title: Solid-phase synthesis and spectroscopic studies of TRH analogues incorporating cis- and trans-4-hydroxy-L-proline.
abstract: An efficient solid-phase synthesis of the TRH analogue Glp-His(Nim-Trt)-Hyp-OH is described. Na-Fmoc protected amino acids and DCC/HOBt activation were employed. The bulky and mild-acid-sensitive 2-chlorotrityl resin, utilised as the solid support, completely suppressed dioxopiperazine formation. The tripeptide is a key intermediate in the synthesis of TRH analogues incorporating cis- and trans-4-hydroxy-L-proline. The tripeptide was converted, with inversion of configuration at C-4 of the Hyp residue, to Glp-His(Nim-Trt)-cHyp lactone in the presence of triphenylphosphine-diethyl azodicarboxylate (TPP-DEAD). One-pot MeOH-TPP-DEAD transesterification of the lactone, followed by Nim-detritylation, provided Glp-His-cHyp-OMe. This ester gave the corresponding amide and acid on ammonolysis and saponification, respectively. A high-field 1H NMR investigation of Glp-His-cHyp-OH and its diastereomer Glp-His-Hyp-OH, obtained by Nim-detritylation of the key tripeptide, showed that the configuration at C-4 of the prolyl residues is critical for the determination of the preferred three-dimensional structure of the molecules.
authors.affiliation: Department of Chemistry, University of Patras, Greece.
authors.forename: G
authors.initials: G
authors.lastname: Stavropoulos
authors.forename: K
authors.initials: K
authors.lastname: Karagiannis
authors.forename: D
authors.initials: D
authors.lastname: Vynios
authors.forename: D
authors.initials: D
authors.lastname: Papaloannou
authors.forename: D W
authors.initials: DW
authors.lastname: Aksnes
authors.forename: N
authors.initials: N
authors.lastname: Age Frøystein
authors.forename: G W
authors.initials: GW
authors.lastname: Francis
mesh_terms: D000595:Amino Acid Sequence; D006909:Hydroxyproline / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D015394:Molecular Structure; D013057:Spectrum Analysis; D013237:Stereoisomerism; D013973:Thyrotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: D013973:Thyrotropin-Releasing Hormone; D006909:Hydroxyproline