JMSSJ On-line

JMSSJ On-line, Vol. 48 (2000) No. 1, pp. 8-22

Mechanism of Formation of Dehydrated Ions from Abscisic Acid and Its 1′,4′-Diol Methyl Esters in Electron Ionization Mass Spectrometry		>> Full Text PDF >> References
*Nobuhiro HIRAI,^a) Masahiko OKAMOTO,^a) Masaki FUJIMURA,^a) Tetsuya ICHIYAMA,^a) Yasushi TODOROKI,^a) Hajime OHIGASHI,^a) Naohito TAKEDA,^b) Hideo YOSHIZUMI,^b) and the late Akira TATEMATSU^b)** ^† This paper is dedicated to the memory of the late Professor Akira TATEMATSU. ^a) Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University (Kitashirakawa-oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan)* ^b) Faculty of Pharmacy, Meijo University (Yagotoyama 150, Tempaku-ku, Nagoya 468-8503, Japan) *Abbreviations:* ABA, abscisic acid; EI MS, electron ionization mass spectrometry; GC, gas chromatography; HPLC, high performance liquid chromatography; -Me(s), methyl ester(s); NMR, nuclear magnetic resonance; rel. int., relative intensity; THF, tetrahydrofuran; THP, tetrahydropyranyl; t_R, retention time.

Hydrogen atoms lost by dehydration in electron ionization mass spectrometry of methyl esters of abscisic acid and 1′,4′-trans and 1′,4′-cis diolabscisic acids were identified using their deuterated analogs. Analysis of mass spectra of the deuterated analogs showed that, in methyl ester of abscisic acid, the 4-hydrogen atom bonded to a double bond was mainly eliminated with a 1′-hydroxyl group to give a dehydrated ion at m/z 260. This unusual dehydration could be due to a proximity effect between the 1′-hydroxyl group and 4-hydrogen. In methyl esters of 1′,4′-diolabscisic acids, the first dehydration derived from loss of the 4′-hydroxyl group was accompanied with a hydrogen atom of the 1′-hydroxyl group, and the second dehydration derived from 1′-oxygen involved 3′-,4′-,5′-, and 7′-hydrogen atoms, and partially involved the 4-hydrogen atom. This indicated that the structure of the first dehydrated ion of the 1′,4′-diolabscisic acid methyl esters was not 4′-deoxyabscisic acid methyl ester. The migration of the hydroxyl hydrogen atom to another hydroxyl group in the first dehydration has also been demonstrated in dehydration of cis-1,4-cyclohexanediol. Based on these results, we proposed dehydration mechanisms in EI MS of methyl esters of abscisic acid and 1′,4′-diolabscisic acids.

Key words: Abscisic acid, Fragmentation, Deuterated analog, Dehydrated ion, 1′,4′-Diolabscisic acid

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