C–H Functionalization Strategies in Peptide Synthesis

Recent advances in peptide synthesis have leveraged direct C–H functionalization to streamline the installation of diverse side-chain modifications, cyclisations and labelling motifs without recourse to extensive protecting-group manipulations. By engaging ubiquitous C–H bonds as latent sites for bond formation, chemists now exploit transition-metal catalysis or radical-based methods to achieve precise, site-selective transformations on complex peptide frameworks. These strategies include late-stage arylation, alkylation and trifluoromethylation of aromatic residues, metal-catalysed macrocyclisation to generate stapled or constrained topologies, and incorporation of bioorthogonal handles for imaging or conjugation. Major breakthroughs have centred on the design of internal directing groups and the development of mild, additive-free conditions compatible with unprotected peptides. Together, these innovations open new avenues for rapid generation of peptide libraries, enhanced metabolic stability and the creation of multifunctional peptide-based probes and therapeutics.

Research from Nature Portfolio

In 2023, a rhodium(III)-catalysed protocol enabled direct C(7)–H maleimidation of tryptophan residues, affording cyclic and clickable peptide architectures in high regioselectivity and with broad functional-group tolerance. The resulting maleimide–tryptophan adducts proved competent in Michael-type click conjugations and were applied to assemble peptide–drug conjugates with enhanced cellular uptake and antiproliferative activity. A 2021 study introduced an earth-abundant manganese(I) catalyst for direct alkynylation and alkenylation of peptide C–H bonds, yielding modular fluorogenic probes on unprotected peptides. This method accommodated sensitive side chains and permitting assembly of BODIPY-tagged peptides for real-time fluorescence imaging. Complementing these approaches, a 2019 report established a ruthenium(II)-catalysed C–H alkylation manifold operative on solid-phase supports. The additive-free, racemisation-free procedure enabled late-stage installation of alkyl fragments directly on resin-bound peptides, thereby facilitating bioorthogonal diversification within standard solid-phase peptide synthesis workflows.

C–H Functionalization Strategies in Peptide Synthesis publication trend

The graph below shows the total number of articles in c–h functionalization strategies in peptide synthesis across all publications each year (not limited to Nature Index journals).

Technical terms

C–H functionalization: Direct conversion of carbon–hydrogen bonds into new carbon–heteroatom or carbon–carbon bonds, bypassing pre-installed functional groups.

Late-stage modification: Introduction of new chemical functionality into a complex molecule at a late point in its synthetic sequence, minimising protecting-group steps.

Directing group: A native or installed moiety that coordinates to a metal catalyst to guide and activate a specific C–H bond toward transformation.

Bioorthogonal reaction: A chemical reaction that can proceed inside living systems without perturbing native biochemical processes or biomolecules.

Regioselectivity: Preference for bond formation at one specific position among several possible sites on a molecule.

Solid-phase peptide synthesis (SPPS): A method in which peptides are assembled stepwise on insoluble resin beads, allowing repeated cycles of coupling and deprotection without isolating intermediates.

Photoredox catalysis: Use of light-activated catalysts to generate reactive radical intermediates under mild conditions for C–H functionalization.

References

1. Modular synthesis of clickable peptides via late-stage maleimidation on C(7)-H tryptophan. Nature Communications (2023).
2. Chemodivergent manganese-catalyzed C–H activation: modular synthesis of fluorogenic probes. Nature Communications (2021).
3. Late-stage peptide C–H alkylation for bioorthogonal C–H activation featuring solid phase peptide synthesis. Nature Communications (2019).
4. Protecting group free radical C–H trifluoromethylation of peptides. Chemical Science (2018).
5. Pd-catalyzed site-selective C(sp 2 )–H radical acylation of phenylalanine containing peptides with aldehydes. Chemical Science (2019).
6. Photocatalytic methods for amino acid modification. Chemical Society Reviews (2021).