(S)-C-ALPHA-ETHYL, C-ALPHA-BENZYLGLYCINE [(S)-(ALPHA-ET)PHE] PEPTIDESFOLD IN LEFT-HANDED HELICAL STRUCTURES

The first x-ray diffraction structure analysis of a C-alpha-ethyl, C-a lpha-benzylglycine [(alpha Et)Phe]-containing peptide, obutyryl-alpha- amino-isobutyryl-(S)-C-alpha-ethyl, C-alpha-benzylglycal-alpha-aminois obutyric acid (methanol solvate), has been performed. In the crystal s tate the N-alpha-protected tetrapeptide is folded iii all incipient, l eft-handed 3(10)-helical structure. This finding confirms that the rel ationship between (alpha Et)Phe alpha-carbon chirality and screw sense of the helix that is formed is opposite to that exhibited by protein amino acids, including Phe.