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. 2019 Oct 8;24(19):3617. doi: 10.3390/molecules24193617

Figure 3.

Figure 3

Representative MALDI-TOF-MS spectra of derivatized SL standards under different conditions using HOBt as catalyst. 2,3-SL (A–C) and 2,6-SL (D–F) incubated for 1 h at 37 °C in ethanol, with EDC and HOBt, at native (B,E) low (A,D) or high (C,F) pH. Lactonized reaction product: [M + Na]+ = 638.190 Da, ethyl esterified reaction product: [M + Na]+ = 684.232 Da. *: reaction product derived from misconversion of the standard (i.e., ethyl esterification of 2,3-SL or lactonization of 2,6-SL), standard impurity (reported purity: ≥98%), or a combination thereof. Symbols indicate the monosaccharide residues glucose (blue circle), galactose (yellow circle), and N-acetylneuraminic acid (purple diamond). In case of derivatized sialic acids, an α2,3-linkage is indicated by a left angle, an α2,6-linkage by a right angle, while non-derivatized sialic acids are depicted without an angle. Note: mass spectra are main peak normalized.