TRYPTOPHAN-DERIVED PEPTIDES .1. CRYSTAL-STRUCTURE AND SOLUTION CONFORMATION OF BOC-GLY-TRP-ALA-O(T)BU

The solid-state structure of Boc-Gly-Trp-Ala-OBu(t) was determined by single-crystal X-ray diffraction analysis. The tripeptide gave crystal s belonging to the orthorhombic system P2(1)2(1)2(1) and at 122.0(5) K : a = 11.0663(12), b = 14.107(2), c = 17.275(2) Angstrom, V = 2697.0(5 ) Angstrom(3), Z = 4, R(F) = 0.0259, and R(w)(F) = 0.0695. The peptide adopts a type-I beta-turn in the solid state with a single, rather we ak, intramolecular hydrogen bond between the Boc-CO and Ala-NH groups (N ... O 3.082(1) Angstrom, <NH ... O 167(1)degrees). The conformation of the Boc-Gly-Trp-Ala-OBu(t) peptide has also been studied by H-1 NM R spectroscopy. The solvent and temperature dependencies of N (H) unde r bar chemical shifts suggests that this hydrogen bond is broken and t hat all amide protons are solvent exposed in CDCl3 and (CD3)(2)SO.