Enhanced β-turn conformational stability of tripeptides containing Δphe in cis over trans configuration
Conformations of three pairs of dehydropeptides with the opposite configuration of the Delta Phe residue, Boc-Gly-Delta(Z/E)Phe-Phe-p-NA (Z- p -NA and E- p -NA), Boc-Gly-Delta(Z/E)Phe-Phe-OMe (Z-OMe and E-OMe), and Boc-Gly-Delta(Z/E)Phe-Phe-OH (Z-OH and E-OH) were compared on the basis of CD and NMR studies in MeOH, TFE, and DMSO. The CD results were used as the additional input data for the NMR-based calculations of the detailed solution conformations of the peptides. It was found that Z- p -NA, E- p -NA, Z-OMe, and Z-OH adopt the beta-turn conformations and E-OMe and E-OH are unordered. There are two overlapping type III beta-turns in Z- p -NA, type II' beta-turn in E- p -NA, and type II …
1H and 13C shielding measurements in comparison with DFT calculations performed for two 2-(acetyloamino)-N,N-dimethyl-3-phenylacrylamide isomers
Abstract We present measurements of 1H and 13C shielding for (2E)- and (2Z)-2-(acetyloamino)-N,N-dimethyl-3-phenylacrylamide isomers in solutions. Practically the same values of the shielding were obtained using internal and external referencing. For the interpretation, we explore DFT calculations of shieldings performed at the rovibrationally averaged geometries. The comparison of the experimental and theoretical results is verified both for the shielding and chemical shift. It appears that some inaccuracies in the calculations of the chemical shift can be reduced due to the error compensation while subtracting the reference shielding. As shown the measurement of magnetic shielding can be …
Effect of the ΔPhe residue configuration on a didehydropeptides conformation: A combined CD and NMR study.
Conformations of two pairs of dehydropeptides with the opposite configuration of the ΔPhe residue, Boc-Gly-Δ(Z)Phe-Gly-Phe-OMe (Z-OMe), Boc-Gly-Δ(E)Phe-Gly-Phe-OMe (E-OMe), Boc-Gly-Δ(Z)Phe-Gly-Phe-p-NA (Z-p-NA), and Boc-Gly-Δ(E)Phe-Gly-Phe-p-NA (E-p-NA) were compared on the basis of CD and NMR studies in MeOH, trifluoroethanol (TFE), MeCN, chloroform, and dimethylsulfoxide (DMSO). The CD results were used as the additional input data for the NMR-based determination of the detailed solution conformations of the peptides. It was found that E-OMe is unordered and Z-OMe, Z-p-NA, and E-p-NA adopt the β-turn conformation. There are two overlapping β-turns in each of those peptides: type II and ty…