Fused bi-heteroaryl substituted hydantoin compounds as TACE inhibitors.

We have identified a series of hydantoin-derived TNF-a converting enzyme (TACE) inhibitors containing a pendant fused bi-heteroaryl group, which demonstrate sub-nanomolar potency (Ki), excellent activity in human whole blood assay, and improved DMPK profiles over prior series.

Discovery of novel spiro 1,3,4-thiadiazolines as potent, orally bioavailable and brain penetrant KSP inhibitors.

Kinesin spindle protein (KSP) is a mitotic kinesin that is expressed only in proliferating cells and plays a key role in spindle pole separation, formation of a bipolar mitotic spindle, as well as centrosome separation and maturation. Inhibition of KSP has the potential to provide anti-tumor activity while avoiding peripheral neuropathy associated with some microtubule-targeted drugs. Based on MK-0731 and related heterocyclic compounds targeting the KSP monastrol binding site, structurally constrained spiro-cyclic KSP inhibitors were designed. In particular, rapid evaluation and optimization of the novel spiro 1,3,4-thiadiazolines resulted in a series of potent KSP inhibitors demonstrating mechanism based activities in cells, including induction of the mitotic marker phospho-histone H3 and induction of monaster spindle formation. Further optimization of the pharmacokinetic (PK) properties afforded MK-8267 as a potent, orally bioavailable and brain penetrant KSP inhibitor which showed anti-tumor activity in preclinical xenograft models.

Modulating the interaction between CDK2 and cyclin A with a quinoline-based inhibitor.

A new class of quinoline-based kinase inhibitors has been discovered that both disrupt cyclin dependent 2 (CDK2) interaction with its cyclin A subunit and act as ATP competitive inhibitors. The key strategy for discovering this class of protein-protein disrupter compounds was to screen the monomer CDK2 in an affinity-selection/mass spectrometry-based technique and to perform secondary assays that identified compounds that bound only to the inactive CDK2 monomer and not the active CDK2/cyclin A heterodimer. Through a series of chemical modifications the affinity (Kd) of the original hit improved from 1 to 0.005µM.

Structure-based design and optimization of 2-aminothiazole-4-carboxamide as a new class of CHK1 inhibitors.

Drug design efforts in the emerging 2-aminothiazole-4-carboxamide class of CHK1 inhibitors have uncovered specific combinations of key substructures within the molecule; resulting in significant improvements in cell-based activity while retaining a greater than one hundred-fold selectivity against CDK2. The X-ray crystal structure of a complex between compound 39 and the CHK1 protein detailing a 'U-shaped' topology and key interactions with the protein surface at the ATP site is also reported.

Synthesis and SAR studies of imidazo-[1,2-a]-pyrazine Aurora kinase inhibitors with improved off-target kinase selectivity.

The structure-activity relationships of new Aurora A/B kinase inhibitors derived from the previously identified kinase inhibitor 12 are described. Introduction of acetic acid amides onto the pyrazole of compound 12 was postulated to influence Aurora A/B selectivity and improve the profile against off-target kinases. The SAR of the acetic acid amides was explored and the effect of substitution on enzyme inhibition as well as mechanism-based cell activity was studied. Additionally, several of the more potent inhibitors were screened for their off-target kinase selectivity.

Design and synthesis of potent Gram-negative specific LpxC inhibitors.

Antibiotic resistant hospital acquired infections are on the rise, creating an urgent need for novel bactericidal drugs. Enzymes involved in lipopolysaccharide (LPS) biosynthesis are attractive antibacterial targets since LPS is the major structural component of the outer membrane of Gram-negative bacteria. Lipid A is an essential hydrophobic anchor of LPS and the first committed step in lipid A biosynthesis is catalyzed by a unique zinc dependent metalloamidase, UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC). LpxC is an attractive Gram-negative only target that has been chemically validated by potent bactericidal hydroxamate inhibitors that work by coordination of the enzyme's catalytic zinc ion. An exploratory chemistry effort focused on expanding the SAR around hydroxamic acid zinc-binding 'warheads' lead to the identification of novel compounds with enzyme potency and antibacterial activity similar to CHIR-090.

Bioisosteric approach to the discovery of imidazo[1,2-a]pyrazines as potent Aurora kinase inhibitors.

Our continued effort toward the development of the imidazo[1,2-a]pyrazine scaffold as Aurora kinase inhibitors is described. Bioisosteric approach was applied to optimize the 8-position of the core. Several new potent Aurora A/B dual inhibitors, such as 25k and 25l, were identified.

2-(2-Aminothiazol-4-yl)pyrrolidine-based tartrate diamides as potent, selective and orally bioavailable TACE inhibitors.

TNF-α converting enzyme (TACE) inhibitors are promising agents to treat inflammatory disorders and cancer. We have investigated novel tartrate diamide TACE inhibitors where the tartrate core binds to zinc in a unique tridentate fashion. Incorporating (R)-2-(2-N-alkylaminothiazol-4-yl)pyrrolidines into the left hand side amide of the tartrate scaffold led to the discovery of potent and selective TACE inhibitors, some of which exhibited good rat oral bioavailability.

Design, synthesis and SAR of thienopyridines as potent CHK1 inhibitors.

A novel series of CHK1 inhibitors based on thienopyridine template has been designed and synthesized. These inhibitors maintain critical hydrogen bonding with the hinge and conserved water in the ATP binding site. Several compounds show single digit nanomolar CHK1 activities. Compound 70 shows excellent enzymatic activity of 1 nM.

Discovery of imidazo[1,2-a]pyrazine-based Aurora kinase inhibitors.

The synthesis and structure-activity relationships (SAR) of novel, potent imidazo[1,2-a]pyrazine-based Aurora kinase inhibitors are described. The X-ray crystal structure of imidazo[1,2-a]pyrazine Aurora inhibitor 1j is disclosed. Compound 10i was identified as lead compound with a promising overall profile.

Discovery of orally bioavailable imidazo[1,2-a]pyrazine-based Aurora kinase inhibitors.

We report a series of potent imidazo[1,2-a]pyrazine-based Aurora kinase inhibitors. Optimization of the solvent accessible 8-position led to improvements in both oral bioavailability and off-target kinase inhibition. Compound 25 demonstrates anti-tumor activity in an A2780 ovarian tumor xenograft model.

Biaryl substituted hydantoin compounds as TACE inhibitors.

We disclose further optimization of hydantoin TNF-alpha convertase enzyme (TACE) inhibitors. SAR with respect to the non-prime region of TACE active site was explored. A series of biaryl substituted hydantoin compounds was shown to have sub-nanomolar K(i), good rat PK, and good selectivity versus MMP-1, -2, -3, -7, -9, and -13.

Structure and activity relationships of tartrate-based TACE inhibitors.

The syntheses and structure-activity relationships of the tartrate-based TACE inhibitors are discussed. The optimization of both the prime and non-prime sites led to compounds with picomolar activity. Several analogs demonstrated good rat pharmacokinetics.

Novel TNF-α converting enzyme (TACE) inhibitors as potential treatment for inflammatory diseases.

Our research on hydantoin based TNF-α converting enzyme (TACE) inhibitors has led to an acetylene containing series that demonstrates sub-nanomolar potency (K(i)) as well as excellent activity in human whole blood. These studies led to the discovery of highly potent TACE inhibitors with good DMPK profiles.

Discovery and SAR of hydantoin TACE inhibitors.

We disclose inhibitors of TNF-alpha converting enzyme (TACE) designed around a hydantoin zinc binding moiety. Crystal structures of inhibitors bound to TACE revealed monodentate coordination of the hydantoin to the zinc. SAR, X-ray, and modeling designs are described. To our knowledge, these are the first reported X-ray structures of TACE with a hydantoin zinc ligand.

Discovery of 4H-pyrazolo[1,5-a]pyrimidin-7-ones as potent inhibitors of hepatitis C virus polymerase.

A series of 4H-pyrazolo[1,5-a]pyrimidin-7-one derivatives was synthesized and evaluated for inhibitory activity against HCV NS5B RNA-dependent RNA polymerase. A number of these compounds exhibited potent activity in enzymatic assay. The synthesis and structure-activity relationship are also described.

Pyrazolo[1,5-a]pyrimidine-based inhibitors of HCV polymerase.

The present paper describes a novel series of HCV RNA polymerase inhibitors based on a pyrazolo[1,5-a]pyrimidine scaffold bearing hydrophobic groups and an acidic functionality. Several compounds were optimized to low nanomolar potencies in a biochemical RdRp assay. SAR trends clearly reveal a stringent preference for a cyclohexyl group as one of the hydrophobes, and improved activities for carboxylic acid derivatives.

SCH 2047069, a novel oral kinesin spindle protein inhibitor, shows single-agent antitumor activity and enhances the efficacy of chemotherapeutics.

Kinesin spindle protein (KSP) is a mitotic kinesin required for the formation of the bipolar mitotic spindle, and inhibition of this motor protein results in mitotic arrest and cell death. KSP inhibitors show preclinical antitumor activity and are currently undergoing testing in clinical trials. These agents have been dosed intravenously using various dosing schedules. We sought to identify a KSP inhibitor that could be delivered orally and thus provide convenience of dosing as well as the ability to achieve more continuous exposure via the use of dose-dense administration. We discovered SCH 2047069, a potent KSP inhibitor with oral bioavailability across species and the ability to cross the blood-brain barrier. The compound induces mitotic arrest characterized by a monaster spindle and is associated with an increase in histone H3 and mitotic protein monoclonal 2 phosphorylation both in vitro and in vivo. SCH 2047069 showed antitumor activity in a variety of preclinical models as a single agent and in combination with paclitaxel, gemcitabine, or vincristine.

Discovery of a Potent, Injectable Inhibitor of Aurora Kinases Based on the Imidazo-[1,2-a]-Pyrazine Core.

The imidazo-[1,2-a]-pyrazine (1) is a dual inhibitor of Aurora kinases A and B with modest cell potency (IC50 = 250 nM) and low solubility (5 µM). Lead optimization guided by the binding mode led to the acyclic amino alcohol 12k (SCH 1473759), which is a picomolar inhibitor of Aurora kinases (TdF K d Aur A = 0.02 nM and Aur B = 0.03 nM) with improved cell potency (phos-HH3 inhibition IC50 = 25 nM) and intrinsic aqueous solubility (11.4 mM). It also demonstrated efficacy and target engagement in human tumor xenograft mouse models.

Method for quantitative protein-ligand affinity measurements in compound mixtures.

This manuscript describes an affinity selection-mass spectrometry (AS-MS) method for quantitative protein-ligand binding affinity (Kd) measurements in large compound libraries. The ability of a titrant ligand to displace a target-bound library member-as measured by MS-reveals the affinity ranking of the mixture component relative to "internal affinity calibrants", compounds of known affinity for the target. This technique does not require that the precise concentration of each ligand is known; therefore, unpurified products of mixture-based combinatorial synthesis may be used for affinity optimization and developing structure-activity relationships. The method is demonstrated for a series of ligands to the important oncology target CDK2 that were discovered by AS-MS screening of combinatorial libraries against the basal form of the protein. AS-MS displacement curves for select hits were acquired over a range of compound concentrations, confirming that binding affinity measurement results are concentration-insensitive. These hits were evaluated in pools of purified compounds to verify the method's applicability to hit triage in large chemical libraries. The method was further tested using unpurified, mixture-based combinatorial libraries of >1000 compounds, yielding results that mirror those obtained from mixtures of purified compounds. The technique was then used to identify optimized CDK2 ligands from compound mixtures, quantitatively measure their affinities, and establish structure-activity relationships among these drug leads.