Hydroxyl radical generation via photoreduction of a simple pyridine N-oxide by an NADH analogue

Photoreduction of pyridine N-oxide, which has a key structure of antitumor agents for hypoxic solid tumors, by 1-benzyl-1,4-dihydronicotinamide in deaerated aprotic media resulted in generation of hydroxyl radical, leading to the oxidation of salicylic acid to 2,3- and 2,5-dihydroxybenzoic acids, and catechol.     

Biomimetic reduction of benzoylformic acid by an acid stable NADH analogue : a model reaction of lactate dehydrogenase

By the use of an acid-stable NADH analogue (3-carbamoyl-N-benzyl-1,4-dihydroquinoline) NADH model reduction of benzoylformic acid in aqueous solution was achieved, for the first time, at pH region where the carboxyl group is undissociated.     

Enhanced acid stability of a reduced nicotinamide adenine dinucleotide (NADH) analogue

A methyl substituent at C-5 of the nicotinamide ring is found to confer increased acid stability in a reduced nicotinamide model (5-20 fold) and in a reduced dinucleotide coenzyme (2-3 fold), while retaining reactivity towards hydride transfer.     

Biomimetic reduction of inacivated carbonyl compounds by an acid-stable NADH analogue plus brönsted acid

The NADH model reduction of inactivated carbonyl compounds was achieved by he combination of an acid-stable NADH analogue and strong proton sources (HCl or benzenesulfonic acid).     

A mechanistic dichotomy in scandium ion-promoted hydride transfer of an NADH analogue: delicate balance between one-step hydride-transfer and electron-transfer pathways

The rate constant (kH) of hydride transfer from an NADH analogue, 9,10-dihydro-10-methylacridine (AcrH2), to 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ) increases with increasing Sc(3+) concentration ([Sc(3+)]) to reach a constant value, when all TolSQ molecules form the TolSQ-Sc(3+) complex. When AcrH2 is replaced by the dideuterated compound (AcrD2), however, the rate constant (kD) increases linearly with an increase in ([Sc(3+)]) without exhibiting a saturation behavior. In such a case, the primary kinetic deuterium isotope effect (kH/kD) decreases with increasing ([Sc(3+)]). On the other hand, the rate constant of Sc(3+)-promoted electron transfer from tris(2-phenylpyridine)iridium [Ir(ppy)3]to TolSQ also increases linearly with increasing ([Sc(3+)]) at high concentrations of Sc(3+) due to formation of a 1:2 complex between TolSQ*- and Sc(3+), [TolSQ*--(Sc(3+)2], which was detected by ESR. The significant difference with regard to dependence of the rate constant of hydride transfer on ([Sc(3+)]) between AcrH2 and AcrD2 in comparison with that of Sc3+-promoted electron transfer indicates that the reaction pathway is changed from one-step hydride transfer from AcrH2 to the TolSQ-Sc3+ complex to Sc3+-promoted electron transfer from AcrD2 to the TolSQ-Sc3+ complex, followed by proton and electron transfer. Such a change between two reaction pathways, which are employed simultaneously, is also observed by simple changes of temperature and concentration of Sc3+.     

Interfacing an analogue infrared spectrometer to a microcomputer

An Apple microcomputer has been interfaced to a Perkin-Elmer model 577 infrared spectrometer. The spectral data are digitized with the aid of an in-house designed 12-bit analogue-to-digital interface unit. Control and status signals are obtained from the spectrometer and an optical encoder unit is used to provide an accurate wavenumber marker for the conversion and data recording. The digital data are formatted by the microcomputer and then can be manipulated by programs already developed for handling spectral data recorded from digital spectrometers.     

DNA cleavage induced by thermal electron transfer from a dimeric NADH analogue to acridinium ions in the presence of oxygen

Acridinium ions, which can intercalate to DNA, act as thermal DNA cleavers in the presence of a dimeric NADH analogue and O2 in an aqueous solution via thermal electron transfer from a dimeric NADH analogue to acridinium ions, followed by the electron-transfer reduction of O2 to O2*- by the resulting NAD radicals.     

Mechanistic aspects of biological redox reactions involving NADH 2: A combined semiempirical and ab initio study of hydride-ion transfer between the NADH analogue, 1-methyl-dihydronicotinamide,and folate and dihydrofolate analogue substrates of dihydrofolate reductase

As part of a study of factors controlling biological redox reactions of nicotinamide cofactors [nicotinamide adenine dinucleotide (phosphate) NAD(P)H], we have investigated the effect on a model reaction of the conformational state (cis or trans) of the carboxamide side chain, using quantum chemical methods. The reaction is that for the enzyme dihydrofolate reductase between the NADPH analogue, 1-methyl-dihydronicotinamide, and the protonated forms of the folate and dihydrofolate substrate analogues, pyrazine and dihydropyrazine. Some calculations on pterin and dihydropterin substrate analogues were also carried out in order to gauge the effects of inter-ring coupling. The influence of carboxamide side-chain conformation of nicotinamide on the energetics of the hydride-ion transfer, and on the structures of the transition states and stable intermolecular-interaction complexes, are examined as a function of the orientation of approach of the reactants. These approach geometries include those corresponding to the observed binding of cofactor and either substrate or inhibitor in the enzyme active site. Reactant, product, reactants-complex, and transition-state geometries were optimized at the semiempirical AM1 level, while ab initio SCF/STO-3G and SCF/3-21G single-point calculations were carried out at the AM1 optimized geometries for all species, as well as full geometry optimizations for isolated reactants and products. The results show that reactants-complex and transition-state energies are lower for the trans conformer of dihydronicotinamide than for the cis conformer, due to more favorable H-bonding or electrostatic interactions with the protonated substrate. Also, consideration of the structural parameters, including reaction coordinate bond lengths, ring geometries, and charge distributions, indicate that the trans transition states are more product-like than those for the cis. For the (trans) approaches corresponding to the enzymic orientation for substrate, the intermolecular interaction for the folate reaction lacks the stabilizing influence of the formal H-bond which is present for the dihydrofolate reaction, and consequently the reactants-complex and transition state are less stable.     

Synthesis of a thymidine dinucleotide analogue containing an internucleotide silyl linkage

The synthesis of a silyl-linked analogue of a thymidine dinucleotide is described. The use of 5′-dimethoxytrityl and 3′-levulinyl protection allows mild and completely selective deprotection.     

Synthesis of an iminosugar based peptidomimetic analogue

The synthesis of an 1-deoxymannojirimycin based analogue of a known HIV-protease inhibitor is described. The strategies employed for introduction of the pharmacophore groups onto the azasugar scaffold were based on regioselective reactions of the hydroxyl groups of the natural product and of d-fructopyranoside derivatives.     

An expedient synthesis of an isofervenulin analogue

An efficient approach has been developed for the synthesis of an isofervenulin analogue 1 employing a one‐pot condensation‐substitution reaction of a chlorocarboethoxytriazine (electrophile) with a urea (nucleophile). The resulting cyclization reaction resulted in the synthesis of a pyrimido‐heterocycle in good yield in either acidic or basic media. The former was assisted by utilizing trimethylsilyl chloride.     

Facile synthesis of an azido-labeled thalidomide analogue

[reaction: see text] A five-step synthesis of an azido-thalidomide analogue is presented. The sequence requires cheap and readily available starting materials and reagents, and only two steps require purification. Additionally, the azido-labeled analogue possesses activity comparable to that of thalidomide in inhibiting the proliferation of human microvascular endothelial cells, thus providing impetus for its use as a potential photoaffinity label of thalidomide.     

Donor-acceptor-stabilized silicon analogue of an acid anhydride

A stable silicon analogue of an acid anhydride {PhC(Bu(t)N)(2)}Si{═O·B(C(6)F(5))(3)}O-Si(H){═O·B(C(6)F(5))(3)}{(NBu(t))(HNBu(t))CPh} (4) with a O═Si-O-Si═O core has been prepared by treating monochlorosilylene PhC(Bu(t)N)(2)SiCl (1) with H(2)O·B(C(6)F(5))(3) in the presence of NHC (NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Compound 4 has been characterized by elemental analysis and multinuclear NMR spectroscopic investigations. The molecular structure of 4 has been established by single-crystal X-ray diffraction studies, and DFT calculations support the experimental results.     

A reductase-mimicking thiourea organocatalyst incorporating a covalently bound NADH analogue: efficient 1,2-diketone reduction with in situ prosthetic group generation and recycling

A new class of bifunctional organocatalyst promotes the chemoselective reduction of diketone electrophiles at catalytic loadings in the presence of an inorganic co-reductant.     

Katalytische Oxidation von NADH an Graphitelektroden durch adsorbierte Phenoxazinderivate

Zusammenfassung Phenoxazin und 2-Naphthoylderivate von Aminophenoxazinen wie Nilblau (E ₀=–220 mV/SCE bei pH 7) wurden an Graphitelektroden adsorbiert. Diese Substanzen sind sehr gute Katalysatoren zur NADH Oxidation zu NAD⁺, wenn ihr Redoxpotential nicht unter –300mV/SCE liegt. Die Vergrößerung des Moleküls durch die Napthoylgruppe oder die Benzolringe kondensierter Polyaromaten als zusätzliche Haftgruppen setzt ihre Löslichkeit in wäßrigen Lösungen stark herab. Auf Graphit kann 2-Naphthoylnilblau bis pH 8 benützt werden, bei größeren pH-Werten hat es durch die Umwandlung in seine Iminoform eine geringere Aktivität. In Lösung ist die Iminoform vollständig inaktiv. Es wird angenommen, daß die Reaktion über einen Charge-Transfer-Komplex verläuft, ohne daß ungebundene Elektronen und Wasserstoff freigesetzt werden (H^– in der Gesamtreaktion).

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Catalytic oxidation of NADH on graphite electrodes with adsorbed phenoxazine derivates

Summary Phenoxazines and 2-naphthoyl derivates of aminophenoxazines like Nilblue (E ₀=–220mV/SCE at pH 7) had been adsorbed on graphite electrodes. These substances are very good catalysts for NADH oxidation to NAD⁺, if their redox potential is not under –300 mV/SCE. The enlargement of the molecule by the naphthoyl group or by the benzene rings of condensed polyaromatics as additional adhesive group very strongly lower their solubility in aqueous solutions. 2-Naphthoyl nilblue can be used up to pH 8, in case of higher pH values it has a lower activity due to its conversion into the imino form. In solution the imino form is completely inactive. It is suggested that the reaction involves a charge-transfer complex without releasing unbound electrons and hydrogen (H^– in the overall reaction).

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Diese Arbeit wurde vom Bundesministerium für Forschung und Technologie unterstützt. Herrn Prof. H.-L. Schmidt danke ich für die Förderung dieser Arbeit.     

Remote NADH imaging through an ordered array of electrochemiluminescent nanoapertures

In this report, we present an ordered array comprising thousands of nanoapertures for the electrochemiluminescent (ECL) detection of NADH. It was fabricated on the distal face of a coherent optical fiber bundle. Such a high-density array of nanoapertures combines optical, imaging and electrochemical properties. Indeed, each nanoaperture is surrounded by a gold nanoring, which acts as an electrode material. The behavior of the array was characterized by cyclic voltammetry and it shows excellent electrochemical performances. NADH is the analyte, which is measured in presence of Ru(bpy)3(2+). The ruthenium complex mediates the NADH oxidation and this coenzyme acts as a co-reactant in the ECL mechanism. ECL light is generated at the distal face of the array by each gold ring electrode. A fraction of this ECL light is collected by the corresponding nanoaperture, transmitted through the optical fiber bundle and finally imaged on the proximal face with a CCD camera. In this work, we show that NADH concentration is remotely detected by an oxidative-reductive ECL mechanism. We present also some preliminary results about the ECL process of NADH with Ru(bpy)3(2+). The ECL behavior of NADH on gold surface is reported. The influence of the applied potential on the collected light intensity was investigated. The variation of the ECL intensity measured through the nanoaperture array with NADH concentration is linear. Remote ECL detection of NADH is spatially resolved over a large area with a micrometer resolution through the array. Therefore, such array integrates several complementary functions: ECL light generation, collection, transmission and remote imaging in an array format.     

Synthesis of a simplified transition-state analogue in an attempt to obtain an inhibitor of CMP-KDO synthetase

The thioglycoside 5 of 3-deoxy-beta-D-manno-2-octulosonic acid (beta-KDO) has been synthesized in an attempt to make a simplified transition-state analogue inhibitor of the enzyme CMP-KDO synthetase (3-deoxy-D-manno-octulosonate cytidylyltransferase). Compound 5 was tested in vitro and was found to have no inhibitory activity.