Electrospray‐Ionization Mass Spectrometry. Part 2. Neighboring‐Group Participation in the Mass‐Spectral Decomposition of 4‐Hydroxycinnamoyl‐spermidines

The three mono substituted N ‐[( E )‐3‐(4‐hydroxyphenyl)prop‐2‐enoyl]spermidines 1–3 have been studied by positive‐ion electrospray‐ionization tandem mass spectrometry (ESI‐MS/MS). Because of the neighboring‐group participation, the MS/MS of [ 1 + H] + and [ 2 + H] + are essentially similar, while compound 3 can be easily distinguished from 1 and 2 because of the characteristic ions at m/z 218. However, with the source collision‐induced dissociation (source‐CID) MS/MS technique, the compounds 1 and 2 can be unambiguously distinguished by the signal of the pyrrolidinium ion ( m/z 72) from their daughter ion ( m/z 275). The source‐CID MS/MS of the labeled compound N ‐(4‐aminobutyl)‐ N ‐(3‐aminopropyl)‐ N ‐[3‐(4‐ hydroxyphenyl)prop‐2‐en[ 15 N]amide] ([ 15 N(4)]‐ 2 ) provide more information on the decomposition mechanisms and proved the occurrence of a partial transamidation reaction 2→1 during the measurement.