N-acetyl-N'-methylamide derivative of (2S,3S)-1-amino-2,3-diphenylcyclopropanecarboxylic acid: theoretical analysis of the conformational impact produced by the incorporation of the second phenyl group to the cyclopropane analogue of phenylalanine

The intrinsic conformational preferences of (2S,3S)-1-amino-2,3-diphenylcyclopropanecarboxylic acid, a phenylalanine cyclopropane analogue bearing two phenyl substituents, have been examined theoretically. For this purpose, its N-acetyl-N'-methylamide derivative, Ac-(2S,3S)c(3)diPhe-NHMe, has been investigated by using ab initio HF and DFT methods. Results have been compared with those previously reported for other cyclopropane analogues of phenylalanine, and with experimental data available for c(3)diPhe-containing peptides.