Protonated N‐benzyl‐ and N‐(1‐phenylethyl)tyrosine amides dissociate via ion/neutral complexes. (29th July 2015)

• Record Type: Journal Article
• Authors: Paulose, Justin; Achuthan, Revi P.; Linsha, Maria P. L.; Mathai, George; Prasanth, B.; Kumar Talluri, M. V. N.; Srinivas, Ragampeta
• Is Part Of: Rapid communications in mass spectrometry. Volume 29:Number 17(2015)
• Page Start: 1577
• Page End: 1584
• Publication Date: 2015-07-29
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.7256
• Languages: English
• ISSNs: 0951-4198

Abstract

Abstract : Rationale: The collisional‐induced dissociations (CID) of the [M+H] + ions of molecules having benzyl groups attached to N‐atoms have been proposed to involve migration of the benzyl group through the intermediacy of ion/neutral complexes (INCs). We report the investigation of the mechanism of dissociation of protonated N ‐benzyl‐ and N ‐(1‐phenylethyl)tyrosine amides by electrospray ionization (ESI) tandem mass spectrometry (MS/MS) and density functional theory (DFT) calculations. Methods: The amides were synthesized from the corresponding amino acids and amines. The ESI‐MS/MS spectra were recorded using an Agilent QTOF 6540 mass spectrometer. The DFT calculations were performed by using Gaussian 09 software. The structures of the [M+H] + ions, intermediates, products and transition states (TS) were optimized at the B3LYP/6‐31G(d, p) level of theory. Results: CID of the [M+H] + ions of N ‐benzyltyrosine amide yields two product ions due to rearrangements: (i) the [M+H–74] + ion ( m/z 197) due to benzyl migration to the hydroxyphenyl ring and (ii) the [M+H–45] + ion ( m/z 226) due to benzyl migration to the NH2 group. DFT calculations suggest that the rearrangements occur through an INC in which the benzyl cation is the cation partner. The [M+H] + ion of N ‐(1‐phenylethyl)tyrosine amide rearranges to an INC of the 1‐phenylethyl cation. Subsequent elimination of styrene occurs by transfer of a proton from the 1‐phenylethyl cation to the neutral partner. Conclusions: The [M+H] + ions of both N ‐benzyl (1 ) and N ‐(1‐phenylethyl) (2 ) tyrosine amide rearrange into INCs. The dissociation of [M+H] + ion of1 yields the benzyl cation and [M+H–74] + and [M+H–45] + due to benzyl migration to the hydroxyphenyl ring and NH2 group, respectively. However, the formation of the [M+H–74] + ion is not observed when the aromatic ring is deactivated. The [M+H] + ion of2 either dissociates to form the 1‐phenylethyl cation or [M+H–styrene] + . Copyright © 2015 John Wiley & Sons, Ltd.