Thiosemicarbazones, reduction

The electrochemical behavior of an aqueous/ethanol solution of [Ir(sat)2]Cl, satH = salicylaldehyde thiosemicarbazone (235), has been studied on mercury. A two-electron, ligand-based reduction at —1.09 V vs. SCE (independent of pH) is observed at fast scan rates.406... 

Amino-5-phenyl-l,3,4-thiadiazole is reduced by sodium amalgam to benzaldehyde thiosemicarbazone, but the 5-H and 5-methyl analogs do not react (68AHC(9)165, p. 197) (see also Scheme 9 for LAH reduction). 

When the thiosemicarbazones of benzaldehyde, 2-hydroxybenzaldehyde, methyl phenyl ketone, or methyl 2-hydroxyphenyl ketone were reacted with aryl tellurium trichlorides, reduction to the aryl tellurium chlorides occurred. The aryl tellurium chlorides were stabilized by coordination to excess thiosemicarbazone2. 

The thiosemicarbazone complexes CuPTSM and CuA-TSM, Fig. , have been used to image perfusion and hypoxia, respectively (36). It is believed that these compounds freely diffuse into cells. Reduction from Cu(II) to Cu(I) inside the cell causes the complex to faU apart, and the copper is trapped inside the ceU. The redox potential of CuATSM is lower than that of CuPTSM, and this redox potential is believed to be the root of the selectivity of CuATSM for hypoxic tissue. 

After considering the matter of copper complexation with INH, Krivis and Rabb [536] suggested that a 1 1 cuprous complex was more likely than a cupric complex. They pointed out that the copper complex formed with INH followed the reduction of Cu(II) to Cu(I), so that 1 1 cuprous complexes were formed upon addition of Cu(II) to solutions containing INH. Krivis and Rabb also suggested that the formation of Cu(I) complexes of thiosemicarbazones accounted for the synergistic effect of copper with the antitubercular agent... 

Cu-ATSM is selectively trapped in highly reducing hypoxic tissue but not in less reducing normal tissue. On the other hand, Cu-PTSM is reduced in both normoxic and hypoxic tissue. Hypoxia selectivity has been correlated to the reduction potential of the molecule that is in turn related to the alkyl group substitution. The reduction potential of Cu-ATSM is about 100 mV lower than that of Cu-PTSM. Density Functional Theory and chemical reactivity studies attempt to correlate the structure and redox properties of bis(thiosemicarbazones) with the characteristics of the LUMOs (metal or ligand based) and chemical reactivity. The fast and selective uptake of jjj hypoxic... 

Fluoroquinoline (173, X=H) was obtained by reduction of 2-bromo-3-fluoroquinoline 173 (X=Br) with Pd/C and NEts in methanol. Bromo derivative 176 (R =COOH) has been shown to form the corresponding organomagnesium compound, which was transformed on treatment with DMF into aldehyde 176 [R =COOH, X=C(0)H] and its thiosemicarbazone derivative 176 [R =COOH, X=CH NNHC(S)NH2] [106], In a similar way 2-bromo-3-fluoroquinolm-4-carbaldehyde and its 1,3-dioxalan were obtained from 4-lithium-3-fluoro-2-bromoquinoline and DMF. 

The properties of quinones are to a certain extent similar to those of carbonyl compoimds. They form oximes, thiosemicarbazones, and phenylhydrazones. The rate of the reaction of quinones with hydroxylamine varies, and a number of quinones do not react with it at all. Substituents already present in the quinone molecule play a predominant role (16). In acid media hydroxylamine can have an oxidative influence, parallel to oximation, for example in the case of quinol, which is converted to quinone dioxime (17) free hydroxylamine can, however, have a reductive influence it reduces quinone to hydroquinone (18). 

The related antitumor copper salicylaldoxime complexes gave irreversible reduction with potentials of -0.47 to -0.64 V . Another class of Cu(II) coordination compounds, the thiosemicarbazones, is known to... 

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