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At least 595 records · Page 33Linked to original sources
PubMed2004

Benzylidene acetal fragmentation route to 6-deoxy sugars: direct reductive cleavage in the presence of ether protecting groups, permitting the efficient, highly stereocontrolled synthesis of beta-D-rhamnosides from D-mannosyl glycosyl donors. Total synthesis of alpha-D-Gal-(1-->3)-alpha-D-Rha-(1-->3)- beta-D-Rha-(1-->4)-beta-D-Glu-OMe, the repeating unit of the antigenic lipopolysaccharide from Escherichia hermannii ATCC 33650 and 33652.

An approach to the stereocontrolled synthesis of beta-d-rhamnopyranosides is described in which 2,3-O-benzyl or related 4,6-O-[alpha-(2-(2-iodophenyl)ethylthiocarbonyl)benzylidene]-mannosyl thioglycosides are first used to introduce the beta-d-mannopyranoside linkage in high yield and stereoselectivity. Following glycosylation, treatment with tributyltin hydride in toluene at reflux brings about reductive radical fragmentation directly to the 6-deoxy sugar in high yield. A variation of these donors bearing a carboxylated donor on O3 is a highly alpha-selective mannosyl and, after radical fragmentation, alpha-d-rhamnosyl donor. Using this stereoselective glycosylation/radical-fragmentation approach, a concise synthesis of the title tetrasaccharide is realized in which both the beta-d- and alpha-d-rhamnopyranosyl units are obtained in a single step by a double radical fragmentation of the modified benzylidene acetals.

Benzylidene Compounds↗
PubMed2004

Bulky nonproteinogenic amino acids permit the design of very small and effective cationic antibacterial peptides.

The rate of multidrug-resistant infections is rapidly rising. Cationic antibacterial peptides are active against resistant pathogens and have low propensity for resistance development, but because of their unfavorable medicinal properties, cationic antibacterial peptides have been a limited clinical success. We have found that introduction of nongenetically coded amino acids and other lipophilic modifications opens the opportunity for development of extremely short and highly active antibacterial peptides with improved medicinal properties.

Anti-Bacterial Agents↗
PubMed2005

Surface grafted antibodies: controlled architecture permits enhanced antigen detection.

The attachment of antibodies to substrate surfaces is useful for achieving specific detection of antigens and toxins associated with clinical and field diagnostics. Here, acrylated whole antibodies were produced through conjugation chemistry, with the goal of covalently photografting these proteins from surfaces in a controlled fashion, to facilitate rapid and sensitive antigenic detection. A living radical photopolymerization chemistry was used to graft the acrylated whole antibodies on polymer surfaces at controlled densities and spatial locations by controlling the exposure time and area, respectively. Copolymer grafts containing these antibodies were synthesized to demonstrate two principles. First, PEG functionalities were introduced to prevent nonspecific protein interactions and improve the reaction kinetics by increasing solvation and mobility of the antibody-containing chains. Both of these properties lead to sensitive (pM) and rapid (<20 min) detection of antigens with this surface modification technique. Second, graft composition was tailored to include multiple antibodies on the same grafted chains, establishing a means for simultaneously detecting multiple antigens on one grafted surface area. Finally, the addition of PEG spacers between the acrylate functionality and the pendant detection antibodies was tuned to enhance the detection of a short-half-life molecule, glucagon, in a complex biological environment, plasma.

Acrylates↗
PubMed2006

Electroactive self-assembled monolayers that permit orthogonal control over the adhesion of cells to patterned substrates.

This article describes an electroactive substrate that displays two independent dynamic functions for controlling the adhesion of cells. The approach is based on self-assembled monolayers on gold that are patterned into regions presenting the Arg-Gly-Asp peptide cell adhesion ligand. The patterned regions differ in the electrochemical properties of the linkers that tether the peptides to the monolayer. In this work, three distinct chemistries are employed that provide for release of the ligand on application of a negative potential, release of the ligand on application of a positive potential, and no change in response to a potential. Cells were allowed to attach to a monolayer patterned into circular regions comprising the three chemistries. Treatment with electric potentials of 650 or -650 mV resulted in the selective release of adherent cells only from regions that display the relevant electroactive groups. This example establishes the preparation of dynamic substrates with multiple functions and will be important to preparing model cultures derived from multiple cell types, with control over the temporal interactions of each cell population.

Animals↗
PubMed1998

Cooling System Permits Effective Transcutaneous Ultrasound Clot Lysis In Vivo Without Skin Damage.

Previous in vivo studies have shown that transcutaneous ultrasound enhances clot dissolution in the presence of either streptokinase or microbubbles. However, ultrasound-induced skin damage has been a major drawback. The objective was to evaluate the effect of a cooling system to prevent the skin damage that has heretofore been associated with transcutaneous low-frequency, high-intensity ultrasound clot dissolution. After thrombi were induced in both iliofemoral arteries in 15 rabbits, streptokinase (25,000 U/kg) was given intravenously and dodecafluoropentane was injected slowly (2 mL/15 min) through an infusion catheter into the abdominal aorta. One iliofemoral artery was randomized to receive ultrasound treatment, and the contralateral artery was treated as a control (receiving streptokinase and dodecafluoropentane alone). In six rabbits (group 1), the skin below the ultrasound transducer was protected by the use of a balloon cooling system, and in the other nine rabbits (group 2), ultrasound was used without a cooling system. Seven of nine (78%) arteries treated without the cooling system, and six of six (100%) arteries treated with the cooling system were angiographically recanalized after ultrasound + streptokinase + dodecafluoropentane treatment. Thermal damage was present in the skin and soft tissues of all nine rabbits treated without a cooling system. However, the skin and soft tissues were grossly and histologically normal in the six rabbits in which the transcutaneous ultrasound was used with the cooling system. Low-frequency, high-intensity ultrasound energy can be delivered transcutaneously for clot dissolution without concomitant tissue damage when coupled with the use of a cooling system to prevent thermal injury.

Journal Article↗
PubMed2003

Impaired NF-kappaB activation in T cells permits tolerance to primary heart allografts and to secondary donor skin grafts.

T-cell activation is essential for acute allograft rejection. However, the biochemical signaling pathways used by T cells mediating rejection have not been extensively investigated. In vitro, T-cell activation is associated with nuclear translocation of specific transcription factors that regulate expression of genes critical for T-cell function. Given the central role of NF-kappaB in T-cell activation In vitro, we examined its role in the acute rejection of skin and cardiac allografts using mice with defective NF-kappaB translocation in T cells due to the presence of a super repressor IkappaBalpha transgene. T-cell-intrinsic NF-kappaB activation was required for cardiac but not skin allograft rejection, suggesting differential T-cell priming by the two tissues. Strikingly, priming with heart allografts induced complete acceptance of subsequently transplanted donor skin grafts, indicating that impaired NF-kappaB activation in T cells facilitates the induction of donor-specific tolerance to highly immunogenic tissues. These data suggest the biochemical pathways necessary for allograft rejection vary, based on the antigen and the context in which it is presented, and that inhibition of T-cell-intrinsic NF-kappaB activation during allogeneic priming may represent a novel strategy whereby tolerance to transplanted organs can be achieved.

Abdomen↗
PubMed1997

Stimulus contingencies that permit classical conditioning of opioid activity in the rat fetus.

In a prenatal model of classical conditioning, rat fetuses received presentations of an artificial nipple (conditioned stimulus; CS) paired with milk (unconditioned stimulus). Infusion of milk promotes activity in the kappa opioid system of the fetus, but after 2, 3, or 6 pairings with the artificial nipple, milk evoked both kappa and mu opioid activity. The nipple CS has no effect on opioid activity, but after pairing with milk evoked a mu opioid response. Conditioned mu opioid activity was evident in 60% of subjects tested after 1 paired conditioning trial. Significantly more fetal subjects (90%) exhibited conditioned opioid activity if preexposed to the nipple twice before conditioning. CS preexposure altered behavior during the conditioning trial, with preexposed fetuses showing more pronounced responses to milk infusion. Exposure to familiar stimuli facilitates classical conditioning of physiological responses, including opioid activity, during the first suckling episode.

Animals↗
PubMed2006

Haptic tracking permits bimanual independence.

This study shows that in a novel task-bimanual haptic tracking-neurologically normal human adults can move their 2 hands independently for extended periods of time with little or no training. Participants lightly touched buttons whose positions were moved either quasi-randomly in the horizontal plane by 1 or 2 human drivers (Experiment 1), in circle and square patterns in the vertical plane by 2 human drivers (Experiment 2), or at different frequencies in the horizontal plane by 2 human drivers (Experiment 3). Bimanual contact was maintained equally well in all conditions even though in Experiment 1 the left- and right-hand motions were uncorrelated (in the 2-driver condition), in Experiment 2 the left- and right-hand motions were spatially incongruous when circles and squares were tracked at the same time, and in Experiment 3 the left- and right-hand motions maintained different frequency ratios. Because haptic tracking has revealed that humans can in fact move their 2 hands independently, it may have potential as a new behavioral tool for revealing other perceptual-motor capabilities.

Form Perception↗
PubMed2001

Telomere looping permits gene activation by a downstream UAS in yeast.

In yeast (Saccharomyces cerevisiae), transcriptional activators, such as Gal4 and Gal4-VP16, work ordinarily from sites located in the upstream activating sequence (UAS) positioned about 250 base pairs upstream of the transcription start site. In contrast to their behaviour in mammalian cells, however, such activators fail to work when positioned at distances greater than approximately 600-700 base pairs upstream, or anywhere downstream of the gene. Here we show that, in yeast, a gene bearing an enhancer positioned 1-2 kilobases downstream of the gene is activated if the reporter is linked to a telomere, but not if it is positioned at an internal chromosomal locus. These observations are explained by the finding that yeast telomeres form back-folding, or looped, structures. Because yeast telomeric regions resemble the heterochromatin found in higher eukaryotes, these findings might also explain why transcription of some higher eukaryotic genes depends on their location in heterochromatin.

Chromatin↗