Discovery of Phosphodiesterase 10A (PDE10A) PET Tracer AMG 580 to Support Clinical Studies.

We report the discovery of PDE10A PET tracer AMG 580 developed to support proof of concept studies with PDE10A inhibitors in the clinic. To find a tracer with higher binding potential (BPND) in NHP than our previously reported tracer 1, we implemented a surface plasmon resonance assay to measure the binding off-rate to identify candidates with slower washout rate in vivo. Five candidates (2-6) from two structurally distinct scaffolds were identified that possessed both the in vitro characteristics that would favor central penetration and the structural features necessary for PET isotope radiolabeling. Two cinnolines (2, 3) and one keto-benzimidazole (5) exhibited PDE10A target specificity and brain uptake comparable to or better than 1 in the in vivo LC-MS/MS kinetics distribution study in SD rats. In NHP PET imaging study, [(18)F]-5 produced a significantly improved BPND of 3.1 and was nominated as PDE10A PET tracer clinical candidate for further studies.

Discovery and Structure-Guided Optimization of Diarylmethanesulfonamide Disrupters of Glucokinase-Glucokinase Regulatory Protein (GK-GKRP) Binding: Strategic Use of a N → S (nN → σ*S-X) Interaction for Conformational Constraint.

The HTS-based discovery and structure-guided optimization of a novel series of GKRP-selective GK-GKRP disrupters are revealed. Diarylmethanesulfonamide hit 6 (hGK-hGKRP IC50 = 1.2 µM) was optimized to lead compound 32 (AMG-0696; hGK-hGKRP IC50 = 0.0038 µM). A stabilizing interaction between a nitrogen atom lone pair and an aromatic sulfur system (nN → σ*S-X) in 32 was exploited to conformationally constrain a biaryl linkage and allow contact with key residues in GKRP. Lead compound 32 was shown to induce GK translocation from the nucleus to the cytoplasm in rats (IHC score = 0; 10 mg/kg po, 6 h) and blood glucose reduction in mice (POC = -45%; 100 mg/kg po, 3 h). X-ray analyses of 32 and several precursors bound to GKRP were also obtained. This novel disrupter of GK-GKRP binding enables further exploration of GKRP as a potential therapeutic target for type II diabetes and highlights the value of exploiting unconventional nonbonded interactions in drug design.

Discovery and in vivo evaluation of (S)-N-(1-(7-fluoro-2-(pyridin-2-yl)quinolin-3-yl)ethyl)-9H-purin-6-amine (AMG319) and related PI3Kδ inhibitors for inflammation and autoimmune disease.

The development and optimization of a series of quinolinylpurines as potent and selective PI3Kδ kinase inhibitors with excellent physicochemical properties are described. This medicinal chemistry effort led to the identification of 1 (AMG319), a compound with an IC50 of 16 nM in a human whole blood assay (HWB), excellent selectivity over a large panel of protein kinases, and a high level of in vivo efficacy as measured by two rodent disease models of inflammation.

Discovery of clinical candidate 1-(4-(3-(4-(1H-benzo[d]imidazole-2-carbonyl)phenoxy)pyrazin-2-yl)piperidin-1-yl)ethanone (AMG 579), a potent, selective, and efficacious inhibitor of phosphodiesterase 10A (PDE10A).

We report the identification of a PDE10A clinical candidate by optimizing potency and in vivo efficacy of promising keto-benzimidazole leads 1 and 2. Significant increase in biochemical potency was observed when the saturated rings on morpholine 1 and N-acetyl piperazine 2 were changed by a single atom to tetrahydropyran 3 and N-acetyl piperidine 5. A second single atom modification from pyrazines 3 and 5 to pyridines 4 and 6 improved the inhibitory activity of 4 but not 6. In the in vivo LC-MS/MS target occupancy (TO) study at 10 mg/kg, 3, 5, and 6 achieved 86-91% occupancy of PDE10A in the brain. Furthermore, both CNS TO and efficacy in PCP-LMA behavioral model were observed in a dose dependent manner. With superior in vivo TO, in vivo efficacy and in vivo PK profiles in multiple preclinical species, compound 5 (AMG 579) was advanced as our PDE10A clinical candidate.

Discovery of dehydro-oxopiperazine acetamides as novel bradykinin B1 receptor antagonists with enhanced in vitro potency.

In a series of bradykinin B1 antagonists, we discovered that replacement of oxopiperazine acetamides with dehydro-oxopiperazine acetamides provided compounds with enhanced activity against the B1 receptor. The synthesis and SAR leading to potent analogs with reduced molecular weight will be discussed.

Discovery of amide replacements that improve activity and metabolic stability of a bis-amide smoothened antagonist hit.

A bis-amide antagonist of Smoothened, a seven-transmembrane receptor in the Hedgehog signaling pathway, was discovered via high throughput screening. In vitro and in vivo experiments demonstrated that the bis-amide was susceptible to N-acyl transferase mediated amide scission. Several bioisosteric replacements of the labile amide that maintained in vitro potency were identified and shown to be metabolically stable in vitro and in vivo.

Design and synthesis of novel amide AKT1 inhibitors with selectivity over CDK2.

Through the analysis of X-ray crystallographic information and previous SAR studies, a novel series of protein kinase B (PKB/AKT) inhibitors was developed. The compounds showed nanomolar inhibition of AKT1 and were selective against cyclin-dependent kinase 2 (CDK2).

3-Oxo-2-piperazinyl acetamides as potent bradykinin B1 receptor antagonists for the treatment of pain and inflammation.

The discovery of novel and highly potent oxopiperazine based B1 receptor antagonists is described. Compared to the previously described arylsulfonylated (R)-3-amino-3-phenylpropionic acid series, the current compounds showed improved in vitro potency and metabolic stability. Compound 17, 2-((2R)-1-((4-methylphenyl)sulfonyl)-3-oxo-2-piperazinyl)-N-((1R)-6-(1-piperidinylmethyl)-1,2,3,4-tetrahydro-1-naphthalenyl)acetamide, showed EC(50) of 10.3 nM in a rabbit biochemical challenge model. The practical syntheses of chiral arylsulfonylated oxopiperazine acetic acids are also described.

Synthesis and optimization of novel 4,4-disubstituted cyclohexylbenzamide derivatives as potent 11ß-HSD1 inhibitors.

The synthesis and SAR of a series of 4,4-disubstituted cyclohexylbenzamide inhibitors of 11ß-HSD1 are described. Optimization rapidly led to potent, highly selective, and orally bioavailable inhibitors demonstrating efficacy in both rat and non-human primate ex vivo pharmacodynamic models.

Dipeptidyl-quinolone derivatives inhibit hypoxia inducible factor-1α prolyl hydroxylases-1, -2, and -3 with altered selectivity.

Intracellular levels of the hypoxia-inducible transcription factor (HIF) are regulated under normoxic conditions by prolyl hydroxylases (PHD1, 2, and 3). Treatment of cells with PHD inhibitors stabilizes HIF-1α, eliciting an artificial hypoxic response that includes the transcription of genes involved in erythropoiesis, angiogenesis, and glycolysis. The different in vivo roles of the three PHD isoforms are not yet known, making a PHD-selective inhibitor useful as a biological tool. Although several chemical series of PHD inhibitors have been described, significant isoform selectivity has not been reported. Here we report the synthesis and activity of dipeptidyl analogues derived from a potent but non-selective quinolone scaffold. The compounds were prepared by Pd-catalyzed reductive carbonylation of the 6-iodoquinolone derivative to form the aldehyde directly, which was then attached to a solid support via reductive amination. Amino acids were coupled, and the resulting dipeptidyl-quinolone derivatives were screened, revealing retention of PHD inhibitory activity but an altered PHD1, 2, and 3 selectivity profile. The compounds were found to be ∼10-fold more potent against PHD1 and PHD3 than against PHD2, whereas the specific parent compound had shown no appreciable selectivity among the different PHD isoforms.

Addressing PXR liabilities of phthalazine-based hedgehog/smoothened antagonists using novel pyridopyridazines.

Pyridopyridazine antagonists of the hedgehog signaling pathway are described. Designed to optimize our previously described phthalazine smoothened antagonists, a representative compound eliminates a PXR liability while retaining potency and in vitro metabolic stability. Moreover, the compound has improved efficacy in a hedgehog/smoothened signaling mouse pharmacodynamic model.

Aryl sulfonamides containing tetralin allylic amines as potent and selective bradykinin B1 receptor antagonists.

The bradykinin B1 receptor has been shown to mediate pain response and is rapidly induced upon injury. Blocking this receptor may provide a promising treatment for inflammation and pain. We previously reported tetralin benzyl amines as potent B1 antagonists. Here we describe the synthesis and SAR of B1 receptor antagonists with homobenzylic amines. The SAR of different linkers led to the discovery of tetralin allylic amines as potent and selective B1 receptor antagonists (hB1 IC(50)=1.3 nM for compound 16). Some of these compounds showed modest oral bioavailability in rats.

Discovery of a potent, orally active 11beta-hydroxysteroid dehydrogenase type 1 inhibitor for clinical study: identification of (S)-2-((1S,2S,4R)-bicyclo[2.2.1]heptan-2-ylamino)-5-isopropyl-5-methylthiazol-4(5H)-one (AMG 221).

Thiazolones with an exo-norbornylamine at the 2-position and an isopropyl group on the 5-position are potent 11beta-HSD1 inhibitors. However, the C-5 center was prone to epimerization in vitro and in vivo, forming a less potent diastereomer. A methyl group was added to the C-5 position to eliminate epimerization, leading to the discovery of (S)-2-((1S,2S,4R)-bicyclo[2.2.1]heptan-2-ylamino)-5-isopropyl-5-methylthiazol-4(5H)-one (AMG 221). This compound decreased fed blood glucose and insulin levels and reduced body weight in diet-induced obesity mice.

Design of 1-piperazinyl-4-arylphthalazines as potent Smoothened antagonists.

The Hedgehog (Hh) signaling pathway regulates cell proliferation and differentiation in developing tissues, and abnormal activation of the Hh pathway has been linked to several tumor subsets. As a transducer of Hh signaling, the GPCR-like protein Smoothened (Smo) is a promising target for disruption of unregulated Hh signaling. A series of 1-amino-4-arylphthalazines was developed as potent and orally bioavailable inhibitors of Smo. A representative compound from this class demonstrated significant tumor volume reduction in a mouse medulloblastoma model.

2-Aminothiadiazole inhibitors of AKT1 as potential cancer therapeutics.

A series of 2-aminothiadiazole of inhibitors of AKT1 is described. SAR relationships are discussed, along with selectivity for protein kinase A (PKA) and cyclin-dependent kinase 2 (CDK2). Moderate selectivity observed in several compounds for AKT1 versus PKA is rationalized by X-ray crystallographic analysis. Key compounds showed activity in cellular assays measuring phosphorylation of two AKT substrates, PRAS40 and FKHRL1. Compound 30 was advanced to a mouse liver PD assay, where it showed dose-dependent inhibition of AKT activity, as measured by the inhibition of phospho-PRAS40.

Azole-based inhibitors of AKT/PKB for the treatment of cancer.

Through a combination of screening and structure-based rational design, we have discovered a series of N(1)-(5-(heterocyclyl)-thiazol-2-yl)-3-(4-trifluoromethylphenyl)-1,2-propanediamines that were developed into potent ATP competitive inhibitors of AKT. Studies of linker strand-binding adenine isosteres identified SAR trends in potency and selectivity that were consistent with binding interactions observed in structures of the inhibitors bound to AKT1 and to the counter-screening target PKA. One compound was shown to have acceptable pharmacokinetic properties and to be a potent inhibitor of AKT signaling and of in vivo xenograft tumor growth in a preclinical model of glioblastoma.

Discovery and optimization of chromenotriazolopyrimidines as potent inhibitors of the mouse double minute 2-tumor protein 53 protein-protein interaction.

Tumor protein 53 (p53) is a critical regulator of cell cycle and apoptosis that is frequently disabled in human tumors. In many tumor types, p53 is deleted or mutated, but in others p53 is inactivated by overexpression or amplification of its negative regulator mouse double minute 2 (MDM2). A high-throughput screening effort identified 6,7-bis(4-bromophenyl)-7,12-dihydro-6H-chromeno[4,3-d][1,2,4]triazolo[1,5-a]pyrimidine as a potent inhibitor of the MDM2-p53 protein-protein interaction. This screening hit was found to be chemically unstable and difficult to handle due to poor DMSO solubility. Co-crystallization with the target protein helped to direct further optimization and provided a tractable lead series of novel MDM2-p53 inhibitors. In cellular assays, these compounds were shown to upregulate p53 protein levels and p53 signaling and to cause p53-dependent inhibition of proliferation and apoptosis.

Stereoselective synthesis of anti-N-protected 3-amino-1,2-epoxides by nucleophilic addition to N-tert-butanesulfinyl imine of a glyceraldehyde synthon.

A di-O-TBS protected glyceraldehyde synthon was condensed with Ellman's reagent to form a bench-stable N-tert-butanesulfinyl imine 6, which served as a common intermediate for the stereoselective introduction of various R groups. The Ellman adducts were converted to useful multifunctional intermediates 18a-i in one pot. The alcohols 18a-i were efficiently elaborated to both known and novel anti-N-protected-3-amino-1,2-epoxides in two steps. Compound 2a is a key intermediate toward HIV protease inhibitors.

Discovery and optimization of piperidyl benzamide derivatives as a novel class of 11beta-HSD1 inhibitors.

Discovery and optimization of a piperidyl benzamide series of 11beta-HSD1 inhibitors is described. This series was derived from a cyclohexyl benzamide lead structures to address PXR selectivity, high non-specific protein binding, poor solubility, limited in vivo exposure, and in vitro cytotoxicity issues observed with the cyclohexyl benzamide structures. These efforts led to the discovery of piperidyl benzamide 15 which features improved properties over the cyclohexyl benzamide derivatives.

Optimization of novel di-substituted cyclohexylbenzamide derivatives as potent 11 beta-HSD1 inhibitors.

Novel 4,4-disubstituted cyclohexylbenzamide inhibitors of 11beta-HSD1 were optimized to account for liabilities relating to in vitro pharmacokinetics, cytotoxicity and protein-related shifts in potency. A representative compound showing favorable in vivo pharmacokinetics was found to be an efficacious inhibitor of 11beta-HSD1 in a rat pharmacodynamic model (ED(50)=10mg/kg).