Imidazole-5-acrylic acids: potent nonpeptide angiotensin II receptor antagonists designed using a novel peptide pharmacophore model

Catalyst-free synthesis of α-thioacrylic acids via cascade thiolation and 1,4-aryl migration of aryl alkynoates at room temperature

A simple and facile catalyst-free strategy has been developed for the synthesis of α-thioacrylic acids from readily-available aryl alkynoates and thiols at room temperature under air.

Synthesis of cribrostatin 6

The synthesis of cribrostatin 6 (1) is described. A regioselective bromination, a biaryl coupling, and an intramolecular cyclization are the key steps in the synthesis.

Stereoselective synthesis of acetoacetate-derived enol triflates

A highly stereoselective method for preparing ( Z)- and ( E)-enol triflates derived from substituted acetoacetate derivatives is described. The salient feature of this methodology is the use of Schotten-Baumann-type conditions to control enolate geometry using either aqueous LiOH ( Z-selective) or aqueous (Me)(4)NOH ( E-selective) in combination with triflic anhydride to provide a practical and predictable approach to these valuable substrates.

Structure-activity relationships of a novel class of endothelin-A receptor antagonists and discovery of potent and selective receptor antagonist, 2-(benzo[1,3]dioxol-5-yl)-6-isopropyloxy-4-(4-methoxyphenyl)-2H-chromene-3-carboxylic acid (S-1255). 1. Study on structure-activity relationships and basic structure crucial for ET(A) antagonism

A novel series of endothelin-A (ET(A)) selective receptor antagonists having a 2H-chromene skeleton are described. A lead compound, 2-(benzo[1,3]dioxol-5-yl)-2H-chromene-3-carboxylic acid (3), was found by modifications of our own angiotensin II antagonist. A structure-activity relationship (SAR) study of 3 reveals that the structural requirements essential for potent and selective ET(A) receptor binding affinity are the m,p-methylenedioxyphenyl, carboxyl, and isopropoxy groups at the 2-, 3-, and 6-positions, respectively, on the (R)-2H-chromene skeleton. The substituent at the 4-position is also important for improving the activity, and various hydrophobic functional groups of 6-9 A such as liner, branched, and cyclic aliphatic groups, unsubstituted and substituted aryl groups, and even halogen atoms were acceptable. These results suggest that (R)-2-(benzo[1,3]dioxol-5-yl)-6-isopropoxy-2H-chromene-3-carboxylic acid, formula 108, is the crucial basic structure to be recognized by the ET(A) receptor. The most potent compound is (R)-48 (S-1255), which binds to the ET(A) receptor with an IC(50) value of 0.19 nM and is 630-fold selective for the ET(A) receptor than for the ET(B) receptor. This compound has 55% oral bioavailability in rats. On the basis of the SAR, the roles of each substituent in the receptor binding are discussed.

Synthesis and biological evaluation of the geometric farnesylated analogues of the a-factor mating peptide of Saccharomyces cerevisiae

The a-factor of Saccharomyces cerevisiae is a dodecapeptide pheromone (YIIKGVFWDPAC(Farnesyl)-OCH(3), 1), in which post-translational modification with a farnesyl isoprenoid and carboxymethyl group is required for full biological activity. This peptide has been used as a model system to explore the biological function of the farnesylcysteine moiety, which is found on and required for the biological activity of many key mammalian proteins. The objective of this particular study was the determination of the biological effect of double bond isomerization of the natural E, E-farnesyl moiety on the biological activity of the a-factor. A unified, stereoselective synthetic route to the three geometric isomers of E,E-farnesol (12, 13, and 14) has been developed. The key feature of this synthesis is the ability to control the stereochemistry of triflation of the beta-ketoester 22 to give either 23 or 25. The three farnesol isomers were converted to the corresponding isomeric a-factors (9, 10 and 11) via a modified version of a previously utilized synthetic route. Biological evaluation of these peptides indicates that, surprisingly, all three possess nearly equivalent activity to the natural a-factor bearing the E,E-farnesyl moiety.

Synthesis of Isocoumarins and alpha-Pyrones via Palladium-Catalyzed Annulation of Internal Alkynes

A number of 3,4-disubstituted isocoumarins and polysubstituted alpha-pyrones have been prepared in good yields by treating halogen- or triflate-containing aromatic and alpha,beta-unsaturated esters, respectively, with internal alkynes in the presence of a palladium catalyst. Synthetically, the methodology provides an especially simple and convenient, regioselective route to isocoumarins and alpha-pyrones containing aryl, silyl, ester, tert-alkyl, and other hindered groups. The reaction is believed to proceed through a seven-membered palladacyclic complex in which the regiochemistry of the reaction is controlled by steric factors. A number of 3,4-disubstituted isocoumarins and polysubstituted alpha-pyrones have been prepared in good yields by treating halogen- or triflate-containing aromatic and alpha,beta-unsaturated esters, respectively, with internal alkynes in the presence of a palladium catalyst. Synthetically, the methodology provides an especially simple and convenient regioselective route to isocoumarins and alpha-pyrones containing aryl, silyl, ester, tert-alkyl, and other hindered groups. The reaction is believed to proceed through a seven-membered palladacyclic complex in which the regiochemistry of the reaction is controlled by steric factors.

Specific nonpeptide photoprobes as tools for the structural study of the angiotensin II AT(1) receptor

The aim of this work was to obtain photoactivatable nonpeptide antagonists of the angiotensin II AT(1) receptor. Based on structure-function relationships, two chemical structures as well as appropriate synthetic schemes were chosen as a frame for the design of radiolabeled azido probes. The feasibility of the strategy was first assessed by the synthesis of two tritiated ligands 21 and 22 possessing a high affinity for the AT(1) receptor and a low nonspecific binding to membrane or cell preparations. We then prepared two unlabeled azido derivatives 7 and 14 which retained a fairly high affinity for the AT(1) receptor. The latter compound proved to be suitable for receptor irreversible labeling and was prepared in its tritiated form 28. This tritiated azido nonpeptide probe displayed a K(d) value of 11.8 nM and a low nonspecific binding. It was suitable for specific and efficient covalent labeling of the recombinant AT(1A) receptor stably expressed in CHO cells. The electrophoretic pattern of the specifically labeled entity was strictly identical to that of purified receptor photolabeled with a biotinylated peptidic photoactivatable probe. This new tool should be useful for the mapping of the nonpeptide receptor binding site. These potential applications are discussed in light of the current knowledge of molecular mechanisms of G-protein coupled receptor activation and inactivation.

Nonpeptide angiotensin II receptor antagonists: synthesis, biological activities, and structure-activity relationships of imidazole-5-carboxylic acids bearing alkyl, alkenyl, and hydroxyalkyl substituents at the 4-position and their related compounds

A series of imidazole-5-carboxylic acids bearing alkyl, alkenyl, and hydroxyalkyl substituents at the 4-position and their related compounds were prepared and evaluated for their antagonistic activities to the angiotensin II (AII) receptor. Among them, the 4-(1-hydroxyalkyl)-imidazole derivatives had strong binding affinity to the AII receptor and potently inhibited the AII-induced pressor response by intravenous administration. Various esters of these acids showed potent and long-lasting antagonistic activity by oral administration. The most promising compounds were (5-methyl-2-oxo-1,3-dioxol-4-yl)methyl (CS-866) and (pivaloyloxy)-methyl esters of 4-(1-hydroxy-1-methylethyl)-2-propyl-1-[(2'-1H-tetrazol-5- ylbiphenyl-4-yl)-methyl]imidazole-5-carboxylic acid (26c). A study involving stereochemical comparison of 26c with the acetylated C-terminal pentapeptide of AII was also undertaken.

The conformation and activity relationship of fused analogs of DuP753

We have prepared three conformationally restricted analogs of DuP753 in which one of the phenyl rings in the biphenyl moiety is fused to the imidazole ring, and have investigated the conformation-biological activity relationship of these compounds. Conformational analysis on DuP753 and these compounds confirms that a specific 3-dimensional arrangement of pharmacophoric elements is essential for biological activity.