“…All alanyl methyl substituents adopt the syn configuration with respect to the oxotechnetium group. Technetium bond lengths are given in Table and are very similar to those reported in the literature for other technetium(V) oxo complexes. − 3 ORTEX drawing of the anion (cyclotetra- l -alanyl)oxotechnetium(V).…”
Section: Resultssupporting
confidence: 67%
“…Technetium bond lengths are given in Table 3 and are very similar to those reported in the literature for other technetium(V) oxo complexes. [23][24][25] The conversion of 99m Tc-A4-A to 99m Tc-A4-B follows firstorder kinetics, and the rate is largely dependent on the pH. The conversion proceeds with the highest rate at pH 6, whereas at pH 10 no conversion was observed (Table 4).…”
Complexation of technetium with tetraalanine yields an unstable
complex that converts to a monooxotechnetium(V)
complex of cyclic tetraalanine. The structure of the latter was
determined by single-crystal X-ray analysis. In
this negatively charged complex, the technetium atom is coordinated to
one oxygen and four amide nitrogen
atoms. The more polar complex that is initially formed is assumed
to be an oxotechnetium(V) complex of
tetraalanine, with the oxotechnetium moiety coordinated to three amide
nitrogen atoms and the amine nitrogen
atom. In this complex, the carboxyl group would be forced in the
vicinity of the free amine group, thereby
facilitating amide formation and cyclization. Cyclization of
tetra-l-alanine occurs on both no carrier
added
(technetium-99m) and carrier added (technetium-99) scale.
“…All alanyl methyl substituents adopt the syn configuration with respect to the oxotechnetium group. Technetium bond lengths are given in Table and are very similar to those reported in the literature for other technetium(V) oxo complexes. − 3 ORTEX drawing of the anion (cyclotetra- l -alanyl)oxotechnetium(V).…”
Section: Resultssupporting
confidence: 67%
“…Technetium bond lengths are given in Table 3 and are very similar to those reported in the literature for other technetium(V) oxo complexes. [23][24][25] The conversion of 99m Tc-A4-A to 99m Tc-A4-B follows firstorder kinetics, and the rate is largely dependent on the pH. The conversion proceeds with the highest rate at pH 6, whereas at pH 10 no conversion was observed (Table 4).…”
Complexation of technetium with tetraalanine yields an unstable
complex that converts to a monooxotechnetium(V)
complex of cyclic tetraalanine. The structure of the latter was
determined by single-crystal X-ray analysis. In
this negatively charged complex, the technetium atom is coordinated to
one oxygen and four amide nitrogen
atoms. The more polar complex that is initially formed is assumed
to be an oxotechnetium(V) complex of
tetraalanine, with the oxotechnetium moiety coordinated to three amide
nitrogen atoms and the amine nitrogen
atom. In this complex, the carboxyl group would be forced in the
vicinity of the free amine group, thereby
facilitating amide formation and cyclization. Cyclization of
tetra-l-alanine occurs on both no carrier
added
(technetium-99m) and carrier added (technetium-99) scale.
to the metal are capable of binding nonsynergistic anions and of affecting the reactivity of the metal.24,25 A different spatial arrangement of these clusters of positive charges in the two sites could account for the intersite differences. Refinement at higher resolution of the X-ray three-dimensional structure, which is now available for iron lactoferrin at 3.2-Á resolution,26 could give the appropriate answers.The results of the kinetic experiments on other metallotransferrins such as manganese(III) transferrin and copper(II) transferrin give us the opportunity of discussing the role played by the metal in the overall process.In the case of manganese(III) transferrin, the profiles of the kinetic parameters versus PP concentration strictly resemble those observed for iron transferrin. Again, the data may be reproduced quite well with eq 2. The major difference between the two series of data resides in the fact that for the same values of PP concentration both of the kinetic constants of the manganese derivative are about 1 order of magnitude larger than the corresponding kinetic constants of iron transferrin. This suggests that the same
“…Comparing 9 with [ 99m Tc]technepine 7 shows the Ga‐DO3A chelator is larger than its Tc‐MAMA (monoamine–monoamide dithiol) counterpart. Although a larger ligand field is formed by the longer Tc−S bonds (∼2.25 Å) compared to Ga−O (∼1.93 Å), the Ga‐DO3A complex is octahedral compared to the square‐pyramidal Tc–MAMA complex, occupying much more space on the z ‐axis through the carboxy groups lying opposite [19,20] . The C 3 linker therefore seems to be the breakpoint.…”
Section: Resultsmentioning
confidence: 98%
“…Although a larger ligand field is formed by the longer TcÀ S bonds (~2.25 Å) compared to GaÀ O (~1.93 Å), the Ga-DO3A complex is octahedral compared to the squarepyramidal Tc-MAMA complex, occupying much more space on the z-axis through the carboxy groups lying opposite. [19,20] The C 3 linker therefore seems to be the breakpoint. With the help of the hexadiyne structure in 11, an IC 50 value of 157 nM comparable to cocaine could be achieved.…”
The development of radiometal‐labelled pharmaceuticals for neuroimaging could offer great potential due to easier handling during labelling and availability through radionuclide generator systems. Nonetheless, to date, no such tracers are available for positron emission tomography, primarily owing to the challenge of crossing the blood–brain barrier (BBB) and loss of affinity through chelator attachment. We have prepared a variety of 68Ga‐labelled phenyltropanes showing that, through a simple hydrocarbon‐linker, it is possible to introduce a chelator onto the lead structure while maintaining its high affinity for hDAT (human dopamine transporter) and simultaneously achieving adequate lipophilicity. One of the candidates, [68Ga]Ga‐HBED‐hexadiyne‐tropane, showed an IC50 value of 66 nM, together with a log D7.4 of 0.96. A μPET study in a hemi‐parkinsonian rat model showed a fast wash‐out of the tracer, and no specific uptake in the brain, thus implying an inability to penetrate the BBB.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
