Liquid chromatography–mass spectrometry studies of St. John's wort methanol extraction: active constituents and their transformation

The influence of light and solution pH on the stability behavior of phloroglucinols (hyperforin and adhyperforin) and naphthodianthrones (hypericin, pseudohypericin, protohypericin and protopseudohypericin) extracted with methanol from St. John's wort powder ( Hypericum perforatum L.) were studied using liquid chromatography–mass spectrometry (LC–MS). When exposed to light, hyperforin and adhyperforin in this extract solution degraded rapidly, particularly at pH 7, where within 12 h complete transformation was observed. Contrastingly, when protected from light, the solutions regardless of pH, underwent minimal transformation after 36 h. Under light and neutral pH conditions, phloroglucinols and naphthodianthrones had different stability behaviors, which were attributed to the different oxidation mechanisms. Four experiments performed on naphthodianthrones exhibited serious transformation at acidic pHs. One hyperforin transformation product was studied using LC–MS. The molecular structure was proposed on the basis of ion fragmentation patterns obtained from MS/MS studies.