Comparative Study of Chromatographic Medium-Associated Mass and Potential Antitumor Activity Loss with Bioactive Extracts

Natural product drug discovery programs often rely on the use of silica (Si) gel, reversed-phase media, or size-exclusion resins (e.g., RP-C<sub>18</sub>, Sephadex LH-20) for compound purification. The synthetic polymer-based sorbent Diaion HP20SS (cross-linked polystyrene matrix) is used as an alternative to prepare purified natural product libraries. To evaluate the impact of chromatographic media on the isolation of biologically active, yet chromatographically unstable natural products, Diaion HP20SS was evaluated side-by-side with normal-phase sorbents for irreversible binding of extract constituents and their effects on bioactivity. An array of chemically diverse natural product-rich extracts was selected as a test panel, and a cell-based reporter assay for hypoxia-inducible factor-1 (HIF-1) was employed to monitor potential change(s) in bioactivity. Silica gel caused significant irreversible binding of three out of 10 extracts. <i>Curcuma longa</i>, <i>Saururus cernuus</i>, and <i>Citrus reticulata</i> extracts showed decreased HIF-1 inhibitory activity after elution through Si gel. An additional nonpolar column wash of HP20SS with EtOAc retained considerable bioactivities of active extracts. In general, Si gel produced the greatest loss of bioactivity. However, HP20SS elution reduced significantly HIF-1 inhibitory activity of certain extracts (e.g., <i>Asimina triloba</i>).