Of nalidixic acid

The greatest medicinal interest in pyridopyrimidines has been in another type of antibacterial derivative, the analogues of nalidixic acid, piromidic (68) (71CPB1426) and pipemidic (69) acids (75JMC74). 

Derivatives of nalidixic acid (69a-69d), containing an amino or acetyl-amino substituent at position 7 and an alkyl group at N-1, were successfully nitrated to give (70a-70d). However, in all cases hydrolysis of the amino and acetylamino group was observed (79YZ155 80CPB235). 

Treatment of ethyl 4-chloro-7-diethylamino-6-nitro-l,8-naphthyridine 3-carboxylate (104) with the amines RH [R = N(CH2)s NH(CH2)N(C2Hs)2] gives the corresponding 4-amino derivatives [105, R = N(CH2)s, 74% and 105, R = NH(CH2)N(C2Hs)2, 50%]. With diethylamine the 7-chloro-6-nitro derivative of nalidixic acid (i.e., 106) yields the 7-diethylamino compound 107 (62%) (79YZ155). 

Anti-mycobacterium avium activity in vitro of 3-carboxy-7-methyl-6-nitro-l-ethyl-l,8-naphthyridin-4(lH)-one (6-nitro derivative of nalidixic acid) was demonstrated (93MI1). 

Because of the number of citations, only selected imidazoquinolines are described, and biological activity is mentioned only briefly. The largest increase in the number of citations was caused by the discovery of the antibacterial properties of nalidixic acid type drugs. Efforts to prepare the bioisosters, for example of oxolinic acid, intensified in the early 1970s, and the discovery of the carcinogenic properties of 2-aminoimidazoquinolines followed in the early 1980s. These azoloquinolines can be considered as benzene-separated deazapurines. 

Abdominal pain, nausea, vomiting, anorexia, diarrhea, rash, drowsiness, dizziness, photosensitivity reactions, blurred vision, weakness, and headache may occur with the administration of nalidixic acid. Visual disturbances, when they occur, are noted after each dose and often disappear after a few days of therapy. 

The Jacobs-Gould intramolecular cyclization of diethyl N-(6-methyl-2-pyridyl)amino-methylenemalonate to 3-ethoxycarbonyl-7-methyl-l,8-naphthyrid-4-one is another reaction ideally suited to microwave heating, although conductively heated equipment was employed for laboratory-scale experiments [45]. The product is a key intermediate in the synthesis of nalidixic acid, the first of the quinolone antibacterials. The process usually is conducted at temperatures of 200-250 °C and in high dilution, with heat transfer oils such as the eutectic mixture of diphenyl ether and biphenyl. However, it proceeded rapidly, predictably and controllably under solvent-free conditions. 

Since the introduction of nalidixic acid in 1963, structural modifications on the quinolones have been performed to improve either the antibacterial efficacy or pharmacokinetic/toxicologic profiles of these compounds. The newest quinolones possess broad-spectrum activity, favorable pharmacokinetic/toxicologic profiles, and potency against bacterial strains that are resistant to older generations of quinolones. This section describes the synthetic procedures for the new generation of quinolones that were studied during the 1995-2005 period. 

The infrared spectrum of nalidixic acid in a KBr pellet is presented in Figure 3. The spectrum was obtained on a Perkin-Elmer Infrared Spectrophotometer Model 21. It agrees with the spectrum presented by Salim and Shupe.(2)... 

The NMR spectrum of nalidixic acid is presented in Figure 4. It was obtained on a Varian A60 spectrometer. This spectrum is in agreement with the spectrum presented by Hamilton and coworkers. (1 0 The following assignments have been made. 

Figure 5 shows the ultraviolet spectra of nalidixic acid at about 7.5 mcg/ml in 0.1 N NaOH, methanol, and chloroform, obtained on a Perkin-Elmer 323 recording spectrophotometer. The intensity, position, and fine structure present in each spectrum is related to the solvent polarity. These spectra are in agreement with the spectra published by Salim and Shupe.(2) Zubenko and Shcherba also report that there are two bands in methanol and 0.1 IJ NaOH, at 258 nm and 324 or 332 nm, respectively.(5) Gafari( ) has reported three bands in methanol 213-216 nm (lLa), 255 nm (lLb) and 320-322 nm (oc). Gafari also reports an absorbance in 0.1 II NaOH at 279-281 nm and 325 nm. These wavelengths are about 3-10 nm lower than those reported by other sources.(2)(5)(7)... 

The solubilities of nalidixic acid in various solvents at 23° are listed below. 

The pKa of the protonation of the nitrogen in position 8 has been reported as 6.02 and the pKa for the carboxylate anion formulation has been reported as -0.94. These were determined by Staroscik and Sulkowska by a spectrophotometric method.(14) Further study by the same workers on the partition equilibria of nalidixic acid between water and various organic solvents led to calculations of the pKa values of 5.99 + 0.03 for N-protonation and -0.86 4- 0.07 for carboxylate anion formation.(12) Takasugi and co-workers reported the apparent pKa of nalidixic acid to be 5.9 at 28° by a spectrophotometric method.(13)... 

The melting range of nalidixic acid is reported to be 225-231°, determined as a class 1 compound. (1)(2)... 

The synthesis of nalidixic acid was reported by Lesher and Gruett.(15)(16) it may be prepared by the procedure shown in Figure 8. 

Nalidixic acid is stable up to five years under reasonable conditions of temperature and humidity. Pawelczyk and Plotkowiakowa(17) subjected sodium nalidixate solutions to accelerated aging, but were unable to identify decomposition products. Detzer and Huber(lS) studied the photolysis and thermolysis of nalidixic acid in the presence of oxygen. Photolysis produced de-carboxylated nalidixic acid, structure A, and a diketone product, structure B, as well as carbon dioxide and ethylamine. 

Similar metabolites were found produced by man (19)(20)(21)t monkeys( ), dogs (8), chickens(22)> calves(23) and microorganisms(4). The ratios of these metabolites, however, were found to vary with the individual. The overall conversion of nalidixic acid to hydroxynalidixic acid had been reported by McChesney(S) to be normally about 32% bicarbonate supplementation increased this to about 40%. Bicarbonate supplementation also increased the amount of total naphthyridine excreted in the biologically active form. 

The mechanism of action of nalidixic acid against E. coli. was found to be inhibition of DNA synthesis.(25) No selective effect on purines or pyrimidines was found and no inhibition of initiator synthesis was demonstrated. In addition the nalidixic acid could be removed from cultures after exposures up to 75 minutes by rinsings and cells would recover from the block. 

The pharmacokinetics of nalidixic and hydroxy-nalidixic acids have been studied by several different groups. Takasugi ejt al studied in-situ and in-vitro absorption of nalidixic acid from the gastrointestinal tracts of rats as a function of pH. They reported that the absorption of non-ionized nalidixic acid was faster than the ionized form, with the maximum absorption rate constant found when the drug was administered from a pH=3 buffer solution. The absorption in-sltu was found to be ten times the rate in-vitro, but this was dependent on several factors.(13)... 

Simplified Model for Kinetic pathways of Nalidixic acid in Man... 

This data was then used in another study by Portmann and co-workers(24) of nalidixic acid metabolism in man in which a more elaborate model was developed and various rate constants were reported (Figure 10). This model was based on the oral administration of 1 g of nalidixic acid. Theoretical curves for plasma levels of nalidixic and hydroxynalidixic acid vs. time agreed with experimental values. 

McChesney and co-workers(27) then studied the effect of repeated oral dosage of nalidixic acid and found some carry-over of nalidixic acid from day to day but reported no important change in the metabolism due to multiple dosings. 

The half-life of nalidixic acid in plasma in man was found to be between 85 and 100 minutes by McChesney and co-workers(8) and was reported as about 100 minutes by Bruehl and co-workers(27). 

Another study by McChesney and co-workers on the metabolism of nalidixic acid in the immature calf(23) demonstrated a pattern of metabolism very different than in man. The half-life of nalidixic acid was found to be about 24 hours and a large amount was excreted into the feces. The immature calves were also unable to excrete nalidixic acid into the urine at concentrations greater than found in the plasma and conjugated drug was present at low levels only. Calves seven months old had metabolic patterns much closer to man the plasma half-life was about 1.5 hours, the concentration of excretion into the urine was at least ten times that in plasma and the extent of conjugation was increased. The inability to metabolize nalidixic acid by the immature calf was considered to be due to incomplete development of its metabolic system. 

The titration of nalidixic acid in DMF with lithium methoxide has been reported(1)(2) with thymolphthalein as the indicator. It has also been titrated with sodium methoxide in ethylene-diamine or DMF methanol 1 2 with thymol blue indicator.(31) An error for this titration was reported as + 0.7%. A titration with sodium borohydride followed potentiometrically or with thymol blue indicator has also been reported by Bachrata and co-workers. The standard deviation was reported as + 0.60%.(32)... 

The ultraviolet absorption spectrum of nalidixic acid in methanol or chloroform has an absorption maximum at about 258 nm and a broad double peak at 324 to 333 nm. In 0.1 N NaOH the band at 324 nm is shifted to a single peak at about 332 nm. The a of the band at about 258 nm is approximately 110 but varies with the solvent. (2)(5)(6)(7)... 

Nalidixic acid and sodium nalidixate form a strong colored complex with iron III. The maximum of absorbance of the complex is 410 nm and Beer s Law is obeyed from 10 to 250 yg of nalidixic acid per ml(33)5 and from 0.43 to 17.05 mg iron III per ml.(34) Nalidixic acid complexes through the oxo-group on C-4 and the carboxylic acid group on C-3. Three moles of nalidixic acid complex with one mole of iron III. The instability constant of the complex was calculated to be 2.11 x 10 8 by Dick and Murgu.(34)... 

The polarographic behavior of nalidixic acid has been studied by Staroscik and co-workers.(35) The pH range of -2.9 to 11 in 20% DMF was investigated in the concentration range of 5 x 10-V and three stages of reduction were found. The potentials were found to vary linearly with pH for the first two reduction stages, while the third was constant and appeared at pH >8. The carbonyl on C-4 was shown to be reduced to the 4-hydroxy product. Nalidixic acid was reduced with sodium borohydride and the product was demonstrated to be the same as that in the polarographic reduction by TLC. 

The first spectrofluorimetric methods reported for the determination of nalidixic acid and its metabolites in biological fluids did not differentiate between nalidixic acid and hydroxynalidixic acid. The determination of free nalidixic acid and the hydroxy-metabolite in human urine plasma and feces was performed by extraction by toluene from acidified biological fluid and subsequent fluorimetric measurement at 325/375 nm of sample re-extracted into aqueous solution.(8) Conjugated nalidixic and hydroxynalidixic acids were determined by acid hydrolysis and then toluene extraction for fluorimetric measurement of the total drug. The conjugated nalidixic acid was then determined by difference. 

Extraction of nalidixic acid with chloroform from utine has also been reported.(40) Another fluorimetric method for chicken liver and muscle containing not less than 100 ppb nalidixic acid was reported by Browning(9) using an ethyl-acetate extraction and alumina column to retain the nalidixic acid. The fluorescence was measured at 325/408 nm. 

Spectrophotometric measurements of nalidixic acid have been reported. Gafari et aJL(41) used an extraction with ultraviolet measurement at 255 or 327 nm for blood and tissue samples. Takasugi and co-workers extracted buffered tissue homogenate with chloroform and measured the optical density at 334 nm.(13)... 

A microbiological detection has been described for use for pharmaceutical preparations of nalidixic acid. A diffusimetric determination using E. coli (Bruxelles) was reported by Monciu.(48)... 

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