Aggregation studies in crystals of apolar helical peptides: Boc‐Aib‐Val‐Ala‐Leu‐Aib‐Val‐Ala‐Leu‐Aib‐OMe

Abstract

In the crystal, the backbone of Boc‐(Aib‐Val‐Ala‐Leu) 2 ‐Aib‐OMc adopts a helical form with four α‐type hydrogen bonds in the middle, flanked by 3 10 ‐type hydrogen bonds at either end. The helical molecules stack in columns with head‐to‐tail hydrogen bonds, either directly between NH and CO, or bridged by solvent molecules. The packing of the helices is parallel, even in space group P2 1 . Cell parameters are a = 9.837(2) Å. b = 15.565(3) Å. c = 20.087(5) Å, β= 96.42(2)°. d calc = 1.091 g/cm 3 for C 46 H 83 ,N 9 O 12 · 1.5H 2 O·0.67CH 3 OH. There appears to be some hydration of the backbone in this apolar helix.