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We report the discovery and optimization of substituted 2-piperazinecarboxamides as potent and selective agonists of the melanocortin subtype-4 receptor. The 5- and 6-alkylated piperazine compounds exhibit low bioactivation potential as measured by covalent binding in microsome preparations.

We report the discovery and optimization of substituted 2-piperazinecarboxamides as potent and selective agonists of the melanocortin subtype-4 receptor. Further in vivo development of lead agonist, MB243, is disclosed.

(R)-N-[4-[2-[[2-Hydroxy-2-(pyridin-3-yl)ethyl]amino]ethyl]phenyl]- 4-[4-(4-trifluoro-methylphenyl)thiazol-2-yl]benzenesulfonamide (1) is a potent and selective agonist of the human beta3-adrenergic receptor. We report herein the data from studies of the metabolism and excretion of 1 in rats. Five metabolites were identified in the bile of male Sprague-Dawley rats administered 3H-labeled 1 by either oral gavage (10 mg/kg) or intravenous injection (3 mg/kg). These included a pyridine N-oxide derivative (M2), a primary amine resulting from N-dealkylation and loss of the pyridinyl-2-hydroxyethyl group (M4), a carboxylic acid derived from N-dealkylation and loss of the pyridyl-2-hydroxyethyl amine (M5), and the corresponding taurine and isethionic acid conjugates (M1 and M3). Metabolites M1 and M3 also were identified in rats treated with M5 and were generated in incubations of M5 with rat liver subcellular fractions in the presence of ATP and coenzyme A with supplementary taurine or isethionic acid. These results suggest that M5 is the precursor of M1 and M3 and that the formation of these conjugated metabolites follows similar mechanisms of amino acid conjugation. On the other hand, M2, M4, and M5 were produced from 1 in an NADPH-dependent manner in incubations with liver microsomes from rats, dogs, monkeys, and humans. In human liver preparations, these routes of biotransformation were shown to be catalyzed by cytochrome P450 3A4. In a bidirectional transport assay, transport of 1 across a monolayer of cells expressing P-glycoprotein (Pgp) was observed to be similar to that of vinblastine, which is an established substrate of the transporter protein. This finding, together with the observation that the parent compound was excreted in the feces of bile duct-cannulated animals following intravenous dosing, suggests that 1 is subject to Pgp-mediated excretion from intestine of rats.

L-770,644 (9c) is a potent and selective agonist of the human β3 adrenergic receptor (EC50 = 13 nM). It shows good oral bioavailability in both dogs and rats (%F = 27), and is a full agonist for glycerolemia in the rhesus monkey (ED50 = 0.21 mg/kg). Based on its desirable in vitro and in vivo properties, L-770,644 was chosen for further preclinical evaluation.

Human beta3 adrenergic receptor agonists containing 5-membered ring ureas were shown to be potent partial agonists with excellent selectivity over beta1 and beta2 binding. L-760,087 (4a) and L-764,646 (5a) (beta3 EC50 = 18 and 14 nM, respectively) stimulate lipolysis in rhesus monkeys (ED50 = 0.2 and 0.1 mg/kg, respectively) with minimal effects on heart rate. Oral absorption in dogs is improved over other urea analogs.

A series of conformationally restricted acetanilides were synthesized and evaluated as β3-adrenergic receptor agonists (β3-AR) for the treatment of overactive bladder (OAB). Optimization studies identified a five-membered ring as the preferred conformational lock of the acetanilide. Further optimization of both the aromatic and thiazole regions led to compounds such as 19 and 29, which have a good balance of potency and selectivity. These compounds have significantly reduced intrinsic clearance compared to our initial series of pyridylethanolamine β3-AR agonists and thus have improved unbound drug exposures. Both analogues demonstrated dose dependent β3-AR mediated responses in a rat bladder hyperactivity model.

Finasteride is employed in treatment of benign prostatic hyperplasia in man, where its target enzyme is steroid 5α-reductase. It is a novel, potent mechanism-based inhibitor of the human prostate (type 2) isozyme. Although it is accepted as an alternate substrate and is ultimately reduced to dihydrofinasteride, this proceeds through an enzyme-bound NADP−dihydrofinasteride adduct. Finasteride is processed with a second-order rate constant, ki/Ki = 1 × 106 M-1 s-1, that approaches kcat/Km for reduction of testosterone, 3 × 106 M-1 s-1, and essentially every catalytic event is lethal (partition ratio ≤ 1.07). The membrane-bound enzyme−inhibitor complex formed from [3H]finasteride appears to release [3H]dihydrofinasteride with a half-life of 1 month at 37 °C (k = (2.57 ± 0.03) × 10-7 s-1), as identified by mass spectroscopy. The intermediate NADP−dihydrofinasteride adduct can be recovered intact by denaturation of the enzyme−inhibitor complex and has been purified. Free in solution, it likewise decomposes to ...

5-n-Pentyl oxadiazole substituted benzenesulfonamide 8 is a potent and selective beta3 adrenergic receptor agonist (beta3 EC50 = 23 nM, beta1 IC50 = 3000 nM, beta2 IC50 = 3000 nM). The compound has high oral bioavailability in dogs (62%) and rats (36%) and is among the most orally bioavailable beta3 adrenergic receptor agonists reported to date.

Pyridyloxypropanolamines L-749,372 ( 8 , β 3 EC 50 = 3.6 nM) and L-750,355 ( 29 , β 3 EC 50 = 13 nM) are selective partial agonists of the human receptor, with 33% and 49% activation, respectively. Both stimulate lipolysis in rhesus monkeys (ED 50 = 2 and 0.8 mg/kg, respectively), with minimal effects on heart rate. Oral bioavailability in dogs, 41% for L-749,372 and 47% for L-750,355, is improved relative to phenol analogs.