Lipase-catalyzed regioselective acylation of sucrose in two-solvent mixtures

The enzymatic synthesis of 6-O-lauroylsucrose and 6-O-palmitoylsucrose was performed by transesterification of sucrose with the corresponding vinyl esters in a medium constituted by two solvents. More specifically, the acylation was carried out in 2-methyl-2-butanol (tert-amyl alcohol) containing a low percentage (not higher than 20%) of dimethyl sulfoxide. Several lipases were able to catalyze the transesterification, but that from Humicola lanuginosa (adsorbed on diatomaceous earth) was particularly useful. We optimized the synthesis of 6-O-lauroylsucrose varying the percentage and nature of the cosolvent, the molar ratio sucrose/vinyl laurate, the nature of bulk solvent and the enzyme content. Under the best conditions (2-methyl-2-butanol/DMSO 4:1 v/v), a sucrose conversion of 70% to 6-O-lauroylsucrose was achieved in 24 h using 50 mg biocatalyst/mL. As a side process, a low percentage (<5% in 24 h) of the initial sucrose is converted into the diesters 6,1'-di-O-lauroylsucrose and 6,6'-di-O-lauroylsucrose. The above methodology was also extended to the synthesis of 6-O-palmitoylsucrose. The acylation process was even faster, giving rise to an 80% conversion to monoester in 48 h using 25 mg biocatalyst/mL. This study shows that the use of two-solvent mixtures may become a feasible alternative for the synthesis of sucrose esters, allowing to exploit the catalytic potential of lipases.