B. Prasad, N. Shamala, R. Nagaraj
Jul 1, 1979
Citations
1
Influential Citations
63
Citations
Journal
Biopolymers
Abstract
The crystal and molecular structure of N‐benzyloxycarbonyl‐α‐aminoisobutyryl‐L‐prolyl methylamide, the amino terminal dipeptide fragment of alamethicin, has been determined using direct methods. The compound crystallizes in the orthorhombic system with the space group P212121. Cell dimensions are a = 7.705 Å, b = 11.365 Å, and c = 21.904 Å. The structure has been refined using conventional procedures to a final R factor of 0.054. The molecular structure possesses a 4 → 1 intramolecular N‐H—O hydrogen bond formed between the CO group of the urethane moiety and the NH group of the methylamide function. The peptide backbone adopts the type III β‐turn conformation, with ϕ2 = −51.0°, ψ2 = −39.7°, ϕ3 = −65.0°, ψ3 = −25.4°. An unusual feature is the occurrence of the proline residue at position 3 of the β‐turn. The observed structure supports the view that Aib residues initiate the formation of type III β‐turn conformations. The pyrrolidine ring is puckered in Cγ‐exo fashion.