Conformational studies of cyclo(L-Phe-L-Pro-Gly-L-Pro)2 by 1H- and 13C-nuclear magnetic resonance spectroscopy, and its enantioface-differentiating ability

Article abstract of DOI:10.1248/cpb.41.235

Analyses of the ¹H- and ¹³C-nuclear magnetic resonance (¹H- and ¹³C-NMR) spectra of the cyclooctapeptide cyclo (L-Phe-L-Pro-Gly-L-Pro)₂ (3) in CDCl₃ with the aid of the C-H correlated spectroscopy (C-H COSY) two-dimensional NMR spectrum (Fig. 2) suggested that two kinds of C₂-symmetric conformation with all trans and cis-trans-trans-trans forms coexist. When 0.5 eq of CsSCN or 1 eq of D- and L-PheOMe · HCl (D/L ratio = 1/2) was added to a solution of the cyclooctapeptide (3) in CDCl₃, the ¹H- and ¹³C-NMR spectra (Fig. 3) suggested the presence of only one C₂-symmetric conformation (all trans), resulting from the formation of complexes with CsSCN or D- and L-PheOMe · HCl. The ¹³C-NMR spectra of the complexes of the cyclooctapeptide (3 or 4) with D- and L-PheOMe · HCl displayed separate resonances for each carbon atom of D-PheOMe · HCl and L-PheOMe · HCl. Furthermore, the ability of 3 to distinguish the D from the L enantiomer, is superior to that of 4 (Table II).

Full text of DOI:10.1248/cpb.41.235

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