D. Ranganathan, V. Haridas, S. Kurur
Aug 7, 1998
Citations
0
Influential Citations
38
Citations
Journal
Journal of the American Chemical Society
Abstract
endo-cis-(2S,3R)-Bicyclo[2.2.1]hept-5-en (norbornene) dicarbonyl unit with a built-in U-architecture has been demonstrated to be an excellent reverse-turn molecular scaffold. A large variety of endo-cis-(2S,3R)-norborneno bispeptides containing almost all of the coded amino acids were synthesized and examined for conformational preferences by 1H NMR, FT-IR, CD, and X-ray crystallographic studies. While FT-IR and 1H NMR variable-temperature studies ruled out the presence of any significant amount of intramolecular hydrogen bonding in simple bispeptides (3a−h) (except in Aib bispeptide), the CD studies were clearly in favor of a β-turn type structure. Single-crystal X-ray studies on Aib, Val and Leu containing norborneno bispeptides (3b−d) provided convincing proof for the presence of reverse-turn conformation. While the interstrand Cα−Cα‘ distances (5.2−5.7 A) were well within the range of those for β-turn structures, no interstrand intramolecular hydrogen bonding was seen in Val and Leu bispeptides; the A...