Conductive boron-doped chemical vapor-deposited diamond thin films, already known to have superior properties for general electroanalysis, including low background current and a wide potential window, are here shown to have additional advantages with respect to electrochemical oxidation of nicotinamide adenine dinucleotide (NADH), including high resistance to deactivation and insensitivity to dissolved oxygen. Cyclic voltammetry, amperometry, and the rotating disk electrode technique were used to study the reaction in neutral pH solution. Highly reproducible cyclic voltammograms for NADH oxidation were obtained at as-deposited diamond electrodes. The response was stable over several months of storage in ambient air, in contrast to glassy carbon electrodes, which deactivated within 1 h. The diamond electrode exhibited very high sensitivity for NADH, with an amperometric detection limit of 10 nM (S/N = 7). The response remained stable, even in the very low concentration range, for several months. In addition, interference effects due to ascorbic acid were minimal when the concentrations of NADH and ascorbic acid were comparable. An NADH-mediated dehydrogenese-based ethanol biosensor incorporating an unmodified diamond electrode is demonstrated. The present results indicate that diamond is a useful electrode material for the analytical detection of NADH, making it attractive for use in sensors based on enzyme-catalyzed reactions involving NADH as a cofactor.

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Chemo-immunotherapy with lentinan offers a significant advantage over S-1-based chemotherapy alone in terms of survival in patients with advanced gastric cancer.

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In our preliminary communication 1) we reported a new preparative method for 3-(benzylthio)thieno [3,4-b]indolizine derivatives having unique stacked structures due to the contribution of intramolecular arene-arene interactions. We also found that this method using 5-arylcarbonyl-4-ethoxycarbonylmethyl-3-(1-pyridinio)thiophene-2-thiolates as key intermediates is much more effective than those described earlier by us [2][3][4] and is widely applicable to the preparation of various 3-alkylthio-and 3-(benzylthio)thieno [3,4-b]indolizine derivatives. To the best of our knowledge, the intramolecular arene-arene interaction through a highly flexible spacer such as the sulfide bond is scarcely reported, 5,6) and if its conformational control is possible through such interaction, these molecules might be used as low energy molecular switches and chiral auxiliaries. 7,8) For the staggered conformations in relation to the sulfide spacer in 3-(benzylthio)thieno [3,4-b]indolizine derivatives, there are two gauche (G1, G2) and one anti form. The latter is further subdivided into A1, A2, and A3 (see Fig. 1). Only the G1 form and the eclipse form (E) have the attractive arene-arene interactions. However, the E form has the greatest steric hindrance and is not a stable conformer. The title compounds, 3-(benzylthio)thieno [3,4-b]indolizine derivatives, with intramolecular arene-arene interactions (G1 form) have the following structural features in comparison with the analogs with a ethylene spacer: 1) the sulfur atom does not have any substituent and hence the steric repulsion with the proton(s) and/or group(s) on the adjacent carbon atom is absent, 2) the long sulfide linkage decreases the energy difference between the anti (A1, A2, A3) and gauche conformers (G1, G2), 3) the narrow C-S-C bond angle (near 100°), in contrast with the C-C-C bond angle (109.5°), makes the through-space interaction between the two remote aromatic rings possible, 4) the 5-and 6-positions of the thieno[3,4-b]indolizine and the phenyl ring in the G1 form are close and therefore an attractive interaction can be expected, while the other G2 form has no arene-arene interaction and is considerably crowded, 5) the A3 form is considerably hindered than the others (A1, A2). In addition, the electronic property of the indolizine skeleton in which the pyridine moiety has a cationic character may also assist this attractive interaction in the G1 form. In this paper we report a novel and effective preparative method of ethyl 1-arylcarbonyl-3-[(un)substituted methylthio]thieno[3,4-b]indolizine-9-carboxylates starting from 1-(ethoxycarbonylacetonyl)pyridinium chlorides and also describe their structures involving the intramolecular arene-arene interactions. Results and DiscussionPreparations of 5-Arylcarbonyl-4-ethoxycarbonylmethyl-3-(1-pyridinio)thiophene-2-thiolates When we found the unexpected formation of ethyl 3-(R-thio)-1-cynothieno [3,4-January 2003 Chem. Pharm. Bull. 51(1) 75-84 (2003) 75 * To whom correspondence should be addressed. Wakasato, Nagano 3...