Novelties in the field of macrolides

Mechanistic Insights into Clinically Relevant Ribosome-Targeting Antibiotics

Antibiotics targeting the bacterial ribosome are essential to combating bacterial infections. These antibiotics bind to various sites on the ribosome, inhibiting different stages of protein synthesis. This review provides a comprehensive overview of the mechanisms of action of clinically relevant antibiotics that target the bacterial ribosome, including macrolides, lincosamides, oxazolidinones, aminoglycosides, tetracyclines, and chloramphenicol. The structural and functional details of antibiotic interactions with ribosomal RNA, including specific binding sites, interactions with rRNA nucleotides, and their effects on translation processes, are discussed. Focus is placed on the diversity of these mechanisms and their clinical implications in treating bacterial infections, particularly in the context of emerging resistance. Understanding these mechanisms is crucial for developing novel therapeutic agents capable of overcoming bacterial resistance.

A conformational NMR analysis of methymycin aglycones: complete and unambiguous assignments of stereochemically diverse glycosylated methymycin analogs by 1D and 2D NMR techniques and molecular modeling

The (1)H and (13)C NMR spectra of 10-deoxymethynolide (1), 8.9-dihydro-10-deoxymethynolide (2) and its glycosylated derivatives (3-9) were analyzed using gradient-selected NMR techniques, including 1D TOCSY, gCOSY, 1D NOESY (DPFGSENOE), NOESY, gHMBC, gHSQC and gHSQC-TOCSY. The NMR spectral parameters (chemical shifts and coupling constants) of 1-9 were determined by iterative analysis. For the first time, complete and unambiguous assignment of the (1)H NMR spectrum of 10-deoxymethynolide (1) has been achieved in CDCl(3), CD(3)OD and C(6)D(6) solvents. The (1)H NMR spectrum of 8,9-dihydro-10-deoxymethynolide (2) was recorded in CDCl(3), (CD(3))(2)CO and CD(3)OD solutions to determine the conformation. NMR-based conformational analysis of 1 and 2 in conjugation with molecular modeling concluded that the 12-membered ring of the macrolactones may predominantly exist in a single stable conformation in all solvents examined. In all cases, a change in solvent caused only small changes in chemical shifts and coupling constants, suggesting that all glycosylated methymycin analogs exist with similar conformations of the aglycone ring in solution.

Antibacterial natural products in medicinal chemistry--exodus or revival?

To create a drug, nature's blueprints often have to be improved through semisynthesis or total synthesis (chemical postevolution). Selected contributions from industrial and academic groups highlight the arduous but rewarding path from natural products to drugs. Principle modification types for natural products are discussed herein, such as decoration, substitution, and degradation. The biological, chemical, and socioeconomic environments of antibacterial research are dealt with in context. Natural products, many from soil organisms, have provided the majority of lead structures for marketed anti-infectives. Surprisingly, numerous "old" classes of antibacterial natural products have never been intensively explored by medicinal chemists. Nevertheless, research on antibacterial natural products is flagging. Apparently, the "old fashioned" natural products no longer fit into modern drug discovery. The handling of natural products is cumbersome, requiring nonstandardized workflows and extended timelines. Revisiting natural products with modern chemistry and target-finding tools from biology (reversed genomics) is one option for their revival.

Biosensor-guided screening for macrolides

Macrolides are complex polyketides of microbial origin that possess an extraordinary variety of pharmacological properties, paired with an impressive structural diversity. Bioassays for specific detection of such compounds will be of advantage for a class-specific drug screening. The current paper describes a cell-based microbial biosensor, assigning a luminescence response to natural or chemically modified macrolides, independent from their biological activity. This biosensor is based on the coupling of the structural luciferase genes of Vibrio fischeri to the regulatory control mechanism of a bacterial erythromycin resistance operon. The bioassays is easy to handle and can be applied to various screening formats. The feasibility of the test system for natural products screening is exemplified by the isolation and characterization of picromycin from a Streptomyces species. Biosensor-guided screening for macrolides is based on macrolide-promoted expression of lux genes and induction of luminescence (independent of macrolide antibiotic activity).

A novel ketolide class: Synthesis and antibacterial activity of a lead compound

Synthesis and antibacterial activity of a new class of ketolide antibiotics, exemplified by the prototype GW680788X (1), are described. The structure of (1) has been elucidated by spectroscopic analysis. The good antibacterial activity shown by (1) in comparison with clarithromycin prompted us to consider this compound as a lead molecule for further exploration.

New research in macrolides and ketolides since 1997

Macrolide and ketolide antibacterials remain a very dynamically active group. To overcome erythromycin A resistance within Gram-positive cocci and bacteria, novel compounds have been semi-synthesised, such as ketolides and C-4'' carbamate erythromycylamine derivatives. The continual efforts of those studying macrolides have led to molecular level investigations into the mechanism of action of these antibacterials. Among all novel derivatives, only telithromycin and AB-773 are currently under development. No real novel developments have been seen with the 15- and 16-membered ring macrolides, however, research is also continuing in this area. This review is an update of our knowledge in the field of macrolides.

ABT-773: a new ketolide antibiotic

ABT-773 is a new semisynthetic derivative of erythromycin A, the ketolide class of broad spectrum antibacterial agents, in Phase II development by Abbott. With good broad spectrum activity against Gram-positive, some Gram-negative organisms and intracellular bacteria, ABT-773 is being developed as a respiratory agent. Structural changes in the ketolide class agents such as ABT-773 provides expanded activity in vitro against macrolide-resistant strains of Streptococcus pneumoniae and improved activity against MLS(B) (macrolide-lincosamide-streptogramin) constitutive expressing streptococci.

Ketolides-telithromycin, an example of a new class of antibacterial agents

Ketolides are new medicinal chemical entities. They are obtained by removing the 3-L-cladinose sugar moiety from erythronolide A and oxidation of the resulting 3-hydroxyl. They were designed to overcome erythromycin A resistance within Gram-positive cocci. The 3-keto group is responsible for the lack of induction of macrolide resistance, high stability in acidic environments, and the ability to overcome resistance due to methylation of 23SrRNA. The C11-C12 carbamate ketolides are able to overcome efflux and hydrolysis mechanisms of resistance and possess additional mechanisms of action at the ribosome level in comparison with erythromycin A. The nature of the side-chain substituting the C11-C12 carbamate residue is responsible for enhancing the in vitro and in vivo activities in comparison with clarithromycin, for the pharmacodynamic and pharmacokinetic properties, for the intracellular features, and for tolerance. This C11-C12 side-chain is supporting the development of new ketolides.