Dihydroxybenzoic additives

Dihydroxybenzoic acid (DHB) is also a commonly used tool to measure the pharmacological effects of HIF-la stabilization via PHD inhibition. Recently, it was shown that mice pretreated with DHB (100 mg/kg, i.p.) showed a marked resistance to the neurotoxic effects of l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP) via protection of dopaminergic cell loss and striatal denervation. Importantly, this protection was seen to coincide with HIF-la stabilization, and the prevention of the MPTP-induced loss of ferroportin and striatal iron. Additionally, in these studies, DHB was also observed to block MPTP-induced reduction in mitochondrial pyruvate dehydrogenase, at both the mRNA level and through the measurement of enzyme activity in midbrain substantia nigra [26]. 

Methyl 3,5-dihydroxybenzoate (25.39 g, 0.151 mol, Aldrich) and potassium carbonate (52.69 g, 0.381 mol) were placed into a 1 L round bottom flask with 200 mL of acetone and a magnetic stirrer. Benzyl bromide (55.04 g, 0.322 mol) was added and washed into the flask with an additional 150 mL of acetone, followed by the addition of a catalytic amount of 18-crown-6 (0.57 g, 2.2 mmol). 

B. Strapat, K. Hdlenkamp, F. Grehl, M. Krebs, B. MALDI-MS Widi Additives to 2,5-Dihydroxybenzoic Acid. Org. Mass Spectrom. 1993, 28, 1476-1481. 

Regioselective aminomethylation and subsequent cyclization of methyl 2,4-dihydroxybenzoate 517 was accomplished through a Mannich reaction with formaldehyde and primary amines in methanol to yield 3-substituted-3,4-dihydro-2/7-l,3-benzoxazine derivatives 518 (Equation 60). Simultaneous mixing of the reactants resulted in poor yields, but good yields were achieved by the pretreatment of paraformaldehye with a primary amine to form a Schiff base, followed by the addition of compound 517 <2001TL7273>. 

With the benzene-derived Ugands 26a,b the Cu-catalyzed orfho-hydroxyl-ation of methyl-4-hydroxybenzoate was only highly selective at low temperature, as at room temperature bound catecholate was shown to undergo a formal Michael addition with unreacted phenolate to yield methyl 2-[4-(carbomethoxy)phenoxy]-3,4-dihydroxybenzoate [181,270]. With the amine-based ligand 27, no such reactivity was observed and the catechol product methyl 3,4-dihydroxybenzoate was formed selectively. Interestingly, this latter ligand system also displayed some selective reactivity with the neutral 4-hydroxybenzoic acid substrate. 

The fluorination of 2,5-dihydroxybenzo-l,4-quinone and 2-hydroxynaphtho-l,4-quinone results, as well as replacement of the carbonyl oxygen atoms by fluorines, in replacement of the hydroxy groups and addition of a hydrogen fluoride molecule across a C = C bond to give,... 

More than 100 organochlorines have been identified and structurally characterized in the laboratory chlorination of terrestrial humic acid, although the major products are chloroform and trichloroacetic acid, followed by dichloroacetic acid and chlorinated C-4 dicarboxylic acids (324). In addition, other products that form in the chlorination of both humic acid and the model compound 3,4-dihydroxybenzoic acid are shown in Scheme 3.11. A more recently discovered source of natural organically bound chlorine is peat, reaching to 0.2% of the dry weight, and estimated to have accumulated globally to the extent of 280-1,000 million tons (169). 

Dihydroxybenzoic acid (DHB) Benchmark matrix for the analysis of carbohydrates including glycopeptides and glycoproteins (most effective < 5000 Da), free sugars and glycolipids.24 A number of additives have been used to alter the matrix s properties (see text)... 

The reaction of Mo(H20)63+ and nitrate in aqueous solutions results in the formation of Mo2Oi(H20)62+ and nitrite. Mo(III) coordinated to oxygen and nitrogen donor atoms of EDTA also reduces nitrate in aqueous solutions. The reduction of nitrate by a Mo(III)-EDTA complex results in the formation of nitrite and a Mo(V)-EDTA complex, as determined by chemical and spectrophotometric techniques. These reactions serve as models for biological nitrate reduction. In addition, molybdate coordinates to naturally produced phenolates. The molybdenum-coordinating phenolates also coordinate tungstate and ferric iron. Two of these phenolates contain threonine, glycine, alanine, and 2,3-dihydroxybenzoic acid. 

The reaction mixture was contained in a volume of 1 mL Tris-HCl buffer (pH 7.9), S-adenosylmethionine, MgCl2,3,4-dihydroxybenzoic acid, and dithi-othreitol. Reactions were started by the addition of the activity and terminated... 

However, the IpAia obtained after correction for the pH shift of the mobile phase (Figure 4-34, line B) does not correspond to ZpK from the theoretical curve (Figure 4-34, line C). The overall difference between the theoretical curve and spH curve is due to the pKa shift of the acidic analyte. The difference between the pH curve and the theoretical curve is due to a change of the acidic analyte ionization state at a particular hydro-organic composition upon addition of acetonitrile in the mobile phase. In essence, there is a larger pKa shift for the 2,4-dihydroxybenzoic acid than for the phosphoric acid (used as a buffer). 

In Figure 4-36 the acidic analyte wp a and IpKa values determined as a function of acetonitrile composition from 10 to 35 v/v% MeCN are shown. It is shown that even after correcting for the pH shift of the mobile phase upon addition of organic, the chromatographic IpA a values does not correlate to the pKa that was determined by titration in aqueous solvents, ZpK. An increase of 0.27 pKa units per 10% v/v MeCN for 2,4-dihydroxybenzoic acid was determined. A similar slope for other mono- and disubstituted aromatic benzoic... 

The stability of the radiolabelled peptides prepared under the conditions described above was studied. The "Ln-DOTATATE was found to be adequately stable over a period of 7 d at room temperature. The addition of free radical scavengers such as 2,5-dihydroxybenzoic acid (40 mg/mL of the final mixture) was found to be essential for the storage of high specific activity Lu labelled DOTATATE preparations. 

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