Sequence-Specific β-Peptide Synthesis by a Rotaxane-Based Molecular Machine

We report on the synthesis and operation of a three-barrier, rotaxane-based, artificial molecular machine capable of sequence-specific beta-homo (beta(3)) peptide synthesis. The machine utilizes nonproteinogenic beta(3)-amino acids, a class of amino acids not generally accepted by the ribosome, particularly consecutively. Successful operation of the machine via native chemical ligation (NCL) demonstrates that even challenging 15- and 19-membered ligation transition states are suitable for information translation using this artificial molecular machine. The peptide-bond-forming catalyst region can be removed from the transcribed peptide by peptidases, artificial and biomachines working in concert to generate a product that cannot be made by either machine alone.