* modified with succinic acid (Berger and Schneider, 1993); or
* modified with amino acids (Aha, 1999; Berger, 1993; Berger and Schneider,
1993).
Furthermore, the 1,3-sn-diglycerides constitute attractive coupling partners for the
synthesis of numerous conjugates aimed at the lipid modification of pharmaceuti-
cals, e.g., aspirin, (S)-ibuprofen,b-blockers (Figure 10) or the preparation of various
reagents for the lipid modification of proteins (Berger, 1993; Berger and Schneider,
1993).
6.5 Enzyme-catalyzed synthesis of isomerically pure
1(3)-monoglycerides
Two basically different strategies can be employed for the synthesis of isomerically
pure 1(3)-sn-monoglycerides:
* Strategy 1: The use of permanent or temporary protection groups of two of the
three hydroxy groups of glycerol, followed by the enzymatic acylation and sub-
sequent removal of the protection groups.
* Strategy 2: Enzymatic acylation of glycerol itself, leading directly to the desired
molecules.
Examples for the employment of temporary protection groups according to Strategy
1 can be found in the literature describing the enzymatic esterification of isopropy-
lidene glycerol (Figure 11) (Bornscheuer, 1995; Bornscheuer and Yamane, 1995;
Hess et al., 1995). Alternatively, the glycerol esters of phenylboronic acid (Figure
12) may be used for temporary protection (Steffen et al., 1992; 1995; Papendorf et
al., 1995).
6.5 Enzyme-catalyzed synthesis of isomerically pure 1(3)-monoglycerides 107
Figure 11. Esterification of isopropylidene glycerol.
Figure 12. Acylation of glycerol esters from phenylboronic acid.