Synthesis of Imidazo[4,5-b]quinoxaline Ribonucleosides as Linear Dimensional Analogs of Antiviral Polyhalogenated Benzimidazole Ribonucleosides

Quantum mechanical study of the structure and spectroscopic (FT-IR, FT-Raman, 13C, 1H and UV), NBO and HOMO-LUMO analysis of 2-quinoxaline carboxylic acid

The FTIR and FT-Raman spectra of 2-quinoxaline carboxylic acid (2-QCA) has been recorded in the region 4000-450 and 4000-100 cm(-1), respectively. The conformational analysis, optimized geometry, frequency and intensity of the vibrational bands of 2-QCA were obtained by the density functional theory (DFT) with complete relaxation in the potential energy surface using 6-31G(d) basis set. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The (1)H and(13)C NMR spectra have been recorded and (1)H and (13)C nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method and their respective linear correlations were obtained. The theoretical UV-visible spectrum of the compound using CIS method and the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The Mulliken charges, the values of electric dipole moment (μ) of the molecule were computed using DFT calculations. The change in electron density (ED) in the σ* antibonding orbitals and stabilization energies E(2) have been calculated by natural bond (NBO) analysis to give clear evidence of stabilization originating in the hyper conjugation of hydrogen-bonded interactions.

An unprecedented nitrogen elimination reaction: mechanistic studies using 15N-labeled 4-amino-7-benzylpyrrolo[2,3-d][1,2,3]triazine-5-carbonitrile

[formula: see text] In the course of our work on novel pyrrolo[2,3-d][1,2,3]triazines we have discovered that 1 undergoes an elimination of nitrogen at 250 degrees C to give 2. We have conducted 15N labeling studies that establish that the loss of N-2 and N-3 from 1 had occurred rather than N-1 and N-2, presumably via a retro Diels-Alder reaction of the imino tautomer 7. This study provides an alternative to the commonly accepted mechanism which involves the loss of N-1 and N-2 via the transient formation of a diazonium compound generated from 4-amino- or 4-oxo-substituted 1,2,3-triazines condensed with carbocycles or heterocycles.