Reaction of PQQ and Its Analogues with NADH; Application to the HLADH-Catalyzed Oxidation of Alcohols

Abstract

Redox reaction between PQQ and NADH occurs readily to give reduced PQQ (quinol) and NAD⁺, respectively. When the reaction is carried out under aerobic conditions, NADH is converted into NAD⁺ almost quantitatively even in the presence of a catalytic amount of PQQ (1 mol %). The catalytic reaction has therefore been applied to the HLADH-catalyzed oxidation of alcohols. Cyclohexanol (2.0 mM), for example, is oxidized to cyclohexanone in good yield (75%) when reacted with HLADH (5.0 × 10^-7M), NAD+(0.1 mM), PQQ (0.1 mM), and catalase at pH 8.3 for 24 h. As a result, we find that PQQ acts as an efficient catalyst to regenerate NAD⁺ with the aid of molecular oxygen. Catalytic efficiency of PQQ analogues is also examined in this system.