Synthesis, Characterization, and Antibacterial Activity of Structurally Complex 2-Acylated 2,3,1-Benzodiazaborines and Related Compounds

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 class of 2‐acyl‐1‐hydroxy‐2,3,1‐diazaborines has been found to be able to exist in several interconvertable structural forms along a continuum comprised of an open hydrazone a, a monomeric B‐hydroxy diazaborine b, and an anhydro dimer c. X‐Ray crystallography of one of the anhydro dimers, 17c, revealed it to have an unprecedented structure featuring a double intramolecular O→B chelation. The crystal structure of another compound, 37, showed it to be based on a new pentacyclic B heterocycle framework. Nine compounds were found to possess activities against E. coli, and two others were active against M. smegmatis. The finding that these two contain isoniazid covalently embedded in their structures suggests that they might possibly be acting as prodrugs of this well‐known antituberculosis agent in vivo.