Enhanced Synthesis of Alkyl Galactopyranoside by <i>Thermotoga naphthophila</i> β‑Galactosidase Catalyzed Transglycosylation: Kinetic Insight of a Functionalized Ionic Liquid-Mediated System

Abstract

Green synthesis is of pivotal importance for environmental sustainability. This work reports a novel approach to synthesize an array of alkyl galactopyranosides using thermophilic β-galactosidase from <i>Thermotoga naphthophila</i> RKU-10 (TN1577) as biocatalyst and milk processing waste lactose as galactosyl donor. Ammoeng 102 (only 2.5% addition of total reaction volume), a functionalized ionic liquid (IL) containing tetraaminum cation with C₁₈ acyl and oligoethylene glycol, is identified as the most promising one from a variety of structurally diverse ILs, affording a 2.37-fold increase in octyl galactopyranoside yield compared to the buffer system. Up to 18.2 g L^–1 octyl galactopyranoside could be produced in 7 h, which is significantly higher than any previous report in terms of time-space efficiency. Kinetic study and COSMO-RS <i>in silico</i> predictions elucidate that the thermophilic nature of TN1577 β-galactosidase, increased solubility of substrate, suppression of hydrolysis, and excellent biocompatibility of Ammoeng 102 with enzyme (allowing TN1577 β-galactosidase to perform optimal catalysis up to 95 °C) are the main driving forces. The general applicability of the Ammoeng 102 system is verified, by which a series of alkyl galactopyranosides are successfully synthesized with <i>n</i>-butanol to <i>n</i>-tetradecanol as alkyl acceptors and lactose as galactosyl donor