Regioselective glycosylation of hydroquinone to alpha-arbutin by cyclodextrin glucanotransferase from Thermoanaerobacter sp.

Hydroquinone glycosides were produced by transglycosylation reactions catalyzed by cyclodextrin glucanotransferase (CGTase) from Thermoanaerobacter sp. (Toruzyme (R) 3.0L). The reactions were carried out in an aqueous system containing hydroquinone (HQ) and maltodextrin as acceptor and donor substrate molecules respectively. The conditions for the synthesis of hydroquinone glucoside (alpha-arbutin) were 9 mM hydroquinone, maltodextrin (5%, w/v) in 20 mM citrate phosphate buffer, pH 5.5 and 0.025 mg/ml toruzyme at 40 degrees C for 24 h. The transfer efficiency of hydroquinone glycosylation was 31.8% and 29.2% respectively, when alpha-cyclodextrin and maltodextrin were employed as donor substrates. The major glycoside product was identified as hydroquinone-1-O-alpha-D-glucopyranoside (alpha-arbutin) on the basis of mass spectrometric, nuclear magnetic resonance analysis and component analysis of its enzymatic hydrolysates. The highest molar yield of alpha-arbutin (21.2%) was obtained when alpha-cyclodextrin was used as the donor substrate. A two step enzymatic reaction system comprising of CGTase and amyloglucosidase helped to attain a molar yield of 30% for alpha-arbutin. At room temperature the solubility of alpha-arbutin in water was determined to be 12.8 g/100 ml which is approximately 1.8 fold higher than that of hydroquinone. (C) 2013 Elsevier B.V. All rights reserved.