An isoform-selective inhibitor of tropomyosin receptor kinase A behaves as molecular glue.

The production of TrkA-selective inhibitors is considerably difficult because the kinase domains of TrkA and its isoforms TrkB/C have highly homologous amino acid sequences. Here we describe the structural basis for the acquisition of selectivity for a isoform-selective TrkA inhibitor, namely compound V1. The X-ray structure revealed that V1 acts as a molecular glue to stabilize the symmetrical dimer of the TrkA kinase domains. V1 binds to the ATP-binding site and simultaneously engages in the dimeric interface of TrkA. The region of the dimeric interface in TrkA is not conserved in TrkB/C; thus, dimer formation may be a novel mechanism for the production of selective TrkA inhibitors. The biochemical and biophysical assay results confirmed that V1 selectively inhibited TrkA and induced the dimer formation of TrkA, but not TrkB. The binding pocket at the TrkA dimer interface can be used for the production of new isoform-selective TrkA inhibitors.

Photoaffinity Labeling of the Human A2A Adenosine Receptor and Cross-link Position Analysis by Mass Spectrometry.

Photoaffinity labeling (PAL) is widely used for the identification of ligand-binding proteins and elucidation of ligand-binding sites. PAL has also been employed for the characterization of G protein-coupled receptors (GPCRs); however, a limited number of reports has successfully identified their cross-linked amino acids. This report is the first of its kind to determine the cross-link position of the human A2A adenosine receptor by PAL with the novel diazirine-based photoaffinity probe 9.

The juxtamembrane region of TrkA kinase is critical for inhibitor selectivity.

Although numerous crystal structures for protein kinases have been reported, many include only the kinase domain but not the juxtamembrane (JM) region, a critical activity-controlling segment of receptor tyrosine kinases (RTKs). In this study, we determined the X-ray crystal structure of the tropomyosin receptor kinase (Trk) A selective inhibitor A1 complexed with the TrkA kinase domain and the JM region. This structure revealed that the unique inhibitor-binding pocket created by a novel JM configuration yields significant potency and high selectivity against TrkB and TrkC. Moreover, we validated the importance of the JM region for the potency of A1 using in vitro assays. The introduction of moieties that interact with the JM region will be one of the most effective strategies for producing highly selective RTK inhibitors.

Synthesis and structure-activity relationships of 1-benzylindane derivatives as selective agonists for estrogen receptor beta.

The estrogen receptor beta (ERß) selective agonist is considered a promising candidate for the treatment of estrogen deficiency symptoms in ERß-expressing tissues, without the risk of breast cancer, and multiple classes of compounds have been reported as ERß selective agonists. Among them, 6-6 bicyclic ring-containing structures (e.g., isoflavone phytoestrogens) are regarded as one of the cyclized analogues of isobutestrol 5b, and suggest that other cyclized scaffolds comprising 5-6 bicyclic rings could also act as selective ERß ligands. In this study, we evaluated the selective ERß agonistic activity of 1-(4-hydroxybenzyl)indan-5-ol 7a and studied structure-activity relationship (SAR) of its derivatives. Some functional groups improved the properties of 7a; introduction of a nitrile group on the indane-1-position resulted in higher selectivity for ERß (12a), and further substitution with a fluoro or a methyl group to the pendant phenyl ring was also preferable (12b, d, and e). Subsequent chiral resolution of 12a identified that R-12a has a superior profile over S-12a. This is comparable to diarylpropionitrile (DPN) 5c, one of the promising selective ERß agonists and indicates that this indane-based scaffold has the potential to provide better ERß agonistic probes.

Orally active factor Xa inhibitors: investigation of a novel series of 3-amidinophenylsulfonamide derivatives using an amidoxime prodrug strategy.

A series of novel and potent 3-amidinophenylsulfonamide derivatives of factor Xa inhibitors were designed and synthesized using an amidoxime prodrug strategy. We focused on systemic clearance of parent compounds in rats, and performed in vivo pharmacokinetic screening. Incorporation of a carboxymethoxy group markedly improved systemic clearance (compound 43), and the related amidoxime 44 showed sufficient prodrug conversion. Compound 45, the double prodrug of 43, exhibited practicable bioavailability after oral administration in rats. Among the various compounds under investigation, KFA-1982 was selected for clinical development.

Relationship between stereochemistry and the beta3-adrenoceptor agonistic activity of 4'-hydroxynorephedrine derivative as an agent for treatment of frequent urination and urinary incontinence.

This report proposes a beta(3)-adrenoceptor (AR) selective agonist, 2-[2-chloro-4-(2-([(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino)ethyl)phenoxy]acetic acid (1a), as a novel agent for treating urinary bladder dysfunction. This compound and its relatives have a unique feature among beta(3)-AR agonists: two chiral carbons are adjacently structured on the left side of the molecule. To study the relationship between the stereoconfiguration of the vicinal chiral carbons in 1a and beta-AR agonistic activity, the four stereoisomers were synthesized via oxazolidinone prepared by intracyclization involving inversion of the beta-hydroxy group. The in vitro assays using rat atria for beta(1)-AR, rat uteri for beta(2)-AR, and ferret detrusor for beta(3)-AR showed that 1a possessed potent beta(3)-AR agonistic activity (EC(50) = 3.85 nM) and 3700- and 1700-fold selectivity for beta(3)-AR relative to beta(1)- and beta(2)-AR, respectively. Comparison of the four isomers revealed that the (alphaS,betaR)-compound (1a) was not only the most potent agonist but was also the most selective for beta(3)-AR. In the anesthetized rat, intravenous administration of 1a brought about a sufficient decrement of the intrabladder pressure (ED(50) = 12 microg/kg), and intraduodenal administration of 2a, which is the ethyl ester of 1a, led to same result (ED(50) = 0.65 mg/kg). Moreover, no effects on the cardiovascular system were observed in either test.