Investigation on Metal and Halogen Dependent Cyclization of Schiff base or Reduced Schiff base Precursor into Fluorescent Pyrido[1,2-a]quinoxalin-11-ylium Derivatives

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Quinoxalines are an important class of heterocyclic compounds used as dyes, pharmaceuticals and the moiety is present in a number of antibiotics.1 Previously, the synthesis of a new tricyclic quinoxaline derivative, pyrido[1,2-a]quinoxalin-11-ylium perchlorate [P1]ClO4, formed by Cu(II) mediated cyclization of a simple Schiff base precursor was published by Koner and Ray.2 Structurally, only three other tricyclic heterocycles with similar structure are known (Figure 1). The 3-5 benzo[e]pyrido[2,1-c][1,2,4]triazin-11-ium (I) salts reported by Goswami et al. are highly fluorescent and shows strong binding with calf thymus DNA.3 Goswami and Adak reported synthesis of cyclic pyrido[1,2-a]quinoxaline phosphate (II) by phosphorylation of the quinoxaline derivative of sugar precursor with (PhO)P(O)Cl2.4 Pyrido[1,2-a]quinoxalinium ions (III) reported by Chernavskaya et al.5 and structurally characterized by Duffy et al.6 showed antimicrobial activity as well as pH sensitive fluorescence. None of these syntheses involves metal ion and syntheses were not trivial. Figure 1.Reported structures of tricyclic heterocycles and fluorescent dyes Compound [P1]ClO4 as well as I are fluorescent with emission in the highly useful region (550 to 600 nm) with reasonable quantum yield( approximately 0.2. The water solubility, emission properties, planarity and charged nature of the compound are comparable with popular..
Supervisor: Manabendra Ray