3,4-dihydroxybenzoate

Dihydroxybenzoic acid [490-79-9] M 154.1, m 204.5-205", pK 2.95. Crystd from hot water or benzene/acetone. Dried in a vacuum desiccator over silica gel. 

Dihydroxybenzoic acid [303-07- ] M 154.1, m 167"(dec), pK 1.05. Dissolved in aqueous NaHC03 and the soln was washed with ether to remove non-acidic material. The acid was ppted by adding H2SO4, and recrystd from water. Dried under vacuum and stored in the dark [Lowe and Smith J Chem Soc, Faraday Trans I 69 1934 1973],... 

Tropolone has been made from 1,2-cycloheptanedione by bromination and reduction, and by reaction with A -bromosuccinimide from cyolo-heptanone by bromination, hydrolysis, and reduction from diethyl pimelate by acyloin condensation and bromination from cyclo-heptatriene by permanganate oxidation from 3,5-dihydroxybenzoic acid by a multistep synthesis from 2,3-dimethoxybenzoic acid by a multistep synthesis from tropone by chlorination and hydrolysis, by amination with hydrazine and hydrolysis, or by photooxidation followed by reduction with thiourea from cyclopentadiene and tetra-fluoroethylene and from cyclopentadiene and dichloroketene. - ... 

Further evidence regarding the mechanism was provided by LynnandBoums643 , who found a pH-dependent carbon-13 isotope effect in the decarboxylation of 2,4-dihydroxybenzoic acid in acetate buffers. The dependence was interpreted in favour of the A-SE2 mechanism, for an increase in acetate concentration would increase kL t and hence partitioning of the intermediate so that k 2 becomes more rate-determining. 

In 1996, Hawker and Frechet83 discussed a comparison between linear hyperbranched and dendritic macromolecules (Fig. 5.17) obtained with the same monomeric structure, 3,5-dihydroxybenzoic. The thermal properties (glass transition and thermal decomposition) were not affected by the architecture. 

All dihydroxybenzoates with an o-hydroxy group are more active against MCF-7 cells than the substituted salicylates screened previously. ... 

Zhang et al. isolated Clostridium hydroxybenzoicum containing two inducible 4-hydroxybenzoate decarboxylase and 3,4-dihydroxybenzoate decarboxylase that form phenol and catechol (1,2-dihydroxybenzene), respectively. The organism does not further metabolize phenol and catechol produced by these reactions. The carboxylation activities of the two purified decarboxylases are not... 

A 3,4-dihydroxybenzoate decarboxylase (EC 4.1.1.63) was purified from C. hydroxybenzoicum and characterized for the first time. The estimated molecular mass of the enzyme is 270 kDa. The subunit molecular mass is 57kDa, suggesting that the enzyme consists of five identical subunits. The temperature and pH optima are 50°C and pH 7.0, respectively. The Arrhenius energy for decarboxylation of 3,4-dihydroxybenzoate was 32.5 kJ mol for the temperature range from 22 to 50°C. The and for 3,4-dihydroxybenzoate were 0.6 mM and 5.4 X 10 min respectively, at pH 7.0 and 25°C. The enzyme catalyzes the reverse reaction, that is, the carboxylation of catechol to 3,4-dihydroxybenzoate, at pH 7.0. The enzyme does not decarboxylate 4-hydroxybenzoate. Although the equilibrium of the reaction is on the side of catechol, it is postulated that C. hydroxybenzoicum uses the enzyme to convert catechol to 3,4-dihydroxybenzoate. ... 

The occurrence of 3,4-dihydroxybenzoate decarboxylase was also found widely in facultative anaerobes. Among them, Enterobacter cloacae P241 showed the highest activity of 3,4-hydroxybenzoate decarboxylase, and the activity of the cell-free extract of E. cloacae P241 was determined to be 0.629 p.mol min (mg protein) at 30°C, which was more than that of C. hydroxybenzoicum, 0.11 (xmol min mg protein)" at 25°C. The E. cloacae P241 enzyme has a molecular mass of 334 kDa and consists of six identical 50 kDa subunits. The value for 3,4-dihydroxybenzoate was 177 p.M. The enzyme is also characteristic of its narrow substrate specificity and does not act on 4-hydroxybenzoate and other benzoate derivatives. The properties of E. cloacae P241 3,4-hydroxybenzoate decarboxylase were similar to those of C. hydroxybenzoicum in optimum temperature and pH, oxygen sensitivity, and substrate specificity. 

Figure 2 Time course of carboxylation reaction of catechol. Closed circles, 3,4-dihydroxybenzoate open squares, catechol.

The reaction product of the reserve carboxylation reaction was isolated and identified to be 3,4-dihydroxybenzoic acid by NMR and NMR with the authentic 3,4-dihydroxybenzoic acid as a reference. The carboxylation reaction of catechol to 3,4-dihydroxybenzoate was affected by the concentration of KHCO3. The carboxylation activity of E. cloacae P241 3,4-dihydroxybenzoate decarboxylase in the presence of 0.1 M KHCO3 was only 15% of that in the presence of 3 M KHC03. In the case of C. hydroxybenzoicum 3,4-dihydroxybenzote decarboxylase, only 0.01 mM 3,4-dihydroxybenzoate was formed from 6mM catechol in the presence of 50 mM NaHC03 by 40 min incubation. The difference in molar conversion ratios might be caused by the concentration of bicarbonate added to the reaction mixture. 

A novel decarboxylase, 2,6-dihydroxybenzoate decarboxylase, was found in Agrobacterium tumefaciens 1AM 12048 at first. Thereafter, the same activity was found in Rhizobium species by two groups independently. Furthermore, Pandoraea sp. 12B-2, the most powerful producer of 2,6-dihydroxybenzoate decarboxylase, was isolated. These enzymes have been purified and characterized. 

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