1H NMR determination of hypericin and pseudohypericin in complex natural mixtures by the use of strongly deshielded OH groups

The 1H NMR spectra of the commercially available compounds hypericin and its derivative pseudohypericin in CD3OH solutions indicate significantly deshielded signals in the region of 14–15 ppm. These resonances are attributed to the peri hydroxyl protons OH(6), OH(8) and OH(1), OH(13) of hypericins which participate in a strong six-membered ring intramolecular hydrogen bond with CO(7) and CO(14), respectively, and therefore, they are strongly deshielded. In the present work, we demonstrate that one-dimensional 1H NMR spectra of hypericin and pseudohypericin, in Hypericum perforatum extracts show important differences in the chemical shifts of the hydroxyl groups with excellent resolution in the region of 14–15 ppm. The facile identification and quantification of hypericin and its derivative compound pseudohypericin was achieved, without prior HPLC separation, for two H. perforatum extracts from Greek cultivars and two commercial extracts: a dietary supplement, and an antidepressant medicine. The results were compared with those obtained from UV–vis and LC/MS measurements.