moved from the reaction mixture. Recently, a reaction system was reported in which
the byproducts from lipase-catalyzed sugar ester synthesis were removed by azeo-
tropic distillation using ethyl methyl ketone (for water) or acetone (for methanol) at
‘lipase-friendly’ temperatures (Yan et al., 1999). The authors claimed this to be an
adjuvant-type process, as only 10 % of the solvent was present in the round-bottomed
flask, whereas 90 % was circulating through the condenser and Soxhlet extractor.
The authors believed that this method might be developed into a process that is
practicable on a large scale.
17.2.3 Lipase-mediated catalysis using hydrophobized sugars
The typical reaction scheme of glycolipid synthesis using alkyl-glycosides for the
fatty acid acylation is shown in Figure 2. In order to bypass the problems of low
solubility of mono- and disaccharides in nonpolar organic solvents and those of
their high melting points, Bjo ̈rkling et al. (1989) first recommended hydrophobiza-
tion of the carbohydrates prior to lipase-catalyzed acylation. Besides 1-O-ethyl-D-
glucoside, the synthesis worked well withn-propyl,iso-propyl, butyl,iso-butyl, and
even with phenyl glucoside. Fatty acids were in the range of C8:0to C18 : 0or C18 : 1,
and also with C22 : 1. In addition, the reaction was performed at reduced pressure and
under solvent-free conditions. Using lipase B fromCandida antarctica, more than
95 % yield of the 6-O-monoester could be obtained. The transfer of the process to
pilot plant scale caused no major problems, and a production in 20-kg scale was set
370 17 Enzymatic Synthesis and Modification of Glycolipids
Figure 2. Scheme of the lipase-catalyzed synthesis of ethyl-b-D-glucoside 6–O-monooctadecanoate.