Phase-Trafficking Methods in Natural Products, Modulators of Organic Anion Transporting Polypeptides from Rollinia emarginata, and Pregnane and Cardiac Glycosides from Asclepias spp.

Abstract

For decades, chemists and medicinal chemists have found in nature the source of inspiration for drug discovery and development. This work describes several aspects of the interaction between the fields of natural products and medicinal chemistry, from isolation and characterization of bioactive molecules to semi-synthetic analogs preparation. A new phase-trafficking approach for acidic, basic, and neutral compounds separation from organic plant extracts was developed, validated and successfully applied to crude plant extracts. This new method could be applied to natural extracts of diverse origin in order to generate better quality samples for initial bioassays. Furthermore, this new catch-and-release methodology allowed the isolation and identification of three compounds new to the literature from the extensively studied ginger rhizomes. Using a more traditional bioassay guided fractionation, we have identified six small-molecules from Rollinia emarginata that modulate organic anion transporting polypeptide´s (OATPs) function. The results of this study show that diverse plant materials are a promising source for the isolation of OATP modulating compounds, and that a bioassay-guided approach can be used to efficiently identify selective OATP modulators. In addition, a 1H NMR-based metabolomic approach was used as a dereplication tool to study the effect of aqueous green tea extracts on OATP1B1-mediated uptake of estrone-3-sulfate. Our findings suggested that not only the gallate catechins were important for the observed uptake inhibition, but also compounds theogalline and 3-p-cumaroyl quinic acid could have been involved. A screening against breast cancer cell line Hs578T was conducted with ten plant species from the Asclepiadaceae family and, based on our findings, three plants were selected for detailed investigation: Asclepias verticillata, Asclepias syriaca, and Asclepias sullivantii. As a result, a total of 46 compounds were isolated and identified, half of which represented novel structures. The isolates showed a wide variety of structures including pregnane and cardiac glycosides, pentacyclic triterpenes, glycosylated flavonoids and lignans, among others. Furthermore, a group of cardiac glycosides were found to have strong cytotoxicity selected breast cancer cell lines. Finally, using a semi-synthetic approach, cardiac glycoside analogs with modifications in the butenolide ring were pursued in order to better understand their SAR. Starting from the commercially available trans-aldosterone, the cardiac glycoside core was built up using a microwave-promoted allylic oxidation using SeO2 (Riley oxidation). In addition, a microwave-promoted Miyaura-Suzuki cross-coupling was utilized to obtain the desired 17β-aryl analogs.