The solvent-dependent conformations of cyclo(-delta-Ava-L-Pro-)(2) were cha
racterized by means of the H-1 and H-13 NMR, CD, and LR spectra. CD results
in CH2Cl2, CH3CN, CH3-OH, and H2O indicated that the change in polarity of
the solvent induces a reversible change in the conformation of cyclo(-delt
a-Ava-L-Pro-)a, revealed by the decrease of the negative peak near to 230 n
m and then by the gradual appearance of a negative trough near to 210 nm. T
he NMR data in CD3Cl, CD2Cl2, CD3CN, and CD3OH confirmed that cyclo(-delta-
Ava-L-Pro-)(2) has a C2 symmetric conformation consisting of all-trans pept
ide-bond backbones, in all solvents, and that the change in polarity of the
solvent induces a difference in the rotational states of the Pro C-alpha-C
=O single bond.