title: Fragmentation of protonated 2-(2-phenylethyl)chromones from agarwood: the diagnostic role of ion/neutral complexes as reactive intermediates.
abstract: A positive-ion electrospray ionisation collision-induced dissociation mass spectrometric study on the fragmentation of the [M + H](+) ions of 2-(2-phenylethyl)chromone and a set of nine hydroxyl- and/or methoxy-substituted derivatives has revealed a highly prominent fragmentation channel, the loss of benzoquinomethanes or a benzaldehyde, respectively, as a diagnostic feature for 2-(2-phenylethyl)chromones that bear a hydroxyl group at the para- (4'-), ortho- (2'-) and/or benzylic (α-) position of the phenylethyl residue. Derivatives that bear only a meta- (3'-) hydroxyl group do not undergo this elimination. The intermediacy of ion/neutral complexes (INCs) is invoked to explain this fragmentation, which involves the remarkable intra-complex proton or hydrogen atom transfer from the remote 4'-OH (or the 2'- or α-OH) functionalities. Density functional theory (B3LYP/6-31G(d)) calculations confirm the energetic preference for these elimination channels and agree with the limited thermochemical data known for para- and ortho- benzoquinomethanes. The INC-mediated losses of the benzaldehydes from the [M + H](+) ions of the α-hydroxy-substituted 2-(2-phenylethyl)chromones correspond to a particularly facile (vinylogous) Grob fragmentation. The study may be viewed as a telling example of the diagnostic role of ion/neutral complexes as intermediates for the structural assignment of constitutional isomers by mass spectrometry.
authors: Key Laboratory of Biology and Genetic Resources of Tropical Crops, Ministry of Agriculture, Institute of Tropical Bioscience and Biotechnology, Chinese Academy of Tropical Agriculture Sciences, Haikou 571101, P.R. China. delanyang@126.com.
authors: Delan
authors: D
authors: Yang
authors: Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, P. R. China. xiabing@cib.ac.cn.
authors: Bing
authors: B
authors: Xia
authors: Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, P. R. China. jiangyan@cib.ac.cn.
authors: Yan
authors: Y
authors: Jiang
authors: Key Laboratory of Biology and Genetic Resources of Tropical Crops, Ministry of Agriculture, Institute of Tropical Bioscience and Biotechnology, Chinese Academy of Tropical Agriculture Sciences, Haikou 571101, P.R. China. meiwenli@itbb.org.cn.
authors: Wenli
authors: W
authors: Mei
authors: Department of Chemistry, Bielefeld University,33615 Bielefeld, Germany. dietmar.kuck@uni-bielefeld.de.
authors: Dietmar
authors: D
authors: Kuck
mesh_terms: D005419:Flavonoids / Q000032:analysis* / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014934:Wood / Q000032:analysis* / Q000737:chemistry*
chemical_list: D005419:Flavonoids; D007477:Ions; D011522:Protons; C062550:2-(2-phenylethyl)chromone