NADH analogues

Koop, B., Schafer, H.J. and Straub, A., 2000, Steroselective interconversion of NaDH and NaDH" Analogues by Electrochemical Oxidation and Reduction , Paper presented at 197 meeting of the electochemical society . May 2000, Toronto, Canada, Abstract no. 1032. 

Cyclocondensations of NADH analogues with / ara-benzoquinone are described in [368, 369]. For example, upon addition of dihydropyridine 338 to an acetonitrile solution of 339 in the presence of scandium trifluoromethane-sulfonate, the cycloaddition reaction occurs efficiently at room temperature, yielding cycloadduct 340 [368] (Scheme 3.113). This reaction passes via formation of a complex between azine and scandium trifluoromethanesulfonate. 

The radical anion Cw, can also be easily obtained by photoinduced electron transfer from various strong electron donors such as tertiary amines, fer-rocenes, tetrathiafulvalenes, thiophenes, etc. In homogeneous systems back-electron transfer to the reactant pair plays a dominant role resulting in a extremely short lifetime of Qo. In these cases no net formation of Qo is observed. These problems were circumvented by Fukuzumi et al. by using NADH analogues as electron donors [154,155], In these cases selective one-electron reduction of C6o to Qo takes place by the irradiation of C6o with a Xe lamp (X > 540 nm) in a deaerated benzonitrile solution upon the addition of 1-benzyl-1,4-dihydronicoti-namide (BNAH) or the corresponding dimer [(BNA)2] (Scheme 15) [154], The formation of C60 is confirmed by the observation of the absorption band at 1080 nm in the near infrared (NIR) spectrum assigned to the fullerene radical cation. 

Novel and efficient [2 - - 3] cycloaddition reactions of NADH analogues with Q derivatives rather than the hydride-transfer reactions occur in the presence of scandium triflate, Sc(OTf)3, in MeCN to afford the cycloadducts (142). When 1 -benzyl-4-tert-butyl-1,4-dihydronicotinamide (t-BuBNAH) is used as an NADH analogue in the Sc +-catalyzed reaction with Q, the crystal structure of the cycloadduct was determined successfully, as shown in Fig. 53 (142). 

The dependence of the observed second-order rate constant (/ obs) on [Sc +] was examined for the cycloaddition reactions of t-BuBNAH with Q at various concentrations of Sc +. The A obs value increases with an increase in [Sc +] to exhibit a first-order dependence on [Sc +] at low concentrations, changing to a second-order dependence at high concentrations [Fig. 5A d) (142). Virtually the same dependence of the rate constant (a mixture of first- and second-order dependence) on [Sc +] is observed in ET from (TPP)Co to Q [Fig. 54(Z )] (142). This result indicates that the cycloaddition of the NADH analogue with Q proceeds via a rate-determining ET from the NADH analogue to Q, which is accelerated by formation of the 1 1 and 1 2 complex between Q with Sc " ", as in the case of an ET from (TPP)Co to Q (142). 

Thus, the hydride-transfer pathway is changed to the cycloaddition pathway through the metal ion-promoted ET from NADH analogues to Q derivatives, depending on the Lewis acidity of the metal ion (Scheme 23) (142). 

Bronsted acid catalysis in electron transfer described in Section 1.3.1 has also been effective for redox reactions via the electron transfer step. As shown in the case of metal ion-catalyzed hydride transfer reactions (see above), hydride transfer reactions from an NADH analogue to /7-benzoquinones also proceed via Bronsted acid-catalyzed electron transfer [255, 256]. Since NADH and ordinary NADH model compounds are subjected to the acid-catalyzed hydration [98, 257, 258], an acid-stable NADH model compound, 10-methyl-9,10-dihydroacridine (AcrH2), was used as a hydride donor to / -benzoquinone (Eq. 24) ... 

Matsuo, T. Mayer, J. M. 2005 Inorg. Chem. 44, 2150—2158 Oxidations of NADH analogues by ds-[Ru (bpys)2(py)0] + occur by hydrogen-atom transfer rather than by hydride transfer. 

Hydride Reduction of High-Valent Metal-Oxo Complexes by NADH Analogues... 

Hydride transfer reactions from NADH analogues to high-valent metal-oxo species provide excellent opportunity to clarify such a mechanistic difference by comparing the hydride transfer reactions with those with /)-benzoquinone derivatives, which have been discussed in the previous section. A series of NADH analogues, 10-methyl-9,10-dihydroacridine (AcrH2) and its 9-subsituted derivatives (AcrHR R =... 

FIGURE 2.14 Plots of kH for hydride transfer from NADH analogues to [(Bn-TPEN) FeIV(0)]2+ ( ), [(TMC)Ferv(0)]2+ ( ), and [(N4Py)Ferv(0)]2+ (O) versus kH for hydride transfer from the same series of NADH analogues to C14Q in MeCN at 298K."... 

Linear correlations between hydride transfer reactions of NADH analogues with (L)FeIV(0)]2 f and CI4Q in Figure 2.14 imply that the hydride transfer mechanism of (L)FeIV(0)]2+ is virtually the same as that of C14Q." Although there is still debate on the mechanism(s) of hydride transfer from NADH analogues to hydride acceptors in terms of an ET pathway versus a one-step hydride transfer pathway, the ET pathway is now well accepted for hydride transfer from NADH analogues to hydride acceptors... 

Other studies have dealt with hydrogen abstraction from the solvent by the photosensitizing drug nalidixic acid [98a], hydrogen transfer in an-thraquinone/xanthene systems [98b], photoreductions of quinones by alcohols [98c] and of acetylenic ketones by various hydrogen donors [98d], the oxidation of NADH analogues [98e-98g], and the reaction of 4-methyl-2-quinolinecarbonitrile with optically active phenylpropionic acid [98h],... 

Other Zinc Enzymes. Studies aimed at elucidating the mechanism of dimeric alcohol dehydrogenase enzymes have also been reported. Cobalt(n) can replace zinc(ii) at the two catalytic and non-catalytic sites in the liver enzyme, LADH. Reduction of pyridinealdehyde derivatives by the yeast enzyme has been examined. In acetonitrile solution, reduction by NADH analogues is catalysed by metal ions and mechanistic studies of the reaction have been carried out. Biomimetic studies of zinc-catalysed carbonyl reduction have also been reported. ... 

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