<i>K</i>‑Targeted Metabolomic Analysis
Extends Chemical Subtraction to DESIGNER Extracts: Selective Depletion
of Extracts of Hops (Humulus lupulus)
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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 <sup>1</sup>H NMR, LC-MS, and HiFSA-based
NMR fingerprinting