PEPTIDE WITH BUILT-IN CONFORMATIONAL CONSTRAINTS - STRUCTURE OF Z-(AIB)7-O(T)BU

C40H65N7O10.2H2O, M(r) = 803.1, triclinic, P1BAR, a = 10.082 (3), b = 15.523 (5), c = 16.301 (5) angstrom, alpha = 87.32 (3), beta = 77.00 ( 3), gamma = 79.70 (2)-degrees, V = 2445.7 (8) angstrom3, Z = 2, D(x) = 1.09 g cm-3, lambda(Cu Kalpha) = 1.5418 angstrom, mu = 6.1 cm-1, F(00 0) = 868, T = 293 K, final R = 0.077 for 5187 observed reflections. Th e peptide adopts a 3(10)-helical conformation consisting of five conse cutive 10-atom hydrogen-bonded beta-turns of type III. Both helical se nses (left- and right-handed) are present in the crystal. The molecule s are hydrogen bonded head-to-tail in the crystal forming infinitely l ong helical columns along the direction [110]BAR.