A super versatile flexizyme system with phenol esters for genetic code reprogramming

Genetic code reprogramming enables ribosomal incorporation of multiple nonproteinogenic amino acids (npAAs), supporting bioactive peptide development. Flexizyme technology with npAA-benzyl(thio)esters (BZEs) as acyl-donors has been crucial for preparing diverse npAA-tRNAs. However, low acylation yields for some npAAs hinder peptide library construction. Here we report a versatile flexizyme system using phenol esters as alternative acyl-donors. Computational pK_a predictions guided the synthesis of five phenol esters, which are mild enough to prevent random aminoacylation yet reactive with tRNA 3'-hydroxy groups. Among them, 3-nitrophenol (3NP) was chosen to prepare 18 structurally distinct npAA-3NPs, demonstrating direct tRNAs aminoacylation in 15-41% yields. Moreover, the flexizyme eFx drastically enhances aminoacylation efficiency, yielding near-quantitative conversion for some npAAs, e.g. cyclic β-npAAs. This eFx/npAA-3NP system facilitates access to diverse npAA-tRNAs, expanding ribosomal synthesis of nonstandard peptides, including macrocyclic structures. Thus, our approach provides an efficient tool for constructing peptide libraries with multiple npAA building blocks.