Complexes of cobalt(III) with d-fructose and phenanthroline

d-Fructose and 1,10-phenanthroline form complexes with Co(III). Configurations about Co(III) are assigned from the CD and ORD spectra of the separated Λ and Δ diastereomers, and Λ strongly predominates in the mixture. Most of the 1H NMR signals of the complexes are shifted strongly upfield, relative to those of d-fructose, due to shielding by aromatic residues, and the effect is especially strong for hydrogens at positions 1 and 6. Signals of the fructose residue are assigned for the Λ diastereomer and coupling constants estimated, but only some of the signals can be assigned for the Δ diastereomer. The marked changes in chemical shifts on formation of the complexes from fructose are rationalized in terms of predicted conformations based on molecular-mechanics calculations with MM2 parameters, which predict the higher stability of the Λ over the Δ diastereomer, and also complexation at positions 2 and 3.