Chemoenzymatic synthesis and pH-responsive properties of amphoteric block polysaccharides

Abstract

Here, we investigated the chemoenzymatic synthesis of α(1→4)-linked amphoteric block polysaccharides. Amylouronic acid as an acidic block was first synthesized by 2,2,6,6-tetramethylpiperidine 1-oxyl-mediated oxidation of a water-soluble amylose (chemical reaction). A short maltooligosaccharide chain, serving as an initiating site for the following enzymatic polymerization, was then introduced at the nonreducing end of the product by thermostable α-glucan phosphorylase-catalyzed enzymatic oligomerization of α-d-glucose 1-phosphate. Finally, thermostable α-glucan phosphorylase-catalyzed enzymatic polymerization of α-d-glucosamine 1-phosphate from the produced primer provided a basic block at the nonreducing end, leading to the desired amphoteric block polysaccharides. The structures of the products at each step were determined by (1)H NMR analysis. Furthermore, amphoteric products exhibited specific inherent isoelectric points (pIs). When the pH-responsive properties in aqueous solutions were evaluated using a divalent acid and base, similar hierarchical assembling/disassembling processes were observed by shifting the pH values from the pI to both the acidic and basic pH.

α-Glucan Phosphorylase-Catalyzed Enzymatic Reactions Using Analog Substrates to Synthesize Non-Natural Oligo- and Polysaccharides

“…The thermostable GP-catalyzed enzymatic copolymerizations of Glc-1-P with GlcN-1-P, and with Man-1-P, have successfully progressed under the conditions of removal of Pi in ammonia/MgCl 2 buffer to obtain non-natural glucosaminoglucan comprising Glc/GlcN units and mannoglucan composed of Glc/Man units [60,61]. The thermostable GP-catalyzed enzymatic polymerization of GlcN-1-P using maltooligosaccharide-functionalized amylouronic acid (amylouronic acid with a short α(1→4)-linked Glc chain at the non-reducing end) as the primer under the same operation yielded an amylose analog amphoteric block polysaccharide composed of GlcN and GlcA chains ( Figure 7) [62]. The product showed pH-responsive properties.…”