Water-based carbodiimide mediated synthesis of polysaccharide-amino acid conjugates: Deprotection, charge and structural analysis

Fazilet Gürer; Rupert Kargl; Matej Bračič; Damjan Makuc; Martin Thonhofer; Janez Plavec; Tamilselvan Mohan; Karin Stana Kleinschek

doi:10.1016/j.carbpol.2021.118226

Water-based carbodiimide mediated synthesis of polysaccharide-amino acid conjugates: Deprotection, charge and structural analysis

Carbohydr Polym. 2021 Sep 1:267:118226. doi: 10.1016/j.carbpol.2021.118226. Epub 2021 May 20.

Authors

Fazilet Gürer¹, Rupert Kargl², Matej Bračič¹, Damjan Makuc³, Martin Thonhofer⁴, Janez Plavec⁵, Tamilselvan Mohan⁶, Karin Stana Kleinschek⁷

Affiliations

¹ Laboratory for Characterisation and Processing of Polymers, Faculty of Mechanical Engineering, University of Maribor, Smetanova Ulica 17, 2000 Maribor, Slovenia.
² Institute of Chemistry and Technology of Biobased System (IBioSys), Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria; Institute of Automation, Faculty of Electrical Engineering and Computer Science, University of Maribor, Koroška cesta 46, 2000 Maribor, Slovenia.
³ Slovenian NMR Centre, National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia.
⁴ Institute of Chemistry and Technology of Biobased System (IBioSys), Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria.
⁵ Slovenian NMR Centre, National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia; EN-FIST Centre of Excellence, Trg OF 13, SI-1000 Ljubljana, Slovenia; Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia.
⁶ Laboratory for Characterisation and Processing of Polymers, Faculty of Mechanical Engineering, University of Maribor, Smetanova Ulica 17, 2000 Maribor, Slovenia; Institute of Chemistry and Technology of Biobased System (IBioSys), Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria. Electronic address: tamilselvan.mohan@tugraz.at.
⁷ Institute of Chemistry and Technology of Biobased System (IBioSys), Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria; Institute of Automation, Faculty of Electrical Engineering and Computer Science, University of Maribor, Koroška cesta 46, 2000 Maribor, Slovenia. Electronic address: karin.stanakleinschek@tugraz.at.

PMID: 34119179
DOI: 10.1016/j.carbpol.2021.118226

Abstract

We report here a one-step aqueous method for the synthesis of isolated and purified polysaccharide-amino acid conjugates. Two different types of amino acid esters: glycine methyl ester and L-tryptophan methyl ester, as model compounds for peptides, were conjugated to the polysaccharide carboxymethylcellulose (CMC) in water using carbodiimide at ambient conditions. Detailed and systematic pH-dependent charge titration and spectroscopy (infrared, nuclear magnetic resonance: ¹H, ¹³C- DEPT 135, ¹H- ¹³C HMBC/HSQC correlation), UV-vis, elemental and ninhydrin analysis provided solid and direct evidence for the successful conjugation of the amino acid esters to the CMC backbone via an amide bond. As the concentration of amino acid esters increased, a conjugation efficiency of 20-80% was achieved. Activated charcoal aided base-catalyzed deprotection of the methyl esters improved the solubility of the conjugates in water. The approach proposed in this work should have the potential to tailor the backbone of polysaccharides containing di- or tri-peptides.

Keywords: Amino acids; Carbodiimide; Charges; Conjugates; Deprotection; NMR; Polysaccharide.

MeSH terms

Carbodiimides / chemistry*
Carboxymethylcellulose Sodium / analogs & derivatives*
Carboxymethylcellulose Sodium / chemical synthesis
Glycine / analogs & derivatives*
Glycine / chemical synthesis
Indicators and Reagents / chemistry*
Molecular Structure
Tryptophan / analogs & derivatives*
Tryptophan / chemical synthesis

Substances

Carbodiimides
Indicators and Reagents
Tryptophan
Carboxymethylcellulose Sodium
Glycine