Purification natural products dereplication

Analysis strategies that use on-line ESI-LC/MS approaches provide an integrated format for natural product dereplication by combining traditional fraction collection, sample preparation, and multi-component analysis into a single step. In this way, crude extracts are screened without extensive purification and chemical analysis. Furthermore, less material is required due to the sensitivity of the technique and chromatographic resolution is retained. 

Ultimately, the definitive structure elucidation of unknown molecules is most often accomplished via NMR. NMR has traditionally been performed on the purified natural product isolated using bioassay-guided fractionation. With the advent of hyphenated techniques such as LC/NMR, these data can now be obtained prior to purification [130,131]. LC/NMR can prove useful even in the dereplication phase, particularly when LC/UV/MS data are insufficient for unambiguous peak identification. LC/NMR has played an important role in natural products structure elucidation, where several related compounds (factors) are often encountered in a single sample. For example, isobaric or isomeric mixtures that may prove difficult or impossible to differentiate by MS, can often be readily distinguished by NMR. Several thorough reviews of LC/NMR in natural products discovery and phytochemical analysis have recently appeared [132,133]. 

The isolation and purification of a bioactive compound is a rate-limiting step in a natural products chemistry project, and significant improvement in this area is urgently needed. We have approached this problem with a view toward exploring the application of sophisticated modern scientific instruments. Our goal was to develop a process that is not only capable of effective fractionation, but also yields sufficient quantities necessary for structure elucidation and extensive biological evaluation. In addition, the process would allow us to distinguish between known and new compounds (dereplication) at an earlier phase of the project. 

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