SAR of biphenyl carboxamide ligands of the human melanin-concentrating hormone receptor 1 (MCH R1): discovery of antagonist SB-568849.

We report here the discovery of a class of MCH R1 ligands based on a biphenyl carboxamide template. A docked-in model is presented indicating key interactions in the putative binding site of the receptor. Parallel high throughput synthetic techniques were utilised to allow rapid exploration of the structure-activity relationship around this template, leading to compound SB-568849 which possessed good receptor affinity and selectivity. This compound proved to be an antagonist with stability in vivo, an acceptable brain-blood ratio and oral bioavailability.

Discovery of potent and stable conformationally constrained analogues of the MCH R1 antagonist SB-568849.

A strategy of systematically targeting more rigid analogues of the known MCH R1 receptor antagonist, SB-568849, serendipitously uncovered a binding mode accessible to N-aryl-phthalimide ligands. Optimisation to improve the stability of this compound class led to the discovery of novel N-aryl-quinazolinones, benzotriazinones and thienopyrimidinones as selective ligands with good affinity for human melanin-concentrating hormone receptor 1.

Discovery and optimisation of potent, selective, ethanolamine inhibitors of bacterial phenylalanyl tRNA synthetase.

High throughput screening of Staphylococcus aureus phenylalanyl tRNA synthetase (FRS) identified ethanolamine 1 as a sub-micromolar hit. Optimisation studies led to the enantiospecific lead 64, a single-figure nanomolar inhibitor. The inhibitor series shows selectivity with respect to the mammalian enzyme and the potential for broad spectrum bacterial FRS inhibition.

S-alkyl dithioformates as 1,3-dipolarophiles. Generation of C(2)-unsubstituted penems.

S-Alkyl dithioformates, generated by a cycloreversion process, react as 1,3-dipolarophiles with beta-lactam-based azomethine ylids to provide, after (net) elimination of MeSH, C(2)-unsubstituted penems. The overall cycloreversion/cycloaddition sequence was accelerated by microwave irradiation. [reaction: see text]

Definition of the heterocyclic pharmacophore of bacterial methionyl tRNA synthetase inhibitors: potent antibacterially active non-quinolone analogues.

Potent inhibitors of bacterial methionyl tRNA synthetase (MRS) have previously been reported. Through SAR of the quinolone moiety, the right hand side pharmacophore for MRS inhibition has now been defined as an NH-C-NH functionality in the context of a bicyclic heteroaromatic system. Potent antibacterial fused-pyrimidone and fused-imidazole analogues have been obtained and enantioselective activity demonstrated. Compound 46 demonstrated very good antibacterial activity against panels of antibiotic-resistant staphylococci and enterococci.

Synthesis and activity of analogues of the isoleucyl tRNA synthetase inhibitor SB-203207.

Twenty two analogues of SB-203207 have been prepared by total synthesis, and evaluated as inhibitors of a range of tRNA synthetases. Changes to the bicyclic core, removing either the terminal amino substituent or the sulfonyl group from the side chain, and altering either the carbon skeleton or stereochemistry of the isoleucine residue, decreases the potency of inhibition of isoleucyl tRNA synthetase. Substituting the isoleucine residue with other amino acids produces inhibitors of the corresponding synthetases. In particular, a methionine derivative is 50-100 times more potent against methionyl tRNA synthetase than against any of the corresponding isoleucyl, leucyl, valyl, alanyl and prolyl synthetases.

Lipopeptide substrates for SpsB, the Staphylococcus aureus type I signal peptidase: design, conformation and conversion to alpha-ketoamide inhibitors.

Pre-protein sequence data was used to design substrates for SpsB, the bacterial signal peptidase I enzyme from Staphylococcus aureus. Key elements were an alkyl membrane anchor, proline at P5 and lysine at P2. The proline at P5 induced a helical turn in the lipopeptide, as deduced from NMR studies, from P6 to P2 in membrane mimetic solvents. The substrate Decanoyl-LTPTAKAASKIDD-OH was cleaved by SpsB, as expected, between the P1 and P1' alanines with a k(cat)/K(m) of 2.3x10(6) M(-1)s(-1) at pH 8.5. Insertion of proline at P1' converted substrates to competitive inhibitors, whilst the incorporation of an alpha-ketoamide at the cleavage site transformed substrates to time dependent inhibitors of SpsB.

Variable sensitivity to bacterial methionyl-tRNA synthetase inhibitors reveals subpopulations of Streptococcus pneumoniae with two distinct methionyl-tRNA synthetase genes.

As reported previously (J. R. Jarvest et al., J. Med. Chem. 45:1952-1962, 2002), potent inhibitors (at nanomolar concentrations) of Staphylococcus aureus methionyl-tRNA synthetase (MetS; encoded by metS1) have been derived from a high-throughput screening assay hit. Optimized compounds showed excellent activities against staphylococcal and enterococcal pathogens. We report on the bimodal susceptibilities of S. pneumoniae strains, a significant fraction of which was found to be resistant (MIC, > or =8 mg/liter) to these inhibitors. Using molecular genetic techniques, we have found that the mechanism of resistance is the presence of a second, distantly related MetS enzyme, MetS2, encoded by metS2. We present evidence that the metS2 gene is necessary and sufficient for resistance to MetS inhibitors. PCR analysis for the presence of metS2 among a large sample (n = 315) of S. pneumoniae isolates revealed that it is widespread geographically and chronologically, occurring at a frequency of about 46%. All isolates tested also contained the metS1 gene. Searches of public sequence databases revealed that S. pneumoniae MetS2 was most similar to MetS in Bacillus anthracis, followed by MetS in various non-gram-positive bacterial, archaeal, and eukaryotic species, with streptococcal MetS being considerably less similar. We propose that the presence of metS2 in specific strains of S. pneumoniae is the result of horizontal gene transfer which has been driven by selection for resistance to some unknown class of naturally occurring antibiotics with similarities to recently reported synthetic MetS inhibitors.

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.

The antimicrobial natural product chuangxinmycin and some synthetic analogues are potent and selective inhibitors of bacterial tryptophanyl tRNA synthetase.

The antimicrobial natural product chuangxinmycin has been found to be a potent and selective inhibitor of bacterial tryptophanyl tRNA synthetase (WRS). A number of analogues have been synthesised. The interaction with WRS appears to be highly constrained, as only sterically smaller analogues afforded significant inhibition. The only analogue to show inhibition comparable to chuangxinmycin also had antibacterial activity. WRS inhibition may contribute to the antibacterial action of chuangxinmycin.

Nanomolar inhibitors of Staphylococcus aureus methionyl tRNA synthetase with potent antibacterial activity against gram-positive pathogens.

Potent nanomolar inhibitors of Staphylococcus aureus methionyl tRNA synthetase have been derived from a file compound high throughput screening hit. Optimized compounds show excellent antibacterial activity against staphylococcal and enterococcal pathogens, including strains resistant to clinical antibiotics. Compound 11 demonstrated in vivo efficacy in an S. aureus rat abscess infection model.