A new route to 2-amino- or 2-hydroxy-3-pyridinecarboxylic acid derivatives

Schiff's bases derived from ketones and t-butylamine ( 1 ) reacted with methyl methoxymethylenemalonate to give 2-hydroxy-3-pyridinecarboxylates. Similarly, treatment of 1 with ethoxymethylenemalononitrile gave 2-amino-3-pyridinecarbonitriles. Compounds 1 on reaction with ethyl 2-cyano-3-ethoxypropenoate afforded 2-amino-3-pyridinecarboxylates.     

Chromotropic acid,a fluorogenic chelating agent for aluminium(III)

Complexation of aluminium(III) with the fluorogenic ligand chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulfonic acid) has been revisited with the aim of using enhancement of the fluorescence intensity as an analytical tool. Complexation at the optimum pH4 was shown to lead to a 1:1 complex with a stability constant log ₁₁₀=18.4±0.7. The fluorogenic effect was thoroughly investigated. Nearly selective excitation of the chelate rather than the ligand could be achieved at wavelengths longer than 360 nm. For analytical purposes the main interfering ion was Ga³⁺. The strongest competing ligand was shown to be citric acid. Competitive complexation by acetate or formate ions can also make their use in a buffer at the usual concentration, 0.2 mol L^–1, questionable, whereas a 10^–2 mol L^–1 formic acid buffer was shown to be a good alternative. The calibration plot showed that the dependence of response on Al(III) concentration was linear up to 500 g L^–1; the detection limit was 0.65 g L^–1 (3SD _blank, n=10, SD=±1.4% at 10 g L^–1 and ±0.8% at 100 g L^–1). The analytical procedure was successfully applied to several samples of tap water and the results were in good agreement with those from AAS determination.     

Dehydration of 4-hydroxy-4-methyl-3-phenylamino-oxazolidin-2-ones

The dehydration of two 5,5-disubstituted 4-hydroxy-4-methyl-3-phenylaminooxazolidin-2-ones into the corresponding 4-methylene-3-phenylaminooxazolidin-2-ones has been carried out. The structure of the products was confirmed by X-ray diffraction analysis.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1512–1517, October, 2004.     

Preparation of 3-hydroxy- and 3-methoxy-N-heteroaryl-2-methyl-4-pyridones

A number of new 3-hydroxy- and 3-methoxy-2-methyl-4-pyridones substituted on the nitrogen atom with selected heterocycles has been prepared. Novel chelating properties of the hydroxy-compounds are expected.     

Syntheses and crystal structures of diorganotin (IV) moieties with 3-hydroxy-2-pyridinecarboxylic acid

A series of new organotin (IV) complexes with 3-hydroxy-2-pyridinecarboxylic acid (3-OH-2-picH) of two types: R₂SnCl(3-OH-2-pic) (I) (R = Me 1, n-Bu 2, Ph 3, PhCH₂4) and R₂ Sn(3-OH-2-pic)₂ (II) (R = Me 5, n-Bu 6, Ph 7, PhCH₂8)have been synthesized by reactions of diorganotin (IV) dichloride with 3-hydroxy-2-pyridinecarboxylic acid in the presence of sodium ethoxide. All complexes are characterized by elemental analyses, IR spectra and NMR spectra analyses. Among them, complexes 1, 5, 6 and 7 are also characterized by X-ray crystallography diffraction analyses. Complex 1 is a 1D polymeric chain with six-coordinate tin atoms and the packing of complex 1 is stabilized by the C-H?Cl intermolecular weak interactions, thus a 2D network of 1 is formed. Complex 5 is also a 1D polymeric chain with seven-coordinate tin atoms. Complex 6 is a zigzag polymeric chain linked by Sn?O intermolecular weak interactions. Complex 7 is a monomeric complex with distorted octahedral geometry.     

Evaluation of 1-methyl-3,4-hydroxypyridinecarboxylic acids as possible bidentate chelating agents for iron(III): Metal–ligand solution chemistry

The chemical interactions of 1-methyl-3-hydroxy-4-pyridinecarboxylic acid (1M3H4P) and 1-methyl-4-hydroxy-3-pyridinecarboxylic acid (1M4H3P) with Fe(III) were investigated in aqueous 0.6 m (Na)Cl at 25 °C by means of potentiometric titrations and UV–Vis spectrophotometry. A large number of complexes were formed in solution with stoichiometry FeL_xH_y, x = 1, 2, 3 and y = 0, −1, −2. In view of a possible application to Fe(III) chelation therapy, the efficiencies of the ligands to chelate the metal ion were evaluated in vitro at physiological pH. 1M3H4P and 1M4H3P show a lower complexation efficiency with Fe(III) than that of other available chelators, but higher than that of their non-methylated analogs 3H4P and 4H3P.     

Synthesis of N-substituted 3-hydroxy-2-methyl-4-pyridones and -pyridonimines

Carbohydrates with 1,4 glycosidic bonds like maltose, lactose, dextrin or starch react with primary amines as well as amino acids or proteins to give i.e. 3-hydroxy-2-methyl-4-pyridones 5 and 3-hydroxy-2-methyl-4-pyridonimines 7. A generally applicable synthesis of compounds of this type is described. The pyridones 5 and pyridonimines 7 are strongly complexing agents. Molybdenum-derivatives, for instance, are suitable as fairly stable oxidation catalysts.     

Hydroxamic acid polymers. II. Design of a polymeric chelating agent for iron

The iron chelating ability of hydroxamic acid polymers was studied as a function of the atomic chain spacing separating neighboring hydroxamic acid units. Two polymers were prepared, one having the hydroxamic acid group separated by 11 atoms and the other by three atoms. The iron binding of these polymers was compared with the model compound desferrioxamine B (DFO) and with a previously prepared polymer having a nine-atom spacing. Mole ratio plots indicated the following order of stability: DFO ≈ 11 atom > 9 atom > 3 atom. These results are in accordance with the picture derived from molecular models which shows that with a spacing of 11 atoms, three neighboring hydroxamic acids can fit the octahedral arrangement of the iron (III) complex without appreciable strain. Some strain is introduced when the spacing becomes only nine atoms, and with three atoms, complex formation between three neighboring groups becomes virtually impossible.     

4-hydroxy-2-quinolones. 96. Synthesis and properties of 4-methyl-2-oxo-1,2-dihydroquinoline-3-carboxylic acid

Alkaline hydrolysis of the ethyl ester of 4-(cyanoethoxycarbonylmethyl)-2-oxo-1,2-dihydroquinoline-3-carboxylic acid is accompanied by decarboxylation with loss of two molecules of CO₂ and leads to 4-methyl-2-oxo-1,2-dihydroquinoline-3-carboxylic acid. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 887–893, June, 2006.     

Spectrophotometric determination of tungsten as a mixed thiocyanate-1-phenyl-2-methyl-3-hydroxy-4-pyridone complex

Spectrophotometric determination of tungsten with thiocyanate was described. Tungsten(VI) was reduced with tin(II) chloride in hydrochloric acid solution, complexed with thiocyanate ions, and the complex formed was extracted with 1-phenyl-2-methyl-3-hydroxy-4-pyridone (HX) in chloroform. The extracted complex had the ratio W:SCN:HX 1:3:2. The method described is sensitive, selective, and reproducible. The color of the tungsten-thiocyanate complex in the organic phase is stable. Few metals interfere; the separation of the interfering elements was discussed.     

Synthesis of 2-carbethoxy-3-methyl-4-hydroxy-6-phenylbenzofuran derivatives

4-Hydroxybenzofuran derivatives were synthesized, and their reactions with bromine and nitric acid were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 879–882, July, 1976.     

4-hydroxy-2-quinolones. 153*. Synthesis of hetarylamides of 4-methyl-2-oxo-1,2-dihydroquinoline-3-carboxylic acid

4-Methyl-2-oxo-1,2-dihydroquinoline-3-carboxylic acid hetarylamides can be prepared by two fundamentally different routes with allowance made for the thermal stability of the starting hetarylamines. * For Communication 152 see [1]. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 426–432, March, 2009.     

Spectrophotometric determination of iron with 2-hydroxy-3-napthoic acid

2-Hydroxy-3-napthoic acid is presented as a new, highly sensitive and selective reagent for its colour reaction with ferric ion. The sensitivity of the reaction is 0.025 μg/cm² (SANDELL). The blue-coloured complex is maximally absorbed at 590 mμ and obeys Beer's law up to 24 p.p.m. of iron. The optimum range of concentration is from 4 to 20 p.p.m. of iron, where the percent relative analysis error per 1% absolute photometric error is 2.9. The composition of the complex, as evaluated by JOB's method and as verified by the Molar and Slope ratio methods, shows that in solution, the complex contains the iron and the reagent in a ratio of l : 1. The empirical formula of the complex is suggested to be [Fe(C₁₁H₇O₃)]⁺². The molar extinction coefficient is 2212 and the instability constant of the complex is about 4.29 ? 10^-4. Coloured ions or those ions that give coloured products are tolerated to a limited extent during the determination of iron.     

A new bis(3-hydroxy-4-pyridinone)-IDA derivative as a potential therapeutic chelating agent. Synthesis, metal-complexation and biological assays

A new bis(3-hydroxy-4-pyridinone) derivative of iminodiacetic acid, imino-bis(acetyl(1-(3'-aminopropyl)-3-hydroxy-2-methyl-4-pyridinone)), IDAPr(3,4-HP)(2), has been prepared and studied in its interaction with a set of hard metal ions. This tetradentate ligand presents a much higher chelating efficiency for trivalent hard metal ions (Fe, Ga, Al) than the monodentate derivative Deferriprone, namely at the diluted conditions prevailing in physiological conditions and at low clinical doses. A similar behaviour was also observed for the complexation with Zn(II) but at a significantly lower extent. This compound presents a moderate hydrophilic character at physiological pH (logD=-1.72). In vivo assays showed much more rapid clearance of (67)Ga from most tissues of metal-loaded mice than the drug Deferriprone and the radioactivity excretion occurs mostly through the kidneys. Therefore, results from in vitro and in vivo studies indicated good perspectives for this compound to be a potential decorporating agent for hard metal ions in overload situations without depletion of essential metal ions such as zinc.     

Syntheses of 2-acetyl-3-hydroxy-1-n-propylpyrrole from isomaltol and 1-n-alkyl-3-hydroxy-2-methyl-4-pyridones from maltol

2-Acetyl-3-hydroxyfuran (2) reacts with n-propylamine affording 2-acetyl-3-hydroxy-1-n-propylpyrrole (3) in 63% yield. The transformation of 2-methyl-3-hydroxy-4-pyrone (4) into 1-n-alkyl-3-hydroxy-2-methyl-4-pyridones is achieved by benzylation of the 3-hydroxyl group whereupon the product reacts with ammonia and the corresponding pyridone is obtained. The pyridone is alkylated with alkyl bromides and after hydrobromic acid in acetic acid cleavage of the 3-position ether function, 1-n-alkyl-3-hydroxy-2-methyl-4-pyridones are obtained in 48% overall yield.