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] pseudodipeptides. Conformational analyses of tripeptide analogues Ac-[Trp-Gly]-Leu-NH(2) 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.