Alexander Pasternak

Potent, orally bioavailable somatostatin agonists: Good absorption achieved by urea backbone cyclization

Backbone cyclization of urea-based somatostatin agonists resulted in novel, orally bioavailable agonists. Binding assays confirmed that the resulting conformationally constrained cyclic ureas retained the potency of their acyclic counterparts. SAR studies subsequently led to highly potent analogs, selective for receptor subtype 2, and having good oral bioavailability.

Pharmacologic Inhibition of the Renal Outer Medullary Potassium Channel Causes Diuresis and Natriuresis in the Absence of Kaliuresis

The renal outer medullary potassium (ROMK) channel, which is located at the apical membrane of epithelial cells lining the thick ascending loop of Henle and cortical collecting duct, plays an important role in kidney physiology by regulating salt reabsorption. Loss-of-function mutations in the human ROMK channel are associated with antenatal type II Bartter’s syndrome, an autosomal recessive life-threatening salt-wasting disorder with mild hypokalemia. Similar observations have been reported from studies with ROMK knockout mice and rats. It is noteworthy that heterozygous carriers of Kir1.1 mutations associated with antenatal Bartter’s syndrome have reduced blood pressure and a decreased risk of developing hypertension by age 60. Although selective ROMK inhibitors would be expected to represent a new class of diuretics, this hypothesis has not been pharmacologically tested. Compound A [5-(2-(4-(2-(4-(1H-tetrazol-1-yl)phenyl)acetyl)piperazin-1-yl)ethyl)isobenzofuran-1(3H)-one)], a potent ROMK inhibitor with appropriate selectivity and characteristics for in vivo testing, has been identified. Compound A accesses the channel through the cytoplasmic side and binds to residues lining the pore within the transmembrane region below the selectivity filter. In normotensive rats and dogs, short-term oral administration of compound A caused concentration-dependent diuresis and natriuresis that were comparable to hydrochlorothiazide. Unlike hydrochlorothiazide, however, compound A did not cause any significant urinary potassium losses or changes in plasma electrolyte levels. These data indicate that pharmacologic inhibition of ROMK has the potential for affording diuretic/natriuretic efficacy similar to that of clinically used diuretics but without the dose-limiting hypokalemia associated with the use of loop and thiazide-like diuretics.

Design, synthesis, and structure-activity relationship of novel CCR2 antagonists.

A series of novel 1-aminocyclopentyl-3-carboxyamides incorporating substituted tetrahydropyran moieties have been synthesized and subsequently evaluated for their antagonistic activity against the human CCR2 receptor. Among them analog 59 was found to posses potent antagonistic activity.

Discovery and optimization of novel 4-[(aminocarbonyl)amino]-N-[4-(2-aminoethyl)phenyl]benzenesulfonamide ghrelin receptor antagonists.

This Letter describes optimization of ghrelin receptor antagonists and inverse agonists starting from a screening hit.

The Inwardly Rectifying Potassium Channel Kir1.1: Development of Functional Assays to Identify and Characterize Channel Inhibitors

The renal outer medullary potassium (ROMK) channel is a member of the inwardly rectifying family of potassium (Kir) channels. ROMK (Kir1.1) is predominantly expressed in kidney where it plays a major role in the salt reabsorption process. Loss-of-function mutations in the human Kir1.1 channel are associated with antenatal Bartters syndrome type II, a life-threatening salt and water balance disorder. Heterozygous carriers of Kir1.1 mutations associated with antenatal Bartters syndrome have reduced blood pressure and a decreased risk of developing hypertension by age 60. These data suggest that Kir1.1 inhibitors could represent novel diuretics for the treatment of hypertension. Because little is known about the molecular pharmacology of Kir1.1 channels, assays that provide a robust, reliable readout of channel activity-while operating in high-capacity mode-are needed. In the present study, we describe high-capacity, 384- and 1,536-well plate, functional thallium flux, and IonWorks electrophysiology assays for the Kir1.1 channel that fulfill these criteria. In addition, 96-well (86)Rb(+) flux assays were established that can operate in the presence of 100% serum, and can provide an indication of the effect of a serum shift on compound potencies. The ability to grow Madin-Darby canine kidney cells expressing Kir1.1 in Transwell supports provides a polarized cell system that can be used to study the mechanism of Kir1.1 inhibition by different agents. All these functional Kir1.1 assays together can play an important role in supporting different aspects of drug development efforts during lead identification and/or optimization.

Potent heteroarylpiperidine and carboxyphenylpiperidine 1-alkyl-cyclopentane carboxamide CCR2 antagonists.

This report describes replacement of the 4-(4-fluorophenyl)piperidine moiety in our CCR2 antagonists with 4-heteroaryl piperidine and 4-(carboxyphenyl)-piperidine subunits. Some of the resulting analogs retained potency in our CCR2 binding assay and had improved selectivity versus the I(Kr) channel; poor selectivity against I(Kr) had been a liability of earlier analogs in this series.

Stimulation of Glucose-Dependent Insulin Secretion by a Potent, Selective sst3 Antagonist

This letter provides the first pharmacological proof of principle that the sst3 receptor mediates glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells. To enable these studies, we identified the selective sst3 antagonist (1R,3R)-3-(5-phenyl-1H-imidazol-2-yl)-1-(tetrahydro-2H-pyran-4-yl)-2,3,4,9-tetrahydro-1H-β-carboline (5a), with improved ion channel selectivity and mouse pharmacokinetic properties as compared to previously described tetrahydro-β-carboline imidazole sst3 antagonists. We demonstrated that compound 5a enhances GSIS in pancreatic β-cells and blocks glucose excursion induced by dextrose challenge in ipGTT and OGTT models in mice. Finally, we provided strong evidence that these effects are mechanism-based in an ipGTT study, showing reduction of glucose excursion in wild-type but not sst3 knockout mice. Thus, we have shown that antagonism of sst3 represents a new mechanism with potential in treating type 2 diabetes mellitus.

Conformational studies of 3-amino-1-alkyl-cyclopentane carboxamide CCR2 antagonists leading to new spirocyclic antagonists.

In an effort to shed light on the active binding conformation of our 3-amino-1-alkyl-cyclopentane carboxamide CCR2 antagonists, we prepared several conformationally constrained analogs resulting from backbone cyclization. Evaluation of CCR2 binding affinities for these analogs gave insight into the optimal relative positions of the piperidine and benzylamide moieties while simultaneously leading to the discovery of a new, potent lead type based upon a spirocyclic acetal scaffold.

The Discovery of MK-4256, a Potent SSTR3 Antagonist as a Potential Treatment of Type 2 Diabetes

A structure-activity relationship study of the imidazolyl-β-tetrahydrocarboline series identified MK-4256 as a potent, selective SSTR3 antagonist, which demonstrated superior efficacy in a mouse oGTT model. MK-4256 reduced glucose excursion in a dose-dependent fashion with maximal efficacy achieved at doses as low as 0.03 mg/kg po. As compared with glipizide, MK-4256 showed a minimal hypoglycemia risk in mice.

Design and synthesis of a new class of malonyl-CoA decarboxylase inhibitors with anti-obesity and anti-diabetic activities

A new series of thiazole-substituted 1,1,1,3,3,3-hexafluoro-2-propanols were prepared and evaluated as malonyl-CoA decarboxylase (MCD) inhibitors. Key analogs caused dose-dependent decreases in food intake and body weight in obese mice. Acute treatment with these compounds also led to a drop in elevated blood glucose in a murine model of type II diabetes.