X-ray study on homo-oligopeptides t-Boc(L-Nva)6OMe and HCl.H(L-Nva)6OMe

Observations of extended peptide chains, whose direction is perpendicular to the fiber axis (cross-beta-structure) have hitherto been confined to fibrous proteins and to some synthetic polydisperse polypeptides of rather low molecular weight. This structure has now been found in some monodisperse linear homo-oligopeptides with aliphatic hydrocarbon side chains. X-ray fiber diagrams of t-Boc(L-Nva)6OMe and HCl.H(L-Nva)6OMe show the characteristic reflections of this form. In addition, the good orientation of suitably prepared specimens has enabled a fairly complete determination of the hexapeptides unit cell to be made. Both molecules are packed in a pseudomonoclinic lattice whose dimensions are: a = 4.80, b = 59.0, c = 14.86 A, beta = 85 degrees and a = 4.80, b = 58.50, c = 14.84 and beta = 86 degrees for t-Boc(L-Nva)6-OMe and HCl.H(L-Nva)6OMe respectively. It has not been possible from the available experimental data to establish whether the arrangement of the chains within the sheets is parallel or antiparallel.