Electron ionization mass spectrometry of curcumin analogues: an olefin metathesis reaction in the fragmentation of radical cations

• Published in: Journal of mass spectrometry. Vol. 33; no. 4; pp. 319 - 327
• Main Authors: van Baar, Ben L. M., Rozendal, Jelle, van der Goot, Henk
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.04.1998; Wiley
• Subjects: Biochemical Research Methods; Biochemistry & Molecular Biology; Chemistry; Chemistry, Analytical; curcumin; Exact sciences and technology; Life Sciences & Biomedicine; Mass spectrometry; Organic chemistry; Physical Sciences; Reactivity and mechanisms; rearrangement; Science & Technology; Spectroscopy; Technology; TRANS-DECALIN DERIVATIVES; EI; ANNULAR ENE SEQUENCE; rearrangement; STEREOCONTROLLED SYNTHESIS; curcumin; Electron impact; Intramolecular reaction; Chemical rearrangement; Reaction path; Metathesis; Fragmentation pattern; Diketone; Stilbene derivatives; MNDO method; Phenols; Curcumin; PM3 method; Semiempirical method; Mass spectrometry; Organic radical cation
• ISSN: 1076-5174; 1096-9888
• DOI: 10.1002/(SICI)1096-9888(199804)33:4<319::AID-JMS636>3.0.CO;2-U

The natural compound curcumin, used in cosmetics, traditional medicines and as a spice in food, is known as a multi‐factorial anti‐inflammatory agent. To study the anti‐inflammatory activity of curcumin derivatives, 24 analogues were synthesized and their structures were confirmed by 1H NMR and electron ionization (EI) mass spectrometry. Most signals in the EI mass spectra can be attributed to commonly known fragmentations, but the formation of ring‐substituted 1,2‐diphenylethene (stilbene)‐type radical cations, observed in the spectra of all compounds investigated and resulting in the base peak for some compounds, requires a peculiar rearrangement. Metastable ion spectra and 13C 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 formation of stilbene‐type ions results from an intramolecular olefin metathesis reaction; this suggestion is supported by semi‐empirical (MNDO/PM3) calculations. © 1998 John Wiley & Sons, Ltd.