22959-81-5Relevant articles and documents
Lewis or Br?nsted? A Rectification of the Acidic and Aromatic Nature of Boranol-Containing Naphthoid Heterocycles
Ang, Hwee Ting,Ferguson, Michael J.,Hall, Dennis G.,Johnson, Matthew A.,Kazmi, M. Zain H.,Paladino, Marco,Rygus, Jason P. G.
, p. 10143 - 10156 (2021/07/21)
Boron-containing heterocycles are important in a variety of applications from drug discovery to materials science; therefore a clear understanding of their structure and reactivity is desirable to optimize these functions. Although the boranol (B-OH) unit of boronic acids behaves as a Lewis acid to form a tetravalent trihydroxyborate conjugate base, it has been proposed that pseudoaromatic hemiboronic acids may possess sufficient aromatic character to act as Br?nsted acids and form a boron oxy conjugate base, thereby avoiding the disruption of ring aromaticity that would occur with a tetravalent boronate anion. Until now no firm evidence existed to ascertain the structure of the conjugate base and the aromatic character of the boron-containing ring of hemiboronic "naphthoid"isosteres. Here, these questions are addressed with a combination of experimental, spectroscopic, X-ray crystallographic, and computational studies of a series of model benzoxazaborine and benzodiazaborine naphthoids. Although these hemiboronic heterocycles are unambiguously shown to behave as Lewis acids in aqueous solutions, boraza derivatives possess partial aromaticity provided their nitrogen lone electron pair is sufficiently available to participate in extended delocalization. As demonstrated by dynamic exchange and crossover experiments, these heterocycles are stable in neutral aqueous medium, and their measured pKa values are consistent with the ability of the endocyclic heteroatom substituent to stabilize a partial negative charge in the conjugate base. Altogether, this study corrects previous inaccuracies and provides conclusions regarding the properties of these compounds that are important toward the methodical application of hemiboronic and other boron heterocycles in catalysis, bioconjugation, and medicinal chemistry.
Synthesis, characterization, and antibacterial activity of structurally complex 2-acylated 2,3,1-benzodiazaborines and related compounds
Kanichar, Divya,Roppiyakuda, Lance,Kosmowska, Ewa,Faust, Michelle A.,Tran, Kim P.,Chow, Felicia,Buglo, Elena,Groziak, Michael P.,Sarina, Evan A.,Olmstead, Marilyn M.,Silva, Isba,Xu, H. Howard
, p. 1381 - 1397 (2015/04/14)
A set of 2-acylated 2,3,1-benzodiazaborines and some related boron heterocycles were synthesized, characterized, and tested for antibacterial activity against Escherichia coli and Mycobacterium smegmatis. By high-field solution NMR, the heretofore unknown
Planar boron heterocycles with nucleic acid-like hydrogen-bonding motifs
Groziak, Michael P.,Chen, Liya,Yi, Lin,Robinson, Paul D.
, p. 7817 - 7826 (2007/10/03)
To promote the development of boron-containing purine analogues that exist in planar, non-zwitterionic dominant structural form. in aqueous solution, rigorous solution and solid state structural analyses of 1-hydroxy-1H-2,3,1-benzoxazaborine (1), 1,2-dihydro-1-hydroxy-2,3,1-benzodiazabo (2), and related 2,3,1-benzodiheteraborines were undertaken. With the aid of isotope-enriched compounds, a multisolvent 1H, 13C, 11B, and 15N NMR spectroscopic analysis of 1 and 2 was conducted, providing structurally-diagnostic chemical shift data for all non-oxygen atoms that constitute their heterocyclic peripheries. In addition, single-crystal X-ray diffraction analyses of 1 and 2 were performed. In stark contrast to their 2,4,1 isomeric counterparts, the 2,3,1-benzoxaza- and benzodiazaborines exist in planar structural form in protic solution and in the solid state and display proton dissociative and associative tendencies reflective of the predominant Bronsted, yet still Lewis acidic-capable character of the B-OH group together with the basic one at the C4-N3 imine group. In the solid state, 1 and 2 display intermolecular hydrogen-bonding patterns not too dissimilar from the motifs of certain natural nucleic acid bases. Diazaborine 2 was shown by VT-NMR to undergo a triple hydrogen-bonding solution association with a 2',3',5'-tri-O-protected cytidine in a demonstration of one biomimetic potential held by a 1-hydroxy-2,3,1-diheteraborine periphery. In general, 1, 2, and related 1-hydroxy-2,3,1-benzodiheteraborine heterocycles were found to be characterized by an environment-dependent O1 → N3 Bronsted prototropy and B-OH group Bronsted/Lewis acid ambidency so sensitive and subtle that certain past difficulties encountered in attempts to delineate their physicochemical properties now become readily appreciated.
