Metal chelation by the common 2-amino-2-deoxy-, 2-N-acetylamino-2-deoxy-, and 2-deoxy-hexoses

Abstract

The chelating properties of the common aldohexoses D-glucose, D-mannose, and D-galactose are characteristically modified in 2-substituted derivatives. The 2-amino-2-deoxy-aldohexoses provide mono- and bis-metallisable anionic ligands after their reaction with metal probes of the Pd^IIN₂ type (N₂ = bidentate nitrogen ligand). The 2-amino function reliably participates in metal binding of the, mostly pyranoidic, carbohydrate chelators. Acetylation of the amino function yields the biologically important 2-N-acetylamino-2-deoxy-hexoses (GlcNAc, ManNAc, and GalNAc). On reaction with the palladium probe, the metal-binding properties of the deprotonated acetylamino function depends on the steric requirements introduced by the acetyl residue which is forced into a coplanar arrangement with the chelate ring. In the two 2-deoxy-aldohexoses, 2-deoxy-arabino-D-hexose (the 2-deoxy derivative of both D-glucose and D-mannose, ‘2-deoxy-glucose’) and 2-deoxy-lyxo-D-hexose (‘2-deoxy galactose’), the 2-position cannot contribute to metal binding. As a result, furanose-1,3 chelation becomes an important metal-binding mode. Due to the decreased acidity of the 2-deoxy-glycose's 1-hydroxy function, monometallation also takes place at the pyranose's 3,4-site.