279 results for Brimble, Margaret

  • The Effect of Glycosylation on the Potency of Pramlintide, An Anti-Diabetic Drug

    Fletcher, Madeleine; Kowalczyk, Renata; Fairbanks, A; Brimble, Margaret; Hay, DL (2013-12-18)

    Conference poster
    The University of Auckland Library

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  • Synthesis of 5,6- and 6,6-Spirocyclic Compounds

    Brimble, Margaret; Stubbing, LA (2014-01)

    Book item
    The University of Auckland Library

    The selective and efficient synthesis of spiroacetals has attracted attention from the synthetic community, both because of the synthetic challenge of complex spiroacetal natural product scaffolds, as well as the drive to develop and improve existing methods. A number of recently reported methods for the synthesis of spiroacetals are discussed, including their application in the synthesis of natural products containing the spiroacetal scaffold.

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  • Chemical synthesis of γ-secretase activating protein using pseudoglutamines as ligation sites

    Harris, Paul; Squire, Christopher; Young, PG; Brimble, Margaret (2015-01)

    Journal article
    The University of Auckland Library

    The chemical synthesis of analogue of a novel γ-secretase activating protein, which may play a pivotal role in the formation of amyloid peptides, the precursor to Alzheimer's disease, is described. The linear polypeptide sequence, consisting of 121 amino acids was assembled from four unprotected peptide building blocks using a convergent ligation-based synthesis. A strategic mutation of three glutamine residues to cysteine enabled the ligations, and the cysteines were subsequently converted to pseudoglutamines, to mimic the native glutamine. The full length unfolded protein was obtained in milligram amounts and was demonstrated to be homogeneous by liquid chromatography and mass spectrometry.

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  • Glicentin-related pancreatic polypeptide inhibits glucose-stimulated insulin secretion from the isolated pancreas of adult male rats

    Whiting, L; Stewart, KW; Hay, Deborah; Harris, Paul; Choong, YS; Phillips, Anthony; Brimble, Margaret; Cooper, Garth (2015-12)

    Journal article
    The University of Auckland Library

    Peptides derived from the glucagon gene Gcg, for example, glucagon and glucagon-like peptide 1 (GLP-1), act as physiological regulators of fuel metabolism and are thus of major interest in the pathogenesis of diseases, such as type-2 diabetes and obesity, and their therapeutic management. Glicentin-related pancreatic polypeptide (GRPP) is a further, 30 amino acid Gcg-derived peptide identified in human, mouse, rat, and pig. However, the potential glucoregulatory function of this peptide is largely unknown. Here, we synthesized rat GRPP (rGRPP) and a closely related peptide, rat GRPP-like peptide (rGRPP-LP), and investigated their actions in the liver and pancreas of adult male rats by employing isolated-perfused organ preparations. Rat GRPP and rGRPP-LP did not affect glucose output from the liver, but both elicited potent inhibition of glucose-stimulated insulin secretion (GSIS) from the rat pancreas. This action is unlikely to be mediated by glucagon or GLP-1 receptors, as rGRPP and rGRPP-LP did not stimulate cyclic adenosine monophosphate (cAMP) production from the glucagon or GLP-1 receptors, nor did they antagonize glucagon- or GLP-1-stimulated cAMP-production at either receptor. GRPP and GRPP-LP may be novel regulators of insulin secretion, acting through an as-yet undefined receptor.

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  • Synthesis and evaluation of disulfide bond mimetics of amylin-(1-8) as agents to treat osteoporosis

    Kowalczyk, Renata; Harris, Paul; Brimble, Margaret; Callon, Karen; Watson, Maureen; Cornish, Jillian (2012-04-15)

    Journal article
    The University of Auckland Library

    Osteoporotic fracture is a significant public health problem, resulting in fractures in >50% of women and in almost one third of men age 65 and older. Most of the existing therapies act by slowing bone loss, through inhibiting the action of bone resorbing cells. However, more substantial reductions of fracture numbers will only result from treatments that can rebuild bone. Our own animal studies demonstrated the anabolic potential of the small but unstable octapeptide fragment of amylin-(1-37), namely amylin-(1-8) containing one disulfide bridge (Cys/2 and Cys/7) [Am. J. Physiol. Endocrinol. Metab. 2000, 279, E730]. Herein, we describe the synthesis of amylin-(1-8) octapeptide and seven analogues thereof wherein the disulfide bridge is modified either via insertion of different linkers or bridges of a different nature in order to improve the stability and/or bone anabolic activity of the parent peptide. The peptide analogues were screened for proliferative activity in primary foetal rat bone-forming cells or osteoblasts at physiological concentrations. One such analogue showed promising biological activity.

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  • Synthesis and biological evaluation of the osteoblast proliferating cyclic peptides dianthins G and H

    Kaur, Harveen; Heapy, AM; Kowalczyk, Renata; Amso, Z; Watson, Maureen; Cornish, Jillian; Brimble, Margaret (2014-10-21)

    Journal article
    The University of Auckland Library

    The first synthesis and osteoblast proliferative activity of the naturally occurring cyclic peptides dianthins G and H is described. The greater potency of naturally occurring dianthin G over dianthin H at physiological concentrations mirrored the osteoblast proliferative activity observed for synthetic dianthins G and H. Six alanine-scan analogues of the more potent dianthin G were also synthesised and osteoblast assays revealed that four of the six residues can be further modified for improved activity. We also confirmed by variable temperature 1H NMR spectroscopic analysis that the sets of major and minor signals observed for dianthins G and H in DMSO-d6 are in fact due to cis–trans rotational isomers of the proline ring.

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  • Synthesis of truncated analogues of preptin-(1-16), and investigation of their ability to stimulate osteoblast proliferation

    Kowalczyk, Renata; Yang, Sung Hyun; Brimble, Margaret; Callon, Karen; Watson, Maureen; Park, Y-E; Cornish, Jillian (2014-07-15)

    Journal article
    The University of Auckland Library

    Preptin, a 34-amino acid residue peptide hormone is co-secreted with insulin from the β-pancreatic cells and is active in fuel metabolism. We have previously established that a shorter fragment of preptin, namely preptin-(1–16), stimulates bone growth by proliferation and increasing the survival rate of osteoblasts. This was demonstrated in both in vitro and in vivo models. These findings suggest that preptin-(1–16) could play an important role in the anabolic therapy of osteoporosis. However, due to the large size of the peptide it is not an ideal therapeutic agent. The aim of this study was to identify the shortest preptin analogue that retains or even increases the bone anabolic activity as compared to the parent preptin-(1–16) peptide. Truncations were made in a methodical manner from both the N-terminus and the C-terminus of the peptide, and the effect of these deletions on the resulting biological activity was assessed. In order to improve the enzymatic stability of the shortest yet active analogue identified, ruthenium-catalysed ring closing metathesis was used to generate a macrocyclic peptide using allylglycine residues as handles for ring formation. We have successfully identified a short 8-amino acid preptin (1–8) fragment that retains an anabolic effect on the proliferation of primary rat osteoblasts and enhances bone nodule formation. Preptin (1–8) is a useful lead compound for the development of orally active therapeutics for the treatment of osteoporosis.

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  • Structure activity relationship study on the peptide hormone preptin, a novel bone-anabolic agent for the treatment of osteoporosis

    Brimble, Margaret; Kowalczyk, Renata; Watson, M; Park, YE; Callon, KE; Musson, David; Cornish, Jillian; Brimble, MA (2016-10-21)

    Journal article
    The University of Auckland Library

    Preptin is a 34-residue pancreatic hormone shown to be anabolic to bone in vitro and in vivo. The bone activity of preptin resides within the (1-16) N-terminal fragment. Due to its peptidic nature, the truncated fragment of preptin is enzymatically unstable; however it provides an attractive framework for the creation of stable analogues using various peptidomimetic techniques. An alanine scan of preptin (1-16) was undertaken which showed that substitution of Ser at position 3 or Pro at position 14 did not inhibit the proliferative activity of preptin in primary rat osteoblasts (bone-forming cells). Importantly, Ser-3 to Ala substitution also showed a significant activity on osteoblast differentiation in vitro and increased the formation of mineralised bone matrix. Additional modifications with non-proteinogenic amino acids at position 3 improved the stability in liver microsomes, but diminished the osteoblast proliferative activity. In addition, to provide greater structural diversity, a series of macrocyclic preptin (1-16) analogues was synthesised using head-to-tail and head-to-side chain macrolactamisation as well as ring-closing metathesis. However, a detrimental effect on osteoblast activity was observed upon macrocyclisation.

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  • Synthesis and structural insight into ESX-1 Substrate Protein C, an immunodominant Mycobacterium tuberculosis-secreted antigen

    Son, Soo; Harris, Paul; Squire, Christopher; Baker, Edward; Brimble, Margaret (2016-05)

    Journal article
    The University of Auckland Library

    Tuberculosis, the second leading cause of death from a single infectious agent, is recognized as a major threat to human health due to a lack of practicable vaccines against the disease and the widespread occurrence of drug resistance. With a pressing need for a novel protein target as a platform for new vaccine development, ESX-1 Substrate Protein C (EspC) was recently identified as a novel Mycobacterium tuberculosis-secreted antigen that is as immunodominant as the two specific immunodiagnostic T-cell antigens, CFP-10 and ESAT-6. Here, we present the first chemical total synthesis, folding conditions, and circular dichroism data of EspC.

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  • Total chemical synthesis of an Orf virus protein, ORFV002, an inhibitor of the master gene regulator NF-κB

    Son, Soo; Harris, Paul; Squire, Christopher; Baker, Edward; Kent, SBH; Brimble, Margaret (2014-03)

    Journal article
    The University of Auckland Library

    ORFV002 is a novel orf viral protein (117 Aa) that inhibits nuclear events through the regulation of the transcriptional activity of NF-κB, a master regulator of human gene expression (Diel et al., J Virol 2011, 85, 264–275). It is identified as the first nuclear inhibitor of NF-κB produced by orf virus (ORFV) and no homologues in other genera of the Chordopoxvirinae subfamily have been reported to date (Diel et al., J Virol 2011, 85, 264–275). Our molecular structure predictions suggest that ORFV002 may mimic part of IκB, an inhibitor and natural human partner of NF-κB. Recent advances in total chemical synthesis of proteins have provided solutions in overcoming challenges of current recombinant methods of protein isolation for structure elucidation. Aided by Boc solid phase peptide synthesis and native chemical ligation, ORFV002 was successfully synthesized in multimilligram amounts in good yield and high purity.

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  • Preparation of truncated orf virus entry fusion complex proteins by chemical synthesis

    Yeung, Ho; Harris, Paul; Squire, Christopher; Baker, Edward; Brimble, Margaret (2014-06)

    Journal article
    The University of Auckland Library

    Members of the Chordopoxvirinae subfamily possess an unusual 11 protein entry-fusion complex (EFC) that is highly conserved and present in all species. The mode of action of this EFC is unknown, and the interactions of the constituent proteins are uncharacterised. Here, we present the chemical synthesis of membrane domain truncated linear constructs of two EFC proteins in orf virus, ORFV036 and 049. By using Boc solid phase peptide synthesis and native chemical ligation methods, these truncated proteins have been readily prepared in milligram quantities. These robust synthetic protocols allow ready access to these polypeptides to facilitate biological studies.

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  • Receptor Activity-modifying Proteins 2 and 3 Generate Adrenomedullin Receptor Subtypes with Distinct Molecular Properties

    Watkins, HA; Chakravarthy, M; Abhayawardana, RS; Gingell, Joseph; Garelja, M; Pardamwar, M; McElhinney, JMWR; Lathbridge, A; Constantine, A; Harris, Paul; Yuen, TY; Brimble, Margaret; Barwell, J; Poyner, DR; Woolley, MJ; Conner, AC; Pioszak, AA; Reynolds, Christopher; Hay, Deborah (2016-05-27)

    Journal article
    The University of Auckland Library

    Adrenomedullin (AM) is a peptide hormone with numerous effects in the vascular systems. AM signals through the AM1 and AM2 receptors formed by the obligate heterodimerization of a G protein-coupled receptor, the calcitonin receptor-like receptor (CLR), and receptor activity-modifying proteins 2 and 3 (RAMP2 and RAMP3), respectively. These different CLR-RAMP interactions yield discrete receptor pharmacology and physiological effects. The effective design of therapeutics that target the individual AM receptors is dependent on understanding the molecular details of the effects of RAMPs on CLR. To understand the role of RAMP2 and -3 on the activation and conformation of the CLR subunit of AM receptors, we mutated 68 individual amino acids in the juxtamembrane region of CLR, a key region for activation of AM receptors, and determined the effects on cAMP signaling. Sixteen CLR mutations had differential effects between the AM1 and AM2 receptors. Accompanying this, independent molecular modeling of the full-length AM-bound AM1 and AM2 receptors predicted differences in the binding pocket and differences in the electrostatic potential of the two AM receptors. Druggability analysis indicated unique features that could be used to develop selective small molecule ligands for each receptor. The interaction of RAMP2 or RAMP3 with CLR induces conformational variation in the juxtamembrane region, yielding distinct binding pockets, probably via an allosteric mechanism. These subtype-specific differences have implications for the design of therapeutics aimed at specific AM receptors and for understanding the mechanisms by which accessory proteins affect G protein-coupled receptor function.

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  • Total Synthesis of the Fungal Metabolite Virgatolide B

    Hume, Paul; Furkert, Daniel; Brimble, Margaret (2015)

    Book item
    The University of Auckland Library

    This account describes the total synthesis of the title compound, a polyketide metabolite with in vitro antitumor activity. A first-generation approach involving an sp3–sp2 Suzuki cross-coupling reaction of a chiral trifluoroboratoamide and a rotationally symmetric aryl bromide successfully established the carbon framework required to construct the spiroketal core of the molecule. However, removal of the phenolic protecting groups with concomitant spiroketalization could not be achieved. A revised strategy was therefore devised, employing different protecting groups and incorporating greater functionality on the aryl bromide coupling partner. Suzuki cross-coupling, extension of the carbon backbone using a diastereoselective Mukaiyama aldol reaction and deprotection/cyclization furnished the spiroketal ring system. The final transformation required was carboalkoxylation of the aromatic ring to form the phthalide subunit present in the molecule. This manipulation was difficult to achieve due to competing protodehalogenation. Finally, a reordering of synthetic events provided access to virgatolide B by exploitation of an intramolecular hydrogen-bonding interaction in order to control the regioselectivity of the spiroketalization process.

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  • Investigation into the racemic X-ray structure of the antimicrobial protein snakin-1

    Yeung, Ho; Yosaatmadja, Yuliana; Squire, Christopher; Harris, Paul; Baker, Edward; Brimble, Margaret (2015-08-31)

    Conference poster
    The University of Auckland Library

    Snakin-1 is a 63 residue antimicrobial protein originally isolated from potato (Solanum tuberosum).1 It is active against a number of bacterial and fungal phytopathogens such as Clavibacter michiganensis, Pseudomonas syringae and Fusarium solani. Snakin-1 is a member of the GASA (gibberellic acid stimulated in Arabidopsis)/snakin family and the mature protein consists of a GASA domain incorporating six intramolecular disulfide bonds.2 The amino acid sequences of these proteins do not correspond to any known structural motifs. GASA/snakin proteins are found in a variety of plant species and appear to be involved in a range of functions including cell elongation and cell division.2 Their expression profiles support these roles and are commonly linked to development.2 It has also been speculated that the 12 conserved cysteines in these proteins perform a role in redox regulation.2 We have recently completed the total chemical synthesis of native Snakin-1 and showed that its antimicrobial activity is comparable to that of the naturally occurring protein.3 In an attempt to understand how this small protein functions we have determined its threedimensional structure by X-ray crystallography using a quasi-racemic protein system.4 Phase information for structural determination was obtained by radiation-damage induced phasing.5 The structure of snakin-1 appears to be novel, different to known classes of cysteine-rich plant antimicrobial peptide. Its features include a large and distinctly electropositive loop that we speculate to be membrane targeting, and a two helix bundle which is a potential membrane-interacting feature able to disrupt the structural integrity of its target bacteria.

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  • Investigation into the racemic X-ray structure of the antimicrobial protein snakin-1

    Yeung, Ho; Yosaatmadja, Yuliana; Squire, Christopher; Harris, Paul; Baker, Edward; Brimble, Margaret (2015-10-22)

    Conference poster
    The University of Auckland Library

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  • Divergent Reactivity via Cobalt Catalysis: An Epoxide Olefination

    Jamieson, ML; Hume, Paul; Furkert, Daniel; Brimble, Margaret (2016-02-05)

    Journal article
    The University of Auckland Library

    Cobalt salts exert an unexpected and profound influence on the reactivity of epoxides with dimethylsulfoxonium methylide. In the presence of a cobalt catalyst, conditions for epoxide to an oxetane ring expansion instead deliver homoallylic alcohol products, corresponding to a two-carbon epoxide homologation/ring-opening tandem process. The observed reactivity change appears to be specifically due to cobalt salts and is broadly applicable to a variety of epoxides, retaining the initial stereochemistry. This transformation also provides operationally simple access to enantiopure homoallylic alcohols from chiral epoxides without use of organometallic reagents. Tandem epoxidation–homologation of aldehydes in a single step is also demonstrated.

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  • Total Synthesis of Virgatolide B

    Hume, Paul; Furkert, Daniel; Brimble, Margaret (2013-09-06)

    Journal article
    The University of Auckland Library

    The first total synthesis of the benzannulated spiroketal virgatolide A is presented. Key features include sp3–sp2 Suzuki coupling of an enantiomerically enriched β-trifluoroboratoamide and an aryl bromide, regioselective intramolecular carboalkoxylation, and a 1,3-anti-selective Mukaiyama aldol reaction followed by global deprotection/cyclization with regioselectivity governed by internal hydrogen bonding.

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  • Regioselective iridium(I)-catalysed remote borylation of oxygenated naphthalenes

    Hume, Paul; Furkert, DP; Brimble, Margaret (2012-07-18)

    Journal article
    The University of Auckland Library

    We present our investigations into the regioselective borylation and halogenation of polyoxygenated naphthalene systems that are key precursors to dimeric pyranonaphthoquinone natural products. A variety of oxygenated naphthalenes were successfully borylated with pinacolborane in high yield and excellent regioselectivity using [Ir(COD)OMe]2 and di-tert-butylbipyridine (dtbpy). The boronates were also readily transformed into the corresponding halides, opening new avenues for the preparation of advanced Suzuki coupling substrates useful for the synthesis of natural products.

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  • Total Synthesis of Virgatolide B via Exploitation of Intramolecular Hydrogen Bonding

    Hume, Paul; Furkert, Daniel; Brimble, Margaret (2014-06-06)

    Journal article
    The University of Auckland Library

    A full account of the enantioselective total synthesis of virgatolide B is reported. Key features of the synthesis include an sp3–sp2 Suzuki–Miyaura cross-coupling of a β-trifluoroboratoamide with an aryl bromide, regioselective intramolecular carboalkoxylation, and a 1,3-anti-selective Mukaiyama aldol reaction. Intramolecular hydrogen bonding governed the regioselectivity of the key spiroketalization step, affording the natural product as a single regioisomer.

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  • DNA adduct formation of mitomycin C. A test case for DFT calculations on model systems

    Hume, Paul; Brimble, Margaret; Reynisson, Johannes (2013-02-01)

    Journal article
    The University of Auckland Library

    Mitomycin C is a DNA alkylating agent activated by bioreduction. It has been in clinical use against a range of solid tumours since the 1960s. Its DNA adduct formation mechanism has been extensively studied and it therefore presents an excellent test case for the applicability of Density Functional Theory (DFT) calculations based on simple model systems. The reaction cascades proposed in the literature were calculated and the results revealed that many of the mechanistic features were correctly predicted: the one- and two-electron reduction was deemed plausible, the pH-dependence of the rate of aziridine ring opening, and that the alkylating agent is required to be formed in the proximity of DNA for adduct formation to occur. The DFT method was unable to predict where adduct formation takes place on the guanine based on the exothermicity of the nucleophilic attack. Overall, the DFT method does well to predict the mechanism for adduct formation considering that the model systems are simple and modest CPU requirements.

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