Linear oligopeptides. Part 329. Synthesis, characterization and solution conformational analysis of Cα-ethyl, Cα-benzylglycine[(αEt)Phe] containing peptides

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

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