The chemistry of vitamin B12. Part VI. Steroisomerism involving the axial ligands

Abstract

Present experiments support Friedrich's conclusion that corrinoids in which the axial ligands are H₂O and CN^–, e.g., aquocyanocobinamide (Factor B) and aquocyanocobyric acid (Factor V_1a), exist in solution as a mixture of stereoisomers. It is shown that thin-layer chromatography is better than column or paper chromatography in separating the isomers. Mercury(II) salts inhibit the isomerisation and decompose the dicyanide complexes to the aquocyano-complexes without decomposing the latter; it is concluded that isomerisation requires the presence of free cyanide and proceeds through the intermediate formation of the dicyanide. The probable identity of the isomers has been established in the case of Factor V_1a, whose structure is known in the solid state. Organo-aquocobinamides, where the axial ligand cannot exist free in solution, do not isomerise