Synthesis of 3-aminolactams as X-Gly constrained pseudodipeptides and conformational study of a Trp-Gly surrogate

3-Amino-delta-valerolactams trans-11a-c were synthesized through conjugate addition and Curtius rearrangement and converted into Fmoc-{Trp-Gly}, Fmoc-{Ile-Gly}, and Fmoc-{Phe-Gly} pseudo-dipeptides. Conformational analyses of tripeptide analogues Ac-{Trp-Gly}-Leu-NH2 17a and 17b by NMR experiments and molecular modeling calculations showed that diastereomer 17a adopted a gamma-turn/distorted type II beta-turn structure, whereas diastereomer 17b adopted mainly a gamma-turn structure.