Structural versatility of peptides from Cα,α-dialkylated glycines. I. A conformational energy computation and x-ray diffraction study of homo-peptides from Cα,α-diethylglycine

✍ Scribed by E. Benedetti; V. Barone; A. Bavoso; B. Di Blasio; F. Lelj; V. Pavone; C. Pedone; G. M. Bonora; C. Toniolo; M. T. Leplawy; K. Kaczmarek; A. Redlinski

• Publisher: Wiley (John Wiley & Sons)
• Year: 1988
• Tongue: English
• Weight: 730 KB
• Volume: 27
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360270302

✦ Synopsis

Conformational energy computations on a derivative and a homo-dipeptide of C"*"-diethylglycine were performed. In both cases the Nand C-terminal groups are blocked as acetamido and methylamido moieties, respectively. It was found that the C"3"-diethylglycine residues are conformationally restricted and that the minimum energy conformation corresponds to the fully extended C, structure when the N-C"--C' bond angle is smaller than 108" (as experimentally observed). The results of the theoretical analysis are in agreement with the crystal-state structural propensity of the complete series of N-trifluoroacetylated homo-peptides of this C"*"-dialkylated residue from monomer to pentamer, determined by x-ray diffraction and also described in this work. Interestingly, for the first time, a crystallographically planar peptide backbone was observed (in the protected tripeptide). A comparison with peptides of C","-dimethylglycine, C"-methyl, C"-ethylglycine, and C"-"-di-n-propylglycine indicates that the fully extended conformation becomes more stable than the helical structures when both amino acid side-chain Cp atoms are substituted.