Synthesis of novel oligomeric anionic alkyl glycosides using laccase/TEMPO oxidation and cyclodextrin glucanotransferase (CGTase)-catalyzed transglycosylation

Modification of alkyl glycosides, to alter their properties and widen the scope of potential applications, is of considerable interest. Here, we report the synthesis of new anionic alkyl glycosides with long carbohydrate chains, using two different approaches: laccase/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation of a long-carbohydrate-chain alkyl glycoside and cyclodextrin glucanotransferase (CGTase)-catalyzed elongation of anionic alkyl glycosides. The laccase/TEMPO oxidation of dodecyl beta-D-maltooctaoside proceeded efficiently with the formation of aldehyde and acid products. However, depolymerization occurred to a large extent, limiting the product yield and purity. On the other hand, CGTase-catalyzed coupling/disproportionation reactions with alpha-cyclodextrin and dodecyl beta-D-maltoside diuronic acid (DDM-2COOH) or octyl beta-D-glucuronic acid (OG-COOH) as substrates gave high conversions, especially when the CGTase Toruzyme was used. It was found that pH had a strong influence on both the enzyme activity and the acceptor specificity. With non-ionic substrates (dodecyl beta-D-maltoside and octyl beta-D-glucoside), Toruzyme exhibited high catalytic activity at pH 5-6, but for the acidic substrates (DDM-2COOH and OG-COOH) the activity was highest at pH 4. This is most likely due to the enzyme favoring the protonated forms of DDM-2COOH and OG-COOH, which exist at lower pH (pKa about 3).

Automated summary

The study focuses on the synthesis of new anionic alkyl glycosides with long carbohydrate chains using laccase/TEMPO oxidation and CGTase catalysis approaches. The efficiencies and product stabilities of the two methods varied, with laccase/TEMPO oxidation showing depolymerization issues, while CGTase catalysis yielding high conversions especially when using Toruzyme. pH was found to have a strong influence on enzyme activity and acceptor specificity, with optimal pH ranges differing for non-ionic and acidic substrates.