α,β-Dehydro-amino acid residues in the design of peptide structures: Synthesis, crystal structure, and molecular conformation of two homologous peptides—N-Ac-Dehydro-Phe-L-Leu-OCH3 and N-Ac-Dehydro-Phe-NorVal-OCH3

✍ Scribed by Pushkar Sharma; Punit Narula; Tej P. Singh

• Publisher: Wiley (John Wiley & Sons)
• Year: 1994
• Tongue: English
• Weight: 470 KB
• Volume: 34
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360340912

✦ Synopsis

The dehydro-residue containing peptides N-Ac-dehydro-Phe-L-Leu-OCH3 ( I ) and N-Acdehydro-Phe-NorVal-OCH, (11) were synthesized by the usual workup procedures. The peptides crystallize from their solutions in methanol in space group P6,: ( I ) a = b = 12.528(2) A, c = 21.653(5) A; (11) a = b = 12.532(2) A, c = 21.695(4) A. Thestructures were determined by direct methods. Both peptides adopt similar conformations with @,# of dehydro-Pheasfollows: ( I ) -57.0(5)" and -37.0(5)"; (11) -56.0(5),' and-37.5(5)".

The observed data on dehydro-Phe when placed at the ( i + 1) position show that the &J,# values of dehydro-Phe are either -60°, 140" or -60", -30". The conformation of -Boo, 140" can be accommodated only with a flexible residue at the ( i + 2 ) position while the 4,$ values of -60", -30" are obtained with a bulky residue at the ( i + 2 ) position as in the present structures. The molecules are packed in a helical way along the c axis. These are held by two strong intermolecular hydrogen bonds involving both NH as donors and acetyl group and dehydro-Phe oxygen atoms as acceptors.