Linear Oligopeptides .329. Synthesis, Characterization and Solution Conformational-analysis of C-alpha-ethyl, C-alpha-benzylglycine [(alpha-et)phe] Containing Peptides

For the first time a variety of derivatives and terminally blocked model peptides (to the pentapeptide level) of the sterically demanding (alpha Et)Phe residue have been synthesized (by solution methods) and fully characterized. The results of a solution conformational analysis, performed by using FTIR and H-1 NMR spectroscopy, favour the conclusion that (alpha Et)Phe is a beta-turn and helix promoter as strong as (alpha Me)Phe (C-alpha-methyl, C-alpha-benzylglycine) but more efficient than the Phe parent amino acid. In addition, a CD study of N-alpha-para-bromobenzoylated peptides suggests, that the relationship between (alpha Et)Phe chirality and the screw sense of the turn and helical structures;that are formed is the same as that found for (alpha Me)Phe peptides, L-e. L-amino acids give left-handed helicities. Interestingly, this relationship is opposite to that exhibited by protein amino acids, including Phe.