Abstract
Three isomers of (trifluoromethoxy)phenylboronic acids were studied in the context of their physicochemical, structural, antimicrobial and spectroscopic properties. They were characterized by 1H, 13C, 11B and 19F NMR spectroscopy. The acidity of all the isomers was evaluated by both spectrophotometric and potentiometric titrations. The introduction of the -OCF3 group influences the acidity, depending, however, on the position of a substituent, with the ortho isomer being the least acidic. Molecular and crystal structures of ortho and para isomers were determined by the single crystal XRD method. Hydrogen bonded dimers are the basic structural motives of the investigated molecules in the solid state. In the case of the ortho isomer, intramolecular hydrogen bond with the -OCF3 group is additionally formed, weaker, however, than that in the analogous -OCH3 derivative, which has been determined by both X-Ray measurements as well as theoretical DFT calculations. Docking studies showed possible interactions of the investigated compounds with LeuRS of Escherichia coli. Finally, the antibacterial potency of studied boronic acids in vitro were evaluated against Escherichia coli and Bacillus cereus.
Highlights
Fluorinated arylboronic acids constitute an important group of compounds with a wide range of applications [1]
A number of one- and two-dimensional experiments were conducted to fully characterize all isomers of phenylboronic acids substituted with the OCF3 group (1–3) in solution
The antibacterial activity of compounds was tested against Gram-positive bacteria— Bacillus cereus (CCM 2010) and Gram-negative bacteria—Escherichia coli (CCM 5172), obtained from the Czech Collection of Microorganisms (Masaryk University)
Summary
Fluorinated arylboronic acids constitute an important group of compounds with a wide range of applications [1]. The perfluoroalkyl groups (e.g., -CF3) display only an electron-withdrawing effect, which should result in higher acidity of the corresponding phenylboronic acid in comparison with their fluorine substituted analogues It is not, the case of the ortho isomer, primarily due to the steric hindrance. TNoetehdeleinssdtuocstiavye, tehfafetcpthoefntyhlebo-OroCnFic agcrioduspa,rewLheiwchisi,nncootmBrpoaernissotendwacitidhst.hTehterrifelfuoorero, dmeestphiytel the strong inductive effect of the -OCF3 group, the acidity of the ortho isomer (1) is much weaker than that for the unsubstituted phenylboronic acid. This can be explained by the influence of a bulky substituent proximal to the boronic group, which decreases the acid strength due to the steric inhibition of the formation of the tetrahedral boronate ion.
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