Preparation and conformational analysis of C-glycosyl β- and β/β-peptides

Ten C-glycosyl β²- and β/β²-peptides with three to eight amino acid residues have been prepared. Solution and solid-phase peptide syntheses were employed to assemble β²-amino acids in which C-glycosylic substituents are attached to the C-2 position of β-amino acids. Conformational analysis of the C-glycosyl β²-peptides using NMR and CD spectra indicates that the tripeptide can form a helical secondary structure. Besides, helix directions of the C-glycosyl β/β²-peptides are governed by the configuration at the α-carbon of the peptide backbone that originates from the stereocenter of the C-glycosyl β²-amino acids.     

Indium-mediated alkynylation of sugars: synthesis of C-glycosyl compounds bearing a protected amino alcohol moiety

The coupling of glycals with an alkynyl iodide bearing a protected amino alcohol moiety was achieved in the presence of metallic indium under Barbier conditions. It gave functionalized C-glycosyl compounds, precursors of C-glycosyl amino acids with α configuration.     

Reaction of organocuprate reagents with protected 1,2-anhydro sugars. Stereocontrolled synthesis of 2-deoxy-C-glycosyl compounds

The reaction of protected 1,2-anhydro-α-d-gluco- and β-d-manno-pyranoses with alkyl and phenyl organocuprates afforded the corresponding C-glycosyl compounds in acceptable to high yield. Complete stereocontrol was obtained, leading respectively to the β-d or the α-d anomer. With the perbenzylated manno derivative, deoxygenation at C-2 was achieved in high yield, affording 2-deoxy-α-d-C-glycosyl compounds.     

Photo-oxygenation of glycosylfurans. Rearrangement of C-glycosyl into O-glycosyl derivatives

Photo-oxygenation of 3-ethoxycarbonyl-5-(2,3-O-isopropylidene-β-d-erythrofuranosyl)-2-methylfuran and 3-hydroxymethyl-5-(2,3-O-isopropylidene-β-d-erythrofuranosyl)-2-methylfuran yields the corresponding endo-peroxides which rearrange at room temperature into the O-glycosyl derivatives ethyl 2,3-O-isopropylidene-β-d-erythrofuranosyl 2-acetylfumarate and 2,3-O-isopropylidene-β-d-erythrofuranosyl 3-acetyl-3-hydroxymethylacrylate, respectively. The endo-peroxides can be reduced without rearrangement, yielding C-glycosyl derivatives. Alcoholysis of the O-glycosyl derivatives yields 2,3-O-isopropylidene-d-erythrose, dialkyl 2-acetyl-3-alkoxysuccinates, 4-ethoxycarbonyl-5-methoxy-5-methyl-2-oxo-2,5-dihydrofuran and 4-hydroxymethyl-5-methoxy-5-methyl-2-oxo-2,5-dihydrofuran.     

Flavonoids,stilbenoids, and phenolic derivatives from the stems of Gnetum macrostachyum (Gnetaceae)

Gnetum species have been traditionally consumed as food and used as folk medicine to treat various pathological conditions. Ten compounds including three simple phenolic compounds (1–3), five stilbenoids (4, 5, 8–10), and two C-glycosyl flavanones (6 and 7), were isolated from the stems of Gnetum macrostachyum Hook. f. The structures of these compounds were elucidated by the analysis of spectroscopy data and their comparison with the reported values. This is the first report of the isolation of compounds 1–4 and 6–9 from G. macrostachyum. Compounds 1–3, 6, and 7 have not been previously reported from the genus Gnetum. The C-glycosyl flavanones in G. macrostachyum can be used as chemotaxonomic markers.     

Structural determination of 6-C-diglycosyl-8-C-glycosyl-flavones and 6-C-glycosyl-8-C-diglycosylflavones by mass spectrometry of their permethyl ethers

Permethylated 6-C-diglycosyl-8-C-glycosylflavones and 6-C-glycosyl-8-C-diglycosylflavones gave well defined EIMS including the molecular peak and a fragmentation pattern characteristic of the 6-C-glycosyl residue. X″′-O-glycosides (8-C-disaccharides) are thus easily distinguished from X″-O-glycosides (6-C-disaccharides) and, in the latter, the position of the O-glycosidic bond should be deduced from the MS, after acid hydrolysis. Three new C-glycosylflavones have been characterized in this way from Spergularia rubra and Stellaria holostea.     

Distribution of flavonoids and their systematic significance in Clematis subsection Viornae

Fifteen flavonoids were identified in the eight taxa of Clematis subsection Viornae. Flavonols, flavones, and C-glycosyl flavones were present. The compounds were based primarily on luteolin, apigenin, quercetin, and kaempferol. The systematic significance of the distribution of these compounds among the taxa is discussed.     

Synthesis of a C-galactopyranosyl-linked N-substituted 1,2-ethylenediamine

A straightforward route to a C-galactopyranosyl-linked 1,2-ethylenediamine is described. The five-step synthetic procedure involves: (i) C-allenylation of d-galactopyranose pentaacetate with propargyl trimethylsilane in the presence of a Lewis acid, (ii) iodination of allenyl galactopyranosyl tetraacetate to diiodoallyl galactopyranosyl tetraacetate, (iii) displacement of the allylic iodide with N-Boc-ethylenediamine, (iv) catalytic hydrogenation of vinyl iodide to alkane, (v) deprotection of the acetyl and N-Boc-groups using acid-catalyzed hydrolysis. This method demonstrates a general method to access a new class of carbohydrate-ethylenediamine C-glycosyl chelators.     

N,N-Diacetylsialyl chloride—a novel readily accessible sialyl donor in reactions with neutral and charged nucleophiles in the absence of a promoter

N,N-Diacetylneuraminic acid glycosyl chloride was prepared for the first time and made to react with various nucleophiles to give the corresponding α-glycosyl phosphate, β-glycosyl dibenzyl phosphate, α-glycosyl azide, α-phenyl thioglycoside and α-glycosyl xanthate in 65-82% yields and high stereoselectivity while its reactions with simple alcohols were not stereoselective. The new sialyl donor made possible the first stereoselective synthesis of sialic acid glycosyl phosphate with α-configuration and highly efficient synthesis of β-configured sialic acid glycosyl dibenzyl phosphate.     

Preparation of 2-amino-2-C-glycosyl-acetonitriles from C-glycosyl aldehydes by Strecker reaction

Synthesis of new 2-amino-2-C-d-glycosyl-acetonitriles in a Strecker reaction from various C-glycosyl aldehydes, chiral amines, and HCN was carried out. While aminonitriles from glycal and 2-deoxy-β-d-glycosyl aldehydes were prepared in satisfactory yields, lower yields were obtained with C-glycosyl aldehydes. Strecker reaction with the benzyl-protected 1-C-formyl-d-galactal and S- or R-1-phenylethylamine (S-PEA or R-PEA) yielded predominantly the R-configured C-glycosyl aminoacetonitrile. The direction of the nucleophilic addition appears to be governed by the configuration of the anomeric carbon with β-linked sugars. Since the stereochemistry of the transition state is unknown according to the configuration of the major product a Felkin–Ahn selectivity can be mainly presumed.     

Improving the carbonic anhydrase inhibition profile of the sulfamoylphenyl pharmacophore by attachment of carbohydrate moieties

One of the most successful approaches for designing carbonic anhydrase (CA, EC 4.2.1.1) inhibitors was denominated ‘the sugar approach’. The sugar approach consists in attaching different carbohydrates to CA inhibiting pharmacophores for modulating the physicochemical properties of these pharmacological agents. In line with this approach, in this paper, we present a new class of C-glycosides incorporating the sulfamoylphenyl moiety. These compounds have been prepared by sulfamoylation of C-glycosyl phenols, which have been synthetized by aldol reaction of glycosyl ketones with the appropriate aromatic aldehydes. The inhibition profile of the new glycomimetics was determined against four human (h) CA isozymes, comprising hCAs I and II (cytosolic, ubiquitous isozymes), hCA IV and hCA IX (tumor associated isozyme). Peracetylated and deprotected C-glycosyl sulfamates showed better inhibition selectivity compared to structurally related phenylsulfamates. In this study, deprotected compound 12 was identified as selective inhibitor of hCA IX. These results confirm that attaching carbohydrate moieties to CA sulfamoylphenyl pharmacophore improves its inhibitory activity.     

Triterpenoid saponins and C-glycosyl flavones from stem bark of Erythrina abyssinica Lam and their cytotoxic effects.

Six new compounds including two oleanane-type triterpenoid saponins (1, 2) and four C-glycosyl flavones (3–6), along with a known saponin (7), three di-C-glycosyl flavones (8–10) and a glycosyl auronol (11), were isolated from the stem bark of Erythrina abyssinica Lam. The structures of the new compounds, identified as 3-O-[α-l-rhamnopyranosyl-(1 → 2)-β-d-galactopyranosyl-(1 → 2)-β-d-glucuronopyranosyl]-22-O-β-d-glucopyranosyl sophoradiol (1), 3-O-[α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl-(1 → 2)-β-d-glucuronopyranosyl]-22-O-β-d-glucopyranosyl sophoradiol (2), 6-C-β-glucopyranosyl-8-C-β-quinovopyranosyl apigenin (3), 6-C-β-quinovopyranosyl-8-C-β-glucopyranosyl apigenin (4), 8-C-[6″-O-α-l-rhamnopyranosyl-(1‴ → 6″)]-β-glucopyranosyl 7,4′-dihydroxyflavone (5) and 8-C-[6″-O-β-d-xylopyranosyl-(1‴ → 6″)]-β-glucopyranosyl 7,4′-dihydroxyflavone (6), were determined by comprehensive spectroscopic analysis, including 1D and 2D NMR techniques, mass spectrometry and acid hydrolysis. These new compounds together with the known saponins 7 were evaluated for their cytotoxic activity against MCF-7 (estrogen dependent) and MDA-MB-231 (estrogen independent) cell lines. The new saponin 2 exhibited the highest cytotoxic activity among tested compounds, exerting a selective inhibitory effect against the proliferation of MCF-7 cells, with lower IC₅₀ value (12.90 μM) than that of the positive control, resveratrol (13.91 μM). Structure–activity relationship of these compounds is also discussed.     

Glycosylflavonoids from Cecropia pachystachya Trécul are quorum sensing inhibitors

The Cecropia genus is widely distributed in Latin America including at least 60 species, and some of them are commonly used in traditional medicine for the treatment of several diseases. We used Cecropia pachystachya Trécul to search for quorum sensing (QS) inhibitors compounds and found that the aqueous extract of C. pachystachya leaves is a promising source of substances with this activity. Using as biosensor Chromobacterium violaceum ATCC 31532 and Escherichia coli pSB403, the compounds chlorogenic acid (2), isoorientin (3), orientin (4), isovitexin (6), vitexin (7), and rutin (9) were identified as QS inhibitors. None of these compounds inhibited the growth of neither the used biosensors nor the microorganisms Staphylococcus aureus ATCC 23591, Escherichia coli ATCC 25922 and Saccharomyces cerevisiae, used here as growth inhibition controls. Along with the rutin, here we presented for the first time the QS-inhibition potential of the C-glycosyl flavonoids. The prospective of this evidence lead to the use of these compounds as antipathogenic drugs or antifoulants.     

Discriminative flavonoid patterns within a preliminary collection of the Setaria italica specific complex

One hundred and eighty individuals of Setaria italica ssp. italica, reflecting the worldwide variability of cultivated foxtail millet, and 40 individuals of wild S. i. ssp. viridis, were analysed for their flavonoid content. S. i. spp. italica accumulates native or acylated O-glycosyl derivatives of 8-Cglycosylflavones and O-glycosylfiavones, showing a large qualitative as well as quantitative inter-varietal diversity. The subspecies is strongly organized into seven chemotypes clearly defined by the presence or absence of O-pentosylation and acylation, and by the balance between apigenin and luteolin derivatives. This organization only partly corroborates a previous classification based on morphological and electrophoretical data, chemotypes affording an additional discriminative criterion in most cases. Flavonoid patterns of S. i. ssp. viridis fall in the chemotypes defined from the cereal, and underlines the conspecific nature of the two taxa. Similarities between wild and cultivated foxtail millet from same geographical origin suggest independent domestication from already differentiated gene pools.     

C3 and C4 leaf anatomy types in Camphorosmeae (Camphorosmoideae,Chenopodiaceae)

Complementary to our previous project on the molecular phylogeny of Camphorosmeae, the leaf anatomy of ca. 35 species including all non-Australian and selected Australian species was studied by use of light microscopy. Nine anatomical leaf types were described, compared to previous classifications, and discussed with regard to their putative evolution on the background of phylogenetic trees. Particular emphasis was given to the relationships between the C₃ and C₄ leaf types: Chenolea type (C₃), Eokochia type (C₃), Neokochia type (C₃), Sedobassia type (C₃/C₄ intermediate), Bassia prostrata type (C₄), B. muricata type (C₄), B. eriantha type, B. lasiantha type (C₄), Camphorosma type (C₄). The main results and conclusions were: (1) Two unusual new C₃ leaf types: Chenolea with microfenestrate chlorenchyma, Eokochia with unique complex vascular bundles; (2) Sedobassia interpreted as anatomically C₃/C₄ intermediate by kranz-like bundle sheath cells is the first C₃/C₄ intermediate in Camphorosmeae and found in a derived position; (3) Neokochia type detected as the likely starting point for all four C₄ leaf types and for the C₃/C₄ intermediate; (4) hypodermis of C₄ types originated from outermost chlorenchyma layer of C₃ types and lost multiple times during further evolution; (5) atriplicoid Bassia. lasiantha type without water storage tissue evolved from kochioid B. muricata type; (6) two independent gains of C₄ photosynthesis, one in Bassia and one in Camphorosma; (7) depending on the lineage, leaf architecture remains comparatively stable (Australian Camphorosmeae) or shows an unexpected plasticity (Bassia scoparia group).     

Sugar-based peptidomimetics as potential inhibitors of the vascular endothelium growth factor binding to neuropilin-1

Neuropilin-1 (NRP-1) is a co-receptor of VEGFR₁₆₅ and molecules interfering with VEGF₁₆₅ binding to NRP-1 seem to be promising candidates as new angiogenesis modulators. Based on the minimal four amino acid sequence of peptidic ligands known to bind NRP-1, we describe here the design, synthesis and biological evaluation of series of original sugar-based peptidomimetics using a C-glycosyl compound, derived from d-gulonolactone, as a scaffold, which was functionalized with side chains of the amino-acids arginine, and tryptophane or threonine. At 100 μM, all compounds exhibited a weak affinity for NRP-1, the most efficient being the bis-guanidinylated compound 32 (IC₅₀ = 92 μM) which could be considered as a new NRP-1 non-peptidic ligand.     

The synthesis of mono- and oligosaccharide 1,2-orthoesters by way of a glycosyl nitrate intermediate

Sugar orthoesters with complex alcohols were obtained in high yield in the reaction of acylated 1,2-cis-glycosyl halides with partially protected sugar derivatives in the presence of silver nitrate and 2,4,6-trimethylpyridine in dry acetonitrile. The reaction has been shown to proceed by way of the acylated 1,2-trans-glycosyl nitrate intermediate.     

Comparative amino acid sequence analysis of Thermotoga maritima β-glucosidase (BglA) deduced from the nucleotide sequence of the gene indicates distant relationship between β-glucosidases of the BGA family and other families of β-1,4-glycosyl hydrolases

The primary structure of the bglA gene region encoding a β-glucosidase of Thermotoga maritima strain MSB8 was determined. The bglA gene has the potential to code for a polypeptide of 446 amino acids with a predicted molecular mass of 51545 Da. The T, maritima β-glucosidase (BglA) was overexpressed in E. coli at a level comprising approximately 15–20% of soluble cellular protein. Based on its amino acid sequence, as deduced from the nucleotide sequence of the gene, BglA can be classified as a broad-specificity β-glucosidase and as a member of the β-glucosidase family BGA, in agreement with the results of enzymatic characterization of the recombinant protein. Comparative sequence analysis revealed distant amino acid sequence similarities between BGA family β-glucosidases, a β-xylosidase, β-1,4-glycanases of the enzyme family F (mostly xylanases), and other families of β-1,4-glycosyl hydrolases. This result indicates that BGA β-glucosidases may comprise one enzyme family within a large ‘enzyme order’ of retaining β-glycosyl hydrolases, and that the members of these enzyme groups may be inter-related at the level of active site architecture and perhaps even on the level of overall three-dimensional fold.     

Absence of long chain aldehydes in the wax of the Glossy II mutant of maize

Wax from the glll mutant of maize lacks aldehydes, which constitute 20 % in the normal genotype. The absence of aldehydes is not associated with a block in the synthesis of alcohols. Moreover in contrast to the wild type, glll wax is characterized by a higher content of C₁₆ and C₁₈ free acids, with a clear defect in the synthesis of C₂₄, C₂₆ and C₂₈ homologues. The results from this study are taken as evidence that the wild type elongation-decarboxylation I (EDI) pathway, leading to the synthesis of all the wax classes of compounds except esters, may be split into an early (EDIa) and a late (EDIb) group of reactions. Mutant glll is apparently defective at the EDIa, governing the synthesis of C₂₄–C₂₈ fatty acyl chains.     

A new method for degradation of the protein part of glycoproteins: isolation of the carbohydrate chains of asialofetuin

A new method has been developed for degrading the protein part of several glycoproteins, whilst leaving the carbohydrate portion virtually intact apart from partial degradation at the reducing end. The method is based upon stabilization of the glycosidic linkages of the sugar residues by trifluoroacetyl groups and subsequent cleavage of the peptide bonds by transamidation. The two reactions are carried out in a mixture of trifluoroacetic anhydride and trifluoroacetic acid. After O- and N-detrifluoroacetylation, the carbohydrate portion can be isolated and re-N-acetylated. The applicability of the method is demonstrated by the isolation from asialofetuin of the carbohydrate chains that are attached by N- and O-glycosyl links.