Design,Synthesis And Properties Of Nitrogen Bridge-head Heterocycles

Two kinds of new heterocyclic compounds were designed and synthesized in this thesis:one was pyrido[1,2-a]benzimidazole derivatives; the other was imidazo[1,5-a]pyridine containing1,3,4-oxadiazole derivatives.Nitrogen bridge-head heterocycles are of special interest due to their wide variety of biological activities and optical/electrical properties, and a lot of attractive methods have been developed for synthesizing this class of compounds. Of these heterocycles, compounds containing indolizines, pyrazolo[1,5-a]pyridines, pyrido[1,2-a]benzimidazoles, imidazo[1,2-a]pyridines and imidazo[1,5-a]pyridines have been reported to possess a wide variety of biological and pharmacological properties. Furthermore, some of these compounds were also found to display interesting photophysical and fluorescent properties.Due to the conjugated π-electron system and non-uniform charge distribution within the pyrido[1,2-a]benzimidazole unit, this kind of compounds exhibit unique optical properties. In previous works, we have reported the synthesis of pyrido[1,2-a]benzimidazole containing different substituents, which emit blue-green fluorescence and have acceptable fluorescence quantum yields. In order to investigate in detail the photophysical properties of compounds containing the pyrido[1,2-a] benzimidazole moiety and extend the conjugated π-electron system, a series of aromatic ring such as phenyl ring, naphthyl ring, thiophene ring were introduced to the C-2position of the pyrido[1,2-a]benzimidazole ring. As a result,8target compounds were synthesized and their structures were characterized by1H NMR,13C NMR, ESI-MS and IR. Their optical properties were also investigated in detail.Optical data revealed that the absorption maxima of the compounds varied from 220to284nm and exhibited blue-green fluorescence (463-475nm) in dilute solutions with acceptable fluorescence quantum yields.The imidazo[1,5-a]pyridines are regarded as a promising class of bioactive heterocyclic compounds due to their broad range of biological activities. They have been investigated in a varity of pharmaceutical applications, including cardiotonic agents, aromatase inhibitors in estrogen-dependent diseases, thromboxane A2synthetase inhibitors, and angiotensin Ⅱ receptor antagonists. Oxadiazole is an important five-membered aromatic heterocyclic ring present in variety of biologically active molecules inclusive of antiinflammatory, anticonvulsant, analgesic, antibacterial and muscle relaxant properties. Among this heterocyclic ring,1,3,4-oxadiazoles are of particular interest, the derivatives of which exhibit a wide range of pharmaceutical and biological activities. Looking at the significance of imidazo[1,5-a]pyridine and oxadiazole nucleus, we designed and synthesized some new imidazo[1,5-a]pyridine derivatives containing1,3,4-oxadiazole moiety and screen them for potential biological activities. As a result,10target compounds were synthesized and evaluated against different human cancer cell lines.