Butenolide endothelin antagonists with improved aqueous solubility.

Continued development around our ETA-selective endothelin (ET) antagonist 1 (CI-1020) has led to the synthesis of analogues with improved aqueous solubility profiles. Poor solubility characteristics displayed by 1 required a complex buffered formulation in order to conduct iv studies. To overcome the use of specific iv formulations for preclinical studies on additional drug candidates, analogues with improved aqueous solubility were desired. Several analogues were synthesized with substitution patterns that allowed for the formation of either acid or base addition salts. These derivatives had dramatically improved aqueous solubility. In addition, these analogues retained equivalent or improved ETA receptor selectivity and antagonist potency, versus 1, both in vitro and in vivo. Compound 29, which contains as a substituent the sodium salt of a sulfonic acid, has an ETA IC50 = 0.38 nM, ETA selectivity of 4200-fold, and ETA functional activity of KB = 7.8, all of which are similar or superior to those of 1. Compound 29 also has vastly superior aqueous solubility and solubility duration, compared to 1. Furthermore, 29 after iv infusion displays improved activity to 1 in preventing acute hypoxia-induced pulmonary hypertension in rats with an ED50 = 0.3 microg/kg/h.

Characterization of [125I]-PD164333, an ETA selective non-peptide radiolabelled antagonist, in normal and diseased human tissues.

1 We have synthesized a new low molecular weight, non-peptide radioligand, [125I]-PD164333, an analogue of the orally active butenolide antagonists of the endothelin ETA receptor. 2 Analysis of saturation binding assays demonstrated that [125I]-PD164333 bound with high affinity to a single population of receptors (n > or = 3 individuals +/- s.e.mean) in human aorta (KD=0.26+/-0.08 nM; Bmax=8.8+/-3.95 fmol mg(-1) protein), left ventricle from the heart (KD=0.16+/-0.02 nM; Bmax=34.2+/-3.02 fmol mg(-1) protein) and kidney (KD=1.24+/-0.16 nM; Bmax=125.3+/-35.07 fmol mg(-1) protein). In each case Hill slopes were close to unity. 3 In kinetic experiments, the binding of [125I]-PD164333 to ETA receptors in sections of heart was time-dependent and rapid at 23 degrees C. The data were fitted to a one site model, with an association rate constant (K1 of 2.66+/-0.213x10(8) M(-1) min(-1), and a half-time for association of 11 min. The binding was reversible at 23 degrees C: analysis of the data indicated [125I]-PD164333 dissociated from a single site, with a dissociation rate constant of 0.0031+/-0.0004 min(-1), a half-time for dissociation of 216 min and a KD calculated from these kinetic data of 0.01 nM. 4 Unlabelled PD164333 inhibited the binding of [125I]-ET-1 to left ventricle (which expresses both subtypes) in a biphasic manner with a KDETA of 0.99+/-0.32 nM and KDETB of 2.41+/-0.22 microM, giving a selectivity of 2500 fold. ETA-selective ligands competed monophasically for [125I]-PD164333 binding in left ventricle, a one site fit was preferred to a two site model giving similar nanomolar affinities: BQ123, KD=3.93+/-0.18 nM; FR139317 KD=3.53+/-0.69 nM. In contrast, the ETB selective agonists, BQ3020 and sarafotoxin S6c (1 microM) did not inhibit binding. 5 In human isolated saphenous vein, unlabelled PD164333 was a functional antagonist, producing parallel rightward shifts of the endothelin-1 (ET-1) concentration-response curve (pA2=8.84) and a slope of unity. 6 In the human brain, autoradiography revealed high levels of [125I]-PD164333 binding to the pial arteries of the cerebral cortex and to the numerous smaller intercerebral vessels penetrating the underlying grey and white matter. Conduit and resistance vessels contributing to the control of blood pressure from the heart, kidney, lungs and adrenal also displayed high densities of binding. In diseased vessels, binding of [125I]-PD164333 was confined to the medial layer of both coronary arteries with advanced atherosclerotic lesions or occluded saphenous vein grafts. In contrast, little or no binding was detected in the proliferated smooth muscle of the intimal layer or occluded lesion. 7 These results show [125I]-PD164333 is a specific, high affinity, reversible non-peptide radioligand for human ETA receptors, which will facilitate the further characterization of this subtype, in vitro and in vivo.

Synthesis of novel substituted pyridines as inhibitors of endothelin converting enzyme-1 (ECE-1).

A series of bi-aryl pyridine carboxylic acids has been prepared and evaluated as inhibitors of ECE-1. The analogs were prepared by Pd catalyzed cross couplings of halogenated pyridines with heteroaryl organo-boranes, -tinate or -zincate derivatives.

Structure-activity relationships in a series of orally active gamma-hydroxy butenolide endothelin antagonists.

The design of potent and selective non-peptide antagonists of endothelin-1 (ET-1) and its related isopeptides are important tools defining the role of ET in human diseases. In this report we will describe the detailed structure-activity relationship (SAR) studies that led to the discovery of a potent series of butenolide ETA selective antagonists. Starting from a micromolar screening hit, PD012527, use of Topliss decision tree analysis led to the discovery of the nanomolar ET(A) selective antagonist PD155080. Further structural modifications around the butenolide ring led directly to the subnanomolar ETA selective antagonist PD156707, IC50's = 0.3 (ET(A)) and 780 nM (ET(B)). This series of compounds exhibited functional activity exemplified by PD156707. This derivative inhibited the ETA receptor mediated release of arachidonic acid from rabbit renal artery vascular smooth muscle cells with an IC50 = 1.1 nM and also inhibited the ET-1 induced contraction of rabbit femoral artery rings (ETA mediated) with a pA2 = 7.6. PD156707 also displayed in vivo functional activity inhibiting the hemodynamic responses due to exogenous administration of ET-1 in rats in a dose dependent fashion. Evidence for the pH dependence of the open and closed tautomerization forms of PD156707 was demonstrated by an NMR study. X-ray crystallographic analysis of the closed butenolide form of PD156707 shows the benzylic group located on the same side of the butenolide ring as the gamma-hydroxyl and the remaining two phenyl groups on the butenolide ring essentially orthogonal to the butenolide ring. Pharmacokinetic parameters for PD156707 in dogs are also presented.

Structure-activity relationships of a novel series of orally active nonpeptide ETA and ETA/B endothelin receptor-selective antagonists.

The development of nonpeptide, low molecular weight antagonists with high potency, oral activity, and selectivity is an important objective to adequately define the potential role of endothelin (ET) and its isopeptides in human diseases. This report describes the structure-activity relationships, ETA/ETB selectivity, and pharmacokinetics of the PD 155080 and PD 156707 series of orally active nonpeptide ET receptor-selective antagonists. Modification of the substituents around the butenolide ring has led to compounds with differing selectivity for human ETA and ETB receptors. Thus, compounds with increased lipophilicity at R2 show increased ETB affinity and a more balanced ETA/ETB profile. For example, the 4-O-n-pentyl analogue of PD 156707 is a potent competitive inhibitor of [125I]ET-1 and [125I]ET-3 binding to human cloned ETA and ETB receptors, with IC50s of 0.8 nM and 44 nM, respectively. Pharmacokinetic properties can also be significantly influenced by structural modifications at the R2 group. The pharmacokinetics of PD 155719, PD 155080, and PD 156707 were compared in male Wistar rats after a 15 mg/kg intravenous or oral gavage dose (three animals per dose). Plasma concentrations were determined by a specific HPLC assay. Oral bioavailability ranged from less than 5% for PD 155719 to 41% for PD 156707 and 87% for PD 155080.

Effect of an orally active renin inhibitor Cl-992 on blood pressure in normotensive and hypertensive monkeys.

Cl-992, a novel potent inhibitor of primate renin, was tested for blood pressure-lowering efficacy in sodium-restricted, furosemide-treated conscious normotensive cynomolgus monkeys and conscious renal hypertensive monkeys. The hypertensive monkey model provided an opportunity to determine the response to a renin inhibitor in a pathological nonhuman primate model of hypertension without concurrent diuretic treatment or dietary sodium restriction and on repeated oral administration. Cl-992 has IC50 values of 0.58 +/- 0.06 (n = 4) and 0.36 +/- 0.03 nM (n = 8) against human and monkey renin, respectively. In normotensive monkeys, oral Cl-992 at doses of 3, 10 and 30 mg/kg reduced mean arterial blood pressure (MABP) by 8 +/- 2, 15 +/- 7 and 29 +/- 7 mm Hg (n = 5 animals per dose level, P < .05), respectively (base line, 103 +/- 3 mm Hg). Intravenous Cl-992 (0.0001 to 0.1 mg/kg) also caused dose-dependent decreases in MABP and a maximum reduction of 23 +/- 4 mm Hg. The decrease in MABP after Cl-992 was paralleled by an inhibition of plasma renin activity (PRA) and a reduction in immunoreactive angiotensin II. In renal hypertensive monkeys, oral Cl-992 at doses of 3, 10 and 30 mg/kg reduced MABP by 6 +/- 2, 18 +/- 6 and 37 +/- 8 mm Hg (n = 3 or 4, P < .05), respectively (base line, 134 +/- 4 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Structure-activity relationships of a series of 2-amino-4-thiazole-containing renin inhibitors.

A series of renin inhibitors was synthesized that contained a 2-amino-4-thiazolyl moiety at the P2 position. These derivatives are potent inhibitors of monkey renin in vitro and are selective in that they only weakly inhibit the closely related aspartic proteinase, bovine cathepsin D. Four compounds exhibited oral blood pressure lowering activity in high-renin normotensive monkeys. One of these compounds, 22 (PD 134672), was selected for further evaluation in renal hypertensive monkeys, on the basis of its superior efficacy and duration of action in the in vitro assays and the normotensive primate model.

Perfluorocarbon-based antidiabetic agents.

In a preliminary communication (J. Med. Chem. 1989, 32, 11-13) a series of perfluoro-N-[4-(1H-tetrazol-5ylmethyl)phenyl]alkana mides (perfluoro anilides I), designed as novel analogues of ciglitazone, were reported to possess oral antidiabetic activity in two genetic animal models of non-insulin-dependent diabetes mellitus (NIDDM): obese (ob/ob) and diabetic (db/db) mice. In this report, the results from a structure-activity relationship (SAR) study of the series I are described. Comprehensive statistical analysis among the 86 analogues screened for blood glucose lowering in ob/ob mice was achieved by a new application of a general statistical procedure which made it possible to make meaningful comparisons between more than 140 separate experiments (N = 2966). Perfluoro anilides I lowered plasma glucose in the hyperglycemic ob/ob and db/db mice but not in euglycemic normal rats. In the hyperinsulinemic ob/ob mouse, decreases in plasma insulin levels paralleled the decline in plasma glucose. Potency and efficacy in the series was shown to be dependent on the length of the perfluorocarbon chain (RF) of I. Optimal activity occurred with the C7 and C8 RF chains. The more extensive SAR studies reported here, indicated that the lipophilic RF chain is the most important structural element of I since neither the phenyl nor tetrazole rings present in anilides I were necessary for antihyperglycemic activity while medium length (C7-C8) RF chains, especially the C7F15 chain, were shown to confer antihyperglycemic activity in ob/ob mice to a wide variety of structures.

N6-substituted adenosine receptor agonists: potential antihypertensive agents.

Adenosine is known to exert a wide range of pharmacological effects including hypotension. This effect of adenosine suggested that modified analogues of adenosine might provide useful antihypertensive agents. Thus, we prepared a series of novel N6-benzocycloalkyladenosines and studied their receptor binding and antihypertensive activity. The structure-activity relationship study shows that the adenosine analogues having the hydrophobic phenyl moiety one carbon away from the C6-nitrogen have modest affinity and selectivity for the A1 receptor, whereas those with the phenyl moiety two carbons away from the C6-nitrogen have excellent affinity and selectivity for the A1 receptor. Many of these analogues showed excellent antihypertensive activity with a wide range of effects on heart rate. There is no direct correlation between the receptor binding affinities and antihypertensive activity; however, it is more closely associated with A1 than A2 affinity. The bradycardic effect of these agonists seems to be due to the A1 affinity. From this set, compound 3 was further evaluated in secondary antihypertensive screens. It lowered the blood pressure dose dependently with effects lasting for over 20 h following administration of a 30 mg/kg dose. Compound 3 was also effective in lowering blood pressure in a renal hypertensive rat model. Thus, appropriately modified N6-substituted adenosines represent a novel class of antihypertensive agents.

Ribose-modified adenosine analogues as adenosine receptor agonists.

Analogues of the potent adenosine receptor agonist (R)-N-(1-methyl-2-phenylethyl)adenosine (R-PIA), modified at N9, were prepared and evaluated for adenosine A1 and A2 receptor binding and in vivo central nervous system and cardiovascular effects. The modifications at N9 include deoxy sugars, 5'-substituted-5'-deoxyriboses, non-ribose sugars, sugar ring homologues, and acyclic sugar analogues. Most of the derivatives have poor affinity for adenosine receptors. Only minor modifications at C5' and C3' maintain potent binding. In general, those derivatives exhibiting in vivo behavioral or cardiovascular effects also have the highest affinity for adenosine receptors.