Synthesis and conformational studies by 1H- and 13C-NMR spectroscopy of a novel, sterically constrained analogue of thyrotropin-releasing hormone.
A novel thyrotropin-releasing hormone (TRH) analogue, [2,4-MePro3]-TRH (2,4-MePro: 2-carboxy-2,4-methanopyrrolidine), has been synthesized using a rapid solid phase peptide synthesis method, and its conformational properties investigated by one- and two-dimensional (2D) nmr spectroscopy and by proton Overhauser measurements. Following a published approach, calibrated interproton Overhauser effects were used together with distance geometry analysis to deduce that the single conformation of the His-2,4-MePro tertiary amide bond is trans in aqueous solution. This conclusion was corroborated by 2D dipolar-correlated (NOESY) spectroscopy. A preferentially extended conformation is indicated by the nmr data, similar to that of TRH. The phi, psi conformational space of 2,4-MePro is, however, significantly different from that of trans proline and the structural consequences of these differences at the C-terminus are discussed. The distribution of histidine side-chain conformations in the TRH analogue was deduced from coupling constants and from the short-range interaction between the imidazole ring and one of the prochiral faces of the 2,4-MePro side chain.
Mapelli
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C
School of Chemical Sciences, Department of Chemistry, University of Georgia, Athens 30602.
Van Halbeek
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H
Stammer
C H
CH
D002247:Carbon Isotopes; D003903:Deuterium; D006639:Histidine; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D010455:Peptides; D011487:Protein Conformation; D011522:Protons; D013057:Spectrum Analysis / Q000379:methods; D013237:Stereoisomerism; D013973:Thyrotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000138:chemical synthesis
D002247:Carbon Isotopes; D010455:Peptides; D011522:Protons; C063926:thyrotropin-releasing hormone, 2,4-MePro(3)-; D006639:Histidine; D013973:Thyrotropin-Releasing Hormone; D003903:Deuterium