Glycolipid preparations

IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Nomenclature of glycolipids, in preparation. 

Fig. 11 Symmetrical fatty P-diketones 63 used to prepare the C-glycolipids 64 and 65...

In order to prepare carbohydrate-based amphiphiles by this efficient methodol-ogy, symmetrical p-diketones 63a, b were used [111]. The reactions of these diketones with o-glucose (10) in EtOH/H20 as the solvent and NaHC03 as the base were complete and the C-glycolipids were isolated in 75% (64a) and 52% yield (64b) using the less soluble diketone 63b. The condensation was also applied to D-maltose (49) to obtain 65a or 65b (Fig. 11) [111, 121]. 

Glycolipid incorporated liposomes have found extensive use as sensors for the detection of Escherichia coli bacteria. Liposomes prepared using a diacetylene and a glucosyl lipid underwent a chromatic transition upon the addition of E. coli (Ma et al. 1998). The chromatic transition is sensitive to the diyne and glycolipid stmc-ture (Ma et al. 2000). An optimized vesicle assembly, consisting of a maltotriosyl lipid, phospholipid, and diyne, detected E. coli at a concentration of 2x10 cells/mL... 

Due to the biological roles of glycolipids, many papers have been devoted to their syntheses over the last ten years. The coupling of a fully protected carbohydrate donor to a lipid acceptor requires efficient and highly stereoselective glycosylation methods because lipid derivatives often have low reactivity. A few examples of glycosphingolipids syntheses will be discussed below as well as multistep preparations of other amphiphilic carbohydrates designed as biochemical mimetics, surfactants or liquid crystals. 

Alkyl (or acyl) derivatives of the 6-amino-6-deoxy carbohydrates are examples of derivatives in which the hydrophilic and hydrophobic moieties are linked at other positions than C-1. Thus 6-amino-6-deoxy-D-galactose derivatives 34 were prepared from l,2 3,4-di-0-isopropylidene-6-0-tosyl-a-D-galacto-pyranose by the following reactions (1) substitution of the leaving group at C-6 by a phthaloyl function, (2) hydrazinolysis to afford a 6-amino-6-deoxy intermediate, (3) reaction of acyl or sulfonyl chlorides at the amino function, (4) deprotection of the acetal rings to afford the expected glycolipid 34 [56]. 

These few examples, which do not constitute an exhaustive coverage of the literature, were selected for their diversity and to illustrate the finding that, besides the amazing multisteps syntheses of natural glycolipids analogs, even the simplest structures could require complex preparations. 

In work on enzymic deacetylation, a series of D-glucose derivatives acetylated at specific positions was prepared, and the O-trimethylsilyl derivatives of these D-glucose acetates were separated by gas-liquid chromatography.352,353 Research on bacterial glycolipids required the characterization of 3- and 6-O-palmitoyl-D-glucose, the separation of which, as their O-trimethylsilyl and acetyl derivatives, was studied.354... 

The incubation mixture for the biosynthesis of glycosphingolipids usually includes an enzyme preparation, a glycosyl donor, a glycolipid acceptor, a detergent, and metal ions. Most of the glycosyltransferases are membrane bound and are usually associated with the microsomal... 

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