Synthesis and evaluation of carbocyclic nicotinamide cofactor analogues

The history of the discovery and structure elucidation of many important nucleotides and coenzymes is reviewed in chapter 1. Some recent developments in nucleotide chemistry are also discussed including the discovery and biological importance of cyclic ADP ribose and carbocyclic nucleosides such as Aristeromycin and Neplanocin A.;In chapter 2, the preparation of a carbocyclic analogue of NAD+ (figure 1) is reported. This analogue is synthesised both as a mixture of diastereoisomers which are separated by HPLC and as a single diastereoisomer via the homochiral synthesis. (Fig. 8742).;In chapter 3, the kinetic parameters of carbocyclic NAD+ with yeast alcohol dehydrogenase and glycerl-3-phosphate dehydrogenase are established. Carbocyclic NAD+ is observed to be a good substrate for both these enzymes. NMR and molecular modelling studies provide evidence that carbocyclic NAD+ can adopt the same conformation as NAD+ without causing any unfavourable interactions. The kinetic isotope effects of carbocyclic NAD+ and NAD+ with CH3CD2OH and yeast alcohol dehydrogenase were measured and compared. They both were found to have a primary isotope effect of about 2 which is consistent with a C-H bond being broken in the rate limiting step. Carbocyclic NAD+ was used to probe the stereoselectivity of dehydrogenases, the class A (yeast alcohol dehydrogenase) and class B (glycerol-3-phosphate dehydrogenase) enzymes exhibited the same stereoselectivity with carbocyclic NAD+ as the NAD+. The mechanistic consequences of these observations are discussed.