Synthesis and nmr analysis of cyclo-[85% 13C-asp]-pro: 13C-13C vicinal coupling constants and conformation

Proteinogenic amino acids labelled with 15N and/or 13C for application in peptide synthesis: a short review with a comprehensive list of published derivatives

A review is given of the literature dealing with the most common protected derivatives of 15N- and/or 13C-labelled amino acids of interest in peptide synthesis. The list contains all such Boc-, Z- and Fmoc-amino acids as well as published methyl, ethyl, t-butyl and benzyl esters.

Nuclear magnetic resonance analyses of side chain conformations of histidine and aromatic amino acid derivatives. Solvent and pH dependence

Stereoselectively beta-deuterated species were synthesized of Ac-His-NHMe, Ac-His-OEt, Ac-His-OH and H-His-NHMe, which are useful as models of histidine residues in peptides. From the spectral comparison of 1H n.m.r., the beta-proton resonances of the normal species were unambiguously assigned. In (C2H3)2SO, C2(2)H5O2H, C2H3O2H, and C5(2)H5N solution and in aqueous solution, the lower-field and higher-field components of beta-proton resonances of the four histidine derivatives are assigned to the pro-R and pro-S protons, respectively. The alternative assignments apply for Ac-His-NHMe, Ac-His-OEt and Ac-His-OH in non-polar solvents such as C2HCl3. Vicinal coupling constants 3J alpha beta S and 3J alpha beta R were obtained for calculating the fractional populations of rotamers about the C alpha-C beta bond. The rotamer populations depend little on the ionization states of the alpha-amino and carboxyl groups or the imidazole ring. The rotamer populations depend significantly on the solvent polarity, similar to those of Phe, Tyr and Trp derivatives. For the two beta-proton resonances of His, Phe, Tyr, and Trp derivatives in a variety of solvents, linear relationships are found between the differences in chemical shifts and the differences in vicinal coupling constants.

Preferred solution conformation of des-Arg9-bradykinin and analysis of structure-conformation-activity relationships in the series [Alan]des-Arg9-bradykinin

This paper describes the solution conformation of the vasoactive peptide hormone des-Arg9-bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe). 1. By 1H-NMR spectroscopy we studied des-Arg9-bradykinin and its fragments bradykinin-(1-5), bradykinin-(1-6) in aqueous solution as a function of pH (titration) and in dimethylsulfoxide solution at two ionic states (cation and neutral ion species). 2. The preferred solution conformation which is most strongly stabilized in dimethylsulfoxide in the neutral ion species includes a distorted beta-turn II involving the N-terminal sequence of Pro2-Pro3-Gly4-Phe5 and most likely a C7-type bend in the C-terminal part Ser-Pro-Phe. 3. A complete series of analogous ([Alan]des Arg9-bradykinin, with n = 1, 2...8) was then investigated by circular dichroism and 1H-NMR spectroscopy in order to study the conformational role played by each residue and to delineate the local and the long-range effects on conformation brought about by the Xaa leads to Ala substitutions. Chosen spectral parameters (circular dichroic spectra, chemical shift variations and vicinal coupling constants) characteristic of the preferred solution conformation of the native sequence of des-Arg9-bradykinin are followed from analogue to analogue. The important conformational role of the arginine-1 side chain and its positive charge and the spatial proximity of the N-terminal and C-terminal groups, i.e. the folded structure of the peptide can be inferred from these data. 4. A comparison of the biological activities of the analogues with the conformative perturbations caused by the chemical alterations shows des-Arg9-bradykinin conformation and receptor affinity to be equally sensitive to single-residue substitutions. The correct orientation of the arginine-1 side chain, the precise geometry of the turn involving residues 2-5 and of the C-terminal Pro-Phe sequence are of primary importance.