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-OMe adopts a helical form with four .alpha.-type hydrogen bonds in the middle, flanked by 310-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 P21. Cell parameters are a = 0.837(2) .ANG., b = 15.565(3) .ANG., c = 20.087(5) .ANG., .beta. = 96.42(2).degree., dcalc = 1.091 g/cm3 for C46H83N9O12 .cntdot. 1.5H2O .cntdot. 0.67CH3OH. There appears to be some hydration of the backbone in this apolar helix.