Application of liquid chromatography–nuclear magnetic resonance spectroscopy to the identification of natural products

LC–NMR combines the separation power of high-performance liquid chromatography (HPLC) with the superior structural information content of nuclear magnetic resonance (NMR). These two techniques traditionally have been the primary tools used by natural products chemists to isolate and determine the structures of molecules of interest. Recent advances in NMR technology have allowed the practical application of LC–NMR, thus providing natural products chemists with a hyphenated technique which combines the two most important tools in their field. A brief review of the literature describing how LC–NMR has been applied to natural products research is followed by a specific example illustrating how this technique was used to identify the marine alkaloid aaptamine (1). Aaptamine was identified as the active component in the crude dichloromethane extract of the sponge Aaptos sp. which had been determined to possess inhibitory activity against the enzyme glutamine:fructose-6-phosphate amidotransferase (GFAT) by a high throughput screening (HTS) effort. Isolated aaptamine (1) exhibited an IC50=120 μM against this enzyme. The experience gained from the identification of aaptamine was used to define a strategy for the use of LC–NMR in a natural products HTS program.