Effect of a hydrophobic amino acid at position (i −1) on the stability of β-turns in hydrophilic pentapeptides as studied by NMR and molecular mechanics

A detailed NMR study of the peptide NAc-FDEKA-NH2 in aqueous and in CD3OH/H2O solutions as well as the N-acetylpentapeptide amides YDEKA, VDEKA, GDEKA, and the protected tetrapeptide NAc-DEKA-NH2 in methanolic solutions indicates the importance of the first amino acid (at i −1) on stabilizing the type I β-turn. The data illustrate the hydrophobic stabilization of this turn, which is present in FDEKA, YDEKA, and VDEKA. For GDEKA and DEKA, the NMR data indicate that this turn is not present. Molecular mechanics calculations support this conclusion and indicate that for FDEKA and GDEKA the type I β-turn is distorted in both the vacuum and the solvated structures. For the solvated structures, the Cα(i) − Cα(i + 3) distance is 4.87 Å for FDEKA and 6.00 Å for GDEKA, which are to be compared with the value of 4.64 Å for an ideal type I β-turn, i.e., the distortion is far greater in GDEKA than in FDEKA. The calculations can be interpreted to indicate the presence of two major conformations in solution. Keywords: β-turns, FDEKA, pentapeptide.

The crystal structure of Z-Leu-Aib-Pro-Leuol, the synthetic, protected C-terminal tetrapeptide of trichovirin

The structure of the synthetic, protected tetrapeptide Z-Leu-Aib-Pro-Leuol(C

The 4-(methylthio)phenyl ester for the synthesis of polypeptides of a known repeating sequence of amino acids. Synthesis of poly-(L-lysylglycyl)glycine 1-C14 ethyl ester hydrobromide

The synthesis of the tetrapeptide, N-t-butoxycarbonyl-ε-N-carbobenzoxy-L-lysylglycyl-ε-N-carbobenzoxy-L-lysylglycine 4-(methylthio)phenyl ester is described. The utility of this protective ester is shown by its easy conversion to the protected tetrapeptide 4-(methylsulfonyl)phenyl activated ester without decomposition. Removal of the N-butoxycarbonyl protecting group afforded the polymerizing unit, ε-N-carbobenzoxy-L-lysylglycyl-ε-N-carbobenzoxy-L-lysylglycine 4-(methylsulfonyl)phenyl ester. Polymerization of this material on the partially blocked monomer glycine-1-C14 ethyl ester hydrochloride, at a relatively high dilution, gave poly-(ε-N-carbobenzoxyl-L-lysylglycyl)glycine-1-C14 ethyl ester. The carbobenzoxy protective groups were removed to give the title compound.

Insulin peptides. I. Some protected peptides with sequences derived from the A-chain of ovine insulin

Syntheses are described of two pentapeptide derivatives with the A5-9 and A17-21 sequences, respectively, of ovine insulin, and of a protected tetrapeptide with a modified A1-4 sequence. Preparation of the three compounds involved the use of the 2,4,6-trimethylbenzyl carboxyl-protecting group in conjunction with the o-nitrophenylsulphenyl and benzyloxycarbonyl amino-protecting groups.