Formation of several stable complexes between the minor components of the cyclic tetrapeptide cyclo-(-Pro1-Ala2-D-Phe3-Leu4-) and some specific Boc-amino acids.
The cyclic tetrapeptide cyclo (-Pro1-Ala2-D-Phe3-Leu4-) was modeled and synthesized to be used for molecular interactions and chiral discrimination studies in CDCl3. Total correlation spectroscopy and nuclear Overhauser effect spectroscopy spectra of the cyclic tetrapeptide showed the presence of one dominant stereoisomer-1- and three minor ones--2a, 2b, and 2c--in a relationship of 92:6:1:1. They formed three- to five-hydrogen bond complexes with Boc-D-Ser, Boc-L-Ser and Boc-L-Thr (Boc: t-butyloxylcarbonyl). These three Boc-amino acids interact more strongly with 2a, 2b, and 2c than with 1, altering their relative concentrations to 48:40:6:6. In the complex between the cyclic tetrapeptide and Boc-D-Ser, the stereoisomer 2a exchanged chemically with 1, 2b, and 2c, while 1 did not exchange with either 2b or 2c. This chemical exchange is due to cis-trans isomerization of the peptide bonds. The chiral discrimination of 2a, 2b, and 2c was stronger than that of 1. No complexation occurred with Boc-L-Ala or Boc-L-Trp.
Department of Organic Chemistry, University of Gothenburg, Sweden.
I
I
McEwen
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K
Ottosson
D000595:Amino Acid Sequence; D005563:Formic Acid Esters / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry*; D011487:Protein Conformation; D013237:Stereoisomerism
D005563:Formic Acid Esters; D009842:Oligopeptides; D010456:Peptides, Cyclic; C000345:t-butyloxycarbonyl group; C083361:cyclo(prolyl-alanyl-phenylalanyl-leucyl)