Collision-induced decompositions of metal-cationized methyl-6-deoxy-6-bromo-α-D-glucopyranoside derivatives

Tandem mass spectra of ammonium ion, metal ion and ligated metal ion adducts of acyclic sugar derivatives

The tandem mass (MS/MS) spectra of ammonium ion, metal ion and ligated metal ion adducts of chain-extended acyclic nitro-containing deoxyglucose and deoxygalactose derivatives have been studied. The ammonium adducts fragment primarily by elimination of ammonia followed by acetic acid, thus not giving much structural information. In contrast, cationization of these compounds by metal ions and ligated metal ions gave structurally informative and useful fragment ions on MS/MS. The metal ions and ligated metal ions play an important role in controlling and directing fragmentation. Retro-aldol fragmentation is facilitated by metal ions such as Li(+), Na(+), Ag(+) and Cu(+), whereas the adducts with higher alkali metal ions such as Rb(+) and Cs(+) fragment to give only the corresponding metal ions. The divalent metal ions such as Cu(2+) and Ba(2+) also induce retro-aldol fragmentation. However, the charge is carried by the aldehyde fragment in the case of Cu(2+) adducts, whereas the nitroalkane fragment carries the charge in the case of Ba(2+) adducts. Ligated metal ions such as ZnCl(+), CuCl(+), InCl(2) (+) and BaCl(+) also behave similarly and induce retro-aldol fragmentation in these acyclic sugars. Both the metal ion and ligated metal ion adducts can fragment by elimination of metal-containing neutral molecules.

Effect of metal cationization on the low-energy collision-induced dissociation of loganin, epi-loganin and ketologanin studied by electrospray ionization tandem mass spectrometry

The effect of alkali metal and silver cationization on the collision-induced dissociation (CID) of loganin (1), epi-loganin (2) and ketologanin (3) is discussed. Their protonated molecular ions fragment mainly by glycosidic cleavages. The epimeric pairs (1 and 2) show differences in the abundances of the resulting fragment ions. Lithium cationization induces new dissociation pathways such as the retro-Diels-Alder (RDA) fragmentation followed by rearrangement. Unlike the dissociation of protonated molecular ions, the dissociation of lithiated molecules also provides lithiated sugar fragments. The CID of dilithiated molecules is substantially different from that of the monolithiated precursors. RDA reaction appears to be favoured by the presence of the additional lithium atom in the molecule. In addition, other ring cleavages are also induced. The abundances of the various fragment ions are different in the CID spectra of the epimeric pairs. Extensive D labelling and (6)Li labelling experiments confirmed many of the ion structures proposed. The CID spectra of the sodiated ions are generally weaker, although similar to those of the corresponding lithiated species. Higher alkali metal ion (K(+), Rb(+) and Cs(+)) adducts generated only the corresponding metal ions as products of CID. Similar fragmentations were also observed in the CID of the [M + Ag](+) ions of these compounds, the epimeric pairs showing characteristic differences in their CID behaviour. Copyright 2000 John Wiley & Sons, Ltd.

Characterization of iridoids by fast atom bombardment mass spectrometry followed by collision-induced dissociation of

Fast atom bombardment mass spectra of a series of naturally occurring and synthetically modified iridoid glycosides were studied using lithium cationization and collision-induced dissociation of the resulting [M+Li]+ ions. Lithium cationization leads to the unambiguous determination of the molecular masses of these compounds. Collision-induced dissociation of the lithiated molecular ions give valuable structural information regarding the nature of the substituent on both the aglycone and the sugar moieties. The characteristic fragmentation pathways identified are (1) elimination of neutral molecules comprising the substituents on either the aglycone or sugar moieties, (2) formation of lithiated aglycone and their fragment ions, (3) formation of lithiated sugar and their fragment ions, (4) fragmentation corresponding to the cleavage of the aglycone or sugar ring and (5) fragmentation characteristic of the substituents present in either the aglycone or sugar parts of the molecule. Elimination of two acyloxy radicals from the lithiated molecular ion is a characteristic fragmentation in the case of acyloxy derivatives.