CONFORMATION OF CYCLO(-l-PRO-d-LEU-d-TYR(ME)-l-ILE-) PREDICTED BY EMPIRICAL RULES FOR CYCLIC TETRAPEPTIDES WAS EVIDENCED BY 1H- AND 13C-NMR SPECTROSCOPY

The predicted cis-trans-cis-trans backbone conformation of cyclo(-l-Pro-d-Leu-d-Tyr(Me)-l-Ile-) (2) has been evidenced by 1H-NMR experiments. Peptide 2 and cyclo(-l-Pro-l-Leu-d-Tyr(Me)-l-Ile-) are the first diaste-reomeric peptides having cis (Dd) and trans (Ld) Leu-Tyr(Me) peptide bonds.