The total synthesis of mixed‐sequence alginate oligosaccharides, featuring both β‐D ‐mannuronic acid (M) and α‐L ‐guluronic acid (G), is reported for the first time. A set of GM, GMG, GMGM, GMGMG, GMGMGM, GMGMGMG, and GMGGMG alginates was assembled using GM building blocks, having a guluronic acid acceptor part and a mannuronic acid donor side to allow the fully stereoselective construction of the cis‐glycosidic linkages. It was found that the nature of the reducing‐end anomeric center, which is ten atoms away from the reacting alcohol group in the key disaccharide acceptor, had a tremendous effect on the efficiency with which the building blocks were united. This chiral center determines the overall shape of the acceptor and it is revealed that the conformational flexibility of the acceptor is an all‐important factor in determining the outcome of a glycosylation reaction. 相似文献
The structure of the title compound, C28H38O18S, has been determined. The torsion angles of the glycosidic linkage in the non‐reducing disaccharide, ?H and ?H′, have values of 3 and 53°, respectively. The latter torsion angle is in agreement with the exo‐anomeric effect, whereas the former shows an eclipsed conformation. Both glycopyranosyl residues adopt a slightly distorted chair conformation. 相似文献
A water‐soluble benzenesulfonamidoquinolino‐β‐cyclodextrin has been successfully synthesized in 30 % yield by incorporating a N‐(8‐quinolyl)‐p‐aminobenzenesulfonamide (HQAS) group to β‐cyclodextrin through a flexible linker. This compound exhibits a good fluorescence response in the presence of Zn2+ in water but gives poor fluorescence responses with other metal ions commonly present in a physiological environment under similar conditions. Fluorescence microscopic and two‐dimensional NMR experiments showed that benzenesulfonamidoquinolino‐β‐cyclodextrin could bind to the loose bilayer membranes. As a result, benzenesulfonamidoquinolino‐β‐cyclodextrin was found to act as an efficient cell‐impermeable Zn2+ probe, showing a specific fluorescent sensing ability to Zn2+‐containing damaged cells whilst exhibiting no response in the presence of healthy cells. 相似文献
A fluorescent turn‐on probe for specifically targeting γ ‐glutamyltranspeptidase (GGT ) was designed and synthesized by integrating boron‐dipyrromethene (BODIPY ) as a chromophore and glutathione (GSH ) as the GGT substrate. GGT ‐catalyzed the cleavage of the γ ‐glutamyl bond and generated the aromatic hydrocarbon transfer between the sulfur and the nitrogen atom in BODIPY , leading to distinct optical changes. Such specific responsiveness provides an easily distinguishable fluorescence signal to visualize the GGT activity in living cells and differentiate GGT ‐positive cancer cells from GGT ‐negative cells. 相似文献
The water content of the title compound, C13H24O10·3H2O, creates an extensive hydrogen‐bonding pattern, with all the hydroxyl groups of the disaccharide acting as hydrogen‐bond donors and acceptors. The water molecules are arranged in columns along the crystallographic b axis and form, together with one of the hydroxyl groups, infinite hydrogen‐bonded chains. The conformation of the disaccharide is described by glycosidic torsion angles of −38 and 18°. 相似文献
The protected apiose-containing disaccharide, benzyl O-(2,3, 3'-tri-O-acetyl-β-D-apiofuranosyl)-( 1→3)-2, 4-di-O-benzoyl-α-D-xylopyranoside, was synthesized and its X-ray structure provided. 相似文献
We have developed an expeditious procedure to yield large amounts of orthogonally protected Gal‐β1,3/4‐GlcNAc, which allowed for the systematic introduction of a sulfate group onto the C3/C6 positions of Gal and/or the C6 position of GlcNAc. In particular, the disaccharide precursors were prepared in five or six steps and high overall yield from para‐tolyl‐6‐O‐tert‐butyldiphenylsilyl‐1‐thio‐β‐D ‐galactopyranoside. After deprotection and sulfation steps, the final products were characterized by using several NMR methods to unambiguously confirm the location of each introduced sulfate group and they were examined for their binding specificity of human galectin‐1 and galectin‐8. 相似文献
7‐Alkynylated 7‐deazaadenine (pyrrolo[2,3‐d]pyrimidin‐4‐amine) 2′‐deoxyribonucleosides show strong fluorescence which is induced by the 7‐alkynyl side chain (Table 3). A large Stokes shift with an emission around 400 nm is observed when the compound is irradiated at 280 nm. The solvent dependence indicates the formation of a charged transition state. The fluorescence appears when the triple bond is in conjugation with the heterocyclic base. Electron‐donating substituents at the triple bond increase the fluorescence, while electron‐withdrawing residues reduce it. In comparison, the 7‐alkynylated 8‐aza‐7‐deazaadenine (pyrazolo[3,4‐d]pyrimidin‐4‐amine) 2′‐deoxyribonucleosides are rather weakly fluorescent (Table 4). Quantum yields and fluorescence decay times are measured. The synthesis of the 7‐alkynylated 7‐deaza‐2′‐deoxyadenosines and 8‐aza‐7‐deaza‐2′‐deoxyadenosines was performed with 7‐deaza‐2′‐deoxy‐7‐iodoadenosine ( 6 ) or 8‐aza‐7‐deaza‐2′‐deoxy‐7‐iodoadenosine ( 22 ) as starting materials and employing the Pd0‐catalyzed cross‐coupling reaction with the corresponding alkynes (Schemes 1, 4, and 5). Catalytic hydrogenation of the side chain of the unsaturated nucleosides 5 and 17 afforded the 7‐alkyl derivatives 18 and 19 , respectively, which do not show significant fluorescence (Scheme 2). 相似文献
A simple synthesis of a new, highly fluorescent amino acid and of its protected derivative useful in peptide studies is described. The obtained derivative, N‐[(tert‐butoxy)carbonyl]‐3‐(9,10‐dihydro‐9‐oxoacridin‐2‐yl)‐L ‐alanine ( 6 ), shows intense long‐wave absorption (above 360 nm) and emission (above 400 nm). The quantum yield of fluorescence of the investigated compound is very high, so it can serve as a sensitive analytical probe useful, e.g., in analysis of peptide conformations. 相似文献
A new route for the synthesis of substituted 8‐methyl‐6‐phenyl‐5,6‐dihydro‐4H‐1,3,2‐benzodioxaphosphocine‐2‐oxide derivatives has been developed by using cinnamic acid and p‐cresol via condensation, reduction, and followed by phosphorylation steps. The title compounds were characterized by IR, 1H, 13C, 31P, and mass spectral studies and elemental analysis. The title compounds have been investigated for their antioxidant activity with respect to their IC50 values using 2,2‐diphenyl‐1‐picrylhydrazyl, NO radical scavenging activities, and reducing power assay. The results obtained from the aforementioned methods revealed that 2‐phenylamino derivatives have shown greater free radical scavenging activity when compared with those of the phenoxy derivatives and is attributed to the presence of secondary amino group, which is able to produce free radicals easily. 相似文献
The enzymatic ring‐opening polymerization of a 6‐membered cyclic depsipeptide, 3(S)‐isopropylmorpholine‐2,5‐dione in the bulk, was investigated by using lipases as catalysts at 100 and 130°C. Unchanged monomer was recovered in the absence of the enzyme or using an inactivated enzyme, indicating that the present polymerization proceeds through enzymatic catalysis. Poly(3‐isopropylmorpholine‐2,5‐dione) has a carboxylic acid group at one end and a hydroxy group at the other end. 相似文献
Catalytic base‐induced decarboxylation of polyunsaturated α‐cyano‐β‐methyl acids derived from malonic acid led to the corresponding nitriles 3 (Schemes 2 and 3), 6 (Scheme 5), and 9 (Scheme 6). This decarboxylation occurred with previous deconjugation of the α,β‐alkene moiety of the α‐cyano‐β‐methyl acid, leading to an α‐cyano‐β‐methylene propanoic acid which was easily decarboxylated (see Scheme 2). β‐Methylene intermediates, in some cases, could be isolated; mechanistic pathways are proposed. The nitriles 3, 6 , and 9 were reduced to the sesquiterpene aldehydes 4 (β‐end group), 7 (φ‐end group), and 10 (ψ‐end group), respectively. 相似文献
Preparation of Lipid II analogues containing an enzymatically uncleavable 1‐C‐glycoside linkage between the disaccharide moiety and the pyrophosphate‐ or pyrophosphonate‐lipid moiety is described. The synthesis of a common 1‐C‐vinyl disaccharide intermediate has been developed that allows easy preparation of both an elongated sugar‐phosphate bond and a sugar‐phosphonate moiety, which are coupled with the polyprenyl phosphate to give the desired molecules. Inhibition studies show how a subtle structural modification results in dramatically different potency toward bacterial transglycosylase (TGase), and the results identify Lipid II‐C‐O‐PP (IC50=25 μM ) as a potential TGase inhibitor. 相似文献
A convenient and divergent approach was developed to prepare diverse bacterial 3‐deoxy‐d ‐manno‐oct‐2‐ulosonic acid (Kdo) oligosaccharides containing a Kdo‐α‐(2→4)‐Kdo fragment. The orthogonal protected α‐(2→4) linked Kdo‐Kdo disaccharide 3 , serving as a common precursor, was divergently transformed into the corresponding 8‐, 8′‐, and 4′‐hydroxy disaccharides 5 , 7 , and 14 , respectively. Then, these alcohols were glycosylated, respectively, with the 5,7‐O‐di‐tert‐butylsilylene (DTBS) protected Kdo thioglycoside donors 1 or 2 in an α‐stereoselective and high‐yielding manner to afford a range of Kdo oligosaccharides. Finally, removal of all protecting groups of the newly formed glycosides resulted in the desired free Kdo oligomer. 相似文献
A highly K+‐selective two‐photon fluorescent probe for the in vitro monitoring of physiological K+ levels in the range of 1–100 mM is reported. The two‐photon excited fluorescence (TPEF) probe shows a fluorescence enhancement (FE) by a factor of about three in the presence of 160 mM K+, independently of one‐photon (OP, 430 nm) or two‐photon (TP, 860 nm) excitation and comparable K+‐induced FEs in the presence of competitive Na+ ions. The estimated dissociation constant (Kd) values in Na+‐free solutions (KdOP=(28±5) mM and KdTP=(36±6) mM ) and in combined K+/Na+ solutions (KdOP=(38±8) mM and KdTP=(46±25) mM ) reflecting the high K+/Na+ selectivity of the fluorescent probe. The TP absorption cross‐section (σ2PA) of the TPEF probe+160 mM K+ is 26 GM at 860 nm. Therefore, the TPEF probe is a suitable tool for the in vitro determination of K+. 相似文献
Biotinylated gradient glycopolymers have been synthesized via RAFT copolymerization of an acrylamide derivative of galactose with N‐acryloylmorpholine in the presence of a biotin CTA. The polymerization was controlled with a linear increase in molecular weights up to 80% conversion. Copolymer chains have a gradient microstructure with an increasing proportion of galactose units towards the ω chain end. The presence of the biotin ligand at the α end of the chains was confirmed by 1H NMR and MALDI‐ToF MS. This strategy based on the use of a biotin‐CTA instead of a post‐polymerization labelling of the chains resulted in a high percentage of α‐functionalized chains (92–95%). Such α‐end‐functionalized glycopolymer chains may interact with streptavidin‐modified surfaces.