Synthesis and structure-activity relationships of novel 8a-aza-8a-homoerythromycin A ketolides

Multicomponent synthesis of α-acylamino and α-acyloxy amide derivatives of desmycosin and their activity against gram-negative bacteria

Bacterial resistance to the existing drugs requires constant development of new antibiotics. Developing compounds active against gram-negative bacteria thereby is one of the more challenging tasks. Among the many approaches to develop successful antibacterials, medicinal chemistry driven evolution of existing successful antibiotics is considered to be the most effective one. Towards this end, the C-20 aldehyde moiety of desmycosin was modified into α-acylamino and α-acyloxy amide functionalities using isonitrile-based Ugi and Passerini reactions, aiming for enhanced antibacterial and physicochemical properties. The desired compounds were obtained in 45-93% yield under mild conditions. The antibacterial activity of the resulting conjugates was tested against gram-negative Aliivibrio fischeri. The antibiotic strength is mostly governed by the amine component introduced. Thus, methylamine derived desmycosin bis-amide 4 displayed an enhanced inhibition rate vs. desmycosin (99% vs. 83% at 1 µM). Derivatives with long acyclic or bulky amine and isocyanide Ugi components reduced potency, whereas carboxylic acid reagents with longer chain length afforded increased bioactivity. In Passerini 3-component products, the butyric ester amide 22 displayed a higher activity (90% at 1 µM) than the parent compound desmycosin (2).

The global challenge of new classes of antibacterial agents: an industry perspective

With rising antibiotic resistance and the fear of returning to the pre-penicillin era, incentives are being provided for developing novel antibiotics. The hurdles faced by antibiotic developers include the difficulty in discovering novel chemicals that have selectivity and the increased regulatory scrutiny for safety and efficacy. Furthermore, the demonstration of superiority is essential in order to rationalize pricing and to assure a return on investment. Suggestions are provided to overcome each of these hurdles in order to prevent the antibiotic pipeline from running dry.

Synthesis and Structure-Activity Relationships of α-Amino-γ-lactone Ketolides: A Novel Class of Macrolide Antibiotics

An efficient synthesis of α-amino-γ-lactone ketolide (3) was developed, which provided a versatile intermediate for the incorporation of a variety of aryl and heteroaryl groups onto the C-21 position of clarithromycin via HBTU-mediated amidation. The biological data for this important new class of macrolides revealed significantly potent activity against erythromycin-susceptible strains as well as efflux-resistant and erythromycin MLSB-resistant strains of S. pneumoniae and S. pyogenes. In addition, ketolide 11o showed excellent in vitro antibacterial activity against H. influenzae strain as compared to telithromycin. These results indicate that C-21 substituted γ-lactone ketolides have potential as a next generation macrolide antibiotics.

Discovery of 4''-ether linked azithromycin-quinolone hybrid series: influence of the central linker on the antibacterial activity

A series of novel C-4''-substituted azithromycins was synthesized and evaluated for in vitro antibacterial activity against a panel of representative erythromycin-susceptible and macrolide-lincosamide-streptogramin (MLS) resistant pathogens. In summary, azithromycin and quinolone substructures merged in a mutually SAR-compatible design gave rise to a new class of antimicrobials with an improved spectrum and potency over azithromycin. Prototypical analogues 7f and 8f display an improved potency versus azithromycin against Gram-positive and fastidious Gram-negative pathogens. In particular, these new leads maintain activity against MLS-resistant strains of Streptococcus pneumoniae and Streptococcus pyogenes. In addition, they represent an improvement over telithromycin (1) and cethromycin (2) against the fastidious Gram-negative pathogen Haemophilus influenzae.

Novel hybrids of 15-membered 8a- and 9a-azahomoerythromycin A ketolides and quinolones as potent antibacterials

A series of novel 6-O-substituted and 6,12-di-O-substituted 8a-aza-8a-homoerythromycin A and 9a-aza-9a-homoerythromycin A ketolides were synthesized and evaluated for in vitro antibacterial activity against a panel of representative erythromycin-susceptible and erythromycin-resistant test strains. Another series of ketolides based on 14-membered erythromycin oxime scaffold was also synthesized and their antibacterial activity compared to those of 15-membered azahomoerythromycin analogues. In general, structure-activity studies have shown that 14-membered ketolides displayed favorable antibacterial activity in comparison to their corresponding 15-membered analogues within 9a-azahomoerythromycin series. However, within 8a-azahomoerythromycin series, some compounds incorporating a ketolide combined with either quinoline or quinolone pharmacophore substructures showed significantly potent activity against a variety of erythromycin-susceptible and macrolide-lincosamide-streptogramin B (MLS(B))-resistant Gram-positive pathogens as well as fastidious Gram-negative pathogens. The best compounds in this series overcome all types of resistance in relevant clinical Gram-positive pathogens and display hitherto unprecedented in vitro activity against the constitutively MLS(B)-resistant strain of Staphylococcus aureus. In addition, they also represent an improvement over telithromycin (2) and cethromycin (3) against fastidious Gram-negative pathogens Haemophilus influenzae and Moraxella catarrhalis.