ELECTRON IONIZATION MASS-SPECTROMETRY OF CURCUMIN ANALOGS - AN OLEFINMETATHESIS REACTION IN THE FRAGMENTATION OF RADICAL CATIONS

The natural compound curcumin, used in cosmetics, traditional medicine s and as a spice in food, is known as a multi-factorial anti-inflammat ory agent. To study the anti-inflammatory activity of curcumin derivat ives, 24 analogues were synthesized and their structures were confirme d by H-1 MMR and electron ionization (EI) mass spectrometry. Most sign als in the EI mass spectra can be attributed to commonly known fragmen tations, but the formation of ring-substituted 1,2-diphenylethene (sti lbene)-type radical cations, observed in the spectra of all compounds investigated and resulting in the base peak for some compounds, requir es a peculiar rearrangement. Metastable ion spectra and C-13 labelling studies show that the stilbene-type ions are formed directly from the molecular ions and contain the two original aryl groups and the 1 and 7 carbon atoms of the olefinic system. It is proposed that the format ion of stilbene-type ions results from an intramolecular olefin metath esis reaction; this suggestion is supported by semi-empirical (MNDO/PM 3) calculations. (C) 1998 John Wiley & Sons, Ltd.