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Structural factors influencing the reaction rates of 4-aryloxy-7-nitrobenzofurazans with amino acids

An interesting observation was made when studying the SNAr reaction between several 4-aryloxy-7-nitrobenzofurazans (2) and several amino acids leading to the apparition of detectable fluorescence from the substitution products3. Acidic amino acids reacted very slowly=while basic amino acids react fastest with2 having an unsubstituted phenyl or a 4-formyl-phenyl Ar group. Amongst neutral amino acids, proline reacts fastest at room temperature after 100 min. With2 having a methoxy-subtituted Ar group.

Synthesis of 4-aryloxy-7-nitrobenzofurazan derivatives from 4-chloro-7-nitrobenzofurazan and various phenoxide anions (including pharmaceuticals) in the presence of crown ethers

Abstract4-Chloro-7-nitrobenzofurazan reacts by nucleophilic substitution with phenoxide anions derived from estriol (2c), ethynylestradiol (2d), phenol (3e), guaiacol (3f), 2,6-dimethoxyphenol (3g), eugenol (3h), isoeugenol (3i), the cytostatic Etoposide (4), and Reichardt’s betaine (5) in the presence of crown ethers affording the corresponding 4-aryloxy-7-nitrobenzofurazan derivatives 6c, 6d, 7e-7i, 8, and 9. The structure of these compounds was confirmed by NMR spectra. Hydrophobicity/hydrophilicity parameters were investigated by reverse phase thin-layer chromatography.

1-Picryl-2-phenyl-2-(4-picrylamidophenyl) diazenium betaine and its radical-anion: synthesis and physical properties

The betainic title compound represents a structure with interesting physicochemical properties. These were studied by cyclic voltammetry (CV), electron paramagnetic resonance (EPR) spectroscopy, magnetic and spectral measurements. CV investigations show that the process in acetonitrile corresponds to chemically reversible one-electron reduction leading to the formation of a radical-anion. Chemical reduction of the betaine in dichloromethane with powdered sodium ascorbate in the presence of 15-crown-5 ether yielded a radical-anion (with an EPR spectrum similar to that of 2,2-diphenyl-1-picrylhydrazyl, DPPH). Linnett’s theory explains the similarity of EPR spectra for DPPH and the radical-anion. The title betaine is diamagnetic in solid state. In solution, it shows a weak hypsochromic effect.Graphical abstract