A tandem mass spectrometric investigation of N-(3-ferrocenyl-2-naphthoyl) dipeptide ethyl esters and N-(6-ferrocenyl-2-naphthoyl) dipeptide ethyl esters |
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Authors: | Rai Dilip K Mooney Áine Kenny Peter T M |
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Affiliation: | Department of Food Biosciences, Teagasc Food Research Centre Ashtown, Dublin 15, Ireland. |
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Abstract: | N‐(3‐Ferrocenyl‐2‐naphthoyl) dipeptide ethyl esters 1–4 and N‐(6‐ferrocenyl‐2‐naphthoyl) dipeptide ethyl esters 5–8 were prepared by coupling either 3‐ferrocenylnaphthalene‐2‐carboxylic acid or 6‐ferrocenylnaphthalene‐2‐carboxylic acid to the dipeptide ethyl esters GlyGly(OEt) (1, 5), AlaGly(OEt) (2, 6), GlyPhe(OEt) (3, 7) and GlyLeu(OEt) (4, 8), using the standard N‐(3‐dimethylaminopropyl)‐N'‐ethylcarbodiimide hydrochloride, 1‐hydroxybenzotriazole protocol. Electrospray ionization mass spectrometry (ESI‐MS) and laser desorption ionization mass spectrometry (LDI‐MS) were employed in conjunction with tandem mass spectrometry in the analysis of N‐(3‐ferrocenyl‐2‐naphthoyl) dipeptide ethyl esters 1–4 and N‐(6‐ferrocenyl‐2‐naphthoyl) dipeptide ethyl esters 5–8. Radical cations, [M]+? and [M + H]+ species were both observed in the mass spectra. Intense sodium [M + Na]+ and potassium [M + K]+ adducts were also present. An important diagnostic ion at m/z [M–65]+ was observed in both the MS and MS/MS spectra of the N‐(3‐ferrocenyl‐2‐naphthoyl) dipeptide derivatives. Sequence‐specific ions were generally not observed in the MS/MS spectra of the N‐(3‐ferrocenyl‐2‐naphthoyl) series due to formation of the diagnostic [M–65]+ ion. Sequence‐specific ions were observed in the MS/MS spectra of the N‐(6‐ferrocenyl‐2‐naphthoyl) dipeptide esters with charge retention on the derivatized N‐terminal of the dipeptide. Both series of compounds could be successfully analyzed by MALDI without the use of a matrix (LDI). Copyright © 2011 John Wiley & Sons, Ltd. |
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