Synthesis, antiprotozoal and cytotoxic activities of new N-(3,4-dimethyl-5-isoxazolyl)-1,2-naphthoquinone-4-amino derivatives.

Three derivatives of N-(3,4-dimethyl-5-isoxazolyl)-1,2-naphthoquinone-4-amino (1), a compound which exhibits significant activity against Trypanosoma cruzi and Plasmodium falciparum but with cytotoxicity toward murine L-6 cells, were synthesized with the aim of ameliorating its cytotoxicity. The in vitro antiprotozoal and cytotoxic activities of the synthesized compounds were evaluated against T. cruzi, Trypanosoma brucei rhodesiense, P. falciparum and murine L-6 cells. The hydroxymethyl (2) and the oxime (3) derivatives were active against T. cruzi, with IC50 values in a range comparable to those of 1 (IC50: 0.65 microg/ml) and benznidazole (IC50: 0.56 microg/ml) while the carboxymethyloxime (4) was inactive. Compounds 2 and 3 were cytotoxic toward L-6 cells, with IC50 values identical to that of 1 (IC50: 0.50 microg/ml). The results did not support the suggestion that 2 and 3 may be used as prodrugs of 1.

An "in vitro" system simulates in membranes the antibacterial mechanism postulated for the action of isoxazolylnaphtoquinoneimine in Staphylococcus aureus.

The 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (Q1) revealed good activity against Staphylococcus aureus. Q1 in contact with the bacteria experimented reduction evidenced by changes in its spectrum of absorption simultaneously with loss of colour. During the first 4 hours of incubation, oxygenation restored the original spectrum. Treatment with sodium borohydrure reduces irreversibly Q1. Redox-reaction "in vitro" was detected between Q1 and NADH in the presence of diaphorase. The environment of the probable site of action of Q1 was simulated using an artificial membrane system, instead of S. aureus membranes. Q1 interacts with lisophosphatidylcholine micelles following a cooperative binding model. The kinetics of Q1-reduction was increased by lipid micelles incorporated with the antibacterial compound.

Antibacterial effect of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1, 4-naphthoquinone-4-imine on Staphylococcus aureus.

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.

Antibiotic activity of isoxazolylnaphthoquinone imines on mice infected with Staphylococcus aureus.

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.

Synthesis and some physiochemical properties of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone 4-imine derivatives.

Some derivatives of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)- 1,4-naphthoquinone 4-imine (3), a poorly soluble drug, were synthesized in an attempt to improve their physicochemical properties. The new compounds were characterized by spectroscopic methods including an iterative NMR method (the LAOCOON III program). The physicochemical properties such as solubility, relative lipophilicity (RM), and partition coefficients (Leo-Hansch fragmental system) were determined. Some derivatives were more lipophilic than 3 and one was water soluble. In vitro antibacterial activity was also reported for some derivatives.

[In vitro antibacterial activity of isoxazolyl++ naphthoquinones. I]. / Actividad antibacteriana in vitro de isoxazolilnaftoquinonas. I.

The in vitro antibacterial activity of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl) 1,4 naphthoquinone-4-imine (I) and three of this derivatives against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis y Morganella morganii was investigated. From the four naphthoquinone-imine studied, compound I exhibited activity against S. aureus. This effect was observed even in oxygen atmosphere with 5% CO2 and in the presence of human albumin. The development of drug-resistant strains by serial passage in media with concentrations lower than the C.I.M. was determined in 31 strains of S. aureus from clinical material and one from collection. No significant differences in C.I.M. were observed.

Actividad antibacteriana in vitro de isoxazolilnaftoquinonas. I / [In vitro antibacterial activity of isoxazolyl++ naphthoquinones. I]

The in vitro antibacterial activity of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl) 1,4 naphthoquinone-4-imine (I) and three of this derivatives against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis y Morganella morganii was investigated. From the four naphthoquinone-imine studied, compound I exhibited activity against S. aureus. This effect was observed even in oxygen atmosphere with 5

CO2 and in the presence of human albumin. The development of drug-resistant strains by serial passage in media with concentrations lower than the C.I.M. was determined in 31 strains of S. aureus from clinical material and one from collection. No significant differences in C.I.M. were observed.

Actividad antibacteriana in vitro de isoxazolilnaftoquinonas. I. / [In vitro antibacterial activity of isoxazolyl++ naphthoquinones. I]

The in vitro antibacterial activity of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl) 1,4 naphthoquinone-4-imine (I) and three of this derivatives against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis y Morganella morganii was investigated. From the four naphthoquinone-imine studied, compound I exhibited activity against S. aureus. This effect was observed even in oxygen atmosphere with 5

CO2 and in the presence of human albumin. The development of drug-resistant strains by serial passage in media with concentrations lower than the C.I.M. was determined in 31 strains of S. aureus from clinical material and one from collection. No significant differences in C.I.M. were observed.