Catherine S. V. Houge-Frydrych

Crystal structure of Staphylococcus aureus tyrosyl-tRNA synthetase in complex with a class of potent and specific inhibitors

SB‐219383 and its analogues are a class of potent and specific inhibitors of bacterial tyrosyl‐tRNA synthetases. Crystal structures of these inhibitors have been solved in complex with the tyrosyl‐tRNA synthetase from Staphylococcus aureus, the bacterium that is largely responsible for hospital‐acquired infections. The full‐length enzyme yielded crystals that diffracted to 2.8 Å resolution, but a truncated version of the enzyme allowed the resolution to be extended to 2.2 Å. These inhibitors not only occupy the known substrate binding sites in unique ways, but also reveal a butyl binding pocket. It was reported that the Bacillus stearothermophilus TyrRS T51P mutant has much increased catalytic activity. The S. aureus enzyme happens to have a proline at position 51. Therefore, our structures may contribute to the understanding of the catalytic mechanism and provide the structural basis for designing novel antimicrobial agents.

Optimisation of aryl substitution leading to potent methionyl tRNA synthetase inhibitors with excellent gram-positive antibacterial activity

Optimisation of the left-hand-side aryl moiety of a file compound screening hit against Staphylococcus aureus methionyl tRNA synthetase led to the identification of a series of potent nanomolar inhibitors. The best compounds showed excellent antibacterial activity against staphylococcal and enterococcal pathogens, including strains resistant to clinical antibiotics.

Conformational restriction of methionyl tRNA synthetase inhibitors leading to analogues with potent inhibition and excellent gram-positive antibacterial activity.

Conformationally restricted analogues of the central linker unit of bacterial methionyl tRNA synthetase (MRS) inhibitors have been prepared. The (1S,2R)-cyclopentylmethyl moiety was identified as the preferred cyclic linker, with significant diastereo- and enantioselectivity of activity. Combination of this linker with an optimal substituted aryl right-hand side has resulted in a compound with exceptionally good antibacterial activity against staphylococci and enterococci, including antibiotic resistant strains.

Inhibitors of Bacterial Tyrosyl tRNA Synthetase: Synthesis of Carbocyclic Analogues of the Natural Product SB-219383

Carbocyclic analogues of the microbial metabolite SB-219383 have been synthesised and evaluated as inhibitors of bacterial tyrosyl tRNA synthetase. One compound showed highly potent and selective nanomolar inhibition.

Interaction of tyrosyl aryl dipeptides with S. aureus tyrosyl tRNA synthetase : Inhibition and crystal structure of a complex

Tyrosyl aryl dipeptide inhibitors of S. aureus tyrosyl tRNA synthetase have been identified with IC50 values down to 0.5 microM. A crystal structure of the enzyme complexed to one of the inhibitors shows occupancy of the tyrosyl binding pocket coupled with inhibitor interactions to key catalytic residues.

Conformational and steric modifications of the pyran ring of the potassium-channel activator cromakalim

The syntheses of analogues of the novel smooth muscle relaxant cromakalim, in which the C-2 methyl groups have been successively replaced by hydrogen, are described and the relative stereochemistry of the two corresponding, isomeric monomethyl compounds, unambiguously assigned by 1H NMR spectroscopic techniques. Single-crystal X-ray analysis of the 2α-monomethyl compound showed that it existed in a distorted half-chair conformation in the solid state and confirmed the relative orientation of the C-2, C-3 and C-4 substituents. The 2β-Me isomer appeared to exist in a single conformation in solution, with the pyran ring adopting a half-chair conformation and with all the substituents in this ring occupying a pseudoequatorial position. The solution behaviour of the 2α-Me isomer is more complex, however, although it seems likely to exist as a distorted half-chair conformer similar to that found in the solid state. The syntheses of two related benzoxepines are also described. All compounds were less potent than cromakalim itself, which is consistent with the view that dimethyl substitution at C-2 is essential for optimal activity.

Structural modifications of the potassium channel activator cromakalim: the C-3 position

The syntheses of a selection of C-3 analogues of 6-cyano-3,4-dihydro-2,2-dimethyl-4-(2-oxopyrrolidin-1-yl)-2H-1-benzopyran-3-ol, the potassium channel activator cromakalim 1, are described. Particular interest has focused on the corresponding 3-ketone 2 and compounds in which the hydroxy group of 1 has been replaced by fluorine, carbon and nitrogen containing residues. The hindered neopentylic nature of the C-3 hydroxy group in 1 has a marked effect on its reactivity and has necessitated the independent synthesis of many of these analogues from simpler precursors rather than from the direct modification of compound 1 itself.

Lewis-acid catalysed arylation of the hydroxyamino sugar moiety of the natural product SB-219383

The natural product SB-219383 1a contains an unique bicyclic hydroxyamino sugar moiety. Novel C-glycosidation reactions of this hydroxyamino sugar moiety are reported. The formation of a sugar nitrone intermediate is postulated which is subsequently trapped by electron-rich aromatic rings to yield C-aryl hydroxyamino sugars.