title: Aza-amino acid scanning of secondary structure suited for solid-phase peptide synthesis with fmoc chemistry and aza-amino acids with heteroatomic side chains.
abstract: Aza-peptides, peptide analogues in which the alpha-carbon of one or more of the amino acid residues is replaced with a nitrogen atom, exhibit a propensity for adopting beta-turn conformations. A general Fmoc-protection protocol for the stepwise solid-phase synthesis of aza-peptides has now been developed based on the activation of N'-alkyl fluoren-9-ylmethyl carbazates with phosgene for coupling the aza-amino acid residues. This method has proven effective for introducing aza-amino acid residues with aliphatic (Ala, Leu, Val, and Gly) and aromatic (Phe, Tyr, and Trp) side chains. Acid promoted loss of aromatic side chains was noted with aza-Trp and aza-Tyr residues during peptide cleavage and suppressed by temperature control in the case of the latter. In addition, aza-peptides with heteroatomic side chain residues (Lys, Orn, Arg, and Asp) were conveniently synthesized using this protocol. Partial aza-amino acid scans were performed on three biologically active peptides: the potent tetrapeptide melanocortin receptor agonist, Ac-His-d-Phe-Arg-Trp-NH2; the growth hormone secretagogue hexapeptide, GHRP-6, His-d-Trp-Ala-Trp-d-Phe-Lys-NH2; and the human calcitonin gene-related peptide (hCGRP) antagonist, FVPTDVGPFAF-NH2. This practical procedure for aza-amino acid scanning using Fmoc-based solid-phase synthesis should find general utility for probing the existence and importance of beta-turn conformations in bioactive peptides.
authors.affiliation: Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, Canada.
authors.forename: Damien
authors.initials: D
authors.lastname: Boeglin
authors.forename: William D
authors.initials: WD
authors.lastname: Lubell
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D001372:Aza Compounds / Q000737:chemistry*; D005449:Fluorenes / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D021241:Spectrometry, Mass, Electrospray Ionization; D014364:Tryptophan / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry
chemical_list: D000596:Amino Acids; D001372:Aza Compounds; D005449:Fluorenes; D010455:Peptides; D014443:Tyrosine; D014364:Tryptophan