Molecular structure of t-butyloxycarbonyl-Leu-Aib-Pro-Val-Aib-methyl ester,a fragment of alamethicin and suzukacillin: A 310-helical pentapeptide

The pentapeptide Boc-Leu-Aib-Pro-Val-Aib-OMe, a fragment of alamethicin and suzukacillin, crystallizes in the space group P2₁, with a = 11.034 (2), b = 10.894 (2), c = 15.483 (2) Å, β = 104.80 (2)° and Z = 2. The crystal structure has been solved by direct methods and refined to an R value of 0.069. The peptide backbone folds into a right-handed 3₁₀-helical conformation, stabilized by two intramolecular 4 → 1 hydrogen bonds between the Leu(1) CO and Val(4) NH and Aib(2) CO and Aib(5) NH groups. The solid-state conformation is consistent with results of spectroscopic analysis in solution.