Síntese e propriedades fotofísicas de chalconas e tiocarbamoilpirazolinas pirenil-substituídas

Abstract

The present work presents the synthesis, structural characterization, spectroscopy, and evaluation of the biological activity of a series of five pyrenylchalcones and their subsequent conversion into 3-pyrenylpyrazolines by cyclo-condensation with thiosemicarbazide. For characterization of the two series of compounds, 1H and 13C nuclear magnetic resonance techniques, high-resolution mass spectrometry, melting point, UV-Vis spectroscopy, and fluorescence analysis were used. The synthetic route started with the synthesis of pyrazoline precursors, a series of pyrenylchalcones (3a-e), obtained from the Claisen-Schmidt condensation in an alkaline medium, of five para-substituted aromatic aldehydes (1a-e) with 1-acetylpyrene (2), with yields of 50-80%. Subsequently the precursors 3a-e were used as starting material to obtain the 3-pyrenylpyrazolines (5a-e) by cyclo-condensation with thiosemicarbazide (4) in an alkaline medium, with yields of 55-80%. Both structure and purity were confirmed by employing 1H and 13C NMR, HRMS, and melting point results. The absorption and fluorescence study of the structures were evaluated in DMF, Ether, CH2Cl2, MeCN, and MeOH as solvents and showed a change in absorption and fluorescence for the polar aprotic solvents. In the UV-Vis region, the compounds 3a-e showed bands with absorption maximum between 313 and 418 nm, and with emission maximum between 438-562 nm, after excitation at 350nm. The pyrazoline compounds 5a-e showed two absorption bands in the UV-Vis region with absorption maximum between 285-295 nm for the band I and 392-401 nm referring to the band II, when excited at 350 nm they emit bands between 435-475nm. In the in vitro biological assays, none of the analyzed compounds showed antimicrobial activity against the bacterial and fungal strains used in the methodology, presenting MIC values higher than 125 μg/mL, values out of the standards found in the literature for determining antimicrobial activity.