Amino Acids for Diels–Alder Reactions in Living Cells

Abstract

Under tension: A set of genetically encoded unnatural amino acids can be used for biocompatible site‐specific labeling of proteins with fluorogenic dyes. The new compounds have norbornene and trans‐cyclooctene units that react with tetrazine derivatives in an inverse‐electron‐demand Diels–Alder cycloaddition (left in picture). The technique offers fast labeling that is orthogonal to labeling through azide–cyclooctyne click reaction (right).

Biocompatible Silicon Surfaces through Orthogonal Click Chemistries and a High Affinity Silicon Oxide Binding Peptide

“…28,29 Furthermore, it shows excellent bio-orthogonality and irreversibility. 30,31 In this work, we report on the development of a high affinity silicon oxide binding peptide (highSP) by rational design from a weak binding precursor (SP). 32 The binding properties of the peptides were studied by a biotin-ELISA and atomic force microscopy and revealed a sigmoidal binding behavior with nanomolar affinity of highSP.…”

Norbornenes in Inverse Electron‐Demand Diels–Alder Reactions

“…Indeed, others and us used the unusual reactivity of norbornene [26,27] to label nucleic acids [28][29][30] and proteins. [31][32][33][34] We therefore reasoned that we should investigate the parameters that determine the reactivity of norbornenes and of heteroatom-containing norbornene derivatives [35] with tetrazines to find the best reaction partner in the DAR inv for biomolecule labeling. Here we show that the substitution pattern and in particular the presence of heteroatoms has a dramatic influence on the reactivity (Scheme 1).…”

Single-molecule FRET and crosslinking studies in structural biology enabled by noncanonical amino acids

“…Some proteins are sensitive to the copper catalyst and require extremely mild labeling conditions. In this respect, other 'clickable' ncAAs such as those containing strained cyclooctyne (SCO) [25], trans-cyclooctene (TCO) [26,27], and bicyclononyne (BCN) [28,29] groups provide potential solutions for the site-specific labeling of proteins under fully physiological and catalyst free conditions [19]. Whereas the potential has been nicely demonstrated for various model systems, the high cost of ring-strained ncAAs remains a limiting factor for engineering proteins that are difficult to express.…”