CF 2 H as a hydrogen bond donor group for the fine tuning of peptide bond geometry with difluoromethylated pseudoprolines

CF 2 H-Pseudoprolines obtained from difluoroacetaldehyde hemiacetal and serine are stable proline surrogates. The consequence of the incorporation of the CF 2 H group is an important decrease of the trans to cis amide bond isomerization energy and a remarkable stabilisation of the cis conformer by an hydrogen bond.