Front Matter

ening of the hydrocarbon chain also enhances the surface active properties, while

amidation or esterification of the carboxyl group showed a negative effect. How-

ever, the sophorosides present only minor differences in their surface tension.

One explanation could be the spatial arrangement of the molecules at the air – water

interface. According to a computer-generated model by de Koster et al. (1995), the

classical diacetylated lactonic SL, as well as the acidic SL, should not possess a

defined head/tail order, but a polar and unpolar side. The free hydroxyl groups

of the disaccharide part, as well as the ester and ether groups, are all at one (the

hydrophilic) side of the plane. The outer side of the carbohydrate, together with

the fatty acid bridge, forms the hydrophobic part of the molecule. C6’-OAc is posi-

tioned at the hydrophilic side, whereas C6“-OAc is largely surrounded by the dis-

accharide and the fatty acid parts. This principal structure primary determines

the surface-active characteristics of the molecule, and the modifications represented

in Table 9 should impinge to only a small extent on the entire molecular arrangement.

17.6 Conclusions

The chemo-enzymatic synthesis of glycolipids using lipases, glycosidases and pro-

teases as well as the enzymatic modification of naturally occurring glycolipids will

become important methods for the preparation of new compounds with interesting

interfacial and biological activities. Essential advantages of the biocatalysts are mild

reaction conditions, their regioselectivities and, in some cases, their stereoselectiv-

ities. These methods are well established for preparative use, and may also have an

important impact on the industrial production of glycolipids for use as surfactants,

sweeteners, food ingredients, cosmetics and pharmaceuticals in future. Drawbacks,

which have still to be overcome are low product yields and productivities in case of

lipases and esterases; and low enzyme stabilities, low productivities and limited

substrate specificities in case of glycosidases. Novel methods such as the lipase-

catalyzed solid-phase synthesis, including addition of adjuvants, which can success-

fully be applied at the preparative scale, may not easily be used on an industrial scale.

Potentialities to overcome some of the limitations mentioned above may be the de-

sign of ‘tailor-made’ and more stable biocatalysts. For instance, using rational and

evolutional protein design as well as development and integration of new reaction

processes, e.g. for the continuous removal of water and products in order to obtain

higher yields with the shift of reaction equilibrium. The application and re-use of

immobilized enzymes might reduce costs. With regard to the modification of natu-

rally occurring glycolipids, the availability of low-priced precursors remains the

limiting factor, but this should also be overcome in the future. In spite of these dis-

advantages, the modification of glycolipids using enzymes often represents the only

possibility of synthesizing a specific molecule. However, if a molecule with special

characteristics related to a profitable application is synthesizable, then a process for

its economic production will be determined.

17.6 Conclusions 387