Reactions Involving Modification of Ligands

Compounds of aza macrocycles are prepared by three main types of procedure (1) conventional organic synthesis of the ligand, (2) metal-ion-promoted reactions, involving condensation of non-cyclic components in the presence of a suitable metal ion, and (3) modification of a compound prepared by methods (1) or (2). 

The above examples are ones involving modification of existing amine complexes, but there are also cases where amine ligands can be formed from non-amine precursors the oxidation of NCS coordinated to Co " gives Co—and the reaction of Pt"—Nj with an alkyne gives a coordinated triazole (Chapter 13.5). ... 

Reactions involving the modification of ligands These reactions modify the present ligands, without adding or removing any. These include insertion reactions, carbonyl insertions (also known as alkyl migration), hydride elimination, and abstraction. 

New developments of the RCM reactions involve easy modification of ligands to be used in catalysis, the building of supramolecular systems, host-guest systems or molecular materials. These examples show that alkene metathesis also strongly improves these new fields and allows to ereate new molecular and supramolecular objects. 

The reactions described so far do not require the involvement of the apo-B protein, neither would they necessarily result in a significant amount of protein modification. However, the peroxyl radical can attack the fatty acid to which it is attached to cause scission of the chain with the concomitant formation of aldehydes such as malondialdehyde and 4-hydroxynonenal (Esterbauer et al., 1991). Indeed, complex mixtures of aldehydes have been detected during the oxidation of LDL and it is clear that they are capable of reacting with lysine residues on the surface of the apo-B molecule to convert the molecule to a ligand for the scavenger receptor (Haberland etal., 1984 Steinbrecher et al., 1989). In addition, the lipid-derived radical may react directly with the protein to cause fragmentation and modification of amino acids. 

A large number of ligand reactions exist where both the kinetic patterns and the general mechanistic features are modified, rather than destroyed, by coordination. These reactions can furnish much information on the way coordination per se will affect the kinetic and thermodynamic aspects of a reaction. Generally, these will be reactions where specific redox properties of the central ion are not involved. In many of these cases coordination can provide a rational basis for the modification of synthetic procedures. 

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