Discovery of Novel Pyrido-pyridazinone Derivatives as FER Tyrosine Kinase Inhibitors with Antitumor Activity.

To obtain a new anticancer drug, we focused on FER tyrosine kinase. Starting with high-throughput screening with our in-house chemical library, compound 1, which has a pyridine moiety, was found. Referring to their X-ray crystal structure with FES proto-oncogene tyrosine kinase, as a surrogate of FER followed by chemical modification including scaffold hopping of the pyridine template, we discovered pyrido-pyridazinone derivatives with potent FER kinase inhibitory activity. Here, we disclose the structure-activity relationship on the scaffold and representative compound 21 (DS21360717), which showed in vivo antitumor efficacy in a subcutaneous tumor model.

A novel inhibitor stabilizes the inactive conformation of MAPK-interacting kinase 1.

Mitogen-activated protein kinase (MAPK)-interacting kinases 1 (Mnk1) and 2 (Mnk2) modulate translation initiation through the phosphorylation of eukaryotic translation initiation factor 4E, which promotes tumorigenesis. However, Mnk1 and Mnk2 are dispensable in normal cells, suggesting that the inhibition of Mnk1 and Mnk2 could be effective in cancer therapy. To provide a structural basis for Mnk1 inhibition, a novel Mnk1 inhibitor was discovered and the crystal structure of Mnk1 in complex with this inhibitor was determined. The crystal structure revealed that the inhibitor binds to the autoinhibited state of Mnk1, stabilizing the Mnk-specific DFD motif in the DFD-out conformation, thus preventing Mnk1 from switching to the active conformation and thereby inhibiting the kinase activity. These results provide a valuable platform for the structure-guided design of Mnk1 inhibitors.

Discovery of 3-(3-(4-(1-Aminocyclobutyl)phenyl)-5-phenyl-3H-imidazo[4,5-b]pyridin-2-yl)pyridin-2-amine (ARQ 092): An Orally Bioavailable, Selective, and Potent Allosteric AKT Inhibitor.

The work in this paper describes the optimization of the 3-(3-phenyl-3H-imidazo[4,5-b]pyridin-2-yl)pyridin-2-amine chemical series as potent, selective allosteric inhibitors of AKT kinases, leading to the discovery of ARQ 092 (21a). The cocrystal structure of compound 21a bound to full-length AKT1 confirmed the allosteric mode of inhibition of this chemical class and the role of the cyclobutylamine moiety. Compound 21a demonstrated high enzymatic potency against AKT1, AKT2, and AKT3, as well as potent cellular inhibition of AKT activation and the phosphorylation of the downstream target PRAS40. Compound 21a also served as a potent inhibitor of the AKT1-E17K mutant protein and inhibited tumor growth in a human xenograft mouse model of endometrial adenocarcinoma.

A novel inhibitor of I-kappaB kinase beta ameliorates experimental arthritis through downregulation of proinflammatory cytokines in arthritic joints.

Inhibitor of kappaB (IκB) kinase beta (IKKß) plays a critical role in nuclear factor-kappaB (NF-κB) activation and production of proinflammatory cytokines in various inflammatory diseases including rheumatoid arthritis. We previously reported a novel IKKß inhibitor Compound D, 4-[6-(cyclobutylamino)imidazo[1,2-b]pyridazin-3-yl]-2-fluoro-N-{[(2S,4R)-4-fluoropyrrolidin-2-yl]methyl}benzamide, which is efficacious in experimental arthritis models. In the present study, we characterized the pharmacological properties of Compound D and investigated the mechanisms of the anti-arthritic effect. Compound D inhibited IKKß kinase activity with 160-fold selectivity against IKKα. The cellular analyses revealed that Compound D selectively blocked NF-κB promoter activity among major cellular signaling pathways, such as the activator protein-1 pathway, consistent with inhibition of the NF-κB signaling pathway including phosphorylation of IκBα. In addition, Compound D inhibited NF-κB-driven production of tumor necrosis factor alpha (TNFα) and interleukin-6 comparably. The correlation between inhibitory effect on TNFα production and plasma concentration of the compound was observed in vivo. Consecutive administration of Compound D decreased gene expression of proinflammatory cytokines and inflammatory mediators in the paws of arthritic mice with attenuation of paw swelling. Notably, Compound D was rapidly distributed to the arthritic paws, rather than healthy paws, and where it decreased the gene expression of proinflammatory cytokines by a single oral administration. Furthermore, Compound D completely inhibited arthritis progression even when treatment occurred after disease development. These data suggest that the downregulation of proinflammatory cytokines in local inflamed joints is one of the mechanisms underlying the anti-arthritic effect of the IKKß inhibitor, Compound D.

A novel, potent, and orally active VLA-4 antagonist with good aqueous solubility: trans-4-[1-[[2-(5-Fluoro-2-methylphenylamino)-7-fluoro-6-benzoxazolyl]acetyl]-(5S)-[methoxy(methyl)amino]methyl-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylic acid.

We have carried out the optimization of substituents at the C-3 or the C-5 position on the pyrrolidine ring of VLA-4 antagonist 3 with 2-(phenylamino)-7-fluorobenzoxazolyl moiety for the purpose of improving in vivo efficacy while maintaining good aqueous solubility. As a result, we successfully increased in vitro activity in the presence of 3% human serum albumin and achieved an exquisite lipophilic and hydrophilic balance of compounds suitable for oral administrative regimen. The modification resulted in the identification of zwitterionic compound 7n with (5S)-[methoxy(methyl)amino]methylpyrrolidine, which significantly alleviated bronchial hyper-responsiveness to acetylcholine chloride at 12.5mg/kg, p.o. in a murine asthma model and showed favorable aqueous solubility (JP1, 89 µg/mL; JP2, 462 µg/mL). Furthermore, this compound showed good oral bioavailability (F=54%) in monkeys.

Identification of trans-4-[1-[[7-fluoro-2-(1-methyl-3-indolyl)-6-benzoxazolyl]acetyl]-(4S)-fluoro-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylic acid as a potent, orally active VLA-4 antagonist.

For the purpose of obtaining orally potent VLA-4 inhibitors, we have carried out structural modification of the (N'-phenylureido)phenyl group in compound 1, where the group was found to be attributed to poor pharmacokinetic profile in our previous research. Through modification, we have identified several compounds with both potent in vitro activity and improved oral exposure. In particular, compound 7e with 7-fluoro-2-(1-methyl-1H-indol-3-yl)-1,3-benzoxazolyl group as a novel replacement of the (N'-phenylureido)phenyl group significantly inhibited eosinophil infiltration into bronchoalveolar lavage fluid at 15mg/kg in an Ascaris-antigen-induced murine bronchial inflammatory model, and its efficacy was comparable to that of the anti-mouse α(4) antibody (R1-2).

Discovery of imidazo[1,2-b]pyridazines as IKKß inhibitors. Part 3: exploration of effective compounds in arthritis models.

We have discovered imidazo[1,2-b]pyridazine derivatives that show suppressive activity of inflammation in arthritis models. We optimized the substructures of imidazo[1,2-b]pyridazine derivatives to combine potent IKKß inhibitory activity, TNFα inhibitory activity in vivo and excellent pharmacokinetics. The compound we have acquired, which had both potent activities and good pharmacokinetic profiles based on improved physicochemical properties, demonstrated efficacy on collagen-induced arthritis models in mice and rats.

Discovery of imidazo[1,2-b]pyridazines as IKKß inhibitors. Part 2: improvement of potency in vitro and in vivo.

We have increased the potency of imidazo[1,2-b]pyridazine derivatives as IKKß inhibitors with two strategies. One is to enhance the activity in cell-based assay by adjusting the polarity of molecules to improve permeability. Another is to increase the affinity for IKKß by the introduction of additional substituents based on the hypothesis derived from an interaction model study. These improved compounds showed inhibitory activity of TNFα production in mice.

Discovery of imidazo[1,2-b]pyridazine derivatives as IKKbeta inhibitors. Part 1: Hit-to-lead study and structure-activity relationship.

Imidazo[1,2-b]pyridazine derivatives from high-throughput screening were developed as IKKbeta inhibitors. By the optimization of the 3- and 6-position of imidazo[1,2-b]pyridazine scaffold, cell-free IKKbeta inhibitory activity and TNFalpha inhibitory activity in THP-1 cell increased. Also, these compounds showed high kinase selectivity. The structure-activity relationship was revealed and the interaction model of imidazo[1,2-b]pyridazine compounds with IKKbeta was constructed.

Discovery of trans-4-[1-[[2,5-Dichloro-4-(1-methyl-3-indolylcarboxamido)phenyl]acetyl]-(4S)-methoxy-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylic acid: an orally active, selective very late antigen-4 antagonist.

We have focused on optimization of the inadequate pharmacokinetic profile of trans-4-substituted cyclohexanecarboxylic acid 5, which is commonly observed in many small molecule very late antigen-4 (VLA-4) antagonists. We modified the lipophilic moiety in 5 and found that reducing the polar surface area of this moiety results in improvement of the PK profile. Consequently, our efforts have led to the discovery of trans-4-[1-[[2,5-dichloro-4-(1-methyl-3-indolylcarboxamido)phenyl]acetyl]-(4S)-methoxy-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylic acid (14e) with potent activity (IC(50) = 5.4 nM) and significantly improved bioavailability in rats, dogs, and monkeys (100%, 91%, 68%), which demonstrated excellent oral efficacy in murine and guinea pig models of asthma. Based on its overall profile, compound 14e was progressed into clinical trails. In a single ascending-dose phase I clinical study, compound 14e exhibited favorable oral exposure as expected and had no serious adverse events.

A novel and potent VLA-4 antagonist based on trans-4-substituted cyclohexanecarboxylic acid.

During the course of our study, it was revealed that the poor pharmacokinetic properties of a series of benzoic acid derivatives such as 1 should be attributed to the diphenylurea moiety. Thus, we replaced the diphenylurea moiety in 1 with a 2-(2-methylphenylamino)benzoxazole moiety which mimics the diphenylurea structure. However, this modification resulted in a significant decrease (3, IC(50)=19 nM) in VLA-4 inhibitory activity compared to 1 (IC(50)=1.6 nM). To address this discrepancy, we worked on optimization of the carboxylic acid moiety in compound 3. As a result, our efforts have led to the discovery of trans-4-substituted cyclohexanecarboxylic acid derivative 11b (IC(50)=2.8 nM) as a novel and potent VLA-4 antagonist. In addition, compound 11b exhibited favorable pharmacokinetic properties (CL=3.3 ml/min/kg, F=51%) in rats.

Identification of 4-[1-[3-chloro-4-[N'-(5-fluoro-2-methylphenyl)ureido]phenylacetyl]-(4S)-fluoro-(2S)-pyrrolidinylmethoxy]benzoic acid as a potent, orally active VLA-4 antagonist.

Optimization of benzoic acid derivatives by introducing substituents into the diphenyl urea moiety led to the identification of compound 20l as a potent VLA-4 antagonist. Compound 20l inhibited eosinophil infiltration into bronchial alveolar lavage fluid in a murine asthma model by oral dosing and its efficacy was comparable to anti-mouse alpha4 antibody (R1-2). Furthermore, this compound significantly blocked bronchial hyper-responsiveness in the model.

Synthesis and biological evaluation of benzoic acid derivatives as potent, orally active VLA-4 antagonists.

A series of benzoic acid derivatives was synthesized as VLA-4 antagonists. Introduction of chlorine or bromine into the 3-position on the central benzene of the diphenylurea portion as in lead compound 2 led to improvement in the pharmacokinetic properties. In particular, 12l demonstrated an acceptable plasma clearance and bioavailability in mice and rats as well as dogs (mice, CL=18.5 ml/min/kg,F=28%; rats, CL=5.2 ml/min/kg,F=36%; dogs, CL=3.6 ml/min/kg,F=55%). Additionally, 12l exhibited potent activity with an IC50 value of 0.51 nM and efficacy by oral administration at a dosage of 10 mg/kg in a rat pleurisy model.

4-(Pyrrolidinyl)methoxybenzoic acid derivatives as a potent, orally active VLA-4 antagonist.

A novel series of benzoic acid derivatives as VLA-4 antagonists were synthesized. Optimization, focusing on activity and lipophilicity needed for cell permeability, resulted in the identification of 15b and 15e with good activity (IC50 = 1.6 nM each) and moderate lipophilicity (Log D = 2.0, 1.8). Furthermore, 15e demonstrated efficacy in murine asthma model by an oral dose of 30 mg/kg.

Enantioselective total synthesis of guanacastepene N using an uncommon 7-endo Heck cyclization as a pivotal step.

A convergent, enantioselective total synthesis of (+)-guanacastepene N was developed that features a 7-endo Heck cyclization as the key step. In the course of this synthesis, short syntheses of the enantiomerically pure cyclopentenone and cyclohexene building blocks 5 and 6, which constitute A and C ring fragments of guanacastepene N, were developed. These fragments were linked by a challenging conjugate addition reaction that also generated the C11 quaternary carbon stereocenter. Regioselective 7-endo Heck cyclization gave rise to a tricyclic intermediate, which was elaborated to complete the first total synthesis of guanacastepene N and the second enantioselective total synthesis of a guanacastepene natural product.

New highly active taxoids from 9beta-dihydrobaccatin-9,10-acetals. Part 2.

To investigate structure-activity relationships of the 9,10-acetal-9beta-dihydro taxoids, we modified the 7-hydroxyl groups of the 9,10-acetonide-3'-(4-pyridyl) analogue to deoxy, methoxy, alpha-F, and 7beta,8beta-methano group. As a result of this study, we found that the 7-deoxy analogue was the strongest among these analogues. In addition, we found that the 7-deoxy-3'-(4-pyridyl) and 7-deoxy-3'-(2-pyridyl) analogues showed stronger activity against cell lines expressing P-glycoprotein than the corresponding 3'-phenyl analogue.

New highly active taxoids from 9 beta-dihydrobaccatin-9,10-acetals.

To synthesize new highly active taxoids, we designed and synthesized 9 beta-dihydro-9,10-acetal taxoids. In vitro study of these analogues clearly showed them to be more potent than docetaxel.

Studies on Steric and Electronic Control of 2'-3' Phosphoryl Migration in 2'-Phosphorylated Uridine Derivatives and Its Application to the Synthesis of 2'-Phosphorylated Oligouridylates.

For the synthesis of 2'-phosphorylated oligouridylates by use of new phosphoramidite building units, several masked phosphoryl groups have been examined as 2'-phosphate precursors, which should not be migrated to the 3' position when the 3' hydroxy protecting group must be removed to introduce a phosphoramidite residue into the 3'-position. As a consequence, bis(2-cyano-1,1-dimethylethoxy)thiophosphoryl (BCMETP) was found to be the most suitable 2'-phosphate precursor. This thiophosphoryl group could be introduced into the 2'-hydroxyl of 3',5'-silylated uridine derivative 7 by phosphitylation with bis(2-cyano-1,1-dimethylethoxy)(diethylamino)phosphine followed by sulfurization. Treatment of the 2'-thiophosphorylated product 15 with (HF)(x)().Py in THF gave exclusively the 3',5'-unprotected uridine derivative 16a. Compound 16a was converted to the phosphoramidite unit 22 via a two-step reaction. This building block was used for the solution phase synthesis of U(2'-p)pU (29) and U(2'-ps)pU (30). Both the 2-cyano-1,1-dimethylethyl and 2-cyanoethyl groups were effectively removed from the fully protected derivative 25 by treatment with DBU in the presence of N,O-bis(trimethylsilyl)acetamide (BSA). The resulting 2'-thiophosphoryl group was successfully converted to a phosphoryl group by iodine treatment to give U(2'-p)pU (29). U(2'-ps)pU (30) was also synthesized by a modified procedure without the iodine treatment. Reaction of 29 with a new biotinylating reagent in aqueous solution in the presence of MgCl(2) gave a biotin-labeled product 35 having a pyrophosphate bridge at the 2' position. Reaction of 30 with monobromobimane gave the 2'-S-alkylated product 33 in aqueous solution. Application of the phosphoramidite unit 22 to the solid phase synthesis using aminopropyl CPG gel gave successfully [U(2'-p)p](n)()U (n = 1, 3, 5). It was found that stability of the succinate linker between the CPG and oligouridylates was unaffected by the treatment with DBU when BSA was present. Several enzymatic properties of the synthetic 2'-phosphorylated and 2'-thiophosphorylated oligouridylates are also described.