Atypical cleavage of protonated N-fatty acyl amino acids derived from aspartic acid evidenced by sequential MS3 experiments

作者：Boukerche Toufik Taalibi; Alves Sandra; Le Faouder Pauline; Warnet Anna; Bertrand Michel Justine; Bouchekara Mohamed; Belbachir Mohammed; Tabet Jean Claude

来源：Amino Acids, 2016, 48(12): 2717-2729.

DOI：10.1007/s00726-016-2286-0

• N-fatty-acyl amino-acid
• Regioselectivity
• Ion-dipole
• ESI/MSn

Lipidomics calls for information on detected lipids and conjugates whose structural elucidation by mass spectrometry requires to rationalization of their gas phase dissociations toward collision-induced dissociation (CID) processes. This study focused on activated dissociations of two lipoamino acid (LAA) systems composed of N-palmitoyl acyl coupled with aspartic and glutamic acid mono ethyl esters (as LAA((*D)) and LAA((*E))). Although in MS/MS, their CID spectra show similar trends, e.g., release of water and ethanol, the [(LAA((*DE))+H)-C2H5OH](+) product ions dissociate via distinct pathways in sequential MS3 experiments. The formation of all the product ions is rationalized by charge-promoted cleavages often involving stepwise processes with ion isomerization into ion-dipole prior to dissociation. The latter explains the maleic anhydride or ketene neutral losses from N-palmitoyl acyl aspartate and glutamate anhydride fragment ions, respectively. Consequently, protonated palmitoyl acid amide is generated from LAA((*D),) whereas LAA((*E)) leads to the [*E+H-H2O](+) anhydride. The former releases ammonia to provide acylium, which gives the C (n) H(2n-1) and C (n) H(2n-3) carbenium series. This should offer structural information, e.g., to locate either unsaturation(s) or alkyl group branching present on the various fatty acyl moieties of lipo-aspartic acid in further studies based on MS (n) experiments.

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