Carbonyl functionalised complexes

The coordination of amido functionalised carbene ligands, where the amido function is introduced by the acetylation of an amino functionalised imidazolium salt, to transition metals has already been discussed in Section 3.1. Here it suffices to mention that the synthesis is similar to other carbonyl functionalised NHC ligands and their transition metal complexes. A suitable example is given in Rivera and Crabtree [226]. 

Despite their enormous structural diversity, polyketide metabolites are related by their common derivation from highly functionalised carbon chains whose assemblies are controlled by multifunctional enzyme complexes, the polyketide synthases (PKSs) which, like the closely related fatty acid synthases, catalyse repetitious sequences of decarboxylative condensation reactions between simple acyl thioesters and malonate, as shown in Fig. 3 [7]. Each condensation is followed by a cycle of modifying reactions ketoreduction, dehydration and enoyl reduction. In contrast to fatty acid biosynthesis where the full cycle of essentially reductive modifications normally follow each condensation reduction, the PKSs can use this sequence in a highly selective and controlled manner to assemble polyketide intermediates with an enormous number of permutations of functionality along the chain. As shown in Fig. 3, the reduction sequence can be largely or entirely omitted to produce the classical polyketide intermediate which bears a carbonyl on every alternate carbon and which normally cyclises to aromatic polyketide metabolites. On the other hand, the reductive sequence can be used fully or partially after each condensation to produce highly functionalised intermediates such as the Reduced polyketide in Fig. 3. Basic questions to be answered are (i) what is the actual polyketide intermediate... 

CO-RMs can be thought of as a pro-drug, a means of delivering CO to a target. This typically requires a transition metal carbonyl complex stabilised by a multidentate ligand." The ligand could then be functionalised to enable the molecule to accumulate at a desired location. 

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