Effects of Cyclodextrin Inclusions on the Oxidation Rate of NADH Model Compounds Catalyzed by 1,4-Naphthoquinones

Seizo TAMAGAKI*, Akiko ISHIBASHI and Norimasa MIMURA

Department of Bioapplied Chemistry, Faculty of Engineering, Osaka City University;
3-3-138 Sugimoto, Sumiyoshi-ku, Osaka-shi 558-8585 Japan

The thermal and photochemical oxidations of 1-benzyl- or 1-alkyl-1,4-dihydronicotinamides (BNAH, RNAHs, respectively) were kinetically examined in the presence of unmodified cyclodextrins (CyDs) or modified CyDs with one or two 3-chloro-1,4-dioxo-2-naphthylamino groups (hereafter, naphthoquinone moiety: Q) on the primary or secondary side (QCyDs). The α- and β-CyDs formed an inert binary host-guest complex with either of a BNAH or the CyD-free naphthoquinone (NQ), but γ-CyD afforded a ternary complex exhibiting a weak reactivity only in lower concentrations of γ-CyD than BNAH. The reactivity of QCyDs toward BNAH(kobs/10|4 s|1) decreased in the order: 6-QβCyD(4.1)>3-QβCyD(3.5)>6-QβCyD(2.5)>6-QγCyD(2.2)>3-QαCyD(1.9) at [BNAH]/[QCyDs]=1. The sequence was independent of the nature of the 1-alkyl substituents. Meanwhile, 1-ethyl-1,4-dihydronicotinamide with a benzyl group at the 3-carbamoyl nitrogen (EBNAH) showed a different rate sequence: 6-QβCyD(3.9)>6-QγCyD(2.7)>6-QβCyD(2.3)>3-QβCyD(1.7)>3-QαCyD(1.1). Thus, the RNAH (BNAH) and EBNAH molecules seem most suitable for the β-CyD and γ-CyD cavities, respectively.

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