Crystal and molecular structure of benzyloxycarbonyl-α-aminoisobutyryl-L-prolyl methylamide: The observation of an X2-Pro3 Type III β-Turn
✍ Scribed by B. V. Venkataram Prasad; N. Shamala; R. Nagaraj; R. Chandrasekaran; P. Balaram
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1979
- Tongue
- English
- Weight
- 579 KB
- Volume
- 18
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
The crystal and molecular structure of N-benzyloxycarbonyl-a-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 P212~21. Cell dimensions are a = 7.705 A, b = 11.365 A, and c = 21.904 A. 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---0 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 111 P-turn conformation, with 4 2 = -51.0°, +* = -39.7", &j = -65.0', $3 = -25.4'.
An unusual feature is the occurrence of the proline residue a t position 3 of the P-turn. The observed structure supports the view that Aib residues initiate the formation of type 111 @-turn conformations. The pyrrolidine ring is puckered in Cy-exo fashion.