Structure of the stacked cyclic oligoamides: 1,6-diaza-2,7-cyclodecadione and 1,5,9-triaza-2,6,10-cyclododecatrione. A ring model of the α-helix

Abstract

The structure of two cyclic amides, comprised of methylene and peptide groups, is described. The cyclic amides form parallel columns of stacked hydrogen-bonded rings. The cyclic dimer of butyramide (1,6-diaza-2,7-cyclodecadione) (I), C 8 H 14 N 2 O 2 , forms monoclinic crystals, space group P2 1 /n, a=4.874 (2), b=11.714 (4), c=8.088 (2) A, β=107.3 (3) o , R=0.125 for 536 observed reflections, I>3σ(I), Z=2, D x =1.28 g cm -3 , λ(Cu, Kα)=1.5418 A, μ=7.26 cm -1 , T=298 K. The ten-membered ring skeleton adopts a centrosymmetric crown conformation which is rarely found in other ten-atom ringse, but has been described for its isomer 1,5-diaza-6,10-cyclododecadione