Potent nonpeptide angiotensin II receptor antagonists. 2. 1-(Carboxybenzyl)imidazole-5-acrylic acids.

The further evolution of the imidazole-5-acrylic acid series of nonpeptide angiotensin II receptor antagonists is detailed (for Part 1, see: J. Med. Chem. 1992, 35, 3858). Modifications of the N-benzyl ring substitution were undertaken in an effort to mimic the Tyr4 residue of angiotensin II. Introduction of a p-carboxylic acid on the N-benzyl ring resulted in the discovery of compounds with nanomolar affinity for the receptor and good oral activity. SAR studies of these potent antagonists revealed that the thienyl ring, the (E)-acrylic acid, and the imidazole ring in addition to the two acid groups were important for high potency. Also, overlay comparisons of the parent diacid with both angiotensin II and a representative biphenylyltetrazole nonpeptide angiotensin II receptor antagonist are presented. The parent diacid analog, SK&F 108566 or (E)-3-[2-butyl-1-(4-carboxybenzyl)-1H-imidazole-5-yl]-2-[(2- thienyl)methyl]propenoic acid, is currently in clinical development for the treatment of hypertension.

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

A series of novel nonpeptide angiotensin II receptor antagonists containing a substituted (E)-acrylic acid has been developed. The overlay of 1, an imidazole-5-acetic acid found in the patent literature, on a novel pharmacophore model of AII suggested that extension of the acid side chain and attachment of a second aryl residue to mimic the C-terminal phenylalanine region of AII would lead to increased activity. A study of extended acid side chains at C-5 of the imidazole nucleus led to the discovery of the (E)-acrylic acid 5 as a promising starting point for further exploration. As predicted by the modeling, substitution of a benzyl group on the acrylic acid side chain to mimic the phenylalanine gave increased potency. An extensive study of the SAR of the newly introduced aromatic ring revealed that electron-rich heteroaryl rings provided improved activity, most notably in the in vivo rat models. Compound 40, (E)-3-[2-butyl-1- [(2-chlorophenyl)methyl]imidazol-5-yl]-2-[(2-thienyl)methyl]-2- propenoic acid, has been shown to be a potent, competitive, and orally active small molecule AT-1 receptor antagonist. It exhibits a 2 orders of magnitude increase in binding affinity and a 10-fold improvement in in vivo potency as compared to compound 1 and represents an important milestone in the development of even more potent nonpeptide angiotensin II receptor antagonists.

Cytotoxicity and antitumor activity of some tetrahedral bis(diphosphino)gold(I) chelates.

We report the cytotoxicity toward B16 cells and antitumor activity in three transplantable tumor models of a series of ionic, tetrahedral, bischelated gold diphosphine complexes of the type [Au1(R2PYPR2')2]X, where Y = (CH2)2, (CH2)3, or cis-CH = CH. The anion (X = Cl, Br, I, CH3SO3, NO3, PF6) had little effect upon activity. The R = R' = phenyl complexes 1, 7, and 8 [Y = (CH2)2, (CH2)3, cis-CH = CH, X = Cl] were the most active against P388 leukemia, with an increase in lifespan ranging from 83 to 92% and were also active against M5076 sarcoma and B16 melanoma. Complexes with pyridyl or fluorophenyl substituents had reduced activities. For the latter, 19F and 31P NMR were used to verify the formation of bischelated gold(I) complexes in solution. The reduced activity of the complex with R = Et and R' = Ph and inactivity with R = R' = Et are discussed in terms of their increased reactivity as reducing agents. 31P NMR studies show that [AuI(Et2P(CH2)2PPh2)2]Cl readily reacts with serum, albumin, and Cu2+ ions to give oxidized ligand.

Tetrahydrothiadiazoloisoquinolines: synthesis and inhibition of phenylethanolamine-N-methyltransferase.

A series of 7,8-fused heterocyclic tetrahydroisoquinolines were synthesized and tested as inhibitors of rabbit adrenal phenylethanolamine-N-methyltransferase (PNMT). 6,7,8,9-Tetrahydro[1,2,3]thiadiazolo[5,4-h]isoquinoline 5 (SK&F 86607) was found to be a potent inhibitor of PNMT with an IC50 similar to that of 7,8-dichloro-1,2,3,4-tetrahydroisoquinoline (1, SK&F 64139). The isomeric tetrahydro[1,2,3]thiadiazolo[4,5-h]- and tetrahydro[1,2,5]thiadiazolo[3,4-h]isoquinolines, 13 and 20, were also potent PNMT inhibitors. However, substitution of Cl at position 5 (17) resulted in loss of potency similar to the loss observed in the 5-chloro analogue of 1. The 1,2,5 isomer 20 showed only a small drop in activity at 10(-6) M. All of the thiadiazoles were more potent than the 7,8-benzo-fused analogue 36. Fusion of other five-membered heterocyclic ring systems at the 7,8-position, e.g. triazole 22 and imidazoles 24 and 26, resulted in a decrease of PNMT inhibition. The alpha-adrenoreceptor affinities of 1 and 5 were also compared.

Antitumor activity of bis(diphenylphosphino)alkanes, their gold(I) coordination complexes, and related compounds.

Bisphosphines related to bis(diphenylphosphino)ethane (dppe) and their gold complexes are described that are active in a spectrum of transplantable tumor models. When administered ip on days 1-5 at its maximally tolerated dose (MTD) of 40 mumol/kg, dppe reproducibly gives 100% increase in life span (ILS) in mice bearing ip P388 leukemia. Coordination of chlorogold(I) to each phosphine in dppe gave a complex that had similar activity but at a much lower dose level than dppe; the MTD for the gold(I) complex was 7 mumol/kg. Among other metal complexes of dppe, the Au(III) complex was active (greater than 50% ILS) whereas Ag(I), Ni(II), Pt(II), Pd(II), and Rh(I) complexes were inactive. Among dppe analogues, replacement of phenyl groups with ethyl or benzyl groups resulted in inactivity for both ligands and the corresponding gold complexes whereas substitution with cyclohexyl or heterocyclic ring systems yielded ligands and/or gold complexes with antitumor activity. Among substituted-phenyl dppe and dppe(AuCl)2 analogues, 3-fluoro, 4-fluoro, perdeuterio, 4-methylthio, and 2-methylthio analogues were active; 4-methyl, 3-methyl, 4-methoxy, 4-dimethylamino, and 4-trifluoromethyl analogues were marginal or inactive. Analogues in which the ethane bridge of dppe or dppe(AuCl)2 was varied between one and six carbons, unsaturated or substituted, revealed that activity was maximal with ethane or cis-ethylene. Compounds with good P388 activity were also active in other animal tumor models.

Correlation of the in vitro cytotoxic and in vivo antitumor activities of gold(I) coordination complexes.

A series of gold(I) coordination complexes including analogues of the antiarthritic agent auranofin 1 were evaluated for in vitro cytotoxic potency against both B16 melanoma cells and P388 leukemia cells and in vivo antitumor activity against P388 leukemia in mice. A number of the complexes showed potent cytotoxic activity in vitro and antitumor activity in vivo, with the phosphine-coordinated gold(I) thiosugar complexes demonstrating the greatest in vitro and in vivo activity. The data compiled for 63 complexes of the general structural formula LAuX provide the basis for the following observations: potent in vitro cytotoxic activity is observed for substituted (phosphine) gold complexes, lack of potency in vitro correlates well with lack of antitumor activity, potent cytotoxicity in vitro is not necessarily predictive of activity in vivo, in vivo antitumor activity is generally optimized by ligation of Au(I) with a substituted phosphine and a thiosugar.

Orally active and potent inhibitors of gamma-aminobutyric acid uptake.

3-Pyrrolidineacetic acid (1a), certain piperidinecarboxylic acids--i.e., 3-piperidinecarboxylic acid (2a), 1,2,5,6-tetrahydro-3-pyridinecarboxylic acid (3a), and cis-4-hydroxy-3-piperidinecarboxylic acid (4a)--cis-3-aminocyclohexanecarboxylic acid (5a, cis-3-ACHC), and gamma-aminobutyric acid (6a, GABA) itself are among the most potent inhibitors of [3H]GABA uptake by neurons and glia in vitro. These hydrophilic amino acids, however, do not readily enter the central nervous system in pharmacologically significant amounts following peripheral administration. We now report that N-(4,4-diphenyl-3-butenyl)-3-piperidinecarboxylic acid (2b) is a specific GABA-uptake inhibitor that is more potent, more lipophilic and, in limited testing, as selective as 2a. Similar results were obtained with the N-(4,4-diphenyl-3-butenyl) derivatives of 1a, 3a, and 4a. By contrast, N-(4,4-diphenyl-3-butenyl) derivatives of 5a and 6a were not more potent than the parent amino acids and appear to inhibit GABA uptake, at least in part, by a nonselective mechanism of action. The N-(4,4-diphenyl-3-butenyl)amino acids 1b-4b exhibit anticonvulsant activity in rodents following oral or intraperitoneal administration [Yunger, L.M.; et al. J. Pharmacol. Exp. Ther. 1984, 228, 109].

Inhibitors of phenylethanolamine N-methyltransferase and epinephrine biosynthesis. 1. Chloro-substituted 1,2,3,4-tetrahydroisoquinolines.

In a search for inhibitors of epinephrine biosynthesis as potential therapeutic agents, a series of 13 ring-chlorinated 1,2,3,4-tetrahydroisoquinolines was prepared. These compounds were tested initially for their ability to inhibit rabbit adrenal phenylethanolamine N-methyltransferase (PNMT) in vitro. Enzyme-inhibitor dissociation constants, determined for the six most potent members of the series, indicated the following order of decreasing potency: 7,8-Cl2 greater than 6,7,8-Cl3 greater than 7-Cl approximately 5,6,7,8-Cl4 greater than 5,7,8-Cl3. These compounds were subsequently examined for PNMT-inhibiting activity in intact rats and mice. 7,8-Dichloro-1,2,3,4-tetrahydroisoquinoline (13, SK&F 64139) was the most potent member of the series both in vitro and in vivo and is currently undergoing clinical investigation.