Proteinase K‑Catalyzed Synthesis of Linear and Star Oligo(l‑phenylalanine) Conjugates

Chemoenzymatic synthesis of peptides is a green and clean chemical reaction that offers high yields without using organic synthesis and serves as an alternative to traditional peptide synthesis methods. This report describes the chemoenzymatic synthesis of oligo­(l-phenylalanine) mediated by proteinase K from Tritirachium album, which is one of the most widely used proteases in molecular biological studies. The synthesized linear oligo-phenylalanine showed a unique self-assembly in aqueous solutions. To further functionalize linear oligo­(l-phenylalanine) as a low-molecular-weight gelator, it was cosynthesized with tris­(2-aminoethyl)­amine to obtain star-oligo­(l-phenylalanine), which was bioconjugated to demonstrate its self-assembly into fluorescent fibers. The self-assembled fibers of star-oligo­(l-phenylalanine) formed fibrous networks with various branching ratios, which depended on the molecular weights and molecular aspect ratios of star-oligo­(l-phenylalanine). This is the first study to demonstrate that proteinase K is a suitable enzyme for chemoenzymatic cosynthesis of oligopeptides and star-shaped heteropeptides.