Effects of amino acids and chirality for molecular folding of desoxazoline-ascidiacyclamide derivatives: X-ray crystal structures of four cyclic octapeptides including unusual amino acids, cyclo(–Ile–aThr–D-Val–Thz–)2, cyclo(–Ala–aThr–D-Val–Thz–Ile–aThr–D-Val–Thz–), cyclo(–Val–aThr–D-Val–Thz–Ile–aThr–D-Val–Thz–), and cyclo(–Ile–aThr–Val–Thz–Ile–aThr–D-Val–Thz–)
✍ Scribed by Akiko Asano; Mitsunobu Doi; Kiyomi Kobayashi; Masao Arimoto; Toshimasa Ishida; Yoshio Katsuya; Yoshihiro Mezaki; Hiroshi Hasegawa; Masamichi Nakai; Masahiro Sasaki; Taizo Taniguchi; Akira Terashima
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 2001
- Tongue
- English
- Weight
- 267 KB
- Volume
- 58
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Desoxazoline derivative of ascidiacyclamide (1), cyclo(-L-Ile-L-allo-threonine-D-Val-thiazole-)(2), was modified to disturb the C(2)-symmetry. An Ile(1) residue of 1 was replaced for Ala (2) or Val (3), and the D-Val(3) residue was replaced for Val (4). The crystal structures of 1-4 were analyzed by x-ray diffraction methods. The molecules of all compounds were folded and this type of structure was not observed in x-ray structures of ascidiacyclamide derivatives so far except for patellamide D. The folding patterns of 1-4 were similar to each other and resembled that of patellamide. The asymmetric modifications at position 1 caused the conformational changes at local area, and these were related with the peptide-peptide and peptide-solvent interactions. Despite the diverse backbone conformation by the epimeric modification at position 3, the entire molecule of 4 was folded. These results mean that (1) the desoxazoline-ascidiacyclamides favored the folded structures and (2) the modifications of the side chain size at position 1 and the chirality at position 3 brought the local conformational changes to derivatives, suggesting that (3) the lack of the oxazoline block leads to conformational flexibility of 1-4, which accepts the conformational change with no drastic change on the entire structure.