Scheme 3. Top: synthesis of the GCN4/AT-hook chimera BR(Hk)-Br. See Scheme 1 for solid phase peptide synthesis of BR[Lys(O1Pen)]. Also note that the bromoacetyl unit was introduced in the side chain of the N-terminal lysine of the AT-hook, using Boc-Lys(Fmoc)-OH as orthogonal amino acid. Bottom: chemoselective modification of the GAGA Cys₂His₂ peptide in solution.