Conformationally-constrained, nitroxide, achiral, Cα-tetrasubstituted α-amino acid used as a spin-label for protein structure determination. Prepn: A. Rassat, P. Rey, FR 1501917 (1967 to Commissariat à l'Energie Atomique); eidem, Bull. Soc. Chim. Fr. 1967, 815. Use as probe for structure conformation studies: T. A. Pertinhez et al., Biopolymers 42, 821 (1997); T. T. T. Bui et al., J. Chem. Soc. Perkin Trans. 2000, 1043; of interchain interactions: A. Polese et al., J. Am. Chem. Soc. 121, 11071 (1999).