Mannose was labelled with anthranilic acid (2-aminobenzoic acid) (2AA) through a Maillard reaction similarly to already reported [11] (link). Briefly, 6 mg of anthranilic acid (2AA) was dissolved in 100 µL of dimethyl sulfoxide: acetic acid (7:3, v: v) containing 1 M of sodium cyanoborohydride (NaBH 3 CN). Then, mannose (25.2 mg) was dissolved in the previously prepared solution. The resulting mixture was vigorously vortexed at maximum speed (Fisherbrand, USA), protected from light, and incubated for 12 h at 37 °C. After this time, the labelled mannose was diluted in acetate buffer, purified employing a cyano-modified silica gel-SPE column (Chromabond ® ), and lyophilized.
Proton nuclear magnetic resonance spectroscopy analysis ( 1 H-NMR) was conducted to confirm the labelling. For this purpose, fluorescently labelled mannose and unlabelled mannose were dissolved in deuterated water (D 2 O) obtained from Sigma Aldrich (St Louis, MO, USA) at 200 mM, while anthranilic acid was dissolved in deuterated dimethyl sulfoxide (DMSO-D6; Cambridge Isotope Laboratories, Inc. (Andover, MA, USA)) at the same concentration. The solutions were then placed in NMR tubes (600 µl) to be characterized using a Bruker NEO-750 equipment (Karlsruhe, Germany). (
Proton nuclear magnetic resonance spectroscopy analysis ( 1 H-NMR) was conducted to confirm the labelling. For this purpose, fluorescently labelled mannose and unlabelled mannose were dissolved in deuterated water (D 2 O) obtained from Sigma Aldrich (St Louis, MO, USA) at 200 mM, while anthranilic acid was dissolved in deuterated dimethyl sulfoxide (DMSO-D6; Cambridge Isotope Laboratories, Inc. (Andover, MA, USA)) at the same concentration. The solutions were then placed in NMR tubes (600 µl) to be characterized using a Bruker NEO-750 equipment (Karlsruhe, Germany). (
