Dereplication mass spectrometry

The system relies upon preliminary fractionation of the microbial crude extract by dualmode countercurrent chromatography coupled with photodiode array detection (PDA). The ultraviolet-visible (UV-Vis) spectra and liquid chromatography-mass spectrometry (LC-MS) of biologically active peaks are used for identification. Confirmation of compound identity is accomplished by nuclear magnetic resonance (NMR). Use of an integrated system countercurrent chromatography (CCC) separation, PDA detection, and LC-MS rapidly provided profiles and structural information extremely useful for metabolite identification (dereplication, Figure 14.1). 

Strege summarized the technique of high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) in dereplication of natural products. In contrast to earlier electron impact ionization (El), ESI technique is applicable to virtually any ion in solution with a soft ionization process. A comparison of ESI with fast atom bombardment (FAB), matrix assisted laser desorption ionization (MALDI), atmospheric pressure chemical ionization (APCI) and other techniques demonstrates its superior sensitivity, compatibility and reliability when coupled with HPLC [51]. 

The phenylpropanoids rrans-anethole (61) and rran -cinnamaldehyde (62) are used as flavoring agents in foods in the United States and some other countries [20]. tranj-Cinnamaldehyde (62) Avas isolated from Cinnamomum osmophloeum Kanehira (Lauraceae) as a sweet principle, while tra/w-anethole (61) was isolated as the volatile oil constituent responsible for the sweet taste of several plant species, as listed in Table 1 [92]. These two compounds occur widely in the plant kingdom. Therefore, it is necessary to rule out their presence in any candidate sweet plant by a dereplication procedure in a natural product sweetener discovery program using gas chromatography-mass spectrometry (GC/MS) [46,47]. 

This chapter explores in more detail the role of mass spectrometry in several phases of the natural product discovery process, including (1) selection of source material, (2) screening, (3) dereplication of known compounds, and... 

Mass spectrometry has been, and will continue to be, a critical tool for the discovery of new lead chemistries from nature. It continues to play a central role in several phases of the natural products discovery processes that include source selection, screening, dereplication, and identification. Mass spectrometry will likely remain a key technology that should contribute to the success of natural product lead generation programs in both the pharmaceutical and agrochemical industries. 

Cremin, P. Zeng, L. High Throughput Parallel LC-MS Accurate Mass Measurements for the Dereplication of Natural Products, in Proceedings ofthe 50th ASMS Conference on Mass Spectrometry and Allied Topics Orlando, Florida, June 2-6, 2002. 

Cordell, G.A. Shin, Y.G. Finding the Needle in the Haystack. The Dereplication of Natural Product Extracts, Pure Appl. Chem. 71(6), 1089-1094(1999). Janota, K. Carter, G.T. Natural Products Library Screening Using LC/MS and LC/MS/MS, in Proceedings ofthe 46th ASMS Conference on Mass Spectrometry and Allied Topics, Orlando, Florida, May 31-June4, 1998. 

In most cases, mass spectrometry (MS) is the most sensitive method for obtaining dereplication information about an unknown compound. Microgram amounts are usually enough for several MS experiments, even though <1% of any sample undergoes ion formation by any single ionization technique. 

One difficulty in employing mass spectrometry in natural product dereplication is the lack of a universal ionization condition under which any unknown compound could be expected to be ionized. Optimization of ionization conditions involves many factors. In addition to the mode of ionization, the pH modifiers used in the HPLC solvent can be critical to the ionization process, and the choice of ion source and strength of electric field are all critical parameters. 

Dieckmann R, Graeber I, Kaesler I, Szewzyk U, von Dohren H. Rapid screening and dereplication of bacterial isolates from marine sponges of the sula ridge by intact-eell-MALDl-TOF mass spectrometry (ICM-MS). Appl Microbiol Biotechnol. 2005 67(4) 539-48. doi 10.1007/ S00253-004-1812-2. 

Gilbert, J.R. Lewer, P. Carr, A.W. Snipes, C.E. Balcer, J.L., Gerwick, W. Natural Product Dereplication and Structural Elucidation Using LC/MSn Combined With Accurate Mass LC/MS and LC/MS/MS, in Proceedings ofthe 47th ASMS Conference onMass Spectrometry and Allied Topics, Dallas, Texas, June 13-17, 1999. 

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