Unimolecular and collision‐induced dissociation reactions of peracetylated methyl glucopyranoside

Abstract

The mechanism of the collision-induced fragmentation of peracetylated methyl-a-D-glucopyranoside was investigated using deuterium-labelled acetates and sequential mass spectrometry. Loss of the substituent at C(l), the anomeric carbon, yields an ion of m/z 331, [C,,H,,O,]+. This ion further dissociates via two pathways, the first including m/z 271, [C,,H,,O,]+, 169, [C8H,0,]+ and 109, [C6HS02]+, and the second including m/z 211, [CloHllOS]*, 169, [C,H,O,I+ and 127 [C,H,O,]+. The first path proceeds via loss of acetate at C( 3), followed by a single-step concerted loss of acetates from C(2) and C(4), and ending with loss of acetate from C(6). The second path proceeds predominantly via loss of acetates from C(3) and C(4), elimination of ketene from the C(Z)-acetate and finally loss of ketene from the acetate at C(6). This path is also characterized by an illdefined series of parallel decomposition reactiowholving acetates from other sites on the molecule. At low collision energy, and in the absence of collision gas (unimolecular reaction conditions), the former pathway predominates; m/z 331 dissociates via loss of acetate at C(3), followed by a single-step concerted loss of acetates from C(2) and C(4).

Time course of hepatic gluconeogenesis during hindlimb suspension unloading

“…However, even if one ignores isomerism from the location of the double bond, there exist several isobaric structures for m / z 169. Acetate groups can be found on each of the C2, C3, C4 or C6 positions of the carbohydrate ring (Biemann et al 1963; Guevremont et al 1990). Wright and colleagues showed in his isotope labelling experiments (Guevremont et al 1990) that 16 different isobaric species are represented by the m / z 169, and about 30% of these ions were formed via hydrogen shift from acetate to the carbohydrate ring.…”

“…Acetate groups can be found on each of the C2, C3, C4 or C6 positions of the carbohydrate ring (Biemann et al 1963; Guevremont et al 1990). Wright and colleagues showed in his isotope labelling experiments (Guevremont et al 1990) that 16 different isobaric species are represented by the m / z 169, and about 30% of these ions were formed via hydrogen shift from acetate to the carbohydrate ring. Competitive fragmentation pathways that lead to the formation of m / z 169 occur also in accordance with other studies that have investigated a dissociation behaviour of peracetylated carbohydrates (Biemann et al 1963; Kulkarni et al 1985).…”

Anomeric distinction and oxonium ion formation in acetylated glycosides

“…It has been proposed that favored acetic acid loss in ionized peracetylated hexoses involves the acetyl group at C 3 and one of the adjacent hydrogen atoms at C 4 or C 5 . 22 This could explain the absence of an ion at m/z 271 in the CID spectra of [M C NH 4 ]…”

Carbohydrate analysis of hemicelluloses by gas chromatography–mass spectrometry of acetylated methyl glycosides

“…The glucose derivative (methyl 2,3,4,6-tetra-O-acetyl-D-glucopyranoside) exhibits a relatively strong signal at m/z 243 (mass spectrum not shown). This ion has previously been assigned to the consecutive loss of methyl formate and an acetoxy radical, as supported by deuterium labeling [13,20,24]. The mass shifts observed here in the spectra of methyl 2,3,4,6-tetra-O-acetyl-D-glucopyranoside-13 C 6 (m/z 243 to m/z 248) and methyl 2,3,4,6-tetra-O-acetyl-D-glucopyranoside-13 C 1 (m/z 243 unchanged) were in complete agreement with this previous assignment.…”

“…The electron impact-induced fragmentation of similarly derivatized monosaccharide compounds was studied as early as 1963 by Biemann et al and was later studied in detail by collision-induced fragmentation and theoretical methods [13,15,[20][21][22][23][24]. The interpretation of the spectra is rather difficult due to the fact that the signals for the molecular ion and the first fragments are typically of very low intensity.…”