RESUMEN
Classically, low frequency losses in soft magnetic materials and ferrites in particular are measured by flux metric method under sinusoidal waveform excitation voltage. However, in typical application of modern power electronics, the frequency currently exceeds 100 kHz. This feature is at the origin of a difficulty: the phase shift between current and voltage can be disturbed by current probe delay. Thus, the results can be affected by large errors. As a consequence, it becomes more and more important to develop alternative methods to measure losses in magnetic materials. It is proposed to use calorimetric method which is by principle free of the above mentioned problems. The experimental device is described in details and the results are reported for experiments conducted on a commercial Mn-Zn ferrite under sinusoidal waveform regime for frequencies varying from 10 to 200 kHz. Comparisons with flux metric measurement show that significant differences appear typically for Bf products above 5000 V/m(2) (50 kHzx100 mT).
RESUMEN
A novel series of novobiocin analogues has been synthesised by removing the lipophilic aryl chain in novobiocin and introducing an amino substituent. The structural modifications have been dictated by the control of lipophilicity and the dissociation constant of the resulting compounds. Antibacterial activity of the new coumarin derivatives could be correlated with the amount of uncharged form in physiological conditions.
Asunto(s)
Antibacterianos/síntesis química , Novobiocina/síntesis química , Antibacterianos/química , Antibacterianos/farmacología , Cumarinas/química , Pruebas de Sensibilidad Microbiana , Novobiocina/análogos & derivados , Novobiocina/química , Novobiocina/farmacología , Staphylococcus aureus/efectos de los fármacosRESUMEN
In the search for new ketolides with improved activities against erythromycin-resistant S. pneumoniae and H. influenzae we synthesized a new 11,12 carbamate ketolide substituted by an imidazo-pyridyl side chain: HMR 3647. This compound demonstrated a potent activity against erythromycin susceptible and resistant pathogens, including penicillin G/erythromycin A-resistant S. pneumoniae and H. influenzae. In vivo, HMR 3647 displayed good pharmacokinetic parameters (Cmax = 2.9 microg/ml, bioavailability=49%, AUC0.8 = 17.2 microg.h/l, t1/2=1h) and was shown to have a high therapeutic efficacy in mice infected by various respiratory pathogens, including multi-resistant S. pneumoniae and Gram negative bacteria such as H. influenzae. HMR 3647 appears to be a very promising agent for the treatment of respiratory infections and is currently in clinical trials.
Asunto(s)
Antibacterianos/síntesis química , Eritromicina/farmacología , Cetólidos , Macrólidos , Animales , Antibacterianos/farmacología , Farmacorresistencia Microbiana , Bacterias Gramnegativas/efectos de los fármacos , Bacterias Grampositivas/efectos de los fármacos , Haemophilus influenzae/efectos de los fármacos , Ratones , Pruebas de Sensibilidad Microbiana , Estructura MolecularRESUMEN
In the search for new antibiotics active against macrolide-resistant pneumococci and Haemophilus influenzae, we synthesized a new class of 3-oxo-6-O-methylerythromycin derivatives, so-called "ketolides". A keto function was introduced in position 3 after removal of L-cladinose, a sugar which has long been thought essential. Further modifications of the macrolactone backbone allowed us to obtain three different series of 9-oxime, 11,12-carbamate, and 11, 12-hydrazonocarbamate ketolides. These compounds were found to be very active against penicillin/erythromycin-resistant pneumococci and noninducers of MLSB resistance. The 11,12-substituted ketolide 61 (HMR 3004) demonstrated a potent activity against multiresistant pneumococci associated with a well-balanced activity against all bacteria involved in respiratory infections including H. influenzae, Mycoplasma catarrhalis, group A streptococci, and atypical bacteria. In addition HMR 3004 displayed high therapeutic activity in animals infected by all major strains, irrespective of their resistance phenotype.