Generation of Leads for γ-Secretase Modulation.

Herein, we disclose three structurally differentiated γ-secretase modulators (GSMs) based on an oxadiazine scaffold. The analogues from series I potently inhibit the generation of Aß42 in vitro when the substituents at 3 and 4 positions of the oxadiazine moiety adopt an α orientation (cf. 11). To address the concern around potential reactivity of the exocyclic double bond present in series I toward nucleophilic attack, compounds containing either an endocyclic double bond, such as 20 (series II), or devoid of an olefinic moiety, such as 27 (series III), were designed and validated as novel GSMs. Compound 11 and azepine 20 exhibit robust lowering of CSF Aß42 in rats treated with a 30 mg/kg oral dose.

Overcoming Time-Dependent Inhibition (TDI) of Cytochrome P450 3A4 (CYP3A4) Resulting from Bioactivation of a Fluoropyrimidine Moiety.

Herein we describe structure-activity relationship (SAR) and metabolite identification (Met-ID) studies that provided insight into the origin of time-dependent inhibition (TDI) of cytochrome P450 3A4 (CYP3A4) by compound 1. Collectively, these efforts revealed that bioactivation of the fluoropyrimidine moiety of 1 led to reactive metabolite formation via oxidative defluorination and was responsible for the observed TDI. We discovered that substitution at both the 4- and 6-positions of the 5-fluoropyrimidine of 1 was necessary to ameliorate this TDI as exemplified by compound 19.

Discovery of MK-8318, a Potent and Selective CRTh2 Receptor Antagonist for the Treatment of Asthma.

A novel series of tricyclic tetrahydroquinolines were identified as potent and selective CRTh2 receptor antagonists. The agonism and antagonism switch was achieved through structure-based drug design (SBDD) using a CRTh2 receptor homologue model. The challenge of very low exposures in pharmacokinetic studies was overcome by exhaustive medicinal chemistry lead optimization through focused SAR studies on the tricyclic core. Further optimization resulted in the identification of the preclinical candidate 4-(cyclopropyl((3aS,9R,9aR)-7-fluoro-4-(4-(trifluoromethoxy)benzoyl)-2,3,3a,4,9,9a-hexahydro-1H-cyclopenta[b]quinolin-9-yl)amino)-4-oxobutanoic acid (15c, MK-8318) with potent and selective CRTh2 antagonist activity and a favorable PK profile suitable for once daily oral dosing for potential treatment of asthma.

Discovery of a highly potent orally bioavailable imidazo-[1, 2-a]pyrazine Aurora inhibitor.

Imidazo-[1, 2-a]pyrazine 1 is a potent inhibitor of Aurora A and B kinase in vitro and is effective in in vivo tumor models, but has poor oral bioavailbility and is unsuitable for oral dosing. We describe herein our effort to improve oral exposure in this class, resulting ultimately in the identification of a potent Aurora inhibitor 16, which exhibited good drug exposure levels across species upon oral dosing, and showed excellent in vivo efficacy in a mouse xenograft tumor model when dosed orally.

Can We Make Small Molecules Lean? Optimization of a Highly Lipophilic TarO Inhibitor.

We describe our optimization efforts to improve the physicochemical properties, solubility, and off-target profile of 1, an inhibitor of TarO, an early stage enzyme in the biosynthetic pathway for wall teichoic acid (WTA) synthesis. Compound 1 displayed a TarO IC50 of 125 nM in an enzyme assay and possessed very high lipophilicity (clogP = 7.1) with no measurable solubility in PBS buffer. Structure-activity relationship (SAR) studies resulted in a series of compounds with improved lipophilic ligand efficiency (LLE) consistent with the reduction of clogP. From these efforts, analog 9 was selected for our initial in vivo study, which in combination with subefficacious dose of imipenem (IPM) robustly lowered the bacterial burden in a neutropenic Staphylococci murine infection model. Concurrent with our in vivo optimization effort using 9, we further improved LLE as exemplified by a much more druglike analog 26.

Discovery of Novel 3,3-Disubstituted Piperidines as Orally Bioavailable, Potent, and Efficacious HDM2-p53 Inhibitors.

A new subseries of substituted piperidines as p53-HDM2 inhibitors exemplified by 21 has been developed from the initial lead 1. Research focused on optimization of a crucial HDM2 Trp23-ligand interaction led to the identification of 2-(trifluoromethyl)thiophene as the preferred moiety. Further investigation of the Leu26 pocket resulted in potent, novel substituted piperidine inhibitors of the HDM2-p53 interaction that demonstrated tumor regression in several human cancer xenograft models in mice. The structure of HDM2 in complex with inhibitors 3, 10, and 21 is described.

Selective small-molecule inhibition of an RNA structural element.

Riboswitches are non-coding RNA structures located in messenger RNAs that bind endogenous ligands, such as a specific metabolite or ion, to regulate gene expression. As such, riboswitches serve as a novel, yet largely unexploited, class of emerging drug targets. Demonstrating this potential, however, has proven difficult and is restricted to structurally similar antimetabolites and semi-synthetic analogues of their cognate ligand, thus greatly restricting the chemical space and selectivity sought for such inhibitors. Here we report the discovery and characterization of ribocil, a highly selective chemical modulator of bacterial riboflavin riboswitches, which was identified in a phenotypic screen and acts as a structurally distinct synthetic mimic of the natural ligand, flavin mononucleotide, to repress riboswitch-mediated ribB gene expression and inhibit bacterial cell growth. Our findings indicate that non-coding RNA structural elements may be more broadly targeted by synthetic small molecules than previously expected.

Bioavailable pyrrolo-benzo-1,4-diazines as Na(v)1.7 sodium channel blockers for the treatment of pain.

A series of pyrrolo-benzo-1,4-diazine analogs have been synthesized to improve the profile of the previous lead compound 1. The syntheses, structure-activity relationships, and selected pharmacokinetic data of these analogs are described. The optimization efforts allowed the identification of 33, a quinoline amide exhibiting potent Na(v)1.7 inhibitory activity and moderate selectivity over Na(v)1.5. Compound 33 displayed anti-nociceptive oral efficacy in a rat CFA inflammatory pain model at 100 mpk and in a rat spinal nerve ligation neuropathic pain model with an EC50 75 µM.

Design, synthesis, structure-function relationship, bioconversion, and pharmacokinetic evaluation of ertapenem prodrugs.

Described here are synthesis and biological evaluations of diversified groups of over 57 ertapenem prodrugs which include alkyl, methylenedioxy, carbonate, cyclic carbonate, carbamate esters, and esters containing active transport groups (e.g., carboxyl, amino acid, fatty acids, cholesterol) and macrocyclic lactones linking the two carboxyl groups. Many of the prodrugs were rapidly hydrolyzed in rat plasma but not in human plasma and were stable in simulated gastrointestinal fluid. The diethyl ester prodrug showed the best total absorption (>30%) by intredeudenal dosing in dogs, which could potentially be improved by formulation development. However, its slow rate of the hydrolysis to ertapenem also led to the presence of large amounts of circulating monoester metabolites, which pose significant development challenges. This study also suggests that the size of susbtituents at C-2 of carbapenem (e.g., benzoic acid of ertapenem) has significant impact on the absorption and the hydrolysis of the prodrugs.

Discovery of pyrrolo-benzo-1,4-diazines as potent Na(v)1.7 sodium channel blockers.

A series of pyrrolo-benzo-1,4-diazine analogs have been synthesized and displayed potent Nav1.7 inhibitory activity and moderate selectivity over Nav1.5. The syntheses, structure-activity relationships, and selected pharmacokinetic data of these analogs are described. Compound 41 displayed anti-nociceptive efficacy in the rat CFA pain model at 100 mpk oral dosing.

Quality by design (QbD) of amide isosteres: 5,5-Disubstituted isoxazolines as potent CRTh2 antagonists with favorable pharmacokinetic and drug-like properties.

Isoxazoles are frequently used amide isosteres, as shown in the context of discovery of CRTh2 antagonists from amide 1 to isoxazole 2. However, persistent agonism and poor solubility in isoxazole series presented challenges to its further development. Based on the concept of quality by design (QbD), 5,5-disubstituted isoxazolines 3 were introduced. The chirality at 5 position of isoxazolines controlled the switch between two modes of actions, which led to a novel series of pure antagonists. This non-planar motif also conferred a change of shape of these molecules, which avoided flat structures and improved their physical properties.

Design, synthesis, and evaluation of prodrugs of ertapenem.

Carbapenems are intravenous lifesaving hospital antibiotics. Once patients leave the hospital, they are sent home with antibiotics other than carbapenems since they cannot be administered orally due to lack of oral absorption primarily because of very highly polarity. A prodrug approach is a bona fide strategy to improve oral absorption of compounds. Design and synthesis, in vitro and in vivo evaluation of diversified prodrugs of ertapenem, one of the only once daily dosed carbapenems is described. Many of the prodrugs prepared for evaluation are rapidly hydrolyzed in rat plasma. Only bis-(5-methyl-2-oxo-1,3-dioxol-4-yl)methyl (medoxomil) ester prodrug was rapidly hydrolyzed in most of the plasmas including rat, human, dog, and monkey. Although the rate of conversion of ertapenem diethyl ester prodrug (6) was slow in in vitro plasma hydrolysis, it showed the best in vivo pharmacokinetic profile in dog by an intraduodenal dosing giving >31% total oral absorption.

The SAR development of dihydroimidazoisoquinoline derivatives as phosphodiesterase 10A inhibitors for the treatment of schizophrenia.

The identification of potent and orally active dihydroimidazoisoquinolines as PDE 10A inhibitors is reported. The SAR development led to the discovery of compound 35 as a potent, selective, and orally active PDE10A inhibitor. Compound 35 inhibited MK-801-induced hyperactivity at 3mg/kg and displayed a 10-fold separation between the minimal effective doses for inhibition of MK-801-induced hyperactivity and hypolocomotion in rats.

The discovery of potent, selective, and orally active pyrazoloquinolines as PDE10A inhibitors for the treatment of Schizophrenia.

High-throughput screening identified a series of pyrazoloquinolines as PDE10A inhibitors. The SAR development led to the discovery of compound 27 as a potent, selective, and orally active PDE10A inhibitor. Compound 27 inhibits MK-801 induced hyperactivity at 3mg/kg with an ED(50) of 4mg/kg and displays a ∼6-fold separation between the ED(50) for inhibition of MK-801 induced hyperactivity and hypolocomotion in rats.

Discovery of orally active pyrazoloquinolines as potent PDE10 inhibitors for the management of schizophrenia.

A series of pyrazoloquinoline analogs have been synthesized and shown to bind to PDE10 with high affinity. From the SAR study and our lead optimization efforts, compounds 16 and 27 were found to possess potent oral antipsychotic activity in the MK-801 induced hyperactive rat model.

T-type calcium channel blockers: spiro-piperidine azetidines and azetidinones-optimization, design and synthesis.

A series of spiro-azetidines and azetidinones has been evaluated as novel blockers of the T-type calcium channel (Ca(V)3.2) which is a new therapeutic target for the potential treatment of both inflammatory and neuropathic pain. Confirmation and optimization of the potency, selectivity and DMPK properties of leads will be described.

Diaminocyclobutenediones as potent and orally bioavailable CXCR2 receptor antagonists: SAR in the phenolic amide region.

A series of potent and orally bioavailable 3,4-diaminocyclobutenediones with various amide modifications and substitution on the left side phenyl ring were prepared and found to show significant inhibitory activities towards both CXCR2 and CXCR1 receptors.

Fluoroalkyl alpha side chain containing 3,4-diamino-cyclobutenediones as potent and orally bioavailable CXCR2-CXCR1 dual antagonists.

A series of potent and orally bioavailable 3,4-diaminocyclobutenediones with various fluoroalkyl groups as alpha side chain were prepared and found to show significant improvements in the binding affinities towards both CXCR2 and CXCR1 receptors.

Spiro-piperidine azetidinones as potent TRPV1 antagonists.

A series of spiro-piperidine azetidinone were synthesized and evaluated as potential TRPV1 antagonists. An important issue of plasma stability was investigated and resolved. Further focused SAR study lead to the discovery of a potent antagonist with good oral pharmacokinetic profile in rat.

Synthesis and structure-activity relationships of heteroaryl substituted-3,4-diamino-3-cyclobut-3-ene-1,2-dione CXCR2/CXCR1 receptor antagonists.

Comprehensive SAR studies were undertaken in the 3,4-diaminocyclobut-3-ene-1,2-dione class of CXCR2/CXCR1 receptor antagonists to explore the role of the heterocycle on chemokine receptor binding affinities, functional activity, as well as oral exposure in rat. The nature of the heterocycle as well as the requisite substitution pattern around the heterocycle was shown to have a dramatic effect on the overall biological profile of this class of compounds. The furyl class, particularly the 4-halo adducts, was found to possess superior binding affinities for both the CXCR2 and CXCR1 receptors, functional activity, as well as oral exposure in rat versus other heterocyclic derivatives.