Application of phase-trafficking methods to natural products research

Abstract

A novel simultaneous phase-trafficking approach using spatially separated solid-supported reagents for rapid separation of neutral, basic, and acidic compounds from organic plant extracts with minimum labor is reported. Acidic and basic ion-exchange resins were physically separated into individual sacks ("tea bags") for trapping basic and acidic compounds, respectively, leaving behind in solution neutral components of the natural mixtures. Trapped compounds were then recovered from solid phase by appropriate suspension in acidic or basic solutions. The feasibility of the proposed separation protocol was demonstrated and optimized with an "artificial mixture" of model compounds. In addition, the utility of this methodology was illustrated with the successful separation of the alkaloid skytanthine from Skytanthus acutus Meyen and the main catechins and caffeine from Camellia sinensis L. (Kuntze). This novel approach offers multiple advantages over traditional extraction methods, as it is not labor intensive, makes use of only small quantities of solvents, produces fractions in adequate quantities for biological assays, and can be easily adapted to field conditions for bioprospecting activities.

Figure 1

Saturation curves for 12-hours period adsorption of quinine (black diamonds) and 3,4,5-trimethoxybenzoic acid (gray squares).

Figure 2

HPLC profile of artificial mixture (A) and recovered fractions: acidic (B), basic (C), and neutral (D).

Figure 3

Basic (diamonds), acidic (squares), and neutral (triangles) model compounds sequestration into solid phase in a 24-hour period. Percentage is expressed as the fraction of the original concentration (t=0 h) removed from solution.

Figure 4

Structures of recovered compounds using catch-and-release approach (from S. acutus and C. sinensis)

Scheme 1

Catch-and-release principle of selective separation using ion-exchange resins. In the first phase the acidic and basic resins are kept spatially separated by employing porous bags. In the second phase the resin bags are withdrawn and separately eluted.

Scheme 2

General catch-and-release protocol scheme. The neutral components remain in the original methanol-water solution and are recovered by evaporation.