Hydroxyapatite as an Enzyme Carrier in Continuous-Flow Biocatalysis: An Improved Synthesis of γ-Glutamyl Derivatives

Biocatalysis has proved to be of great importance to pursue a more sustainable production of fine chemicals, and enzyme immobilization is a crucial tool to achieve this goal. In this work, hydroxyapatite, an eco-friendly material, was used as a support for the immobilization of a gamma-glutamyltransferase from Escherichia coli, an enzyme that catalyzes the synthesis of bioactive gamma-glutamyl derivatives, exploiting the noncovalent interactions between the support and the enzyme. After screening the immobilization conditions, the storage (up to 90 days) and the thermal stability (50 degrees C) of the obtained immobilized biocatalyst were studied, as well as its reuse in up to 10 consecutive reactions of gamma-glutamylation of S-allyl-l-cysteine, to give gamma-l-glutamyl-S-allyl-l-cysteine (3), a flavor enhancer occurring in garlic extract. Finally, the immobilized enzyme was used to prepare a packed-bed reactor and 3 was synthesized under continuous-flow conditions improving both the productivity (from 19.4 to 35.1 mu mol & centerdot;h-1) and the space-time yield (9.7 vs 381 mu mol & centerdot;h-1 & centerdot;mL-1) of the reaction.