Countercurrent Separation of Natural Products: An Update

Abstract

This work assesses the current instrumentation, method development, and applications in countercurrent chromatography (CCC) and centrifugal partition chromatography (CPC), collectively referred to as countercurrent separation (CCS). The article provides a critical review of the CCS literature from 2007 since our last review (J. Nat. Prod. 2008, 71, 1489-1508), with a special emphasis on the applications of CCS in natural products research. The current state of CCS is reviewed in regard to three continuing topics (instrumentation, solvent system development, theory) and three new topics (optimization of parameters, workflow, bioactivity applications). The goals of this review are to deliver the necessary background with references for an up-to-date perspective of CCS, to point out its potential for the natural product scientist, and thereby to induce new applications in natural product chemistry, metabolome, and drug discovery research involving organisms from terrestrial and marine sources.

Figure 1

Cladistics tree of liquid–liquid separation techniques showing the position of the widely practiced and contemporary laboratory and scale-up methods, the historical methods such as Craig’s counter-current distribution (CCD), as well as the related extraction and chromatography techniques found in natural product and related literature.

Figure 2

Visual representation of this review article. Shown are the main building blocks of CCS technology addressed in the previous review and updated here, as well as the new components, optimization (O), workflow (W), and bioactivity (B). Guidelines (G) and reporting (R) continue to apply as published earlier.

Figure 3

Reported column volumes of all countercurrent separation instruments used in natural product separations since 2007.

Figure 4

Abundance and diversity of solvents and solvent systems (SSs) in reported natural product countercurrent separations since 2007: (A) frequency of particular solvents as solvent system components in all articles; (B) number of solvents per SS employed; (C) number of SSs per published study.

Figure 5

Solvent system (SS) selection in the CCS literature with regard to the number of SS families (A) and the diversity of SSs evaluated per individual study (B) in the literature since 2007.

Figure 6

Sample loading in the countercurrent separation (CCS) of natural products in mg sample per mL of column volume reported since 2007: (A) sample loadings for separations with low g-force hydrodynamic instruments; (B) sample loadings reported for all CCS instruments. The red boxes indicate changes that were a result of including CPC and high g-force hydrodynamic instruments to the totals.

Figure 7

Scheme explaining the process of multi-dual-mode operation in CCS.