Biochemical Systematics and Ecology 96 (2021) 104262
6
De Simone et al., 1980, De Simone et al., 1981; Riccio et al., 1981, 1982;
Kicha et al., 2015). When identification was not possible, only molecular
masses are reported as a support for further investigations (Table 2). The
global results, i.e. merging all the animals, are summarized in Table 2
and Fig. 6.
Before starting to analyze the MS/MS, and based on the potential
structure of the m/z 921 ions, i.e. sepositoside A and the m/z 981 ions, i.
e. luzonicoside A reported in the literature (Fig. 1), it is important to
remind some dissociation rules that will be relevant to the present discussion. The negative charge is localized on the glucuronic acid group
attached on the sugar moiety. Therefore, all the expected collisioninduced dissociation (CID) processes must provide fragment ions containing the glycone moiety or part of the glycone moiety. The sugar
sequence in the oligosaccharide chains can be defined by following the
successive losses of the monosaccharide residues from the mass-selected
parent ions. Characteristic losses of 176 Da, 162 and 132 Da can be
associated to the presence of glucuronic acid, Galactose or Glucose and
arabinose residues, respectively. Consequently, characteristic fragment
ions from consecutive loss of sugar groups can provide information for
the distinction of different aglycone.
The ions at m/z 921.4455 and m/z 891.4354 were selected to HRESI- MS/MS analysis, in order to reconstruct the collision-induced
fragmentation pattern of the parent confirming that ions detected at
m/z 921.4455 and m/z 891.4354 correspond to the sepositoside A and
luzonicoside A, respectively (Fig. 4).
The HR-ESI-MS/MS mass spectrum for the ion detected at m/z
921.4455 in the oral body show two competitive dissociation pathways.
First, black lines in Fig.4 (A) and Fig. S2, demonstrate consecutive losses
of glucuronic acid, galactose residues and the aglycone part producing
ions detected at m/z 745.4136, 583.3608, and 185.0423, respectively.
This sequence of decomposition confirms the proposed sepositoisde A
(structure 2 in Fig. 6).
In the second fragmentation pathways, represented by a dotted black
line (Fig. 4 (A)), the fragmentation of the parent ions is initiated by the
loss of the aglycone moiety, as well as the occurrence of formal successive eliminations of the monosaccharide residues (glucuronic acid
and galactose). Ultimately, the fragmentation process leads to signals
detected at m/z 347.0951 and 185.0432 and unambiguously reveals the
presence of sepositoside A ions (Fig. S2).
The MS/MS spectrum of m/z 891.4354 detected upon ESI ionization
of the oral body wall extract shows the co-occurrence of two fragmentation pattern as m/z 921.4455 ions had did. The first fragmentation
Fig. 3. Comparison of the distribution and the relative intensity of the saponin ions (m/z) of the five selected organs (STO: stomach; CAE: pyloric caeca; GON:
gonads; OBW: oral body wall; ABW: aboral body wall) for males and females individuals collected at different seasons. In this diagram, the saponins are only
identified by their compositions with no distinction between isomeric saponins.
B. Dahmoune et al.
6
De Simone et al., 1980, De Simone et al., 1981; Riccio et al., 1981, 1982;
Kicha et al., 2015). When identification was not possible, only molecular
masses are reported as a support for further investigations (Table 2). The
global results, i.e. merging all the animals, are summarized in Table 2
and Fig. 6.
Before starting to analyze the MS/MS, and based on the potential
structure of the m/z 921 ions, i.e. sepositoside A and the m/z 981 ions, i.
e. luzonicoside A reported in the literature (Fig. 1), it is important to
remind some dissociation rules that will be relevant to the present discussion. The negative charge is localized on the glucuronic acid group
attached on the sugar moiety. Therefore, all the expected collisioninduced dissociation (CID) processes must provide fragment ions containing the glycone moiety or part of the glycone moiety. The sugar
sequence in the oligosaccharide chains can be defined by following the
successive losses of the monosaccharide residues from the mass-selected
parent ions. Characteristic losses of 176 Da, 162 and 132 Da can be
associated to the presence of glucuronic acid, Galactose or Glucose and
arabinose residues, respectively. Consequently, characteristic fragment
ions from consecutive loss of sugar groups can provide information for
the distinction of different aglycone.
The ions at m/z 921.4455 and m/z 891.4354 were selected to HRESI- MS/MS analysis, in order to reconstruct the collision-induced
fragmentation pattern of the parent confirming that ions detected at
m/z 921.4455 and m/z 891.4354 correspond to the sepositoside A and
luzonicoside A, respectively (Fig. 4).
The HR-ESI-MS/MS mass spectrum for the ion detected at m/z
921.4455 in the oral body show two competitive dissociation pathways.
First, black lines in Fig.4 (A) and Fig. S2, demonstrate consecutive losses
of glucuronic acid, galactose residues and the aglycone part producing
ions detected at m/z 745.4136, 583.3608, and 185.0423, respectively.
This sequence of decomposition confirms the proposed sepositoisde A
(structure 2 in Fig. 6).
In the second fragmentation pathways, represented by a dotted black
line (Fig. 4 (A)), the fragmentation of the parent ions is initiated by the
loss of the aglycone moiety, as well as the occurrence of formal successive eliminations of the monosaccharide residues (glucuronic acid
and galactose). Ultimately, the fragmentation process leads to signals
detected at m/z 347.0951 and 185.0432 and unambiguously reveals the
presence of sepositoside A ions (Fig. S2).
The MS/MS spectrum of m/z 891.4354 detected upon ESI ionization
of the oral body wall extract shows the co-occurrence of two fragmentation pattern as m/z 921.4455 ions had did. The first fragmentation
Fig. 3. Comparison of the distribution and the relative intensity of the saponin ions (m/z) of the five selected organs (STO: stomach; CAE: pyloric caeca; GON:
gonads; OBW: oral body wall; ABW: aboral body wall) for males and females individuals collected at different seasons. In this diagram, the saponins are only
identified by their compositions with no distinction between isomeric saponins.
B. Dahmoune et al.