Structure and Conformations of GABA-Transaminase Inhibitors. III. Synthesis and Crystal Structure of a Novel Tetracyclic Benzoxazaborinone

Abstract

Reduction of the substituted Schiff base (1) with sodium borohydride gave a product which was found by X-ray crystallographic analysis to be a mixture of two unexpected tetracyclic benzoxazaborinones (3a,b). X-ray analysis showed that, in the dipolar molecules, the pyridine nitrogen is protonated and the boron carries the negative charge. The crystals have site disorder, the exocyclic attachment at the boron being 73% methoxy (3a) and 27% hydroxy (3b). The stability, conformational rigidity and potential biology activity of these cyclic boron chelates all combine to give them particular interest as targets for further chemical and biological studies.