U.S. Department of Energy

Pacific Northwest National Laboratory

Alkyne-Substituted Unnatural Tryptophan Moieties

The cover of Organic Chemistry.

The Science                      

There is a great demand for chemical probes that can mimic and react analogously to biological molecules, and that can be used to investigate cellular processes. One class of chemical probes are non-canonical amino acids that can be incorporated into elongating proteins. These non-canonical amino acids facilitate the incorporation of a unique chemical structure into proteins, allowing for downstream bioorthogonal reactions and analysis. This can enable the sensitive detection and identification of newly synthesized proteins within defined time intervals.  

Synthesizing non-canonical amino acids is accomplished by modifying the alpha-carbon (alpha-carbon). These unnatural alpha-carbonderivativeshave been shown to mimic natural amino acids and are actively incorporated into proteins. Chemical synthesis of non-canonical aromatic amino acids has been limited due to the difficulty of modifying the ring structure.

An Organic Chemistry Frontierspaper from researchers at the Pacific Northwest National Laboratory (PNNL), led by Aaron Wright, reports the de novosynthesis of new alkyne-substituted tryptophan. The alkyne moiety enables multimodal analyses through the attachment of different reporter groups mediated by click chemistry. The group was able to synthesize a suite of tryptophan molecules that varied in size and composition.  

The Impact

These new non-canonical tryptophan molecules have the potential to help scientists understand the biologically active conformations of peptides, and can be used to analyze protein synthesis. Future synthesis would include the incorporation of a diazirine to enable applications of protein-profiling studies and the identification of proteins that bind tryptophan.


There is continued desire to be able to synthesize molecules that mimic biologically active metabolites. Using non-canonical amino acidsfacilitates determining newly synthesized proteins from the total proteome, and identifying cellular interactions.  

Synthesizing aromatic non-canonical aminoacids, including tryptophan, is now possible due to the Wright group at PNNL, which has identified a synthesis route to create them. The group demonstrated that these alkyne-substituted tryptophan molecules can be incorporated into proteins. This is a first step towards the group’s goal of developing an alkynylated version of tryptophan that would allow them to evaluate both incorporating unnatural amino acids into proteins and characterizing amino acid-protein binding.


This research was funded by the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory and the Foundational Scientific Focus Area program sponsored by the U.S. Department of Energy, Office of Biological and Environmental Research, as part of its Genomic Science Program.  


Nair RN, JJ Rosnow, TA Murphree, ME Bowden, SR Lindemann, and AT Wright. 2017. “De novosynthesis of alkyne substituted tryptophans as chemical probes for protein profiling studies.” Org. Chem. Front. 4 (495-499). DOI: 10. 1039/C6QO00819D


December 2016
| Pacific Northwest National Laboratory