Catecholate functional groups

In an EXAFS study of a soil contaminated by alkyltetravalent Pb compounds, Pb is found in the divalent state and complexed to salicylate- and catechol-type functional groups of HS (Manceau et al., 1996). The best spectral resemblance to reference compounds is obtained for a mixture of 60% salicylate and 40% catechol functional groups. Varying the proportion of salicylate and catechol forms within 10 to 20% has minor effects on the general shape of the combined EXAFS spectrum (Manceau et al., 1996). 

Figure 26. Speciation of lead in a soil affected by alkyllead compounds used as antiknock additives in gasoline. The soil EXAFS spectrum (solid) is compared to model spectra from a library of lead compounds. This comparison identifies salicylate and catechol functional groups as the predominant complexing chelates for divalent Pb. Adapted from Manceau et al. (1996). Figure continued on facing page.)...

From tyrosine, a series of enzymatic reactions including ring hydroxyla-tion, deciurboxylation, deamination, and D-methylation are responsible for over 20 majof metabolites of neurochemical interest. All of the above metabolites retain at least an electroactive phent nudeus, and most provide enhanced detectability via vanillyl or catechol functional groups. Table III provides cyclic voltammctric data in 90% 0.1 M citrate (pH 4)/10% methanol for a series of these metabolites. Substituent effects are evident. Gener-aUy the catecholamines with their OKlihydroxyphenyl structures are easiest to oxidize, followed by vanillyl dmvatives such as normetanephrine and vanillylmandelic acid. Simple phenols such as tyrosine remain the most difficult to oxidize in this series. 

Siderophores typically contain hydroxamate or catecholate functional groups which are arranged to form an octahedral cavity the exact size of a ferric iron. 

Using a different approach, the group of Jean-Marie Lehn, the third of Pedersen s fellow Nobel Laureates in 1987, prepared chiral derivatives of 18-crown-6 from protected tartaric acid to give crowns with four acid groups. As an alternative strategy, the Voyer group later used the catechol functional group of L-3,4-dihydroxyphenylalanine (l-DOPA) as a way to incorporate a chiral center into a... 

Azaloxan (12) is an antidepressant agent. Its synthesis can be accomplished starting with the reaction of catechol (7) and 3,4-dibromobutyronitrile (obtained by addition of bromine to the olefin) to give l,4-benzodioxan-2-ylacetonitrile (8). A series of functional group transformations ensues [hydrolysis to the acid (9), reduction to the alcohol (10) and conversion to a tosylate (11)] culminating in an SN-2 displacement reaction on tosylate 11 with l-(4-piperidinyl)-2-imidazolidi-none to give azaloxan (12) [3]. 

Polar functional groups such as alcohols or phenols 11 or trimethylsilanol 4 are transformed by monofunctional silylating reagents Me3SiX 12 into their hpophilic and often volatile trimethylsilyl ethers 13 whereas water is converted into persilyl-ated water (=Me3SiOSiMe3, hexamethyldisiloxane, HMDSO, 7, b.p. 100 °C). The persilylation of phenols and, in particular, catechol (or hydroquinone) systems (Scheme 2.1) protects them efficiently against air oxidation even at temperatures of up to 180 °C. (cf, e.g., the silylation-amination of purine nucleosides with dopamine hydrochloride in Section 4.2.4)... 

Catechol methyl transferases require the catechol function to be present to bind to the Mg ion. In the search for p2-adrenoceptor selectivity to produce potent bron-chodilators with low cardiovascular effects, changing the 3,4-hydroxy grouping of the catechol to 3,5- or 3-hydroxyl, 4-methyl-hydroxy, proved to be important (Figure 7.25). These compounds now have much improved bioavailability and pharmacokinetics due to their resistance to catechol methyl transferases. 

Many drugs are quite stable but functional groups such as esters and lactam rings which occur in some drugs are susceptible to hydrolysis and functional groups such as catechols and phenols are quite readily oxidised. The most common types of degradation which occur in pure and formulated drugs obey zero or first order kinetics. 

Compared to NE, the metabolism of the false neurotransmitter metaramind (MR), mediated by catechol-O-methyl transferase (COMT) and MAO, is reduced because of the absence of the catechol function and the presence of an a-methyl group, respectively (Fig. 24) [161],... 

Some functional groups such as phenol, pyridyl, catechol, imidazole, and amine, which are attached to the carbon atoms of macrocyclic framework, also affect the coordination geometry of the metal ions (39-44). 

Novel carbonylative carbocyclizations of 1,6-diynes promoted by Ru3(CO)i2/P(hex-c)3 in the presence of HSiMc2Bu-Z give bicyclic o-catechol derivatives by incorporating two carbon monoxide molecules as the 1,2-dioxyethenyl moiety (equations 148 and 149)346. This reaction is tolerant of functional groups such as ester, ketone, ether and amide. The disilylated product 366 is formed through dehydrogenative silylation of the initially formed mono-silyl product 365 under the reaction conditions. 

These new siderophores are identified by acronyms based upon CAM derived from catecholamide which results from substituting 2,3-dihydroxylbenzoyl or its derivatives (29) on a series of polyamines. The introduction of a carboxylic moiety at C-4 or a sulpho moiety at C-5 in the benzene ring extends the acronym to CAMC (29, R = -COOH, Ri = H) or CAMS (29, R = H, Ri = -S03H). The introduction of these two substituents leads to increased oxidation resistance of the catechol functions as well as increasing the hydrophilicity257. The participation of the hydroxy group at C-3 in chelation was established by preparation of an equivalent salicylamide siderophore227. Around 30 CAM-type siderophores have now been reported. 

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