Submitted to: Subtropical Technology Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 9/12/2005
Publication Date: 10/20/2005
Citation: Manthey, J.A. 2005. Fourier transform infrared (FTIR) analysis of a series of bergamottin-related compounds in grapefruit juice. Subtropical Technology Conference Proceedings. 56:20.
Technical Abstract: The isolation of many of the furanocoumarins, including the furanocoumarins, in grapefruit juice can be typically accomplished with well-established chromatographic methods (silica gel and reversed phase column and thin layer chromatography. Yet, the isolation of sufficient amounts necessary for the complete structural anslysis of these grapefruit compounds is severely limited to the trace levels at which these compounds naturally occur. Methods of analysis for the grapefruit furanocoumarins include melting points, UV spectroscopy, mass spectrometry (MS), Fourier Transform Infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. With the exception of a number of the compounds that can be isolated in 5-10 mg quantities, and thus analyzed by NMR, analyses of most of the minor-occurring compounds are limited to the first 4 methods. Although there are important differences in the UV spectra of separate classes of coumarins and furanocoumarins, the UV spectra of most compounds within a structural class are strikingly similar, and little further structural detail can be learned. Fragmentation by ion trap MS, or by collision induction during electrospray-ionization MS is useful in gaining insights into potential structural components, and is one of the most important tools available for structural studies of these grapefruit compounds. In addition to these techniques, I have also found FTIR spectroscopy to be a complementary tool which provides the detection of key functional groups in the furanocoumarins, and is sensitive to subtle changes in resonance structures of the aromatic ring systems, and thus provides valuable structural analysis of many of the minor-occurring compounds. Useful FTIR spectra of bergamottin-derived compounds can be obtained with as little as 2 micrograms. A presentation will be made of my work to characterize the FTIR spectra of coumarins and furanocoumarins, and to determine to what level this analysis can differentiate between the minor-occurring furanocoumarins currently isolated and tested in the “grapefruit/drug interaction” study.