Protozoan parasites of the genus Leishmania synthesize lipophosphoglycans (LPGs), phosphoglycans and proteophosphoglycans that contain phosphosaccharide repeat units of [-6)Gal(β1-4)Man(α1-OPO3H-]. The repeat structures are assembled by sequential addition of Manα1-OPO3H and β-Gal. In this study, an UDP-Gal-dependent activity was detected in L. donovani and L. major membranes using synthetic phospho-oligosaccharide fragments of lipophosphoglycan as acceptor substrates. Incubation of a microsomal preparation from L. donovani or L. major parasites with synthetic substrates and UDP-[6-3H]Gal resulted in incorporation of radiolabel into these exogenous acceptors. The [3H]galactose-labeled products were characterized by degradation into radioactive, low molecular mass fragments upon hydrolysis with mild acid and treatment with β-galactosidases. We showed that the activity detected with L. donovani membranes is the elongating β-d-galactosyltransferase associated with LPG phosphosaccharide backbone biosynthesis (eGalT). The eGalT activity showed a requirement for the presence of at least one phosphodiester group in the substrate and it was enhanced dramatically when two or three phosphodiester groups were present. Using the same substrates we detected two types of galactosyltransferase activity in L. major membranes: the elongating β-d-galactosyltransferase and a branching β-d-galactosyltransferase (bGalT). Both L. major enzymes required a minimum of one phosphodiester group present in the substrate, but acceptors with two or three phosphodiester groups were found to be superior.

An anomeric phosphodiester linkage formed by a glycosyl phosphate unit and a hydroxyl group of another monosaccharide is found in many glycopolymers of the outer membrane in bacteria (e.g., capsular polysaccharides and lipopolysaccharides), yeasts and protozoa. The polymers (phosphoglycans) composed of glycosyl phosphate (or oligoglycosyl phosphate) repeating units could be chemically classified as poly(glycosyl phosphates). Their importance as immunologically active components of the cell wall and/or capsule of numerous microorganisms upholds the need to develop routes for the chemical preparation of these biopolymers. In this paper, we (1) present a review of the primary structures (known to date) of natural phosphoglycans from various sources, which contain glycosyl phosphate units, and (2) discuss different approaches and recent achievements in the synthesis of glycosyl phosphosaccharides and poly(glycosyl phosphates).

A neutral disaccharide beta-D-Ga1p-(1 -> 4)-alpha-D-Manp and phosphorylated di- and tri-saccharides beta-D-Galp-(1 -> 3)-[H(2)PO(3-)6]-beta-D-Ga1p-O[CH2](8)CH=CH2 and beta-D-Ga1p-(1 -> 3)-[H(2)PO(3-)6]-beta-D-Ga1p-(1 -> 4)-alpha-D-Manp, which are fragments of the phosphoglycan portion of the surface lipophosphoglycan from Leishmania donovani (the disaccharide) or Leishmania major (all three compounds), were prepared and used as TLC standards to help the identification and differentiation of the elongating and branching P-D-galactosyl transferase activities in Leishmania. The phosphosaccharides were synthesised using the H-phosphonate method for phosphorylation. (c) 2006 Elsevier Ltd. All rights reserved.

The phosphorylated branched heptasaccharides 7 and 8, the octasaccharide 9 and the phosphorylated trisaccharides 5 and 6, which are fragments of the phosphoglycan portion of the surface lipophosphoglycans from Leishmania mexicana (5) or L. major (6-9), were synthesised by using the glycosyl hydrogenphosphonate method for the preparation of phosphodiester bridges. The compounds were tested as acceptor substrates/putative inhibitors for the Leishmania elongating alpha-D-mannosylphosphate transferase.

A tetrasaccharide fragment of Leishmania major lipophosphoglycan (which seems to be involved in a biological mechanism for the parasite transmission) has been synthesised using the thioglycoside, trichloroacetimidate and halide-exchange glycosylation procedures and step-wise chain elongation strategy.

A set of phosphodisaccharides, substrate analogues, which will be used to study acceptor-substrate specificity of the Leishmania biosynthetic enzymes, are synthesized using the Koenigs-Knorr and trichloroacetimidate methods for the glycosylation reactions, S(N)2 nucleophilic displacement of a triflic ester for epimerization, and the glycosyl hydrogenphosphonate method for phosphorylation.

Leishmania express lipophosphoglycans and proteophosphoglycans that contain Gal beta 1-4Man alpha 1-P phosphosaccharide repeat structures assembled by the sequential addition of Man alpha 1-P and beta Gal. The synthetic acceptor substrate Gal beta 1-4Man alpha 1-P-decenyl and a series of analogues were used to probe Leishmania alpha-D-mannosyl phosphate transferase activity. We show that the activity detected with Gal beta 1-4Man alpha 1-P-decenyl is the elongating cx-D-mannosyl phosphate transferase associated with lipophosphoglycan biosynthesis (eMPT(LPG)). Differences in the apparent K-m values for the donor and acceptor substrates were found using L, major, L. mexicana, and L. donovani promastigote membranes, but total activity correlated with the number of lipophosphoglycan repeats. Further comparisons showed that lesion-derived L mexicana amastigotes, that do not express lipophosphoglycan, lack eMPT(LPG) and that nondividing L. major metacyclic promastigotes contain 5-fold less eMPT(LPG) activity than dividing procyclic promastigotes. The fine specificity of promastigote eMPT(LPG) activity was determined using 24 synthetic analogues of Gal beta 1-4Man alpha 1-P-decenyl. The three species gave similar results: the negative charge of the phosphodiester and the C-6 hydroxyl of the alpha Man residue are essential for substrate recognition, the latter most likely acting as a hydrogen bond acceptor. The C-6' hydroxyl of the beta Gal residue is required for substrate recognition as well as for catalysis, The rate of Man alpha 1-P transfer declines with increasing acceptor substrate chain length. The presence of a monosaccharide substituent at the C-3 position of the terminal beta Gal residue abrogates Man-P transfer, showing that chain elongation must precede side chain modification during lipophosphoglycan biosynthesis. In contrast, substitution of the penultimate phosphosaccharide repeat does not abrogate transfer but is slightly stimulatory in L. mexicana and inhibitory in L. major.

An oil from soybean [Glycine max (L.) Merr.] cultivars with <20 g kg−1 linolenate would have a desirable oxidative stability. The objective of our study was to compare the agronomic and seed traits of lines with the genotype fan1(A5)fan1(A5)fan2(A23)fan2(A23)fan3fan3, designated as 1%‐linolenate (<20 g kg −1) lines, and the genotype fan1(A5)fan1(A5)fan2(A23)fan2(A23), designated as 2%‐linolenate lines (>20 g kg−1). Three backcross populations were developed by crossing three high‐yielding, recurrent parents with ≈25 g kg−1 linolenate to a donor line with ≈13 g kg−1 linolenate. For each population, 27 1%‐ and 27 2%‐linolenate BC1F2:4 lines were evaluated at Ames, Grand Junction, and Hubbard, IA during 1998. The mean seed yields of the 1%‐linolenate lines were 47 kg ha−1 lower in Population 1, 65 kg ha−1 lower in Population 2, and 164 kg ha−1 lower in Population 3 than the 2%‐linolenate lines, but the difference was only significant in Population 3. The maximum mean differences between the 1%‐ and 2%‐linolenate lines in any of the populations for the remaining agronomic and seed traits were 1 d for maturity, 0.1 score for lodging, 2 cm for plant height, 4 mg seed−1 for seed weight, 5 g kg−1 each for protein and oil content, 0.6 g kg−1 for palmitate, 2.2 g kg−1 for stearate, 16.4 g kg−1 for oleate, and 6.8 g kg−1 for linoleate. The lack of major differences between the 1%‐ and 2%‐linolenate lines indicated that it should be possible to develop acceptable cultivars with <20 g kg−1 linolenate.

Leishmania express lipophosphoglycans and proteophosphoglycans that contain Galbeta1-4Manalpha1-P phosphosaccharide repeat structures assembled by the sequential addition of Manalpha1-P and betaGal. The synthetic acceptor substrate Galbeta1-4Manalpha1-P-decenyl and a series of analogues were used to probe Leishmania alpha-D-mannosyl phosphate transferase activity. We show that the activity detected with Galbeta1-4Manalpha1-P-decenyl is the elongating alpha-D-mannosyl phosphate transferase associated with lipophosphoglycan biosynthesis (eMPT(LPG)). Differences in the apparent K(m) values for the donor and acceptor substrates were found using L. major, L. mexicana, and L. donovani promastigote membranes, but total activity correlated with the number of lipophosphoglycan repeats. Further comparisons showed that lesion-derived L. mexicana amastigotes, that do not express lipophosphoglycan, lack eMPT(LPG) and that nondividing L. major metacyclic promastigotes contain 5-fold less eMPT(LPG) activity than dividing procyclic promastigotes. The fine specificity of promastigote eMPT(LPG) activity was determined using 24 synthetic analogues of Galbeta1-4Manalpha1-P-decenyl. The three species gave similar results: the negative charge of the phosphodiester and the C-6 hydroxyl of the alphaMan residue are essential for substrate recognition, the latter most likely acting as a hydrogen bond acceptor. The C-6' hydroxyl of the betaGal residue is required for substrate recognition as well as for catalysis. The rate of Manalpha1-P transfer declines with increasing acceptor substrate chain length. The presence of a monosaccharide substituent at the C-3 position of the terminal betaGal residue abrogates Man-P transfer, showing that chain elongation must precede side chain modification during lipophosphoglycan biosynthesis. In contrast, substitution of the penultimate phosphosaccharide repeat does not abrogate transfer but is slightly stimulatory in L. mexicana and inhibitory in L. major.

A polymer (MPEG) supported synthesis of the phosphorylated tetra- and hexa-saccharide fragments of the lipophosphoglycan from Leishmania has been developed using mono- and di-saccharide H-phosphonates for construction of the phosphodiester bridges.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A set of phosphodisaccharides, substrate analogues, which will be used to study the acceptor substrate specificity of the Leishmania biosynthetic enzymes, have been synthesized using the trichloroacetimidate method for the glycosylation reactions, S(N)2 nucleophilic displacement of triflic esters for epimerization and the glycosyl hydrogenphosphonate method for phosphorylation.

The three structural analogues of dec-9-enyl β-D-galactosyl-(1→4)-α-D-mannosyl phosphate, comprising thiophosphate, boranophosphate and methylphosphonate derivatives, were prepared via disaccharide H-phosphonate or trichloroacetimidate (for the methylphosphonate synthesis) intermediates.