Ca-methyl, Ca-n-propylglycine homo-oligomers.

A series of Na-protected, monodispersed homo-oligopeptide esters to the octamer level from L-Ca-Me, Ca-propylglycine [or Ca-methylnorvaline, (aMe)Nva] has been synthesized by soln. methods and fully characterized. The preferred conformation of these homo-oligomers in soln. has been assessed by FT-IR absorption and 1H NMR techniques. Moreover, the mol. structures of the homotrimer and homotetramer have been detd. in the crystal state by X-ray diffraction. The obtained results strongly support the view that right-handed, single or multiple, and consecutive b bends are preferentially adopted by the conformationally restricted L-(aMe)Nva homo-oligomers. In particular, 310 helixes are formed by the longest homo-oligomers. It is our contention that the [(aMe)Nva]n peptides represent the best available choice among Ca-tetrasubstituted a-amino acid-based homo-oligomers for the construction of relatively easy to make, rigid foldamers with a well-defined screw-sense bias.