up in order to prepare material for application tests (Andresen and Kirk, 1995). One
disadvantage for economic purposes could be that selective removal of the protecting
group is difficult.
Table 3 provides an overview of studies performed by other groups in this field.
Two special reactions deserve mention: a new type of cationic surfactant, 6-O-
monoester of 3-(trimethylammonio)-propyl-D-glucopyranoside, was prepared in
high yields by a chemo-enzymatic synthesis. For instance, to introduce dodecanoic
acid into the 6–position of 1-protected glucose,C. antarcticalipase B was used
successfully in a solvent-free system at 75 8 C with 90 % conversion (Kirk et al.,
1998). In another study using porcine pancreatic andC. antarcticalipase B, the
ring-opening polymerization of bothe-caprolactone (e-CL) and of trimethylene car-
bonate (TMC) by the multifunctional ethyl glucopyranoside (EGP) was catalyzed
and resulted in the formation of EGP-oligo(e-CL) and EGP-oligo(TMC) conjugates
with molecular weights up to 7200 Da.
Besides the 1-O-alkyl glycosides, isopropylidene, benzylidene and phenyl(butyl)
boronic acid are especially suitable protectional agents for sugars. The advantage is
their facile removal from the carbohydrate after successful enzymatic acylation. In
contrast to the ester linkage between the fatty acid and the sugar, the acetalic and
boronic acid protection groups can be removed selectively by trifluoroacetic acid or
mild acetone (or methanol)/water hydrolysis, respectively (Figure 3). Some studies
based on these approaches are presented in Table 4. For example, Ward et al. (1997)
investigated theRhizomucor mieheilipase-catalyzed synthesis of a sugar ester con-
taining arachidonic acid. When the fatty acid to 1,2–O-isopropylidene-D-xylofur-
anose ratio was 1–2 : 1, a maximum conversion of 84 % was obtained. After down-
stream processing, the chemical structure was confirmed to be xylose 5-arachido-
nate. A new chemo-enzymatic approach to the preparation of dimeric (gemini) sugar
fatty acid esters has been developed by Gao et al. (1999). First, lipases (Candida
antarctica,Rhizomucor miehei) catalyzed the monoacylation (6- or 6’-OH) of acet-
372 17 Enzymatic Synthesis and Modification of Glycolipids
Figure 3. Scheme of the lipase-mediated synthesis of sugar ester from isopropylidene-D-xylofuranose
and fatty acid.