The well-known Merrifield peptide synthesis, named after its inventor R. Bruce Merrifield, allows all reaction steps, including washing, to be carried out in the same reaction vessel thus paving the way for the synthetic production of peptides as well as for automated synthesis by machines. The C-terminus of the first amino acid is attached to a solid support, typically low-crosslinked polystyrene beads. Stepwise, the peptide chain is then grown from the C- to the N-terminus by repetitive cycles of coupling and deprotection of N-alpha protected amino acids. Separation and purification are accomplished by filtering and washing the beads with appropriate solvents. In the final step, the desired full-length peptide is cleaved from the solid support.

With the introduction of the base-labile 9-fluorenylmethoxycarbonyl (Fmoc) amino protecting group by Carpino and Han, the solid-phase peptide synthesis (SPPS) was further improved as TFA-labile groups can now be used for side chain protection. In addition, the fluorescence property of the dibenzofulvene adducts formed after treatment of the Fmoc resin with piperidine enables the estimation of the efficiency of each peptide coupling step.

Nowadays, commercially available automated peptide synthesizers are repeating deprotection, coupling, and washing steps "on their own", allowing for the fast and convenient simultaneous synthesis of peptides. Especially for long sequences, this automation saves resources and helps to minimize potential human sources of error. Even heating can be performed via microwave-assisted systems.

Besides natural amino acids, modified building blocks can also be introduced. Especially the incorporation of side-chain clickable amino acids and building blocks opens the door for a variety of applications, e.g. macrocyclization, labeling or any type of further conjugation. Due to its high thermodynamic driving force, which is usually greater than 20 kcal/mol, the click reaction of an alkyne and an azide rapidly proceeds to completion in almost all cases. Besides, it is orthogonal to many other types of chemical transformations.

In our online workshop “Click Chemistry in the Context of Automated Peptide Synthesis” we showcase the incorporation of alkyne- and azide-modified amino acids and Biotin building blocks, respectively, by using automated synthesis.

• Interested? Register for our online workshop on December 13^th, 3 pm CET! 
• You want to learn more about Click Chemistry? Download our brochure! 

References:

Automated Peptide Synthesizers and Glycoprotein Synthesis; J. Tian, Y. Li, B. Ma, Z. Tan, S. Shang; Front. Chem. 2022; 10. https://doi.org/10.3389/fchem.2022.896098

Automated Solid-Phase Peptide Synthesis; D. F. H. Winkler; Methods Mol. Biol. 2020; 2103: 59-94. https://doi.org/10.1007/978-1-0716-0227-0_5