Discovery of Novel UDP-N-Acetylglucosamine Acyltransferase (LpxA) Inhibitors with Activity against Pseudomonas aeruginosa.

This study describes a novel series of UDP-N-acetylglucosamine acyltransferase (LpxA) inhibitors that was identified through affinity-mediated selection from a DNA-encoded compound library. The original hit was a selective inhibitor of Pseudomonas aeruginosa LpxA with no activity against Escherichia coli LpxA. The biochemical potency of the series was optimized through an X-ray crystallography-supported medicinal chemistry program, resulting in compounds with nanomolar activity against P. aeruginosa LpxA (best half-maximal inhibitory concentration (IC50) <5 nM) and cellular activity against P. aeruginosa (best minimal inhibitory concentration (MIC) of 4 µg/mL). Lack of activity against E. coli was maintained (IC50 > 20 µM and MIC > 128 µg/mL). The mode of action of analogues was confirmed through genetic analyses. As expected, compounds were active against multidrug-resistant isolates. Further optimization of pharmacokinetics is needed before efficacy studies in mouse infection models can be attempted. To our knowledge, this is the first reported LpxA inhibitor series with selective activity against P. aeruginosa.

Antibacterial medicinal chemistry - what can we design for?

INTRODUCTION: The need for new antibacterial agents continues to grow, but success in development of antibiotics in recent years has been limited. To improve the chances that new compounds will progress into clinical trials and beyond, it is vital that we consider as early as possible in the process the various challenges that discoverers and developers of new antibiotics will face. AREAS COVERED: The author looks at the factors that affect medicinal chemistry aimed at providing successful antibacterial agents. Target selection, target inhibition, accumulation in bacteria, and pharmacokinetics are all discussed, with a particular emphasis on how our current understanding should impact design and optimization strategies. EXPERT OPINION: From the perspective of a medicinal chemist, the primary question when considering the various aspects of antibacterial drug discovery should be 'what can I design for?' It is important to be aware of the limitations of our understanding, and also the constraints and challenges that arise due to the diversity of the bacteria we try to address. Progress is needed to simplify approval pathways and to increase return on investment for the next generations of clinically useful agents to succeed.

RNA: prebiotic product, or biotic invention?

Spectacular advances in structural and molecular biology have added support to the 'RNA world' hypothesis, and provide a mandate for chemistry to explain how RNA might have been generated prebiotically on the early earth. Difficulties in achieving a prebiotically plausible synthesis of RNA, however, have led many to ponder the question posed in the title of this paper. Herein, we review recent experimental work on the assembly of potential RNA precursors, focusing on methods for stereoselective C-C bond construction by aldolisation and related processes. This chemistry is presented in the context of a broader picture of the potential constitutional self-assembly of RNA. Finally, the relative accessibility of RNA and alternative nucleic acids is considered.

Hybrid antibiotics - clinical progress and novel designs.

INTRODUCTION: There is a growing need for new antibacterial agents, but success in development of antibiotics in recent years has been limited. This has led researchers to investigate novel approaches to finding compounds that are effective against multi-drug resistant bacteria, and that delay onset of resistance. One such strategy has been to link antibiotics to produce hybrids designed to overcome resistance mechanisms. AREAS COVERED: The concept of dual-acting hybrid antibiotics was introduced and reviewed in this journal in 2010. In the present review the authors sought to discover how clinical candidates described had progressed, and to examine how the field has developed. In three sections the authors cover the clinical progress of hybrid antibiotics, novel agents produced from hybridisation of two or more small-molecule antibiotics, and novel agents produced from hybridisation of antibiotics with small-molecules that have complementary activity. EXPERT OPINION: Many key questions regarding dual-acting hybrid antibiotics remain to be answered, and the proposed benefits of this approach are yet to be demonstrated. While Cadazolid in particular continues to progress in the clinic, suggesting that there is promise in hybridisation through covalent linkage, it may be that properties other than antibacterial activity are key when choosing a partner molecule.

On the prebiotic synthesis of ribonucleotides: photoanomerisation of cytosine nucleosides and nucleotides revisited.

Recent work has emphasised the importance of D-ribose aminooxazoline 1 in the synthesis of cytidine ribonucleosides under potentially prebiotic conditions. Upon treatment with cyanoacetylene, 1 is transformed into alpha-D-cytidine (alpha-2), and if an efficient means of anomerising this nucleoside or a derivative thereof were to be found, then the synthesis of one of the key beta-D-nucleosides required to make RNA would be realised. Photoanomerisation of alpha-2 has previously been described, but the yield was extremely low. Therefore, the present study was initiated to determine whether this low yield was the result of a low conversion or competing reaction pathways.

Asymmetric conjugate reductions with samarium diiodide: asymmetric synthesis of (2S,3R)- and (2S,3S)-[2-2H,3-2H]-leucine-(S)-phenylalanine dipeptides and (2S,3R)-[2-(2)H,3-2H]-phenylalanine methyl ester.

The highly diastereoselective samarium diiodide and D(2)O-promoted conjugate reduction of homochiral (E)- and (Z)-benzylidene and isobutylidene diketopiperazines (E)-5,7 and (Z)-6,8 has been demonstrated. This methodology allows the asymmetric synthesis of methyl (2S,3R)-dideuteriophenylalanine 27 in > or = 95% de and >98% ee, and (2S,3R)- or (2S,3S)-dideuterioleucine-(S)-phenylalanine dipeptides 37 and 38 in moderate de, 66% and 74% respectively. A mechanism is proposed to account for this process.