RESUMO
The effects of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and Polyvinylpyrrolidone (PVP-K30) on the solubility of 2-Hydroxyl-N-(3-methyl-5-ethylisoxazolyl-4-yl)-1,4-naphthoquinone-4-imine (I) were investigated, this compound, a synthetic derivative of isoxazolylnaphthoquinones, has proved to exhibit important biological activity against the causative agent of Chagas' disease and against Staphylococcus aureus. In addition, the effect of co-administration of a water-soluble polymer (PVP-K30) and ionization of I on the HP-beta-CD solubilizing effect was also examined. HP-beta-CD and PVP-K30 possess a significant solubilizing effect by themselves. PVP-K30 increases the solubilizing effect of HP-beta-CD by enhancing the apparent stability constant (Kc) of the I: HP-beta-CD complex. The addition of 0.5% (w/v) PVP-K30 to the complexation medium results in a 83% increase in the stability constant of the complex. The HP-beta-CD solubilization of I can also be improved by ionization of the drug molecule through pH adjustments. Although the Kc of the I complex is larger in the neutral form, a higher overall solubility is attained when I is in its ionized form. A 38-fold solubility enhancement is possible by using a combined approach of pH adjustment and complexation with HP-beta-CD.
Assuntos
Naftoquinonas/química , beta-Ciclodextrinas , 2-Hidroxipropil-beta-Ciclodextrina , Ciclodextrinas , Concentração de Íons de Hidrogênio , Indicadores e Reagentes , Povidona , SolubilidadeRESUMO
The complexation of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (I) with a highly soluble cyclodextrin, hydroxypropyl-beta-cyclodextrin (HP-beta-CD) was studied in aqueous media by solubility methods. I is an antibacterial and trypanocidal agent that is undergoing preclinical testing. Unfortunately, I exhibits low water solubility, and it is therefore difficult to prepare the solutions for biological tests. I inclusion took place with 1:1 stoichiometry. The stability constants of the I complexes calculated from the slope and the intercept of the phase solubility diagrams are larger in the less ionized form, whereas greater overall solubility is obtained in basic media.
Assuntos
Anti-Infecciosos/química , Ciclodextrinas/química , Isoxazóis/química , Naftóis/química , Tripanossomicidas/química , beta-Ciclodextrinas , 2-Hidroxipropil-beta-Ciclodextrina , Excipientes/química , Concentração de Íons de Hidrogênio , Solubilidade , Água/químicaRESUMO
Water, ethanol and n-hexane solubility and pH-solubility behavior of a homologous series of isoxazolyl-naphthoquinone derivatives, which exhibit important biological activity, were studied. Their pK(a) values were determined spectrophotometrically as well as from their pH-solubility profiles. Also, the molar aqueous solubility of these compounds was estimated with the equations developed by Yalkowsky and Valvani using the data of their melting points and octanol/water partition coefficients.
Assuntos
Isoxazóis/química , Naftóis/química , Fenômenos Químicos , Química Farmacêutica , Físico-Química , Etanol/química , Hexanos/química , Concentração de Íons de Hidrogênio , Octanóis/química , Solubilidade , Temperatura , Água/químicaRESUMO
The chemical stability of 3-chloro-2-hydroxy-(3, 4-dimethyl-5-isoxazolyl)-1,4-naphthoquinon-4-imine (ClQ(1)), a new potential antimicrobial agent was analyzed at different pH values by first-derivative spectroscopy. The degradation of ClQ(1) followed a pseudo-first-order kinetics in aqueous media at different pH values. The interaction of antibiotics with respiratory chain of Staphylococcus aureus generates superoxide anion, an oxygen radical capable of producing damage to the bacteria. The performed assays have demonstrated that ClQ(1) presents higher activity and toxic oxidant generation at pH 5.0 than at pH 7.5. In addition, the antibacterial activity of other halogenated isoxazolylnaphthoquinones was also studied in different collection and clinical strains which presented the following decreasing activity, ClQ(1) > BrQ(1) > DClQ(1) whereas DBrQ(1) did not show inhibition properties. The antibacterial and stability properties evidenced by ClQ(1) are so important that must be taken into account when new alternative treatments against beta-lactamase-positive S. aureus strains are investigated.
Assuntos
Antibacterianos/farmacologia , Cloro , Isoxazóis/farmacologia , Naftoquinonas/farmacologia , Staphylococcus/efeitos dos fármacos , Antibacterianos/química , Antibacterianos/metabolismo , Estabilidade de Medicamentos , Transporte de Elétrons/efeitos dos fármacos , Bacilos e Cocos Aeróbios Gram-Negativos/efeitos dos fármacos , Concentração de Íons de Hidrogênio , Hidrólise , Isoxazóis/química , Isoxazóis/metabolismo , Testes de Sensibilidade Microbiana , Naftoquinonas/química , Naftoquinonas/metabolismo , Relação Estrutura-Atividade , Superóxidos/metabolismoRESUMO
Staphylococcus aureus was inhibited by exposure to 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (Q1). This compound was cleavaged in the presence of bacteria and an efflux of isoxazolamine was detected whereas in the S. aureus membrane and cytoplasm was observed an absorption band similar to that of the bencenoid ring. Non-viable bacteria showed intact Q1 intracellularly and in the membrane. Antistaphylococcus effect was associated to Q1 interaction with the respiratory chain, the oxidative metabolites were stimulated; there was cellular injury simultaneous to reduction of antibiotic molecule and efflux of isoxazolamine. The bacteria treated with Q1 increased its oxygen consumption and superoxide anion generation. Superoxide dismutase (SOD) production was stimulated, but it was principally extracellular in S. aureus. Escherichia coli, a species resistant to the antibiotic, did not reduce Q1 and showed lower superoxide anion generation; besides, there was an increase of intracellular SOD with extracellular decrease.
Assuntos
Antibacterianos/metabolismo , Antibacterianos/farmacologia , Isoxazóis/metabolismo , Isoxazóis/farmacologia , Naftóis/metabolismo , Naftóis/farmacologia , Staphylococcus aureus/efeitos dos fármacos , Staphylococcus aureus/metabolismo , Resistência Microbiana a Medicamentos , Escherichia coli/metabolismo , Estresse Oxidativo/efeitos dos fármacos , Consumo de Oxigênio/efeitos dos fármacos , Espectrometria de Fluorescência , Espectrofotometria , Superóxido Dismutase/biossíntese , Superóxidos/metabolismoRESUMO
The goal of this study was to determine the kinetic parameters involved in the decomposition of 2-(5-methyl-4-isoxazolylamino)-N-(5-methyl-4-isoxazolyl)-1,4-naphthoquinone-4-imine (1) in aqueous solution and to identify the main degradation products. An isocratic HPLC assay was used to study the degradation rate of 1. The products of hydrolysis were identified by comparison of their retention times with those of authentic samples. The amount of 1 and the two degradation products resulting from storage of 1 in various buffer solutions was followed in function of time by a reversed-phase HPLC stability-indicating method. The observed degradation rates followed pseudo-first-order kinetics at constant pH, temperature and ionic strength. The logk-pH-profile was constructed at 35 degrees C from the first-order rate constants obtained from studies at pH values ranging from 0.88 to 10.80 (mu=0.5 M). Hydrolysis in the acidic and alkaline media resulted in the formation of two degradation products in each case. The pH-rate profile of 1 in buffer solution was adequately described using a four-term rate equation. The obtained pH-rate profile indicated specific acid-base catalysis with a region of maximum stability between pH 6.40 and 7.40 which can be adequate for formulations of 1.
RESUMO
The application of the second-derivative UV spectrophotometry for determining the stability of 3-bromo-N-bromo-N-(3,4-dimethyl-5-isoxazolyl-4-amine)-1,2-naphthoquinone in ethanolic solutions is described. The validity of this method was evaluated using synthetic mixtures of the intact drug and its degradation products and by statistical analysis of the calibration data. In order to verify the usefulness of this method for stability studies, recovery experiments by the standard addition method were also carried out.
RESUMO
The mechanism by which a new naphthoquinone derivative, the 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1, 4-naphthoquinone-4-imine (INQI-E) has antibacterial effect against Staphylococcus aureus was studied. The interaction of INQI-E with the bacteria was followed by absorption spectroscopy at 323 and 490 nm. The absorption band of INQI-E at 490 nm undergoes a hypochromic shift with a decrease of intensity. This effect was found to be reversible by oxygenation during the first hours of incubation. The participation of an oxidation-reduction process related to the respiratory chain was demonstrated by oxygen consumption. An increase in O2 uptake and inhibition of S. aureus growth was observed. Experiments with three inhibitors of the respiratory chain demonstrated that the pathway induced by INQI-E was antimycin-resistant and KCN- and salicylhydroxamic acid (SHAM)-sensitive, which suggests that INQI-E is capable of diverting the normal electron flow to an alternate superoxide-producing route. On the other hand, experiments with Tiron, a specific scavenger of superoxide, hindered the effect of INQI-E against S. aureus, indicating that the inhibitory growth effect of this quinone-imine is mainly due to the production of the cytotoxic superoxide radical.
Assuntos
Antibacterianos/farmacologia , Isoxazóis/farmacologia , Naftóis/farmacologia , Staphylococcus aureus/efeitos dos fármacos , Antimicina A/farmacologia , Transporte de Elétrons/efeitos dos fármacos , Sequestradores de Radicais Livres/farmacologia , Isoxazóis/administração & dosagem , Naftóis/administração & dosagem , Oxirredução , Consumo de Oxigênio , Cianeto de Potássio/farmacologia , Salicilamidas/farmacologia , Espectrofotometria , Staphylococcus aureus/crescimento & desenvolvimentoRESUMO
The kinetics of enolization and degradation of N-(5-methyl-4-isoxazolyl)-4-amino-1,2-naphthoquinone (1) was investigated in aqueous solutions over a pH range of 7.30 to 12.25, at 35 degrees C and at constant ionic strength (mu = 0.5) using reversed-phase HPLC. Pseudo-first-order kinetics was observed throughout the pH range studied. The rate of enolization (ke), the keto-enol equilibrium constant (Kt), and specific base catalysis rate constant (kCH) were determined. Good agreement between the theoretical pH-rate profile and the experimental data supports the proposed transformation process. The average recovery for 1 and its tautomerization product 2-hydroxy-N-(5-methyl-4-isoxazolyl)-1,4-naphthoquinone 4-imine (2) from mixtures of different composition was evaluated.
Assuntos
Isoxazóis/química , Naftoquinonas/química , Soluções Tampão , Cromatografia Líquida de Alta Pressão , Concentração de Íons de Hidrogênio , Isomerismo , Cinética , Soluções , Espectrofotometria UltravioletaRESUMO
The antibiotic activity of new synthetic isoxazolylnaphthoquinone imines was studied. Pseudomonas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922 were resistant to the four compounds studied (MIC > 128 micrograms ml-1), but Staphylococcus aureus ATCC 25923, ATCC 29213 and 30 clinical isolates of Staph. aureus were inhibited by 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (I). This compound diminished bloodstream infection of mice injected i.m. with Staph. aureus; septicaemia decayed significantly when I was applied at the beginning of the infection while when I was given 3 d after bacterial challenge, a significant protection was afforded. Bactericidal activity in serum increased during the 5 h after I was administered i.p. The acetyl derivative of I had a high MIC but when inoculated orally in mice decreased the Staph. aureus counts in circulation. This protection occurred only when the schedule of administration started close to the bacterial challenge. Antibiotic activity in vivo may be associated with in vitro effects.