Chemistry Reference
In-Depth Information
that of lipid A, which is present as part of the lipopolysaccharides of Gram- negative
bacteria cell walls. Based on their hydrophobic portion, mammalian glycolipids
can be divided into two classes - glycosphingolipids (or gangliosides when sialic
acid is present) and glycoglycerolipids (Scheme 4.1). The facile synthesis of lipidic
glucosylamides having potent immunomodulatory properties deprived of mito-
genic activity refl ects the high commercial potential of neoglycolipid mimetics and
further exploits the strength of organic chemistry.
Concerning synthetic strategies, enzymatic degradation of natural glycosphin-
golipids by ceramide glycanase represents a powerful method. Thus, it has been
possible to effect '
trans
-lipidation' reactions of natural glycolipids. The complete
chemical syntheses are much more tedious. The aforementioned ' cluster effect '
has been studied through these glycolipids that can form liposomes (Figure 4.4).
These self-assemblies, obtained by suspending suitable lipids in aqueous media,
can offer structural versatility in terms of chemical composition and molecular
fl uidity, and allow very special carbohydrate domains at the surface. However, in
spite of their simplicity, one of the major drawbacks of liposomes results from the
fact that they can be unspecifi cally incorporated into various cell membranes.
Moreover, the micellar concentrations necessary to obtain micellar species are not
necessarily retained in
in vivo
experiments.
Scheme 4.1
Structures of natural and synthetic glycolipids.
