Shoji Nakashima

University of Illinois, Urbana-Champaign, Urbana, Illinois, United States

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Publications (4)30.59 Total impact

  • Taiho Park · Eric M Todd · Shoji Nakashima · Steven C Zimmerman ·
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    ABSTRACT: An exceptionally strong quadruply hydrogen-bonded complex is formed between 2,7-diamido-1,8-naphthyridine 3 (DAN) and the butylurea of guanosine 6 (UG) in chloroform. The UG unit can be prepared in four steps from guanosine on a 10 g scale in excellent yields without chromatographic purification. The association constant (Kassoc approximately 5 x 10(7) M(-1)) for the UG.DAN complex determined by fluorescence energy transfer from the naphthyridine unit of 3 to coumarin 343 covalently linked UG (18) is among the highest reported for a neutral DNA base-pair analogue. The weak self-association of DAN (Kdimer < 10 M(-1)) and UG (Kdimer ca. 200-300 M(-1)) means that the UG.DAN complex forms with unparalleled fidelity.
    Journal of the American Chemical Society 01/2006; 127(51):18133-42. DOI:10.1021/ja0545517 · 12.11 Impact Factor
  • Taiho Park · Michael F. Mayer · Shoji Nakashima · Steven C. Zimmerman ·
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    ABSTRACT: A two-step conversion of 2-chloro-7-amido-1,8-naphthyridine to 2,7-diamino-1,8-naphthyridine is described. The process, which involves a nucleophilic aromatic substitution reaction with 4-methoxybenzylamine and subsequent deprotection, can be carried out on a large scale.
    ChemInform 10/2005; 36(41). DOI:10.1002/chin.200541152
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    Michael F Mayer · Shoji Nakashima · Steven C Zimmerman ·
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    ABSTRACT: [structure; see text] An iterative synthetic route to organic-soluble ureido-naphthyridine oligomers has been developed. Use of this protocol allowed synthesis of a short ureido-naphthyridine oligomer, which presents a self-complementary DDAADDAA hydrogen bonding array (D = hydrogen bond donor, A = hydrogen bond acceptor). Strong self-association via eight hydrogen bonds was observed in organic solution.
    Organic Letters 08/2005; 7(14):3005-8. DOI:10.1021/ol050987f · 6.36 Impact Factor
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    Taiho Park · Steven C Zimmerman · Shoji Nakashima ·
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    ABSTRACT: The butyl urea of guanosine (UG) presents an ADDA hydrogen-bonding array that is complementary to the DAAD array of 2,7-diamido-1,8-naphthyridine (DAN). The stability of the DAN.UG complex was measured by fluorimetry using the fluorescence resonance energy transfer (FRET) from the naphthyridine ring to a coumarin 343 moiety linked covalently to the UG unit. The quadruply hydrogen-bonded complex is extremely stable with a measured association constant, Kassoc, of 3 x 108 M-1. Unlike related hydrogen-bonding modules, the guanosine urea, UG, contains a relatively fixed tautomeric form and only weakly self-associates (Kdimer = ca. 200 M-1). The DAN unit was linked to a styrene-based monomer and copolymerized with styrene to form a polymer (PS-DAN) containing a controlled number of the DAAD recognition units. Likewise, a methacrylate monomer containing the UG unit was copolymerized with butyl methacrylate to form a polymer (PBMA-UG). Blends formed from PS-DAN and PBMA-UG were characterized by DSC, SEC, and viscometry. The importance of selective heterocomplexation and weak self-association in forming the blended networks was demonstrated by using a ureidopyrimidinone (UPy) unit, which also forms strong heterocomplexes with DAN but is able to strongly self-associate.
    Journal of the American Chemical Society 06/2005; 127(18):6520-1. DOI:10.1021/ja050996j · 12.11 Impact Factor