Boron, Biologically Active Compounds
Boron-containing compounds are primarily utilized by bacteria as quorum autoinducers and by plants as components of the cell wall. Many synthetic organoboron compounds are used as enzyme inhibitors.
Boron is a ubiquitous element in rocks, soil, and water; its average concentration ranging from 1 mg/kg in water to 100 mg/kg in rocks. Boron is electron-poor and prefers to form tetracoordinate complexes with “hard” nucleophiles. In physiological environment, it is present in +3 oxidation state, usually in the form of borate anion or borate esters. Borate anions form stable complexes with organic acids, polysaccharides, and other biopolymers. Usually borate complexes two hydroxyl groups (either a diol or a hydroxycarboxylic acid) to form a borate diester. Since boron can bind four ligands, in many cases, borate esters cross-link two organic molecules together.