Chemoenzymatic synthesis and incorporation of -2-quinoxalylalanine into a tandem β-turn peptide motif

-2-Quinoxalylalanine was synthesized chemoenzymatically and incorporated through solid-phase peptide synthesis at both termini of one repeat unit of the carboxy-terminal domain (CTD) of RNA polymerase II. The resulting structure closely resembles members of the quinoxaline class of bis-intercalating antitumor antibiotics and may eventually assist in probing the DNA binding mechanism of the CTD.