargyl-4-thiolphenylalanine: conformationally biased and tunable amino acids for bioorthogonal reactions

Bioorthogonal reactions allow the introduction of new functionalities into peptides, proteins, and other biological molecules. The most readily accessible amino acids for bioorthogonal reactions have modest conformational preferences or bases for molecular interactions. Herein we describe the synthesis of 4 novel amino acids containing functional groups for bioorthogonal reactions. (2S,4R)- and (2S,4S)-iodophenyl ethers of hydroxyproline are capable of modification via rapid, specific Suzuki and Sonogashira reactions in water. The synthesis of these amino acids, as Boc-, Fmoc- and free amino acids, was achieved through succinct sequences. These amino acids exhibit well-defined conformational preferences, with the 4S-iodophenyl hydroxyproline crystallographically exhibiting β-turn (ϕ, ψ∼-80°, 0°) or relatively extended (ϕ, ψ∼-80°, +170°) conformations, while the 4R-diastereomer prefers a more compact conformation (ϕ∼-60°). The aryloxyproline diastereomers present the aryl groups in a highly divergent manner, suggesting their stereospecific use in molecular design, medicinal chemistry, and catalysis. Thus, the 4R- and 4S-iodophenyl hydroxyprolines can be differentially applied in distinct structural contexts. The pentynoate ester of 4R-hydroxyproline introduces an alkyne functional group within an amino acid that prefers compact conformations. The propargyl thioether of 4-thiolphenylalanine was synthesized via copper-mediated cross-coupling reaction of thioacetic acid with protected 4-iodophenylalanine, followed by thiolysis and alkylation. This amino acid combines an alkyne functional group with an aromatic amino acid and the ability to tune aromatic and side chain properties via sulfur oxidation. These amino acids provide novel loci for peptide functionalization, with greater control of conformation possible than with other amino acids containing these functional groups.

Protein kinase C inhibition ameliorates functional endothelial insulin resistance and vascular smooth muscle cell hypersensitivity to insulin in diabetic hypertensive rats

OBJECTIVE

Insulin resistance, diabetes, and hypertension are considered elements of metabolic syndrome which is associated with vascular dysfunction. We investigated whether inhibition of protein kinase C (PKC) would affect vascular function in diabetic hypertensive (DH) rats.

METHODS

A combination of type 2 diabetes and arterial hypertension was produced in male Sprague Dawley rats by intrauterine protein deprivation (IUPD) followed by high salt diet. At the age of 32 weeks, DH rats were treated for 2 weeks with the angiotensin-converting enzyme inhibitor captopril (Capto, 30 mg/kg), PKC inhibitor ruboxistaurin (RBX, 50 mg/kg) or vehicle (n = 8 per group) and blood pressure was monitored using telemetry. At the end of experiments, femoral arteries were dissected, and vascular reactivity was evaluated with isovolumic myography.

RESULTS

The IUPD followed by high salt diet resulted in significant elevation of plasma glucose, plasma insulin, and blood pressure. Endothelium-dependent vascular relaxation in response to acetylcholine was blunted while vascular contraction in response to phenylephrine was enhanced in the DH rats. Neither Capto nor RBX restored endothelium-dependent vascular relaxation while both suppressed vascular contraction. Ex-vivo incubation of femoral arteries from control rats with insulin induced dose-response vasorelaxation while insulin failed to induce vasorelaxation in the DH rat arteries. In the control arteries treated with endothelial nitric oxide synthase inhibitor L-NAME, insulin induced vasoconstriction that was exacerbated in DH rats. Capto and RBX partially inhibited insulin-stimulated vascular contraction.

CONCLUSION

These findings suggest that PKC inhibition ameliorates functional endothelial insulin resistance and smooth muscle cell hypersensitivity to insulin, but does not restore acetylcholine-activated endothelium-dependent vasodilation in DH rats.

Exploiting the CNC side chain in heterocyclic rearrangements: synthesis of 4(5)-acylamino-imidazoles

A new variation on the Boulton-Katritzky reaction is reported, namely, involving use of a CNC side chain. A novel Montmorillonite-K10 catalyzed nonreductive transamination of a 3-benzoyl-1,2,4-oxadiazole afforded a 3-(alpha-aminobenzyl)-1,2,4-oxadiazole, which was condensed with benzaldehydes to afford the corresponding imines. In the presence of strong base, these imines underwent Boulton-Katritzky-type rearrangement to afford novel 4(5)-acylaminoimidazoles.

ACE inhibitors hypothesis generation for selective design, synthesis and biological evaluation of 3-mercapto-2-methyl-propanoyl-pyrrolidine-3-imine derivatives as antihypertensive agents

A series of new 3-mercapto-2-methyl-propanoyl-pyrrolidine derivatives (V, VIa-e) were designed. A new validated ACE inhibitors pharmacophore model (hypothesis) was generated for the first time in this research from the biologically active (frozen) conformation of Lisinopril-Human ACE complex that was downloaded from PDB, using stepwise technique of CATALYST modules. The molecular modeling compare-fit study of the designed molecules (V, VIa-e), with such ACE inhibitors hypothesis was fulfilled, and several compounds showed significant high simulation fit values. The compounds with high fit values were synthesized and biologically evaluated in vivo as hypotensive agents. It appears that the in vivo hypotensive activity of compounds V, VIa, VIb, and VIe was consistent with their molecular modeling results, and compound VIe showed the highest activity in comparison to Captopril.

Recent Progress in the Catalytic Synthesis of Imidazoles

Imidazole is one of the important heteroaromatic compounds that have found a broad range of uses in, for example, pharmaceutical and industrial applications. Several conventional methodologies for the synthesis of imidazole rings are known; however, they are limited in terms of substrate generality and are not always efficient. Recent studies toward the development of catalytic reactions have brought significant improvements to the preparation of imidazoles. This Focus Review highlights the very recent progress in the catalytic synthesis of imidazoles, particularly those involving the formation of five-membered ring cores.

Synthesis of Substituted Imidazoles via Organocatalysis

A one-pot synthesis of substituted imidazoles is described. The cornerstone of this methodology involves the thiazolium-catalyzed addition of an aldehyde to an acyl imine to generate the corresponding alpha-ketoamide in situ followed by ring closure to the imidazole in a one-pot sequence. The extension of this methodology to the one-pot synthesis of substituted oxazoles and thiazoles is also described. [reaction: see text]

Identification of TNF-alpha inhibitors from a split-pool library based on a tyrosine-proline peptidomimetic scaffold

The design and synthesis of a combinatorial library based on a 4-aryloxyproline scaffold with tyrosine as the aryl portion is described. The 1728 member library was prepared using the split-pool method to generate pools of compounds. Screening of the library components as mixtures followed by deconvolution led to the discovery of novel inhibitors of TNF-alpha induced apoptosis.

Inhibition of angiotensin II-induced inositol phosphate production by triacid nonpeptide antagonists in CHO cells expressing human AT1 receptors

PURPOSE

The aim of the present work is to describe the inhibitory properties of LY301875 and LY303336, two polysubstituted 4-aminoimidazole AT1 receptor antagonists, on CHO cells expressing human recombinant AT1 receptors.

METHODS

The binding of [3H]-angiotensin II to intact cells as well as to angiotensin II induced inositol phosphate accumulation is measured.

RESULTS

Both antagonists inhibit specific [3H]-angiotensin II binding to AT1 receptors in these cells, with IC50 values of 5.9 and 5.2 nM, respectively. Preincubation of the cells with LY301875 results in a decline of up to 80% of the maximal angiotensin II-stimulated inositol phosphate (IP) production. A near complete decline of the maximal response is observed for LY303336. This insurmountable inhibition is attenuated for both antagonists when losartan is included during the preincubation of the cells.

CONCLUSIONS

Functional recovery experiments, in which antagonist-preincubated cells are washed and exposed to fresh media, suggest that the insurmountable inhibition by LY301875 and LY303336 is related to their relatively slow dissociation from the AT1 receptors. As already described for losartan and the derived insurmountable AT1 antagonists candesartan. EXP3174, and irbesartan, coincubation experiments reveal that LY301875 and LY303336 interact with the AT1 receptor in a manner that is competitive with angiotensin II.

An investigation of imidazole and oxazole syntheses using aryl-substituted TosMIC reagents

This article describes efficient and mild protocols for preparing polysubstituted imidazoles in a single pot from aryl-substituted tosylmethyl isocyanide (TosMIC) reagents and imines generated in situ. Traditional imine-forming reactions employing virtually any aldehyde and amine followed by addition of the TosMIC reagent delivers 1,4,5-trisubstituted imidazoles with predictable regiochemistry. Employing chiral amines and aldehydes, particularly those derived from alpha-amino acids, affords imidazoles with asymmetric centers appended to N-1 or C-5 with excellent retention of chiral purity. 1,4-Disubstituted imidazoles are also readily prepared by a simple variant of the above procedure. Selecting glyoxylic acid as the aldehyde component of this procedure leads to intermediates such as 48, which readily undergo decarboxylation and elimination of the tosyl moiety to deliver 1,4-disubstituted imidazoles in high yields. Alternatively, using NH(4)OH as the amine component in conjunction with a variety of aldehydes delivers 4, 5-disubstituted imidazoles in moderate to good yields in a single pot while avoiding the need for protecting groups. Finally, the facile preparation of mono- and disubstituted oxazoles from these TosMIC reagents and aldehydes is described.