Silver ion chromatography enables the separation of 2-methylalkylresorcinols from alkylresorcinols

Alkylresorcinols (∑ARs) is the generic term for a highly varied class of lipids found mainly in cereals. These bioactive compounds consist mainly of 5-alkylresorcinols (ARs), which differ in length, unsaturation, and substituents on the alkyl side chain on C-5. In addition, 2-methyl-5-alkylresorcinols (mARs) are scarcely studied minor compounds that are supposed to exist with the same structural diversity. In the first step, ∑ARs were enriched by solid-phase extraction from wheat grain and quinoa seed extracts. The subsequent application of silver ion chromatography (SIC), silica gel, coated with 20% AgNO₃, then deactivated with 1% water) enabled an unprecedented full separation of saturated mARs from conventional ARs. Specifically, saturated mARs were eluted with n-hexane/ethyl acetate (92:8, v/v), and conventional ARs with n-hexane/ethyl acetate (80:20, v/v). The unpreceded separation indicated that the SIC method could be useful not only for separations according to the degree of unsaturation, but also in the case of steric hindrance by additional (alkyl) substituents. Continued fractionation enabled the collection of unsaturated ARs in wheat and quinoa extracts. In this way, 35 ∑ARs (including five mARs) were detected by gas chromatography/mass spectrometry analysis in wheat and 45 ∑ARs (including 21 mARs) in quinoa. These included several low abundant and partly unknown ∑ARs such as 1,3-dihydroxy-5-tricosadienylbenzene.