pyrroloquinolinequinone : a versatile biological electron carrier

The redox properties of the pyrrolo quinoline quinone (PQQ) were studied by means of the specific one-electron reductans NAD dimers, (NAD)2 and (NADP)2. PQQ and (NAD)2 or (NADP)2 give rise to a redox process whose products are pyrrolo quinoline quinol (PQQH2) and coenzymes NAD+ or NADP+. The process implies a two-step one electron transfer via the intermediate pyrrolo quinoline semiquinone radical (PQQ

Photocatalyzed anaerobic oxidation of nicotinamide coenzyme dimers to NAD+ by adriamycin

The NAD dimers (NAD)2 obtained by electrochem. redn. of NAD are oxidized by adriamycin in anaerobic photocatalyzed reaction yielding NAD and 7-deoxyadriamycinone. Under the same conditions, NADH is not oxidize

Dithionite adducts of pyridinium salts: regioselectivity of formation and mechanisms of decomposition

H-1 and C-13 NMR spectroscopy has been used to detect and to characterize the adducts formed, in alkaline solutions, by the attack of dithionite anion on 3-carbamoyl or 3-cyano substituted pyridinium salts. In all studied cases, only 1,4-dihydropyridine-4-sulfinates, formed by attack of dithionite oxyanion on the carbon 4 of pyridinium ring, were found. This absolute regioselectivity seems to suggest a very specific interaction between the pyridinium cation and the dithionite through the formation of a rigidly oriented ion pair, determining the position of attack. In weak alkaline solution, the adducts decompose according to two mechanisms S(N)i and S(N)i ': the SNi path is operative in all studied cases and preserves the 1,4-dihydro structure yielding the corresponding 1,4-dihydropyridines, whereas the S(N)i ' path involves the shift of 2,3 or 5,6 double bonds yielding 1,2- or 1,6-dihydropyridines, respectively. The formation of 1,2- or 1,6-dihydropyridines, in addition to 1,4-dihydro isomers, depends on their respective thermodynamic stabilities. (c) 2005 Elsevier Ltd. All rights reserved

STRUCTURE OF THE DIMERS ARISING FROM ONE-ELECTRON ELECTROCHEMICAL REDUCTION OF PYRIDINIUM SALTS 3,5-DISUBSTITUTED WITH ELECTRON-WITHDRAWING GROUPS.

One-electron electrochemical reduction of the salts 1-benzyl-3,5-bis(methylcarbamoyl)pyridinium bromide 3a and 1-benzyl-3,5-dicarbamoylpyridinium bromide 3b yields mixtures of four isomeric dimers, as shown by HPLC analysis and mass spectrometry. 1H and 13C NMR spectrometry allows us to determine the structures of the mixture components. In both mixtures, the two most abundant products are identified as 4,4′- and 2,4′-tetrahydrobipyridines (5a, 5b and 6a, 6b, respectively), while minor amounts of a pair of diastereomeric 2,2′-linked dimers are also detected in (7a, 8a and 7b, 8b respectively). Therefore, the NMR studies lead to the conclusion that the structure assignment of conformers of 5a, made previously for 6a and 7a, is not correct. All the 2,2′- and 2,4′-linked dimers undergo photochemical dissociation into two pyridinyl radicals which recombine to yield 4,4′-linked dimer

Facile and Efficient Synthesis of 4-Alkyl Derivatives of 3-Carbamoyl- and 3,5-Dicarbamoylpyridines as Nicotinamide Mimetics

Nicotinamide plays a key role in many biological processes and, as a consequence, its derivatives could be attractive for the synthesis of biologically active compounds. Here a rapid and efficient way of preparing alkyl derivatives of nicotinamide, precisely, 4-alkyl-3-carbamoylpyridine and 4-alkyl-3,5-dicarbamoylpyridine is reported. The synthetic route developed adopts mild reaction conditions and produces target compounds in higher yields compared with methods described in literature

1H , 13C, 31P NMR studies and conformational analysis of NADP+ , NADPH coenzymes and dimers from electrochemical reduction of NADP+

One-electron electrochemical reduction of 4-methyl- and 6-methyl-substituted nicotinamide salts 1 and 4, produces free radicals which irreversibly dimerize. A diastereomeric pair of 6,61-linked dimers (2a and 2b) were the main products obtained from salt 1; this represents the first example of a symmetrical dimerization of 3-carbamoyl-substituted pyridinyl radicals implicating the 6 positions. In contrast, salt 4 yielded a diastereomeric pair of 4,4′-linked dimers (5a and 5b) as the main products. Minor amounts of 4,6′-linked dimers were also obtained from both 1 and 4. These results show that, in the present case, steric hindrance is the prevalent factor controlling the regioselectivity of the pyridinyl radical dimerization, but that the electron spin density on the coupling positions is still a relevant element. Furthermore, the studied dimers exhibited anomalous UV spectral properties with respect to both the absorption bands and molar absorbances. © CNRS-Gauthier-Villars