Journal of the Chemical Society. Perkin transactions I p. 2115 - 2122 (1995)
Update date:2022-08-04
Topics:
Kawai, Masao
Omori, Yoshimasa
Yamamura, Hatsuo
Butsugan, Yasuo
Taga, Tooru
Miwa, Yishihisa
The crystal structures of the isovaline-contatinig dipeptides, Boc-D-Iva-L-Pro-NHBzl 4 and Boc-L-Iva-L-Pro-NHBzl 5 were determined by X-ray diffraction.The diastereomeric peptides adopt intramolecular hydrogen-bonded β-turn conformations closely similar to each other (4: φIva -51 deg, ψIva -38 deg C, φPro - 70 deg C and ψPro -17 deg C and 5: φIva -53 deg C, φPro -72 deg C and ψPro -14 deg C).The Pro ring of each peptide is in Cγ-exo conformation.These conformations are essentially the same as those in the reported crystal structures of the Aib-L-Pro sequence possessing an NH group directly attached to the carbonyl of the L-Pro, indicating that replacement of either one of the two methyl groups of the Aib moiety with an ethyl group does not cause any significant change in the β-turn conformation of the Aib-L-Pro sequence in the crystalline state.CD spectral analysis of the terminal chromophoric group-carrying peptides Dnp-Gly-X-L-Pro-Gly-pNa (X = Aib 6 and D/L-Iva 7/8) has shown that these three tetrapeptides in CHCl3 and THF solutions also adopt a β-turn-type conformation.CD spectra of glycolic acid residue-containing analogues in place of the fourth Gly residue revealed a lack of β-turn tendency in these analogues, indicating the importance of intramolecular hydrogen bonding for the β-turn conformation of the central dipeptide moieties.The results are consistent with the reported unturned crystal structures of Aib-L-Pro and D/L-Iva-L-Pro sequence-containing peptides lacking the NH group which directly follows the Pro residue available for intramolecular hydrogen bonding.
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