Chemical and Chromatographic Behavior of Pseudohypericin and Isopseudohypericin, and the Occurrence of Isopseudohypericin in Saint John’s Wort (Hypericum perforatum) Extracts

Summary.

Isopseudohypericin is formed from pseudohypericin in an alkaline, alcohol/water environment. The conditions for this conversion are specified, showing that these two compounds are in equilibrium at pH values of 5–10; pseudohypericin is stable below pH 5, and isopseudohypericin is stable above pH 10. It is also shown that the HPLC behavior of isopseudohypericin is dependent on the pH of the mobile phase: pH determines both the retention time and the UV-Vis spectrum characteristics of the corresponding peak analyzed using a diode array detector. Finally, different extraction conditions yield extracts containing different proportions of isopseudohypericin: it is suggested that this isopseudohypericin may be an artefact of extraction conditions and/or it may correspond to the compound cyclopseudohypericin, discussed by other experts but never formally characterized.