Reduction by a Model of NAD(P)H. 27. Role of Bivalent Metal Ion in the Reduction of 2-Acylpyridines and 1-Acylisoquinolines

Reductions of 1-acetylisoquinoline (AQ), 1-benzoylisoquinoline (BQ), and isoquinoline-1-carbaldehyde have been studied kinetically and the results are compared with those of 2-acetylpyridine (AP), 2-benzoylpyridine (BP), and pyridine-2-carbaldehyde. Equilibrium constants for complexes between these substrates and zinc ion have also been studied. Kinetic deuterium isotope effects for AQ and BQ are smaller than the corresponding product isotope effects, respectively, whereas those for AP and BP are identical. The results are discussed in terms of stability and reactivity of intermediate radical-ion pair, and it is concluded that strong coordination of a metal ion onto the reaction site of a substrate facilitates the complexation but interferes the reduction.