title: Substituent effects on pyrid-2-yl ureas toward intramolecular hydrogen bonding and cytosine complexation.
abstract: Equilibria between two conformational isomers of pyrid-2-yl ureas, the (E,Z) and (Z,Z) forms, have been studied in DMF-d(7) at -70 degrees C. Most of them show a small preference for the (E,Z) form with an equilibrium constant K(i) around 1-2. However, the K(i) value for 1-methyl-2-(3-(pyrid-2-yl)ureido)pyridinium iodide (12) was found to be 14.2 +/- 1.2. That is 1 order of magnitude larger than those of the others, which indicates that the positively charged 1-methylpyridinium-2-yl substituent would facilitate the (E,Z) form formation. Pyrid-2-yl ureas bind cytosine in DMF-d(7) with binding constants K(B) ranging from 30 to 1700 M(-1). Electron withdrawing substituents, such as the 4-O(2)NC(6)H(4)- or 1-methylpyridinium-4-yl substituent, preferentially facilitate the intermolecular cytosine complexation with large binding constants.
authors.affiliation: Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China.
authors.forename: Chia-Hui
authors.initials: CH
authors.lastname: Chien
authors.forename: Man-kit
authors.initials: MK
authors.lastname: Leung
authors.forename: Jen-Kuan
authors.initials: JK
authors.lastname: Su
authors.forename: Gene-Hsiang
authors.initials: GH
authors.lastname: Li
authors.forename: Yi-Hung
authors.initials: YH
authors.lastname: Liu
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D018360:Crystallography, X-Ray; D003596:Cytosine / Q000031:analogs & derivatives*; D004126:Dimethylformamide / Q000737:chemistry; D006860:Hydrogen Bonding; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D011726:Pyridinium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013816:Thermodynamics; D014508:Urea / Q000031:analogs & derivatives* / Q000737:chemistry*
chemical_list: D011726:Pyridinium Compounds; D012997:Solvents; D004126:Dimethylformamide; D003596:Cytosine; D014508:Urea