Zur konformation geschützter aminosäuren—I: NMR-untersuchungen von t-BOC-glycin

Z, E-Isomerism of the urethane bond of t-BOC-glycine was observed by ¹H- and ¹³C-NMR spectroscopy at various temperatures in several solvents. The special stabilization of the Z isomer at low temperatures in CDCl₃ has been explained by intra- and intermolecular H-bond forming a 7-membered ring. Thermodynamic data have been determined for the ground state (AH°= ?7 kcal/mol, Δ° = ?25 Clausius) as well asfor the barrier of interconversion (ΔG° = 15·4 kcal/mole for the deuterated title compound) in CDCl₃. The equilibrium between the Z and the E conformation is shifted towards the E conformation in more polar solvents (acetonitril-d₃, acetone-d₆, DMSO-d₆), in which cyclization of the Z conformation is not important.