Nmr and computer-aided studies of the three interchanging stereoisomers of the cyclic hexapeptide cyclo[-Pro1-Gly2-Glu3(OBzl)-Pro4-Phe5-Leu6-]: Unexpected observation of a cis isomer of a secondary amide peptide bond in the presence of two trans proline peptide bonds
✍ Scribed by Ian Mc Ewen
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1993
- Tongue
- English
- Weight
- 692 KB
- Volume
- 33
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
The cyclic hexapeptide cycle[ -Pro'-Gly2-Glu3 (OBzl) -Pro4-Phe5-Leu6-] ( 1 ; OBzl: benzyl ester) was modeled and synthesized to be used as a chiral site for the separation of enantiomers. Total correlation spectroscopy and nuclear Ovehauser effect spectroscopy spectra of the peptide in CDCIB showed the presence of three stereoisomers. The two dominant stereoisomers la and lb exchanged chemically with each other, while the minor stereoisomer lc exchanged exclusively with the stereoisomer lb. Stereoisomer la had two cis proline peptide bonds while stereoisomer lb had all-trans peptide bonds. The stereoisomer lc had, for nonstrained peptides, an unusual cis phenylalanine peptide bond while both proline peptide bonds were trans.