6-hydroxypicolinic Acid Research Articles

Regioselective hydroxylation of quinolinic acid, lutidinic acid and isocinchomeronic acid by resting cells of pyridine dicarboxylic acid-degrading microorganisms.

Microorganisms aerobically degrading quinolinic acid, lutidinic acid or isocinchomeronic acid were isolated and the microbial regioselective hydroxylation of these pyridine dicarboxylic acids was studied. Alcaligenes sp. UK21 cells converted quinolinic acid into 6-hydroxypicolinic acid, suggesting the involvement of two enzyme reactions catalyzing hydroxylation at position C6 and decarboxylation at position C3 of quinolinic acid. Resting cells of Alcaligenes sp. UK21 accumulated 94.9 mM 6-hydroxypicolinic acid (13.2 g l(-1)), with a 96% molar conversion yield by 48 h incubation. Rhizobium sp. LA17 and Hydrogenophaga sp. IMA01 catalyzed the regioselective hydroxylation of lutidinic acid and isocinchomeronic acid into 6-hydroxylutidinic acid and 6-hydroxyisocinchomeronic acid, respectively. 6-Hydroxylutidinic acid accumulated up to 95.4 mM (17.5 g l(-1)) by 24 h incubation in the resting cells reaction, using Rhizobium sp. LA17, with a 99% molar conversion yield. Resting cells of Hydrogenophaga sp. IMA01 produced 88.7 mM 6-hydroxyisocinchomeronic acid (16.2 g l(-1)) by 24 h incubation, with a 81% molar conversion yield.

Reactions of the triply-bonded complex cis-Re2(μ-O2CCH3)2Cl2(μ-dppm)2with pyridine carboxylic acids. The isolation and structural characterization of a third structural isomer of Re2(dipic)Cl2(μ-dppm)2(dipic = pyridine-2,6-dicarboxylate)

The diamagnetic dirhenium(II) complexes Re2(pic)Cl3(μ-dppm)2 (2), Re2(dipic)Cl2(μ-dppm)2 (3), Re2(HnicO)2Cl2(μ-dppm)2 (4) and Re2(picO)2(μ-dppm)2 (5) that are formed by the reactions of cis-Re2(μ-O2CCH3)2Cl2(μ-dppm)2 (1) with picolinic acid (Hpic), dipicolinic acid (H2dipic), 2-hydroxynicotinic acid (HnicOH) and 6-hydroxypicolinic acid (HpicOH) represent four different types of reaction products from the displacement of the cis acetate groups of 1. All four compounds have been characterized by X-ray crystallography. Compound 2 can be prepared more logically and in higher yield from Re2Cl4(μ-dppm)2. Compound 3, which retains the same cis,cis coordination of μ-dppm ligands that is present in 1, is the third structural isomer of Re2(dipic)Cl2(μ-dppm)2; the other two, which are prepared from Re2Cl4(μ-dppm)2, contain trans,trans and trans,cis ligation by the pair of μ-dppm ligands. Compounds 4 and 5 are the first dirhenium(II) compounds that contain bridging 2-pyridonate ligands; in 4 the carboxylic acid group of μ-HnicO does not coordinate, whereas the μ-picO ligands in 5 are bound in a tridentate fashion and, consequently, the two axial Re–Cl bonds of 1 have been replaced by axial Re–O (carboxylate) coordination. Complexes 3–5 have quite accessible oxidation chemistry as shown by cyclic voltammetric measurements.

Chemical oxidative polymerization of pyrrole in the presence of m-hydroxybenzoic acid- and m-hydroxycinnamic acid-related compounds

Chemical oxidative polymerization of pyrrole was performed in the presence of two families of aromatic compounds with electron-withdrawing substituents. The first one includes 3-hydroxybenzoic acid (HBA) and two HBA-related compounds, such as 6-hydroxypicolinic acid (HPA) and citrazinic acid (CA). The second one includes trans-3-hydroxycinnamic acid (HCA) and two HCA-related compounds, such as trans-4-hydroxy-3-methoxycinnamic acid (HMA) and urocanic acid (UA). It was found that HBA, HPA and HCA enhance both the conductivity and stability of the resulting PPy. UA improves only the PPy stability whereas CA and HMA lead to low conducting PPy. Maximum PPy conductivity values of 81, 74 and 123 S/cm were obtained by using [HBA]=0.25 M, [HPA]=0.025 M and [HCA]=0.025 M, respectively. Elemental analysis data and FTIR results showed no incorporation of the additives to the obtained PPy, except for HMA. The formation of additive-iron(III) charge–transfer complexes was identified by means of UV spectroscopy of the starting solutions containing the organic additive and FeCl 3·6H 2O. The redox potential of these solutions was affected by the presence of the HBA- and HCA-related compounds.

Analysis of 1-aminopyrene-3,6,8-trisulfonate-derivatized oligosaccharides by capillary electrophoresis with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), has been used for structure characterization of 1-aminopyrene-3,6,8-trisulfonate (APTS)-derivatized oligosaccharides previously separated by capillary electrophoresis (CE). The resolved components were first isolated by employing an automated high-resolution fraction collector. Using on-probe sample cleanup with a cation-exchange resin and a matrix mixture of (1:1) 6-hydroxypicolinic acid and 3-hydroxypicolinic acid, APTS-labeled oligosaccharides were successfully detected by MALDI-TOF MS in the negative ionization mode. Each APTS-labeled oligosaccharide produced single [M-H]-1 peaks. Detection limits for standard APTS-derivatized oligosaccharide (maltoheptaose) were down to 30 fmol. APTS labeled maltooligosaccharides and various standard carbohydrates were separated and collected by CE, followed by molecular weight determination with MALDI-TOF MS. The mass spectral characterization enhances the power of the CE analysis of oligosaccharides.

Picolinic acid hydroxylase of Arthrobacter picolinophilus.

Picolinic acid is oxidized by cells and extracts of Arthrobacter picolinophilus to 6-hydroxypicolinic acid. The enzyme involved is a particulate hydroxylase which appears to incorporate the hydroxyl group of water into the substrate. The enzyme was purified about 60-fold. The molecular weight as determined by gel filtration was 230 000 daltons. Activity of the purified enzyme was stimulated by ferrous ions and was inhibited by quinacrine. Flavin mononucleotide reversed the inhibition by quinacrine.

Microbial oxidation of kynurenic, xanthurenic and picolinic acids

1. 1. Resulta of a study of the degradation of kynurenic acid by an Aerococcus are in agreement with a reaction sequence proposed for Pseudomonas by other workers. This sequence includes Compounds I and II below. 2. 2. Partial inhibition of oxidation of kynurenic acid by cell suspensions caused an accumulation of pyruvate with arsenite as inhibitor; α-ketoglutarate and aspartate accumulated when semicarbazide was used. 3. 3. Crystals of Compound II, having properties expected for 5-β(carboxyethyl)-4,6-dihydroxypicolinic acid were isolated from cultures of the Aerococcus oxidizing kynurenic acid. 4. 4. The properties are described of a solution of purified Compound I, also isolated from culture fluids. These properties are those expected for 5-(γ-carboxy, γ-oxopropenyl)-4,6-dihydroxypicolinic acid. 5. 5. Dialysed cell-free extracts converted 7,8-dihydroxykynurenic acid to Compound I; the latter was degraded when reduced triphosphopyridine nucleotide was added to the extract. 6. 6. Compound II was degraded by cell-free extracts; pyruvate, α-ketoglutarate, aspartate and glutamate were identified as reaction products; and when extracts were inhibited by semicarbazide the first of these compounds to appear were aspartate and α-ketoglutarate. 7. 7. Evidence is presented that xanthurenic acid is not an intermediate in the conversion of kynurenic to 7,8-dihydroxykynurenic acid. 8. 8. The Aerococcus and a Rhodotorula both attacked picolinic acid, and 6-hydroxypicolinic acid was isolated from arsenite-inhibited cultures. 9. 9. Cell-free extracts of Rhodotorula converted picolinic to 6-hydroxypicolinic acid. The reaction can occur anaerobically in the presence of methylene blue and resembles the conversion of nicotinic acid to 6-hydroxynicotinic acid described by other workers for Pseudomonas.