Isolated alpha-turn and incipient gamma-helix

The unique abilities of homo-oligo-adamantyl peptides to adopt alpha- and gamma-turn conformations are demonstrated by X-ray diffraction, and NMR and FT-IR absorption spectroscopies. Assembled by an Ugi multiple component reaction strategy, N-alpha-formyl-adamantyl tripeptide iso-propyl and tert-butyl amides are respectively found to adopt an isolated alpha-turn and an incipient gamma-helix conformation by X-ray diffraction crystallography. The shortest example of a single alpha-turn with ideal geometry is observed in the crystalline state. In solution both peptides predominantly assume gamma-helical structures.