Unexpected stability of the urea cis-trans isomer in urea-containing model pseudopeptides.
In contrast to the situation observed in the crystal state, the urea moiety in N-Boc-N'-carbamoyl-gem-diaminoalkyl derivatives (single-residue ureidopeptides) 1-4 exclusively assumes a cis-trans conformation in solution. When R(3) = H, the resulting structure can be further stabilized by an intramolecular hydrogen bond that closes an eight-membered pseudocycle. The root-mean-square deviation calculated for heavy atoms between a peptide gamma-turn and the folded conformation that we propose to call urea turn is 0.60 A. [structure: see text]
Semetey
V
V
Immunologie et Chimie Thérapeutiques, UPR CNRS 9021, IBMC, 15, rue Descartes, F-67084 Strasbourg, France.
Hemmerlin
C
C
Didierjean
C
C
Schaffner
A P
AP
Giner
A G
AG
Aubry
A
A
Briand
J P
JP
Marraud
M
M
Guichard
G
G
D007536:Isomerism; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry*; D014508:Urea / Q000737:chemistry*
D010455:Peptides; D014508:Urea