Mass spectroscopy Natural products

J. Schmidt and S. Huneck, Mass spectroscopy of natural products. V. Mass spectroscopic studies of ring A substituted allobetulane derivatives, Org. Mass Spectrom., 14, 646 655 (1979). 

The N-oxide of the alkaloid dihydrocorynantheol (21) has also been mentioned as a natural product from the leaves of Mitragyna parvifolia (Roxb.) Korth. however, it was detected only by mass spectroscopy and no further evidence for the structure has been given (31). 

Complete structure elucidation of individual resin glycoside constituents is now achieved readily by the use of a combination of high-resolution mass spectrometry and NMR spectroscopy. These methods are applicable to the isolated natural products or to their peracetylated and methylated derivatives. 

In search of new natural products, crude extracts are classically subjected to multi-step work-up and isolation procedures which include various separation methods (besides HPLC, for instance, column, gel or counter-current chromatography) in order to obtain pure compounds which are then structurally elucidated by using off-line spectroscopic methods such as nuclear magnetic resonance spectroscopy and mass spectrometry. 

The complementary structural information of both NMR spectroscopy and MS detection is particularly valuable for the analysis of closely related glycosidic natural products, where compounds of the same molecular mass (isobars, see Table 5.1.1), and even with identical MS/MS fragmentation patterns, frequently occur, as this example demonstrates. 

Often used in concert with mass spectrometry, NMR spectroscopy remains an invaluable structural diagnostic tool of particular importance to tricyclic natural products chemistry. For example, the tricyclic phenolic compound moracin P (3) was one of eight previously known compounds identified together with two new isoprenoid-substituted flavanones in isolates of the root bark of mulberry trees <89H(29)807>. In a series of studies of 6-7-5 tricyclic natural products, ID and 2D H and l3C NMR spectroscopy were employed extensively in the structure determination of sesquiterpene lactones (4)—(8) found among the aerial natural products of toxic plants (85P1378,90P551, 90P3875). 

Sandvoss, M. Weltring, A. Preiss, A. Levsen, K. Wuensch, G. Combination of matrix solid-phase dispersion extraction and direct on-line chromatography-nuclear magnetic resonance spectroscopy-tandem mass spectrometry as a new efficient approach for the rapid screening of natural products Application to the total asterosaponin fraction of the starfish Asterias rubens. J. Chromatogr., A 2001, 917, 75-86. 

A resurgence of interest and accomplishment in the field of biosynthe sis of natural products - including antibiotics - has occurred. The powerful methods for determination of a new structure with small amounts of material (mass and nmr spectroscopy, etc.) together with the development of 13C nmr spectroscopy for following the pattern of incorporation of precursors into these structures is one major reason. The subject of biogenesis of antibiotics has not been dealt with specifically in this series and this brief review will include some literature from earlier years than 1976. 

---