Leishmaniasis (the disease caused by a genus of
Leishmania protozoan parasite) is the second largest, after malaria, parasitic killer in the world responsible for an estimated 500,000 cases and 60,000 deaths each year worldwide. Infectious metacyclic promastigotes of
Leishmania synthesise lipophosphoglycans (LPGs, the predominant cell-surface antigenic macromolecules), which contain phosphosaccharide repeats of [-OPO
3H-6)(R-3)Gal(ß1-4)Man(ą1-]. In
L. donoivani R = H, but in
L. major R is mainly ß-Gal. It’s been found that there are monoclonal antibodies (IVD3, kindly provided by Dr M. Hommel, Liverpool School of Tropical Medicine) to detect the
L. donoivani phosphoglycan structure. Here, we report the synthesis of the structures
1-
3 and their use in a search of a dimension of an effective binding site of the LPG with anti-phosphoglycan MAbs. Compounds
1-
3 represent fragments of the LPG containing one, two or three phosphosaccharide repeats, respectively, and bearing a biotin moiety at the non-reducing end of the chain. Structures
2 and
3 were prepared by stepwise chain elongation using the 6-
O-TBS or 6-
O-DMT protected disaccharide H-phosphonates
5 and
6, the disaccharide
7 (as the first alcohol acceptor) and the
N-biotinyl-6-aminohexyl H-phosphonate
4 (for the final biotinylation). The synthons
4 and
7 used to make the shorter phosphosaccharide
1. Compounds
1-
3 were tested for their ability to bind with monoclonal IVD3 antibodies in an ELISA assay using neutra-avidin pre-coated plates to enable linking the biotinylated phosphosaccharides to the surface. Early results indicate that the LPG binding site with the MAbs comprises neither 1 nor 2, but at least 3 phosphosaccharide repeats. Former studies of binding sites of
Salmonella lipopolysaccharide (LPS) with anti-LPS serum antibodies performed profiting by synthetic oligosaccharides are also to be discussed.
