title: Combining bifunctional chelator with (3 + 2)-cycloaddition approaches: synthesis of dual-function technetium complexes.
abstract: A new concept for the synthesis of dual-functionalized technetium (Tc) compounds is presented, on the basis of the reactivity of fac-{Tc(VII)O(3)}(+) complexes. The concept combines the "classical" bifunctional chelator (BFC) approach with the new ligand centered labeling strategy of fac-{TcO(3)}(+) complexes with alkenes ((3 + 2)-cycloaddition approach). To evidence this concept, fac-{(99)TcO(3)}(+) model complexes containing functionalized 1,4,7-triazacyclononane (tacn) derivatives N-benzyl-2-(1,4,7-triazonan-1-yl)acetamide (tacn-ba) and 2,2',2″-(1,4,7-triazonane-1,4,7-triyl)triacetic acid (nota·3H) were synthesized and characterized. Whereas [(99)TcO(3)(tacn-ba)](+) [2](+) can be synthesized following a established oxidation procedure starting from the Tc(V) complex [(99)TcO(glyc)(tacn-ba)](+) [1](+), a new synthetic pathway for the synthesis of [(99)TcO(3)(nota)](2-) [5](2-) had to be developed, starting from [(99)Tc(nota·3H)(CO)(3)](+) [4](+) and using sodium perborate tetrahydrate (NaBO(3)·4H(2)O) as oxidizing reagent. While [(99)TcO(3)(nota)](2-) [5](2-) is a very attractive candidate for the development of trisubstituted novel multifunctional radioprobes, (3 + 2)-cycloaddition reactions of [(99)TcO(3)(tacn-ba)](+) [2](+) with 4-vinylbenzenesulfonate (styrene-SO(3)(-)) demonstrated the suitability of monosubstituted tacn derivatives for the new mixed "BFC-(3 + 2)-cycloaddition" approach. Kinetic studies of this reaction lead to the conclusion that the alteration of the electronic structure of the nitrogen donors by, e.g., alkylation can be used to tune the rate of the (3 + 2)-cycloaddition.
authors.affiliation: Institute of Inorganic Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland. braband@aci.uzh.ch
authors.forename: Henrik
authors.initials: H
authors.lastname: Braband
authors.forename: Sebastian
authors.initials: S
authors.lastname: Imstepf
authors.forename: Michael
authors.initials: M
authors.lastname: Benz
authors.forename: Bernhard
authors.initials: B
authors.lastname: Spingler
authors.forename: Roger
authors.initials: R
authors.lastname: Alberto
mesh_terms: D001881:Borates / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006571:Heterocyclic Compounds / Q000737:chemistry; D006801:Humans; D007553:Isotope Labeling / Q000379:methods; D007700:Kinetics; D008024:Ligands; D015394:Molecular Structure; D015609:Organotechnetium Compounds / Q000138:chemical synthesis*; D010084:Oxidation-Reduction; D019275:Radiopharmaceuticals / Q000138:chemical synthesis*; D013667:Technetium / Q000737:chemistry*
chemical_list: D001881:Borates; D002614:Chelating Agents; D006571:Heterocyclic Compounds; D008024:Ligands; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C075712:1,4,7-triazacyclononane; D013667:Technetium; C027707:sodium perborate