G.H. Veeneman

Iodonium ion promoted reactions at the anomeric centre. II An efficient thioglycoside mediated approach toward the formation of 1,2-trans linked glycosides and glycosidic esters☆

Abstract N-iodosuccinimide (NIS) in the presence of an organic acid was found to be effective for the activation of fully acylated thioglycosides leading to 1,2-trans linked esters. On the other hand, NIS together with a catalytic amount of trifluoromethanesulfonic acid proved to be very convenient for the rapid, high-yielding and stereoselective (1,2-trans) glycosidation of esterified thioglycosides with glycosyl acceptors.

Amino-acid substitutions at codon 13 of the N-ras oncogene in human acute myeloid leukaemia

DNAs from four out of five patients with acute myeloid leukaemia (AML) tested by an in vivo selection assay in nude mice using transfected mouse NIH 3T3 cells were found to contain an activated N-ras oncogene. Using a set of synthetic oligonucleotide probes, we have detected a mutation at codon 13 in all four genes. The same codon is mutated in an additional AML DNA that is positive in the focus-formation assay on 3T3 cells. DNA from the peripheral blood of one patient in remission does not contain a codon 13 mutation.

An efficient thioglycoside-mediated formation of α-glycosidic linkages promoted by iodonium dicollidine perchlorate

Abstract Chemospecific glycosidation of partially-benzoylated thioglycosides (“disarmed” acceptors) with perbenzylated thioglycosides (“armed” donors) can be realized in the presence of the promotor iodonium dicollidine perchlorate. The reaction results predominantly in the formation of α-linked saccharides and is compatible with the use of various protecting groups.

Topogenesis of Microbody Enzymes - a Sequence Comparison of the Genes for the Glycosomal (microbody) and Cytosolic Phosphoglycerate Kinases of Trypanosoma-brucei

To determine how microbody enzymes enter microbodies, we are studying the genes for cytosolic and glycosomal (microbody) isoenzymes in Trypanosoma brucei. We have found three genes (A, B and C) coding for phosphoglycerate kinase (PGK) in a tandem array in T. brucei. Gene B codes for the cytosolic and gene C for the glycosomal isoenzyme. Genes B and C are 95% homologous, and the predicted protein sequences share approximately 45% amino acid homology with other eukaryote PGKs. The microbody isoenzyme differs from the cytosolic form and other PGKs in two respects: a high positive charge and a carboxy‐terminal extension of 20 amino acids. Our results show that few alterations are required to redirect a protein from cytosol to microbody. From a comparison of our results with the unpublished data for three other glycosomal glycolytic enzymes we infer that the high positive charge represents the major topogenic signal for uptake of proteins into glycosomes.

Characterization of the gene for the microbody (glycosomal) triosephosphate isomerase of Trypanosoma brucei.

To determine how microbody enzymes enter microbodies, we are studying the genes for glycosomal (microbody) enzymes in Trypanosoma brucei. Here we present our results for triosephosphate isomerase (TIM), which is found exclusively in the glycosome. We found a single TIM gene without introns, having one major polyadenylated transcript of 1500 nucleotides with a long untranslated tail of approximately 600 nucleotides. By a novel method, suitable for low abundance transcripts, we demonstrate that TIM mRNA contains the 35‐nucleotide leader sequence (mini‐exon) also found on several other trypanosome mRNAs. The TIM gene and a DNA segment of at least 6 kbp upstream of the gene are transcribed at an equal rate in isolated nuclei, suggesting that the gene is part of a much larger transcription unit. The predicted protein is of the same size as TIMs from other organisms and shares approximately 50% amino acid homology with other eukaryote TIMs, somewhat less with prokaryote TIMs. Trypanosome TIM is the most basic of all TIMs sequenced thus far. This is, in part, due to the presence of two clusters of positively charged residues in the molecule which may act as a signal for entry into glycosomes.

(1 → 5)-linked β-d-galactofuranosides are immunodominant in extracellular polysaccharides of Penicillium and Aspergillus species

Aspergillus and Penicillium species produce extracellular polysaccharides which are immunologically active. Methyl beta-D-galactofuranoside interferes with the reaction between the polysaccharide antigens and the antibodies raised in rabbits. Of the different interlinked dimers of beta-D-galactofuranosides (1----2; 1----3; 1----5; 1----6) the (1----5) interlinked beta-D-galactofuranoside gave the highest inhibition. An increasing inhibitory effect of di-, tri-, tetra-, penta-, hexa-, and heptamer of (1----5) interlinked beta-D-galactofuranosides was observed. It was noticed that the penta-, hexa- and heptamer of (1----5) interlinked beta-D-galactofuranosides were able to link antibodies raised against the extracellular polysaccharides produced by Penicillium species. The tetramer molecule was able to neutralize the binding of antibodies, which are naturally present in human sera, to the polysaccharides produced by Penicillium and Aspergillus species.

Synthesis of Carbohydrate-Antigenic Structures of Mycobacterium Tuberculosis using an Iodonium Ion Promoted Glycosidation Approach

ABSTRACT Analogues of the phenol-phthiocerol glycoside la of Mycobacterium tuberculosis were synthesized starting from properly protected rhamnose and fucose ethyl thioglycosides. A recently developed iodonium ion promoted glycosidation procedure proved to be very efficient for the preparation of 3-aminopropyl 3-O-(α-L-rhamnopyranosyl)-2-O-methyl-α-L-rhamnopyranoside (2), 3-aminopropyl 3-O-[3-O-(2,3,4-tri-O-methyl-α-L-fucopyranosyl)-α-L-rhamnopyranosyl]-2-O-methyl-α-L-rhamnopyranoside (3) and 3-aminopropyl 3-O-(2,3,4-tri-O-methyl-α-L-fucopyranosyl)-α-L-rhamnopyranoside (4).

An efficient route to 3-deoxy-d-manno-2-octulosonic acid (KDO) derivatives via a 1,4-cyclic sulfate approach

Abstract Treatment of 2,3:5,6-di-O-isopropylidene-D-mannitol with thionyl chloride followed by oxidation gave the corresponding 1,4-cyclic sulfate. Ring opening of the cyclic sulfate with the anion of ethyl 1,3-dithiane-2-carboxylate, and subsequent acidolysis and unmasking of the thioketal, afforded ethyl 4,5:7,8-di-O-isopropylidene-3-deoxy-α(β)-D- manno -2-octulosonate in an excellent yield.

Synthesis of fragments of a streptococcus pneumoniae type-specific capsular polysaccharide

Abstract Fragments of the teichoic acid-type polysaccharide of Streptococcus pneumoniae serotype 17F, containing a D-arabinitol phosphate moiety and a spacer, were synthesized. Starting from D-lyxose or D-mannose key intermediate 1- O -allyl-2,3-di- O -benzyl-5- O -benzoyl-D-arabinitol was prepared, which was condensed with tri- O -acetyl-α-L-rhamnosyl bromide. The resulting dimer was, after removal of the allyl group, phosphorylated with either N -benzyloxycarbonyl-3-aminopropyl(2-cyanoethyl)- N,N -diethylphosphoramidite or 2-cyanoethoxy( N,N -diethylamino)chlorophosphine, the latter reagent leading to a suitable phosphitedonor. The phosphite-acceptors N -benzyloxycarbonyl-3-aminopropyl 2,3-di- O -(2-methylbenzoyl)-α-L-rhamnopyranoside and N -benzyloxycarbonyl-3-aminopropyl 2,3-di- O -benzoyl-4- O -[2,3-di- O -(2-methylbenzoyl)-α-L-rhamnopyranosyl]-6- O -(2-methylbenzoyl)-β-D-glucopyranoside were prepared by selective removal of a 4-O-dichloroacetyl group from the fully protected monomer and dimer, respectively. Condensation of the phosphite-donor with the individual acceptors led to the isolation of spacer containing trimer and tetramer fragments of the title polysaccharide.

Synthesis of the fragment GlcNAc-α(1→p→6)-GlcNAc of the cell wall polymer of staphylococcus lactis having repeating N-acetyl-D-glucosamine phosphate units

Abstract The monofunctional phosphitylating reagents chloro-β-cyanoethyl-N,N-diisopropylamino-phosphoramidite ( 3 ) and salicylchlorophosphite ( 4 ) have been applied towards the introduction of an α(1→6) interglycosidic phosphodiester bond between two properly-protected N-acetyl-D-glucosamine units. Evidence will be presented to show that 4 gives a higher yield of the required dimer than 3 .