Mark Whittaker

Antibiotic activity and characterization of BB-3497, a novel peptide deformylase inhibitor.

ABSTRACT Peptide deformylase (PDF) is an essential bacterial metalloenzyme which deformylates the N-formylmethionine of newly synthesized polypeptides and as such represents a novel target for antibacterial chemotherapy. To identify novel PDF inhibitors, we screened a metalloenzyme inhibitor library and identified anN-formyl-hydroxylamine derivative, BB-3497, and a related natural hydroxamic acid antibiotic, actinonin, as potent and selective inhibitors of PDF. To elucidate the interactions that contribute to the binding affinity of these inhibitors, we determined the crystal structures of BB-3497 and actinonin bound to Escherichia coli PDF at resolutions of 2.1 and 1.75 Å, respectively. In both complexes, the active-site metal atom was pentacoordinated by the side chains of Cys 90, His 132, and His 136 and the two oxygen atoms of N-formyl-hydroxylamine or hydroxamate. BB-3497 had activity against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis, and activity against some gram-negative bacteria. Time-kill analysis showed that the mode of action of BB-3497 was primarily bacteriostatic. The mechanism of resistance was via mutations within the formyltransferase gene, as previously described for actinonin. While actinonin and its derivatives have not been used clinically because of their poor pharmacokinetic properties, BB-3497 was shown to be orally bioavailable. A single oral dose of BB-3497 given 1 h after intraperitoneal injection of S. aureus Smith or methicillin-resistant S. aureusprotected mice from infection with median effective doses of 8 and 14 mg/kg of body weight, respectively. These data validate PDF as a novel target for the design of a new generation of antibacterial agents.

A Monte Carlo pharmacophore generation procedure: Application to the human PAF receptor

SummaryA novel pharmacophore definition procedure is described, which uses a Monte Carlo method to superimpose molecules. Pharmacophore space is searched by a technique similar to high temperature annealing. Subsequent refinement of candidate pharmacophores by energy minimization produces low-energy conformations that may be involved in receptor binding. The method has been applied to compounds that bind to the human platelet-activating factor (PAF) receptor. Alternative binding site models for the PAF receptor are presented and discussed.

A partial pharmacophore for the platelet activating factor (PAF) receptor

Abstract A partial pharmacophore for the platelet activating factor receptor has been generated by a molecular modelling comparison of five heterocyclic sp2 nitrogen PAF antagonists using a Monte Carlo ‘Boltzmann Jump’ technique. This pharmacophore defines the relative spatial orientation of the plane of the heterocyclic ring, the sp2 nitrogen, a carbonyl/sulphony pharmacophoric group and a sulphur atom.

Chiral organometallic NADH mimics: Preparation of homochiral (R)-(−)[(η5-c5h5)fe(co)(pph2(o-(l)-menthyl1))]-1-methyl-1,4-dihydronicotinand asymmetric reduction of ethyl benzoylformate.

Abstract The homochiral complex (R)-(−)-[(η 5 -C 5 H 5 )Fe(CO)(PPh2(O-( l )-menthyl))]-1-methyl-1,4-dihydronicotinoyl reduces ethyl benzoylformate to ethyl mandelate in 52% enantiomeric excess.

Stereochemical studies on marine cyclic peroxides : an unequivocal alignment of absolute stereochemistry by asymmetric synthesis

Abstract Absolute stereochemical assignments for norterpene cyclic peroxides from marine sponges, previously determined by application of the Horeau procedure of asymmetric esterification, have been independently confirmed by degradation and asymmetric synthesis.

The Selection and Design of GPCR Ligands: From Concept to the Clinic

Virtual screening methods using structure-based, pharmacophore-based and descriptor based protocols may be used to identify ligands for the G-protein coupled receptor target family. A complementary approach is the synthesis and screening of compound libraries designed using privileged motifs and/or based on validated hit molecules. A virtual screening approach based on molecular docking performed with GOLD using a templated homology model and a consensus scoring procedure can identify vasopressin 1a receptor antagonists. In a separate project a library design and synthesis approach based around validated hit GPCR ligands led to the identification of potent oxytocin antagonists. Subsequent optimisation of the initial library compounds has provided compounds that are now being evaluated in the clinic for the treatment of preterm labour.

Cyclic ether acetal platelet activating factor (PAF) receptor antagonists. II: Imidazo[4,5-c]pyridyl derivatives

Abstract The 1H-2-methylimidazo[4,5-c]pyridyl group has been found to be the optimal heterocycle for a series of cyclic ether acetal PAF antagonists. A lead compound 8 inhibits [3H]-PAF receptor binding to washed human platelets with an IC50 value of 15 nM, and both PAF-induced hypotension and endotoxin-induced hypotension in anaesthetised rats with ED50 values of 1.4 μg/kg i.v. and 19 μg/kg i.v. respectively.

Asymmetric synthesis via chiral transition metal auxiliaries

Stoichiometric reagents for the control of the absolute stereochemistry of new chiral centres produced during reactions involving carbon-carbon bond formation are described. Chiral iron acyl reagents act as chiral equivalents of a variety of carbonyl functionalities and their potential for asymmetric synthesis can be illustrated for pseudopeptides, amino acids, P-lactams, y-lactams and lactones. A simple methodology based on arene chromium tricarbonyl chemistry allows the elaboration of benzylic chiral centres with complete control over the absolute stereochemistry. This may be illustrated, for example, by the conversion of amphetamine derivatives into pseudoephedrines.

Cyclic ether acetal platelet activating factor (PAF) receptor antagonists. I: 3-pyridyl derivatives

Abstract A novel series of 2-(3-pyridyl)alkoxy-5-aryltetrahydrofuran PAF antagonists has been identified and the effect of variation of the alkoxy chain length, aryl substitution and stereochemistry about the tetrahydrofuran ring studied. The optimal compound, cis-(±)-2-(3-(3-pyridyl)propanoxy)-5-(3,4,5-trimethoxyphenyl)tetrahydrofuran (27a), inhibits 3H]-PAF receptor binding to washed human platelet membranes with an IC50 value of 100 nM.

Application of the chiral auxiliary [(η5-C5H5)Fe(CO)(PPh3)] to the stereoselective formation of 4-substituted-1,4-dihydronicotinoyl complexes

Abstract In solution reglo- and stereoselective additions of nucleophiles to (RS)-[(η5-C5H5)Fe(CO)(PPh3)CO-3- pyridyl] (1) occur at C-4 to give the corresponding nitrogen-stabilised anions. Subsequent quenching of these anions by a proton, a chloroformate or dimethyl sulfate gives the corresponding 1,4-dihydropyridine complexes as single diastereoisomers. The predicted stereochemical course of the nucleophilic additions is confirmed by a single crystal X-ray structure determination of (Fe-RS,4-RS)-[(η5-C5H5)Fe(CO) (PPh3)CO-3-(N-methoxycarbonyl-4-methyl-1,4-dihydropyridyl)].