which contain up to 50 % (w/w) of glycerol. The new compositions of matter ob-
tained in this way behave completely different from glycerol itself. Suspensions of
these materials in nonpolar organic solvents (e.g.n-hexane ort-BuOMe) react as if
the glycerol were dissolved homogeneously in these media. They are treated with the
corresponding acyl donor (saturated or unsaturated free fatty acid, fatty acid methyl
ester, fatty acid vinyl ester, triglycerides or natural fats and oils) and a variety of
lipases (Berger et al., 1992; Berger and Schneider, 1992; Schneider and Berger,
1992; 1993; Berger, 1993; Waldinger and Schneider, 1996). The acyl transfer reac-
tions proceed under these conditions smoothly and without problems, their progress
can be monitored conveniently by thin-layer chromatography (TLC).
On completion of the esterification, both the enzyme and the solid support can be
removed by simple filtration or centrifugation. After evaporation of the solvent, the
resulting glycerides were isolated in high yields and purified further, preferably by
recrystallization.
It is interesting to note that our proprietary method (Berger and Schneider, 1991;
1992; Schneider and Berger, 1992; 1993), i.e., the immobilization of glycerol onto a
solid support – the key to the solubility problem – and subsequent enzymatic ester-
ification is now used by several other researchers (Charlemange and Legoy, 1995;
Kwon et al., 1995; Castillio et al., 1997, Selmi et al., 1997; Stamatis et al., 1998;
Elfman-Borjesson and Ha ̈rro ̈d, 1999), a clear indication for the major breakthrough
which was achieved in the direct enzymatic acylation of glycerol.
6.4 Synthesis of regioisomerically pure
1,3-sn-diglycerides
Using a molar ratio of glycerol and acyl donor of 1 : 2, numerous isomerically pure
1,3-sn-diacylglycerols were prepared in very high yields and purities. Examples for
preparations of this type are given in Figure 7 (using fatty acids), Figure 8 (using fatty
acid methyl esters) and Figure 9 (using fatty acid vinyl esters).
104 6 Lipase-Catalyzed Synthesis of Regioisomerically Pure Mono- and Diglycerides
Figure 6. Enzymatic esterification of glycerol in organic media.