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Feytens, Debby,Chaume, Gré,gory,Chassaing, Gé,rard,Lavielle, Solange,Brigaud, Thierry,Byun, Byung Jin,Kang, Young Kee,Miclet, Emeric American Chemical Society 2012 The Journal of physical chemistry B Vol.116 No.13
<P>NMR studies and theoretical calculations have been performed on model peptides Ac-Ser(ΨPro)-NHMe, (<I>S</I>,<I>S</I>)Ac-Ser(Ψ<SUP>H,CF3</SUP>Pro)-NHMe, and (<I>R,S</I>)Ac-Ser(Ψ<SUP>CF3,H</SUP>Pro)-NHMe. Their thermodynamic and kinetic features have been analyzed in chloroform, DMSO, and water, allowing a precise description of their conformational properties. We found that trifluoromethyl C<SUP>δ</SUP>-substitutions of oxazolidine-based pseudoprolines can strongly influence the <I>cis</I>–<I>trans</I> rotational barriers with only moderate effects on the <I>cis</I>/<I>trans</I> population ratio. In CHCl<SUB>3</SUB>, the configuration of the CF<SUB>3</SUB>–C<SUP>δ</SUP> entirely controls the ψ-dihedral angle, allowing the stabilization of γ-turn-like or PPI/PPII-like backbone conformations. Moreover, in water and DMSO, this C<SUP>δ</SUP>-configuration can be used to efficiently constrain the ring puckering without affecting the <I>cis</I>/<I>trans</I> population ratio. Theoretical calculations have ascertained the electronic and geometric properties induced by the trifluoromethyl substituent and provided a rational understanding of the NMR observations.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcbfk/2012/jpcbfk.2012.116.issue-13/jp300284u/production/images/medium/jp-2012-00284u_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp300284u'>ACS Electronic Supporting Info</A></P>