BIOACTIVE PEPTIDES - CONFORMATIONAL STUDIES OF [TYR(4)]CYCLOLINOPEPTIDE-A

The solid state conformational analysis of [Tyr(4)] cyclolinopeptide a has been carried out by x-ray diffraction studies. The crystal struct ure of the monoclinic form, grown from a dioxane-water mixture [a = 9. 849 (5) Angstrom, b = 20.752 (4) Angstrom, c = 16.728 (5) Angstrom, be ta = 98.83 (3)degrees, space group P2(I), Z = 2], shows the presence o f five intramolecular N-H ... O=C hydrogen bonds, with formation of on e C-17 ring structure, one alpha-turn (C-13), one inverse gamma-turn ( C-7), and two beta-turns (C-10, one of type III and one of type 1). Th e Pro(1)-Pro(2) peptide unit is cis (omega = 5 degrees), all others ar e trans. The structure is almost superimposable with that of cyclolino peptide A. The rms deviation for the atoms of the backbones is on the average 0.33 Angstrom. (C) 1995 John Wiley & Sons, Inc.