On-Resin Ugi Reaction for C-Terminally Modified and Head-to-Tail Cyclized Antibacterial Peptides.

Here we report a method to synthesize C-terminally modified peptides on resin. A four-component Ugi reaction of isocyanide resin, an Fmoc-protected amino acid, an amine, and a 6-nitroveratrylaldehyde gives C-terminal photocaged peptide amides, which can be photolyzed to generate C-terminal peptide amides. Changing the amine component in the Ugi reaction gives peptides with different C-terminal modifications including substituted anilides, alkyne, and azide.

On-Resin Passerini Reaction toward C-Terminal Photocaged Peptides.

An on-resin, three-component Passerini reaction was developed to synthesize C-terminal photocaged peptides. Highly compatible with conventional Fmoc SPPS, this reaction produces peptides with a C-terminal -amido-6-nitroveratryl (αANV) ester in one pot with conserved chirality. Under physiological conditions, the C-terminal αANV ester rapidly photolyzed to revert to carboxylate, offering a convenient method for optical control of cellular signals by modulating the C-terminal carboxylate.

Site-selective covalent reactions on proteinogenic amino acids.

To achieve precise control of the signaling events or to achieve unmistakable synthesis of biomolecules, nature has evolved organic reactions involving proteinogenic amino acids with unparalleled site selectivity. For example, dedicated enzymes accurately dictate the site of post-translational modifications in signaling proteins, and ribosomes precisely link the C-terminal carboxylic acid of one unprotected amino acid with the N-terminal amino group of the other amino acid through spatially confined proximity. For many years, chemists have been striving to achieve site selectivity on biomolecules by mimicking nature.