Die katalytische Hydrierung von Aziden

Schiff bases from D-glucosamine and aliphatic ketones

Despite the comprehensive literature and enormous versatility of chiral imines derived from aminosugars and aldehydes, the corresponding counterparts generated from ketones remain an underestimated research subject. Filling in the gap, this manuscript sheds light on the synthetic and structural aspects of such substances and updates the few antecedents reported so far.

N-Glycosyl-thiophene-2-carboxamides: Effects on endothelial cell growth in the presence and absence of bFGF—A significant increase in potency using per-O-acetylated sugar analogues

Inhibitors of endothelial cell proliferation are of interest in development of therapies for angiogenesis related disease. N-Glucosyl-thiophene-2-carboxamides have been synthesized and evaluated for their effects on proliferation in bovine aortic endothelial cells. Per-O-acetylated-N-glucosyl-thiophene-2-carboxamides showed improved inhibition of both serum and bFGF stimulated uptake of [(3)H]thymidine, when compared to non-acetylated analogues.

Synthesis of a glucuronic acid and glucose conjugate library and evaluation of effects on endothelial cell growth

Compounds that alter endothelial cell growth are of interest in the development of angiogenesis modulators. A structurally diverse series of saccharide derivatives (glycosylamide conjugates) have been synthesized and evaluated for their effects on bovine aortic endothelial cell (BAEC) growth. Heparin-albumin (HA) reduced BAEC growth by 32% at 10 microg/mL and a number of the novel saccharide conjugates from the library were found to mimic the effect of HA as they also inhibit endothelial cell survival under identical conditions. Two thiophene conjugates, thioglucamide (24% inhibition at 35 microM) and a related glucuronide (26% inhibition at 33 microM) were the most potent inhibitors of BAEC growth, as determined using a methylthiazol tetrazolium (MTT) assay. The effects of thioglucamide and HA on absolute cell number were also studied using cell counting experiments; thioglucamide (47% after 24 h) was more potent than indicated by the MTT assay and initially reduced the BAEC number to a greater extent than HA (30% after 24 h); however, its actions were over more rapidly than were HA's as cell growth had returned to levels of the control after 72 h where HA still caused 25% inhibition. The binding of the monosaccharide conjugates to fibroblast growth factor (FGF-2) in competition with heparin-albumin by ELISA was investigated to establish the possible mechanism by which glycoconjugates could alter growth but there was no general correlation between reduction in viable cell population and binding to FGF-2. No glycoconjugate reduced the proliferation of mouse mammary epithelial cells, nor did any alter gross cell morphology, supporting a proposal that the reduction in BAEC survival by monosaccharide conjugates such as thioglucamide is a result of the inhibition of cell proliferation rather than being an induction of cytotoxicity. These studies indicate that cell biological studies to determine the mechanism of action of the simple monosaccharide conjugates may be worthwhile.

Development of carbohydrate-based scaffolds for restricted presentation of recognition groups. Extension to divalent ligands and implications for the structure of dimerized receptors

The solution structure of glycosyl amides has been studied by using NMR. A strong preference is displayed by tertiary aromatic glycosyl amides for E-anti structures in contrast with secondary aromatic glycosyl amides where Z-anti structures predominate. The structural diversity displayed by these classes of molecules would seem to be important as the directional properties of the aromatic ring, or groups attached to the aromatic ring, would be determined by choosing to have either a secondary or tertiary amide at the anomeric center and could be considered when designing bioactive molecules with carbohydrate scaffolds. The structural analysis was also carried out for related divalent secondary and tertiary glycosyl amides and these compounds display preferences similar to that of the monovalent compounds. The constrained divalent compounds have potential for promoting formation of clusters that will have restricted structure and thus have potential for novel studies of mechanisms of action of multivalent ligands. Possible applications of such compounds would be as scaffolds for the design and synthesis of ligands that will facilitate protein-protein or other receptor-receptor interactions. The affinity of restricted divalent (or higher order) ligands, designed to bind to proteins that recognize carbohydrates which would facilitate clustering and concomitantly promote protein-protein interactions, may be significantly higher than monovalent counterparts or multivalent ligands without these properties. This may be useful as a new approach in the development of therapeutics based on carbohydrates.

Studies on the origin of stereoselectivity in the synthesis of 1,2-trans glycofuranosyl azides

The stereoselectivity of the 1,2-trans directed, Lewis acid-catalysed azidation of peracylated furanoses was found to depend on the reactivity of the azide donor (azide nucleophilicity) and the configuration at the anomeric centre relative to the neighbouring 2-O-acyl group. Reactions of 1,2-trans glycosyl esters with highly nucleophilic azide donors, generated from SnCl4 and Me3SiN3, were stereospecific. The results are interpreted in terms of the rapid reaction of the azide species with bicyclic 1,2-acyloxonium (1,2-O-alkyliumdiyl-D-glycofuranose) ions, which were the primarily formed reactive intermediates. When using 1,2-cis glycosyl esters as starting materials the selectivity was reduced (90-94% de); the same is true with 1,2-trans counterparts if less nucleophilic Me3SiN3 in combination with Me3SiOTf catalyst was used. This occurred due to the appearance of the more reactive but less selective oxocarbenium (glycofuranoxonium) ions either as primarily formed reactive intermediates in the former case or after equilibration with acyloxonium ions in the latter case. Protected 1,2-trans beta-D-glycofuranosyl azides with ribo, xylo and 3-deoxy-erythro-pento configurations were best prepared from the corresponding glycosyl esters using 0.05 equivalents of SnCl4, i.e., under anomerization-free conditions. Azidation of methyl glycofuranosides proceeds with inferior (80-90% de) and less predictable selectivity irrespective of the starting anomeric configuration.

Article

The synthesis of N-glycosyl phosphonamidates has been accomplished via the coupling of peracetylated glycosylamines with an appropriate phosphonochloridate in the presence of pyridine. The resulting glycosyl phosphonamidate esters are dealkylated with bromotrimethylsilane and then deacetylated to give the target compounds, which are potential transition-state analogue inhibitors of glycopeptidases and may prove useful as haptens for generating catalytic antibodies with glycopeptidase activity.Key words: enzyme inhibition, PNGase, phosphonamidate, amide hydrolysis.

Glycosyl azides as building blocks in convergent syntheses of oligomeric lactosamine and Lewis(x) saccharides

Oligosaccharides containing type 2 lactosamine repeating units, e.g. neo-lacto-octaose and trimeric Lewis(x) derivatives, are constructed using neo-lactosamine azide building blocks. The azido group provides a favorable protection of the anomeric position which is stable to versatile protecting group manipulations and glycosylation reactions. On the other hand, glycosyl azides can be converted into glycosyl fluorides via a 1,3-dipolar cycloaddition with di-tert-butyl-acetylenedicarboxylate and subsequent treatment of the resulting N-glycosyl triazoles with hydrogen fluoride-pyridine complex. Activation of the lactosamine fluorides with Lewis acids affords the possibility to extend the oligosaccharide chain with disaccharide units. Suitable protecting group combinations within the galactose and the glucosamine portion of the lactosamine unit enable selective deprotection reactions and, subsequently, chain extension or branching, e.g. to yield Lewis(x) structures.

Synthesis and biological activity of substance P analogues

The synthesis of the hexapeptide [Glu6]SP6-11 and its glycosylated analogue at the Glu6 gamma-carboxyl position by solution procedures according to several strategies is discussed. The biological activity of SP, [Glu6]SP6-11 (VI) and [Glu(beta-D-Glcp)6]SP6-11 (VIII) have been determined and compared to SP by the GPI and RVD assays. The introduction of a beta-D-glucopyranosyl moiety at the sixth position of the [Glu6]SP6-11 did not affect to a great extent the in vitro activity pattern of the parent hexapeptide.

[D-Met2,Pro5] enkephalin [N1.5-beta-D-glucopyranosyl] amide: a glycosylpeptide with high antinociceptive activity

Different synthetic strategies have been attempted for the synthesis of a glycosylpeptide resulting from the covalent bonding of a sugar residue to the C-terminal carboxyl group of an enkephalin related pentapeptide. The final structure is: Tyr-D-Met-Gly-Phe-Pro [N1.5-beta-D-glucopyranosyl] amide. The in vitro potency on the GPI test of this analogue was IC50 = 64.0 nM. However, its antinociceptive activity by tail immersion tests, after intraperitoneal administration, was 2000 and 200 times higher than morphine in rats and mice, respectively.

Synthesis and biological activity of glycosylated analogs of the C-terminal hexapeptide and heptapeptide of substance P

The synthesis of two glycosylated analogs of Substance P is described. The activity of the peptides was assayed on the isolated guinea-pig ileum and their degradation was studied using rat hypothalamus slices. While glycosylation noticeably enhances the solubility of the corresponding compounds, the beta-glucopyranosyl moiety only slightly modifies the biological half-life and the bioactivity of the glycopeptides.

Solid-phase synthesis of two glycopeptides containing the amino acid sequence 5 to 9 of somatostatin

2,3,4,6-Tetra-O-acetyl-1-N-[N-(tert-butyloxycarbonyl)-L-aspart-4-oyl]-D-g lucopyranosylamine and 2-acetamido-3,4,6-tri-O-acetyl-1-N-[N-(tert-butyloxycarbonyl)-L-aspart-4-oyl]-2 -deoxy-D-glucopyranosylamine were introduced, respectively, by the solid-phase procedure in the amino acid sequence 5 to 9 of somatostatin. The two resulting glycopeptides beta-D-Glcp-(1 leads to 4)- and beta-D-GlcpNAc-(1 leads to 4)-Asn-Phe-Phe-Trp-Lys-OH were homogeneous on examination by t.l.c. and l.c., and their structures were confirmed by m.s. of the N-acetyl, permethyl derivatives.