Design of photoactivated DNA oxidizing agents: synthesis and study of photophysical properties and DNA interactions of novel viologen-linked acridines

A new series of photoactivated DNA oxidizing agents in which an acridine moiety is covalently linked to viologen by an alkylidene spacer was synthesized, and their photophysical properties and interactions with DNA, including DNA cleaving properties, were investigated. The fluorescence quantum yields of the viologen-linked acridines were found to be lower than that of the model compound 9-methylacridine (MA). The changes in free energy for the electron transfer reactions were found to be favorable, and the fluorescence quenching observed in these systems is explained by an electron transfer mechanism. Intramolecular electron transfer rate constants were calculated from the observed fluorescence quantum yields and singlet lifetime of MA and are in the range from 1.06x10(10) s(-1) for 1 a (n=1) to 6x10(8) s(-1) for 1 c (n=11), that is, the rate decreases with increasing spacer length. Nanosecond laser flash photolysis of these systems in aqueous solutions showed no transient absorption, but in the presence of guanosine or calf thymus DNA, transient absorption due to the reduced viologen radical cation was observed. Studies on DNA binding demonstrated that the viologen-linked acridines bind effectively to DNA in both intercalative and electrostatic modes. Results of PM2 DNA cleavage studies indicate that, on photoexcitation, these molecules induce DNA damage that is sensitive to formamidopyrimidine DNA glycosylase. These viologen-linked acridines are quite stable in aqueous solutions and oxidize DNA efficiently and hence can be useful as photoactivated DNA-cleaving agents which function purely by the co-sensitization mechanism.     

Stereoselective synthesis of 4-hydroxy-2-phenylproline framework

Highly diastereoselective (>20:1) bromo-lactonization of N-sulfonyl-2-allyl-2-phenylglycine methyl ester (11) was observed. Successive treatment of the chiral lactone with MeONa gave the desired (2S,4R)-4-hydroxy-2-phenylproline derivative in high yield without erosion of the diastereoselectivity. The starting chiral non-racemic compound (5) was prepared from the racemic 2-phenylglycine using a classical kinetic resolution (crystallization), an asymmetric phase transfer alkylation, and an enzyme-catalyzed kinetic resolution.     

A mild and efficient process for detoxifying polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) were effectively dechlorinated to biphenyl under mild conditions using an aqueous solution of sodium hypophosphite in the presence of a palladium catalyst.     

Metalation of α-diazocarbonyl compounds using Grignard reagents. A convenient synthesis of α-diazo-β-ketoesters and mixed esters of α-diazomalonate

α-Diazocarbonyl compounds react with methylmagnesium bromide at −78 °C generating the corresponding α-diazo-α-bromomagnesio species, which can be intercepted by various electrophilic reagents. For example, with alkyl chloroformates α-diazo-β-ketoesters or mixed esters of α-diazomalonate are obtained in good yields.     

The synthesis and characterisation of ferromagnetic CaMn2O4 nanowires.

The synthesis of marokite CaMn(2)O(4) nanowires using a hydrothermal method is reported. Transmission electron microscopy and electron diffraction measurements show that the nanowires are polycrystalline in nature with diameters between 10 and 20 nm and lengths ranging from approximately 100 to 500 nm. Most interestingly, in contrast with the bulk material, magnetization measurements show that these nanowires exhibit ferromagnetic ordering with a Curie temperature (T(C)) of approximately 40 K.     

Synthesis of monofluorinated 1-(naphthalen-1-yl)piperazines

A series of regioisomerically monofluorinated 1-(naphthalen-1-yl)piperazines is described.     

A convenient synthesis of diaminoglyoxime and diaminofurazan: Useful precursors for the synthesis of high density energetic materials

The reaction of glyoxime ( 4 ) and hydroxylamine hydrochloride in aqueous sodium hydroxide was found to be a safe and inexpensive method for the preparation of multigram quantities of diaminoglyoxime ( 5 ). Potassium hydroxide mediated dehydration of 5 furnished diaminofurazan ( 1 ) in good yield of exceptional purity. The ready availability of 1 and 5 has facilitated the synthesis of new energetic furazan derivative 8 .