The polypeptide 3(10)-helix as a template and a spacer

X-ray diffraction analyses have provided detailed structural information on the 3(10)-helices of (i) pBrBz-D-(alpha Me)Phe-(Aib)(2)-D-(alpha Me)Phe-Aib-OtBu and Ac-(Aib)(2)-L-Lys(Bz)-(Aib)(2)-L-Lys(Bz)-(Aib)(2)-NHMe as suitable templates for molecular recognition studies, and (ii) pBrBz-TOAC-(L-Ala)(2)-TOAC-L-Ala-NHtBu as an appropriate spacer for an ESR study of side chain to side chain interactions. In addition, in Ac-TOAC-(Aib)(2)-L-Trp-Aib-OMe, forming a 3(10)-helix, the TOAC residue plays the role of an effective quencher of the fluorescence of the tryptophan residue located one turn apart.