Cyclic peptides. XIX. Synthesis, conformation, and biological activity of cyclo(-Pro-Val-Pro-Val-) with L-L-L-L and L-D-L-D sequences.

cyclo(-L-Pro-L-Val-L-Pro-L-Val-) (1L) and cyclo(-L-Pro-D-Val-L-Pro-D-Val-) (1D) were synthesized by the conventional method for peptide synthesis. Conformations of 1L and 1D in solution were studied. Compound 1L has a cis-trans-cis-trans backbone conformation with C2 symmetry in CDCl3. This conformation is slightly different from that in crystalline state and in DMSO-d6 solution. Compound 1D has a cis-trans-cis-trans conformation in DMSO-d6 and an all-trans conformation in trifluoroethanol-d3. Compound 1L retarded stem-growth of rice seedlings and, in contrast, compound 1D promoted root-growth of rice seedlings.