Variety Of Acceptors Research Articles

Glycosylation of vicinal di- and trifluorinated glucose and galactose donors.

The acid-catalysed formation of glycosidic bonds is more difficult when glycosyl donors are fluorinated, especially at the 2-position. Here we report high-yielding glycosidation and glycosylation reactions of 2,3-difluorinated- and 2,3,4-trifluorinated gluco- and galactopyranoside donors with a variety of acceptors under conventional trichloroacetimidate/TMSOTf activation in moderate to high anomeric selectivities. This methodology allows access to highly fluorinated glycans, illustrated with the synthesis of a pentafluorinated disaccharide.

Spiroconjugated Tetraaminospirenes as Donors in Color-Tunable Charge-Transfer Emitters with Donor-Acceptor Structure.

Charge‐transfer emitters are attractive due to their color tunability and potentially high photoluminescence quantum yields (PLQYs). We herein present tetraaminospirenes as donor moieties, which, in combination with a variety of acceptors, furnished 12 charge‐transfer emitters with a range of emission colors and PLQYs of up to 99 %. The spatial separation of their frontier molecular orbitals was obtained through careful structural design, and two DA structures were confirmed by X‐ray crystallography. A range of photophysical measurements supported by DFT calculations shed light on the optoelectronic properties of this new family of spiro‐NN‐donor‐acceptor dyes.

Twisted One-Dimensional Charge Transfer and Related Y-Shaped Chromophores with a 4H-Pyranylidene Donor: Synthesis and Optical Properties.

Three series of push–pull derivatives bearing 4H-pyranylidene as electron donor group and a variety of acceptors were designed. On one hand, one-dimensional chromophores with a thiophene ring (series 1H) or 5-dimethylaminothiophene moiety (series 1N) as an auxiliary donor, non-coplanar with the π-conjugated system, were synthesized. On the other hand, related two-dimensional (2D) Y-shaped chromophores (series 2) were also prepared to compare how the diverse architectures affect the electrochemical, linear, and second-order nonlinear optical (NLO) properties. The presence of the 5-dimethylaminothiophene moiety in the exocyclic C=C bond of the pyranylidene unit gives rise to oxidation potentials rarely low, and the protonation (with an excess of trifluoroacetic acid) of its derivatives results in the apparition of a new blue-shifted band in the UV–visible spectra. The analysis of the properties of derivatives with and without the additional thiophene ring shows that this auxiliary donor leads to a higher NLO response, accompanied by an enhanced transparency. Y-shaped chromophores of series 2 present a blue-shifted absorption, higher molar extinction coefficients, and higher Eox values compared to their linear twisted counterparts. As concerns NLO properties, 2D Y-shaped architecture gives rise to somewhat lower μβ values (except for thiobarbiturate derivatives).

ChemInform Abstract: Selective Synthesis of 1,2‐cis‐α‐Glycosides Without Directing Groups. Application to Iterative Oligosaccharide Synthesis.

AbstractA variety of acceptors is applied in the reactions of thioglycosides (I) or (IV), including (II), cholesterol, and mono‐ and disaccharides.

ChemInform Abstract: Glycosyl Iodides Are Highly Efficient Donors under Neutral Conditions.

Abstract Glycosyl iodides have been prepared and subjected to glycosylation under neutral conditions. The reactions are highly efficient, giving α glycosides even with sterically demanding glycosyl acceptors. Glucosyl iodides react with allyl alcohol slowest and require refluxing conditions. Galactosyl iodides are intermediate in reactivity, providing the allyl glycoside in 3 h at room temperature, whereas glycosylation of fucosyl iodides occurs in less than 1 h under similar conditions. The scope and limitations of the reactions were demonstrated with a variety of acceptors, including an anomeric hydroxyl group, to give trehalose analogs. β-Selective glycosylation of glucosyl iodides, in the absence of C-2 participation, could be achieved by simply changing the solvent from benzene to acetonitrile.

Probing Persistent Intramolecular C−H···X (X = O, S, Br, Cl, and F) Bonding in Solution Using Benzyl Meldrum’s Acid Derivatives

Persistent intramolecular interactions between acidic C-H hydrogens and a variety of acceptors (X) (X = O, S, Br, Cl, and F) in solution were probed by (1)H NMR experiments, using 5-benzyl Meldrum's acid derivatives. To bring about formation of intramolecular C-H...X bonding, ortho-substituted benzyl Meldrum's acids were designed, for which hydrogen bonding occurred through a six-membered ring. Introduction of substituents on the aromatic moiety and in the tether allowed variation of electronic and steric factors. The superior acidity of Meldrum's acids impacted the ability of the C-H hydrogen to engage in nonclassical C-H...X bonds and drove the conformational properties of benzyl Meldrum's acid, in combination with steric factors, namely A(1,3)-allylic strain. Further understanding of intramolecular C-H...X bonds was gained by characterization of benzyl Meldrum's acids in the solid state, by X-ray analysis, and by the conformation correlated to the observations made in solution.

Metallophosphite‐Induced Nucleophilic Acylation of α,β‐Unsaturated Amides: Facilitated Catalysis by a Diastereoselective Retro [1,4] Brook Rearrangement

Metallophosphite‐Induced Nucleophilic Acylation of α,β‐Unsaturated Amides: Facilitated Catalysis by a Diastereoselective Retro [1,4] Brook Rearrangement

Glycosyl iodides are highly efficient donors under neutral conditions

Glycosyl iodides have been prepared and subjected to glycosylation under neutral conditions. The reactions are highly efficient, giving α glycosides even with sterically demanding glycosyl acceptors. Glucosyl iodides react with allyl alcohol slowest and require refluxing conditions. Galactosyl iodides are intermediate in reactivity, providing the allyl glycoside in 3 h at room temperature, whereas glycosylation of fucosyl iodides occurs in less than 1 h under similar conditions. The scope and limitations of the reactions were demonstrated with a variety of acceptors, including an anomeric hydroxyl group, to give trehalose analogs. β-Selective glycosylation of glucosyl iodides, in the absence of C-2 participation, could be achieved by simply changing the solvent from benzene to acetonitrile.

LBP does not substitute for CD14 as a signaling membrane bound LPS receptor

CD14 is well known as a receptor for LPS. However, the mechanism of signal transduction which LPS initiates upon binding to CD14 is not known. One theory is that CD14 presents LPS to another molecule which in turn initiates cellular activation [Ulevitch RJ, Tobias PS. Receptor-dependent mechanisms of cell stimulation by bacterial endotoxin. Annu Rev Immunol 1995; 13: 437]. In this context one may ask whether the postulated presentation function of CD14 is limited to simple concentration of LPS at the cell surface or whether CD14 performs some other more specific function. LPS binding protein (LBP) is able to bind and transfer LPS to a variety of acceptors [Wurfel MM, Wright SD. Lipopolysaccharide-binding protein and soluble CD14 transfer lipopolysaccharide to phospholipid bilayers: preferential interaction with particular classes of lipid. J Immunol 1997; 158: 3925] and, as such, is a candidate as an alternative to CD14 if the function of CD14 is simply to concentrate LPS at the cell surface. To address this, CHO and U373 cells were engineered to express a membrane anchored form of LBP (mLBP) for comparison with cells expressing membrane anchored CD14 (mCD14) as well as empty vector transfected cells. Activation of the cells by LPS was assessed using activation of NFκB (CHO and U373 cells), and surface expression of ICAM and secretion of IL-6 (U373 cells). Despite the observation that LBP did concentrate LPS at the cell surface, as assessed by binding of either fluorescein or tritium labeled LPS, the activation of LBP expressing cells was several orders of magnitude less efficient than activation of the mCD14 expressing cells and only minimally more efficient than activation of empty vector transfected cells. This slight effect is likely to be due to the presence of a small amount of soluble CD14 (sCD14) and the ability of mLBP to foster formation of LPS-sCD14 complexes which are agonistic for these cells. Thus LBP clearly cannot act as an efficient surrogate for CD14, and the function of CD14 is more complicated than the simple concentration of LPS at the cell surface.

LBP does not substitute for CD14 as a signaling membrane bound LPS receptor

CD14 is well known as a receptor for LPS. However, the mechanism of signal transduction which LPS initiates upon binding to CD14 is not known. One theory is that CD14 presents LPS to another molecule which in turn initiates cellular activation [Ulevitch RJ, Tobias PS. Receptor-dependent mechanisms of cell stimulation by bacterial endotoxin. Annu Rev Immunol 1995; 13: 437]. In this context one may ask whether the postulated presentation function of CD14 is limited to simple concentration of LPS at the cell surface or whether CD14 performs some other more specific function. LPS binding protein (LBP) is able to bind and transfer LPS to a variety of acceptors [Wurfel MM, Wright SD. Lipopolysaccharide-binding protein and soluble CD14 transfer lipopolysaccharide to phospholipid bilayers: preferential interaction with particular classes of lipid. J Immunol 1997; 158: 3925] and, as such, is a candidate as an alternative to CD14 if the function of CD14 is simply to concentrate LPS at the cell surface. To address t...

Human α1,3/4-Fucosyltransferases: II. A SINGLE AMINO ACID AT THE COOH TERMINUS OF FucT III AND V ALTERS THEIR KINETIC PROPERTIES

An analysis of the acceptor substrate specificity of domain swap mutants of human alpha1,3/4-fucosyltransferases (FucTs) III and V has been carried out. The results demonstrate that changing Asp336 of FucT III to Ala (as in FucT V) produced a protein (III/V1) with a reduced activity with a variety of acceptors. An analysis of the kinetic properties of FucT III and the III/V1 mutant demonstrated that III/V1 had a 40-fold reduction in its affinity for the H-type 1 acceptor substrate (Fucalpha1,2Galbeta1,3GlcNAc) and 4-fold reduction in its affinity for GDP-fucose when compared with FucT III. Further, the overall catalytic efficiency of III/V1 was approximately 100-fold lower than that of FucT III with an H-type 1 acceptor substrate. The complementary domain swap resulting from the change of Ala349 of FucT V to Asp (V/III1) produced a FucT that had higher enzyme activity with a range of acceptor substrates and had a higher affinity for an H-type 2 acceptor substrate (Fucalpha1, 2Galbeta1,4GlcNAc) with an 8-fold higher overall catalytic efficiency than that of FucT V. No significant change occurred in the Km for GDP-fucose for this protein when compared with FucT V. Kinetic parameters of two other FucT domain swaps (III8/V and V8/III), resulting in proteins that differed from FucT III and V at the NH2 terminus of their catalytic domain, were not significantly different from those of the parental enzymes when H-type 1 and H-type 2 acceptor substrates were utilized. Thus, substitution of an acidic amino acid for a nonpolar amino acid (i.e. Asp versus Ala) at the COOH terminus of FucTs produces an enzyme with enhanced enzyme activities. These results, together with the results presented in the accompanying papers (Nguyen, A. T., Holmes, E. H., Whitaker, J. M., Ho, S., Shetterly, S., and Macher, B. A. (1998) J. Biol. Chem. 273, 25244-25249; Sherwood, A. L., Nguyen, A. T., Whitaker, J. M., Macher, B. A., and Holmes, E. H. (1998) J. Biol. Chem. 273, 25256-25260), provide new insights into the structure/function relationships of human alpha1,3/4-FucT enzymes.

Increased sialylation of complex glycopeptides during differentiation of mouse embryonal carcinoma cells

High-molecular-weight, asparagine-linked glycopeptides – the lactosaminoglycans – are the major class of protein-bound carbohydrates synthesized by F9 cells; these cells synthesize only minor amounts of smaller glycopeptides. In contrast, F9ACC19, an endodermal cell line derived from F9 cells, synthesizes only minor amounts of lactosaminoglycans and a high proportion of smaller glycopeptides. Biochemical analysis of the small glycopeptides from F9ACC19 cells revealed that they are larger, bind less efficiently to concanavalin-A Sepharose and contain more sialic acid than their counterparts from F9 cells. Both cell types contain a small proportion of high-mannose glycopeptides. When synthesized by F9ACC19 cells, the glycopeptides of vesicular stomatitis virus show a high level of sialylation as compared to those synthesized by F9 cells, where few or no sialic-acid residues are present; this shows that the differences observed in total glycopeptides reflect differences in the glycosylation machinery of the cells. Consistent with this observation, sialyltransferase activity in vitro using a variety of acceptors was found to be markedly higher in F9ACC19 than in F9 cells, while galactosyltransferase activity was reduced several fold in F9ACC19 cells. These data support the hypothesis that the increased sialyltransferase activity in endodermal differentiated F9ACC19 cells may block the terminal galactose residue of glycopeptides, thereby inhibiting the synthesis of lactosaminoglycans in these cells.

35Cl nuclear quadrupole resonance of donor–acceptor complexes. Part II

35 Cl N.q.r. frequencies of chlorine atoms in various donor molecules forming complexes with Lewis acids are reported and compared with those of the free donor molecule. An extensive study of complexes of 2-, 3-, and 4-chloropyridine with a variety of acceptors shows that the nature of the acceptor has little effect on the resonance frequency and that the further the chlorine atom is removed from the donor center the smaller is the effect on the resonance frequency. Both σ and π bonding of the chlorine atom to the donor group are affected to about the same extent.

Protective effects of histones against drug-induced alterations of deoxyribonucleic acid in thymus chromatin

When S-(1,2-dichlorovinyl)- l-cysteine is cleaved by a lyase in vitro, a very reactive alkylating fragment (AF) is produced which can combine with a variety of acceptors, including DNA. Using 35S as tracer of AF, it was shown that histone, added as such, and particularly in the form of bovine thymus chromatin reacted with AF and greatly decreased the extent to which AF combined with DNA. In contrast to DNA treated directly with AF, DNA which was isolated from AF-treated chromatin retained most of its primer activity for DNA and RNA polymerases and its susceptibility to hydrolysis by pancreatic DNase I. These results illustrate the role which histones and perhaps other nuclear proteins may have in protecting DNA against interaction with various toxic agents. They may also have a bearing on the susceptibility of various cells, tissues and species to the effects of proximate carcinogens and other proximate toxicants formed by metabolic reactions of toxic or therapeutic agents in vivo.

The Donor Properties of Pyridine N-Oxide

Abstract : The coordination chemistry of pyridine N-oxide with a variety of acceptors has been investigated. The new substances Co(ClO4)2.6L, Co(NO3)2.6L, CoCl2.3L, CoCl2.L.H20, Ni(ClO4)2.6L, NiCl2.L.H2O, NiBr2.6L, NiI2.6L, NiBr2.L. H2O, Cu(ClO4)2.4L, Cu(NO3)2.2L, CuCl2.L, CuCl2.2L, Zn(ClO4)2.6L, ZnCl2.2L, Zn(NO3)2.6L, Fe(ClO4)2.6L, Fe(ClO4)3.6L, and SnBr4.2L (where L is pyridine N-oxide) have been isolated and characterized by molecular conductance measurements in non-aqueous solvents, magnetic susceptibility measurements, and infrared spectra. All of the perchlorates and some of the nitrates and halides have only the pyridine N-oxide in the first coordination sphere. However, in some cases, both nitrates and halides are coordinated to the central ion.

The site of electron transfer to various acceptors in sucinoxidase system, with special reference to that of ethylurethane.

A study of succinoxidase system in rat liver mitochondria has been made, with special reference to the site of action of ethylurethane, and the site of electron transfer to several electron acceptors in this system.1. The inhibitory action of ethylurethane on succinoxidase system varied with the variety of acceptors used and it was not observed when brilliant cresyl blue was the acceptor. The inhibition was completely reversible up to the concentration of 0.5 M.2. The existence of two pathways: an “antimycin A-sensitive” and an “antimycin A-resistant, ” was indicated to link ferricyanide, 2, 6-dichlorophenolindophenol, and methylene blue with the succinoxidase system. One of the factors involved in the antimycin A-sensitive pathway is cytochrome c.3. The sensitivity of succinoxidase toward ethylurethane was exaggerated by the treatment with antimycin A and BAL and by the addition of cytochrome c. On the other hand, simultaneous addition of ethylurethane failed to protect the inhibition by BAL. Antimycin A titer of succinoxidase was decreased slightly by the presence of ethylurethane.4. From these results, the mechanism of action of ethylurethane was discussed together with that of antimycin A and BAL, and it was concluded that the site of action of ethylurethane lies at the portion of cytochrome b and Slater factor.