Reversal by syngeneic spleen cells of inhibitory effects of drugs and irradiation on Friend virus

Novel ureas and thioureas of 15-membered azalides with antibacterial activity against key respiratory pathogens

The new ureas and thioureas of 15-membered azalides, N''-substituted 9a-(N'-carbamoyl-gamma-aminopropyl) (4), 9a-(N'-thiocarbamoyl-gamma-aminopropyl) (6), 9a-[N'-(beta-cyanoethyl)-N'-(carbamoyl-gamma-aminopropyl)] (8) and 9a-[N'-(beta-cyanoethyl)-N'-(thiocarbamoyl-gamma-aminopropyl)] (10) of 9-deoxo-9-dihydro-9a-aza-9a-homoerythromycin A (2), were synthesized and structurally characterized by NMR and IR spectroscopic methods and mass spectrometry. The new compounds were evaluated in vitro against a panel of erythromycin susceptible and erythromycin-resistant gram-positive and gram-negative bacterial strains. These compounds displayed an excellent overall antibacterial in vitro activity against erythromycin sensitive gram-positive strains, Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, and good against negative strains, Moraxella catarrhalis and Haemophilus influenzae. In addition, several ureas with naphthyl substituents (4f, 4g, 4h) showed better activity in comparison to azithromycin against inducible resistant S. pyogenes. Ureas with naphthyl substituents 4g, 4h and thiourea 8h displayed moderate activity against constitutively resistant S. pneumoniae.

Binding studies of macrolides, lincosamides and streptogramins to Streptococcus G group using [3H]-erythromycin

Parameters of [3H]-erythromycin binding to Streptococcus are determined in vivo using both equilibrium and kinetic methods. This binding is saturable, reversible and independent of energetic systems. Whatever the methods used, the binding parameters are identical as 14 nM for the dissociation constant of the complex erythromycin-Streptococcus and a density of binding sites of 11,865 molecules/cell. Other macrolides, streptogramins and lincosamides competitively displaced bound [3H]-erythromycin suggesting that these compounds share common binding sites on the bacteria. In parallel, the MIC values of these antibiotics against Streptococcus are determined by agar dilution method in Mueller-Hinton medium with 5% of horse blood in order to compare the binding and microbiological parameters. A strong correlation (n = 0.863) has been found between the corresponding inhibition constants and MIC values. Such binding studies could be used in conjunction with microbiological assays for primary screening of active analogous or other compounds with interfere with [3H]-erythromycin binding to the bacteria.

Binding parameters and microbiological activity of macrolides, lincosamides and streptogramins against Staphylococcus aureus

Parameters of erythromycin binding to Staphylococcus aureus were measured in-vitro using an equilibrium method with [3H]erythromycin. The dissociation constant of the complex, erythromycin-S. aureus sensitive strain, was KD = 0.11 microM. The maximal binding, representing the density of binding sites was 14,847 molecules/cell. No binding was detectable on the constitutive resistant strain. Macrolides, streptogramins and lincosamides displaced bound [3H]erythromycin by a competitive process indicating that these compounds share common binding sites on the bacteria, i.e. 50 S ribosomal subunits. A good correlation (r = 0.99) was demonstrated between the corresponding inhibition constants (Ki) and the minimal inhibitory concentration. It is proposed that knowledge of the binding parameters provides a good indication of bacterial susceptibility and may serve as a useful adjunct in developing new compounds.

Determination of binding parameters of macrolides, lincosamides, and streptogramins to Legionella pneumophila

Parameters of [3H]erythromycin binding to Legionella pneumophila were determined in vitro using both an equilibrium and a kinetic method. Different L. pneumophila serogroups, 1-3, and a virulent strain serogroup, 1, were tested. All strains of bacteria exhibited the same binding pattern, with a dissociation constant of 0.15 microM. Other macrolides, streptogramin B-types, and lincosamides competitively displaced bound erythromycin suggesting that these compounds share common binding sites on the bacteria. Minimum inhibitory concentration (MIC) values for macrolides, streptogramin B-types, and lincosamides were determined with buffered charcoal yeast extract (BCYE) medium. A good correlation (r = 0.994) was found between the corresponding inhibition constants of these antibiotics and their MIC. It was also noted that for lincosamides the microbiological inactivity was associated with a very low bacterium affinity. Thus, it is concluded that binding parameters of these antibiotics reflect their efficacy against L. pneumophila in vitro and may serve as a useful adjunct in developing new compounds.

Spectrophotometric assay for cephalosporin C in fermentation broths

Several N-substituted erythromycylamines were evaluated for their ability to inhibit the binding of [¹⁴C]erythromycin to ribosomes. The association and dissociation constants for the binding of each compound to Escherichia coli ribosomes were determined. These studies have resulted in the development of three types of probes for topological studies of the erythromycin-binding site and the ribosome: the chemically reactive bromoacetamido, the photoreactive N-(2)-nitro-4-azidophenyl)glycinamido, and the fluorescent fluorescein isothiocyanate derivatives of 9(S)-erythromycylamine.

Induction of erythromycin resistance in Staphyloccus aureus by erythromycin derivatives

The ability of 53 erythromycin analogues to induce resistance to erythromycin in Staphlococcus aureus was evaluated. Only derivatives with antibacterial activity induced resistance, although some antibacterial compounds did not induce resistance. No derivatives without antibacterial activity but with ability to induce resistance were found.

Hedamycin, a new antitumor antibiotic. I. Production, isolation, and characterization

We examined the effect of leucomycins, leucomycin derivatives, and other 16-membered macrolides (tylosin, niddamycin, spiramycin I, and spiramycin III) on [ 14 C]erythromycin binding to ribosomes. Results of these studies enabled determination of the association and dissociation constants for the binding of each of these compounds to Escherichia coli ribosomes. In addition, the binding of the leucomycins and the leucomycin derivatives to ribosomes in general correlated with their antimicrobial activity.

Effect of erythromycin analogues on binding of [14C]erythromycin to Escherichia coli ribosomes

The relative ability of 44 erythromycin analogues to bind to ribosomes was determined by their effect on [(14)C]erythromycin binding to Escherichia coli ribosomes. The association and dissociation constants of each of these erythromycin derivatives were determined as well as their interaction coefficient for their binding to ribosomes. Substitutions were made on various portions of the erythromycin molecule with retention of substantial activity as measured by inhibition of [(14)C]erythromycin binding to ribosomes. Since the effect of erythromycin analogues on [(14)C]erythromycin binding to ribosomes provides a relatively sensitive assay for these compounds, erythromycin analogues with relatively little affinity for ribosomes could be detected. Compounds with association constants of 10(4) M(-1) were detectable; the association constant for erythromycin binding to ribosomes was approximately 10(8) M(-1). Thus, compounds with 0.0001 the association constant of erythromycin were detectable. This assay could be used alone or in conjunction with microbiological assays for primary screening of active analogues or other compounds which interfere with [(14)C]erythromycin binding to ribosomes. It permits an estimate of the general activity of compounds rapidly and directly. Variables such as metabolic modifications of the compounds and permeability are excluded. The present assay reflects the ability of the compounds to interact directly with their target organelle and may serve as a useful adjunct in developing new compounds.