A combined experimental-computational study of benzoxaborole crystal structures

Abstract

International audienceBenzoxaboroles are organoboron molecules which are gaining growing interest in different fields, notably for the development of new drugs. However, extensive characterization of these molecules in the solid state is still lacking. Here, questions related to the structure and spectroscopic signatures of crystalline benzoxaborole phases are thus addressed, using a combined experimental-computational approach. Two simple benzoxaboroles were studied: 1,3-dihydro-1-hydroxy-2,1-benzoxaborole (denoted as BBzx) and 5-fluoro-1,3-dihydro-1-hydroxy-2,1-benzoxaborole (also referred to as AN2690, a newly developed antifungal drug). First, the crystal structures of AN2690 and BBzx at room temperature are discussed, emphasizing the intermolecular interactions which play an important role in their formation. Then, results of IR and multinuclear (H-1, B-11, C-13 and F-19) solid state NMR characterization are presented, together with density functional theory (DFT) calculations which were carried out to assist in the interpretation of the spectra. Finally, the influence of polymorphism and anisotropic thermal expansion properties of the crystal structures on the NMR parameters of BBzx and AN2690 is discusse

Bis-benzoxaboroles: Design, Synthesis, and Biological Evaluation as Carbonic Anhydrase Inhibitors

“…Indeed, the benzoxaborole rings in the squarate derivative adopt a nearly coplanar configuration, while, for the thiophene derivative, the dihedral angle between the benzoxaborole aromatic planes is ∼32°. Interestingly, in contrast to many benzoxaborole crystal structures in which the organoboron units face each other forming H-bonds, 37 no such interaction was observed here, due to the presence of DMSO in the crystal lattices of 3 and 4, which plays the role of hydrogen-bond acceptor for the B−O−H units in both cases.…”

NMR crystallography of molecular organics

“…the value of Z' = 0.5 inferred from 13 C NMR similarly significantly constrained the number of space groups to be considered [326]. The value of Z' is not always evident from 13 C spectra; DFT calculations are helpful in these cases to confirm that symmetry independent sites have locally very similar environments [157,327].…”

“…The changes in isotropic shielding (of the order of ±0.2 ppm for 13 C) were significantly smaller than those directly due to thermal motion. In contrast, anisotropic thermal expansion has a major effect on diffraction results, making it difficult to compare PXRD patterns obtained at very different temperatures [157].…”

Investigations of Uranyl Fluoride Sesquihydrate (UO2F2·1.57H2O): Combining 19F Solid-State MAS NMR Spectroscopy and GIPAW Chemical Shift Calculations

“…[3][4]21 Therefore, the approach in this work, as suggested in the literature for 19 F NMR of other systems, used a linear scaling of the calculated values to compare to the experimental 19 F chemical shifts. [5][6][22][23][24][25][26][27][28][29][30][31][32] From the principal components of the symmetric part of the shielding tensor, the shielding anisotropy (∆σ 𝑐𝑐𝑎𝑎𝑖𝑖𝑖𝑖𝑖𝑖 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 ), which describes the largest separation from the center of gravity, and asymmetry parameter (η), which describes line shape deviation, can be calculated:…”