GLYCOSIDES IN Viola Tricolor L.

CHAPTER 2: INTRODUCTION
Figure 2.5: Fragment nomenclature commonly appliedforfor flavonoid glyco-
sidesand aglycones.
nect to the aglycone, therefore the numbering starts at the C-glycosyl moiety
[96]. In addition, for C,O-glycosides, the Y0 or Z0 ions represent fragments,
resulting from the loss of the C-glycosyl moiety.
Fragments Bi andYi areobserved both inpositive andnegativeion spectra,
andaregeneratedthroughthecleavageoftheglycosidicbondwithretentionof
the glycosidic oxygene atom by the fragments containing the aglycone. In pos-
itive ion mode, Bi and Yj result from the protonation and subsequent cleavage
oftheglycosidicbondoralternativelyfromthecleavageoftheglycosidicbond
accompanied by a protontransfer (Fig. 2.6a) [95]. In the negative ion mode,
this fragmentation follows a more complex pathway. There the deprotonated
molecular ion undergoes epoxide formation accompanied by the opening of
the sugar ring, the cleavage of the glycosidic bond, and a competitive proton-
transfer(Fig.2.6b)[97]. Inaddition,theglycosidicbondcanalsofragmentwith
the retention of the glycosidic oxygene by the carbohydrate fragment without
aglycone yielding the Ci and Zj ions. In the negative ion mode the deproto-
nated sugar ring undergoes epoxide formation resulting in the cleavage of the
glycosidic bond. This process is also accompanied by protontransfer reactions
(Fig. 2.6c). The formation of Zjin the positive ion mode, however, is a two
step process involving a loss of water molecule from the corresponding Yj ion
(Fig. 2.6d)[98].
Productionsgeneratedthroughthecleavagesofthesugarring’sC–Cbonds
are labeled with k,l Ai and k,l Xj, where k and l indicate the broken sugar ring
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