In the reaction related to NAD (P) H and its model compound, it has been reported that orientation of carbamoyl moiety in the nicotinamide ring of the coenzyme plays one of the crucial role to determine the stereochemistry of the reaction. In the oxidation of 3- (
N-methyl-
N-α-methylbenzylcarbamoyl) - 1, 2, 4-trimethyl-1, 4-dihydroquinoline (Me
3MQPH), the stereochemistry of the product, 3- (
N-methyl-
N-α-methylbenzylcarbamoyl) -1, 2, 4-trimethylquinolinium ion (Me
3MQP
+), is influenced largely by the reactivity of the reagent employed (oxidation potential of the quinone or p
Ka of the amine). This interesting phenomenon has been interpreted in terms of the differences in stabilities of the two conformations concerning to the carbonyl rotation at the transition-state. The energy difference between the two conformations at the transition-state has been estimated from the temperature dependency of the product ratio. We also studied the conformational analysis of Me
3MQPH, the ground-state itself, by means of the dynamic NMR technique. The contribution of the ground-state conformation and role of magnesium ion, which is used as a catalyst, are discussed.
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