Cyclic peptides. XIV. Syntheses of [4-l-leucine]-, [4-D-leucine]-, and [3-L-proline, 4-D-leucine]-Cyl-2.

Cyl-2 is a phytotoxic cyclic tetrapeptide with the sequence of cyclo(D-Tyr(Me)-L-Ile-L-Pip-Aoe-): Aoe, 2-amino-8-oxo-9,10-epoxydecanoic acid. The configuration of Aoe is unknown. Three analogs, cyclo(-D-Try(Me)-L-Ile-L-Pip-L(and D)-Leu-) (1 and 2) and cyclo(-D-Tyr(Me)-L-Ile-L-Pro-D-Leu-) (3), were synthesized and spectroscopic features of these analogs were compared. 1H-N.m.r. spectra of cyclo(D-Tyr(Me)-L-Ile-L-Pip-L-Leu) (1), cyclo(-D-Tyr(Me)-L-Ile-L-Pro-L-Leu-) (4), and Cyl-2 showed a similar pattern. On the other hand, the spectra of analogs 2 and 3 showed a different pattern, the Ile-Pro bond in 3 being in cis conformation.