C-alpha-methyl,C-alpha-allylglycine (Mag) homooligomers

A complete series of N-alpha-protected, monodispersed homooligopeptide esters to the pentamer level from L-C-alpha-methyl,C-alpha-allylglycine (L-Mag) have been synthesized step-by-step in solution and fully characterized. The solution preferred conformation of these homooligomers has been assessed-by FT-IR absorption and H-1 NMR techniques. Moreover, the molecular structures of the homodimer and trimer have been determined in the crystal state by X-ray diffraction, and the conformational energy map of the homotrimer has been computed. The results obtained point to the conclusion that right-handed, single, or multiple beta -bends are preferentially adopted by the conformationally restricted L-Mag homooligomers. In particular, 3(10)-helices are formed by the longest homooligomer (pleionomer). The implications for the use of the Mag residue in designing conformationally constrained peptide substrates for reactions involving the side-chain C=C functionality are briefly discussed.