Enzymatic synthesis and polymerisation of β-mannosyl acrylates produced from renewable hemicellulosic glycans

Abstract

We show that glycoside hydrolases can catalyse the synthesis of glycosyl acrylate monomers using renewable hemicellulose as a glycosyl donor, and we also demonstrate the preparation of novel glycopolymers by radical polymerisation of these monomers. For this, two family 5 β-mannanases (TrMan5A from Trichoderma reesei and AnMan5B from Aspergillus niger) were evaluated for their transglycosylation capacity using 2-hydroxyethyl methacrylate (HEMA) as a glycosyl acceptor. Both enzymes catalysed conjugation between manno-oligosaccharides and HEMA, as analysed using MALDI-ToF mass spectrometry (MS) as an initial product screening method. The two enzymes gave different product profiles (glycosyl donor length) with HEMA, and with allyl alcohol as acceptor molecules. AnMan5A appeared to prefer saccharide acceptors with lower intensity MS peaks detected for the desired allyl and HEMA conjugates. In contrast to AnMan5A, TrMan5A showed pronounced MS peaks for HEMA-saccharide conjugation products. TrMan5A was shown to catalyse the synthesis of β-mannosyl acrylates using locust bean gum galactomannan or softwood hemicellulose (acetyl-galactoglucomannan) as a donor substrate. Evaluation of reaction conditions using galactomannan as a donor, HEMA as an acceptor and TrMan5A as an enzyme catalyst was followed by the enzymatic production and preparative liquid chromatography purification of 2-(β-manno(oligo)syloxy) ethyl methacrylates (mannosyl-EMA and mannobiosyl-EMA). The chemical structures and radical polymerisations of these novel monomers were determined using 1H and 13C NMR spectroscopy and size-exclusion chromatography. The two new water soluble polymers have a polyacrylate backbone with one or two pendant mannosyl groups per monomeric EMA unit, respectively. These novel glycopolymers may show properties suitable for various technical and biomedical applications responding to the current demand for functional greener materials to replace fossil based ones.