Solvated helical backbones: X-ray diffraction study of Boc-Ala-Leu-Aib-Ala-Leu-Aib-OMe · H2O

✍ Scribed by I. L. Karle; J. L. Flippen-Anderson; K. Uma; P. Balaram

• Publisher: Wiley (John Wiley & Sons)
• Year: 1989
• Tongue: English
• Weight: 439 KB
• Volume: 28
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360280307

✦ Synopsis

Synopsis

A second example of insertion of a water molecule into the helical backbone of an apolar peptide is presented here and compared to a similar occurrence in a longer peptide with the same type of sequence of residues, i.e., Boc-Aib-(Ala-Leu-fib),-OMe. The backbone of the title compound assumes an approximate 3,,-helical form with three 4 + 1 hydrogen bonds. In the place of a fourth 4 4 1 hydrogen bond, a water molecule is inserJed between 0(1) and N(4), and acts as a bridge by forming hydrogen bonds N(4) . . . W(1) (2.95 A) and W(l) . . . O(1) (2.81 A). The water molecyle participates in a third hydrogen bond with a neighboring peptide molecule, W(1) . . . O(4) (2.91 A). The insertion of the water molecule causes the apolar peptide to mimic an amphiphilic helix. Crystals grown from ethyl acetate/petroleum eth:r (reported here)p from methan$/water solution are in space group P2,2,2, with a = 12.024(4) A, b = 15.714(6) A, c = 21.411(7) A, Z = 4 and dealt = 1.124 g/cm3 for C,,H,N,Q . H20. The overall agreement factor R is 6.3% for 2707 reflections observed with intensities > 3 4 F ) and the resolution is 0.90 A.