Biomedical subjects
Publications and source records attributed to Mark Bradley.
pH indicating resins were prepared by covalently attaching carboxylic acid derivatives of sulfthalein dyes, synthesized using a Suzuki cross-coupling, onto resin beads. The resin-bound indicators showed the expected colour changes according to pH and their behaviour was analysed using a micro UV/Vis spectrometer.
New deprotection conditions for the Dde amine protecting group that are fully orthogonal to Fmoc are described and successfully applied to the dual synthesis of PNA-peptide conjugates.
Self-indicating methylisocyanate resin, which functions as both a scavenger and an indicator for amines, was used for in-situ reaction monitoring and purification of a urea based library.
The ability of non-viral gene delivery systems to overcome extracellular and intracellular barriers is a critical issue for future clinical applications of gene therapy. In recent years much effort has been focused on the development of a variety of DNA carriers, and cationic liposomes have become the most common non-viral gene delivery system. Solid-phase synthesis was used to produce three libraries of polyamine-based cationic lipids with diverse hydrophobic tails. These were characterised, and structure-activity relationships were determined for DNA binding and transfection ability of these compounds when formulated as cationic liposomes. Two of the cationic lipids produced high-efficiency transfection of human cells. Surprisingly, these two compounds were from the library with two headgroups and one aliphatic tail, a compound class regarded as detergent-like and little investigated for transfection. These cationic lipids are promising reagents for gene delivery and illustrate the potential of solid-phase synthesis methods for lipoplex discovery.
A solid-phase approach was used to prepare 20 cystine amide derivatives with disulfide bond formation resulting from an intra-site reaction between neighbouring cysteine residues. Library members were screened as potential organogelators in a range of solvent mixtures and resulted in the identification of a potent gelator able to rigidify water/DMSO mixtures at concentrations as low as 1.3 mM.
A linear pixel-array detector was employed to create spatially resolved multi-layered IR-images of a large collection of polymer beads supporting carbonyl and nitrile monomers. The feasibility of creating multi-layered IR-images with nitrile IR-band separation of 4 cm(-1) was demonstrated, an important issue when considering that many monomers used to develop combinatorial libraries are structurally analogous and therefore occupy very similar positions in the IR-spectrum. Strategies for obtaining high quality spectral data from both imaging and mapping IR-microscopes without compromising on sample area, analysis time, or spatial resolution are also described.
Combinatorial chemistry has had a major impact on the discovery and optimisation of potential lead compounds. This review details some of the fundamental principles behind combinatorial chemistry and describes a variety of methods employed in the search for new therapeutically interesting compounds including the concept of dynamic combinatorial chemistry as a method of selecting active compounds from a mixture. It also outlines methods used to analyse resin bound products and describes how solution phase library generation may be aided by the use of resin bound reagents and scavengers.
Using a highly efficient solid-phase route a series of fluorescein conjugated peptoid oligomers were synthesised and observed to display remarkable cell penetrating properties, offering the possibility of highly efficient cellular targeting.
Dyad beads, bearing both a substrate and a catalyst, were prepared to enable direct split and mix bead based screening for catalysis.
Two new probes for the detection of calpain I activity based on fluorescence resonance energy transfer technology have been synthesized and evaluated. The probes incorporated the cleavage site present in alpha-spectrin, a naturally occurring substrate of calpain I. The design of the internally quenched substrates is such that the calpain-sensitive bond of the peptides (between the Tyr-Gly residues) is located centrally between the donor and the quencher chromophores. The calpain assay protocol is capable of detecting enzymatic activity in the nanomolar region.
Prolonged cerebral ischaemia initiates complex intra- and inter-cellular signalling cascades ultimately resulting in neuronal death. Well-characterised mediators of ischaemic cell death are glutamate, free radicals and nitric oxide. Many drugs that block these mechanisms are neuroprotective in vitro, but have unfavourable side-effect profiles in man. We have recently demonstrated that the compound L-arginyl-3,4-spermidine (L-Arg3,4) is neuroprotective in vitro through an interaction with several of these mechanisms, and prevents ischaemic neurodegeneration in vivo with no gross side effects. In this study, we have used solid-phase combinatorial chemistry, to synthesise a number of analogues of L-Arg3,4, and investigate the structure-activity relationship using an in vitro, organotypic hippocampal slice culture model of cerebral ischaemia. A number of molecular features were identified which were essential for the neuroprotective activity including the requirement for a positive charge and an amino acid in the L-configuration. Relatively minor alterations to both the terminal arginine and polyamine moieties significantly attenuated neuroprotective efficacy. Our data implies that these compounds are neuroprotective through a currently undefined mechanism rather than non-specific ionic interactions described previously for other polyamine-containing compounds.
[reaction: see text] Catalytic Sc(OTf)(3) greatly increases the efficiency of hydrogen peroxide mediated monooxidation of alkyl-aryl sulfides and methyl cysteine containing peptides. The method is high yielding, compatible with many widely used protecting groups, suitable for solid-phase applications and proceeds with minimum over-oxidation.
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The concept of a 'head-to-tail linker' designed to allow the regeneration and reuse of a variety of solid supports is introduced. The synthesis of this linker, its coupling to various solid supports, its application in a number of standard solid phase reactions and resin regeneration are presented.
Solid-phase dendrimer chemistry using a symmetrical 1 --> 3 C-branched isocyanate monomer was used to prepare radiation-grafted polymers with enhanced loading. After evaluation of the physical and chemical properties of these new high-loading supports, they were tested in the multiple parallel synthesis of hydantoins.
The benefits of microwave irradiation are described for a number of important reactions such as amid and ester formation and dehydration of formamide to the corresponding isonitriles. Not only were reaction times dramatically reduced but the transformations were less prone to side reactions and decomposition.
Advances in high throughput screening (HTS), together with the rapid progress in combinatorial chemistry, genomic and proteomic sciences have dramatically stimulated the development of a variety tools to enable the drug discovery process to become more efficient. Major future challenges in HTS include obtaining high density and good quality data based on assays that are rapid, reliable, inexpensive, sensitive, simple and miniaturised. This paper reviews the development and role of bead-based assays for HTS including DNA and single nucleotide polymorphism (SNP) assays, particularly from a multiplex perspective and evaluating the recent advances in bead-based arrays. The encoding strategies that are commonly used in bead-based assays are highlighted, while the importance of magnetic beads in genomic and proteomic purifications is discussed. In conclusion, bead-based assays offer a powerful promising approach for many aspects of drug discovery.
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