Novel erythromycin derivatives with aryl groups tethered to the C-6 position are potent protein synthesis inhibitors and active against multidrug-resistant respiratory pathogens

Design, synthesis and antibacterial evaluation of novel C-11, C-9 or C-2'-substituted 3-O-descladinosyl-3-ketoclarithromycin derivatives

A novel series of 3-O-descladinosyl-3-keto-clarithromycin derivatives, including 11-O-carbamoyl-3-O-descladinosyl-3-keto-clarithromycin derivatives and 2',9(S)-diaryl-3-O-descladinosyl-3-keto-clarithromycin derivatives, were designed, synthesized and evaluated for their in vitro antibacterial activity. Among them, some derivatives were found to have activity against resistant bacteria strains. In particular, compound 9b showed not only the most significantly improved activity (16 µg/mL) against S. aureus ATCC43300 and S. aureus ATCC31007, which was >16-fold more active than that of CAM and AZM, but also the best activity against S. pneumoniae B1 and S. pyogenes R1, with MIC values of 32 and 32 µg/mL. In addition, compounds 9a, 9c, 9d and 9g exhibited the most effective activity against S. pneumoniae AB11 with MIC values of 32 or 64 µg/mL as well. Unfortunately, 2',9(S)-diaryl-3-O-descladinosyl-3-keto-clarithromycin derivatives failed to exhibit better antibacterial activity than references. It can be seen that the combined modification of the C-3 and C-11 positions of clarithromycin is beneficial to improve activity against resistant bacteria, while the single modification of the C-2'' position is very detrimental to antibacterial activity.

Design, synthesis and structure-activity relationships of novel N11-, C12- and C13-substituted 15-membered homo-aza-clarithromycin derivatives against various resistant bacteria

Bacterial infections are still the main significant problem of public health in the world, and their elimination will greatly rely on the discovery of antibacterial drugs. In the processes of our searching for novel macrolide derivatives with excellent activity against sensitive and resistant bacteria, three series of novel N11-, C12- and C13-substituted 15-membered homo-aza-clarithromycin derivatives were designed and synthesized as Series A, B and C by creatively opening the lactone ring of clarithromycin (CAM), introducing various 4-substituted phenyl-1H-1,2,3-triazole side chains at the N11, C12 or C13 position of CAM and macrolactonization. The results from their in vitro antibacterial activity demonstrated that compounds 20c, 20d and 20f displayed not only the most potent activity against S. aureus ATCC25923 with the MIC values of 0.5, 0.5 and 0.5 µg/mL, but also greatly improved activity against B. subtilis ATCC9372 with the MIC values of less than or equal to 0.25, 0.25 and 0.25 µg/mL, respectively. In particular, compound 11g exhibited the strongest antibacterial effectiveness against all the tested resistant bacterial strains and had well balanced activity with the MIC values of 4-8 µg/mL. Further study on minimum bactericidal concentration and kinetics confirmed that compound 11g possessed a bacteriostatic effect on bacterial proliferation. Moreover, the results of molecular docking revealed an potential additional binding force between compound 11g and U790 in addition to the normal binding force of macrolide skeleton, which may explain why this compound performed the most potent activity against resistant bacteria. The results of cytotoxic assay indicated that compounds 20c, 20d and 20f were non-toxic to human breast cancer MCF-7 cells at its effective antibacterial concentration.

The impact and fate of clarithromycin in anaerobic digestion of waste activated sludge for biogas production

Clarithromycin retained in waste activated sludge (WAS) inevitably enters the anaerobic digestion system. So far, the complex impacts and fate of clarithromycin in continuous operated WAS anaerobic digestion system are still unclear. In this study, two semi-continuous long-term reactors were set up to investigate the effect of clarithromycin on biogas production and antibiotic resistance genes (ARGs) during WAS anaerobic digestion, and a batch test was carried out to explore the potential metabolic mechanism. Experimental results showed that clarithromycin at lower concentrations (i.e., 0.1 and 1.0 mg/L) did not affect biogas production, whereas the decrease in biogas production was observed when the concentration of clarithromycin was further increased to 10 mg/L. Correspondingly, the relative abundance of functional bacteria in WAS anaerobic digestion (i.e., Anaerolineaceae and Microtrichales) was reduced with long-term clarithromycin exposure. The investigation of ARGs suggested that the effect of methylation belonging to the target site modification played a critical role for the anaerobic microorganisms in the expression of antibiotic resistance, and ermF, played dominated ARGs, presented the most remarkable proliferation. In comparison, the role of efflux pump was weakened with a significant decrease of two detected efflux genes. During WAS anaerobic digestion, clarithromycin could be partially degraded into metabolites with lower antimicrobial activity including oleandomycin and 5-O-desosaminyl-6-O-methylerythronolide and other metabolites without antimicrobial activity.

Recent advances in the catalytic cyclopropanation of unsaturated compounds with diazomethane

The main achievements and development trends of the past 10–15 years related to the catalytic cyclopropanation of unsaturated compounds with diazomethane are integrated and analyzed. The attention is focused on the most efficient catalysts based on palladium compounds. Data on the effects of substrate structure and nature of catalyst components on the regio- and stereoselectivity of these reactions are systematized. Characteristic features of safe methods for diazomethane generation are considered, including the use of membrane technologies and continuous-flow and in situ preparation methods, which have prospects for industrial application.

The bibliography includes 281 references.

Synthesis and antibacterial activity of 11,12-cyclic carbonate 4″-O-aralkylacetylhydrazineacyl azithromycin derivatives

Two series of novel 4″-O-aralkylacetylhydrazineacyl azithromycin derivatives were synthesized and evaluated for their in vitro antibacterial activities. Among them, compound B4, B5, B13 and B18 were found to display significantly improved activity than control drugs (MIC > 128 μg/mL) against methicillin-resistant strain S. aureus ATCC 43,300 with an MIC value 2-4 μg/mL. Remarkably, compound B5 and B13 showed potent activity against penicillin-resistant S. aureus ATCC31007 (MIC = 4 μg/mL) and methicillin-resistant S. aureus ATCC 43,300 (MIC = 2 μg/mL).

Synthesis and biological evaluation of solithromycin analogs against multidrug resistant pathogens

Novel antibacterial drugs that treat multidrug resistant pathogens are in high demand. We have synthesized analogs of solithromycin using Cu(I)-mediated click chemistry. Evaluation of the analogs using Minimum Inhibitory Concentration (MIC) assays against resistant Staphylococcus aureus, Escherichia coli, and multidrug resistant pathogens Enterococcus faecium and Acinetobacter baumannii showed they possess potencies similar to those of solithromycin, thus demonstrating their potential as future therapeutics to combat the existential threat of multidrug resistant pathogens.

Design, synthesis and structure-activity relationships of novel macrolones: Hybrids of 2-fluoro 9-oxime ketolides and carbamoyl quinolones with highly improved activity against resistant pathogens

Constitutively erythromycin-resistant apathogens are more difficult to address than inducibly resistant and efflux-resistant strains. Three series of the 4th generation 2-fluoro 9-oxime erythromycin ketolides were synthesized and evaluated. Incorporation of substituted heteroaryl groups (a - m), in contrast to previously reported the unsubstituted heteroaryl groups, proved to the beneficial for enhancement of the activities of the 9-propgargyl ketolide 8 series and the 9-allyl ketolide 14 series. But these aryl groups (a - m) cannot supply the resulting compounds 8 and 14, unlike corresponding the 6-allyl ketolide 20 series, with activity against constitutively resistant Streptococcus pneumoniae. However, hybrids of macrolides and quinolones (8, 14 and 20, Ar = n - t) exhibited not only high activities against susceptible, inducibly erm-mediated resistant, and efflux-mediated resistant strains, but also significantly improved potencies against constitutively resistant Streptococcus pneumoniae and Streptococcus pyogenes. The capacity was highlighted by introduction of newly designed carbamoyl quinolones (q, r, s and t) rather than commonly seen carboxy quinolones (o and p) as the pharmacophores. Structure-activity relationships and molecular modelling indicated that 8r, 14r and 20q may have different binding sites compared to current erythromycins. Moreover, 8r, 14r and 20q have 2.5-3.6 times prolonged half-life and 2.3- to 2.6-fold longer mean residence time in vivo over telithromycin. These findings pave the way for rational design of novel non-telithromycin macrolides that target new binding sites within bacterial ribosomes.

Synthesis and antibacterial evaluation of novel 11-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin derivatives

A series of novel 11-O-aralkylcarbamoyl-3-O-descladinosylclarithromycin derivatives were designed, synthesized and evaluated for their in vitro antibacterial activity. The results showed that the majority of the target compounds displayed potent activity against erythromycin-susceptible S. pyogenes, erythromycin-resistant S. pneumoniae A22072 expressing the mef gene and S. pneumoniae AB11 expressing the mef and erm genes. Besides, most of the target compounds exhibited moderate activity against erythromycin-susceptible S. aureus ATCC25923 and B. subtilis ATCC9372. In particular, compounds 11a, 11b, 11c, 11e, 11f and 11h were found to exert favorable antibacterial activity against erythromycin-susceptible S. pyogenes with the MIC values of 0.015-0.125 μg/mL. Furthermore, compounds 10e, 11a, 11b and 11c showed superior activity against erythromycin-resistant S. pneumoniae A22072 with the MIC values of 0.25-0.5 μg/mL. Additionally, compound 11c was the most effective against all the erythromycin-resistant S. pneumoniae strains (A22072, B1 and AB11), exhibiting 8-, 8- and 32-fold more potent activity than clarithromycin, respectively.

The macrolide antibiotic renaissance

Macrolides represent a large family of protein synthesis inhibitors of great clinical interest due to their applicability to human medicine. Macrolides are composed of a macrocyclic lactone of different ring sizes, to which one or more deoxy-sugar or amino sugar residues are attached. Macrolides act as antibiotics by binding to bacterial 50S ribosomal subunit and interfering with protein synthesis. The high affinity of macrolides for bacterial ribosomes, together with the highly conserved structure of ribosomes across virtually all of the bacterial species, is consistent with their broad-spectrum activity. Since the discovery of the progenitor macrolide, erythromycin, in 1950, many derivatives have been synthesised, leading to compounds with better bioavailability and acid stability and improved pharmacokinetics. These efforts led to the second generation of macrolides, including well-known members such as azithromycin and clarithromycin. Subsequently, in order to address increasing antibiotic resistance, a third generation of macrolides displaying improved activity against many macrolide resistant strains was developed. However, these improvements were accompanied with serious side effects, leading to disappointment and causing many researchers to stop working on macrolide derivatives, assuming that this procedure had reached the end. In contrast, a recent published breakthrough introduced a new chemical platform for synthesis and discovery of a wide range of diverse macrolide antibiotics. This chemical synthesis revolution, in combination with reduction in the side effects, namely, 'Ketek effects', has led to a macrolide renaissance, increasing the hope for novel and safe therapeutic agents to combat serious human infectious diseases.

Synthesis and antibacterial evaluation of novel 11-O-carbamoyl clarithromycin ketolides

A series of novel 11-O-carbamoyl clarithromycin ketolides were designed, synthesized and evaluated for their in vitro antibacterial activity. The results showed that the majority of the target compounds displayed improved activity compared with references against erythromycin-resistant S. pneumoniae A22072 expressing the mef gene, S. pneumoniae B1 expressing the erm gene and S. pneumoniae AB11 expressing the mef and erm genes. In particular, compounds 9, 18, 19 and 22 showed the most potent activity against erythromycin-resistant S. pneumoniae A22072 with the MIC values of 0.5μg/mL. Furthermore, compounds 11, 18, 19, 24 and 29 were also found to exhibit favorable antibacterial activity against erythromycin-susceptible S. pyogenes with the MIC values of 0.125-1μg/mL, and moderate activity against erythromycin-susceptible S. aureus ATCC25923 and B. subtilis ATCC9372.

5-O-Mycaminosyltylonolide antibacterial derivatives: design, synthesis and bioactivity

Tylosin is a 16-membered macrolide broad-spectrum antibiotic that has an important role in veterinary medicine, active against Gram-positive and a restricted range of Gram-negative bacteria. We synthesized 15 types of tylosin-related derivatives by chemical modification and evaluated them against mastitis pathogens. Among them, 20-deoxy-20-{N-methyl-N-[1-(3-quinolyl)-1H-1,2,3-triazol-4-yl]methylamino}-5-O-mycaminosyltylonolide 2f and 20-deoxy-20-{N-benzyl-N-[1-(3-quinolyl)-1H-1,2,3-triazol-4-yl]methylamino}-5-O-mycaminosyltylonolide 2k were found to not only expand their antibacterial impact to include Gram-negative bacteria, such as Escherichia coli and Klebsiella pneumoniae, but also to retain or increase antibacterial activity against Gram-positive bacteria, such as Staphylococcus aureus and Streptococcus uberis in comparison with the parent tylosin.

Synthesis and antibacterial activities of some novel 17, 18-unsaturated carbonyl compounds derivated from josamycin

Some novel josamycin derivatives bearing an arylalkyl-type side chain were designed and synthesized. By HWE or Wittig reaction, 16-aldehyde group of josamycin analogs were converted into unsaturated carbonyl compounds. They were evaluated for their in vitro antibacterial activities against a panel of respiratory pathogens. 8b and 8e exhibited comparable activities against a panel of respiratory pathogens, especially to resistant ones in the series of desmycarosyl josamycin analogs. Among of all the target molecules, 21 showed the best antibacterial activities.

Design, synthesis and structure-bactericidal activity relationships of novel 9-oxime ketolides and reductive epimers of acylides

Erythromycin was long viewed as a bacteriostatic agent. The erythromycin derivatives, 9-oxime ketolides have a species-specific bactericidal profile. Among them, the 3'-allyl version of the 9-oxime ketolide 1 (Ar=3-quinolyl; 17a) is bactericidal against Streptococcus pneumoniae and Streptococcus pyogenes. In contrast, the 2-fluoro analogs of 1, 13a (Ar=6-quinolyl), 13b (Ar=3-quinolyl) and 24a (Ar=4-isoquinolyl), show bactericidal activities against S. pneumoniae, Staphylococcus aureus and Moraxella catarrhalis, while the 2-fluoro analogs 13c (Ar=3-aminopyridyl) and 24b (Ar=3-carbamoylpyridyl) are only bactericidal against S. pneumoniae and Haemophilus influenzae. Reduction of the ketolides led to novel epiacylides, the 3-O-epimers of the acylides. Alteration of linker length (30b vs. 30a), 2-fluorination (33 vs. 30a) and incorporation of additional spacers at the 9-oxime or 6-OH (35, 40 vs. 30a) did not restore the epiacylides back to be as active as the acylide 31. Molecular docking suggested that epimerization at the 3-position reshapes the orientation of the 3-O-sidechain and leads to considerably weaker binding with bacterial ribosomes.

Targeting Antibiotic Resistance

Finding strategies against the development of antibiotic resistance is a major global challenge for the life sciences community and for public health. The past decades have seen a dramatic worldwide increase in human-pathogenic bacteria that are resistant to one or multiple antibiotics. More and more infections caused by resistant microorganisms fail to respond to conventional treatment, and in some cases, even last-resort antibiotics have lost their power. In addition, industry pipelines for the development of novel antibiotics have run dry over the past decades. A recent world health day by the World Health Organization titled "Combat drug resistance: no action today means no cure tomorrow" triggered an increase in research activity, and several promising strategies have been developed to restore treatment options against infections by resistant bacterial pathogens.

Synthesis and antibacterial evaluation of novel 4″-glycyl linked quinolyl-azithromycins with potent activity against macrolide-resistant pathogens

A new azithromycin-based series of antibacterial macrolones is reported, which features the use of a 4″-ester linked glycin for tethering the quinolone side chain to the macrolide scaffold. Among the analogs prepared, compounds 9e and 22f with a quinolon-6-yl moiety were found to have potent and well-balanced activity against clinically important respiratory tract pathogens, including erythromycin-susceptible and MLSB resistant strains of Streptococcus pneumoniae, Streptococcus pyogenes, and Haemophilus influenzae. In addition, potential lead compounds 9e and 22f demonstrated outstanding levels of activity against Moraxella catarrhalis and inducibly MLSB resistant Staphylococcus aureus. The best member of this series 22f rivals or exceeds, in potency, some of the most active ketolide antibacterial agents known today, such as telithromycin and cethromycin.

Synthesis of an azido-tagged low affinity ratiometric calcium sensor

Changes in high localised concentrations of Ca²⁺ ions are fundamental to cell signalling. The synthesis of a dual excitation, ratiometric calcium ion sensor with a K_d of 90 μM, is described. It is tagged with an azido group for bioconjugation, and absorbs in the blue/green and emits in the red region of the visible spectrum with a large Stokes shift. The binding modulating nitro group is introduced to the BAPTA core prior to construction of a benzofuran-2-yl carboxaldehyde by an allylation–oxidation–cyclisation sequence, which is followed by condensation with an azido-tagged thiohydantoin. The thiohydantoin unit has to be protected with an acetoxymethyl (AM) caging group to allow CuAAC click reaction and incorporation of the KDEL peptide endoplasmic reticulum (ER) retention sequence.

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.

Desmethyl Macrolides: Synthesis and Evaluation of 4,8,10-Tridesmethyl Cethromycin

Antibiotic-resistant bacteria are emerging at an alarming rate in both hospital and community settings. Motivated by this issue, we have prepared desmethyl (i.e., replacing methyl groups with hydrogens) analogues of third-generation macrolide drugs telithromycin (TEL, 2) and cethromycin (CET, 6), both of which are semi-synthetic derivatives of flagship macrolide antibiotic erythromycin (1). Herein, we report the total synthesis, molecular modeling, and biological evaluation of 4,8,10-tridesmethyl cethromycin (7). In MIC assays, CET analogue 7 was found to be equipotent with TEL (2) against a wild-type E. coli strain, more potent than previously disclosed desmethyl TEL congeners 3, 4, and 5, but fourfold less potent than TEL (2) against a mutant E. coli A2058G strain.

Synthesis and antibacterial evaluation of novel 11,4″-disubstituted azithromycin analogs with greatly improved activity against erythromycin-resistant bacteria

A series of novel 11,4″-disubstituted azithromycin analogs were synthesized and evaluated for their antibacterial activity. All the 11,4″-disubstituted analogs exhibited excellent activity (0.03-0.12 μg/ml) against erythromycin-susceptible Streptococcus pneumoniae, and significantly improved activity against three phenotypes of erythromycin-resistant S. pneumoniae compared with erythromycin A, clarithromycin or azithromycin. Among them, compounds 26-28 showed the most potent activity (0.25, 0.03 and 2 μg/ml) against S. pneumoniae expressing the erm gene, the mef gene and the erm and mef genes, respectively. In addition, compound 28 was the most effective (0.03 and 0.12 μg/ml) against erythromycin-susceptible S. pneumoniae and Staphylococcus aureus as well. It is noteworthy that the most active compounds described above possess the same terminal 3,5-dinitrophenyl groups on their C-4″ bisamide side chains.

The chemistry of peptidyltransferase center-targeted antibiotics: enzymatic resistance and approaches to countering resistance

The continued ability to treat bacterial infections requires effective antibiotics. The development of new therapeutics is guided by knowledge of the mechanisms of action of and resistance to these antibiotics. Continued efforts to understand and counteract antibiotic resistance mechanisms at a molecular level have the potential to direct development of new therapeutic strategies in addition to providing insight into the underlying biochemical functions impacted by antibiotics. The interaction of antibiotics with the peptidyltransferase center and adjacent exit tunnel within the bacterial ribosome is the predominant mechanism by which antibiotics impede translation, thus stalling growth. Resistance enzymes catalyze the chemical modification of the RNA that composes these functional regions, leading to diminished binding of antibiotics. This review discusses recent advances in the elucidation of chemical mechanisms underlying resistance and driving the development of new antibiotics.

Structure-activity relationships of novel alkylides: 3-O-arylalkyl clarithromycin derivatives with improved antibacterial activities

A series of novel alkylides, possessing 3-O-arylalkyl group instead of 3-O-cladinose, were designed, synthesized and evaluated for in vitro antibacterial activities. The increased potency clearly ranked by the order of 3-O-(3-aryl-2-propargyl), 3-O-(3-aryl-E-prop-2-enyl), 3-O-(3-aryl-propyl), and 3-O-(3-aryl-Z-prop-1-enyl) groups. Some alkylides, exemplified by 7a, 10a, 21, 22, 26, 27 and 33, showed improved activities against inducible MLS(B) resistance and efflux resistance compared to the second-generation macrolides. Among them, 26 possessed comparable activities against erythromycin-susceptible Staphylococcus aureus, Streptococcus pneumoniae and Streptococcus pyogenes (MICs of 0.016-0.5 μg/mL). Moreover, 26 displayed dramatically enhanced potency against both efflux resistant and inducibly MLS(B) resistant strains (MICs of 0.125-0.5 μg/mL) resistant to clarithromycin and azithromycin (MICs of 1- >254 μg/mL), independent of methicillin-susceptible and methicillin-resistant phenotypes.

Synthesis and antibacterial activity of a novel series of acylides active against community acquired respiratory pathogens

A novel series of acylides 4 were designed to overcome antibacterial resistance and evaluated for in vitro and in vivo activity. This series of acylides was designed from clarithromycin by changing the substitution on the desosamine nitrogen, followed by conversion to 3-O-acyl and 11,12-carbamate. These compounds showed significantly potent antibacterial activity against not only Gram-positive pathogens, including macrolide-lincosamide-streptogramin B (MLS(B))-resistant and efflux-resistant strains, but also Gram-negative pathogens such as Haemophilus influenzae. These acylides also showed better activity against telithromycin resistant Streptococcus pneumoniae strains.

Novel C-4'' modified azithromycin analogs with remarkably enhanced activity against erythromycin-resistant Streptococcus pneumoniae: the synthesis and antimicrobial evaluation

Three novel structural series of C-4'' modified azithromycin analogs with two amide groups, which were connected by different alkyl linkage, were designed, prepared and evaluated for their in vitro antibacterial activity against seven phenotypes of respiratory pathogens. Among them, 7d, 8j and 9j, as representatives of corresponding series, exhibited remarkably improved activity against erythromycin-resistant Streptococcus pneumoniae expressing the erm gene, the mef gene, and the erm and mef genes. In addition, 7a-c, 7f-h, 7j, 8d, 8g, 8i, 9a-b and 9i displayed favorable efficacy against erythromycin-resistant S. pneumoniae A22072 expressing the mef gene.

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.

Synthesis, activity and pharmacokinetics of novel antibacterial 15-membered ring macrolones

Synthesis, antibacterial activity and pharmacokinetic properties of a novel class of macrolide antibiotics-macrolones-derived from azithromycin, comprising oxygen atom(s) in the linker and either free or esterified quinolone 3-carboxylic group, are reported. Selected compounds showed excellent antibacterial potency towards key erythromycin resistant respiratory pathogens. However, the majority of compounds lacked good bioavailability. The isopropyl ester, compound 35, and a macrolone derivative with an elongated linker 29 showed the best oral bioavailability in rats, both accompanied with an excellent overall microbiology profile addressing inducible and constitutive MLSb as well as efflux mediated macrolide resistance in streptococci, while compound 29 is more potent against staphylococci.

Chemistry and biology of macrolide antiparasitic agents

Macrolide antibacterial agents inhibit parasite proliferation by targeting the apicoplast ribosome. Motivated by the long-term goal of identifying antiparasitic macrolides that lack antibacterial activity, we have systematically analyzed the structure-activity relationships among erythromycin analogues and have also investigated the mechanism of action of selected compounds. Two lead compounds, N-benzylazithromycin (11) and N-phenylpropylazithromycin (30), were identified with significantly higher antiparasitic activity and lower antibacterial activity than erythromycin or azithromycin. Molecular modeling based on the cocrystal structure of azithromycin bound to the bacterial ribosome suggested that a substituent at the N-9 position of desmethylazithromycin could improve selectivity because of species-specific interactions with the ribosomal L22 protein. Like other macrolides, these lead compounds display a strong "delayed death phenotype"; however, their early effects on T. gondii replication are more pronounced.

In vitro antibacterial activity of modithromycin, a novel 6,11-bridged bicyclolide, against respiratory pathogens, including macrolide-resistant Gram-positive cocci

The in vitro activities of modithromycin against Gram-positive and -negative respiratory pathogens, including macrolide-resistant cocci with different resistance mechanisms, were compared with those of other macrolide and ketolide agents. MICs were determined by the broth microdilution method. All 595 test strains used in this study were isolated from Japanese medical facilities. The erm (ribosome methylase) and/or mef (efflux pump) gene, which correlated with resistance to erythromycin as well as clarithromycin and azithromycin, was found in 81.8%, 21.3%, and 23.2% of Streptococcus pneumoniae, Streptococcus pyogenes, and methicillin-susceptible Staphylococcus aureus (MSSA) strains, respectively. Modithromycin showed MIC(90)s of 0.125 μg/ml against these three cocci, including macrolide-resistant strains. In particular, the MIC of modithromycin against ermB-carrying S. pyogenes was ≥ 32-fold lower than that of telithromycin. The activities of modithromycin as well as telithromycin were little affected by the presence of mefA or mefE in both streptococci. Against Gram-negative pathogens, modithromycin showed MIC(90)s of 0.5, 8, and 0.031 μg/ml against Moraxella catarrhalis, Haemophilus influenzae, and Legionella spp., respectively. The MICs of modithromycin against M. catarrhalis and H. influenzae were higher than those of telithromycin and azithromycin. However, modithromycin showed the most potent anti-Legionella activity among the macrolide and ketolide agents tested. These results suggested that the bicyclolide agent modithromycin is a novel class of macrolides with improved antibacterial activity against Gram-positive cocci, including telithromycin-resistant streptococci and intracellular Gram-negative bacteria of the Legionella species.

Synthesis and antibacterial evaluation of novel clarithromycin derivatives with C-4″ elongated arylalkyl groups against macrolide-resistant strains

Novel clarithromycin derivatives with C-4″ elongated arylalkyl groups were designed, synthesized and evaluated to probe the effect of different lengths of their C-4″ side chains on the activity against resistant bacterial strains. These derivatives had excellent activity against erythromycin-susceptible Streptococcus pneumoniae, Streptococcus aureus or Streptococcus pyogenes and some of them exhibited greatly improved activity against erythromycin-resistant strains. Compounds 18 and 16, which had the C-4″ elongated arylalkyl groups with eight atoms from the 4″-oxygen atom to the terminal benzene ring, were the most effective against S. pneumoniae expressing the erm gene and the erm and mef genes. In contrast, the most potent compounds 3, 5, 9, 17 and 18 against S. pneumoniae expressing the mef gene had C-4″ elongated arylalkyl groups with three to eight atoms between the 4″-oxygen atom and the terminal aromatic ring.

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.

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

A series of novel 6-O-substituted 8a-aza-8a-homoerythromycin A ketolides was synthesized and evaluated for in vitro antibacterial activity. Key strategic elements of the synthesis include the base-induced E-Z isomerization of 3-O-descladinosyl-6-O-allylerythromycin A 9(E)-oxime followed by ring-expanding reaction of the resulting 9(Z)-oxime via Beckmann rearrangement. The ketolides showed potent activity against a variety of erythromycin-susceptible and macrolide-lincosamide-streptogramin B (MLS(B)) resistant Gram-positive and fastidious Gram-negative pathogens. The best compounds in this series overcome all types of resistance in relevant clinical Gram-positive pathogens and display in vitro activity comparable to telithromycin and cethromycin.

Synthesis and antibacterial activity of 11,12-carbamate-3-O-acyl erythromycin derivatives

A novel series of acylide derivatives have been synthesized which exhibit in vitro potency against key respiratory pathogens. Modification of position 3 was accomplished by replacing different 3-O-substituted acyl groups in the macrolide core via a facile procedure. Compounds 7a-7i were eventually yielded by the conjunction of diverse hetero-aryl side chains with the 11-N,12-O-carbamate sub-structure.