Countercurrent chromatographic isolation of 11´-γ-tocomonoenol from and detection of novel minor tocochromanols in pumpkin seed oil

Abstract

A non-refined, organic pumpkin seed oil (PSO) was chosen for the isolation and structure verification of the rare vitamin E compound γ-tocomonoenol (γ-T1). Initial measurements indicated the presence of ~0.4 mg γ-T1 per 100 g pumpkin seed oil. Saponification of ~2 L pumpkin seed oil, followed by repeated countercurrent chromatography (CCC) with the solvent system n-hexane/benzotrifluoride/acetonitrile (10:3.5:6.5, v/v/v) and silica gel column chromatography enabled the isolation of 6.8 mg γ-T1 with a purity of 96.0%. Structural analysis by H NMR spectroscopy and gas chromatography with mass spectrometry (GC/MS) of the γ-T1 isolate confirmed the presence of a double bond in C-11´-position (11´-γ-tocomonoenol). Next to γ-T1, CCC fractionation enabled the detection of 18 different tocochromanols, many of which were reported for the first time in pumpkin seed oil. This unmatched variety covered among others α-/γ-tocopherol, α-/γ-tocomonoenol, two α- and two γ-tocodienol isomers, α-/γ-tocotrienol as well as the rare 11´-β-tocomonoenol (β-T1) and δ-T1. Three uncommon tocochromanols were also detected whose origins and structure remained unclear.