Intermediates of thiamine catalysis immobilized on silica surface as active biocatalysts for α-ketoacid decarboxylation

Thiamine-dependent enzymes catalyse the decarboxylation of alpha-ketoacids, by both non-oxidative and oxidative mechanisms. Based on the ability of thiamine-cofactor to catalyse itself the decarboxylation of pyruvate to some extent, we have immobilized on a silica surface two 'active aldehyde' intermediates of thiamine catalysis, 2-alpha-hydroxybenzyl-thiamine pyrophosphate (HBTPP) and 2-alpha-hydroxyethyl-thiamine pyrophosphate (HETPP). The two intermediates have been tethered by a convenient method on silica support via their phosphate groups providing the covalently heterogenised biomolecules [HBTh-OP2O6-SiO3/2](n)center dot xSiO(2), and [HETh-OP2O6-SiO3/2](n)center dot xSiO(2). These bio-composite materials have been evaluated as catalysts for pyruvate and benzoyl-formate decarboxylation in either the presence or not of an aldehyde additive. Our data show that they are stable, very effective and recyclable catalysts for the production of 2-hydroxy-ketones, acetoine and benzoin. Their catalytic behavior is much better than the corresponding behavior of the homogeneous thiamine-systems due to the selected immobilization mode which bears similarities to that of the thiamine-cofactor binding to the protein. Considering our results, possible catalytic pathways of the prepared bio-composite materials are suggested. (C) 2006 Elsevier B.V. All rights reserved.