| Summary: | 博士 === 國立臺灣大學 === 化學系研究所 === 86 === AbstractDisaccharides and linear oligosaccharides were labeled with p-aminobe
nzoic ethyl ester (ABEE) chromophore and analyzed by on-line coupling of high
performance liquid chromatography (HPLC)/negative ion electrospray mass spectr
ometry (ESIMS). The formation of glycosylamines rather than reductive aminati
on in labeling reaction produced many characteristic fragment ions under in-so
urce collision-induced dissociation (CID). These ions provided unambiguous as
signment of the position of the glycosidic linkages.
This approach was extend
ed to the analysis of linkages as well as the sequence of the linkages of seve
ral linear oligosaccharides. Additionally, anomeric
configuration of ABEE-lab
eled 1-3, 1-4 and 1-6-linked glucose disaccharides could be differentiated acc
ording to the relative abundance of characteristic ions. Semiempirical cacula
tions and comformation analysis support the experimental data which suggest th
at the terminal sugar of b-form 1-4-linked disaccahrides can be determined by
the relative intensity of m/z 263 and m/z 221 ion. Disaccharides tagged with
p-aminobenzoic acid (ABA) chromophore were separated by capillary electrophore
sis (CE) and successfully on-line detected with negative ion ESI/MS/MS. Two e
lectrolyte systems were employed for the separation of the derivatized disacch
arides. The best results of analyzing linkage isomers was obtained by using 5
0 mM NH4OAc containing 10 mM a-CD adjusted to pH 5.5, while 10 mM borate at pH
10.0 provided the best result for the analysis of disaccharides with differen
t monosaccharide composition and anomeric configuration. In general, the link
age-specific ions of the ABA-labeled disaccharides in the MS/MS spectra were s
imilar to that of the ABEE-derivatives in-source CID mass spectra. However, u
nlike the use of intensity ratio in in-source CID mass spectra of ABEE-labeled
disaccharides, anomeric configuration of ABA-labeled 1-4 and 1-6-linked disac
charides could be differentiated according to the presence or absence of the p
eak at m/z 221 in product ion mass spectra. Deuterium labeling in combination
with sequential tandem mass spectrometry were used to explore the mechanism o
f fragmentation of the chromophore-labeled disaccharides under CID. The multi
ple peaks with different number of deuterium atom suggested that the same m/z
fragment ion of nondeuterium-labeled disaccharide could be produced through mu
ltiple reaction pathways. Carbonyl migration in combination with retro-aldol
fragmentation or charge induced dissociation could rationalize the formation o
f the major fragment ions. Other fragmentation paths were also postulated to
explain the formation of the minor ions adjacent to the major one.
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