?-Valerolactamic Quaternary Amino Acid Derivatives: Enantiodivergent Synthesis and Evidence for Stereodifferentiated ?-Turn-Inducing Properties

Enantiopure (R) and (S) cyclic ?,?-disubstituted amino acid derivatives displaying a ?-valerolactam side chain were prepared from common isoxazolidine precursor. The (R)-configured 11 was converted into diastereoisomeric pseudopeptides to investigate its ability induce secondary structures in peptidomimetics. Conformational studies of these carried out the solid state (X-ray diffraction), solution (NMR analyses), silico (computer-aided conformational analysis), which demonstrated that such quaternary acids ?-turn conformations stable enough be retained polar media (DMSO). Incorporation this new type representative pseudopeptidic sequence by N- then C-elongation N-debenzylation is also described herein could serve for synthesis various structured