1983 Volume 56 Issue 12 Pages 3699-3702
N-Acetyl-L-Leu–X–L-Pro–L-Val methylamides (IIa: X=D-Ala, IIb: X=Gly, IIc: X=L-Ala) were synthesized and subjected to CD and 1H NMR measurements to study the β-turn preferences of these peptides. Temperature dependences of L-Val4–NH proton chemical shifts in CD3OH solution were in the order of IIa<IIb<IIc, suggesting that the populations of the β-turn conformer with 4→1 hydrogen bonding were in the order of IIa>IIb>IIc. This order of β-turn preferences coincides with the order of the magnitudes of the Cotton effects in the CD spectra of the chromophoric derivatives, N-(2,4-dinitrophenyl)tetrapeptide p-nitroanilides, having the same sequences. This agreement supports the validity of the chiroptical method to study turn tendency of tetrapeptide sequences using chromophoric derivatives reported previously.
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