High-yield syntheses of ethyl and 2-fluoroethyl β-d-galactopyranosides using Streptococcus thermophilus β-galactosidase

Synthesis of alkylgalactosides using whole cells of Bacillus pseudofirmus species as catalysts

Whole cells of alkaliphilic Bacillus pseudofirmus AR-199, induced for beta-galactosidase activity, were used for the synthesis of 1-hexyl-beta-d-galactoside and 1-octyl-beta-d-galactoside, respectively, by transglycosylation reaction between lactose and the corresponding alcohol acceptor. The product yield was strongly influenced by the initial water content in the reaction mixture. Water content of 10% (v/v) was optimal providing 3.6-36 mM hexyl galactoside from 10 to 150 mM lactose, and no secondary product hydrolysis. Product yield could be enhanced by supplementing the reaction mixture with more cells or partly replacing the product with fresh substrate, but was decreased with time to the initial equilibrium level. Cell permeabilisation or disruption resulted in increased reaction rate and higher product yield but was followed by product hydrolysis. Octyl galactoside synthesis using whole cells was optimal at water content of 2% (v/v) with a yield of 26%. The cells were immobilised in cryogels of polyvinyl alcohol for use in continuous process, where hexyl galactoside was produced with a constant yield of 50% from 50mM lactose for at least a week.

Use of the yeast Hansenula polymorpha (Pichia angusta) to remove contaminating sugars from ethyl β-d-fructofuranoside produced during sucrose ethanolysis catalysed by invertase

Alkyl glycosides are interesting intermediates for the production of biodegradable surfactants. Synthesis of ethyl beta-d-fructofuranoside by invertase-catalysed ethanolysis of sucrose has been extensively reported in literature. However, this procedure yields mixtures of glucose, fructose, sucrose and ethyl beta-d-fructofuranoside. Purification of ethyl beta-d-fructofuranoside from such mixtures by chromatographic methods is laborious, difficult to scale up and requires organic solvents. The yeast Hansenula polymorpha grows rapidly on glucose, fructose and sucrose. Sucrose hydrolysis in this yeast is catalysed by an intracellular alpha-glucosidase ('maltase'); consequently, H. polymorpha should be unable to hydrolyse ethyl beta-d-fructofuranoside. Indeed, aerobic cultivation of H. polymorpha on sugar mixtures obtained by invertase-catalysed ethanolysis of sucrose resulted in the complete removal of contaminating sugars, leaving ethyl beta-d-fructofuranoside as the sole organic compound in culture supernatants. Pure ethyl beta-d-fructofuranoside was recovered from the supernatants by mixed-bed ion exchange chromatography with an 86% yield.