Stereospecific quantitation of 6-prenylnaringenin in commercially available H. lupulus-containing natural health products and dietary supplements

Abstract

6-Prenylnaringenin (6PN) is a chiral prenylflavonoid found most prevalently in hops (Humulus lupulus) and present in hops and hop products. It is an isomer of the potent phytoestrogen, 8-prenylnaringenin. An enantiospecific method for quantitation 6PN by LC-ESI-MS has been developed. Baseline enantiomeric resolution of 6PN was attained on a Chiralpak^® AD-RH column with an isocratic mobile phase consisting of acetonitrile and 10 mM ammonium formate (pH 8.5) (39:61, v/v) and a flow rate of 1.25 mL/min. Quantitative MS data were obtained by selected ion monitoring of the [M-H]^--ion of both enantiomers of 6PN (m/z 339.10) and the internal standard, 4-acetamidobenzoic acid (m/z 178.05). The method was found to be accurate and precise for enantiospecific quantification of 6PN. The method was successfully applied to the content analysis of 39 commercially available natural health products and dietary supplements reported to contain H. lupulus plant material, extracts and label claims of 6PN. 6PN was present in 25 of 34 products containing plant material or extracts of H. lupulus. Of the five products with claimed amounts of 6PN, all were found to possess <50% of label claims. Results of the content analysis indicated a lack of uniformity in botanical nutraceuticals claiming 6PN content.