Discovery and optimization of new oxadiazole substituted thiazole RORγt inverse agonists through a bioisosteric amide replacement approach

Starting from previously identified thiazole-2-carboxamides exemplified by compound 1/6, two new series of RORγt inverse agonists with significantly improved aqueous solubility, ADME parameters and oral PK properties were discovered. These scaffolds were identified from a bioisosteric amide replacement approach. Amongst the variety of heterocycles explored, a 1,3,4-oxadiazole led to compounds with the best overall profile for SAR development and in vivo exploration. In an ex vivo mouse PD model, concentration dependent efficacy was demonstrated and compounds 3/5 and 6/3 were profiled in a 5-day rat tolerability study.     

Structure-activity relationship study of thiazolyl-hydroxamate derivatives as selective histone deacetylase 6 inhibitors

Several human diseases are associated with aberrant epigenetic pathways mediated by histone deacetylases (HDACs), especially HDAC6, a class IIb HDACs, which has emerged as an attractive target for neurodegenerative and autoimmune disease therapeutics. In a previous study, we developed the novel HDAC6-selective inhibitor 9a ((E)-N-hydroxy-4-(2-styrylthiazol-4-yl)butanamide) and showed that it has anti-sepsis activity in vivo. In this study, we conducted structure-activity relationship (SAR) studies to optimize the activity and selectivity of HDAC6, synthesizing its derivatives with various aliphatic linker sizes and cap structures. We identified 6u ((E)-N-hydroxy-3-(2-(4-fluorostyryl)thiazol-4-yl)propanamide), which has nanomolar inhibition activity and a 126-fold selectivity for HDAC6 over HDAC1. Through the docking analyses of 6u against HDAC subtypes, we revealed the importance of the optimal aliphatic linker size, as well as the electronic substituent effect and rigidity of the aryl cap group. Thus, we suggest a new rationale for the design of HDAC6-selective inhibitors.     

The discovery of VU0486846: steep SAR from a series of M1 PAMs based on a novel benzomorpholine core

This letter describes the chemical optimization of a new series of M₁ positive allosteric modulators (PAMs) based on a novel benzomorpholine core, developed via iterative parallel synthesis, and culminating in the highly utilized rodent in vivo tool compound, VU0486846 (7), devoid of adverse effect liability. This is the first report of the optimization campaign (SAR and DMPK profiling) that led to the discovery of VU0486846 and details all of the challenges faced in allosteric modulator programs (both steep and flat SAR, as well as subtle structural changes affecting CNS penetration and overall physiochemical and DMPK properties).     

Antimalarial activity of novel 4-aminoquinolines active against drug resistant strains

In the present study we have synthesized a new class of 4-aminoquinolines and evaluated against Plasmodium falciparum in vitro (3D7-sensitive strain & K1-resistant strain) and Plasmodium yoelii in vivo (N-67 strain). Among the series, eleven compounds (5, 6, 7, 8, 9, 11, 12, 13, 14, 15 and 21) showed superior antimalarial activity against K1 strain as compared to CQ. In addition, all these analogues showed 100% suppression of parasitemia on day 4 in the in vivo mouse model against N-67 strain when administered orally. Further, biophysical studies suggest that this series of compounds act on heme polymerization target.     

Discovery of a novel selective water-soluble SMAD3 inhibitor as an antitumor agent

Targeting the SMAD3 protein is an attractive therapeutic strategy for treating cancer, as it avoids the potential toxicities due to targeting the TGF-β signaling pathway upstream. Compound SIS3 was the first selective SMAD3 inhibitor developed that had acceptable activity, but its poor water solubility limited its development. Here, a series of SIS3 analogs was created to investigate the structure–activity relationship for inhibiting the activation of SMAD3. On the basis of this SAR, further optimization generated a water-soluble compound, 16d, which was capable of effectively blocking SMAD3 activation in vitro and had similar NK cell-mediated anticancer effects in vivo to its parent SIS3. This study not only provided a preferable lead compound, 16d, for further drug discovery or a potential tool to study SMAD3 biology, but also proved the effectiveness of our strategy for water-solubility driven optimization.     

2-Aminobenzimidazoles as potent Aurora kinase inhibitors

This Letter describes the discovery and key structure–activity relationship (SAR) of a series of 2-aminobenzimidazoles as potent Aurora kinase inhibitors. 2-Aminobenzimidazole serves as a bioisostere of the biaryl urea residue of SNS-314 (1c), which is a potent Aurora kinase inhibitor and entered clinical testing in patients with solid tumors. Compared to SNS-314, this series of compounds offers better aqueous solubility while retaining comparable in vitro potency in biochemical and cell-based assays; in particular, 6m has also demonstrated a comparable mouse iv PK profile to SNS-314.     

Optimization of 2-(1H-imidazo-2-yl)piperazines series of Trypanosoma brucei growth inhibitors as potential treatment for the second stage of HAT

A previous publication from our laboratory reported the identification of a new class of 2-(1H-imidazo-2-yl)piperazines as potent T. brucei growth inhibitors as potential treatment for Human African Trypanosomiasis (HAT). This work describes the structure–activity relationship (SAR) around the hit compound 1, which led to the identification of the optimized compound 18, a single digit nanomolar inhibitor (EC₅₀ 7 nM), not cytotoxic and with optimal in vivo profile that made it a suitable candidate for efficacy studies in a mouse model mimicking the second stage of disease.     

The development of a structurally distinct series of BACE1 inhibitors via the (Z)-fluoro-olefin amide bioisosteric replacement

The (Z)-fluoro-olefin amide bioisosteric replacement is an effective tool for addressing various shortcomings of the parent amide. In an effort to fine tune ADME properties of BACE1 preclinical candidate AM-6494, a series of structurally distinct (Z)-fluoro-olefin containing analogs was developed that culminated in compound 15. Herein, we detail design considerations, synthetic challenges, structure activity relationship (SAR) studies, and in vivo properties of an advanced compound in this novel series of BACE1 inhibitors.     

Design,synthesis, and biological evaluation of novel biphenyl-4-carboxamide derivatives as orally available TRPV1 antagonists

A new series of transient receptor potential vanilloid type 1 (TRPV1) antagonists were designed and synthesized from N-(3-hydroxyphenyl)-2-(piperidin-1-ylmethyl)biphenyl-4-carboxamide hydrochloride (8). SAR studies identified (R)-N-(1-methyl-2-oxo-1,2,3,4-tetrahydro-7-quinolyl)-2-[(2-methylpyrrolidin-1-yl)methyl]biphenyl-4-carboxamide hydrochloride (ASP8370, 7), as a compound with high aqueous solubility, satisfactory stability in human liver microsomes, and reduced CYP3A4 inhibition. ASP8370 was selected as a clinical development candidate with significant ameliorative effects on neuropathic pain. SAR studies also revealed the structural mechanisms underlying the switching between TRPV1 antagonism and agonism.     

Discovery of a new HIV-1 inhibitor scaffold and synthesis of potential prodrugs of indazoles

A new oxazole scaffold showing great promise in HIV-1 inhibition has been discovered by cell-based screening of an in-house library and scaffold modification. Follow-up SAR study focusing on the 5-aryl substituent of the oxazole core has identified 4k (EC₅₀ = 0.42 μM, TI = 50) as a potent inhibitor. However, the analogues suffered from poor aqueous solubility. To address this issue, we have developed broadly applicable potential prodrugs of indazoles. Among them, N-acyloxymethyl analogue 11b displayed promising results (i.e., increased aqueous solubility and susceptibility to enzymatic hydrolysis). Further studies are warranted to fully evaluate the analogues as the potential prodrugs with improved physiochemical and PK properties     

Synthesis and characterization of novel isoform-selective IP6K1 inhibitors

Inositol hexakisphosphate kinases (IP6Ks) have been increasingly studied as therapeutically interesting enzymes. IP6K isoform specific knock-outs have been used to successfully explore inositol pyrophosphate physiology and related pathologies. A pan-IP6K inhibitor, N2-(m-trifluorobenzyl)-N6-(p-nitrobenzyl) purine (TNP), has been used to confirm phenotypes observed in genetic knock-out experiments; however, it suffers by having modest potency and poor solubility making it difficult to handle for in vitro applications in the absence of DMSO. Moreover, TNP’s pan-IP6K inhibitory profile does not inform which IP6K isoform is responsible for which phenotypes. In this report we describe a series of purine-based isoform specific IP6K1 inhibitors. The lead compound was identified after multiple rounds of SAR and has been found to selectively inhibit IP6K1 over IP6K2 or IP6K3 using biochemical and biophysical approaches. It also boasts increased solubility and IP6K1 potency over TNP. These new compounds are useful tools for additional assay development and exploration of IP6K1 specific biology.     

Synthesis and pharmacological characterization of functionalized 6-piperazin-1-yl-purines as cannabinoid receptor 1 (CB1) inverse agonists

Antagonists of peripheral type 1 cannabinoid receptors (CB1) may have utility in the treatment of obesity, liver disease, metabolic syndrome and dyslipidemias. We have targeted analogues of the purine inverse agonist otenabant (1) for this purpose. The non-tissue selective CB1 antagonist rimonabant (2) was approved as a weight-loss agent in Europe but produced centrally mediated adverse effects in some patients including dysphoria and suicidal ideation leading to its withdrawal. Efforts are now underway to produce compounds with limited brain exposure. While many structure-activity relationship (SAR) studies of 2 have been reported, along with peripheralized compounds, 1 remains relatively less studied. In this report, we pursued analogues of 1 in which the 4-aminopiperidine group was switched to piperazine group to enable a better understanding of SAR to eventually produce compounds with limited brain penetration. To access a binding pocket and modulate physical properties, the piperazine was functionalized with alkyl, heteroalkyl, aryl and heteroaryl groups using a variety of connectors, including amides, sulfonamides, carbamates and ureas. These studies resulted in compounds that are potent antagonists of hCB1 with high selectivity for hCB1 over hCB2. The SAR obtained led to the discovery of 65 (Ki?=?4?nM, >1,000-fold selective for hCB1 over hCB2), an orally bioavailable aryl urea with reduced brain penetration, and provides direction for discovering peripherally restricted compounds with good in vitro and in vivo properties.     

2,4-Diamino-quinazolines as inhibitors of β-catenin/Tcf-4 pathway: Potential treatment for colorectal cancer

The synthesis and SAR of a series of 2,4-diamino-quinazoline derivatives as β-catenin/Tcf-4 inhibitors are described. This series was developed by modifying the initial lead 1, which was identified by screening of our compound library and found to inhibit the β-catenin/Tcf-4 pathway. Replacement of the biphenyl moiety in compound 1 with the N-phenylpiperidine-4-carboxamide chain as in 2, resulted in a number of new analogues, which are potent inhibitors of the β-catenin/Tcf-4 pathway. Compound such as 16k exhibited good cellular potency, solubility, metabolic stability and oral bioavailability.     

Discovery of triazole-based uracil derivatives bearing amide moieties as novel dipeptidyl peptidase-IV inhibitors

Dipeptidyl peptidase-IV (DPP-4) is a validated target for T2DM treatment. We previously reported a novel series of triazole-based uracil derivatives bearing aliphatic carboxylic acids with potent DPP-4 inhibitory activities in vitro, but these compounds showed poor hypoglycemic effects in vivo. Herein we further optimized the triazole moiety by amidation of the carboxylic acid to improve in vivo activities. Two series of compounds 3a-f and 4a-g were designed and synthesized. By screening in DPP-4, compound 4c was identified as a potent DPP-4 inhibitor with the IC₅₀ value of 28.62 nM. Docking study revealed compound 4c has a favorable binding mode and interpreted the SAR of these analogs. DPP-8 and DPP-9 tests indicated compound 4c had excellent selectivity over DPP-8 and DPP-9. Further in vivo evaluations revealed that compound 4c showed more potent hypoglycemic activity than its corresponding carboxylic acid in ICR mice and dose-dependently reduced glucose levels in type 2 diabetic C57BL/6 mice. The overall results have shown that compound 4c could be a promising lead for further development of novel DPP-4 agents treating T2DM.     

Challenges in the development of an M4 PAM in vivo tool compound: The discovery of VU0467154 and unexpected DMPK profiles of close analogs

This letter describes the chemical optimization of a novel series of M₄ positive allosteric modulators (PAMs) based on a 5-amino-thieno[2,3-c]pyridazine core, developed via iterative parallel synthesis, and culminating in the highly utilized rodent in vivo tool compound, VU0467154 (5). This is the first report of the optimization campaign (SAR and DMPK profiling) that led to the discovery of VU0467154, and details all of the challenges faced in allosteric modulator programs (steep SAR, species differences in PAM pharmacology and subtle structural changes affecting CNS penetration).