Solid-phase synthesis of peptides containing the spin-labeled 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC)

2,2,6,6-Tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) is a nitroxide spin-labeled, achiral C-alpha-tetrasubstituted amino acid recentl y shown to be not only an effective beta -turn and 3(10)/alpha -helix promo ter in peptides, but also an excellent rigid electron paramagnetic resonanc e probe and fluorescence quencher. Here, we demonstrate that TOAC can be ef fectively incorporated into internal positions of peptide sequences using F moc chemistry and solid-phase synthesis in an automated apparatus.