Synthesis of fluorescently labelled rhamnosides: probes for the evaluation of rhamnogalacturonan II biosynthetic enzymes

Three fluorescently labelled saccharides 10-12, representing structures found in pectic glycan rhamnogalacturonan II (RG-II), were synthesised by chemical glycosylation of O-6 of diacetone-d-galactose followed by deprotection and reductive amination with amino-substituted fluorophore APTS. This convenient method installs a common aminogalactitol-based tether in order to preserve the integrity of the reducing end of specific carbohydrates of interest. APTS-labelled glycans prepared in this manner were purified by carbohydrate gel electrophoresis and subjected to capillary electrophoresis analysis, as a basis for the subsequent development of high sensitivity assays for RG-II-active enzymes.