A Dual‐Purpose Non‐Canonical Amino Acid for the Expanded Genetic Code: Combining Metal‐Binding and Click Chemistry

• Published in: Angewandte Chemie International Edition 2024-12, Vol.63 (52), p.e202413073-n/a
• Main Authors: Day, Graham J., Zaytsev, Andrey V., Brewster, Richard C., Kozhevnikov, Valery N., Jarvis, Amanda G.
• Format: Article
• Language: English
• Subjects: Amino acids; Amino Acids - chemistry; bioorthogonal reactivity; Catalysis; Chemical reactions; Chemical synthesis; Click Chemistry; Communication; Cycloaddition Reaction; Genetic Code; genetic code expansion; Iridium; Iridium - chemistry; Labeling; luminescent probes; Metal ions; Monitoring methods; non-canonical amino acids; Optical properties; Payloads; Proteins; Scaffolds; Triazine; Triazines - chemistry
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202413073

A rationally designed dual‐purpose non‐canonical amino acid (Trz) has been synthesised and successfully incorporated into a protein scaffold by genetic code expansion. Trz contains a 5‐pyridyl‐1,2,4‐triazine system, which allows for inverse‐electron‐demand Diels–Alder (IEDDA) reactions to occur on the triazine ring and for metal ions to be chelated both before and after the click reaction. Trz was successfully incorporated into a protein scaffold and the IEDDA utility of Trz demonstrated through the site‐specific labelling of the purified protein with a bicyclononyne. Additionally, Trz was shown to successfully coordinate a cyclometallated iridium(III) centre, providing access to a bioorthogonal luminogenic probe. The luminescent properties of the Ir(III)‐bound protein blue‐shift upon IEDDA click reaction with bicyclononyne, providing a unique method for monitoring the extent and location of the labelling reaction. In summary, Trz is a new dual‐purpose non‐canonical amino acid with great potential for myriad bioapplications where metal‐based functionality is required, for example in imaging, catalysis, and photo‐dynamic therapy, in conjunction with a bioorthogonal reactive handle to impart additional functionalities, such as dual‐modality imaging or therapeutic payloads. Genetic code expansion strategies tend to incorporate non‐canonical amino acids (ncAAs) with singular, specialised functions into proteins. In this study, a dual‐purpose ncAA that can undergo inverse‐electron‐demand Diels–Alder (IEEDA) reactions and coordinate luminogenic metal complexes was designed, synthesised, and incorporated into a protein. Significantly, luminescence studies revealed emission shifts upon dual functionalisation.