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At least 937 records · Page 52Linked to original sources
PubMed2006

A chromogenic macrocycle exhibiting cation-selective and anion-controlled color change: an approach to understanding structure-color relationships.

[reaction: see text] A N-azo-coupled macrocycle (1) with a NO(2)S(2) donor set was synthesized as a chromoionophore and shown to exhibit Hg(2+) selectivity; anion control of the color of the Hg(2+) complex was observed. As a first approach, the nature of the color generation process was probed by determining the crystal structures of the two different colored species obtained with perchlorate and iodide anions. The results can be explained in terms of a "Push-n-Pull Process", which serves to illustrate how the coordinating ability of the anion controls the color change through formation of endo- or exo-metal complexes. The use of "simple" salts to induce color-switching of the above complex species was also reported.

Journal Article↗
PubMed2006

Versatile and practical chiral shift reagent with hydrogen-bond donor/acceptor sites in a macrocyclic cavity.

[structure: see text] Bifunctional macrocycle 1 with C2 symmetry was newly synthesized. NMR studies demonstrated that receptor 1 functions as a chiral shift reagent (solvating agent) that is highly effective for a wide range of chiral compounds having a carboxylic acid, oxazolidinone, lactone, alcohol, sulfoxide, sulfoximine, isocyanate, or epoxide functionality. Binding constants were determined to investigate the binding behavior of 1.

Journal Article↗
PubMed2006

Macrocyclic chiral receptors toward enantioselective recognition of naproxen.

[structure: see text] A macrocyclic receptor based on a bischromenylurea and an alpha,alpha'-(o,o'-dialkyl)diphenyl-p-xylylenediamine spacer provides a C(2) chiral cavity to associate carboxylates by H-bonds. The extent of the selectivity obtained for the racemic receptor 2 and enantiomerically pure (S)-naproxen is 7.2:1. Steric repulsions close to the cavity are decisive for the chiral selectivity.

Binding Sites↗
PubMed2006

Macrocyclic scaffold for the collagen triple helix.

[structure: see text] Three strands of natural collagen are linked by covalent bonds prior to their folding into a triple helix. We report on a synthetic collagen in which the strands are pendent on a rigid macrocyclic scaffold of C(3) symmetry. The scaffold confers substantial conformational stability upon the collagen triple helix and makes its folding independent of concentration, both desirable attributes for exploring and exploiting synthetic collagens.

Amino Acid Sequence↗
PubMed2006

Synthesis of [2]rotaxanes by the catalytic reactions of a macrocyclic copper complex.

We synthesized [2]rotaxanes by the reactions catalyzed by a macrocyclic Cu(I)-phenanthroline complex. The catalytic site was located inside the ring component so that the rotaxane could be selectively formed. A C-S bond-forming reaction and oxidative dimerization of alkyne was utilized for the efficient synthesis of a new series of [2]rotaxanes. [reaction: see text]

Journal Article↗
PubMed1999

A formal total synthesis of roseophilin: cyclopentannelation approach to the macrocyclic core.

[formula: see text] The formal total synthesis of the macrocyclic core of roseophilin 4 has been accomplished in 12 steps from 5-hexenal 8. The cyclopentannelation reaction was used to form the aliphatic five-membered ring of 3. Diene 2 was assembled by means of a Stetter reaction. Ring-closing metathesis of 2, reduction, and Knorr reaction of the 1,4-diketone 5 gave the ketopyrrole 3.

Cyclopentanes↗
PubMed1999

Efficient synthesis of 40- and 48-membered tetraether macrocyclic bisphosphocholines.

An efficient route toward the synthesis of unsaturated (bis-diacetylenic) and saturated 40- and 48-membered macrocyclic biphosphocholines has been developed using 2-phenyl-5-hydroxy-1,3-dioxane as a common glycerol synthon. Ring closure was accomplished using either high-dilution Glaser oxidation of [(Cy3P)2RU==CHPh]Cl2-catalyzed olefin metathesis conditions. Deprotection of benzyl ethers using trimethylsilyl iodide (TMS-I) in the presence of diacetylenic moieties has also been demonstrated for the first time.

Acetylene↗
PubMed2001

Novel mechanism of blocking axonal Na(+) channels by three macrocyclic polyamine analogues and two spider toxins.

1. The mechanism of Na(+) channel block by three macrocyclic polyamine derivatives and two spider toxins was studied with voltage clamp and internal perfusion method in squid axons. 2. All these chemicals specifically block Na(+) channels in the open state only from the internal surface, and do not affect K(+) channels. 3. The blocking effect is enhanced as the depolarizing pulse becomes larger. Blocked channels are unable to shift to the inactivated state. 4. In the case of cyclam and guanidyl-side armed cyclam (G-cyclam), quick release of these chemicals from the binding sites is proven by the increase in the tail current and prolongation of the time course of the off gating current. On the other hand, in the presence of N-4 and the spider toxins, their detachment was delayed significantly. 5. Molecular requirements for the block of Na(+) channels by these molecules are the presence of positive charge and hydrophobicity.

Algorithms↗
PubMed1999

Induction of apoptosis and differentiation by fludarabine in human leukemia cells (U937): interactions with the macrocyclic lactone bryostatin 1.

We have examined interactions between the purine nucleoside analog fludarabine (9-beta-arabinofuranosyl-2-fluoroadenine) and the macrocyclic lactone bryostatin 1 in the human monocytic leukemic cell line U937. Fludarabine exerted dose-dependent effects on U937 cell viability and growth which were associated with both induction of apoptosis, as well as cellular maturation. Incubation of cells with bryostatin 1 (10 nM; 24 h) after, but not before a 6-h exposure to 10 microM fludarabine resulted in a modest but significant increase in apoptosis, and was associated with greater than a 1 log reduction in clonogenicity. Subsequent exposure to bryostatin 1 also increased the percentage of fludarabine-treated cells displaying differentiation-related features (eg plastic adherence, CD11b positivity) compared to cells exposed to fludarabine alone. Bryostatin 1 did not increase the retention of the active fludarabine metabolite, F-ara-ATP, nor did it increase 3H-F-ara-A incorporation into DNA. Despite its capacity to trigger cellular maturation, fludarabine exposure (either with or without bryostatin 1) failed to induce the cyclin-dependent kinase inhibitors (CDKls) p21WAF1/CIP1 and p27KIP1. Nevertheless, dysregulation of p21 (resulting from stable transfection of cells with a p2lWAF1/CIP1 antisense construct) reduced fludarabine-mediated differentiation, while inducing a corresponding increase in apoptosis. Enforced expression of Bcl-2 partially protected cells from fludarabine-related apoptosis, an effect that was overcome, in part, by subsequent exposure of cells to bryostatin 1. Interestingly, Bcl-2-overexpressing cells were as or in some cases, more susceptible to differentiation induction by fludarabine (+/- bryostatin 1) than their empty vector-containing counterparts. Collectively, these results indicate that the antiproliferative effects of fludarabine toward U937 leukemic cells involve both induction of apoptosis and cellular maturation, and that each of these processes may be enhanced by bryostatin 1.

Antineoplastic Agents↗
PubMed1997

Highly selective iodide poly(vinyl chloride) membrane electrode based on a nickel(II) tetraazaannulene macrocyclic complex.

A PVC membrane electrode based on a nickel(II) tetraazaannulene macrocyclic complex as the carrier is described. The electrode exhibits an anti-Hofmeister selectivity sequence with a preference for iodide at pH 3.0-4.0. It has a linear response to iodide from 8.0 x 10(-6) to 1 x 10(-1) mol dm-3 with a slope of -54.7 +/- 0.2 mV per decade (20 degrees C), a satisfactory reproducibility and a rapid response time. The pH dependence of the potential response is discussed. The response mechanism of the electrode was investigated by ac impedance, quartz crystal microbalance and spectroscopic techniques. The electrode can be used for the determination of iodide in drug preparations.

Heterocyclic Compounds↗
PubMed2001

Synthesis of alkenylene-bridged macrocyclic silsesquioxanes by ruthenium or rhodium-catalyzed ring-closing reactions of bis(allyldimethylsilyl) groups.

Novel alkenylene-bridged oligosilsesquioxanes composed of half-caged structures with 16- or 17-membered rings as well as a titanium-containing molecule with a twisted 21-membered macrocycle have been synthesized by ruthenium or rhodium-catalyzed ring-closing reactions of silsesquioxanes with bis(allyldimethylsilyl) groups.

Journal Article↗
PubMed2002

Novel hetero-bimetallic metalla-macrocycles based on the bis-1-pyridyl ferrocene [Fe(eta 5-C5H(4)-1-C5H4N)2] ligand. Design, synthesis and structural characterization of the complexes [Fe(eta 5-C5H(4)-1-C5H4N)2](AgI)2(2+)/(CuII)2(4+)/(ZnII)2(4+).

The bidentate sandwich ligand [Fe(eta 5-C5H(4)-1-C5H4N)2] has been prepared, structurally characterized and employed in the preparation of the novel supramolecular heterobimetallic metalla-macrocycles [Fe(eta 5-C5H(4)-1-C5H4N)2]Ag2(NO3)(2).1.5H2O, [Fe(eta 5-C5H(4)-1-C5H4N)2]Cu2(CH3COO)(4).3H2O and [Fe(eta 5-C5H(4)-1-C5H4N)2]Zn2Cl4.

Journal Article↗
PubMed2002

The formation of a cyclic diacetal of methyl alpha-D-mannopyranoside with a 16-membered macrocyclic loop.

The X-ray structure of a diacetal with a 16-membered macrocyclic loop, which was obtained as a product of the condensation of methyl alpha-D-mannopyranoside and 1,4-bis(2-formylphenoxy)butane is presented together with polymeric compounds resulting from polycondensation; a similar polymer was formed in the reaction of methyl 2,3:4,6-di-O-salicylidene-alpha-D-mannopyranoside with 1,4-dibromobutane.

Carbohydrate Sequence↗