Hideyuki Muranaka

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.

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

The estrogen receptor beta (ERβ) selective agonist is considered a promising candidate for the treatment of estrogen deficiency symptoms in ERβ-expressing tissues, without the risk of breast cancer, and multiple classes of compounds have been reported as ERβ 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 ERβ ligands. In this study, we evaluated the selective ERβ 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 ERβ (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 ERβ agonists and indicates that this indane-based scaffold has the potential to provide better ERβ agonistic probes.

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.

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.

Photoaffinity Labeling in Drug Discovery Research

Photoaffinity labeling (PAL) is a method that forms an irreversible covalent bond between photoreactive ligands and neighboring amino acids under the irradiation of light. PAL is utilized in the pharmacological and biochemical identification of ligand target molecules and ligand binding sites. Recent technological advances in mass spectrometry have enabled measurement of the mass of intact proteins and peptides with extremely high accuracy. Mass spectrometry has also been adopted in PAL to analyze labeled proteins and identify crosslink amino acid, although this application has been mostly for soluble proteins and reports on the successful identification of crosslink amino acids in GPCRs by mass spectrometry are scarce. In this chapter, we describe in detail our PAL technique that determines crosslink amino acid using the human adenosine A2A receptor as a representative class A GPCR.