Trithiacyclononane as a ligand for potential technetium and rhenium radiopharmaceuticals: synthesis of [M(9S3)(SC2H4SC2H4S)][BF4] (M = 99Tc, Re, 188Re) via C-S bond cleavage

Chemical or electrochemical reduction of the 1,4,7-trithiacyclononane (9S3) complexes [MII(9S3)2][BF4]2 (M = Re (3a) or Tc (3b)) results in instantaneous C-S bond cleavage to yield ethene and the stable MIII thiolate complexes [MIII(9S3)L][BF4] (M = Re (4a) or Tc (4b), L = SCH2CH2SCH2CH2S). Compounds 4 have been characterized by 1H NMR spectroscopy, and the pseudo-octahedral geometry of 4b has been confirmed by X-ray crystallography. Upon electrochemical reduction 4a loses ethene, while 4b can be reversibly reduced to [TcII(9S3)L], which is then further reduced to Tc(I) with loss of ethene. Successive ethene loss is observed in the mass spectra of compounds 3 and 4. The radiosynthesis of 4a with 188Re can be comfortably completed within 10 min starting with 188ReO4- from a 188W/188Re generator, with a radiochemical yield in excess of 90%, and thus represents a practical approach to the preparation of stable 188Re (and 99mTc) thioether complex derivatives/conjugates for clinical use. Crystal data: 4b, C10H20S6Tc, orthorhombic Pbca, a = 12.233(2) A, b = 14.341(2) A, c = 20.726(3) A, Z = 8.     

Direct isolation of monoclonal antibodies from tissue culture supernatant using the cation-exchange cellulose Express-Ion S

The chromatography of the murine hybridoma cell C595/102 culture supernatant expressing the therapeutic monoclonal antibody C595, on the cation-exchange cellulose Whatman Express-Ion Exchanger S has been investigated. Initial method scouting studies using purified C595 in 1-ml mini columns demonstrated that binding capacity and binding efficiency were dependent not only on decreasing pH but also on the buffer salts used to prepare the mobile phase. Under optimised conditions of 0.1 M sodium acetate buffer, pH 5.0, we were able to separate purified C595 from BSA, the major contaminant in tissue culture fluid. Under these conditions immunoreactive C595 could be isolated directly from tissue culture supernatant. A scale-down study was carried out using a 25-ml column operated at a flow-rate of 150 cm/h which also yielded purified immunoreactive antibody. This procedure should now be suitable for scale-up.     

EXAFS spectroscopic evidence for an Fe=O unit in the Fe(IV) intermediate observed during oxygen activation by taurine:alpha-ketoglutarate dioxygenase

The Fe(II)- and alpha-ketoglutarate-dependent dioxygenases catalyze hydroxylation reactions of considerable biomedical and environmental significance. Recently, the first oxidized iron intermediate in the reaction of a member of this family, taurine:alpha-ketoglutarate dioxygenase (TauD), was detected and shown to be a high-spin Fe(IV) complex. In this study we have used X-ray absorption spectroscopy to demonstrate the presence of a short (1.62 A) interaction between the iron and one of its ligands in the Fe(IV) intermediate but not in the Fe(II) starting complex. The detection of this interaction strongly corroborates the hypothesis that the intermediate contains an Fe=O structural motif.     

Dissociation energetics and mechanisms of leucine enkephalin (M+H)+ and (2M+X)+ ions (X=H, Li, Na, K, and Rb) measured by blackbody infrared radiative dissociation

The dissociation kinetics of protonated leucine enkephalin and its proton and alkali metal bound dimers were investigated by blackbody infrared radiative dissociation in a Fourier-transform mass spectrometer. From the temperature dependence of the unimolecular dissociation rate constants, Arrhenius activation parameters in the zero-pressure limit are obtained. Protonated leucine enkephalin dissociates to form b(4) and (M-H(2)O)(+) ions with an average activation energy (E(a)) of 1.1 eV and an A factor of 10(10.5) s(-1). The value of the A factor indicates that these dissociation processes are rearrangements. The b(4) ions subsequently dissociate to form a(4) ions via a process with a relatively high activation energy (1.3 eV), but one that is entropically favored. For the cationized dimers, the thermal stability decreases with increasing cation size, consistent with a simple electrostatic interaction in these noncovalent ion-molecule complexes. The E(a) and A factors are indistinguishable within experimental error with values of ~1.5 eV and 10(17) s(-1), respectively. Although not conclusive, results from master equation modeling indicate that all these BIRD processes, except for b(4) --> a(4), are in the rapid energy exchange limit. In this limit, the internal energy of the precursor ion population is given by a Boltzmann distribution and information about the energetics and dynamics of the reaction are obtained directly from the measured Arrhenius parameters.     

Simultaneous determination of perhexiline and its monohydroxy metabolites in biological fluids by gas chromatography-electron-capture detection

A rapid and sensitive method for the simultaneous determination of perhexiline and its cis-4-axial and trans-4-equatorial monohydroxy metabolites (M1 and M3, respectively) in human plasma, urine and bile is described. The assay utilises a single diethyl ether extraction, heptafluorobutyric acid anhydride derivatisation and separation and detection by gas chromatography-electron-capture detection. The limits of detection are 0.1 microgram/ml for perhexiline and 0.025 microgram/ml for the M1 and M3 metabolites. This method has been used in a five-day kinetic study of three healthy adult males who ingested a single 300-mg dose of perhexiline maleate. One of these volunteer subjects exhibited elevated plasma perhexiline and markedly reduced plasma and urinary M1 concentrations together with profoundly prolonged plasma and urinary M1 elimination times when compared with the other two subjects. These differences are thought to be of genetic origin. There were also obvious differences in urinary M3 concentrations which were discussed.