Dereplication of Natural Extracts Diluted in Propylene Glycol, 1,3-Propanediol and Glycerin. Comparison of Leontopodium alpinum Cass. (Edelweiss) Extracts as a Case Study

Many natural extracts used as cosmetic ingredients are available as solutions prepared in high-boiling-point solvents, called carrier solvents, such as propylene glycol (1,2-propanediol), propanediol (1,3-propanediol) and glycerin. The upstream chemical profiling of these extracts represents a major asset for the cosmetic industry, because it accelerates product development. A new workflow for the rapid characterization of the main metabolites present in natural extracts diluted in propylene glycol and 1,3-propanediol is presented here as an extension of previous works on glycerin-containing extracts. This method is an optimized version of a well-established dereplication procedure and consists of a fractionation by centrifugal partition chromatography followed by 13C nuclear magnetic resonance analysis and dedicated data processing. The concentration by evaporation under reduced pressure was considered as a pertinent preliminary step, particularly adapted to the analysis of highly diluted extracts. A dried hydro-ethanolic extract of Leontopodium alpinum Cass. was prepared at laboratory scale and used for method validation. Three solutions at 5% wt. of dry extract were prepared with propylene glycol/water (1:1), 1,3-propanediol/water (1:1) and glycerin/water (1:1) as carrier solvents. The dereplication workflow was applied to the three resulting L. alpinum extracts. Each study led to the quick identification of 26 metabolites including five flavonoids (luteolin and its derivatives), five hydroxycinnamic acids (among which are leontopodic acids), sugars and organic acids.