Targeted allylation and propargylation of galactose-containing polysaccharides in water

Galactose units of spruce galactoglucomannan (GGM), guar galactomannan (GM), and tamarind (galacto)xyloglucan (XG) were selectively allylated. Firstly aldehyde functionalities were formed at the C-6 position via enzymatic oxidation by galactose oxidase. The formed aldehydes were further derivatized by an indium mediated Barbier–Grignard type reaction, resulting in the formation of homoallylic alcohols. In addition to allylic halides, the same reaction procedure was also applicable for GGM, when using propargyl bromide as halide. All reaction steps were done in water, thus the polysaccharides were modified in a one-pot reaction. The formation of the allylated, or propargylated, product was identified by MALDI-TOF–MS. All polysaccharide products were isolated and further characterized by GC–MS or NMR spectroscopy. By this chemo-enzymatic process, we have demonstrated a novel method for derivatization of GGM and other galactose-containing polysaccharides. The derivatized polysaccharides are potential platforms for further functionalizations.

► A novel method for allylation of galactose containing polysaccharides is presented.
► Selective derivatization by enzymatic oxidation and indium mediated allylation.
► All reaction steps are performed in plain water.
► First report of characterization by MALDI–MS of derivatized galactoglucomannans.