title: Dehydrogenation and dehalogenation of amines in MALDI-TOF MS investigated by isotopic labeling.
abstract: Secondary and tertiary amines have been reported to form [M-H](+) that correspond to dehydrogenation in matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). In this investigation, we studied the dehydrogenation of amines in MALDI-TOF MS by isotopic labeling. Aliphatic amines were labeled with deuterium on the methylene of an N-benzyl group, which resulted in the formation of [M-D](+) and [M-H](+) ions by dedeuteration and dehydrogenation, respectively. This method revealed the proton that was removed. The spectra of most tertiary amines with an N-benzyl group showed high-intensity [M-D](+) and [M-H](+) ion peaks, whereas those of secondary amines showed low-intensity ion peaks. Ratios between the peak intensities of [M-D](+) and [M-H](+) greater than 1 suggested chemoselective dehydrogenation at the N-benzyl groups. The presence of an electron donor group on the N-benzyl groups enhanced the selectivity. The dehalogenation of amines with an N-(4-halobenzyl) group was also observed alongside dehydrogenation. The amino ions from dehalogenation can undergo second dehydrogenation. These results provide the first direct evidence about the position at which dehydrogenation of an amine occurs and the first example of dehalogenation of haloaromatic compounds in MALDI-TOF MS. These results should be helpful in the structural identification and elucidation of synthetic and natural molecules.
authors: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, 130022, China.
authors: Chuanqing
authors: C
authors: Kang
authors: Yihan
authors: Y
authors: Zhou
authors: Zhijun
authors: Z
authors: Du
authors: Zheng
authors: Z
authors: Bian
authors: Jianwei
authors: J
authors: Wang
authors: Xuepeng
authors: X
authors: Qiu
authors: Lianxun
authors: L
authors: Gao
authors: Yuequan
authors: Y
authors: Sun
mesh_terms: D000588:Amines / Q000737:chemistry*; D054879:Halogenation; D006865:Hydrogenation; D007477:Ions; D007553:Isotope Labeling; D011522:Protons; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D000588:Amines; D007477:Ions; D011522:Protons
keywords: amines; dehalogenation; dehydrogenation; isotopic labeling; mass spectroscopy