In the above-mentioned examples, the regioselective removal of fatty acids was
achieved using hydrolysis reactions, but alcoholysis reactions may be used for the
same purpose. For example, in the synthesis of lysophospholipids, alcoholysis in
pure alcohol (ethanol or other short-chain alcohols) was carried out usingRhizomu-
cor mieheilipase as catalyst (Sarney et al., 1994). The reaction was regioselective for
thesn-1 position, and a conversion of more than 98 % was achieved. In order to
prepare the other regioisomer, 1-acyl-lysophosphatidylcholine, acyl migration
was induced by ammonia vapors (Sarney et al., 1994) (Figure 6).
14.5 Esterification reactions for the incorporation
of fatty acids into lipids
14.5.1 Lipase-catalyzed esterification
Esterification of glycerophosphate
Glycerophosphate constitutes a basic building block for glycerophospholipids. For
the synthesis of the natural isomers, puresn-3-glycerophosphate should be used as
substrate unless the enzymatic reactions are stereoselective enough to involve only
the natural enantiomer. When an enantiomerically pure product is not needed, ra-
cemic glycerophosphate may be used as starting material.
Glycerophosphate is a highly polar compound, and the reaction to couple it en-
zymatically to hydrophobic fatty acids is not straightforward. The reaction was first
reported using Lipozyme in a solvent-free system with free fatty acid as acyl donor.
The monoacylation product, lysophosphatidic acid (LPA), was obtained in moderate
yield (32 %) and small amounts of the diacylation product, phosphatidic acid, were
also formed (Han and Rhee, 1995). The yield of LPA (containing caproic acid) was
increased to 45 % when the water activity of the solvent-free reaction mixture was
maintained at 0.18 by the introduction of a suitable salt hydrate pair in the headspace
of the reactor (Han and Rhee, 1998).
The use of fatty acid vinyl esters as acyl donors has proven quite favorable in the
acylation of glycerophosphate usingRhizopus arrhizuslipase as catalyst (Virto et al.,
1999). Vinyl esters are frequently used in transesterification reactions to make them
virtually irreversible. The vinyl alcohol formed as reaction product spontaneously
tautomerizes to acetaldehyde, thereby shifting the equilibrium position; hence it is
possible to achieve very high conversions. Vinyl laurate which was used for acyla-
14.5 Esterification reactions for the incorporation of fatty acids into lipids 297
Figure 6. Lipase-catalyzed alcoholysis of phosphatidylcholine. The lipase produces the 2-acyl-lyso-
phosphatidylcholine. In order to obtain the other regioisomer, 1-acyl-lysophosphatidylcholine, acyl mi-
gration was induced by ammonia vapor. (From Sarney et al., 1994.)