<i>K</i>‑Targeted Metabolomic Analysis Extends Chemical Subtraction to DESIGNER Extracts: Selective Depletion of Extracts of Hops (Humulus lupulus)

Abstract

This study introduces a flexible and compound targeted approach to <u>D</u>eplete and <u>E</u>nrich <u>S</u>elect <u>I</u>ngredients to <u>G</u>enerate <u>N</u>ormalized <u>E</u>xtract <u>R</u>esources, generating DESIGNER extracts, by means of chemical subtraction or augmentation of metabolites. Targeting metabolites based on their liquid–liquid partition coefficients (<i>K</i> values), <i>K</i> targeting uses countercurrent separation methodology to remove single or multiple compounds from a chemically complex mixture, according to the following equation: DESIGNER extract = total extract ± target compound(s). Expanding the scope of the recently reported depletion of extracts by immunoaffinity or solid phase liquid chromatography, the present approach allows a more flexible, single- or multi-targeted removal of constituents from complex extracts such as botanicals. Chemical subtraction enables both chemical and biological characterization, including detection of synergism/antagonism by both the subtracted targets and the remaining metabolite mixture, as well as definition of the residual complexity of all fractions. The feasibility of the DESIGNER concept is shown by <i>K</i>-targeted subtraction of four bioactive prenylated phenols, isoxanthohumol (<b>1</b>), 8-prenylnaringenin (<b>2</b>), 6-prenylnaringenin (<b>3</b>), and xanthohumol (<b>4</b>), from a standardized hops (Humulus lupulus L.) extract using specific solvent systems. Conversely, adding <i>K</i>-targeted isolates allows enrichment of the original extract and hence provides an augmented DESIGNER material. Multiple countercurrent separation steps were used to purify each of the four compounds, and four DESIGNER extracts with varying depletions were prepared. The DESIGNER approach innovates the characterization of chemically complex extracts through integration of enabling technologies such as countercurrent separation, <i>K</i>-by-bioactivity, the residual complexity concepts, as well as quantitative analysis by ¹H NMR, LC-MS, and HiFSA-based NMR fingerprinting