Structural Elucidation of Sterols by Reversed-Phase Liquid Chromatography: I. Assignment of Retention Coefficients to Various Groups

Abstract

The retention (k′) relative to cholesterol (α_c) of 20 μg each of several dozen sterols and a few triterpenoids was measured in reversed-phase liquid chromatography in the presence and absence of H-bonding capacity in the mobile phase. The contributions (σ values) that individual molecular features made to α_c with each type of mobile phase were determined from the α_c values for sterols with and without the feature. Features examined included the presence and absence of various methyl and ethyl groups, double bonds and hydroxyl groups in the nucleus and side chain, the chirality at C-3 and C-24, the configuration about certain doubts bonds, the length of the side chain, and branching. Vicinal effects between a variety of these groups were also found and quantitated. The σ values could be used to make a calculation of ac for a given sterol, and a comparison of the calculated value with that observed then provides a way to gain structural information on a sterol when only μg amounts are in hand