Nami Ohashi

Publications (20)61.62 Total impact

• Article: CD4 mimics as HIV entry inhibitors: Lead optimization studies of the aromatic substituents.

  Tetsuo Narumi, Hiroshi Arai, Kazuhisa Yoshimura, Shigeyoshi Harada, Yuki Hirota, Nami Ohashi, Chie Hashimoto, Wataru Nomura, Shuzo Matsushita, Hirokazu Tamamura
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  ABSTRACT: Several CD4 mimics have been reported as HIV-1 entry inhibitors that can intervene in the interaction between a viral envelope glycoprotein gp120 and a cell surface protein CD4. Our previous SAR studies led to a finding of a highly potent analogue 3 with bulky hydrophobic groups on a piperidine moiety. In the present study, the aromatic ring of 3 was modified systematically in an attempt to improve its antiviral activity and CD4 mimicry which induces the conformational changes in gp120 that can render the envelope more sensitive to neutralizing antibodies. Biological assays of the synthetic compounds revealed that the introduction of a fluorine group as a meta-substituent of the aromatic ring caused an increase of anti-HIV activity and an enhancement of a CD4 mimicry, and led to a novel compound 13a that showed twice as potent anti-HIV activity compared to 3 and a substantial increase in a CD4 mimicry even at lower concentrations.
  Bioorganic & medicinal chemistry 03/2013; · 2.82 Impact Factor
• Article: Low-Molecular-Weight CXCR4 Ligands with Variable Spacers.

  Tetsuo Narumi, Haruo Aikawa, Tomohiro Tanaka, Chie Hashimoto, Nami Ohashi, Wataru Nomura, Takuya Kobayakawa, Hikaru Takano, Yuki Hirota, Tsutomu Murakami, Naoki Yamamoto, Hirokazu Tamamura
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  ABSTRACT: Low-molecular-weight CXCR4 ligands based on known lead compounds including the 14-mer peptide T140, the cyclic pentapeptide FC131, peptide mimetics, and dipicolylamine-containing compounds were designed and synthesized. Three types of aromatic spacers, 1,4-phenylenedimethanamine, naphthalene-2,6-diyldimethanamine, and [1,1'-biphenyl]-4,4'-diyldimethanamine, were used to build four pharmacophore groups. As pharmacophore groups, 2-pyridylmethyl and 1-naphthylmethyl are present in all of the compounds, and several aromatic groups and a cationic group from 1-propylguanidine and 1,1,3,3-tetramethyl-2-propylguanidine were also used. Several compounds showed significant CXCR4 binding affinity, and zinc(II) complexation of bis(pyridin-2-ylmethyl)amine moieties resulted in a remarkable increase in CXCR4 binding affinity.
  ChemMedChem 10/2012; · 3.15 Impact Factor
• Article: Synthetic caged DAG-lactones for photochemically controlled activation of protein kinase C.

  Wataru Nomura, Tetsuo Narumi, Nami Ohashi, Yuki Serizawa, Nancy E Lewin, Peter M Blumberg, Toshiaki Furuta, Hirokazu Tamamura
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  ABSTRACT: Switching on kinases: Synthetic caged DAG-lactones have been developed and showed decreases of two orders of magnitude, relative to the corresponding parent compounds, in their binding affinities towards PKC. The caged compounds had no effect on the translocation of PKC until after photoactivation. This approach is a potentially powerful tool for probing the PKC signaling cascade.
  ChemBioChem 03/2011; 12(4):535-9. · 3.94 Impact Factor
• Article: Fluorescence-quenching screening of protein kinase C ligands with an environmentally sensitive fluorophore.

  Wataru Nomura, Nami Ohashi, Yoshiaki Okuda, Tetsuo Narumi, Teikichi Ikura, Nobutoshi Ito, Hirokazu Tamamura
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  ABSTRACT: A novel fluorescence-quenching screening method for protein kinase C (PKC) ligands was developed utilizing solvatochromic fluorophores. Solvatochromic dyes, highly sensitive to the presence or the absence of competitive ligands in their binding to the C1b domain of PKCδ (δC1b), were combined with a known pharmacophoric moiety of 1,2-diacylglycerol (DAG) lactones, PKC ligands. Addition of δC1b to the fluorescent compounds caused a gradual increase in the fluorescent intensity in proportion to the increase of δC1b. As a competitive ligand was added to the complex of δC1b domain and fluorescent compounds, a gradual decrease in the fluorescent intensity was observed. The relative binding affinities of known ligands were successfully determined by this fluorescent method and corresponded well to the K(i) values measured by a radioisotope method. These results indicate that washing, which is a laborious step in binding evaluations, is not required for this environmentally sensitive fluorophore based system. Screening with the system was performed for 2560 preselected library compounds with possible pharmacophores, and some lead compounds were found. This fluorescence-based method could be applied widely to known ligand-receptor combinations.
  Bioconjugate Chemistry 03/2011; 22(5):923-30. · 4.93 Impact Factor
• Article: Azamacrocyclic metal complexes as CXCR4 antagonists.

  Tomohiro Tanaka, Tetsuo Narumi, Taro Ozaki, Akira Sohma, Nami Ohashi, Chie Hashimoto, Kyoko Itotani, Wataru Nomura, Tsutomu Murakami, Naoki Yamamoto, Hirokazu Tamamura
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  ABSTRACT: The chemokine receptor CXCR4 is a member of the seven transmembrane GPCR family, which is implicated in multiple diseases, including HIV infection, cancers, and rheumatoid arthritis. Low-molecular-weight nonpeptidic compounds, including AMD3100 and various pyridyl macrocyclic zinc(II) complexes, have been identified as selective antagonists of CXCR4. In the present study, structure-activity relationship studies were performed by combining the common structural features of alkylamino and pyridiyl macrocyclic antagonists. Several new zinc(II) or copper(II) complexes demonstrated potent anti-HIV activity, strong CXCR4-binding activity, and significant inhibitory activity against Ca(2+) mobilization induced by CXCL12 stimulation. These results may prove useful in the design of novel CXCR4 antagonists, and the compounds described could potentially be developed as therapeutics against CXCR4-relevant diseases or chemical probes to study the biological activity of CXCR4.
  ChemMedChem 02/2011; 6(5):834-9. · 3.15 Impact Factor
• Article: Fluorescent-responsive synthetic C1b domains of protein kinase Cδ as reporters of specific high-affinity ligand binding.

  Nami Ohashi, Wataru Nomura, Tetsuo Narumi, Nancy E Lewin, Kyoko Itotani, Peter M Blumberg, Hirokazu Tamamura
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  ABSTRACT: Protein kinase C (PKC) is a critical cell signaling pathway involved in many disorders such as cancer and Alzheimer-type dementia. To date, evaluation of PKC ligand binding affinity has been performed by competitive studies against radiolabeled probes that are problematic for high-throughput screening. In the present study, we have developed a fluorescent-based binding assay system for identifying ligands that target the PKC ligand binding domain (C1 domain). An environmentally sensitive fluorescent dye (solvatochromic fluorophore), which has been used in multiple applications to assess protein-binding interactions, was inserted in proximity to the binding pocket of a novel PKCδ C1b domain. These resultant fluorescent-labeled δC1b domain analogues underwent a significant change in fluorescent intensity upon ligand binding, and we further demonstrate that the fluorescent δC1b domain analogues can be used to evaluate ligand binding affinity.
  Bioconjugate Chemistry 01/2011; 22(1):82-7. · 4.93 Impact Factor
• Article: CD4 mimics targeting the HIV entry mechanism and their hybrid molecules with a CXCR4 antagonist.

  Tetsuo Narumi, Chihiro Ochiai, Kazuhisa Yoshimura, Shigeyoshi Harada, Tomohiro Tanaka, Wataru Nomura, Hiroshi Arai, Taro Ozaki, Nami Ohashi, Shuzo Matsushita, Hirokazu Tamamura
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  ABSTRACT: Small molecules behaving as CD4 mimics were previously reported as HIV-1 entry inhibitors that block the gp120-CD4 interaction and induce a conformational change in gp120, exposing its co-receptor-binding site. A structure-activity relationship (SAR) study of a series of CD4 mimic analogs was conducted to investigate the contribution from the piperidine moiety of CD4 mimic 1 to anti-HIV activity, cytotoxicity, and CD4 mimicry effects on conformational changes of gp120. In addition, several hybrid molecules based on conjugation of a CD4 mimic analog with a selective CXCR4 antagonist were also synthesized and their utility evaluated.
  Bioorganic & medicinal chemistry letters 10/2010; 20(19):5853-8. · 2.65 Impact Factor
• Article: Peptidic HIV integrase inhibitors derived from HIV gene products: structure-activity relationship studies.

  Shintaro Suzuki, Kasthuraiah Maddali, Chie Hashimoto, Emiko Urano, Nami Ohashi, Tomohiro Tanaka, Taro Ozaki, Hiroshi Arai, Hiroshi Tsutsumi, Tetsuo Narumi, Wataru Nomura, Naoki Yamamoto, Yves Pommier, Jun A Komano, Hirokazu Tamamura
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  ABSTRACT: Structure-activity relationship studies were conducted on HIV integrase (IN) inhibitory peptides which were found by the screening of an overlapping peptide library derived from HIV-1 gene products. Since these peptides located in the second helix of Vpr are considered to have an alpha-helical conformation, Glu-Lys pairs were introduced into the i and i+4 positions to increase the helicity of the lead compound possessing an octa-arginyl group. Ala-scan was also performed on the lead compound for the identification of the amino acid residues responsible for the inhibitory activity. The results indicated the importance of an alpha-helical structure for the expression of inhibitory activity, and presented a binding model of integrase and the lead compound.
  Bioorganic & medicinal chemistry 09/2010; 18(18):6771-5. · 2.82 Impact Factor
• Article: Development of crosslink-type tag-probe pairs for fluorescent imaging of proteins.

  Wataru Nomura, Tomoaki Mino, Tetsuo Narumi, Nami Ohashi, Akemi Masuda, Chie Hashimoto, Hiroshi Tsutsumi, Hirokazu Tamamura
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  ABSTRACT: Useful methods of protein labeling via functional peptide tags have been developed in the field of proteome and chemical biology. New tag-probe pairs based on leucine zipper peptides for labeling target proteins are described. These consist of an α-helical probe peptide with an environmental-sensitive fluorescent dye and two antiparallel α-helical tag peptides, and may be crosslinked, from the Cys residue of the tag peptide to the N(α)-chloroacetyl group of the probe peptide. Binding of the probe peptide to the tag peptides results in movement of the fluorophore from a hydrophilic to a hydrophobic environment inside the leucine zipper structure, causing a dramatic fluorescent change, mediated by the binding of the two peptides. As a spacer between the N(α)-chloroacetyl group and the original probe sequence, a single Gly residue was the most suitable among 0-2 Gly residues. Crosslinking leads to superior fluorescence response, binding affinity, and chemical stability. These ZIP tag-probe pairs are useful for labeling and fluorescent imaging of proteins.
  Biopolymers 01/2010; 94(6):843-52. · 2.87 Impact Factor
• Article: CD4 mimics targeting the mechanism of HIV entry.

  Yuko Yamada, Chihiro Ochiai, Kazuhisa Yoshimura, Tomohiro Tanaka, Nami Ohashi, Tetsuo Narumi, Wataru Nomura, Shigeyoshi Harada, Shuzo Matsushita, Hirokazu Tamamura
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  ABSTRACT: A structure-activity relationship study was conducted of several CD4 mimicking small molecules which block the interaction between HIV-1 gp120 and CD4. These CD4 mimics induce a conformational change in gp120, exposing its co-receptor-binding site. This induces a highly synergistic interaction in the use in combination with a co-receptor CXCR4 antagonist and reveals a pronounced effect on the dynamic supramolecular mechanism of HIV-1 entry.
  Bioorganic & medicinal chemistry letters 11/2009; 20(1):354-8. · 2.65 Impact Factor
• Article: Fluorogenically Active Leucine Zipper Peptides as Tag–Probe Pairs for Protein Imaging in Living Cells

  Hiroshi Tsutsumi Dr, Wataru Nomura Dr, Seiichiro Abe, Tomoaki Mino, Akemi Masuda, Nami Ohashi, Tomohiro Tanaka, Kenji Ohba Dr, Naoki Yamamoto Prof, Kazunari Akiyoshi Prof, Hirokazu Tamamura Prof
  Angewandte Chemie 10/2009; 121(48):9328 - 9330.
• Source

  Available from: tufts.edu

  Article: Fluorogenically active leucine zipper peptides as tag-probe pairs for protein imaging in living cells.

  Hiroshi Tsutsumi, Wataru Nomura, Seiichiro Abe, Tomoaki Mino, Akemi Masuda, Nami Ohashi, Tomohiro Tanaka, Kenji Ohba, Naoki Yamamoto, Kazunari Akiyoshi, Hirokazu Tamamura
  Angewandte Chemie International Edition 10/2009; 48(48):9164-6. · 13.45 Impact Factor
• Article: Structure-activity relationship study on artificial CXCR4 ligands possessing the cyclic pentapeptide scaffold: the exploration of amino acid residues of pentapeptides by substitutions of several aromatic amino acids.

  Tomohiro Tanaka, Wataru Nomura, Tetsuo Narumi, Ai Esaka, Shinya Oishi, Nami Ohashi, Kyoko Itotani, Barry J Evans, Zi-xuan Wang, Stephen C Peiper, Nobutaka Fujii, Hirokazu Tamamura
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  ABSTRACT: Previously, downsizing of a 14-residue peptidic CXCR4 antagonist has led to the development of a highly potent CXCR4 antagonist [cyclo(-d-Tyr(1)-Arg(2)-Arg(3)-Nal(4)-Gly(5)-)]. In the present study, cyclic pentapeptide libraries that were designed by substitutions of several amino acids for d-Tyr(1) and Arg(2) in peptide were prepared and screened to evaluate binding activity for CXCR4. The above structure-activity relationship study led to the finding of several potent CXCR4 ligands.
  Organic & Biomolecular Chemistry 10/2009; 7(18):3805-9. · 3.70 Impact Factor
• Article: Synthesis of protein kinase Cdelta C1b domain by native chemical ligation methodology and characterization of its folding and ligand binding.

  Nami Ohashi, Wataru Nomura, Mai Kato, Tetsuo Narumi, Nancy E Lewin, Peter M Blumberg, Hirokazu Tamamura
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  ABSTRACT: The C1b domain of protein kinase Cdelta (PKCdelta), a potent receptor for ligands such as diacylglycerol and phorbol esters, was synthesized by utilizing native chemical ligation. With this synthetic strategy, the domain was efficiently constructed and shown to have high affinity ligand binding and correct folding. The C1b domain has been utilized for the development of novel ligands for the control of phosphorylation by PKC family members. This strategy will pave the way for the efficient construction of C1b domains modified with fluorescent dyes, biotin, etc.
  Journal of Peptide Science 09/2009; 15(10):642-6. · 1.80 Impact Factor
• Article: Stereoselective synthesis of peptidomimetics based on acid-catalyzed ring-opening of beta-aziridinyl-alpha,beta-enoates.

  Hirokazu Tamamura, Tomohiro Tanaka, Hiroshi Tsutsumi, Koji Nemoto, Satoko Mizokami, Nami Ohashi, Shinya Oishi, Nobutaka Fujii
  Advances in experimental medicine and biology 02/2009; 611:149-50. · 1.09 Impact Factor
• Article: Development of chemokine receptor CXCR4 antagonists using bio-mimetic strategy.

  Hirokazu Tamamura, Tomohiro Tanaka, Hiroshi Tsutsumi, Nami Ohashi, Kenichi Hiramatsu, Takanobu Araki, Akio Ojida, Itaru Hamachi, Zixuan Wang, Stephen C Peiper, John O Trent, Satoshi Ueda, Shinya Oishi, Nobutaka Fujii
  Advances in experimental medicine and biology 02/2009; 611:145-6. · 1.09 Impact Factor
• Article: Structure-activity relationship study of CXCR4 antagonists bearing the cyclic pentapeptide scaffold: identification of the new pharmacophore.

  Tomohiro Tanaka, Hiroshi Tsutsumi, Wataru Nomura, Yasuaki Tanabe, Nami Ohashi, Ai Esaka, Chihiro Ochiai, Jun Sato, Kyoko Itotani, Tsutomu Murakami, Kenji Ohba, Naoki Yamamoto, Nobutaka Fujii, Hirokazu Tamamura
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  ABSTRACT: A highly potent CXCR4 antagonist 2 [cyclo (-D-Tyr1-Arg2-Arg3-Nal4-Gly5-)] has previously been identified by screening cyclic pentapeptide libraries that were designed based on pharmacophore residues of a 14-residue peptidic CXCR4 antagonist 1. In the present study, D-Tyr and Arg in peptide 2 were replaced by a bicyclic aromatic amino acid and a cationic amino acid, respectively, and their binding activity for CXCR4 was evaluated for identification of the novel pharmacophore.
  Organic & Biomolecular Chemistry 01/2009; 6(23):4374-7. · 3.70 Impact Factor
• Article: Therapeutic potential of the chemokine receptor CXCR4 antagonists as multifunctional agents.

  Hiroshi Tsutsumi, Tomohiro Tanaka, Nami Ohashi, Hiroyuki Masuno, Hirokazu Tamamura, Kenichi Hiramatsu, Takanobu Araki, Satoshi Ueda, Shinya Oishi, Nobutaka Fujii
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  ABSTRACT: The chemokine receptor CXCR4 possesses multiple critical functions in normal and pathologic physiology. CXCR4 is a G-protein-coupled receptor that transduces signals of its endogenous ligand, the chemokine CXCL12 (stromal cell-derived factor-1, SDF-1). The interaction between CXCL12 and CXCR4 plays an important role in the migration of progenitors during embryologic development of the cardiovascular, hemopoietic, central nervous systems, and so on. This interaction is also known to be involved in several intractable disease processes, including HIV infection, cancer cell metastasis, leukemia cell progression, rheumatoid arthritis (RA), and pulmonary fibrosis. It is conjectured that this interaction may be a critical therapeutic target in all of these diseases, and several CXCR4 antagonists have been proposed as potential drugs. Fourteen-mer peptides, T140 and its analogues, were previously developed in our laboratory as specific CXCR4 antagonists that were identified as HIV-entry inhibitors, anti-cancer-metastatic agents, anti-chronic lymphocytic/acute lymphoblastic leukemia agents, and anti-RA agents. Cyclic pentapeptides, such as FC131 [cyclo(D-Tyr-Arg-Arg-L-3-(2-naphthyl)alanine-Gly)], were also previously found as CXCR4 antagonist leads based on pharmacophores of T140. This review article describes the elucidation of multiple functions of CXCR4 antagonists and the development of a number of low-molecular weight CXCR4 antagonists involving FC131 analogues and other compounds with different scaffolds including linear-type structures.
  Biopolymers 02/2007; 88(2):279-89. · 2.87 Impact Factor
• Article: Chemical Synthesis of a PKC C1b Domain by a Peptide Ligation Method and Expression of the Protein in E. coli and Their Application

  Nami Ohashi, Mai Kato, Hironori Matsumoto, Tomohiro Tanaka, Hiroshi Tsutsumi, Hiroyuki Masuno, Wataru Nomura, Kiyotsugu Yoshida, Teikichi Ikura, Nobutoshi Ito, Hirokazu Tamamura
• Article: Versatile use of acid-catalyzed ring-opening of β-aziridinyl-α,β-enoates to stereoselective synthesis of peptidomimetics

  Hirokazu Tamamura, Tomohiro Tanaka, Hiroshi Tsutsumi, Koji Nemoto, Satoko Mizokami, Nami Ohashi, Shinya Oishi, Nobutaka Fujii
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  ABSTRACT: Treatment of N-arylsulfonylaziridines bearing α,β-unsaturated esters with alcohols, thiols or weak acids such as AcOH in the presence of catalytic amount of Lewis acids affords regio- and stereoselectively ring-opened products, such as δ-aminated γ-alkoxy-(alkylthio or acetoxy)-α,β-enoates. In addition, the regio- and stereoselective ring-opening reactions can be performed on solid supports and applied to stereoselective synthesis of (E)-alkene dipeptide isosteres.Graphical abstract
  Tetrahedron. 63(37):9243-9254.