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.