Development of orally active oxytocin antagonists: studies on 1-(1-[4-[1-(2-methyl-1-oxidopyridin-3-ylmethyl)piperidin-4-yloxy]-2- methoxybenzoyl]piperidin-4-yl)-1,4-dihydrobenz[d][1,3]oxazin-2-one (L-372,662) and related pyridines.

The previously reported oxytocin antagonist L-371,257 (2) has been modified at its acetylpiperidine terminus to incorporate various pyridine N-oxide groups. This modification has led to the identification of compounds with improved pharmacokinetics and excellent oral bioavailability. The pyridine N-oxide series is exemplified by L-372,662 (30), which possessed good potency in vitro (Ki = 4.1 nM, cloned human oxytocin receptor) and in vivo (intravenous AD50 = 0.71 mg/kg in the rat), excellent oral bioavailability (90% in the rat, 96% in the dog), good aqueous solubility (>8.5 mg/mL at pH 5.2) which should facilitate formulation for iv administration, and excellent selectivity against the human arginine vasopressin receptors. Incorporation of a 5-fluoro substituent on the central benzoyl ring of this class of oxytocin antagonists enhanced in vitro and in vivo potency but was detrimental to the pharmacokinetic profiles of these compounds. Although lipophilic substitution around the pyridine ring of compound 30 gave higher affinity in vitro, such substituents were a metabolic liability and caused shortfalls in vivo. Two approaches to prevent this metabolism, addition of a cyclic constraint and incorporation of trifluoromethyl groups, were examined. The former approach was ineffective because of metabolic hydroxylation on the constrained ring system, whereas the latter showed improvement in plasma pharmacokinetics in some cases.

Design and synthesis of N-alkylated saccharins as selective alpha-1a adrenergic receptor antagonists.

Benign prostatic hyperplasia can be managed pharmacologically with alpha-1 adrenergic receptor antagonists. Agents that demonstrate selectivity for the alpha-1a receptor subtype may offer advantages in clinical applications with respect to hypotensive side effects. The N-alkylated saccharins reported here represent a new class of subtype selective alpha-1a adrenergic receptor antagonists which demonstrate potent effects on prostate function in vivo and are devoid of blood pressure side effects.

L-735,524: the design of a potent and orally bioavailable HIV protease inhibitor.

A series of HIV protease inhibitors possessing a hydroxylaminepentanamide transition state isostere have been developed. Incorporation of a basic amine into the backbone of the L-685,434 (2) series provided antiviral potency combined with a highly improved pharmacokinetic profile in animal models. Guided by molecular modeling and an X-ray crystal structure of the inhibited enzyme complex, we were able to design L-735,524. This compound is potent and competitively inhibits HIV-1 PR and HIV-2 PR with Ki values of 0.52 and 3.3 nM, respectively. It also stops the spread of the HIV-1IIIb-infected MT4 lymphoid cells at concentrations of 25-50 nM. To date, numerous HIV-PR inhibitors have been reported, but few have been studied in humans because they lack acceptable oral bioavailability. L-735,524 is orally bioavailable in three animals models, using clinically acceptable formulations, and is currently in phase II human clinical trials.

Synthesis, antiviral activity, and bioavailability studies of gamma-lactam derived HIV protease inhibitors.

Incorporation of a gamma-lactam in hydroxyethylene isosteres results in modest inhibitors of HIV-1 protease. Additional structural activity studies have produced significantly more potent inhibitors with the introduction of the trisubstituted cyclopentane (see compound 20) as the optimum substituent for the C-terminus. This new amino acid amide surrogate can be readily prepared in large scale from (R)-pulegone. Optimized compounds (36) and (60) are potent antiviral agents and are well absorbed (15-20%) in a dog model after oral administration.

Design and synthesis of HIV protease inhibitors. Variations of the carboxy terminus of the HIV protease inhibitor L-682,679.

A series of tetrapeptide analogues of 1 (L-682,679), in which the carboxy terminus has been shortened and modified, was prepared and their inhibitory activity measured against the HIV protease in a peptide cleavage assay. Selected examples were tested as inhibitors of virus spread in cell culture. Compound 12 was a 10-fold more potent enzyme inhibitor than 1 in vitro and 30-fold more potent in inhibiting the viral spread in cells.

[3H]L-654,284 as a probe of the central alpha 2 adrenoceptor.

L-654,284 [2R, 12bS)-N-(1,3,4,6,7,12b-hexahydro-2H-benzo[b]-furo[2,3-a] quinolizin-2-yl)-N-methyl-2-hydroxyethanesulfonamide], a potent and selective antagonist of the alpha 2 adrenoceptor, was tritiated to high specific activity. Saturation binding to cell membrane suspensions obtained from calf cerebral cortex revealed a high affinity binding site (0.63 nM). Kinetics of association and dissociation were well represented by single exponential processes, and the equilibrium dissociation constant obtained from the ratio of rate constants agreed well with that found by saturation binding. A direct comparison of saturation binding revealed that the antagonist [3H]L-654,284 had roughly the same affinity for the alpha 2 adrenoceptor as the agonist [3H]clonidine and eight times the affinity of the antagonist [3H]rauwolscine. The maximum receptor densities of these radioligands were not significantly different. Competition assays with a series of compounds of known receptor affinity revealed that [3H]L-654,284 selectively binds to a site with all of the characteristics expected of the alpha 2 adrenoceptor.

Structure-affinity relationships of arylquinolizines at alpha-adrenoceptors.

Hexahydroaryl[a]quinolizines comprise a prominent structural element in several alpha 2-adrenoceptor antagonists. Eight hexahydroheteroarylquinolizines were prepared as minimal ligands to investigate the relationship between the nature of the aromatic ring and affinity of these molecules for alpha-adrenoceptors. Affinity for alpha 1-and alpha 2-adrenoceptors was assessed by displacement of [3H]prasozin and [3H]clonidine, respectively. Lipophilicity of the aryl portion of the molecules, reflected by their partition coefficient between octanol and pH 7.4 buffer, correlated well with affinity at both receptor subtypes. Although some compounds showed nanomolar affinity for alpha-adrenoceptors, no subtype selectivity was observed. These results suggest that the aromatic ring enhances binding at both receptors chiefly through hydrophobic interactions and contributes little to subtype selectivity.

Adrenoceptor and tetrabenazine antagonism activities of some pyridinyltetrahydropyridines.

A series of pyridinyltetrahydropyridine derivatives was synthesized and evaluated as adrenoceptor and tetrabenazine antagonists. 4-(3-Fluoro-2-pyridinyl)-1,2,5,6-tetrahydropyridine proved to be the most potent and selective alpha 2-adrenoceptor antagonist of the series as measured in vitro by displacement of [3H]clonidine and [3H]prazosin from membrane binding sites of calf cerebral cortex and by antagonism of the effects of clonidine and methoxamine in the rat isolated, field-stimulated vas deferens. In addition, this compound, and the corresponding desfluoro derivative, blocked tetrabenazine-induced ptosis in the mouse.

Pyridinylpiperazines, a new class of selective alpha 2-adrenoceptor antagonists.

A series of 1-(2-pyridinyl)piperazine derivatives was synthesized and evaluated for adrenergic activity. In vitro activity was assessed through the antagonism of clonidine's effect in the rat, isolated, field-stimulated vas deferens and by the displacement of [3H]clonidine from membrane binding sites of calf cerebral cortex. Antagonism of clonidine-induced mydriasis in the rat was used as an in vivo assay. Several members of the series proved to be potent, selective alpha 2-adrenoceptor antagonists. 1-(3-Fluoro-2-pyridinyl)piperazine was more potent than either yohimbine or rauwolscine in displacement of [3H]clonidine and had a higher affinity for this binding site (alpha 2) than for the [3H]prazosin site (alpha 1). In vivo, the 3-F derivative was more potent than the reference standards in reversing clonidine-induced mydriasis. None of the members of this series was more selective or potent than rauwolscine in antagonizing clonidine in the rat vas deferens.