ISSN:
1573-3904
Keywords:
1H NMR chemical shift comparison
;
N-methylation of amide and urethane groups
;
side-chain–main-chain H-bonding
;
unsymmetrical gramicidin S analog
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Derivatives of gramicidin S (GS) and its mono- and di-d-cyclohexylalanine (d-Cha) analogs possessing various protecting groups on Orn side chains were prepared. 1H NMR spectra of the unsymmetrically protected analogs [Orn(X)2,Orn(X′)2′,d-Cha4]GS were similar to the composites of the spectra of the symmetrical derivatives [Orn(X)2,2′,d-Cha4,4′]GS and [Orn(X′)2,2′]GS, revealing the proximity of the protecting groups of NδH of Orn residues at the 2 and 2′ positions to the side chains of d-Phe (or d-Cha) residues at the 4 and 4′ positions, respectively. The results indicated the presence of H-bonds between the NδH of Orn and the carbonyl of d-Phe residues in the i → i + 2 sense and not in i → i – 3, which was also supported by the ROESY analysis. The substantially strong H-bonds can explain the observed resistance of the urethane NH of the Orn side chains in the GS derivatives to the N-methylation with CH3I–Ag2O in DMF.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1008860509717
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