Tetrazine–trans-cyclooctene ligation for the rapid construction of 18F labeled probes

Abstract

A radiolabeling method for bioconjugation based on the Diels-Alder reaction between 3,6-diaryl-s-tetrazines and an 18F-labeled trans-cyclooctene is described. The reaction proceeds with exceptionally fast rates, making it an effective conjugation method within seconds at low micromolar concentrations.

Development and Evaluation of 18F-TTCO-Cys40-Exendin-4: A PET Probe for Imaging Transplanted Islets

“…The solution was incubated for 30 min at 25°C, and the product was purified by high-performance liquid chromatography (HPLC). 19 F-trans-cyclooctene ( 19 F-TCO) was prepared according to our previously reported procedure (20). 19 F-TCO (0.5 mg, 3 mmol) and tetrazine-Cys 40 -exendin-4 (2 mg, 0.42 mmol) were incubated at room temperature, and the product was purified by HPLC.…”

“…Although the traditionally used 18 F-labeling method, such as N-2-(4-18 F-fluorobenzamido)ethylmaleimide ( 18 F-FBEM) (17,18) and 18 F-fluorobenzaldehyde (19), had been used for producing exendin-based tracers, it is difficult to completely separate the 18 F-labeled compound from the precursor as the difference is relatively small and thus may induce a blocking effect to some extent. Recently, an ultra-efficient 18 F-labeling method was developed by our group based on the tetrazine trans-cyclooctene (TTCO) ligation (20,21). Here, we report the synthesis of 18 F-labeled exendin-4 through this efficient method for in vivo imaging of GLP-1 receptor.…”

A New Highly Reactive and Low Lipophilicity Fluorine-18 Labeled Tetrazine Derivative for Pretargeted PET Imaging

“…19 A 18 F-labeled TCO derivative has been successfully used as a prosthetic group in radiolabeling of peptides and proteins. 9 The use of TCO as a radiolabeled tracer in vivo has failed due to rapid isomerization of TCO in plasma to its less reactive isomer, cis-cyclooctene (CCO), by copper-containing biomolecules. 20 Therefore, the radiolabeling of TCO to accomplish in vivo bioorthogonal reaction has proven to be an unsuccessful strategy.…”

“…12,14 When clinical applications of pretargeted PET imaging are considered, 18 F would be the ideal isotope due to its general availability and optimal physical properties. 9,21,22 However, due to the instability of the tetrazine moiety under conditions typically used in direct 18 Ffluorination, no 18 F-tetrazine was synthesized until very recently. 23−25 A recently reported 18 F propyl tetrazine was synthesized via a direct 18 F-fluorination only in low radiochemical yields (4−18% decay corrected yield), but favorable pharmacokinetics in vivo.…”

Click Reaction: An Applicable Radiolabeling Method for Molecular Imaging

“…The IEDDA reaction is selective, high-yielding, clean, biocompatible and bioorthogonal. In 2011, Li et al reported the first application of the IEDDA ligation in radiochemistry using an 18 F-labeled trans-cyclooctene ( 18 F-TCO) [41]. The synthesis of 18 F-TCO was performed under relatively mild radiolabeling conditions to afford the desired product in yields of up to~70 %; next a rapid, selective, and clean IEDDA ligation was performed without the need for any catalyst ( Table 2, entry 1).…”