A micro-reactor was applied to produce ortho-substituted [ 18 F]fluoroarenes from the reactions of cyclotron-produced [ 18 F]fluoride ion (t 1/2 = 109.7 min) with diaryliodonium salts. The micro-reactor provided a very convenient means for running sequential reactions rapidly with small amounts of reagents under well-controlled conditions, thereby allowing reaction kinetics to be followed and Arrhenius activation energies (E a ) to be measured. Prepared symmetrical iodonium chlorides (Ar 2 I + Cl − ) rapidly (< 8 min) gave moderate (Ar = 2-MeOC 6 H 4 , 51%) to high (Ar = Ph or 2-MeC 6 H 4 , 85%) decay-corrected radiochemical yields (RCYs) of a single radioactive product (Ar 18 F). Reaction velocity with respect to Ar group was 2-MeOC 6 H 4 < Ph < 2-MeC 6 H 4 . Activation energies were in the range 18-28 kcal/mol. Prepared unsymmetrical salts (e.g., 2-RC 6 H 4 I + 2'-R'C 6 H 4 X − ; X = Cl or OTs) also rapidly gave two products (2-RC 6 H 4 18 F and 2-R'C 6 H 4 18 F) in generally high total RCYs (79-93%). Selectivity for product [ 18 F]fluoroarene was controlled by the nature of the ortho substituents. The power of ortho substituents to impart an ortho effect was in the following order, 2,6-di-Me > 2,4,6-tri-Me > Br > Me > Et ∼ i Pr >> H > OMe. For (2-methyphenyl) (phenyl)iodonium chloride, the time-course of reaction product selectivity was constant and consistent with the operation of the Curtin-Hammett Principle. These results will aid in the design of diaryliodonium salt precursors to 18 F-labeled tracers for molecular imaging.
Single crystal X-ray diffraction show that Zr(IV) forms an octa-coordinated complex with 4 bidentate hydroxamates whose solution structures were investigated utilizing density functional theory at the level of B3LYP/DGDZVP. Stability constants obtained by potentiometry were in accordance with the tendency observed when radiolabeling with 89Zr.
A rigidified and symmetrical polymethylated 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) ligand bearing four SSSS methyl groups in both the tetraaza ring and the acetate arms (SSSS-SSSS-M4DOTMA) was prepared. The isomer ratio of SSSS-SSSS-M4DOTMA complexed with a series of lanthanide ions was carefully investigated using RP-HPLC and NMR. A square antiprismatic (SAP) configuration was exclusively observed for the early lanthanides, while the twisted square antiprismatic (TSAP) geometry was preferred as the lanthanide ion size decreases. The late lanthanides preferentially adopted the TSAP geometry. One of the pendant arms was modified with a pyridyl disulfide group (SSSS-SSSS-M8SPy) for cysteine attachment and displayed a similar isomer trend as the parent compound, Ln-SSSS-SSSS-M4DOTMA. Covalent attachment to the ubiquitin S57C mutant showed resonances whose intensities are in agreement with the isomeric population observed by HPLC. Furthermore, the NOE experiments combined with quantum chemical calculations have unequivocally demonstrated that the SAP of Pr-SSSS-SSSS-M4DOTMA and Pr-SSSS-SSSS-M8SPy, as well as the TSAP of Yb-SSSS-SSSS-M8SPy are more stable than their corresponding isomers.
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