Discovery of pyrazolo[1,5-a]pyrimidine-based CHK1 inhibitors: a template-based approach--part 1

The synthesis and hit-to-lead SAR development of a pyrazolo[1,5-a]pyrimidine hit 4 is described leading to a series of potent, selective CHK1 inhibitors such as compound 17r. In the Letter, the further utility of the pyrazolo[1,5-a]pyrimidine template for the development of potent, selective kinase inhibitors is detailed.     

Synthesis,SAR study,and biological evaluation of novel 2,3-dihydro-1H-imidazo[1,2-a]benzimidazole derivatives as phosphodiesterase 10A inhibitors

Phosphodiesterase 10A (PDE10A) inhibitors were designed and synthesized based on the dihydro-imidazobenzimidazole scaffold. Compound 5a showed moderate inhibitory activity and good permeability, but unfavorable high P-glycoprotein (P-gp) liability for brain penetration. We performed an optimization study to improve both the P-gp efflux ratio and PDE10A inhibitory activity. As a result, 6d was identified with improved P-gp liability and high PDE10A inhibitory activity. Compound 6d also showed satisfactory brain penetration, suppressed phencyclidine-induced hyperlocomotion and improved MK-801-induced working memory deficit.     

Imidazo[1,5-a]pyrazines: orally efficacious inhibitors of mTORC1 and mTORC2

The discovery and optimization of a series of imidazo[1,5-a]pyrazine inhibitors of mTOR is described. HTS hits were optimized for potency, selectivity and metabolic stability to provide the orally bioavailable proof of concept compound 4c that demonstrated target inhibition in vivo and concomitant inhibition of tumor growth in an MDA-MB-231 xenograft model.     

Discovery of pyrazolo[1,5-a]pyrimidine-based CHK1 inhibitors: a template-based approach--part 2

Previous efforts by our group have established pyrazolo[1,5-a]pyrimidine as a viable core for the development of potent and selective CDK inhibitors. As part of an effort to utilize the pyrazolo[1,5-a]pyrimidine core as a template for the design and synthesis of potent and selective kinase inhibitors, we focused on a key regulator in the cell cycle progression, CHK1. Continued SAR development of the pyrazolo[1,5-a]pyrimidine core at the C5 and C6 positions, in conjunction with previously disclosed SAR at the C3 and C7 positions, led to the discovery of potent and selective CHK1 inhibitors.     

Novel,potent, selective,and brain penetrant phosphodiesterase 10A inhibitors

Herein we report the discovery of a novel series of phosphodiesterase 10A inhibitors. Optimization of a HTS hit (17) resulted in potent, selective, and brain penetrant 23 and 26; both exhibited much lower clearance in vivo and decreased volume of distribution (rat PK) and have thus the potential to inhibit the PDE10A target in vivo at a lower efficacious dose than the reference compound WEB-3.     

Synthesis and antiproliferative evaluation of 6-aryl-11-iminoindeno[1,2-c]quinoline derivatives

A number of 6-aryl-11-iminoindeno[1,2-c]quinoline derivatives were synthesized and evaluated for their antiproliferative activities. Among them, (E)-6-{4-[3-(dimethylamino)propoxy]phenyl}-2-fluoro-9-hydroxy-11H-indeno[1,2-c]quinolin-11-one O-3-(dimethylamino)propyl oxime (23a) was the most active, exhibited GI₅₀ values of 0.64, 0.39, 0.55, 0.67, and 0.65 μM against the growth of Hep G2, Hep 3B, A549, H1299, and MDA-MB-231, respectively. Compound 23a inhibited the growth of hepatoma cell lines in a dose- and time-dependent manner. The proportion of cells was decreased in the G1 and accumulated in G2/M phase after 12 h treatment of 23a, while the hypodiploid (sub-G0/G1 phase) cells increased. Further investigations have shown that 23a induced cell cycle arrest at G2/M phase and induce apoptosis via activation of p53, Bax, and caspase-8 which consequently cause cell death.     

Imidazo[1,5-a]quinoxalines as irreversible BTK inhibitors for the treatment of rheumatoid arthritis

Imidazo[1,5-a]quinoxalines were synthesized that function as irreversible Bruton's tyrosine kinase (BTK) inhibitors. The syntheses and SAR of this series of compounds are presented as well as the X-ray crystal structure of the lead compound 36 in complex with a gate-keeper variant of ITK enzyme. The lead compound showed good in vivo efficacy in preclinical RA models.     

3-Arylisoquinolines as novel topoisomerase I inhibitors

Topoisomerase I (topo I) is an essential enzyme for vital cellular processes. Inhibition of topo I activities is lethal and leads to cell death, thus establishing topo I as a promising target for cancer treatment. Camptothecin, a natural alkaloid, inhibits topo I. Topotecan and irinotecan, synthetic derivatives of camptothecin, are the most potent anticancer drugs in clinical use. However, several limitations of camptothecins such as solubility, toxicity, stability, resistance and the required high drug dose have encouraged the development of non-camptothecin topo I inhibitors. Natural alkaloid benzo[c]phenanthridines and synthetic indenoisoquinolines have been extensively studied as alternatives to camptothecin. Interestingly, these non-camptothecin topo I inhibitors share a common 3-arylisoquinoline scaffold. This review will describe the development of novel indeno[1,2-c]isoquinolines, isoindolo[2,1-b]isoquinolines, 12-oxobenzo[c]phenanthridines and benz[b]oxepines with a 3-arylisoquinoline nucleus as topo I inhibitors.     

Identification and SAR of a new series of thieno[3,2-d]pyrimidines as Tpl2 kinase inhibitors

We report here the synthesis and SAR of a new series of thieno[3,2-d]pyrimidines as potent Tpl2 kinase inhibitors. The proposed binding mode suggests the potential flipped binding mode depending on the substitution. Biacore studies show evidence of binding of these molecules to the protein kinase. The kinome inhibition profile of these molecules suggests good selectivity.     

Identification of 4H,6H-[2]benzoxepino[4,5-c][1,2]oxazoles as novel squalene synthase inhibitors

Novel squalene synthase inhibitors are disclosed. The design, synthesis, SAR and pharmacological profile of the compounds are discussed.     

Synthesis and biological evaluation of novel F-18 labeled pyrazolo[1,5-a]pyrimidine derivatives: potential PET imaging agents for tumor detection

Two novel pyrazolo[1,5-a]pyrimidine derivatives, 7-(2-[¹⁸F]fluoroethylamino)-5-methylpyrazolo[1,5-a]pyrimidine-3-carbonitrile ([¹⁸F]FEMPPC, [¹⁸F]1) and N-(2-(3-cyano-5-methylpyrazolo[1,5-a]pyrimidin-7-ylamino)ethyl)-2-[¹⁸F]fluoro-4-nitrobenzamide ([¹⁸F]FCMPPN, [¹⁸F]2), have been designed and successively labeled with ¹⁸F by the nucleophilic substitution employing tosylate and nitryl as leaving groups, respectively. The radiochemical synthesis of both compounds was completed within 60 min with final high-performance liquid chromatography purification included. The corresponding radiochemical yields (without decay correction) were approximately 35% and 30%, respectively. Meanwhile, we compared the uptake characteristics of [¹⁸F]1 and [¹⁸F]2 with those of [¹⁸F]FDG and L-[¹⁸F]FET in S180 tumor cells. Furthermore, the tumor uptake of [¹⁸F]1 and [¹⁸F]2 was assessed in mice bearing S180 tumor and compared with [¹⁸F]FDG and L-[¹⁸F]FET in the same animal model. In vitro cell uptake studies showed [¹⁸F]1 had higher uptake than [¹⁸F]FDG, [¹⁸F]2 and L-[¹⁸F]FET over the 2 h period. In ex vivo biodistribution showed tumor/brain uptake ratios of [¹⁸F]2 were 12.35, 10.44, 8.69 and 5.13 at 15 min, 30 min, 60 min and 120 min post-injection, much higher than those of L-[¹⁸F]FET (2.43, 2.54, 2.93 and 2.95) and [¹⁸F]FDG (0.59, 0.61, 1.02 and 1.33) at the same time point. What’s more, the uptake of [¹⁸F]1 in tumor was 1.88, 4.37, 5.51, 2.95 and 2.88 at 5 min, 15 min, 30 min, 60 min and 120 min post-injection, respectively. There was a remarkable increasing trend before 30 min. The same trend was present for L-[¹⁸F]FET before 30 min and [¹⁸F]FDG before 60 min. Additionally, the tumor/brain uptake ratios of [¹⁸F]1 were superior to those of [¹⁸F]FDG at all the selected time points, the tumor/muscle and tumor/blood uptake ratios of [¹⁸F]1 at 30 min were higher than those of L-[¹⁸F]FET at the same time point. MicroPET image of [¹⁸F]1 administered into S180 tumor-bearing mouse acquired at 30 min post-injection illustrated that the uptake in S180 tumor was obvious. These results suggest that compound [¹⁸F]1 could be a new probe for PET tumor imaging.     

Discovery and evaluation of pyrazolo[1,5-a]pyrimidines as neuropeptide Y1 receptor antagonists

A novel series of pyrazolo[1,5-a]pyrimidine derivatives was synthesized and evaluated as NPY Y1R antagonists. High binding affinity and selectivity were achieved with C3 trisubstituted aryl groups and C7 substituted 2-(tetrahydro-2H-pyran-4-ylamino)ethylamine moieties. Efforts to find close analogs with low plasma clearance in the rat and minimal p-glycoprotein efflux in the mouse were unsuccessful. Compound 2f (CP-671906) inhibited NPY-induced increases in blood pressure and food intake after iv and icv administration, respectively, in Sprague-Dawley (SD) rat models. Oral administration of compound 2f resulted in a modest, but statistically significant, reduction in food intake in a Wistar rat model of feeding behavior. Small inhibitions of food intake were also observed in an overnight fasting/refeeding model in SD rats. These data suggest a potential role for Y1R in the regulation of food intake in rodents.     

Triazoloquinazolines as a novel class of phosphodiesterase 10A (PDE10A) inhibitors

Novel triazoloquinazolines have been found as phosphodiesterase 10A (PDE10A) inhibitors. Structure-activity studies improved the initial micromolar potency which was found in the lead compound by a 100-fold identifying 5-(1H-benzoimidazol-2-ylmethylsulfanyl)-2-methyl-[1,2,4]triazolo[1,5-c]quinazoline, 42 (PDE10A IC₅₀ = 12 nM) as the most potent compound from the series. Two X-ray structures revealed novel binding modes to the catalytic site of the PDE10A enzyme.     

Synthesis of novel 5-amino-thiazolo[4,5-d]pyrimidines as E. coli and S. aureus SecA inhibitors

An efficient synthesis of a library of 5-amino-thiazolo[4,5-d]pyrimidines is reported. Regioselective displacements of chlorines, as well as regioselective diazotation reactions are described, which allow the introduction of structural diversity on the scaffold by consecutive reactions. Screening of this focused library led to the discovery of SecA inhibitors from Escherichia coli and Staphylococcus aureus.     

Discovery of benzo[d]imidazo[5,1-b]thiazole as a new class of phosphodiesterase 10A inhibitors

The design, synthesis and structure activity relationship studies of a series of compounds from benzo[d]imidazo[5,1-b]thiazole scaffold as phosphodiesterase 10A (PDE10A) inhibitors are discussed. Several potent analogs with heteroaromatic substitutions (9a–d) were identified. The anticipated binding mode of these analogs was confirmed by performing the in silico docking experiments. Later, the heteroaromatics were substituted with saturated heteroalkyl groups which provided a tool compound 9e with excellent PDE10A activity, PDE selectivity, CNS penetrability and with favorable pharmacokinetic profile in rats. Furthermore, the compound 9e was shown to be efficacious in the MK-801 induced psychosis model and in the CAR model of psychosis.     

Design and synthesis of potent, orally-active DGAT-1 inhibitors containing a dioxino[2,3-d]pyrimidine core

A novel series of potent DGAT-1 inhibitors was developed originating from the lactam-based clinical candidate PF-04620110. Incorporation of a dioxino[2,3-d]pyrimidine-based core afforded good alignment of pharmacophore features and resulted in improved passive permeability. Development of an efficient, homochiral synthesis of these targets facilitated confirmation of predictions regarding the stereochemical-dependence of DGAT-1 inhibition for this series. Compound 10 was shown to be a potent inhibitor of human DGAT-1 (10 nM) and to suppress triglyceride synthesis at oral doses of <3mg/kg.     

Novel bifunctional alkylating agents, 5,10-dihydropyrrolo[1,2-b]isoquinoline derivatives, synthesis and biological activity

A series of linear pyrrolo[1,2-b]isoquinoline derivatives was synthesized for antitumor evaluation. The preliminary antitumor studies reveal that both bis(hydroxymethyl) and their bis(alkylcarbamate) derivatives show significant antitumor activity in inhibiting various human tumor cell growth in vitro. 1,2-Bis(hydroxymethyl)-3-methyl-5,10-dihydropyrrolo[1,2-b]isoquinoline (20a) was selected for antitumor studies in animal models. The results show that this agent can induce complete tumor remission or significant suppression in nude mice bearing human breast (MX-1) xenograft and ovarian (SK-OV-3) xenografts, respectively. Alkaline agarose gel shifting assay showed that 20a is able to cross-link with DNA. Studies on the cell cycle inhibition revealed that this agent induces cell arrest at G2/M phase. The results warrant further antitumor investigation against other human tumor growth in animal models.     

Novel benzimidazole derivatives as phosphodiesterase 10A (PDE10A) inhibitors with improved metabolic stability

In this study, we report the identification of potent benzimidazoles as PDE10A inhibitors. We first identified imidazopyridine 1 as a high-throughput screening hit compound from an in-house library. Next, optimization of the imidazopyridine moiety to improve inhibitory activity gave imidazopyridinone 10b. Following further structure–activity relationship development by reducing lipophilicity and introducing substituents, we acquired 35, which exhibited both improved metabolic stability and reduced CYP3A4 time-dependent inhibition.     

N-Acylhydrazones as inhibitors of PDE10A

Cyclic nucleotide phosphodiesterases (PDEs) are represented by a large superfamily of enzymes. A series of hydrazone-based inhibitors was synthesized and shown to be novel, potent, and selective against PDE10A. Optimized compounds of this class were efficacious in animal models of schizophrenia and may be useful for the treatment of this disease.     

Design and synthesis of novel benzimidazole derivatives as phosphodiesterase 10A inhibitors with reduced CYP1A2 inhibition

A novel class of phosphodiesterase 10A (PDE10A) inhibitors with reduced CYP1A2 inhibition were designed and synthesized starting from 2-{[(1-phenyl-1H-benzimidazol-6-yl)oxy]methyl}quinoline (1). Introduction of an isopropyl group at the 2-position and a methoxy group at the 5-position of the benzimidazole ring of lead compound 1 resulted in the identification of 2-{[(2-isopropyl-5-methoxy-1-phenyl-1H-benzimidazol-6-yl)oxy]methyl}quinoline (25b), which exhibited potent PDE10A inhibitory activity with reduced CYP1A2 inhibitory activity compared to compound 1.