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Structural versatility of peptides from Cα,α-disubstituted glycines: Preferred conformation of the chiral isovaline residue

✍ Scribed by K. Nebel; E. Altmann; M. Mutter; R. Bardi; A. M. Piazzesi; M. Crisma; G. M. Bonora; C. Toniolo

Publisher
Wiley (John Wiley & Sons)
Year
1991
Tongue
English
Weight
976 KB
Volume
31
Category
Article
ISSN
0006-3525

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✦ Synopsis

The molecular structures of four protected isovaline-(Iva-)containing peptides to the pentamer level have been determined by x-ray diffraction. The peptides are t-Boc-Ala-( S ) -1va-Ala-OMe ( t-Boc : tert-butyloxycarbonyl; OMe : methoxy) and its ( R ) -1va diastereomer, and t-Boc-[ Ala-( R ) -Iva],-Ala-OH and its (S) -1va diastereomeric methyl ester analogue. The two tripeptides are folded in an open type I1 @-bend conformation. The fully developed right-handed 310-helix formed by the ( R ) -1va pentapeptide, which includes an unusual intramolecular (acid) 0 -H * . O=C(peptide) H bond, is partially unfolded (near the C-terminus) in the ( S ) -1va pentapeptide. 'H-nmr and Fourier transform ir absorption studies suggest that in CDCl, solution ( a ) the two tripeptides maintain a type I1 @-bend conformation of comparable stability and ( b ) both diastereomeric pentapeptide sequences adopt a fully developed 310-helix. A comparison with the preferred conformation of other extensively investigated C"."-disubstituted glycines is made and the implications for the use of the Iva residue in designing conformationally constrained analogues of bioactive peptides are briefly discussed.

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