Separation of menaquinone-7 geometric isomers by semipreparative high-performance liquid chromatography with silver complexation and identification by nuclear magnetic resonance

Abstract

Dietary supplements containing vitamin K2 are often used to prevent osteoporosis, vascular calcification and coronary heart disease. It has been shown that some of these products contain a mixture of menaquinone-7 geometric isomers. Since the geometric shape may influence biological activity, there was a need for a semipreparative method to isolate single compounds for further studies. Here, we present an argentation chromatographic method for the separation of menaquinone-7 isomers and an nuclear magnetic resonance (NMR) methodology for the configuration assignment of isoprenoid side chain. The DFT calculations were performed to determine more energetically favorable complexes between the cis or trans menaquinone-7 isomers and the silver cation. Seventeen components were resolved, and fractions were collected and subjected to NMR study. Structures and chemical shifts for thirteen new compounds were assigned, and the identity of three known compounds was confirmed.