Activation chelation

Open-chain ligands were the first evaluated for complexation studies with indium and yttrium. The use of diethylenetriaminepentaacetic acid (DTPA) anhydride permitted early evaluation of labeled chelate-conjugates (Figure 2).80 The use of this activated chelating agent was quite popular, until the drawbacks associated with its crosslinking of proteins became apparent. 

The pharmacological properties of 108 are not ideal. It removes iron only slowly and it is not well absorbed by oral administration so it has to be administered by injection. Therefore there is need for new chelators. The orally active chelator l,2-dimethyl-3-hydroxypyridin-4-one (LI) 109 is on clinical trial for the treatment of thalassemia (543). Several other chelators which contain 3-hydroxy-4(H)-pyridinone such as 110-112 also possess oral availability, and have comparable activity to 109 for the removal of iron from the liver (544, 545). These... 

Figure 2 Chemistry of the polymeric chelates used for loading liposomes and micelles with multiple reporter metal atoms, (a) Synthesis of a single terminus-PDP-activated chelating polymer (DTPA-polylysine) starting from CBZ-protected polylysine and SPDR...

Optically active chelating diphosphanes are important in the area of asymmetric catalytic hydrogenation of prostereogenic olefins mediated by Rh(I) complexes. 

Substituted cobalt porphyrins as catalysts in sulfuric acid. Further very active chelates for the reduction of oxygen in acids discovered in the early 70s were CoTPP by Sandstede and co-workers 9,13-15) and CoTAA and FeACC by Beck and co-workers 8 12>. Sandstede et al. determined the activities of their chelate catalysts by the suspension method briefly explained in Section 2.2.2.3. 

The presence of a plateau for r values > 1 suggests the existence of a 1 1 active chelate. This complexe justifies the micro-... 

Therefore in an attempt to distinguish among mechanisms A, B, and C the acetylacetonates of chromium(III), cobalt(III), and rhodium(III) were partially resolved and the optically active chelates were then subjected to several electrophilic substitution reactions. 

Antioxidant and anti-radical activity, chelation of metal ion... 

More successful attempts at asymmetric hydroformylation have involved rhodium and platinum complexes. As in asymmetric hydrogenation, best results have been obtained with optically active chelating diphosphines as ligands, but some studies of monophosphines have been made. Using... 

A variety of unsymmetrical optically active chelate ligands LL have been used as optically active resolving agents in square-pyramidal complexes of the type C5HsM(CO)2LL (M = Mo, W) giving partly cationic species (77-81) and partly neutral complexes (79, 82-91). The field of optically active square-pyramidal complexes has been reviewed (11, 92). All of the known examples are summarized in Table I. 

The l,T-ferrocenediyl-bridged ligand system Fe[(C5H4) NPh]2 give access to redox-active chelate complexes of the type (83). ... 

One of the chemical derivatives of dimercaprol (BAL) is DMSA. DMSA is an orally active chelating agent, much less toxic than BAL, and its therapeutic index is about 30 times higher (Angle and Kuntzelman, 1989). The empirical formula of DMSA is C4H6O4S2 and its molecular weight is 182.21. It is a weak acid soluble in water. 

The halides of all three metals give the covalent 4-coordinate derivatives, LXXXV, but—quite exceptionally—only copper(I) gives 4-coor-dinate salts, such as LXXXVI (X = NO 3 or CIO4). As we have previously seen, gold (I) halides require two molecules of an active chelate ligand to give stable salts of this type (5, 11). 

In the 1970s and early 1980s the development of new catalysts was mainly based on new optically active chelating phosphines used in Wilkinson-type catalysts. This era of design and synthesis of optically active bidentate phosphines started in 1971 with Kagan s tartaric acid derived ligand DIOP [59, 60]. Successful and well-known examples followed, namely DIPAMP [62], prophos [63], chiraphos [64], BPPM [65], BPPFA [66], norphos [67], and BINAP [68]. A selection is depicted in Figure 3. 

Figure 3. Representative optically active chelating phosphines used in enantioselective hydrogenation reactions.

The two square planar species of line 2 are diastereomers. They contain the same optically active chelating phosphine chiraphos, but the rhodium atom is coordinated to different sides of the prochiral olefin (re/si sides). The two diastereomers of line 2 are rapidly interconverting. In this equilibrium the isomer shown on the left-hand side (si-coordination of the olefin) is the minor isomer and the isomer shown on the right-hand side (re-coordination of the olefin) is the major isomer [91, 92]. 

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