Synthesis and conformational analysis of cyclic analogues of inverse gamma-turns.

Gamma-turn analogues comprising a modified dipeptide constrained in an eleven-membered ring were prepared by alkene metathesis and analysed by NMR and molecular modelling studies. The results reveal that some of the cyclic analogues form inverse gamma-turns and preferentially adopt conformations determined by the identity of the incorporated amino acid residues and the nature of the constraining linker (E/Z-alkene or alkane).