Pyrrolyl-, 2-(2-thienyl)pyrrolyl- and 2,5-bis(2-thienyl)pyrrolyl-nucleosides: synthesis, molecular and electronic structure, and redox behaviour of C5-thymidine derivatives
作者:Miguel A. Galindo、Jennifer Hannant、Ross W. Harrington、William Clegg、Benjamin R. Horrocks、Andrew R. Pike、Andrew Houlton
DOI:10.1039/c0ob00466a
日期:——
A series of modified nucleosides based on thymidine have been prepared by Pd-catalysed cross-coupling between N-alkyl-alkynyl functionalised pyrrolyl- (py), 2-(2-thienyl)pyrrolyl- (tp) or 2,5-bis(2-thienyl)pyrrolyl (tpt) groups with 5-iodo-2′-deoxyuridine. The length of the alkyl chain linking the nucleoside and pyrrolyl-containing unit, N(CH2)nCC-nucleoside (where n = 1–3) was also varied. The compounds have been characterised by 1H NMR, ES-MS, UV–vis, cyclic voltammetry (CV) and, in some cases, single-crystal X-ray diffraction. Cyclic voltammetry studies demonstrated that all the py-, tp- and tpt-alkynyl derivatives 1–7 can be electrochemically polymerised to form conductive materials. It was found that increasing the N-alkyl chain length in these cases resulted in only minor changes in the oxidation potential. The same behaviour was observed for the tp- and tpt-modified nucleosides 9–12; however, the py-derivative, 8, produced a poorly conducting material. DFT calculations on the one-electron oxidised cation of the modified nucleosides bearing tp or tpt showed that spin density is located on the pyrrolyl and thienyl units in all cases and that the coplanarity of adjacent rings increases upon oxidation. In contrast, in the corresponding pyrrolyl cases the spin density is distributed over the whole molecule, suggesting that polymerisation does not occur solely at the pyrrolyl-Cα position and the conjugation is interrupted.
通过钯催化交叉偶联,在N-烷基-炔基官能化的吡咯基(py)、2-(2-噻吩基)吡咯基(tp)或2,5-双(2-噻吩基)吡咯基(tpt)基团与5-碘-2′-脱氧尿苷之间,制备了一系列基于胸苷的修饰核苷。连接核苷和含吡咯基单元的烷基链长度(N(CH2)nCC-核苷,其中n = 1-3)也各不相同。通过1H NMR、ES-MS、UV-vis、循环伏安法(CV)以及某些情况下的单晶X射线衍射,对化合物进行了表征。循环伏安法研究表明,所有py、tp和tpt-炔基衍生物1-7都可以电化学聚合形成导电材料。研究发现,在这种情况下,增加N-烷基链长度只会导致氧化电位发生微小变化。tp和tpt修饰核苷9-12也表现出相同的行为;然而,py衍生物8产生的导电材料效果不佳。对带有tp或tpt修饰核苷的单电子氧化阳离子进行DFT计算表明,在所有情况下,自旋密度都位于吡咯基和