David F. Corbett

Pharmacological regulation of insulin secretion in MIN6 cells through the fatty acid receptor GPR40: identification of agonist and antagonist small molecules

1 Long chain fatty acids have recently been identified as agonists for the G protein‐coupled receptors GPR40 and GPR120. Here, we present the first description of GW9508, a small‐molecule agonist of the fatty acid receptors GPR40 and GPR120. In addition, we also describe the pharmacology of GW1100, a selective GPR40 antagonist. These molecules were used to further investigate the role of GPR40 in glucose‐stimulated insulin secretion in the MIN6 mouse pancreatic β‐cell line. 2 GW9508 and linoleic acid both stimulated intracellular Ca2+ mobilization in human embryonic kidney (HEK)293 cells expressing GPR40 (pEC50 values of 7.32±0.03 and 5.65±0.06, respectively) or GPR120 (pEC50 values of 5.46±0.09 and 5.89±0.04, respectively), but not in the parent HEK‐293 cell line. 3 GW1100 dose dependently inhibited GPR40‐mediated Ca2+ elevations stimulated by GW9508 and linoleic acid (pIC50 values of 5.99±0.03 and 5.99±0.06, respectively). GW1100 had no effect on the GPR120‐mediated stimulation of intracellular Ca2+ release produced by either GW9508 or linoleic acid. 4 GW9508 dose dependently potentiated glucose‐stimulated insulin secretion in MIN6 cells, but not in primary rat or mouse islets. Furthermore, GW9508 was able to potentiate the KCl‐mediated increase in insulin secretion in MIN6 cells. The effects of GW9508 on insulin secretion were reversed by GW1100, while linoleic acid‐stimulated insulin secretion was partially attenuated by GW1100. 5 These results add further evidence to a link between GPR40 and the ability of fatty acids to acutely potentiate insulin secretion and demonstrate that small‐molecule GPR40 agonists are glucose‐sensitive insulin secretagogues.

Microwave assisted free radical cyclisation of alkenyl and alkynyl isocyanides with thiols

Alkenyl and alkynyl isocyanides were synthesised and then reacted, using microwave flash-heating technology, with thiophenol, 2-mercaptoethanol and ethanethiol, in the presence of a radical initiator, to give highly functionalised pyrrolines and pyroglutamates. Direct comparison with results obtained using traditional heating techniques showed the advantage of using the microwave technology in terms of faster reactions and better yields.

The synthesis of pseudo-sugars related to allosamizoline

The syntheses of two bicyclic pseudo-sugars related to allosamizoline, the aminocyclitol component of the chitinase inhibitor allosamidin, are described. These carbocyclic pseudo-sugars containing a cyclohexane ring were synthesised from D-glucosamine via a Ferrier rearrangement.

Identification of small molecule agonists of the motilin receptor

High-throughput screening resulted in the identification of a series of novel motilin receptor agonists with relatively low molecular weights. The series originated from an array of biphenyl derivatives designed to target 7-transmembrane (7-TM) receptors. Further investigation of the structure-activity relationship within the series resulted in the identification of compound (22) as a potent and selective agonist at the motilin receptor.

Synthesis of pseudo-disaccharides related to allosamidin

Abstract Suitably protected carbocyclic pseudo-sugars were synthesised from d -glucosamine via a Ferrier rearrangement. Stereospecific coupling with the glycosyl donor, 1,3,4,6-tetra-O-acetyl-2-deoxy-2-phthalimido-β- d -glucopyranoside and subsequent protecting group interconversions furnished β-1,4-pseudo-disaccharides related to the chitinase inhibitor, allosamidin.

Potentiation of Antibiotic Activity by a Novel Cationic Peptide: Potency and Spectrum of Activity of SPR741.

ABSTRACT Novel approaches for the treatment of multidrug-resistant Gram-negative bacterial infections are urgently required. One approach is to potentiate the efficacy of existing antibiotics whose spectrum of activity is limited by the permeability barrier presented by the Gram-negative outer membrane. Cationic peptides derived from polymyxin B have been used to permeabilize the outer membrane, granting antibiotics that would otherwise be excluded access to their targets. We assessed the in vitro efficacies of combinations of SPR741 with conventional antibiotics against Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii. Of 35 antibiotics tested, the MICs of 8 of them were reduced 32- to 8,000-fold against E. coli and K. pneumoniae in the presence of SPR741. The eight antibiotics, azithromycin, clarithromycin, erythromycin, fusidic acid, mupirocin, retapamulin, rifampin, and telithromycin, had diverse targets and mechanisms of action. Against A. baumannii, similar potentiation was achieved with clarithromycin, erythromycin, fusidic acid, retapamulin, and rifampin. Susceptibility testing of the most effective antibiotic-SPR741 combinations was extended to 25 additional multidrug-resistant or clinical isolates of E. coli and K. pneumoniae and 17 additional A. baumannii isolates in order to rank the potentiated antibiotics. SPR741 was also able to potentiate antibiotics that are substrates of the AcrAB-TolC efflux pump in E. coli, effectively circumventing the contribution of this pump to intrinsic antibiotic resistance. These studies support the further development of SPR741 in combination with conventional antibiotics for the treatment of Gram-negative bacterial infections.

Chemical modification of the olivanic acids: Synthesis of substituted 6-[1-(1,2,3-triazol-1-yl)ethyl] carbapenem derivatives

Abstract The 1,3-dipolar cycloaddition of activated acetylenes to 6-(1-azidoethyl) olivanic acid derivatives afforded the corresponding 6-[1-(1,2,3-triazol-1-yl)ethyl] compounds.

Time-kill kinetics of cadazolid and comparator antibacterial agents against different ribotypes of Clostridium difficile.

Purpose. Clostridium difficile infection (CDI) is an increasing cause of nosocomial diarrhoea worldwide, which has been partly attributed to the emergence of hypervirulent strains including C. difficile BI/NAP1/ribotype 027 and BK/NAP7/ribotype 078. Cadazolid is a new antibiotic currently in late‐stage clinical studies for the treatment of CDI. The present study evaluated the in vitro bactericidal effect of cadazolid and comparator antibiotics against four C. difficile strains. The data demonstrate the potent and bactericidal activity of cadazolid against different ribotypes of C. difficile. Methodology. MICs for test antibiotics were determined in brain‐ heart infusion‐supplemented broth (BHIS) containing 5 g l−1 yeast extract and 0.025 % (w/v) l‐cysteine. Time‐kill kinetics to investigate the rate of killing of each antibiotic at sub‐ and supra‐MIC concentrations were performed at concentrations of 0.5, 1, 2, 4, 8 or 16× the MIC of cadazolid, vancomycin and fidaxomicin at intervals over a 48 h period. Results/key findings. Cadazolid‐mediated killing of C. difficile was faster and occurred at lower concentrations than observed for vancomycin, while potency and killing was largely comparable to those observed for fidaxomicin. Notably, cadazolid also displayed a potent bactericidal effect against fluoroquinolone‐resistant hypervirulent ribotype 027 and 078 strains. C. difficile spore formation was largely inhibited by all three antibiotics at concentrations >1× MIC; however, none were able to eliminate spores effectively, which were present at the start of the experiment. Conclusion. The data presented here demonstrate the potent in vitro bactericidal activity of cadazolid against different ribotypes of C. difficile, although on a limited set of strains.